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NAME    [Toc]    [Back]

     spp - Xerox Sequenced Packet Protocol

SYNOPSIS    [Toc]    [Back]

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

     socket(AF_NS, SOCK_STREAM, 0);

     socket(AF_NS, SOCK_SEQPACKET, 0);

DESCRIPTION    [Toc]    [Back]

     The SPP protocol provides a reliable, flow-controlled,  twoway transmission
  of data.  It is a byte-stream protocol used to support
     SOCK_STREAM abstraction.  SPP uses the standard  NS(tm)  address formats.

     Sockets  utilizing the SPP protocol are either ``active'' or
     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

     Passive sockets may ``underspecify'' their location to match
     connection requests from multiple networks.  This technique,
     ``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 to
     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:

           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 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    [Toc]    [Back]

     A socket operation may fail with one of the following errors

     [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

     [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

     [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

SOCKET OPTIONS    [Toc]    [Back]

     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
- 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

SEE ALSO    [Toc]    [Back]

     netintro(4), ns(4)

HISTORY    [Toc]    [Back]

     The spp protocol appeared in 4.3BSD.

BUGS    [Toc]    [Back]

     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.

OpenBSD      3.6                          April      19,     1994
[ Back ]
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