Tymshare Base-Host Protocol

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Humorous visualization of Tymnet protocol

This documents the protocol, as used around 1975, between a PDP-10 host and Varian 620 Tymbase.

Packets start with a 4-octet header. More data may optionally follow after the header, depending on the packet type.

Packet type Port Subtype Data

Packet types. Any number not in this list is illegal.

Number Name Comment
1 ANS System is answering.
2 SHT System is up but shut.
3 CRS Sender is crashed.
4 DIE Recipient should crash.
5 NSP Base taken over by new supervisor.
6 LOG Login, next 4 data characters are the info about terminal type, and port or origin, then name, etc.
7 AUX Supervisor response to establishing auxillary circuit.
10 NOP Backpressure on.
11 OUP Backpressure off.
12 GOB Character gobbler.
13 ZAP Circuit zapper.
14 EDC Enter deferred echo mode.
15 LDC Leave deferred echo mode.
16 GRN Green ball.
17 RED Red ball.
20 YEL Yellow ball.
21 ORG Orange ball.
22 HNG Hang character - not used.
23 ETM Enter 2741 transparent mode.
24 LTM Leave 2741 transparent mode.
25 LOS Lost ball, data has been lost from buffers. The data filed may tell how many were lost.
26 SUP Supervisor request (aux circuits).
27 SUR Supervisor response (aux circuits).
30 AXC Supervisor string character.
31 TSP Test pattern probe.
32 TSR Test pattern response.
33 SAD Host sad.
34 ECN Echo on.
35 ECF Echo off.
36 TCS Term characteristics, first data byte indicates which characteristics second data byte indicates value to set to.
37 TCP Term characteristcs probe, data byte indicates which terminal characteristic were requested.
40 TCR Term characteristcs response, data is just like TCS, comes in response to a probe; also is reflected by remote when terminal characteristics are sent.
41 HSI Host up and answereing with # of ports in port byte, and host # in data byte.

This information comes from the SUMEX-AIM monitor file TYMSRV.MAC, written by Michael A. Heathman in 1975.