The simulator supports several versions of an abstracted TCP sender. These objects attempt to capture the essence of the TCP congestion and error control behaviors, but are not intended to be faithful replicas of real-world TCP implementations. They do not contain a dynamic window advertisement, they do segment number and ACK number computations entirely in packet units, there is no SYN/FIN connection establishment/teardown, and no data is ever transferred (e.g. no checksums or urgent data).