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.\" @(#)spp.4 1.4 (Berkeley) 6/23/90
.TH SPP 4 "June 23, 1990"
spp \- Xerox Sequenced Packet Protocol
.B #include <sys/socket.h>
.B s = socket(AF_NS, SOCK_STREAM, 0);
.B s = socket(AF_NS, SOCK_SEQPACKET, 0);
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
Sockets utilizing the SPP protocol are either \*(lqactive\*(rq or
\*(lqpassive\*(rq. Active sockets initiate connections to passive
sockets. By default SPP sockets are created active; to create a
after binding the socket with the
passive sockets may use the
call to accept incoming connections. Only active sockets may
call to initiate connections.
Passive sockets may \*(lqunderspecify\*(rq their location to match
incoming connection requests from multiple networks. This
technique, termed \*(lqwildcard addressing\*(rq, 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 has the actual 12 byte sequenced packet header
left for the user to inspect:
u_char sp_cc; /* \fIconnection control\fP */
#define SP_EM 0x10 /* \fIend of message\fP */
u_char sp_dt; /* \fIdatastream type\fP */
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 message
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.
A socket operation may fail with one of the following errors returned:
when trying to establish a connection on a socket which
when the system runs out of memory for
an internal data structure;
when a connection was dropped
due to excessive retransmissions;
forces the connection to be closed;
peer actively refuses connection establishment (usually because
no process is listening to the port);
is made to create a socket with a port which has already been
when an attempt is made to create a
socket with a network address for which no network interface
when set, this determines the data stream type and whether
the end of message bit is to be set on every ensuing packet.
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
There should be some way to reflect record boundaries in
For stream mode, there should be an option to get the data stream type of
the record the user process is about to receive.