OC-Minitel/protocol-5.md

Minitel - Layer 5

Language

• Node: a device on a minitel network
• Client: node establishing a connection
• Server: node accepting a connection

Establishing a connection

• Client sends "openstream" to the server on the port it would like to connect to
• Server can refuse, and respond with anything but a number
• Server, upon accepting, sends a string representation of another port, chosen by the server, on the same port, to the client
• Server sends a random string of its chosing to the client, which will be used to close the session
• Client and server can now exchange messages

Ending a connection

• Upon either side deciding to close, it sends the previously generated random string
• Neither side should send packets now

Example exchange:

Acknowledgements are implied.

Client bob sends request to open a connection on port 40:
"packet ID 1", 1, "alice", "bob", 40, "openstream"

Server alice accepts and sends a port to client bob for further communications:
"packet ID 3", 1, "bob", "alice", 40, "32800"

Server alice then sends a string on that port as a close session marker:
"packet ID 4", 1, "bob", "alice", 32800, "asdfghjkl"

Nodes alice and bob can now freely exchange data on that port: "packet ID 5", 1, "alice", "bob", 32800, "random data and stuff"
"packet ID 6", 1, "bob", "alice", 32800, "response data"

Client bob decides to close the connection, and sends the close session marker:
"packet ID 7", 1, "alice", "bob", 32800, "asdfghjkl"