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Profile for DCCP Congestion Control ID 4: the Small-Packet Variant of TFRC Congestion Control

This document describes CCID4, a congestion control mechanism designed for TFRC-SP (Small Packet) variant. It explains the differences between CCID4 and CCID3, such as header size, minimum sending rate, and loss rates for short intervals. It also discusses the Loss Interval option and its fields for calculating loss event rates.

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Profile for DCCP Congestion Control ID 4: the Small-Packet Variant of TFRC Congestion Control

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  1. Profile for DCCP Congestion Control ID 4:the Small-Packet Variant of TFRC Congestion Control draft-floyd-ccid4-00.txt Sally Floyd and Eddie Kohler July 2006, DCCP Working Group

  2. Differences between CCID 4 (for TFRC-SP) and CCID 3 (for TFRC) • Header size: For TFRC-SP, the allowed transmit rate in bytes per second is reduced to account for the packet header size of 32 bytes. • Minimum sending rate: TFRC-SP enforces a minimum interval of 10 ms. between data packets. • Loss rates for short loss intervals: For short lost intervals of at most two round-trip times, the loss rate is computed by counting the actual number of packets lost or marked. • The nominal segment size: In TFRC-SP, the nominal segment size used by the TCP throughput equation is set to 1460 bytes.

  3. The Loss Interval option. ____________________ Loss Interval _____________________ / \ +--------...-------+--------...--------+--------...--------+ | Lossless Length |E| Loss Length | Data Length | +--------...-------+--------...--------+--------...--------+ 3 bytes 3 bytes 3 bytes Loss Intervals in CCID 3. ____________________ Loss Interval ________________________ / \ +-------...-------+------...------+-----...-----+------...-----+ | Lossless Length |E| Loss Length | Data Length | Dropped Pkts | +-------...-------+------...------+-----...-----+------...-----+ 3 bytes 3 bytes 3 bytes 3 bytes Loss Intervals in CCID 4.

  4. Fields in the Loss Intervals Option: • Lossless Length: • Number of packets in lossless part. • Used for ECN Nonce Echo. • Loss Length: • Number of packets in lossy part. • Data Length: • Total number of packets excluding acknowledgements. • Used for calculating the loss event rate. • Dropped Pks: • Number of dropped packets in lossy part. • Used by CCID 4 for calculating the loss event rate for small loss intervals.

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