There are at least two TCP/IP's for PDP-10's - the other, written by Ken Harrenstien, is the one for ITS. I'm not sure how closely related the TWENEX one is the TENEX one done at BBN - I vaguely seem to recall that DEC re-wrote it extensively, but I don't know much about that code. TCP/IP header fields are all multiples of 8 bits. So anytime you want to read/write one on a PDP-10, you have to start LDB'ing and DPB'ing through byte pointers/descriptors all over the place. Which I'm sure is no biggie for most experienced PDP-10 coders, but it would drive me bonkers. Noel