Methods and devices for transferring multi-modal xr data

Abstract

A method for managing data transmission between a transmitter and a receiver of a wireless network, the method comprising, at the transmitter, performing a discard on a first set of one or more protoc

Description

FIELD OF THE INVENTION The present invention generally relates to wireless networks, and more specifically to methods and devices for handling multi-modal XR data. BACKGROUND OF THE INVENTION Extended Reality (XR) technologies, which encompass Virtual Reality (VR), Augmented Reality (AR), and Mixed Reality (MR), represent a new frontier in immersive digital experiences. XR applications are transforming industries such as entertainment, education, healthcare, and manufacturing by merging the physical and virtual worlds. These technologies require large amounts of data, seamless connectivity, and low-latency performance to provide real-time interactions and high-quality visuals. This is where 5G networks play a critical role, offering the infrastructure needed to meet the demanding requirements of XR applications. 5G networks are specifically designed to deliver higher bandwidth, lower latency, and more reliable connections than previous mobile generations. These features are essential forXR, as they enable real-time rendering and streaming of high-definition graphics, ensuring immersive experiences without lag or motion sickness. With 5G's enhanced mobile broadband (eMBB) and ultra-reliable low-latency communication (URLLC), XR devices can access cloud-based processing and edge computing resources, reducing the need for heavy on-device computing and allowing for more compact and lightweight XR hardware. The combination of XR and 5G opens up opportunities for new applications across industries. In entertainment, users can experience real-time multiplayer virtual worlds, while in education and training, simulations can create realistic learning environments. Healthcare professionals can benefit from AR-guided surgeries or remote diagnostics, and industries like manufacturing and retail can use MR for complex design tasks or immersive customer experiences. By leveraging the capabilities of 5G, XR technologies are poised to revolutionize how users interact with digital content, enabling richer, more responsive, and interactive environments. Multimodal XR refers to the integration of multiple sensory inputs, such as visual, auditory, haptic (touch), and even olfactory (smell) feedback, to create a more immersive and realistic extended reality experience. In a 5G-enabled multimodal XR environment, users can interact with virtual or augmented worlds using more than just visual and audio cues, haptic devices can simulate the sense of touch, while other sensory technologies can enhance realism by engaging additional senses. 5G’s ultra-low latency and high bandwidth allow for the seamless transmission of these diverse data streams, ensuring real-time responsiveness across all sensory modalities. This is particularly important in applications like remote surgery, immersive gaming, or advanced simulations, where the combination of multiple senses can dramatically improve user interaction, decision-making, and overall engagement in virtual spaces. For multimodal XR experiences to be effective, the various data streams, visual, auditory, haptic, and other sensory inputs, must be synchronized and received by the user within a tightly controlled time frame. If these multimodal data streams, all related to the same scene or experience, arrive at different times or with noticeable delays, the immersive experience breaks down, causing disjointed or confusing interactions. For instance, in a virtual environment, if the user sees an object move but the corresponding sound or haptic feedback arrives with a delay, it disrupts the sense of realism. In 5G networks, the ultra-low latency ensures that these diverse data inputs can be delivered within milliseconds, allowing the receiver to process and fuse the inputs in real time. This synchronization is critical for maintaining immersion, particularly in complex XR applications such as remote collaboration, training simulations, or interactive gaming, where the timely arrival of multimodal information is essential for a cohesive, responsive experience. However, this synchronization is not always guaranteed due to various network-related factors that can introduce delays or disruptions in the delivery of multimodal data. Network congestion, for example, can increase latency, causing delays in one or more data streams and breaking the real-time flow required for an immersive XR experience. Similarly, issues such as radio link failures or signal degradation can occur, particularly in challenging environments with weak coverage or interference, leading to packet loss or uneven transmission of data. These network impairments can cause certain sensory inputs to arrive out of sync, compromising the seamless interaction and realism thatXR applications demand. While 5G is designed to mitigate these challenges with advanced techniques like network slicing and edge computing, ensuring perfect synchronization under all conditions remains a technical challenge. Moreover, when modal streams do not arrive on time, it can have two significant negative effects. First, the inability to reconstruct the associated scene or experience at the receiver compromises the immersive quality of the XR interaction. For example, if visual data arrives without the corresponding auditory or haptic feedback, the user may be unable to fully comprehend or engage with the virtual environment, leading to confusion and a diminished experience. This disjointedness not only affects user satisfaction but also results in wasted network resources, as data packets that fail to contribute to a coherent experience may need to be resent or adjusted, thereby increasing unnecessary traffic. Secondly, the inefficient use of network resources can exacerbate overall network congestion. When a substantial amount of data is transmitted but fails to synchronize properly, it can overload certain network segments, leading to further delays and interruptions for all users. This cyclical problem can create a feedback loop where congestion leads to more delays, and the delays, in turn, contribute to further congestion. Thus, ensuring the timely delivery and synchronization of multimodal data streams is not only crucial for individual XR experiences but also for maintaining the overall efficiency of the network infrastructure. Thus, there is a need for an improved method of handling the transmission of multimodal XR data. SUMMARY In accordance with a first aspect of the invention, there is provided a method for managing data transmission between a transmitter and a receiver of a wireless network, the method comprising, at the transmitter, performing a discard on a first set of one or more protocol data units, PDUs, carrying collectively a unit of information, the discard being performed as a function of a timer established for an associated second set of one or more PDUs carrying collectively a unit of information. Accordingly, by abandoning unnecessary or delayed transmissions, network resources are conserved, thereby reducing congestion and latency. In embodiments, the first set of PDUs may correspond to a first data modality, and the second set of PDUs may correspond to a second data modality different from the first data modality. In embodiments, the first set of PDUs may be associated with a first data flow, and the second set of PDUs may be associated with a second data flow different from the first data flow. In embodiments, the timer may be initialized with an initialization time value dependent on a predefined synchronization threshold linking the first and second sets of PDUs. In embodiments, the initialization time value may further be dependent on a delay budget associated with the second set of PDUs. In embodiments, the initialization time value may further be dependent on a difference of arrival time between the first and second sets of PDUs. In embodiments, the initialization time value may further be dependent on a time delay upon the expiry of which the second set of PDUs becomes discardable in relation to an associated other set of PDUs. In embodiments, the initialization time value may further be dependent on the earliest-expiring time delay among a plurality of time delays, upon the expiry of each of the time delays, the second set of PDUs becomes discardable in relation to an associated other set of PDUs. In embodiments, the timer may be activated upon delivering, at a PDCP transmitter layer, the first-arriving PDU of the second set of PDUs. In embodiments, the performing a discard may comprise performing the discard on the first set of PDUs, upon or after the expiry of the timer established for the associated second set of PDUs. In embodiments, the performing a discard may comprise at least one of: discarding, from transmission to the receiver, PDUs of the first set of PDUs that have not yet been delivered from upper layers to a PDCP transmitter layer, discarding, from transmission to the receiver, PDUs of the first set of PDUs that are currently under processing at a PDCP transmitter layer, or discarding, from transmission to the receiver, PDUs of the first set of PDUs that have already been delivered to lower layers by a PDCP transmitter layer. In embodiments, the method may further comprise performing a discard on the associated second set of PDUs, upon or after the expiry of the timer. In embodiments, the method may further comprise establishing for each PDU of either of the associated sets of PDUs, a PDU-based discard timer. In embodiments, the PDU-based discard timers established for the PDUs of a same set of PDUs may be initialized with a common PDU initialization time value and are activated upon delivery, at a PDCP transmitter layer, of the respective PDU. In embodiments, the PDU-based discard timers established for the PDUs of at least one of the associated sets of PDUs may be of type discardTimer as defined in 3GPP TS 38.323. In embodiments, the PDU-based discard timers established for the PDUs of at least one of the associated sets of PDUs may be of type discardTimerForLowImportance as defined in 3GPP TS 38.323. In embodiments, upon the expiry of a PDU-based discard timer established for a PDU of either of the associated sets of PDUs, the method may further comprise performing a discard on the corresponding set of PDUs, if a PDU Set Discard as defined in 3GPP TS 38.323 is configured on that set of PDUs. In embodiments, if a discard is performed on one of the associated sets of PDUs, as a result of the expiry of a PDU-based discard timer, the method may further comprise performing a discard on the other associated set of PDUs, even if the established timer has not yet been expired. In embodiments, the established timer for the second set of PDUs may apply to multiple associated sets of PDUs, including the associated first set of PDUs. In embodiments, the performing a discard may comprise performing a discard on the first set of PDUs, as function of multiple timers established for multiple associated sets of PDUs, including the timer established for the associated second set of PDUs. In embodiments, the first or second data modality may be one of the following: video, audio, or haptic. In embodiments, each data modality may be mapped onto a distinct data flow. In embodiments, the transmitter may comprise, or be embedded within, a user equipment or a base station operating within a 3GPP-compliant wireless communication network. In accordance with a second aspect of the invention, there is provided a processing device configured to perform the method according to any aspect or embodiment described above. According to embodiments of the present disclosure, there is provided a method for managing data transmission (e.g., multimodal XR data) between a transmitter and a receiver of a wireless network (e.g., a wireless communication network, such as 3GPP), the method at the transmitter comprising, discarding a first PDU in dependence on a timer for a second PDU. The second PDU may be associated (e.g., linked) to the first PDU and / or the modality of the second PDU may be different to that of the first PDU. Throughout the present disclosure the term ‘flow’ is used to refer to a flow of data from one element of the wireless network to another element. Further, throughout the present disclosure embodiments refer to one or more PDU Sets (e.g., the first PDU Set of the first embodiment), however it will be appreciated that the methods (and apparatuses) described herein may be similarly applicable to one or more PDUs, without departing from the scope of the present disclosure. Any feature in one aspect of the invention may be applied to other aspects of the invention, in any appropriate combination. In particular, method aspects may be applied to apparatus / device / unit aspects, and vice versa. Furthermore, features implemented in hardware may be implemented in software, and vice versa. Any reference to software and hardware features herein should be construed accordingly. For example, in accordance with other aspects of the invention, there are provided a computer program comprising instructions which, when the program is executed by a processing unit, cause the processing unit to carry out the method of any aspect or example described above and a computer readable storage medium carrying the computer program. BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will now be described, by way of example only, and with reference to the following drawings in which: Figure 1 illustrates an example of a wireless communication system in accordance with aspects of the present disclosure, Figure 2 illustrates an example of a user equipment (UE) in accordance with aspects of the present disclosure, Figure 3 illustrates an example of a gNB in accordance with aspects of the present disclosure, Figure 4 illustrates the user plane protocol stack of a 5G NR system in accordance with aspects of the present disclosure, Figure 5 shows a block diagram depicting the activation or deactivation of PDU Set discarding within a communication network in accordance with aspects of the present disclosure, Figure 6 shows a block diagram depicting the transmission of multimodal PDU Sets within a communication network in accordance with aspects of the present disclosure, Figure 7 illustrates a flowchart of a method for managing the transmission of multimodal data performed by a transmitter in accordance with some aspects of the present disclosure, Figure 8 illustrates the interdependency between PDU Sets of different data modalities in accordance with aspects of the present disclosure, Figure 9 illustrates the multimodal discarding in accordance with aspects of the present disclosure, Figure 10 illustrates a flowchart of a process for managing timers related to a PDU belonging to a PDU Set in accordance with aspects of the present disclosure, Figure 11 illustrates a flowchart of a method for managing the transmission of multimodal data performed by a transmitter in accordance with other aspects of the present disclosure, Figure 12 illustrates a flowchart of a method for managing the transmission of multimodal data performed by a transmitter in accordance with further aspects of the present disclosure, Figure 13 illustrates a flowchart of a PDU discarding process in accordance with aspects of the present disclosure, Figure 14 illustrates a flowchart of a PDU Set discarding process in accordance with aspects of the present disclosure. DETAILED DESCRIPTION OF EMBODIMENTS Embodiments of the present invention provide methods, devices, and computer program products for managing the transmission of multimodal data between a transmitter and a receiver within a communication network configured to support Extended Reality (XR) applications. A modality may correspond to, without limitation, visual data, audio data, or haptic feedback. The invention introduces a multimodal-based mechanism that allows the discarding of Protocol Data Unit (PDU) sets, which is configured and permitted on the transmitter side. The transmitter and receiver may correspond to the User Equipment (UE) and the base station (gNB), respectively, or vice versa, depending on the communication direction. This approach ensures that out-of-sync PDU Sets are discarded. By abandoning unnecessary or delayed transmissions, network resources are conserved, thereby reducing congestion and latency. In the present disclosure, the expression ‘PDU Set’ designates a collection of one or more Protocol Data Units (PDUs) that collectively carry the payload of a single unit of information generated at the application level, such as a video frame or a slice used in interactive services like Extended Reality (XR) (as referenced in TR 26.926). More broadly, a PDU Set is a set of one or more PDUs carrying collectively a unit of information. A PDU is a unit of information at a given protocol layer; at the IP layer, a PDU is an IP packet. In some implementations, all PDUs in a PDU Set are essential for the application layer to fully utilize and render the corresponding unit of information. However, in other scenarios, the application layer may still be able to recover parts of the information unit even when some PDUs are missing, allowing for resilience in data transmission. An important aspect of XR application awareness is the PDU Set-based Quality of Service (QoS) handling, which enables the network to manage all PDUs within a Set in an integrated manner and apply differentiated handling across PDU Sets. This capability is critical for optimizing the delivery of time-sensitive and interactive content, ensuring a high-quality user experience in varying network conditions. In the present disclosure, the expression ‘PDU Set Quality of Service (QoS) parameters’ designates one or more parameters designed to ensure effective and efficient delivery of multimedia data, especially for interactive services like Extended Reality (XR). Three main PDU Set QoS parameters are defined to support efficient PDU Set-based handling in the Next Generation Radio Access Network (NG-RAN). First, the PDU Set Delay Budget (PSDB) establishes an upper limit for the delay that a PDU Set may experience during transfer between the User Equipment (UE) and the N6 termination point at the User Plane Function (UPF). According to the 3GPP standard TS 23.501, The PSDB defines a time budget allocated to the transport of the PDU Set across the 5G network. This QoS parameter, defined by the application, is used by a 5G network to assess if a PDU Set (e.g., application data packet) is delivered on time. Second, the PDU Set Error Rate (PSER) defines the acceptable upper limit for the rate of PDU Sets that are processed by the sender but fail to be successfully delivered to the receiver's upper layer. This parameter is crucial for managing non-congestion related PDU Set losses, allowing the network to configure link layer protocols effectively to maintain a high level of service quality. Lastly, the PDU Set Integrated Handling Information (PSIHI) indicates whether all PDUs within a PDU Set are essential for the application at the receiver. This information is critical for optimizing resource allocation and ensuring efficient data handling, particularly in applications where real-time data synchronization is vital. Each of these parameters plays a significant role in enabling robust and adaptive QoS management in 5G networks, ensuring that multimedia content is delivered seamlessly and efficiently to enhance user experiences. Of course, other PDU Set QoS parameters may be considered. For example, the PDU Set Importance parameter allows the network to assign importance levels to different PDU Sets, enabling preferential handling and resource allocation for critical data streams, which is particularly important in real-time XR applications. The PDU Set Size, referring to the total number of PDUs within a set, influences overall transmission efficiency, with larger sizes potentially enhancing data integrity but possibly leading to longer transmission times. The PDU Set Throughput, expressed in bits per second (bps), indicates the rate at which data is successfully delivered, ensuring that sufficient bandwidth is available for high-quality multimedia content. Moreover, monitoring the PDU Set Loss Rate is vital, as it reflects the frequency of packet loss during transmission, which can significantly affect user experience. Lastly, PDU Set Jitter, the variation in packet arrival times, can disrupt the smooth playback of audio and video, making it crucial to minimize jitter for maintaining synchronized and seamless interactions. In the present disclosure, the expression ‘Multimodal PDU Sets’ designates a collection of PDU Sets that each carry different type of sensory data, such as visual, auditory, haptic, or other inputs, related to the same scene or experience. These PDU Sets are handled collectively to ensure that all the data modalities associated with the experience are delivered and processed together in a synchronized fashion. Each PDU Set corresponds to a specific modality (e.g., a video frame, an audio stream, or a haptic feedback unit), but their combined transmission supports a unified, immersive experience for the end user. The key challenge with multimodal PDU Sets is ensuring that the different media streams are received within a tightly controlled time frame. If one PDU Set arrives too early or too late relative to others, the immersive experience can break down, causing delays or disjointed feedback. This approach relies on strict Quality of Service (QoS) handling, where parameters such as delay budgets, error rates, and integrated handling information are used to ensure that all PDU Sets within a multimodal experience are delivered efficiently and synchronously, enabling the user to experience the data as a cohesive whole. In the present disclosure, the expression ‘synchronization threshold’ refers to the maximum tolerable temporal separation between the reception of two PDU Sets related to the same scene or experience, each carrying data fora different sensory modality (e.g., one for visual data and the other for auditory or haptic data). This threshold ensures that the corresponding sensory experiences, such as sight, sound, or touch, are perceived as synchronized by the user. If the temporal separation between the arrival of these PDU Sets exceeds the synchronization threshold, the sensory inputs may appear disjointed or out of sync, disrupting the coherence of the immersive experience. For more than two modalities, such as when additional sensory inputs like haptic feedback are involved, the synchronization threshold becomes more complex and may be defined in various ways. In one approach, the multiple modalities may be ranked according to their importance (from the receiver’s perspective, for example), and the synchronization threshold may be determined by considering only the two most important modalities or by considering the most and least important modalities. In another approach, multiple elementary synchronization thresholds are defined, each characterizing a different pair of modalities. Figure 1 illustrates an example of a wireless communication system 100 in which embodiments of the invention may be implemented. The wireless communication system may include one or more base stations (gNBs) 101, one or more user equipment (UEs) 102, and a core network (CN) 103. The wireless communication system may support various radio access technologies. In some implementations, the wireless communication system may be a New Radio (NR) network, such as a 5G network, a 5G-Advanced network, ora 5G Ultra-Wideband network. In other implementations, the wireless communication system may support radio access technologies beyond 5G, such as 6G. The one or more gNBs may be dispersed throughout the geographic area covered by the wireless communication system. One or more of the gNBs described herein may be, include, or be referred to as a network node, base station, network element, radio access network (RAN), NodeB, next-generation NodeB (gNB), or other suitable terms. Two gNBs may directly communicate via a communication link, which may be a wireless or wired connection, over the Xn interface (e.g., as specified in 3GPP document TS 38.423), enabling coordination and data exchange between them. By handling both control signaling (NG-C) and user data (NG-U), the NG interface supports the efficient and flexible operation of the wireless communication system, enabling features like highspeed data transfer, ultra-low latency, and massive connectivity. Furthermore, each gNBs may control one or more cells, with a cell defined as a specific geographical area where a UE can connect to the network. Each cell is characterized by its unique radio frequencies and signaling parameters, enabling effective communication between the UE and the network. Once a connection is established between a gNBs and a UE, the gNBs to which the UE is connected is referred to as the serving gNBs (or source gNBs) for the UE, and the cell controlled by the serving gNBs, on which the UE is camping, is referred to as the serving cell. The interface between a gNBs and a UE is the Uu interface, The Uu interface may encompass several main user plane and control plane protocols that facilitate communication between the gNBs and the UE. The user plane protocols include the Service Data Adaptation Protocol (SDAP), which manages Quality of Service for data flow; Packet Data Convergence Protocol (PDCP), responsible for header compression and encryption; Radio Link Control (RLC), ensuring reliable data transfer and segmentation; Medium Access Control (MAC), which manages access to the physical channel; and the Physical (PHY) layer, handling the actual transmission of radio signals. The control plane protocols include the Radio Resource Control (RRC), which manages connection establishment and mobility; PDCP for control signaling; RLC for reliable signaling communication; MAC for efficient control message transmission; and the PHY layer for transmitting signaling messages. The one or more UEs may be dispersed throughout the geographic area covered by the wireless communication system. One or more of the UEs described herein may be, include, or be referred to as a remote device, a mobile device, a wireless device, or other suitable terms. More broadly, a UE may refer to any wireless device or terminal capable of communicating with a network, enabling users to access services and applications. This includes a wide range of devices such as smartphones, laptops, tablets, loT devices, and wearables. A UE may be able to support wireless communication directly with another UE over a Device-to-Device (D2D) communication link. In some implementations, such as vehicle-to-everything (V2X) deployments, the communication link may be referred to as a sidelink. For example, a UE may support wireless communication directly with another UE over a PC5 interface, which is specifically designed for direct communication between UEs, enabling applications like emergency alerts, vehicle coordination, and other critical services. Additionally, UEs are increasingly capable of accessing Extended Reality (XR) services over the network, which include Virtual Reality (VR), Augmented Reality (AR), and Mixed Reality (MR) experiences. These services typically require high bandwidth, low latency, and edge computing resources, which are supported by advanced 5G and beyond networks. UEs such as XR wearables, VR headsets, and AR glasses can connect to the network via high-speed 5G or Wi-Fi 6 connections, utilizing features like Network Slicing and Mobile Edge Computing (MEC) to ensure the low latency and high data rates necessary for immersive XR experiences. By leveraging these capabilities, users can seamlessly access real-time XR services for applications in gaming, healthcare, education, and more. The CN is responsible for managing key functions such as user authentication, access authorization, tracking, connectivity management, and various access, routing, and mobility-related functions. In 5G, the CN is often implemented as the 5G Core (5GC), which is structured into two distinct entities: the Control Plane (CP) and the User Plane (UP). The CP is responsible for managing network operations related to access and mobility, as performed by components like the Access and Mobility Management Function (AMF), ensuring that the UE can establish and maintain secure, continuous connections with the network. The Control Plane also handles Non-Access Stratum (NAS) functions, which include critical tasks such as mobility management, user authentication, and bearer management. These NAS functions enable the CP to coordinate both signaling bearers and data bearers for the UEs connected to the network. Additionally, NAS plays a pivotal role in managing UE mobility across cells, ensuring seamless handovers and session continuity, especially in high-mobility scenarios like vehicles or roaming users. Meanwhile, the User Plane (UP), via components like the User Plane Function (UPF), is primarily responsible for the routing of user data packets between the UE and external Data Networks (DNs), such as the public internet, private corporate networks, or specialized cloud services. The UPF handles the actual data modality, implementing Quality of Service (QoS) policies and ensuring efficient routing to meet the application's requirements, such as low-latency communication for services like cloud gaming or Extended Reality (XR) applications. The CN communicates with Packet Data Networks (PDNs) 104 through backhaul links, which serve as the transport medium between the 5GC and external data networks. These PDNs may include the public internet, private corporate networks, or specialized servers, such as XR application servers 105 (as illustrated in Figure 1) or cloud gaming servers. For instance, when a UE needs to access services hosted on these PDNs, a Protocol Data Unit (PDU) session is established between the UE and the CN, allowing for a logical connection. The CN routes both control information and user data through this PDU session, ensuring that the UE can communicate effectively with application servers on the PDN. Overall, the PDU session exemplifies the dynamic and flexible nature of 5G, enabling the CN to manage efficient data transmission, session continuity, and network resource optimization, all while supporting a wide range of use cases, from traditional internet access to latency-sensitive, high-bandwidth applications like XR and autonomous vehicles. Figure 2 illustrates a block diagram of a User Equipment (UE) device 200, which is similar to the UE devices 102 described in Figure 1. The UE device is configured in accordance with the principles of the present disclosure, and may be implemented in one or more embodiments. The UE comprises a plurality of components configured to facilitate wireless communication, interaction with external peripherals, and the execution of processing tasks. These components include, without limitation, a processor 201, memory 202, I / O controller 203, transceiver 204, antenna set 205, and a UE communication manager 206. All of these components are operatively and communicatively coupled to enable the coordinated operation of the UE device. In embodiments, the processor may comprise a Central Processing Unit (CPU), or may alternatively include a combination of processors such as a Digital Signal Processor (DSP), an Application-Specific Integrated Circuit (ASIC), or any other combination thereof. The processor is configured to execute machine-readable instructions stored within the memory to enable the UE to perform various functions, including, but not limited to, wireless communication, management of user interactions, and control of peripheral devices. In embodiments, the processor may execute operating systems such as iOS®, Android®, or Windows®, and may be capable of supporting multiple processing cores to enhance computational performance. Furthermore, the processor may be configured to manage Radio Link Control (RLC) functions, wherein the RLC transmitter and RLC receiver may be implemented as software modules executable by the processor. The memory may comprise Random Access Memory (RAM), Read-Only Memory (ROM), or a combination of both. In certain embodiments, the memory may further include one or more mass storage devices, such as Solid-State Drives (SSD) or disk-based storage devices. The memory is configured to store the operating system, applications, and data required for the operation of the UE, as well as Basic Input Output System (BIOS) instructions, which facilitate low-level hardware management. The execution of machine-readable instructions stored in memory is critical for enabling the UE to perform essential functions, such as establishing communication connections, handling data transactions, and interacting with external peripherals. In embodiments, the memory may be integrated into the processor as an embedded memory module. The I / O controller is operatively coupled to external peripheral devices and is configured to manage input and output signals between the UE and these peripherals. The I / O controller may, in various embodiments, facilitate interaction with devices such as image capture devices (e.g., cameras), image rendering devices (e.g., displays), audio capture devices (e.g., microphones), and audio rendering devices (e.g., speakers). Furthermore, the I / O controller may interact with one or more sensors configured to detect the user's position or other environmental factors. The I / O controller manages the necessary hardware and signaling required for efficient input / output operations and peripheral device interactions. The transceiver is configured to enable bidirectional wireless communication between the UE and external networks and devices. In embodiments, the transceiver may facilitate connectivity to various wireless communication standards, including but not limited to Wi-Fi, Bluetooth, LTE, and 5G NR (New Radio). The transceiver may comprise receiver chains and transmitter chains, with the receiver chains being configured to receive, amplify, demodulate, and decode incoming wireless signals, and the transmitter chains being configured to modulate, amplify, and transmit outgoing signals. The transceiver may also include modems and frequency shifters to process wireless signals across different frequency bands. In embodiments, RLC layer functionalities may be managed by the processor, and the RLC transmitter and receiver may be implemented as software components that are executed by the processor. The antenna set is configured to support wireless communication by enabling the transceiver to send and receive signals across various frequency bands. The antenna set may consist of one or more antennas that are tuned to specific frequency bands to enhance signal reception and transmission. In embodiments, the antenna set may support advanced technologies such as beamforming and Multiple Input Multiple Output (MIMO), thereby improving the efficiency and performance of the UE's wireless communication capabilities. The antenna set allows the UE to manage data transmission and reception across multiple frequency bands, leveraging advanced signal processing techniques to improve overall communication performance. The UE communication manager is configured to control the communication between the UE and a Radio Access Network (RAN). In various embodiments, the communication manager is responsible for managing the establishment, maintenance, and release of wireless connections between the UE and the RAN, which may include communication with a base station, such as a gNB in a 5G network. The communication manager may determine the appropriate time slots and frequencies for transmitting and receiving data, and may manage both control plane and user plane data to ensure that communication protocols are adhered to. In embodiments, the communication manager may implement the Uu interface, facilitating the interaction between the UE and the base station according to predefined radio access technologies. Figure 3 illustrates a block diagram of a base station device 300, such as the gNBs 101 shown in Figure 1, in accordance with embodiments of the present disclosure. The base station device includes various components configured to transmit and receive communications, such as between the base station and user equipment (UE). The base station device may include, without limitation, a processor 301, a memory 302, an inter-station communication manager 303, a transceiver 304, an antenna set 305, a core network communication manager 306, and a base station communication manager 307. These components may be coupled (e.g., operatively, communicatively, functionally, electronically, electrically) to one another via one or more interfaces, facilitating the coordinated operation of the base station device. The processor may be configured to manage and control the various operations of the base station device. In some implementations, the processor may be a Central Processing Unit (CPU) or may alternatively include a combination of processors, such as a Digital Signal Processor (DSP), Application-Specific Integrated Circuit (ASIC), or Field Programmable Gate Array (FPGA). The processor may be configured to execute machine-readable instructions stored in the memory, thereby enabling the base station to carry out functions related to communication management, signal processing, and data handling. In certain embodiments, the RLC transmitter and RLC receiver functionalities may be implemented as software modules executed by the processor. The processor may be an intelligent hardware device configured to support wireless communication functions in the base station device. The memory may include Random Access Memory (RAM), Read-Only Memory (ROM), or a combination of both. Additionally, the memory may comprise mass storage devices, such as a Solid-State Drive (SSD) or disk-based storage. The memory may store the operating system, BIOS instructions, applications, and other data necessary for the functioning of the base station device. Furthermore, the memory may store computer-executable code that, when executed by the processor, enables the base station to perform functions described in this disclosure. In some implementations, the memory may be integrated into the processor or may be coupled to it. The inter-station communication manager is configured to manage communication between the base station and other base stations. In embodiments, the inter-station communication manager provides a standardized Xn interface, as defined by 3GPP, to facilitate inter-base station communication. This manager ensures that data exchange between base stations occurs seamlessly, enabling coordination and synchronization across a network of base stations. The transceiver is configured to enable bi-directional wireless communication between the base station device and external devices, which may include UEs or other base stations. In embodiments, the transceiver may be configured to support communication over various wireless standards, including Time Division Duplex (TDD) and Frequency Division Duplex (FDD). The transceiver may include receiver chains and transmitter chains that handle signal reception and transmission, respectively. The receiver chain may be configured to receive, amplify, and demodulate incoming signals, while the transmitter chain modulates and amplifies outgoing signals for transmission. These chains may support modulation techniques such as phase-shift keying (PSK) and quadrature amplitude modulation (QAM), providing robust signal processing capabilities. In some implementations, the transceiver may handle RLC layer functionalities through software executed by the processor. The antenna set is operatively coupled to the transceiver and is configured to support wireless communication across multiple frequency bands. The antenna set may include one or more antennas, though In embodiments, it preferably includes multiple antennas to support advanced signal processing techniques such as beamforming and Multiple Input Multiple Output (MIMO). These techniques enable the base station to transmit and receive data more efficiently by directing signal beams toward specific UEs, enhancing communication reliability and performance. The core network communication manager manages communication between the base station and the core network. In embodiments, the core network communication manager provides a standardized NG interface, as defined by 3GPP standards, to facilitate communication with the core network. This component ensures that data exchanged between the base station and the core network adheres to the appropriate communication protocols, providing reliable and efficient data transmission. The base station communication manager is configured to manage communication between the base station and multiple UEs. This component may control the establishment, maintenance, and release of communication links with the UEs. In certain embodiments, the base station communication manager may implement the Uu interface to facilitate this communication. The scheduler within the base station communication manager is responsible for allocating time slots and frequency bands to different UEs, and information regarding these slots is regularly transmitted to the UEs. The communication manager may be implemented as a software-based function executable by the processor, or as a dedicated hardware component. Figure 4 illustrates the user plane protocol stack of a 5G NR system. The user plane protocol stack follows the architecture outlined in 3GPP standards for5G systems. The diagram shows key components, including a User Equipment (UE), a gNB (Next Generation Node B or 5G base station), a User Plane Function (UPF), and a Data Network (DN). These elements correspond to the components described in Figure 1, such as UEs 102, gNBs 101, UPF-CN 103, and DN 104. Additionally, In embodiments, there may be an intermediate UPF, positioned between the gNB and the anchor UPF, which connects to the DN. The intermediate UPF helps in traffic routing and optimization, particularly in complex network deployments involving local breakout or traffic management. The interface between the UE and the gNB is the Uu interface, which is composed of several protocol layers. These layers include the SDAP (Service Data Adaptation Protocol) layer responsible for handling QoS flows and mapping them to Data Radio Bearers (DRBs), the PDCP (Packet Data Convergence Protocol) layer, the RLC (Radio Link Control) layer, the MAC (Medium Access Control) layer, and the PHY (Physical) layer. The interface between the gNB and the UPF is the NG-U interface, which consists of the GTP-U (GPRS Tunneling Protocol - User Plane) for encapsulating user plane traffic, along with layers such as UDP (User Datagram Protocol), IP (Internet Protocol), and lower-level data link and physical layers that may be implemented using technologies like Ethernet over fiber cables. In the gNB, a relay layer bridges the SDAP and GTP-U layers, facilitating the smooth transition of user plane data. In cases where there is an intermediate UPF, a similar relay layer bridges the GTP-U layers between the UPFs. The interface between the anchor UPF and the DN is the N6 interface, which handles the final leg of the user data delivery to the data network. This interface can leverage the same data link and physical layers used in the NG-U interface. The PDU (Protocol Data Unit) layer in the UPF plays a crucial role in handling PDU sessions. These sessions provide a logical connection between the UE and the DN, enabling the transfer of user data. Depending on the PDU session type, the PDUs may correspond to IPv4 packets, IPv6 packets, both (in IPv4v6 sessions), or Ethernet frames in the case of non-IP PDU sessions. At the start of a PDU session, particularly during session establishment, the core network assigns QoS (Quality of Service) parameters to the UE, gNB, and UPF. For applications such as Extended Reality (XR), additional QoS parameters such as the PDU Set Delay Budget, PDU Set Error Rate, and PDU Set Integrated Handling Indication are assigned to ensure the session meets the specific needs of XR applications. Each protocol layer handles its specific type of PDU. For example, the RLC layer handles RLC PDUs, while the MAC layer processes MAC PDUs. Unless otherwise stated, the term "PDU" refers to the end-to-end user plane data packet processed by the PDU layer in the UPF. For certain application services, such as media or XR, the UPF performs application packet inspection to determine the boundaries of PDU Sets, inspecting headers like RTP / SRTP and video payloads such as H.264, H.265, and H.266. This inspection is critical for optimizing the handling of data traffic, particularly in real-time services. When PDU Sets are identified, the UPF conveys PDU Set Identification Information to the NG-RAN in the GTP-U header. This information includes a sequence number for the PDU Set, an indication of the end of the PDU Set, the size of the PDU Set, and a PDU Set importance indicator, which helps prioritize traffic within the same QoS flow. This mechanism ensures efficient handling and delivery of data across the network, especially in scenarios where multiple PDU Sets are transmitted with varying levels of importance or delay requirements. In both uplink and downlink directions, data transmission in a 5G system relies on managing application flows and mapping them to protocol layers efficiently. This process involves the identification of PDU Sets and mapping them to QoS flows, ensuring the required Quality of Service (QoS) for applications like video and XR (Extended Reality). In the uplink direction, application data are generated in the UE. When a PDU session is established, the UE obtains the QoS parameters from the core network. These parameters are provided during the PDU session establishment procedure, ensuring that the UE is aware of the quality requirements for data transmission. Once the application layer generates the PDUs, they arrive at the PDU layer in the UE. At the PDU layer, the UE performs application packet inspection to determine the PDU Set boundaries. This step is crucial for ensuring that the generated PDUs are appropriately grouped and managed according to their QoS requirements. The UE detects the PDU Set identification information and applies the mapping rules received from the core network. These rules define how each PDU Set is mapped to one or more QoS flows. Just like in the downlink, multiple PDU Sets can be mapped to the same or different QoS flows within an XR session. After identifying the PDU Set boundaries and mapping them to QoS flows, the UE maps the QoS flows to Data Radio Bearers (DRBs) using the SDAP (Service Data Adaptation Protocol) layer. Each DRB is managed by a dedicated PDCP (Packet Data Convergence Protocol) entity. Multiple application flows can be multiplexed into one DRB, or each flow can be mapped to separate DRBs. Additionally, a single application flow can be divided across multiple DRBs if necessary. Once mapped to DRBs, the data is further mapped to RLC channels, which are then mapped to MAC logical channels, ensuring proper transmission over the physical interface. In the downlink direction, the core network, specifically the UPF, detects the PDU Set identification information and retrieves mapping rules from the core network. These rules define how each PDU Set is mapped to a QoS flow, ensuring that the data packets meet the QoS requirements. The GTP-U (GPRS Tunneling Protocol - User Plane) layer handles the transport of these PDUs between the UPF and the gNB. The GTP-U PDUs are marked with a QoS flow identifier, which is used by the gNB to map the traffic accordingly. The QoS flow identifier assigned in the GTP-U layer helps the gNB manage incoming traffic. The gNB's relay layer extracts the PDU Set identification information and the QoS flow identifier from the GTP-U PDUs and maps them into SDAP QoS flows. During an XR session, multiple PDU Sets can be mapped to a single QoS flow, or alternatively, they may be mapped to different QoS flows depending on the application's specific needs. At the gNB, the SDAP layer maps the QoS flows to DRBs. Each DRB is managed by a PDCP entity, allowing for the efficient handling of user data. As with the uplink, multiple application flows can be multiplexed into one DRB, or each application flow can be mapped to separate DRBs. Alternatively, a single application flow can be divided across multiple DRBs. The DRBs are then mapped to RLC channels, which are further mapped to MAC logical channels, completing the downlink transmission path to the UE. In both uplink and downlink, the application layer is responsible for generating one or more flows, such as video or audio streams, depending on the use case (e.g., XR, streaming). These flows are divided into PDU Sets at the PDU layer, with each PDU Set type being mapped to appropriate QoS flows. Multiple application flows can be multiplexed into a single QoS flow, or each flow can be assigned to different QoS flows. In some cases, a single application flow can be divided across multiple QoS flows to optimize network performance. The SDAP layer then maps the QoS flows to DRBs, ensuring that the data is properly handled by the PDCP layer. Multiple application flows can be combined within a single DRB, or they can be split across multiple DRBs to balance network load and meet QoS requirements. This mapping flexibility allows for efficient handling of complex applications like XR, where various flows (e.g., video, audio, and sensing) may have different performance requirements. In certain situations, some XR data may become obsolete after a delay period has elapsed, making it unusable by the decoder. When a PDU Set is transmitted over a 5G network, information about the reception status of the PDUs and the time elapsed with respect to the PDU Set Delay Budget (PSDB) may be available. In downlink, the gNB, or in uplink, the UE, can detect a PDU transmission failure, even after attempted retransmissions and error correction mechanisms. If the decoder can only process a complete application data packet that is received on time (e.g., if the PDU Set Integrated Handling Indication (PSIHI) is "true"), then any remaining PDUs of the PDU Set, for which transmission is still pending, become useless after the PSDB has elapsed. The RLC protocol operates in three modes: Transparent Mode (TM), Unacknowledged Mode (UM), and Acknowledged Mode (AM). TM transmits data without any protocol headers. UM implements segmentation and duplication detection, while AM adds a retransmission mechanism, such as Automatic Repeat Request (ARQ), to enhance reliability. RLC AM is used when the reliability of the lower layers (e.g., PHY and MAC layers) is insufficient. The retransmission process in RLC AM is configured by the gNB, with one key parameter being the maximum number of allowed retransmissions for a given RLC SDU or its segments, as specified by parameters like 'maxRetxThreshold' in TS 38.322. When an RLC SDU or segment is transmitted but not received by the RLC receiver, the RLC transmitter is configured to retransmit the missing RLC SDU or segment. Multiple retransmissions can occur at scheduled intervals until the missing data is successfully received or the maximum number of retransmissions is reached. Once this limit is exceeded, RLC AM resets the current session and triggers a Radio Link Failure (RLF). The retransmission procedure also depends on the RLC receiver, which sends status reports to the RLC transmitter, indicating which RLC SDUs have been successfully received. Based on these reports, the transmitter schedules retransmissions and adjusts the transmission window. RLC status reporting is either triggered by a polling request from the transmitter or by the detection of missing data by the receiver. If a sequence number gap or segment offset gap is identified, combined with an expired reassembly timer (e.g., t-Reassembly in TS 38.322), the data is considered lost. As a result, retransmission decisions are delayed by both the polling mechanism and the reassembly timer. Although this mechanism helps reduce network overhead and limits the total number of retransmissions, it introduces delays when lower protocol layers fail to transmit the data correctly. These additional delays are unacceptable for certain low-latency, high-reliability applications, such as XR. Additionally, delaying the retransmission of an RLC SDU can negatively impact the management of the transmitting window. The transmitting window defines the sequence numbers of RLC SDUs that are eligible for transmission, bounded by lower and upper limits. The window is only updated when the reception status of the lower-bound RLC SDU is confirmed. If this status remains unconfirmed, the window remains static, even if new RLC SDUs are ready for transmission from upper layers (e.g., PDCP). This results in a situation where transmission of a second PDU Set is stalled because the reception status of an RLC SDU from the first PDU Set is unconfirmed, and the sequence numbers of the second PDU Set fall outside the transmitting window. Figure 5 shows a block diagram depicting the activation or deactivation of PDU (Protocol Data Unit) set discarding 500 within a communication network designed to support XR (Extended Reality) applications. The process begins with the network 501 sending a discard configuration to the User Equipment (UE) 502, where the configuration explicitly specifies whether the PDU Set discarding functionality is to be activated or deactivated for specific radio bearers onto which PDU Sets are mapped. This discard configuration is transmitted based on network conditions and predefined parameters, such as Quality of Service (QoS) requirements or latency constraints, which are critical in ensuring seamless XR application performance. For example, the discard configuration may be part of an RRC configuration (as defined in TS 38.331) and may include at least one of: PDU_Set_discard: True if PDU Set discard is activated, discard_timer: initial value of the discard timer to apply to PDCP PDUs, psi_discard_timer: initial value of the discard timer to apply to PDCP PDUs, when psi discard is activated. The network may then send a PSI discard activation message, explicitly specifying whether the PSIbased PDU Set discarding functionality is to be activated or deactivated for specific radio bearers, i.e., for specific PDU Sets. The discard mechanisms allow the network to manage data transmission efficiently by discarding non-essential PDUs under certain conditions, particularly for XR applications where strict real-time requirements dictate that late packets may no longer be relevant. This ensures optimal resource utilization while maintaining the user experience in latency-sensitive environments like augmented reality (AR) or virtual reality (VR). The PDU Set discarding process thus aids in balancing the trade-off between maintaining low latency and ensuring reliable communication across the network. In some implementations, the network may dynamically adjust the discard policy for PDU Sets based on varying network conditions, such as fluctuating bandwidth or changing levels of network congestion, which are common in XR environments. This dynamic adjustment ensures that the discarding process is tailored to current operational conditions, further optimizing network performance for XR services. Additionally, the network may employ sophisticated algorithms to prioritize certain data types within the PDU Sets, ensuring that critical data is not discarded while allowing less important packets to be dropped if necessary. Through this mechanism, the PDU Set discarding feature contributes to the efficient transmission of data and the seamless operation of XR applications in next-generation communication networks, such as 5G and beyond. Figure 6 illustrates a flowchart depicting an example of Protocol Data Unit (PDU) Sets 600 exchanged between a transmitter 601 and a receiver 602, encompassing different modalities. In this example, four PDU Sets are transmitted from the transmitter to the receiver. PDU Sets 611 and 612 are part of a first modality 610, while PDU Sets 621 and 622 belong to a second modality 620. For example, modality 610 represents a video modality, whereas modality 620 represents a haptic modality. A delay budget requirement may be applied to each individual modality. This requirement specifies the maximum allowable time between the reception of two consecutive PDU Sets at the receiver for an individual modality. In Figure 6, this time limit is represented by intervals 615 and 625 for the first and second modalities, respectively. More broadly, any PDU Set arriving later than the allowed delay budget after the reception of a prior PDU Set may be deemed outdated. Under certain configurations, outdated PDU Sets may be discarded at the receiver and therefore not forwarded to the application layer (e.g., at a UE fordownlink applications), making them effectively lost if unutilized by the receiver. To save radio resources, timers (e.g., discardTimer as defined in 3GPP TS 38.323) may be implemented on the transmitter side to detect outdated PDU Sets before transmission, enabling their discarding prior to sending. A real-time congestion management procedure may additionally be applied to PDU Sets within each modality. In accordance with specific configurations (e.g., d i sea rdT i me rForLowIm porta nee as defined in the PDCP-Config information element in TS 38.331) and activation signals (e.g., the gNB may issue a MAC Control Element to activate the discard for low-importance PDUs), the transmitter may manage a secondary timer (e.g., discardTimerForLowImportance as defined in 3GPP TS 38.323) for each designated low-importance PDU Set. Once this secondary timer elapses, PDUs or PDU Sets are discarded as specified by the defined configurations. Certain Extended Reality (XR) applications require that PDU Sets from different modalities be delivered to the application within predefined time constraints. For example, PDU Set 621 must arrive no later than time interval 630 after receiving the PDU Set 611. In some use cases, the timing relationship between two modalities is asymmetric. As specified in TS 22.847, a maximum delay of 15 ms applies from video reception to tactile reception, while a different delay limit of 50 ms is set from tactile reception to video reception. Accordingly, based on configurations at the receiving side, if a PDU Set from a first modality is delayed beyond the reception time of a PDU Set from a second modality, both PDU Sets are considered obsolete and thus rejected by the application. The timing interrelationship between two modalities cannot be preemptively detected on the transmitter side using timers applied to individual modalities (such as, discardTimer or discardTimerForLowImportance). Thus, a procedure is necessary on the transmitting side to detect inter-dependency violations by PDU Sets before their transmission. Such a procedure enables the transmitter to discard these PDU Sets, conserving valuable radio resources. Figure 7 shows a flowchart illustrating a method 700 for managing the transmission of multimodal data between a transmitter and a receiver within a communication network configured to support Extended Reality (XR) applications, according to some embodiments. The transmitter and receiver may correspond, respectively, to the User Equipment (UE) and the base station (gNB), or vice versa, depending on the direction of communication. The method depicted in Figure 7 encompasses a mechanism where the discarding of Protocol Data Unit (PDU) Sets is permitted and configured at the transmitter side (PDU Set discarding = True). In this method, the multimodal data may be structured into flows, each flow carrying PDU Sets of an individual data modality among the multiple data modalities. These modalities may include various types of data, such as video, audio, haptic feedback, and sensor information, all pertaining to the same XR scene or experience. A PDU Set associated with a first modality may be linked to, or interdependent with, none, one, or multiple other PDU Sets corresponding to other modalities that describe or augment the same XR experience. For instance, a video PDU Set may be associated with an audio PDU Set, or a haptic feedback PDU Set, thereby collectively contributing to the overall immersive XR experience. The discarding functionality is configured to allow the transmitter to selectively discard certain PDUs and / or PDU Sets based on network conditions or predefined criteria, such as Quality of Service (QoS) requirements, latency thresholds, or buffer capacity. This selective discarding ensures that time-sensitive data, which is no longer relevant due to delays or congestion, is discarded to preserve network efficiency and maintain the real-time performance requirements inherent in XR applications. The method depicted in Figure 7 is implemented at the transmitter side, such as at the PDCP layer of the transmitter, and is described in relation to two Protocol Data Unit (PDU) Sets, each corresponding to a distinct data modality, such as video and audio, both related to the same Extended Reality (XR) scene or experience. These two modalities are governed by a predefined synchronization threshold (including one threshold value, also referred to as a delay requirement value, in the case of symmetry between the two modalities, and two threshold values in the case of asymmetry.). This threshold establishes a time constraint: when the time delay between the arrival of the two multimodal PDU Sets at the receiver exceeds this threshold, the user experience is negatively impacted. Specifically, the late-arriving PDU Set, or in some cases both PDU Sets, become irrelevant or unusable, thus compromising the overall XR experience. Depending on some configuration, when the interdependency synchronization threshold is exceeded, only one of the two PDU Sets is deemed irrelevant, while the second one may be delivered to the application. In embodiments, the synchronization between the two modalities is symmetrical, with the same synchronization threshold value applied regardless of which multimodal PDU Set arrives first. In other embodiments, the synchronization is asymmetrical, making the order of arrival of the multimodal PDU Sets relevant, with different synchronization threshold values applied depending on their arrival order. At step S710, two PDU Sets, each corresponding to a distinct data modality and both associated with the same XR scene or experience, are obtained, such as received by the PDCP layer from an upper layer (SDAP layer or application layer). In some scenarios, a PDU Set may be considered obtained if at least its first PDU is obtained. The two PDU Sets may thereby be referred to as linked or associated or interdependent. By way of example, the first PDU Set may correspond to a video data modality, such as representing the moment when a tennis ball makes contact with a racket, while the second PDU Set may correspond to an audio data modality, such as representing the 'tac' sound generated by that event. The first-arriving PDU Set, whether already transmitted or awaiting transmission, is referred to as the 'primary PDU Set', while the other is designated as the 'secondary PDU Set'. Of course, which of the PDU Sets is referred to as the 'primary PDU Set' and which as the 'secondary PDU Set' may depend on parameters other than the arrival time, such as one or more associated QoS parameters, the setting of the multimodal discard timer may, in this case, be modified. The two PDU Sets may be provided either simultaneously or sequentially, depending on their arrival time difference (at the PDCP layer for example). The two PDU Sets may have none, some, or all of their respective parameters in common. These parameters may include intrinsic parameters, such as the size in terms of the number of constituent PDUs, or extrinsic parameters, such as one or more QoS parameters for the PDU Sets. Additionally, a predefined synchronization threshold that establishes the time constraint between the two PDU Sets is also obtained, for illustration purposes, it is assumed that the two modalities are symmetric. At step S720, a discard timer, also referred to as a multimodal discard timer, is initialized and activated based on multiple events and parameters, including the arrival times (at the PDCP layer for example) of the primary and secondary PDU Sets, as well as the synchronization threshold. The initialization time value of the discard timer depends on the time of its activation, meaning that the initialization value of the discard timer is different depending on whether the discard timer is activated at the arrival time of the primary PDU Set or at the arrival time of the secondary PDU Set. For the sake of ease, the timer may function as a decrement timer, initialized at an initialization time value (e.g., in seconds), and expire when it reaches zero. Alternatively, the same mechanism may be implemented using an increment timer, which starts at zero and expires when it reaches the initialization time value. In a first aspect of step S720, the discard timer is activated at the arrival time of the primary PDU Set, such as at the arrival time of the first PDU in the primary PDU Set. In this case, the discard timer is initialized with a time value derived from, such as equal to, the sum of the delay budget of the PDU Set (assumed to be the same for both PDU Sets) and the synchronization threshold. If the two PDU Sets have different delay budgets (PSDB), the delay budget used to compute the initialization time value may preferably be that of the primary PDU Set. In a second aspect of step S720, the discard timer is activated at the arrival time of the secondary PDU Set, such as at the arrival time of the first PDU in the secondary PDU Set. In this case, the discard timer is initialized with a time value derived from, such as equal to, the sum of the delay budget of the PDU Set (assumed to be the same for both PDU Sets) and the synchronization threshold, minus the arrival time difference between the two PDU Sets. If the two PDU Sets have different delay budgets (PSDB), the delay budget used to compute the initialization time value may preferably be that of the primary PDU Set. At step S730, discarding is performed on the secondary PDU Set either upon or after the expiry of the multimodal discard timer, for example regardless of the transmission status of the PDUs of the primary PDU Set, which may not yet have been delivered to the lower layers, may have been delivered to the lower layers but still be in the process of transmission and / or retransmission to the receiver, or may already have been received by the receiver. In another example, the discarding may also be performed on the primary PDU Set either upon or after the expiry of the multimodal discard timer. 'Discarding' refers to abandoning the transmission to the receiver. In embodiments, the discarding may be performed at the PDCP layer of the transmitter by not delivering the PDUs to be discarded to lower protocol layers, such as the RLC layer. In other embodiments, the discarding may also involve lower protocol layers, such as the RLC and MAC layers, where these layers receive discarding instructions from the PDCP layer regarding the PDUs to be discarded. At the RLC layer, the discarding may be applied specifically to PDUs that are subject to retransmissions, such as those following a negative acknowledgment from the receiver. Depending on whether one or more PDUs from the secondary PDU Set were still being processed by the transmitter, at any of its protocol layers, when the multimodal discard timer expired, the discarding may be partial or total. For example, if one or more PDUs from the secondary PDU Set were no longer being processed by the transmitter, such as after successful transmission to the receiver, when the multimodal discard timer expired, the discarding is partial, meaning the transmission of only the remaining PDUs is abandoned. Conversely, if all the PDUs from the secondary PDU Set were still being handled by the transmitted at the expiry of the multimodal discard timer, the discarding is total, with all PDUs of the secondary PDU Set being abandoned. In the context of 5G XR (Extended Reality), discarding mechanisms, according to embodiments of the invention, provide significant benefits. By abandoning unnecessary or delayed transmissions, network resources are conserved, reducing congestion and latency. This is crucial in XR applications, where maintaining low latency and high-quality, synchronized multimodal data is essential for providing seamless, immersive experiences. Discarding also ensures that outdated or irrelevant data does not interfere with the real-time nature of XR content, thereby enhancing the overall user experience. In embodiments, the multimodal discarding mechanism described with reference to Figure 7 may be extended to scenarios involving more than two PDU Sets, with each PDU Set representing a different modality. In this context, multiple pairs of PDU Sets may be defined, and the described discarding mechanism may be applied either successively or in parallel to these pairs. For example, all the defined pairs may share a common PDU Set, which acts as either the primary PDU Set or the secondary PDU Set, as described with reference to Figure 7. In another example, as illustrated with reference to Figure 9, the pairs may be defined such that each PDU Set is part of two pairs: in one, it acts as the primary PDU Set, and in the other, it acts as the secondary PDU Set, as described with reference to Figure 7. In this other example, the delay budget of the PDU Set, when acting as the primary PDU Set, is preferably modified to expire when the PDU Set becomes discardable in its role as a secondary PDU Set. In a further example, one or more QoS parameters of the multimodal PDU Sets may also be used to define the pairs of PDU Sets. The PSIHI may be used to define the pairs of PDU Sets in such a way that at most one item of each pair has its PSIHI set to false. In these embodiments, the synchronization threshold may be the same for all defined pairs of PDU Sets, or each pair of PDU Sets may have its own distinct synchronization threshold. This PDU Set pair-based approach requires the use of multiple timers, with each defined pair of PDU Sets having its own timer. In other embodiments, the multimodal discarding mechanism described with reference to Figure 7 may be extended to scenarios involving more than two PDU Sets, each representing a different modality, while requiring fewer timers than the embodiments described above. In one example, a primary PDU Set and multiple secondary PDU Sets are defined, all sharing the same synchronization threshold with respect to the primary PDU Set. In this case, a single discard timer may be employed, activated at the arrival time of the primary PDU Set, such as the arrival time of the first PDU in the primary PDU Set, and initialized with a time value derived from, such as equal to, the sum of the delay budget of the PDU Sets (assumed to be the same for all PDU Sets) and the synchronization threshold. In these embodiments, the discarding described in step S730 may be applied to all secondary PDU Sets that have not been completely transmitted when the timer expires. In further embodiments, the multimodal discarding mechanism described with reference to Figure 7 may be extended to scenarios where a primary PDU Set of a first modality is associated with multiple successive secondary PDU Sets of a second modality. In these scenarios, a single discard timer may be employed, as described in step S702, by considering only the first-arriving PDU Set for the second modality. Subsequently, the discarding, as described in step S730, may be applied, upon or after the expiry of the discard timer, to each secondary PDU Set that has one or more PDUs that have not yet been transmitted. Figure 8 is a flowchart illustrating the inter-dependency between PDU Sets within a multimodal application. Three distinct modalities are represented: a first modality comprising PDU Sets of type A, which may represent a haptic modality; a second modality comprising PDU Sets of type B, which may represent a video modality; and a third modality comprising PDU Sets of type C, which may represent an audio modality. The inter-dependency requirements between the different modalities are defined at the receiver as follows: From the reception of PDU Set B, the maximum allowable delay to receive PDU Set A is denoted as ba. According to TS 22.261, the standard value for ba, representing the haptic-to-video delay, is 50 ms. From the reception of PDU Set A, the maximum allowable delay to receive PDU Set B is denoted as ab. According to TS 22.261, the standard value for ab, representing the video-to-haptic delay, is 15 ms. From the reception of PDU Set C, the maximum allowable delay to receive PDU Set A is denoted as ca. According to TS 22.261, the standard value for ca, representing the haptic-to-audio delay, is 25 ms. From the reception of PDU Set A, the maximum allowable delay to receive PDU Set C is ac. According to TS 22.261, the standard value for ac, representing the audio-to-haptic delay, is 50 ms. Figure 9 is a flowchart illustrating multimodal discarding at the transmitting side, according to some embodiments. The inter-dependency requirements among different modalities may be checked at the transmitter to detect any violations of these requirements, thereby enabling the discard of PDU Sets prior to transmission, and conserving radio resources. In this example, the multimodal requirements are defined as illustrated in Figure 8, showing the behavior of the transmitter at the PDCP layer. A PDU Set of modality C is first received from the upper layer (e.g., SDAP layer or application layer), followed by a PDU Set of modality A, and then later, a PDU Set of modality B. The three horizontal arrows represent the progression of time. Additionally, the PDU Set discard parameter is set to true for each PDU Set, indicating that the discard of any individual PDU results in the discard of the entire PDU Set to which that PDU belongs. Upon the reception of each PDU of any PDU Set delivered from the higher layer, a discard timer is initialized to a configured time value and activated. The value of this discard timer is consistent across all PDUs of a same PDU Set and may be configured by the gNB. Preferably, this configured value is a function of the PDU Set delay budget; alternatively, it may depend on the PDU delay budget itself; and for low-importance PDU Sets, if congestion management is active, the configured value is preferably shorter than both PDU Set and PDU delay budgets. Thus, the discard timer associated with the first PDU of PDU Set C will expire at time 9c, triggering a delaybased discard event (e.g., time 9c equals the arrival time of PDU Set C at the transmitter plus the PDU Set delay budget, or PSDB). Similarly, delay-based discarding for PDU Set A will occur at time 9a, and for PDU Set B, at time 9b. When the first PDU of PDU Set A is received by the PDCP transmitter layer, processing of PDU Set C has been ongoing since the interval diff_ca. PDU Set C will be discarded when time reaches 9c; therefore, PDU Set A must be delivered to the lower layer no later than ca after the expiration time of PDU Set C at 9c. To initiate multimodal-based discarding of PDU Set A, a multimodal timer is started when the first PDU of PDU Set A is received. This multimodal timer is initialized to the discard timer value (e.g., PSDB), minus the arrival time difference between the first PDUs of PDU Sets A and C (diff_ca), plus the delay requirement ca for A to C. As a result, the multimodal timer for PDU Set A is set to expire at time 10a. Similarly, when the first PDU of PDU Set B is received by the PDCP transmitter layer, processing of PDU Set A has been ongoing since the interval diff_ab. PDU Set A will be discarded at time 10a due to the delay-based discard process and also at time 11a due to the multimodalbased discard process. Since, in this example, time 10a occurs before time 9a, PDU Set B must be delivered to the lower layer no later than ab after PDU Set A's expiration at time 10a. To initiate multimodal-based discarding of PDU Set B, a multimodal timer is started when the first PDU of PDU Set B is received. This multimodal timer is initialized to the initialization multimodal timer value of PDU Set A, minus the time difference in arrival between the first PDUs of PDU Sets B and A (diff_ab), plus the delay requirement ab for B to A. Consequently, the multimodal timer for PDU Set B will expire at time 10b. Figure 10 is a flowchart illustrating the management process of timers triggered in relation to a PDU within a PDU Set belonging to a first data modality 1000, as part of the transmission of multimodal data between a transmitter and a receiver in a communication network configured to support Extended Reality (XR) applications, according to some embodiments. The method depicted in Figure 10 is described with respect to the first-arriving PDU of the PDU Set at the PDCP layer of the transmitter, as illustrated in step S1010, originating from an upper layer (such as the SPAP or application layer). For any subsequently arriving PDUs within the PDU Set, steps S1050 and S1060 may not be applicable or may be omitted. At step S1020, it is determined whether a congestion management procedure is configured on the transmitter and whether the PDU Set to which the received PDU belongs is a low-importance PDU Set to which the congestion management procedure applies. If the congestion management procedure applies to the received PDU, a congestion timer, such as discardTimerForLowImportance as defined in 3GPP TS 38.323, is initialized and activated, as performed at step S1030. Conversely, if the congestion management procedure does not apply to the received PDU, a PDU discard timer, such as discardTimer as defined in 3GPP TS 38.323, is initialized and activated, as performed at step S1040. At step S1050, it is determined whether the PDU Set to which the received PDU belongs is interdependent with a PDU Set of a second data modality. This interdependency is characterized by a synchronization threshold. If the determination is negative, no further timer is set for the received PDU before it is delivered to the lower layers, as performed at step S1070. Conversely, if the determination is positive, step S1060 is performed. At step S1060, a multimodal discard timer is established for the PDU Set to which the received PDU belongs. The initialization of the multimodal discard timer may depend on whether another multimodal discard timer has been established for the interdependent PDU Set of the second data modality in relation to another PDU Set of another data modality, as well as any congestion or discard timers established for its PDUs (as described in steps S1020 to S1040 for the PDU Set). In all cases, the multimodal discard timer is initialized and activated based on the time at which the interdependent PDU Set becomes discardable. The interdependent PDU Set may become discardable if its PDU Set discard is configured to true and the congestion or PDU discard timer established for its first-arriving PDU has expired, or if a corresponding multimodal discard timer expires. If the PDU Set to which the received PDU belongs is interdependent with multiple other PDU Sets, only the first expiring interdependent PDU Set may be considered when defining the multimodal discard timer. After initializing and activating the multimodal discard timer, the received PDU is delivered to the lower layers, as performed at step S1070. The multimodal discarding mechanism described with reference to Figure 7 may be integrated with or operate alongside other discarding mechanisms. For example, the multimodal discarding mechanism may operate alongside a PDU Set-based discarding mechanism by configuring a PDU Set discarding (PDU Set Discarding = True), which can be viewed as a monomodal discarding mechanism, as it applies to a PDU Set independently of any linked or associated or interdependent PDU Sets from other data modalities. Figure 11 shows a flowchart illustrating a method for managing the transmission of multimodal data between a transmitter and a receiver 1100, where a multimodal discarding mechanism operates alongside a PDU Set-based discarding mechanism, according to some embodiments. The method depicted in Figure 11 is implemented on the transmitter side, such as at the PDCP layer of the transmitter, and is described in relation to two Protocol Data Unit (PDU) sets, each corresponding to a distinct data modality, such as video and audio, both related to the same Extended Reality (XR) scene or experience. These two modalities are governed by a predefined synchronization threshold. For simplicity, it is assumed that the two PDU Sets share the same PSDB and are symmetric. Additionally, the firstarriving PDU Set is referred to as the primary PDU Set, while the other is referred to as the secondary PDU Set. It is also assumed, without limitation, that both PDU Sets are required at the receiver in order to utilize them, for example, to reconstruct a scene or experience. This means that if one PDU Set is successfully received by the receiver, but the other is not, the receiver cannot use the successfully received PDU Set to reconstruct the scene or experience. At step S1110, the primary PDU Set is obtained, such as received by the PDCP layer from an upper layer (SDAP layer or application layer). In some scenarios, a PDU Set may be considered obtained if at least its first PDU is obtained. Upon reception of the first-arriving PDU of the primary PDU Set, a first discard timer, initialized at a time value that may be derived from, for example equal to, the PSDB corresponding to the primary PDU Set, is activated. This first discard timer may also be defined similarly for each of the subsequently arriving PDUs of the primary PDU Set. Preferably, the discard timer is a decrement timer configured to expire when it reaches zero. It is to be noted that, upon expiration of the first discard timer (Yes in step S1130), the primary PDU Set, if, for example, one or more of its PDUs are still being processed at any transmitter protocol layer, becomes eligible for discarding (PDU Set discarding = True), as performed at step S1150. Of course, the transmission, and if necessary, retransmission, of PDUs from the first PDU Set is maintained (not represented in Figure 11) while the first discard timer is active (not yet expired). Several factors may result in the primary PDU Set not being entirely transmitted before expiration of the first discard timer. For instance, network congestion may cause transmission delays, preventing the complete transmission of the PDU Set within the allocated time. Furthermore, packet loss or corruption during transmission may necessitate retransmission of certain PDUs, and if such retransmissions cannot be completed before expiration of the discard timer, the remaining PDUs may be discarded. Additionally, scheduling delays at the Medium Access Control (MAC) layer may contribute to the incomplete transmission of the PDU Set within the discard timer window. At step S1120, the secondary PDU Set is obtained. Following the same procedure as for the primary PDU Set, a second discard timer, initialized at a time value that may be derived from, for example equal to, the PSDB corresponding to the secondary PDU Set, which is assumed to be identical to the primary PDU Set, is activated upon reception of the first-arriving PDU of the secondary PDU Set. This second discard timer may also be defined similarly for each of the subsequently arriving PDUs of the secondary PDU Set. It is to be noted that, upon expiration of the second discard timer (Yes in step S1140), the secondary PDU Set, if, for example, one or more of its PDUs are still being processed at any protocol transmitter layer, becomes eligible for discarding (PDU Set discarding = True), as performed at step S1150. Of course, the transmission, and if necessary, retransmission, of PDUs from the second PDU Set is maintained (not represented in Figure 11) while the second discard timer is active (not yet expired). At step S1160, carried out while the first discard timer is still active (not yet expired), a multimodal discard timer is defined. For example, if the secondary PDU Set has not yet been obtained, meaning the second discard timer is not yet activated, the multimodal discard timer may be initialized and activated, as described in the first aspect of step S720. In this case, the multimodal discard timer is initialized with a time value derived from, for example equal to, the sum of the delay budget of the PDU Set (assumed to be identical for both PDU Sets) and the synchronization threshold, and it is activated at the arrival time of the primary PDU Set, such as at the arrival time of the first PDU in the primary PDU Set. In another example, if the secondary PDU Set is obtained, meaning the second discard timer has been activated, the multimodal discard timer may be initialized and activated, as described in the second aspect of step S720. In this case, the multimodal discard timer is initialized with a time value derived from, for example equal to, the sum of the delay budget of the PDU Set (assumed to be the same for both PDU Sets) and the synchronization threshold, minus the arrival time difference between the two PDU Sets, and it is activated at the arrival time of the secondary PDU Set, such as at the arrival time of the first PDU in the secondary PDU Set. At step S1150, carried out upon or after the expiry of either the first or second discard timer, discarding is performed on the PDU Set whose discard timer has expired if, for example, one or more of its PDUs are still being processed at any transmitter protocol layer. Then, the other PDU Set may also be discarded, provided that it is eligible for multimodal-based discarding when the multimodal discard timer also expires, as performed at step S1180. At step S1180, carried out upon or after the expiry of the multimodal discard timer (Yes in step S1170), discarding is performed. This discarding may be applied to both PDU Sets if both PDU Sets are eligible for multimodal-based discarding. Alternatively, the discarding may be performed on the secondary PDU Set if, for example, one or more of its PDUs are still being processed at any transmitter protocol layer. The multimodal discarding mechanism described with reference to Figure 7, and in combination with a PDU Set-based discarding mechanism with reference to Figure 11, may also operate alongside a PDU-based discarding mechanism. The PDU-based discarding mechanism can be viewed as a PDU-level discarding mechanism, as it applies to individual PDUs independently of their association with a PDU Set. Figure 12 shows a flowchart illustrating a method for managing the transmission of multimodal data between a transmitter and a receiver 1200, where a multimodal discarding mechanism operates alongside two distinct PDU-based discarding mechanisms, according to some embodiments. A PDU-based discarding mechanism may be monolayer, implemented at a single protocol layer, including but not limited to the PDCP or RLC or MAC transmitter layers, or it may be multilayer, involving multiple protocol layers, such as both the PDCP and RLC transmitter layers. The method depicted in Figure 12 is implemented on the transmitter side, such as at the PDCP layer of the transmitter, and is described in relation to two Protocol Data Unit (PDU) sets, each corresponding to a distinct data modality, such as video and audio, both related to the same Extended Reality (XR) scene or experience. These two modalities are governed by a predefined synchronization threshold. For illustration purposes, it is assumed that PDU Set discarding is not configured for either PDU Set (PDU Set Discarding = False), meaning that the discard of a PDU does not lead to the discard of the corresponding PDU Set. It is also assumed that PsiDiscard is activated, and the primary PDU Set is a PDU Set of high importance (PSI = High), thus not subject to PSI discarding while the secondary PDU Set is a PDU Set of low importance (PSI=LOW), thus subject to PSI discarding. In other words, the two PDU Sets have distinct PSI values, with congestion-based discarding configured for the secondary PDU Set but not for the primary PDU Set. In this case, the PsiDiscard (PDU Set Importance Discard) mechanism is used for the secondary PDU Set. This mechanism operates, within the PDCP layer, to handles the discarding of outdated or unneeded PDCP PDUs based on specific criteria, typically related to synchronization and QoS (Quality of Service) requirements. At step S1210, upon receiving each PDU of the primary PDU Set, including the first-arriving PDU, at the PDCP layer from the SDAP or application layer, as illustrated in Figure 4, a PDU discard timer, initialized with a time value derived from (for example, equal to) the PSDB corresponding to the primary PDU Set, is activated. Preferably, this PDU discard timer is a decrement timer configured to expire when it reaches zero. Thus, as many PDU discard timers as PDUs within the primary PDU Set are activated. Of course, it is the PDU discard timer activated for the first-arriving PDU of the primary PDU Set that expires first, and the PDU discard timer activated for the last-arriving PDU of the primary PDU Set that expires last. Following a similar procedure as for the primary PDU Set, at step S1220, upon receiving each PDU of the secondary PDU Set, including the first-arriving PDU, at the PDCP layer from the SDAP or application layer, as illustrated in Figure 4, a PsiDiscard timer, initialized with a PsiDiscard value (for example, a predetermined PsiDiscard value), is activated. Preferably, this PsiDiscard timer is also a decrement timer configured to expire when it reaches zero. Of course, it is the PsiDiscard timer activated for the first-arriving PDU of the secondary PDU Set that expires first, and the PsiDiscard timer activated for the last-arriving PDU of the secondary PDU Set that expires last. The initial time value of the PsiDiscard timer is preferably less than (for example, half of) that of the PDU discard timer. This ensures that the PsiDiscard timer for a PDU in the secondary PDU Set expires before the PDU discard timer for a corresponding PDU in the primary PDU Set when both timers are activated at the same time. At step S1260, carried out while at least one PDU discard or PsiDiscard timer is still active (not yet expired), a multimodal discard timer is established. For example, if the secondary PDU Set has not yet been obtained, meaning none of the PsiDiscard timers has been activated, the multimodal discard timer may be initialized and activated, as described in the first aspect of step S720. In another example, if the secondary PDU Set is obtained, meaning that at least one PsiDiscard timer has been activated, the multimodal discard timer may be initialized and activated, as described in the second aspect of step S720. The expiry of the PDU timer for a PDU belonging to the primary PDU Set (Yes in step S1230) results in the discarding of that specific PDU, as performed at step S1250. Since PDU Set discarding is not configured on the primary PDU Set (PDU Set Discarding = False), the discarding of this PDU has no effect on the other PDUs in the primary PDU Set and does not lead to the discarding of the primary PDU Set as a whole. In a scenario where PDU Set discarding is configured (PDU Set Discarding = True), the discarding of an individual PDU will trigger the discarding of the entire primary PDU Set. The expiry of the PsiDiscard timer for a PDU belonging to the secondary PDU Set (Yes in step S1240) results in the discarding of that specific PDU, as performed at step S1250. Since PDU Set discarding is not configured on the secondary PDU Set (PDU Set Discarding = False), the discarding of this PDU has no effect on the other PDUs in the secondary PDU Set and does not lead to the discarding of the secondary PDU Set as a whole. In a scenario where PDU Set discarding is configured (PDU Set Discarding = True), the discarding of an individual PDU will trigger the discarding of the entire secondary PDU Set. Upon or after the expiry of the multimodal discard timer (Yes in step S1270), discarding is performed. This discarding may be applied to both PDU Sets if both PDU Sets are eligible for multimodal-based discarding. Alternatively, discarding may be performed on the secondary PDU Set if, for example, one or more of its PDUs are still being processed at any transmitter protocol layer. In embodiments, the discarding mechanism illustrated in relation to Figure 12 may incorporate, either in addition to or instead of the PDCP PDU-based discarding mechanism, an RLC PDU-based discarding mechanism. In this case, an RLC discard timer is used, typically applied in AM mode (Acknowledged Mode), where PDUs are acknowledged and retransmitted if not successfully received by the receiver. The RLC PDU-based discarding mechanism applies to each PDU of either PDU Set when encapsulated into an RLC PDU, by activating an RLC discard timer initialized with a time value preferably shorter than the PSDB of the PDU Sets. Upon expiry of the timer, the PDU is discarded, and the corresponding PDU Set is discarded if the associated PDU Set Discard is set to true. The use of an RLC discard timer is crucial for preventing excessive retransmissions, avoiding delays, and ensuring that outdated data does not clog the communication pipeline. The discard timer value can be configured based on QoS (Quality of Service) requirements and may range from milliseconds to seconds, depending on the service's real-time needs. The RLC PDU-based discarding mechanism may also be implemented based on the number of allowed retransmissions of an RLC PDU, rather than on a timer. In other embodiments, PDU-based discarding mechanisms, such as PDCP PDU-based or RLC PDU-based discarding mechanisms, may be applied differently to the PDUs of a multimodal data, depending on one or more QoS parameters of the associated PDU Sets. For example, a specific PDU-based discarding mechanism may be applied to the PDU Sets of one modality and not applied to the PDU Sets of another modality, based, for instance, on the QoS parameters of the PDU Sets. In another example, a PDU-based discarding mechanism may be applied differently to the PDU Sets of two distinct modalities, using, for instance, two different time values to initialize the discard timers. Figure 13 is a flowchart illustrating a PDU discarding process 1300 triggered by the expiry of a timer associated with a PDU belonging to a PDU Set of a first data modality, as part of the transmission of multimodal data between a transmitter and a receiver in a communication network configured to support Extended Reality (XR) applications, according to some embodiments. The process depicted in Figure 13 is, for illustration purposes, implemented at the PDCP layer of the transmitter. At step S1310, a timer previously initialized and activated for the PDU at the PDCP layer expires. This timer may be a congestion timer, such as discardTimerForLowImportance as defined in 3GPP TS 38.323, if the congestion management procedure applies to the PDU. Alternatively, the expired timer may be a PDU discard timer, such asdiscardTimeras defined in 3GPPTS 38.323. At step S1320, it is determined whether PDU Set discard is activated for the PDU Set to which the PDU belongs. If PDU Set discard is not configured (PDU Set discard = False), the expiry of the discard timer triggers the discarding of only the PDU, as performed in step S1330. If the PDU is being processed at lower layers, such as RLC or MAC, discard instructions may be sent from the PDCP layer to these lower layers. If PDU Set discard is configured (PDU Set discard = True), the expiry of the discard timer triggers the discarding of the entire PDU Set to which the PDU belongs, including the PDU whose discard timer has expired, as performed in step S1340. This discarding applies to PDUs that have not yet been delivered by the upper layers to the PDCP layer, PDUs currently being processed by the PDCP layer, and PDUs that have been delivered by the PDCP layer to lower layers. At the optional step S1350, performed after discarding the PDU Set to which the PDU belongs, it is determined whether a multimodal interdependency, according to which the receiver requires both PDU Sets to use each one, exists between this PDU Set and another PDU Set of a different modality whose transmission is planned or in ongoing. If such a specific interdependency is found (Yes in step S1350), the other PDU Set is also discarded, following a similar approach as described in step S1340. Figure 14 is a flowchart illustrating a multimodal discarding process 1400 triggered by the expiry of a multimodal timer associated with a PDU Set that is interdependent with at least one PDU Set belonging to another data modalities, as part of the transmission of multimodal data between a transmitter and a receiver in a communication network configured to support Extended Reality (XR) applications, according to some embodiments. The process depicted in Figure 14 is, for illustration purposes, implemented at the PDCP layer of the transmitter. At step S1410, a multimodal discard timer previously initialized and activated for the PDU Set expires. This expired timer may have been initialized in relation to the PDU Set itself, such as upon the arrival of the first PDU in the PDU Set at the PDCP layer, or in relation to an interdependent PDU Set. At step S1420, it is determined whether PDU Set discard is activated for the PDU Set. In embodiments, if PDU Set discard is not configured (PDU Set discard = False), the expiry of the multimodal discard timer does not constitute, alone, a basis for discarding any PDU of the PDU Set. In other embodiments, if PDU Set discard is not configured (PDU Set discard = False), the expiry of the multimodal discard timer leads to the discard of its PDUs. If PDU Set discard is configured (PDU Set discard = True), the expiry of the multimodal discard timer triggers the discarding of the entire PDU Set, as performed at step S1430, and, optionally, the discarding of the entire interdependent PDU Set, as performed at step S1440. In embodiments, the multimodal discarding mechanism, as described, for example, with reference to Figure 7, may be adapted to a scenario involving PDU Sets belonging to a single data modality, such as video. In this case, two types of PDU Sets may be defined, for example, based on their sequence numbers. For instance, PDU Sets with even sequence numbers may be associated with a first data modality, while those with odd sequence numbers may be associated with a second data modality. In another example, where the PDU Sets from a single data modality are mapped to multiple distinct data flows, the PDU Sets in each data flow may be associated with a different data modality. In other embodiments, the multimodal discarding mechanism, as described with reference to Figure 7, may be applied to PDU Sets of the same or different data modalities mapped to distinct data flows. For example, each data modality may be mapped to a different data flow. Whilst the present disclosure has been described with reference to examples and embodiments, it is to be understood that the disclosure is not limited to the disclosed examples and embodiments. It will be appreciated by those skilled in the art that various changes and modification might be made without departing from the scope of the disclosure, as defined in the appended claims. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. Unless otherwise defined herein, scientific and technical terms used in connection with the presently disclosed inventive concept(s) shall have the meanings that are commonly understood by those of ordinary skill in the art, and known techniques and procedures may be performed according to conventional methods well known in the art and as described in various general and more specific references that may be cited and discussed in the present specification. As used in this specification and claim(s), the words 'comprising,' 'having,' 'including,' or 'containing' (and any forms thereof, such as 'comprise' and 'comprises,' 'have' and 'has,' 'includes' and 'include,' or 'contains' and 'contain,' respectively) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps. The use of the term 'a' or 'an' in the claims and / or the specification may mean 'one,' as well as 'one or more,' 'at least one,' and 'one or more than one.' As such, the terms 'a,' 'an,' and 'the,' as well as all singular terms, include plural referents unless the context clearly indicates otherwise. Likewise, plural terms shall include the singular unless otherwise required by context. The use of the term 'or' in the present disclosure (including the claims) is used to mean an inclusive 'and / or' unless explicitly indicated to refer to alternatives only or unless the alternatives are mutually exclusive. Unless otherwise explicitly stated as incompatible, or the physics or otherwise of the embodiments, examples, or claims prevent such a combination, the features of examples disclosed herein, and of the claims, may be integrated together in any suitable arrangement, especially ones where there is a beneficial effect in doing so. This is not limited to only any specified benefit, and instead may arise from an “ex post facto” benefit. This is to say that the combination of features is not limited by the described forms, particularly the form (e.g., numbering) of example(s), embodiment(s), or dependency of claim(s). In the preceding embodiments (i.e., exemplary arrangements), the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over, as one or more instructions or code, a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media, which corresponds to a tangible medium such as data storage media, or communication media including any medium that facilitates transfer of a computer program from one place to another, e.g., according to a communication protocol. In this manner, computer-readable media may correspond to (1) tangible computer-readable storage media which is non-transitory or (2) a communication medium such as a signal or carrier wave. Data storage media may be any available media that can be accessed by one or more computers or one or more processors to retrieve instructions, code and / or data structures for implementation of the techniques described in this disclosure. A computer program product may include a computer-readable medium. By way of example, and not limitation, such computer-readable storage media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage, or other magnetic storage devices, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if instructions are transmitted from a website, server, or other remote source using a coaxial cable, fibre optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fibre optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave may be included in the definition of medium. It should be understood, however, that computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other transient media, but are instead directed to non-transient, tangible storage media. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc, where disks usually reproduce data magnetically, whilst discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

Claims

1. A method for managing data transmission between a transmitter and a receiver of a wireless network, the method comprising, at the transmitter, performing a discard on a first set of one or more protocol data units, PDUs, carrying collectively a unit of information, wherein the discard is performed as a function of a timer established for an associated second set of one or more PDUs carrying collectively a unit of information.

2. The method of claim 1, wherein the first set of PDUs corresponds to a first data modality, and the second set of PDUs corresponds to a second data modality different from the first data modality.

3. The method of claim 1 or 2, wherein the first set of PDUs is associated with a first data flow, and the second set of PDUs is associated with a second data flow different from the first data flow.

4. The method of any of the preceding claims, wherein the timer is initialized with an initialization time value dependent on a predefined synchronization threshold linking the first and second sets of PDUs.

5. The method of claim 4, wherein the initialization time value is further dependent on a delay budget associated with the second set of PDUs.

6. The method of claim 4, wherein the initialization time value is further dependent on a difference of arrival time between the first and second sets of PDUs.

7. The method of claim 4, wherein the initialization time value is further dependent on a time delay upon the expiry of which the second set of PDUs becomes discardable in relation to an associated other set of PDUs.

8. The method of claim 4, wherein the initialization time value is further dependent on the earliest-expiring time delay among a plurality of time delays, wherein, upon the expiry of each of the time delays, the second set of PDUs becomes discardable in relation to an associated other set of PDUs.

9. The method of any of the preceding claims, wherein the timer is activated upon delivering, at a PDCP transmitter layer, the first-arriving PDU of the second set of PDUs.

10. The method of any of the preceding claims, wherein the performing a discard comprises performing the discard on the first set of PDUs, upon or after the expiry of the timer established for the associated second set of PDUs.

11. The method of any of the preceding claims, wherein the performing a discard comprises at least one of:discarding, from transmission to the receiver, PDUs of the first set of PDUs that have not yet been delivered from upper layers to a PDCP transmitter layer,discarding, from transmission to the receiver, PDUs of the first set of PDUs that are currently under processing at a PDCP transmitter layer, ordiscarding, from transmission to the receiver, PDUs of the first set of PDUs that have already been delivered to lower layers by a PDCP transmitter layer.

12. The method of any of the preceding claims, wherein the method further comprises performing a discard on the associated second set of PDUs, upon or after the expiry of the timer.

13. The method of any of the preceding claims, wherein the method further comprises establishing for each PDU of either of the associated sets of PDUs, a PDU-based discard timer.

14. The method of claim 13, wherein the PDU-based discard timers established for the PDUs of a same set of PDUs are initialized with a common PDU initialization time value and are activated upon delivery, at a PDCP transmitter layer, of the respective PDU.

15. The method of claim 14, wherein the PDU-based discard timers established for the PDUs of at least one of the associated sets of PDUs are of type discardTimer as defined in 3GPP TS 38.323.

16. The method of claim 14, wherein the PDU-based discard timers established for the PDUs of at least one of the associated sets of PDUs are of type discardTimerForLowImportance as defined in 3GPP TS 38.323.

17. The method of any of claims 13 to 16, wherein upon the expiry of a PDU-based discard timer established for a PDU of either of the associated sets of PDUs, the method further comprises performing a discard on the corresponding set of PDUs, if a PDU Set Discard as defined in 3GPP TS 38.323 is configured on that set of PDUs.

18. The method of claim 17, wherein if a discard is performed on one of the associated sets of PDUs, as a result of the expiry of a PDU-based discard timer, the method further comprisesperforming a discard on the other associated set of PDUs, even if the established timer has not yet been expired.

19. The method of any of the preceding claims, wherein the established timer for the second set of PDUs applies to multiple associated sets of PDUs, including the associated first set of PDUs.

20. The method of any of the preceding claims, wherein the performing a discard comprises performing a discard on the first set of PDUs, as function of multiple timers established for multiple associated sets of PDUs, including the timer established for the associated second set of PDUs.

21. The method of any of the preceding claims when dependent on claim 2, wherein the first or second data modality is one of the following: video, audio, or haptic.

22. The method of any of the preceding claims when dependent on claims 2 and 3, wherein each data modality is mapped onto a distinct data flow.

23. The method of any preceding claim, wherein the transmitter comprises, or is embedded within, a user equipment or a base station operating within a 3GPP-compliant wireless communication network.

24. A processing device configured to perform a method according to any one of claims 1 to 23.

25. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out a method according to any one of claims 1 to 23.

26. A computer-readable medium carrying a computer program according to claim 25.36

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