TCP Enhancement for Random Loss Jiang Wu Computer Science Lakehead University

Content TCP Issue Queueing Model Model Analysis Enhancement Proposal Conclusion

TCP Issue TCP ref[1], [3] Congestion control algorithm Reduce transmission rate whenever packet loss occurs Issue ref[4] Don’t distinguish between congestion and random loss Take incorrect action to random losses Suffer performance degradation in wireless network

Queueing Model ref[5] TCP Sender Router Buffer Queueing System TCP Receiver Router Some parameter of the queueing system: Queueing delay: the time a packet takes waiting in the queue Transmission delay: the time the router takes to put a packet to the transmission channel Suppose the size of the packets is constant, the router can be modeled as an M/D/1 queue because: Packets arrive according to Poisson process Transmission delay is constant 1 server (Router) for the queue

M/D/1 Queue Properties ref[5] M/D/1 queue properties: Let the packet arrival rate to be, transmission delay to be, then the load of the link is defined as The expectation of the queueing delay The expectation of queue length Q is

M/D/1 Queue Characteristics

Calculate Queue Length Round Trip Time (RTT): The time period between a packet is sent by the sender and its ACK is received by the sender. It consists of: Queueing Delay, a random variable >= 0 Transmission delay Propagation delay: the time the packet travels on the line ACK delay: the time the ACK travels from the receiver to the sender RTTmin : The minimum RTT observed by the sender Calculate the load ( is unknown yet)

Get Transmission Delay Packet pairs in TCP ref[1], [3] Get transmission delay ref[1] A by-product: maximum bandwidth of the bottle link Calculate the parameters: Router SenderReceiver (All parameter is known now)

Detect the Congestion Throughput: new packets received by receiver in unit time The knee occurs when the average queue length is one ref[2]  Ref[2]

Enhancement Proposal Enhancement to TCP Detect the minimum RTT When there are 2 packets ready to be sent, send them back-to- back, and measure the space between the ACK Calculate the load When a packet loss occurs when, don’t lower the transmission rate Anticipated result TCP performance will not degrade heavily due to transmission loss

Research Plan Design the enhancement algorithm Implement the enhancement Evaluate the performance improvement One paper before March 2004 Compare the performance to others One paper

Reference [1] V. Jacobson. Congestion avoidance and control. In ACM SIGCOMM '88, [2] K. Ramakrishnan and R. Jain, “Congestion avoidance in computer networks with a connectionless network layer” Tech. Rep., DEC, August [3] RFC2581 TCP Congestion Control [4] Pan, J.; Mark, J.W.; Shen, X. TCP performance and its improvement over wireless links. Globecom IEEE [5] Robert B. Cooper. Introduction To Queueing Theory. Second Edition North Holland, New York Oxford