protocol
ATCP
GMCP's predecessor. Out-of-band data with a looser payload, largely superseded, and still negotiated by servers that never removed it.
Measured adoption
0 of 886 listed games — 0.0%
The games not counted here are not games without the protocol. A game is counted when we observed its server offering the option in a handshake; the rest are servers that did not offer it to us and servers whose handshake we have not read, and we cannot tell you which.
| codebase | offered it | identified |
|---|---|---|
| AresMUSH | 0 | 18 |
| CircleMUD | 0 | 47 |
| CobraMUSH | 0 | 2 |
| CoffeeMUD | 0 | 32 |
| DikuMUD | 0 | 35 |
| Evennia | 0 | 11 |
| FluffOS | 0 | 28 |
| MUCK | 0 | 24 |
| PennMUSH | 0 | 34 |
| RhostMUSH | 0 | 40 |
| ROM | 0 | 55 |
| SMAUG | 0 | 20 |
| tbaMUD | 0 | 5 |
| TinyMUSH | 0 | 9 |
ATCP — the Achaea Telnet Client Protocol — is telnet option 200, and it is where the idea of sending structured data alongside MUD text was first widely deployed. A server sends a module name and a payload; the client routes it.
Its payload format is looser than GMCP's JSON, which is essentially why GMCP replaced it. Clients that support ATCP now generally document it as deprecated and point you at GMCP instead.
Why it is still here
Because nothing breaks by leaving it on. A server that implemented ATCP in 2008 and added GMCP in 2014 usually still negotiates both, and a client that supports both will take whichever it is offered.
For a new implementation there is no reason to choose it.
What we measure
Servers offering telnet option 200 in a handshake we observed. A low figure here is expected and is about age rather than about anything else.
See also
- GMCP The Generic Mud Communication Protocol — structured JSON messages alongside the text, and the out-of-band channel most modern clients build against.
- MSDP The Mud Server Data Protocol — the same job as GMCP, done with a compact binary encoding and a discovery mechanism GMCP lacks.
- Mudlet Cross-platform, Lua-scripted, and the client with the most thoroughly documented screen-reader support in this section.