My good friend Joel Shea received a most unlikely gift this Christmas - A vintage HP 4951 Protocol Analyser.
According to the HP Computer Museum:
Original Price: $3595 The 4951B was replaced by the 4951C and 4952A in 1986. Both new models handled Async, BSC, SDLC, HDLC, X.25 and SNA protocols. The 4951C also handled DDCMP, while the 4952A did not. The 4952A handled X.21 while the 4951C did not. Both new analyzers used a floppy dive (618 KB) for removable media.
And the original spec sheet: