Lectures notes for 2010 - KTH

Congestion Avoidance
So far we have assumed that the sender is only limited by the receiver’s available
buffer space. But if we inject lots of segments into a network - upto window size
advertised by receiver
• works well if the hosts are on the same LAN
• if there are routers (i.e., queues) between them and if the traffic arrives
faster than it can be forwarded, then either the packets have to be
– buffered or
– thrown away - we refer to this condition as congestion
Lost packets lead to retransmission by the sender
This adds even more packets to the network ⇒ network collapse
Therefore we need to be able to reduce the window size to avoid congestion.
Maguire TCP header continued 5: 23 of 77
maguire@kth.se 2010.03.21 Internetworking/Internetteknik