PTT Call Initialization Latency Reduction via SIP Pre-establishment
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Solution Overview
Problem
Current private digital mobile radio communication systems, particularly Push To Talk (PTT) systems, face challenges in achieving a latency of 300 ms for group calls across multiple users due to limitations in resource allocation and signaling processes, especially in broadband technologies like 3G+ and 4G, which fail to ensure timely resource pre-allocation and efficient communication channel management.
Innovation Solution
Implementing a method that allocates individual unicast sessions for both signaling and media on an IP-WAN cellular network using SIP protocol, allowing for immediate establishment of RTP sessions and maintaining active connections through periodic heartbeat messages to ensure low latency and efficient resource management across all users in a group call.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If PTT over Cellular (PoC) operates on OMA PoC protocol with IP-WAN network, then broadband communication capability is improved, but latency exceeds 300 ms due to lack of pre-allocated resources and paging message requirements
Solution Approach 1:
The patent applies preliminary action by pre-establishing unicast signaling and media sessions between the PTT client and server during the initial connection phase. The SIP INVITE message is sent and processed in advance to reserve RTP resources before the actual PTT call begins, ensuring that when a user presses the PTT button, the media path is already established and ready for immediate voice transmission, thus reducing latency below 300 ms while maintaining broadband capabilities
2Loss of time
If dedicated physical resources and control channels are allocated for each user, then latency is reduced to meet 300 ms requirement, but device complexity and resource allocation overhead increase
Solution Approach 1:
The patent applies universality by using a single IP-WAN connection and default carrier for both signaling and media transmission. The unicast SIP session serves multiple purposes: establishing signaling connectivity, reserving media resources, and creating the RTP path. This multi-functional approach eliminates the need for separate dedicated control channels and physical resources for each user, reducing system complexity while maintaining low latency through pre-established unicast paths
3Loss of time
If resources are pre-allocated for PTT sessions, then latency is reduced, but resource waste occurs when sessions are not actively used
Solution Approach 1:
The patent applies dynamics by making the unicast session establishment conditional and on-demand. The SIP INVITE message and RTP resource reservation are triggered only when a user actually initiates a PTT call or joins a PTT group, not continuously for all users. The session is dynamically created when needed and can be released when no longer required, optimizing the balance between low latency for active users and resource efficiency for inactive users
Data Source
AI summary
A method for initializing a call for a mobile terminal including PTT applications on an IP-WAN cellular network, the method including, for each user of the mobile terminal connected to an IP-WAN modem intended to register for a group call: upon starting up the IP-WAN modem, connecting the mobile terminal to the IP-WAN cellular network; when a PTT client is active and has obtained an IP address of a PTT server, initiating by the PTT client a procedure for registering a SIP with the PTT server on a default IP-WAN carrier; performing by the PTT client a procedure for affiliation to a call group with the PTT server on the default IP-WAN carrier, and as soon as the procedure for affiliation to the call group is performed, executing an “INVITE” (SIP) procedure to RTP resources at an application level on a PTT side and on the PTT client side, to allow the establishment of the RTP session after the affiliation of the PTT client to the group.