TCP-FIT: An Improved TCP Congestion

Control Algorithm and its Performance

Dr. Jingyuan Wang

Beihang University

Background

Transport Control Protocol

– More than 80% traffic over the Internet use TCP

Internet traffic

TCP

user

• Network Congestion

– Speed of packets sending > network capacity

• Congestion collapse: Throughput -> 0 B/S !!!

• TCP Congestion Control

– Control the packets sending speed to avoid network congestion

Background

TCPpacket

TCPSender

TCPpacket

Network

TCPReceiver

ACK

TCPpacket

TCPpacket

TCPpacket

Challenge of TCP over wireless links

• Traditional TCP congestion control algorithms are found

to perform poorly over wireless networks

– Traditional TCP: Packet loss = Congestion

– Wireless networks: Packet loss ≠ Congestion

t

TCP throughput

TCP over wired networks

Congestion losses

Networkcapacity

t

TCP throughput

TCP over wireless networks

Networkcapacity

Random losses

Main Challenge of wireless links: random losses

TCP performance over wireless links

0.1% Loss Rate (WiFi Networks)

0% Loss Rate (Wired Networks)

1% Loss Rate (3G Networks)

Random packet losses lead a serious TCP throughput degradation

Our solution: TCP-FIT

• Run MULTIPLE virtual TCP flows to fully

use network capacity

TCPSender

Network

TCPReceiver

1234567

TCPSender

TCPReceiver

1357

246

Network

Traditional TCP:

TCP-FIT :

Virtual flow

Virtual flow

Use queuing delay to adjust N

Performance of TCP-FIT

• 3G networks (5mbps, 1% Loss , 100 ms RTT)

Experiments

• 245 cities over the Internet

Experiments

TCP-FIT in USTREAM.tv

Improvement to other algorithms

• Ustream.tv

Comparing algorithm Average improvement

bic 51.27%

highspeed 99.74%

htcp 60.80%

hybla 96.91%

illinois 285.33%

scalable 110.58%

TCP-FIT + HTTP Streaming

• Ustream.tv

Customer and Partners

Thank you !

Video Demo

• http://v.youku.com/v_show/id_XMTQ5NzI0ODEy.html

Improvement to other algorithms

• SAMSUNG

TCP-FIT + HTTP Streaming

• 56.com

Average Re-buffer times during 3 days

TCP-FIT

TCP BIC