Tymshare Base-Host Protocol

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.