added protocol documentation

protocol-4.md

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+# Minitel - Layer 4
+
+Minitel implements layer 4, however, it does not have a layer 4 protocol.
+
+Instead of having a protocol, ordered delivery of packets is accomplished by waiting for an acknowledgement of the previous packet before sending the next.

protocol-5.md

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+# Minitel - Layer 4
+
+## 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"`