Information about TCP-Tahoe, TCP-Reno, TCP-New Reno and TCP-Vegas by comparing their mechanisms

TCP-Tahoe: This is a “Congestion avoidance” method in TCP protocol. The algorithms that is uses is:

Slow-start: At the beginning It start with making “congestions windows” value 1 “cwnd = 1” to avoid connection start problem.

Congestion avoidance: it used “Additive increase Multiplicative Decrease”. When a packet is lost it detects it as a congestion and takes half of valid windows size as new threshold level and saves. Congestion window set to ‘1’ and until reaching threshold level it continues with Slow-start.

The most important point in Tahoe is; it can detect the packet loss only when there is time out.

The problem is Tahoe is, to detect if there is a congestion or not, it waits the timeout which during this the pipeline is not used.

TCP-Reno: It is similar to Tahoe and as a difference it can do Fast Retransmit. The Fast Retransmit is method to detect the packet lost from 3 same ACK return (in this method for every packet it returns one ACK). If there is 3 same ACK return then it get as a packet lost and resend the packet by making half the congestion window(cwnd = ½*cwnd) it continues. The problem in this method is, although it is very useful in single packet loss its performance decrease when there is more than one packet loss.

TCP-Reno New: New version of the TCP-Reno. When there is more than one packet loss, without decreasing congestion window it resend the packet. It is more useful in mobile environments where packet loss is bigger. The problem is this method is inside RTT (round trip time) it can send only one packet.

TCP-Vegas: In this protocol when packet send the system time is saves and when ACK returned it also control the time and makes RTT calculations and saves it into timestamp. It controls it in two conditions:

• ·         When there is same ACK return it control the time and check if there is a timeout or not, if there is it retransmits without waiting 3.ACK return.
• ·         When there is different ACK came it check if there is timeout, if there is it retransmits.