Chapter 4 Migrating TCP Applications to SCTP

This chapter discusses the changes required to a migrate a TCP application to SCTP.




	NOTE: TCP calls, such as `bind()`(), `listen()`(), `accept()`(), `connect()`(), `send()`(), `recv()`(), `sendto()`(), `recvfrom()`(), `senmsg()`(), `recvmsg()`(), work in an SCTP stack without incorporating any changes.

To migrate TCP applications to SCTP, you must modify the following:

To migrate native TCP applications, such as FTP, TELNET, RLOGIN, HTTP, to SCTP, modify the IPPROTO_TCP definition in the TCP socket call to IPPROTO_SCTP, as follows:
socket(AF_INET, SOCK_STREAM, IPPROTO_SCTP);
The IPPROTO_SCTP parameter is defined in the netinet/in.h header file.
NOTE: You need not explicitly mention the netinet/in.h header file in the application, because this header file is already included in the TCP applications.
To enable TCP applications to use the advanced features of SCTP, such as sending and receiving ancillary information, and receiving event notifications, TCP applications can use the sendmsg()() and recvmsg()() calls. However, applications must define the _XOPEN_SOURCE_EXTENDED macro and the /usr/lib/libxnet library while compiling the application, because only the X/OPEN style msghdr structure supports the ancillary mechanism.
SCTP APIs provide applications with an alternate method to read and write ancillary information, and receive event notifications, without using the msghdr structure. The alternate method is to use the sctp_sendmsg()() and sctp_recvmsg()() calls instead of using the sendmsg()() and recvmsg()() calls. These applications need not be compiled using the /usr/lib/libxnet library. You can compile these applications using the /usr/lib/libsctp library.

Following are the benefits of migrating TCP applications to SCTP:

The TCP applications can avail all the advanced features of SCTP, such as multi-streaming, multi-homing, and also avoid head-of-line blocking.
An FTP application in a TCP stack uses two sockets to send and receive data. It uses one socket for controlling the connection and the other socket for sending or receiving data. However, in an SCTP stack, an FTP application can use only one socket and use two streams within the same association to achieve the same functionality as that of TCP.
HTTP applications can use the multi-streaming feature, such as multiple queries within the same page wherein queries can be sent in parallel.

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