XTI and sockets

The socket interface, made popular by the Berkeley version of UNIX, is another API that programs can use to access transport providers. A socket closely resembles an XTI transport endpoint. In general, both XTI and the sockets library provide similar functionality.

The list below calls out some of the differences between XTI and sockets. This information may be useful to those who are already familiar with socket programming or who have programs they wish to port from sockets to XTI. Note that a sockets library is available for use on SCO systems with the TCP and UDP protocols.

• XTI defines the t_alloc function for allocating data structures needed by some of the other XTI functions. The data structures allocated are very generic to support a variety of transport providers. There is no analogous socket function.

• A process specifies the protocol associated with a socket by passing in an integer argument (for example, AF_INET) to the socket call. A process specifies the protocol associated with a transport endpoint by passing to the t_open function a string specifying the pathname of the device node associated with the protocol (for example, /dev/tcp).

• A client that makes a connection to a server using XTI calls t_bind before calling t_connect. However, a client that makes a connection to a server using sockets does not call bind before calling connect.

• A server preparing to receive incoming connection requests using XTI in synchronous mode first calls t_bind to establish the length of the incoming request queue, then calls t_listen and blocks. Using sockets, a server calls listen to establish the length of the incoming request queue, then calls accept and blocks.

• Using XTI, a server can reject a connection request by calling t_snddis after returning from t_listen. Using sockets, a server always accepts an incoming connection request when it returns from accept. It must then close the socket to, in effect, reject the connection.

• The socket system call (which creates a socket) permits a number of parameters to be set that have no analog in the t_open function call (which creates a transport endpoint). In particular, the functionality of calling socket with the SOCK_RAW parameter has no analog in XTI.

• Using XTI, it is not possible to ``peek'' at an incoming message (look at it without consuming it).

• Using XTI, it is not possible to perform scatter reads or gather writes.

The above list is not exhaustive. Compare the manual pages for both the sockets library (SSC and SLIB) and XTI for more detailed information.