10.6 Controlling the
Number of Streams
We have seen how SCTP streams can be used, but
how can we control the number of streams an endpoint requests at
association initialization? Our previous examples used the system
default for the number of outbound streams. For the FreeBSD KAME
implementation of SCTP, this default is set to 10 streams. What if
our application and server would like to use more than 10 streams?
In Figure 10.10, we show a
modification that allows a server to increase the number of streams
the endpoint requests on association startup. Note that this change
must be made on the socket before an association is created.
Figure 10.10
Requesting more streams in our server.
sctp/sctpserv02.c
14 if (argc == 2)
15 stream_increment = atoi (argv[1]);
16 sock_fd = Socket (AF_INET, SOCK_SEQPACKET, IPPROTO_SCTP);
17 bzero (&initm, sizeof (initm));
18 initm.sinit_num_ostreams = SERV_MORE_STRMS_SCTP;
19 Setsockopt (sock_fd, IPPROTO_SCTP, SCTP_INITMSG, &initm, sizeof (initm));
Initial setup
14鈥?6
As before, the server sets up the flags based on additional
arguments and opens the socket.
Modifying the streams request
17鈥?9
These lines contain the new code we have added to our server. The
server first zeros out the sctp_initmsg structure. This
change assures that the setsockopt call will not
unintentionally change any other values. The server then sets the
sinit_max_ostreams field to the number of streams it would
like to request. Next, it sets the socket option with the initial
message parameters.
An alternative to setting a socket option would
be to use the sendmsg function and provide ancillary data
to request different stream parameters from the default. This type
of ancillary data is only effective on the one-to-many-style socket
interface.
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