Talk ProtocolsTalk protocols allow two or more users to communicate, using a telnet-like client, with separate send and receive windows.
As a result, Talk protocols have been overshadowed by IRC, MUDs, IPhone, et. al. -- however, many Unix systems still support them.
OverviewTalk can be implemented as a separate talk server daemon and client, or a combined application that works as both server and client.
The server side opens a UDP port (517 for talk, 518 for ntalk), and listens for incoming requests to start a talk session.
The client side generally initiates a talk session by asking for a particular user on a host: email@example.com -- the server resolves the user name to an existing TCP port, or notifies the target user that a request has come in.
Once the session has started, everthing a user types in their send window is sent the the other user; you receive everything typed by the other user in a scrolling receive window.
Many talk implementation support special escape key sequences that allow controlling your (or the other user's) client.
ReferencesTalk MAN Pages
nTalk MAN Pages
Internet Relay Chat (IRC) - RFC 1459
Multi-User Domains (MUD)
For comments/correction/additions regarding this reference, email firstname.lastname@example.org.