(port 8000) "SEND"    PC1    (port 8010) "RECEIVE"
        |                                |
        v ADD                            ^
        |                                |
(port 8000) "RECEIVE" PC2    (port 8010) "SEND"

##</code><code>##

(port 8000) "SEND"    PC1    (port 8010) "RECEIVE"
        |                                |
        ^ ACK                            ^
        |                                |
(port 8000) "RECEIVE" PC2    (port 8010) "SEND"

##</code><code>##

(port 8000) "SEND"    PC1    (port 8010) "RECEIVE"
        |                                |
        v                                ^ STAT
        |                                |
(port 8000) "RECEIVE" PC2    (port 8010) "SEND"