9.13 shutdown
Function
The shutdown function that we discussed
in Section 6.6 can be
used with an SCTP endpoint using the one-to-one-style interface.
Because SCTP's design does not provide a half-closed state, an SCTP
endpoint reacts to a shutdown call differently than a TCP
endpoint. When an SCTP endpoint initiates a shutdown sequence, both
endpoints must complete transmission of any data currently in the
queue and close the association. The endpoint that initiated the
active open may wish to invoke shutdown instead of
close so that the endpoint can be used to connect to a new
peer. Unlike TCP, a close followed by the opening of a new
socket is not required. SCTP allows the endpoint to issue a
shutdown, and after the shutdown completes, the
endpoint can reuse the socket to connect to a new peer. Note that
the new connection will fail if the endpoint does not wait until
the SCTP shutdown sequence completes. Figure 9.5 shows the typical function calls in
this scenario.
Note that in Figure 9.5, we depict the user receiving the
MSG_NOTIFICATION events. If the user had not subscribed to
receive these events, then a read of length 0 would have been
returned. The effects of the shutdown function for TCP
were described in Section 6.6. The
shutdown function howto
holds the following semantics for SCTP:
|
SHUT_RD
|
The same semantics as for TCP discussed in
Section 6.6; no
SCTP protocol action is taken.
|
|
SHUT_WR
|
Disables further send operations and initiates
the SCTP shutdown procedures, which will terminate the association.
Note that this option does not provide a half-closed state, but
does allow the local endpoint to read any queued data that the peer
may have sent prior to receiving the SCTP SHUTDOWN message.
|
|
SHUT_RDWR
|
Disables all read and write
operations, and initiates the SCTP shutdown procedure. Any queued
data that was in transit to the local endpoint will be acknowledged
and then silently discarded.
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