22.4 Summary

22.4 Summary

TCP's persist timer is set by one end of a connection when it has data to send, but has been stopped because the other end has advertised a zero- sized window. The sender keeps probing the closed window using a retransmission interval similar to what we saw in Chapter 21. This probing of the closed window continues indefinitely.

When we ran an example to see the persist timer we also encountered TCP's avoidance of the silly window syndrome. This is to prevent TCP from advertising small windows or from sending small segments. In our example we saw avoidance of the silly window syndrome by both the sender and the receiver.