SPP(4) MachTen Programmer’s Manual SPP(4)

NAME
spp - Xerox Sequenced Packet Protocol

SYNOPSIS
#include <sys/socket.h>
#include <netns/ns.h>
#include <netns/sp.h>

int
socket(AF_NS, SOCK_STREAM, 0)

int
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) sys-
tem 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 ad-
dress 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 corre-
sponds 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. Con-
versely, the user is required to supply a 12 byte header, the only part
of which inspected is the data stream type and end of message 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 retrans-
missions;

[ECONNRESET] when the remote peer forces the connection to be closed;

[ECONNREFUSED] when the remote peer actively refuses connection estab-
lishment (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 net-
work 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 amount of user data in a
single packet. The default is 576 bytes - size-
of(struct spidp). This quantity affects windowing -
increasing it without increasing the amount of
buffering in the socket will lower the number of un-
read packets accepted. Anything larger than the de-
fault will not be forwarded by a bona fide XEROX
product internetwork router. The data argument for
the setsockopt call must be an unsigned short.