#include <netns/sp.h> s = socket(AF_NS, SOCK_SEQPACKET, 0);
Sockets utilizing the SPP are either ``active'' or ``passive''. Active sockets initiate connections to passive sockets. By default, SPP sockets are created active; to create a passive socket the listen() function must be used after binding the socket with the bind() function. Only passive sockets may use the accept() function to accept incoming connections. Only active sockets may use the connect() function to initiate connections.
Passive sockets may ``underspecify'' their location to match incoming connection requests from multiple networks. This technique, termed wildcard addressing, allows a single server to provide service to clients on multiple networks. To create a socket which listens on all networks, the NS address of all zeroes must be bound. The SPP port may still be specified at this time; if the port is not specified the system will assign one. Once a connection has been established the socket's address is fixed by the peer entity's location. The address assigned the socket is the address associated with the network interface through which packets are being transmitted and received. Normally this address corresponds to the peer entity's network.
If the SOCK_SEQPACKET socket type is specified, each packet received includes the actual 12-byte sequenced packet header for the user to inspect. This facilitates the implementation of higher level Xerox protocols which make use of the data stream type field and the end of message bit. Conversely, the user is required to supply a 12-byte header, the only parts of which are inspected are the data stream type and the end of message fields.
For either socket type, packets received with the attention bit set are interpreted as out of band data. Data sent with send(..., ..., ..., MSG_OOB) cause the attention bit to be set.
The following socket options are available: Determines the data stream type and whether the end of message bit is to be set on every ensuing packet. Specifies the maximum amount of user data in a single packet. The default is 576 bytes - sizeof(struct spidp). This quantity affects windowing; increasing it without increasing the amount of buffering in the socket will lower the number of unread packets accepted. Anything larger than the default will not be forwarded by a bona fide Xerox product internetwork router. The data argument for the setsockopt() function must be an unsigned short.
Files: netintro(7), ns(7) delim off