Congestion Control in Cellular Transport Networks
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Solution Overview
Problem
Current congestion control mechanisms in cellular communication networks, particularly when using High-Speed Downlink Packet Access (HSDPA), fail to effectively detect and manage congestion due to retransmission protocols, leading to increased network load and delayed congestion detection by Transmission Control Protocol (TCP).
Innovation Solution
A method involving a radio network controller that creates and transmits empty protocol data units to indicate congestion to TCP, minimizing re-transmissions and unnecessary data transmission, by detecting congestion through notification messages and using sequence numbers to manage protocol data units within the transport network.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the RLC AM protocol re-transmits lost packets to ensure reliable delivery, then packet loss is minimized for TCP, but congestion is concealed and TCP does not detect the congestion situation
Solution Approach 1:
The patent introduces an intermediary mechanism (dummy PDU or explicit indication) between the RLC AM protocol and TCP to convey congestion information. When congestion is detected at the transport network layer, the RNC sends a dummy PDU or congestion indication to the TCP layer, allowing TCP to detect congestion without relying on packet loss from RLC retransmissions.
Solution Approach 2:
The patent implements a feedback mechanism where the transport network layer informs the TCP layer about congestion conditions. Through notification messages or dummy PDUs, the system creates a feedback loop that allows TCP to receive real-time congestion status and adjust its transmission rate accordingly, rather than relying solely on packet loss feedback.
2Productivity
If TCP continues to feed more packets to lower layers when congestion occurs, then network throughput is maintained, but congestion is exacerbated and round trip time increases
Solution Approach 1:
The patent applies preliminary action by detecting congestion at the transport network layer before it significantly impacts TCP performance. The RNC detects congestion conditions and sends notification messages or dummy PDUs to TCP in advance, allowing TCP to proactively reduce its transmission rate before congestion worsens and RTT increases.
Solution Approach 2:
The patent implements real-time feedback from the transport network layer to TCP through congestion indication messages. This feedback mechanism allows TCP to continuously monitor network conditions and dynamically adjust its sending rate, maintaining optimal throughput while avoiding excessive congestion that would increase RTT.
3Adaptability or versatility
If standardized signaling messages are used to inform RNC about detected congestion, then congestion detection is standardized, but device complexity and signaling overhead increase
Solution Approach 1:
The patent leverages existing standardized signaling messages and protocols (such as Iub Framing Protocol) to convey congestion information. By making existing signaling mechanisms multi-functional—capable of carrying both traditional control information and congestion indicators—the patent avoids creating entirely new complex signaling protocols while maintaining standardization benefits.
Data Source
AI summary
A congestion control method of a cellular communication system is disclosed. A first protocol data unit having a first sequence number is transmitted from a radio network controller to a base station via a transport network. The base station detects a congestion situation of the transport network by detecting loss of the first protocol data unit during transmission over the transport network. In response to detecting the congestion situation, a notification message indicative of the detected congestion situation is transmitted from the base station to the radio network controller via the interface of the transport network.