Datagram Congestion Control Protocol

1
Datagram Congestion Control Protocol

• Timothy Sohn
• Eiman Zolfaghari
• CS268 Project
• May 15, 2002

2
Motivation

• Real-time applications built on top of UDP are
  growing in bandwidth usage on the Internet
  (RealAudio, Counter Strike, IP Telephony)
• Do not need Additive Increase Multiplicative
  Decrease congestion mechanism
• But congestion control is difficult to correctly
  implement

3
Protocol Overview

• Plug and Play congestion control mechanisms on
  the fly
• Half-Connections allow each client can choose its
  own congestion control id (CCID) to use
• Low overhead like UDP
• Applications using UDP can easily change to this
  new protocol

4
Congestion Control ID3 (TFRC)

• TCP-Friendly Rate Control is intended for
  applications that do not require a fully reliable
  connection and to be friendly towards TCP flows
  in terms of send rates
• Receiver sends rate estimate and loss event
  history
• Sender uses equation that models SACK TCP to
  determine appropriate send rate

5
Implementation

• Basic Protocol implemented in user space on top
  of UDP using an event-based model rather than
  thread-based
• CCID3 implementation based off of TFRC code in
  ns-simulator

6
Testing

• Tests done using two machines running Nistnet
  (network emulation tool), tcpdump, some parsing
  scripts, and gnuplot to make graphs.
• Performance Metrics
• Send rate over time
• TCP-Friendliness of a single CCID3 over time
• Average TCP-Friendliness of a single CCID3 flow
  competing with TCP flows

7
Friendliness

• Measured friendliness of DCCP with CCID3 with
  respect to increasing TCP connections
• Exhibits relatively fair rate changes with
  respect to background flows

8
More Friendliness

• Friendliness ratio of DCCP with respect to itself
  and with respect to background TCP connections

9
Results

• CCID3 implementation is complete
• CCID3 is, on average, TCP-Friendly

10
Future Work

• We hope to implement CCID2 (TCP-like congestion
  control) and test the idea of half-connections
• There is no sense of reliability in DCCP, but
  implementing and testing a layer on top of the
  protocol would be interesting
• Move our implementation from user space to kernel
  space