Eliminating duplicate messages is another example where we can learn quite a bit by having a closer look at the low-level TCP/IP protocol. When IP network packets are routed across the network, duplicate packets can be generated. The TCP/IP protocol ensures elimination of duplicate packets by attaching a unique identifier to each packet. Sender and receiver negotiate a “window size” that the recipient allocates in order to detect duplicates. For a thorough discussion of how TCP/IP implements this mechanism, see [Stevens].
