TCP Congestion control

Posted by AJ × 05:08

• How TCP prevents congestion

• when connection established, window size chosen

• Receiver specifies seeing its buffer size

• Still congestion occurs

• The two problems are Network Capacity and Receiver Capacity

• Solution?

• Solution

• Sender maintains two windows: one the receiver granted

• the other Congestion Window

• at the connection establishment- the congestion window is set to the size of the

maximum segment in use on the connection

• Each burst acknowledged doubles the congestion window

• Congestion window grow exponentially

• This is called the Slow Start algorithm

• Another Solution?

• Solution

• Uses threshold

• initially some value in addition to the receiver and congestion window

• When timeout threshold is set to half of the current congestion window

• Congestion window is set to one max segment

• Slow start is used to find what the network can handle

• Exponential growth stops when threshold hit

• From that point congestion window grow linearly

• Example

• Segment size=1K

• Congwin=64KB

• when timeout threshold=34KB

• Congwin=1KB

• the congstion window grows exponentially until it hits threshold and then linearly

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