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+The IPC protocol
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+================
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+
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+While the cc-protocol.txt describes the low-level primitives, here we
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+describe how the whole IPC should work and how to use it.
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+
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+Assumptions
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+-----------
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+
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+We assume the low-level protocol keeps ordering of messages. That is,
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+if A sends messages 1 and 2 to B, they get delivered in the same order
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+as they were sent. However, if A sends message 1 to B and 2 to C, the
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+order in which get them or the order in which they answer is not
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+defined.
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+
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+We also assume that the delivery is reliable. If B gets a message from
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+A, it can be sure that all previous messages were delivered too. If A
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+sends a message to B, B either gets the message or either A or B is
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+disconnected during the attempt.
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+
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+Also, we expect the messages don't get damaged or modified on their
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+way.
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+
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+Addressing
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+----------
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+
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+We can specify the recipient in two different ways:
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+
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+ * Directly. Each connected client has an unique address. A message
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+ addressed to that addressed is sent only to the one client.
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+ * By a group. A client might subscribe to any number of groups.
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+ When a message is sent to the group, all clients subscribed to the
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+ group receive it. It is legal to send to an empty group.
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+
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+Feedback from the IPC system
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+----------------------------
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+
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+The IPC system generates some additional information to aid the
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+communicating clients.
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+
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+Undeliverable notification::
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+ If the client requests it (by a per-message flag) and the set of
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+ recipients specified is empty (either because the connection
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+ ID/lname is not connected or because the addressed group is empty),
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+ an answer message is sent from the MSGQ daemon to notify it about
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+ the situation.
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+Notifications about connections and disconnections::
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+ The system generates notification about following events:
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+ * Client with given lname connected
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+ * Client with given lname disconnected
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+ * Client with given lname subscribed to given group
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+ * Client with given lname unsubscribed from given group
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Michal 'vorner' Vaner