10.1 Introduction
We will now use some of the elementary functions
from Chapters
4 and Chapter 9 to write a complete
one-to-many SCTP client/server example. Our simple example is
similar to the echo server presented in Chapter 5, and performs the
following steps:
-
A client reads a
line of text from standard input and sends the line to the server.
The line follows the form [#]
text, where the number in brackets is the SCTP stream
number on which the text message should be sent.
-
The
server receives the text message from the network, increases the
stream number on which the message arrived by one, and sends the
text message back to the client on this new stream number.
-
The
client reads the echoed line and prints it on its standard output,
displaying the stream number, stream sequence number, and text
string.
Figure
10.1 depicts this simple client/server along with the functions
used for input and output.
We show two arrows between the client and server
depicting two unidirectional streams being used, even though the
overall association is full-duplex. The fgets and
fputs functions are from the standard I/O library. We do
not use the writen and readline functions defined
in Section 3.9 since
they are unnecessary. Instead, we use the sctp_sendmsg and
sctp_recvmsg functions defined in Sections 9.9 and
Sections 9.10,
respectively.
For this example, we use a one-to-many-style
server. We make this choice for one important reason. The examples
in Chapter
5 can be modified to run over SCTP with one minor change:
modify the socket function call to specify
IPPROTO_SCTP instead of IPPROTO_TCP as the third
argument. Simply making this change, however, would not take
advantage of any of the additional features provided by SCTP except
multihoming. Using the one-to-many style allows us to exercise all
of SCTP's features.
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