1. Parameswaran, Subramanian
Modeling The Performance of FAST TCP over High-Speed and Wireless Networks by
Dasari, Ramesh Chandra
Parameswaran, Subramanian

2. CONTENTS Introduction What’s Wrong with TCP? Fast TCP – The Promise
Delay-based Congestion Control
Fast TCP over High-Speed Networks
Implementation
Fast TCP over Wireless
Results
Conclusion
References

3. INTRODUCTION
Internet growing in size everyday
Applications demand transfer of huge files
Congestion control algorithm needs improvisation
FAST TCP gives a much better throughput and utilization when compared to TCP

4. TCP has performed remarkably well till now
What’s Wrong with TCP?
TCP has performed remarkably well till now
Problem with TCP over large bandwidth-delay product networks
Packet Level: Linear increase of 1pkt/RTT is too slow.
Packet Level: Oscillations are unavoidable
Flow Level: hard to achieve small equilibrium loss probability
Flow Level: Unstable dynamics
Oscillations at packet and flow level overcome by equation-based control
Wireless links have high BER  data is easily corrupted. This causes retransmission timer to expire
In both cases TCP enters slow-start phase and transmission window drops to one segment

5. FAST TCP – The PROMISE
High-Speed, High Link Utilization and Throughput
Download rates in the order of 100 – 500 Mbps
All this using current infrastructure
Equation-based, hence avoids oscillations
Stable flow dynamics
Uses queuing delay rather than loss probability

7. DELAY-BASED CONGESTION CONTROL
TCP
Source
Destination
Forward Buffer
ACK DELAY
ACK Buffer
Loss probability 1 bit congestion information
Queuing Delay  RTT provides multibit information
Hence estimation is easier
Basic idea of Fast TCP is to delay the ACKs being transferred from the TCP destination towards the TCP source.

8. Fast TCP over High-Speed Networks
Delay ACKS from destination to source
Fast TCP controls ACK output rate
Instead of discarding packets, the congested
node delays ACKS
Hence output rate decreases
Delay in ACKS slows down transmission rate

9. Implementation
Transmission Rate = 15Mbps ;Window Size = 50000; Maximum Segment Size = 512 bytes; Queue Buffer Capacity = ; Delays of 1ms each for the blocks Delay #5 and Delay #7. Delay #8 (Ack Delay) has a delay of 0.13s; Ack Timer – 0.01s Application Delay = 0.01s; Forward Buffer for Fast TCP node = ; Ack Buffer for Fast TCP =

10. Current TCP attributes all losses to buffer overflows
Fast TCP over Wireless
Current TCP attributes all losses to buffer overflows
Packet Losses in Wireless Networks
Buffer Overflows
Wireless Environment like handoffs, interference, fading
When TCP encounters losses due to the wireless environment it gets confused

11. IMPLEMENTATION
The forwarding rate of the TCP source and destination is 106 pkts/s, buffers for both directions are 2Mbit, TCP initial RTO is 1s and TCP maximum segment size is 512 bytes. The routers have IP forwarding rate pkts/s, buffers of 2Mbits and a congestion notification threshold of bits. The links between routers and TCP hosts is 150Mbps while the wireless link between the routers is 30Mbits/s. There is a propagation delay of from the TCP source to router 1 and from router 2 to the TCP destination, which is 1 ms while the propagation delay over the wireless link from Router 1 to Router 2 is 150 ms.

12. RESULTS
FAST TCP’s link utilization exceeds TCP’s by 25%

13. FAST TCP vs TCP: 21% better throughput

14. CONCLUSION
Fast TCP achieves a better link utilization and throughput than TCP with negligible change to infrastructure
Due to Software limitations, we could not implement the Fast TCP node into the router in a wireless network
In due time users can have High-speed Internet access with almost no congestion

15. REFERENCES
[1] Wang Qian, Wu Jing, Cheng Shiduan, Ma Jian, Differentiated service Fast-TCP Policy for Flow Control and Resource Management. Communication Technology Proceedings, WCC - ICCT International Conference on, Volume: 2, 21-25 Aug
[2] Cheng Jin, Wei, D.X., Low, S.H, Fast TCP: Motivation, Architecture, Algorithms, Performance; INFOCOM Twenty-third AnnualJoint Conference of the IEEE Computer and Communications Societies, Volume: 4, 7-11 March 2004.
[3] Fei Peng, Shiduan Cheng, Jian Ma, Performance Analysis Of Fast-TCP Mechanism For Networks With High Bandwidth-Delay Products; Communication Technology Proceedings, WCC - ICCT International Conference on, Volume: 1, 21-25 Aug
[4] Jing Wu, Peng Zhang, Tao Du, Jian Ma, Shiduan Cheng, Improving TCP Performance In ATM Network By The Fast TCP Flow Control. Communication Technology Proceedings, ICCT ' International Conference on, Volume: vol.2, 22-24 Oct
[5] Qian Wang, Jing Wu, Shiduan Cheng, Jian Ma, Fast TCP Flow Control With Differentiated Services. Communications, APCC/OECC '99. Fifth Asia-Pacific Conference on ... and Fourth Optoelectronics and Communications Conference, Volume: 1, 18-22 Oct
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