SPP(4P) SPP(4P)
NAME
spp - Xerox Sequenced Packet Protocol
SYNOPSIS
#include <sys/socket.h>
#include <netns/ns.h>
s = socket(AF_NS, SOCK_STREAM, 0);
#include <netns/sp.h>
s = socket(AF_NS, SOCK_SEQPACKET, 0);
DESCRIPTION
The SPP protocol provides reliable, flow-controlled, two-way transmission of data. It is a byte-stream protocol used to support the
SOCK_STREAM abstraction. SPP uses the standard NS(tm) address formats.
Sockets utilizing the SPP protocol 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(2) system call must be used after binding the socket with the bind(2)
system call. Only passive sockets may use the accept(2) call to accept incoming connections. Only active sockets may use the connect(2)
call 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. Nor-
mally this address corresponds to the peer entity's network.
If the SOCK_SEQPACKET socket type is specified, each packet received has the actual 12 byte sequenced packet header left for the user to
inspect:
struct sphdr {
u_char sp_cc; /* connection control */
#define SP_EM 0x10 /* end of message */
u_char sp_dt; /* datastream type */
u_short sp_sid;
u_short sp_did;
u_short sp_seq;
u_short sp_ack;
u_short sp_alo;
};
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 part of which inspected is the data stream type and end of mes-
sage fields.
For either socket type, packets received with the Attention bit sent are interpreted as out of band data. Data sent with send(..., ...,
..., MSG_OOB) cause the attention bit to be set.
DIAGNOSTICS
A socket operation may fail with one of the following errors returned:
[EISCONN] when trying to establish a connection on a socket which already has one;
[ENOBUFS] when the system runs out of memory for an internal data structure;
[ETIMEDOUT] when a connection was dropped due to excessive retransmissions;
[ECONNRESET] when the remote peer forces the connection to be closed;
[ECONNREFUSED] when the remote peer actively refuses connection establishment (usually because no process is listening to the port);
[EADDRINUSE] when an attempt is made to create a socket with a port which has already been allocated;
[EADDRNOTAVAIL] when an attempt is made to create a socket with a network address for which no network interface exists.
SOCKET OPTIONS
SO_DEFAULT_HEADERS when set, this determines the data stream type and whether the end of message bit is to be set on every ensuing packet.
SO_MTU This specifies the maximum ammount 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 call must be an unsigned short.
SEE ALSO
intro(4N), ns(4F)
BUGS
There should be some way to reflect record boundaries in a stream. For stream mode, there should be an option to get the data stream type
of the record the user process is about to receive.
4.3 Berkeley Distribution July 30, 1985 SPP(4P)