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- Do not name the process from (to) which message is received (sent),
rather use an indirection
- Mailbox (VAX/VMS) - an OS structure independent of both sender
and receiver.
Permits multiple senders and receivers
Implemented as a queue - bound or circular
send to and receive from a queue
- In mailboxes : asynchronous send
No receivers = messages queued
No messages = receiver processes queued
Synchronous send
No receivers = sender process queued
No messages = receiver process queued
- Ports or Sockets (Unix - Berkeley IPC) - data structure associated with a process
- Holds name of source or destination process (usable with any communication primitive)
- Bind(pt1,B) - places name of process in port 1 data structure
OS picks up name when message is sent
![figure79](img6.gif)
Figure 6: VAX Mailboxes
![figure84](img7.gif)
Figure 7: Unix sockets
Omer F Rana
Tue Feb 11 19:19:52 GMT 1997