Network Device Latency Timer Buffer Management
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Solution Overview
Problem
Network switching devices face challenges in maintaining high data rates and avoiding underrun conditions, where a transmitter lacks sufficient data for transmission, leading to erroneous session termination by remote devices.
Innovation Solution
A network device with a transmit buffer and packet buffer that uses a latency timer to determine when to transmit data chunks based on a maximum read latency, independent of the buffer fill level, ensuring data is sent at predetermined intervals to maintain desired data rates and prevent underrun.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If data is transmitted only when transmit buffer fill level reaches a threshold, then underrun conditions are avoided, but transmission latency increases
Solution Approach 1:
The system performs preliminary actions by pre-fetching data chunks from the packet buffer to the transmit buffer before they are actually needed for transmission. This allows the transmit buffer to be populated in advance, so when transmission is triggered by the latency timer rather than buffer fill level, the data is already ready immediately, thus avoiding latency without causing underrun
Solution Approach 2:
The system uses a latency timer that provides feedback about the time elapsed since the previous transmission. This feedback mechanism allows the transmission logic to make informed decisions about when to transmit data, ensuring that transmissions occur at predetermined intervals that prevent underrun while minimizing latency. The feedback loop continuously monitors timing and adjusts transmission timing accordingly
2Speed
If transmit buffer size is increased to reduce latency, then transmission speed improves, but device complexity and memory requirements increase
Solution Approach 1:
The system dynamically manages buffer resources by using a latency timer that adapts transmission timing based on actual data availability and timing requirements. Rather than requiring a statically large buffer to cover all possible latency scenarios, the dynamic timing approach allows the buffer to be smaller while still achieving low latency by transmitting data as soon as the latency interval elapses and data is available
Solution Approach 2:
Data chunks are preliminarily loaded into the transmit buffer from the packet buffer in advance of actual transmission needs. This pre-loading allows the system to use a smaller transmit buffer because data is staged ahead of time, reducing the need for large buffer capacity while maintaining high transmission speed and low latency
3Loss of time
If data chunks are transmitted immediately when available, then latency is reduced, but underrun conditions may occur
Solution Approach 1:
The system implements periodic action by using a latency timer that triggers transmissions at predetermined time intervals rather than immediately when data becomes available. This periodic transmission approach ensures that data is sent at regular intervals, preventing underrun conditions by ensuring sufficient data accumulation time while still maintaining low latency through consistent, predictable transmission timing
Solution Approach 2:
The system performs preliminary actions by pre-loading data chunks into the transmit buffer before the latency interval elapses. This preliminary data preparation ensures that when the latency timer triggers transmission, the data is already ready to be sent immediately, thus achieving low latency without requiring immediate transmission that could cause underrun
Data Source
AI summary
A network device includes a transmit buffer from which data is transmitted to a network, and a packet buffer from which data chunks are transmitted to the transmit buffer in response to read requests. The packet buffer has a maximum read latency from receipt of a read request to transmission of a responsive data chunk, and receives read requests including a read request for a first data chunk of a network packet and a plurality of additional read requests for additional data chunks of the network packet. A latency timer monitors elapsed time from receipt of the first read request, and outputs a latency signal when the elapsed time reaches the first maximum read latency. Transmission logic waits until the elapsed time equals the first maximum read latency, and then transmits the first data chunk from the transmit buffer, without regard to a fill level of the transmit buffer.