Kaichuan, Yes, MSS (maximum segment size) is specified in tcl/lib/ns-default.tcl as 536. It is used in tcp-full.cc and can be tuned in your tcl code with the parameter maxseg_. Hope this helps. > Another issue I'm not clear is whether TCP in ns2 >has a MSS (maximum segment size) specified somewhere, is it >sets to the default value 536 or something else? -- tls