UNICAST and membership
======================

Author: Bela Ban
Date: Aug 10 2006


Sending a unicast message to P
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- When sending the first unicast message to a member P, its seqno is 1 (meaning this is the first message)
- The message is added to the AckSenderWindow, which keeps resending the message until
  it is acked by P, or P leaves the group (or crashes)


View change
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When a member P leaves, the connection for P is removed from the connection table and added to previous_members


Receiving a unicast message from P
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- When receiving a message from P:
  - If there is no entry for P in the connection table:
    - If the message has seqno=1:
      - Create a new entry for P in the connection table
      - Add the message to the entry for P (AckReceiverWindow) and ack it back to P
    - Else:
      - Discard the message and do *not* ack it ! This is necessary, so P keeps retransmitting it !
  - Else:
    - Add the message to the entry for P (AckReceiverWindow) and ack it back to P