Internet Core Protocols: The Definitive Guide

Lost Circuits

Sometimes the connection is established just fine, but then the virtual circuit starts to collapse, with one side appearing to just disappear off the network. Most of the time, that’s exactly what has happened: the remote endpoint has lost physical connectivity with the rest of the network for some reason, possibly due to power failure, link failure, or any number of other potential problems.

This scenario is illustrated in Figure 7.46, which shows an HTTP client on Greywolf requesting a document from the HTTP server on www.ora.com. After issuing the “GET /” request, Greywolf loses physical connectivity with the network.

Figure 7.46. A connection getting dropped due to loss of carrier

Segments four through ten show the HTTP server on www.ora.com attempting to send the contents of the requested document back to Greywolf. However, since Greywolf is no longer “live” on the network, it is unable to acknowledge the data, nor is it able to issue a Finish or Reset segment back to the server. Since the server has not been told that the circuit has been torn down (since it hasn’t been), it just assumes that the data has been lost, and continually tries to resend the questionable data.

What isn’t shown in Figure 7.46 is that the time between the retry operations is increasing while www.ora.com continues trying to resend the data to Greywolf. Since Greywolf is not acknowledging the ...