The point-to-point protocol (PT2PT) is used for sending/receiving unicast messages to/from single members in a group. When a message is sent to a unicast destination (msg.dest == unicast dest instead of null (multicast dest)), if there is not yet a connection to that destination, a connection is established (similar to TCP's connection establishment) and the message sent. ACKs are used to retransmit lost messages, and all messages are delivered in FIFO order. Sliding windows are used at the sending and receiving side (with fixed window size, without window size adaptation).
The JChannel protocol layers often need to make a distinction between unicast and multicast messages; the two cases are often treated differently. For example, in some multicast layers, unicast messages would just be passed up/down the stack. Similarly, in PT2PT, multicast messages are just passed through.
PT2PT maintains a table of recently received messages for each sender. Whenever a message is sent to a member for which no table entry is available, a negotiation protocol similar to TCP's SYN is started, which exchanges the start sequence numbers that the communication partners are going to use. Error recovery through retransmission (NAKs) and FIFO ordering are provided by PT2PT.