CSCI.4220 Network Programming
Class 3, Thurs, Jan 27, 2005

UDP Clients and Servers

Pseudocode for a UDP server

main()
{
    s = socket(... )
    bind(s, ...
    recvfrom(s, ...
    sendto(s, ...
}


Pseudocode for a UDP client


main()
{
    s = socket(...
    sendto(s, ...
    recvfrom(s, ...
}

TCP

Here is a link to a web site that covers a lot of the same material that I covered in class.

Here are the formulas for determining how to set the timer.

RTTn - Round trip time for the nth packet

EstRTT - the estimated average round trip time, calculated with a a decay function. The following is recalculated each time a new segment is ack'ed.

EstRTT = (1 - α) * EstRTT + α * RTTn

A typical α is .125.

Originally TCP simply set the timer at 2 * EstRTT. However, more modern implementations also take the variance of RTT into account.

DevRTT = (1 - β) * DevRTT + (β * abs(RTTn - EstRTT))

A typical β is .25

TimeoutInterval = EstRTT + 4 * DevRTT