The Importance of Being TCPFriendly

1
The Importance of Being TCP-Friendly
DCP
UDP
TCP

• Eiman Zolfaghari
• E190 Professor Hatton
• May 2002

2
What is TCP?

• TCP Transport Layer Protocol The way the
  majority of data on the Internet is passed around
• Web pages, file transfers, chat programs
• Used because its reliable and fair

One TCP connection
Congestion
Max Bandwidth
Packets sent / second
Time (seconds)
3
What is TCP?

• TCP Transport Layer Protocol The way the
  majority of data on the Internet is passed around
• Web pages, file transfers, chat programs
• Used because its reliable and fair

A second TCP connection
Congestion
Max Bandwidth
Packets sent / second
Time (seconds)
4
What is UDP?

• UDP User Datagram Protocol The way video and
  audio streams are passed around
• No congestion control, thus not fair
• Not reliable at all

One Innocent TCP connection
Congestion
Max Bandwidth
Packets sent / second
Time (seconds)
5
What is UDP?

• UDP User Datagram Protocol The way video and
  audio streams are passed around
• No congestion control, thus not fair
• Not reliable at all

A Mean UDP Connection Comes In
Max Bandwidth
Packets sent / second
Innocent TCP Connection
Time (milliseconds)
6
Why wasnt this an issue before?

• Lots of unused bandwidth (not anymore)
• Little number of users (not anymore)
• Video streams? Audio Streams? Wholl use it?
  (Cable/DSL increased the demand)

TCP
UDP
7
The Importance of being TCP-Friendly

• Since the majority of the Internet uses TCP,
  other protocols must behave fairly towards it
• A protocol is TCP-Friendly if its long-term
  throughput does not exceed the throughput of a
  conformant TCP connection under the same
  conditions
• Thus, UDP is out of the picture

8
A TCP-Friendliness Equation

• Calculates estimated TCP throughput
  (packets/second)
• lact is the actual packet loss fraction of TCP
  packets
• tRTT is the TCP round trip time
• t0 is the TCP timeout value
• Source Padhye et al.

9
What about applications that use UDP?

• Make a new protocol that application developers
  can easily convert to
• Make a protocol that is both unreliable and yet
  has congestion control

UDP
TCP
DCP
10
A Solution DCP

• Datagram Control Protocol
• Variable reliability
• Reliable for initial connection rate negotiations
• No guarantees on other data
• Congestion Control Mechanisms
• each direction of flow gets to choose what kind
  of congestion control they wish to use
• The algorithms used for most congestion control
  mechanisms ensure TCP-friendliness
• Lightweight, like UDP

11
Congestion Control Mechanisms

• New research has come up with better ways of
  detecting and dealing with congestion
• TFRC TCP-Friendly Rate Control
• When packet is lost in TCP, throughput fluctuates
  a lot
• TFRC attempts to alleviate this, while
  maintaining TCP-friendliness
• TEAR TCP Emulation At Receivers
• Claims that it will be more TCP-friendly than TFRC

12
The Importance of Being TCP-Friendly
DCP
UDP
TCP

• To reduce Internet congestion, applications must
  use less UDP, and more TCP-friendly protocols
  like DCP