path: root/lib/kernel/doc/src/gen_sctp.xml

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<!DOCTYPE erlref SYSTEM "erlref.dtd">

<erlref>
  <header>
    <copyright>
      <year>2007</year><year>2013</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      Licensed under the Apache License, Version 2.0 (the "License");
      you may not use this file except in compliance with the License.
      You may obtain a copy of the License at
 
          http://www.apache.org/licenses/LICENSE-2.0

      Unless required by applicable law or agreed to in writing, software
      distributed under the License is distributed on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      See the License for the specific language governing permissions and
      limitations under the License.

    </legalnotice>

    <title>gen_sctp</title>
    <prepared>raimo@erix.ericsson.se</prepared>
    <responsible></responsible>
    <docno>1</docno>
    <approved></approved>
    <checked></checked>
    <date>2007-03-21</date>
    <rev>A</rev>
    <file>gen_sctp.sgml</file>
  </header>
  <module>gen_sctp</module>
  <modulesummary>The gen_sctp module provides functions for communicating with sockets using the SCTP protocol.</modulesummary>
  <description>
    <p>The <c>gen_sctp</c> module provides functions for communicating with
      sockets using the SCTP protocol. The implementation assumes that
      the OS kernel supports SCTP
      <url href="http://www.rfc-archive.org/getrfc.php?rfc=2960">(RFC2960)</url> through the user-level
      <url href="http://tools.ietf.org/html/draft-ietf-tsvwg-sctpsocket-13">Sockets API Extensions.</url>
      During development this implementation was tested on 
      Linux Fedora Core 5.0 (kernel 2.6.15-2054 or later is needed),
      and on Solaris 10, 11. During OTP adaptation it was tested on
      SUSE Linux Enterprise Server 10 (x86_64) kernel 2.6.16.27-0.6-smp,
      with lksctp-tools-1.0.6, briefly on Solaris 10, and later on
      SUSE Linux Enterprise Server 10 Service Pack 1 (x86_64)
      kernel 2.6.16.54-0.2.3-smp with lksctp-tools-1.0.7,
      and later also on FreeBSD 8.2.
    </p>
    <p>
      This module was written for one-to-many style sockets
      (type <c>seqpacket</c>). With the addition of
      <seealso marker="#peeloff/2">peeloff/2</seealso>, one-to-one style
      sockets (type <c>stream</c>) were introduced.
    </p>
    <p>Record definitions for the <c>gen_sctp</c> module can be found using:</p>
<pre>  -include_lib("kernel/include/inet_sctp.hrl").    </pre>
    <p>These record definitions use the "new" spelling 'adaptation',
      not the deprecated 'adaption', regardless of which
      spelling the underlying C API uses.</p>
  </description>

  <section>
    <marker id="contents"></marker>
    <title>CONTENTS</title>
    <list type="bulleted">
      <item><seealso marker="#types">DATA TYPES</seealso></item>
      <item><seealso marker="#exports">EXPORTS</seealso></item>
      <item><seealso marker="#options">SCTP SOCKET OPTIONS</seealso></item>
      <item><seealso marker="#examples">SCTP EXAMPLES</seealso></item>
      <item><seealso marker="#seealso">SEE ALSO</seealso></item>
    </list>
    <marker id="types"></marker>
  </section>

  <datatypes>
    <datatype>
      <name><marker id="type-assoc_id">assoc_id()</marker></name>
      <desc>
        <p>An opaque term returned in for example #sctp_paddr_change{}
          that identifies an association for an SCTP socket. The term
          is opaque except for the special value <c>0</c> that has a
          meaning such as "the whole endpoint" or "all future associations".
        </p>
      </desc>
    </datatype>
    <datatype>
      <name name="option"/>
      <desc>
        <p>One of the 
          <seealso marker="#options">SCTP Socket Options.</seealso></p>
      </desc>
    </datatype>
    <datatype>
      <name name="option_name"/>
      <desc><marker id="type-sctp_socket"></marker></desc>
    </datatype>
    <datatype>
      <name><marker id="type-sctp_socket">sctp_socket()</marker></name>
      <desc>
        <p>Socket identifier returned from <c>open/*</c>.</p>
        <marker id="exports"></marker>
      </desc>
    </datatype>
  </datatypes>

  <funcs>
    <func>
      <name name="abort" arity="2"/>
      <fsummary>Abnormally terminate the association given by Assoc, without flushing of unsent data</fsummary>
      <desc>
        <p>Abnormally terminates the association given by <c><anno>Assoc</anno></c>, without
          flushing of unsent data. The socket itself remains open. Other
          associations opened on this socket are still valid, and it can be
          used in new associations.</p>
      </desc>
    </func>
    <func>
      <name name="close" arity="1"/>
      <fsummary>Completely close the socket and all associations on it</fsummary>
      <desc>
        <p>Completely closes the socket and all associations on it. The unsent
          data is flushed as in <c>eof/2</c>. The <c>close/1</c> call 
          is blocking or otherwise depending of the value of
          the <seealso marker="inet#option-linger">linger</seealso> socket
          <seealso marker="#options">option</seealso>.
          If <c>close</c> does not linger or linger timeout expires,
          the call returns and the data is flushed in the background.</p>
      </desc>
    </func>
    <func>
      <name name="connect" arity="4"/>
      <fsummary>Same as <c>connect(Socket, Addr, Port, Opts, infinity)</c>.</fsummary>
      <desc>
        <p>Same as <c>connect(<anno>Socket</anno>, <anno>Addr</anno>, <anno>Port</anno>, <anno>Opts</anno>, infinity)</c>.</p>
      </desc>
    </func>
    <func>
      <name name="connect" arity="5"/>
      <fsummary>Establish a new association for the socket <c>Socket</c>, with a peer (SCTP server socket)</fsummary>
      <desc>
        <p>Establishes a new association for the socket <c><anno>Socket</anno></c>,
          with the peer (SCTP server socket) given by
          <c><anno>Addr</anno></c> and <c><anno>Port</anno></c>. The <c><anno>Timeout</anno></c>,
          is expressed in milliseconds. A socket can be associated with multiple peers.</p>

        <p><b>WARNING:</b>Using a value of <c><anno>Timeout</anno></c> less than
        the maximum time taken by the OS to establish an association (around 4.5 minutes
        if the default values from RFC 4960 are used) can result in
        inconsistent or incorrect return values. This is especially
        relevant for associations sharing the same <c><anno>Socket</anno></c>
        (i.e. source address and port) since the controlling process
        blocks until <c>connect/*</c> returns.
	  <seealso marker="#connect_init/4">connect_init/*</seealso>
	  provides an alternative not subject to this limitation.</p>

        <p><marker id="record-sctp_assoc_change"></marker>
          The result of <c>connect/*</c> is an <c>#sctp_assoc_change{}</c>
          event which contains, in particular, the new 
          <seealso marker="#type-assoc_id">Association ID</seealso>.</p>
<pre>   #sctp_assoc_change{
        state             = atom(),
        error             = atom(),
        outbound_streams  = integer(),
        inbound_streams   = integer(),
        assoc_id          = assoc_id()
  }        </pre>
        <p>The number of outbound and inbound streams can be set by
          giving an <c>sctp_initmsg</c> option to <c>connect</c>
          as in:</p>
<pre>  connect(<anno>Socket</anno>, Ip, <anno>Port</anno>,
        [{sctp_initmsg,#sctp_initmsg{num_ostreams=OutStreams,
                                     max_instreams=MaxInStreams}}])        </pre>
        <p>All options <c><anno>Opt</anno></c> are set on the socket before the
          association is attempted. If an option record has got undefined
          field values, the options record is first read from the socket
          for those values. In effect, <c><anno>Opt</anno></c> option records only
          define field values to change before connecting.</p>
        <p>The returned <c>outbound_streams</c> and <c>inbound_streams</c>
          are the actual stream numbers on the socket, which may be different
          from the requested values (<c>OutStreams</c> and <c>MaxInStreams</c>
          respectively) if the peer requires lower values.</p>
        <p>The following values of <c>state</c> are possible:</p>
        <list type="bulleted">
          <item>
            <p><c>comm_up</c>: association successfully established. This
              indicates a successful completion of <c>connect</c>.</p>
          </item>
          <item>
            <p><c>cant_assoc</c>: association cannot be established
              (<c>connect/*</c> failure).</p>
          </item>
        </list>
        <p>All other states do not normally occur in the output from
          <c>connect/*</c>. Rather, they may occur in
          <c>#sctp_assoc_change{}</c> events received instead of data in
          <seealso marker="#recv/1">recv/*</seealso> calls.
          All of them indicate losing the association due to various
          error conditions, and are listed here for the sake of completeness.
          The <c>error</c> field may provide more detailed diagnostics.</p>
        <list type="bulleted">
          <item>
            <p><c>comm_lost</c>;</p>
          </item>
          <item>
            <p><c>restart</c>;</p>
          </item>
          <item>
            <p><c>shutdown_comp</c>.</p>
          </item>
        </list>
      </desc>
    </func>
    <func>
      <name name="connect_init" arity="4"/>
      <fsummary>Same as <c>connect_init(Socket, Addr, Port, Opts, infinity)</c>.</fsummary>
      <desc>
        <p>Same as <c>connect_init(<anno>Socket</anno>, <anno>Addr</anno>, <anno>Port</anno>, <anno>Opts</anno>, infinity)</c>.</p>
      </desc>
    </func>
    <func>
      <name name="connect_init" arity="5"/>
      <fsummary>Initiate a new association for the socket <c>Socket</c>, with a peer (SCTP server socket)</fsummary>
      <desc>
        <p>Initiates a new association for the socket <c><anno>Socket</anno></c>,
          with the peer (SCTP server socket) given by
          <c><anno>Addr</anno></c> and <c><anno>Port</anno></c>.</p>
	<p>The fundamental difference between this API
	and <c>connect/*</c> is that the return value is that of the
	underlying OS connect(2) system call. If <c>ok</c> is returned
	then the result of the association establishement is received
	by the calling process as
	an <seealso marker="#record-sctp_assoc_change">
	    #sctp_assoc_change{}</seealso>
	event. The calling process must be prepared to receive this, or
	poll for it using <c>recv/*</c> depending on the value of the
	active option.</p>
	<p>The parameters are as described
	in <seealso marker="#connect/5">connect/*</seealso>, with the
	exception of the <c><anno>Timeout</anno></c> value.</p>
	<p>The timer associated with <c><anno>Timeout</anno></c> only supervises
	IP resolution of <c><anno>Addr</anno></c></p>
      </desc>
    </func>
    <func>
      <name name="controlling_process" arity="2"/>
      <fsummary>Assign a new controlling process pid to the socket</fsummary>
      <desc>
        <p>Assigns a new controlling process <c><anno>Pid</anno></c> to <c><anno>Socket</anno></c>. Same implementation
          as <c>gen_udp:controlling_process/2</c>.</p>
      </desc>
    </func>
    <func>
      <name name="eof" arity="2"/>
      <fsummary>Gracefully terminate the association given by Assoc, with flushing of all unsent data</fsummary>
      <desc>
        <p>Gracefully terminates the association given by <c><anno>Assoc</anno></c>, with
          flushing of all unsent data. The socket itself remains open. Other
          associations opened on this socket are still valid, and it can be
          used in new associations.</p>
      </desc>
    </func>
    <func>
      <name name="listen" arity="2" clause_i="1"/>
      <name name="listen" arity="2" clause_i="2"/>
      <fsummary>Set up a socket to listen.</fsummary>
      <desc>
        <p>Sets up a socket to listen on the IP address and port number
	it is bound to.</p>
	<p>For type <c>seqpacket</c> sockets (the default)
	<c><anno>IsServer</anno></c> must be <c>true</c> or <c>false</c>.
	In contrast to TCP, in SCTP there is no listening queue length.
	If <c><anno>IsServer</anno></c> is <c>true</c> the socket accepts new associations, i.e.
	it will become an SCTP server socket.</p>
	<p>For type <c>stream</c> sockets <anno>Backlog</anno> defines
	the backlog queue length just like in TCP.</p>
      </desc>
    </func>
    <func>
      <name name="open" arity="0"/>
      <name name="open" arity="1" clause_i="1"/>
      <name name="open" arity="1" clause_i="2"/>
      <name name="open" arity="2"/>
      <fsummary>Create an SCTP socket and bind it to local addresses</fsummary>
      <desc>
        <p>Creates an SCTP socket and binds it to the local addresses 
          specified by all <c>{ip,<anno>IP</anno>}</c> (or synonymously <c>{ifaddr,<anno>IP</anno>}</c>)
          options (this feature is called SCTP multi-homing).
          The default <c><anno>IP</anno></c> and <c><anno>Port</anno></c> are <c>any</c>
          and <c>0</c>, meaning bind to all local addresses on any
          one free port.</p>

        <p>Other options are:</p>
        <taglist>
          <tag><c>inet6</c></tag>
          <item>
            <p>Set up the socket for IPv6.</p>
          </item>
          <tag><c>inet</c></tag>
          <item>
            <p>Set up the socket for IPv4. This is the default.</p>
          </item>
        </taglist>

        <p>A default set of socket <seealso marker="#options">options</seealso>
          is used. In particular, the socket is opened in 
          <seealso marker="#option-binary">binary</seealso> and
          <seealso marker="#option-active">passive</seealso> mode,
	  with <anno>SockType</anno> <c>seqpacket</c>,
          and with reasonably large
          <seealso marker="inet#option-sndbuf">kernel</seealso> and driver
          <seealso marker="inet#option-buffer">buffers.</seealso></p>
      </desc>
    </func>
    <func>
      <name name="peeloff" arity="2"/>
      <fsummary>
	Peel off a type <c>stream</c> socket from a type <c>seqpacket</c> one
      </fsummary>
      <desc>
	<p>
	  Branch off an existing association <anno>Assoc</anno>
	  in a socket <anno>Socket</anno> of type <c>seqpacket</c>
	  (one-to-many style) into
	  a new socket <anno>NewSocket</anno> of type <c>stream</c>
	  (one-to-one style).
	</p>
	<p>
	  The existing association argument <anno>Assoc</anno>
	  can be either a
	  <seealso marker="#record-sctp_assoc_change">
	    #sctp_assoc_change{}
	  </seealso>
	  record as returned from e.g
	  <seealso marker="#recv-2">recv/*</seealso>,
	  <seealso marker="#connect-5">connect/*</seealso> or
	  from a listening socket in active mode. Or it can be just
	  the field <c>assoc_id</c> integer from such a record.
	</p>
      </desc>
    </func>
    <func>
      <name name="recv" arity="1"/>
      <name name="recv" arity="2"/>
      <fsummary>Receive a message from a socket</fsummary>
      <desc>
        <p>Receives the <c><anno>Data</anno></c> message from any association of the socket.
          If the receive times out <c>{error,timeout</c> is returned.
          The default timeout is <c>infinity</c>.
          <c><anno>FromIP</anno></c> and <c><anno>FromPort</anno></c> indicate the sender's address.</p>
        <p><c><anno>AncData</anno></c> is a list of Ancillary Data items which
          may be received along with the main <c><anno>Data</anno></c>.
          This list can be empty, or contain a single
          <seealso marker="#record-sctp_sndrcvinfo">#sctp_sndrcvinfo{}</seealso>
          record, if receiving of such ancillary data is enabled
          (see option 
          <seealso marker="#option-sctp_events">sctp_events</seealso>).
          It is enabled by default, since such ancillary data
          provide an easy way of determining the association and stream
          over which the message has been received.
          (An alternative way would be to get the Association ID from the
          <c><anno>FromIP</anno></c> and <c><anno>FromPort</anno></c> using the
          <seealso marker="#option-sctp_get_peer_addr_info">sctp_get_peer_addr_info</seealso> socket option,
          but this would still not produce the Stream number).</p>
        <p>The actual <c><anno>Data</anno></c> received may be a <c>binary()</c>,
          or <c>list()</c> of bytes (integers in the range 0 through 255)
          depending on the socket mode, or an SCTP Event.
                    <marker id="sctp_events"></marker>

          The following SCTP Events are possible:</p>
        <list type="bulleted">
          <item>
            <p><seealso marker="#record-sctp_sndrcvinfo">#sctp_sndrcvinfo{}</seealso></p>
          </item>
          <item>
            <p><seealso marker="#record-sctp_assoc_change">#sctp_assoc_change{}</seealso>;</p>
          </item>
          <item>
<pre>  #sctp_paddr_change{
        addr      = {ip_address(),port()},
        state     = atom(),
        error     = integer(),
        assoc_id  = assoc_id()
  }            </pre>
            <p>Indicates change of the status of the peer's IP address given by
              <c>addr</c> within the association <c>assoc_id</c>.
              Possible values of <c>state</c> (mostly self-explanatory) include:</p>
            <list type="bulleted">
              <item>
                <p><c>addr_unreachable</c>;</p>
              </item>
              <item>
                <p><c>addr_available</c>;</p>
              </item>
              <item>
                <p><c>addr_removed</c>;</p>
              </item>
              <item>
                <p><c>addr_added</c>;</p>
              </item>
              <item>
                <p><c>addr_made_prim</c>.</p>
              </item>
              <item>
                <p><c>addr_confirmed</c>.</p>
              </item>
            </list>
            <p>In case of an error (e.g. <c>addr_unreachable</c>), the
              <c>error</c> field provides additional diagnostics. In such cases,
              the <c>#sctp_paddr_change{}</c> Event is automatically 
              converted into an <c>error</c> term returned by 
              <c>gen_sctp:recv</c>. The <c>error</c> field value can be
              converted into a string using <c>error_string/1</c>.</p>
          </item>
          <item>
<pre>  #sctp_send_failed{
        flags     = true | false,
        error     = integer(),
        info      = #sctp_sndrcvinfo{},
        assoc_id  = assoc_id()
        data      = binary()
  }            </pre>
            <p>The sender may receive this event if a send operation fails.
              The <c>flags</c> is a Boolean specifying whether the data have
              actually been transmitted over the wire; <c>error</c> provides
              extended diagnostics, use <c>error_string/1</c>;
              <c>info</c> is the original
              <seealso marker="#record-sctp_sndrcvinfo">#sctp_sndrcvinfo{}</seealso> record used in the failed
              <seealso marker="#send/3">send/*,</seealso> and <c>data</c> 
              is the whole original data chunk attempted to be sent.</p>
            <p>In the current implementation of the Erlang/SCTP binding,
              this Event is internally converted into an <c>error</c> term 
              returned by <c>recv/*</c>.</p>
          </item>
          <item>
<pre>  #sctp_adaptation_event{
        adaptation_ind = integer(),
        assoc_id       = assoc_id()
  }            </pre>
            <p>Delivered when a peer sends an Adaptation Layer Indication
              parameter (configured through the option
              <seealso marker="#option-sctp_adaptation_layer">sctp_adaptation_layer</seealso>).
              Note that with the current implementation of
              the Erlang/SCTP binding, this event is disabled by default.</p>
          </item>
          <item>
<pre>  #sctp_pdapi_event{
        indication = sctp_partial_delivery_aborted,
        assoc_id   = assoc_id()
  }            </pre>
            <p>A partial delivery failure. In the current implementation of
              the Erlang/SCTP binding, this Event is internally converted
              into an <c>error</c> term returned by <c>recv/*</c>.</p>
          </item>
        </list>
      </desc>
    </func>
    <func>
      <name name="send" arity="3"/>
      <fsummary>Send a message using an <c>#sctp_sndrcvinfo{}</c>record</fsummary>
      <desc>
        <p>Sends the <c><anno>Data</anno></c> message with all sending parameters from a
          <seealso marker="#record-sctp_sndrcvinfo">#sctp_sndrcvinfo{}</seealso> record.
          This way, the user can specify the PPID (passed to the remote end)
          and Context (passed to the local SCTP layer) which can be used
          for example for error identification.
          However, such a fine level of user control is rarely required.
          The send/4 function is sufficient for most applications.</p>
      </desc>
    </func>
    <func>
      <name name="send" arity="4"/>
      <fsummary>Send a message over an existing association and given stream</fsummary>
      <desc>
        <p>Sends <c><anno>Data</anno></c> message over an existing association and given
          stream.</p>
      </desc>
    </func>
    <func>
      <name name="error_string" arity="1"/>
      <fsummary>Translate an SCTP error number into a string</fsummary>
      <desc>
        <p>Translates an SCTP error number from for example 
          <c>#sctp_remote_error{}</c> or <c>#sctp_send_failed{}</c> into
          an explanatory string, or one of the atoms <c>ok</c> for no
          error and <c>undefined</c> for an unrecognized error.</p>
      </desc>
    </func>
  </funcs>

  <section>
    <marker id="options"></marker>
    <title>SCTP SOCKET OPTIONS</title>
    <p>The set of admissible SCTP socket options is by construction
      orthogonal to the sets of TCP, UDP and generic INET options:
      only those options which are explicitly listed below are allowed
      for SCTP sockets. Options can be set on the socket using
      <seealso marker="#open/1"><c>gen_sctp:open/1,2</c></seealso>
      or <seealso marker="inet#setopts/2"><c>inet:setopts/2</c></seealso>,
      retrieved using <seealso marker="inet#getopts/2"><c>inet:getopts/2</c></seealso>,
      and when calling <seealso marker="#connect/4"><c>gen_sctp:connect/4,5</c></seealso>
      options can be changed.</p>
    <marker id="option-binary"></marker>
    <marker id="option-list"></marker>
    <taglist>
      <tag><c>{mode, list|binary}</c> or just <c>list</c> or <c>binary</c></tag>
      <item>
        <p>Determines the type of data returned from <c>gen_sctp:recv/1,2</c>.</p>
        <marker id="option-active"></marker>
      </item>
      <tag><c>{active, true|false|once|N}</c></tag>
      <item>
        <list type="bulleted">
          <item>
            <p>If <c>false</c> (passive mode, the default),
              the caller needs to do an explicit <c>gen_sctp:recv</c> call
              in order to retrieve the available data from the socket.</p>
          </item>
          <item>
            <p>If <c>true</c> (full active mode), the pending data or events are
              sent to the owning process.</p>
            <p><em>NB:</em> This can cause the message queue to overflow,
              as there is no way to throttle the sender in this case
              (no flow control!).</p>
          </item>
          <item>
            <p>If <c>once</c>, only one message is automatically placed
              in the message queue, and after that the mode is automatically
              reset to passive. This provides flow control as well as
              the possibility for the receiver to listen for its incoming
              SCTP data interleaved with other inter-process messages.</p>
          </item>
          <item>
            <p>If <c>active</c> is specified as an integer <c>N</c> in the
              range -32768 to 32767 (inclusive), then that number is added to
              the socket's count of the number of data messages to be
              delivered to the controlling process. If the result of the
              addition would be negative, the count is set to 0. Once the
              count reaches 0, either through the delivery of messages or by
              being explicitly set with <seealso
              marker="inet#setopts/2">inet:setopts/2</seealso>, the socket's
              mode is automatically reset to passive (<c>{active,
              false}</c>) mode. When a socket in this active mode transitions to
              passive mode, the message <c>{sctp_passive, Socket}</c> is sent
              to the controlling process to notify it that if it wants to
              receive more data messages from the socket, it must call
              <seealso marker="inet#setopts/2">inet:setopts/2</seealso> to set
              the socket back into an active mode.</p>
          </item>
        </list>
      </item>
     <tag><c>{tos, integer()}</c></tag>
      <item>
        <p>Sets the Type-Of-Service field on the IP datagrams being sent,
          to the given value, which effectively determines a prioritization
          policy for the outbound packets. The acceptable values
          are system-dependent. TODO: we do not provide
          symbolic names for these values yet.</p>
      </item>
      <tag><c>{priority, integer()}</c></tag>
      <item>
        <p>A protocol-independent equivalent of <c>tos</c> above. Setting
          priority implies setting tos as well.</p>
      </item>
      <tag><c>{dontroute, true|false}</c></tag>
      <item>
        <p>By default <c>false</c>. If <c>true</c>, the kernel does not
          send packets via any gateway, only sends them to directly
          connected hosts.</p>
      </item>
      <tag><c>{reuseaddr, true|false}</c></tag>
      <item>
        <p>By default <c>false</c>. If true, the local binding address
          <c>{IP,Port}</c> of the socket can be re-used immediately:
          no waiting in the CLOSE_WAIT state is performed (may be
          required for high-throughput servers).</p>
      </item>
	  <tag><c>{sndbuf, integer()}</c></tag>
      <item>
        <p>The size, in bytes, of the *kernel* send buffer for this socket.
          Sending errors would occur for datagrams larger than
          <c>val(sndbuf)</c>. Setting this option also adjusts
          the size of the driver buffer (see <c>buffer</c> above).</p>
      </item>
      <tag><c>{recbuf, integer()}</c></tag>
      <item>
        <p>The size, in bytes, of the *kernel* recv buffer for this socket.
          Sending errors would occur for datagrams larger than
          <c>val(sndbuf)</c>. Setting this option also adjusts
          the size of the driver buffer (see <c>buffer</c> above).</p>
      </item>

		  <tag><c>{sctp_module, module()}</c></tag>
		  <item> <p>
				  Override which callback module is used. Defaults to
				  <c>inet_sctp</c> for IPv4 and <c>inet6_sctp</c> for IPv6.
			  </p>
		  </item>


      <tag><c>{sctp_rtoinfo, #sctp_rtoinfo{}}</c></tag>
      <item>
<pre>  #sctp_rtoinfo{
        assoc_id = assoc_id(),
        initial  = integer(),
        max      = integer(),
        min      = integer()
  }        </pre>
        <p>Determines re-transmission time-out parameters, in milliseconds,
          for the association(s) given by <c>assoc_id</c>. 
          If <c>assoc_id = 0</c> (default) indicates the whole endpoint. See
          <url href="http://www.rfc-archive.org/getrfc.php?rfc=2960">RFC2960</url> and
          <url href="http://tools.ietf.org/html/draft-ietf-tsvwg-sctpsocket-13">Sockets API Extensions for SCTP</url> for the exact semantics of the fields values.</p>
      </item>
      <tag><c>{sctp_associnfo, #sctp_assocparams{}}</c></tag>
      <item>
<pre>  #sctp_assocparams{
        assoc_id                 = assoc_id(),
        asocmaxrxt               = integer(),
        number_peer_destinations = integer(),
        peer_rwnd                = integer(),
        local_rwnd               = integer(),
        cookie_life              = integer()
  }        </pre>
        <p>Determines association parameters for the association(s) given by
          <c>assoc_id</c>. <c>assoc_id = 0</c> (default) indicates
          the whole endpoint. See 
          <url href="http://tools.ietf.org/html/draft-ietf-tsvwg-sctpsocket-13">Sockets API Extensions for SCTP</url> for the discussion of their semantics. Rarely used.</p>
      </item>
      <tag><c>{sctp_initmsg, #sctp_initmsg{}}</c></tag>
      <item>
<pre>  #sctp_initmsg{
       num_ostreams   = integer(),
       max_instreams  = integer(),
       max_attempts   = integer(),
       max_init_timeo = integer()
  }        </pre>
        <p>Determines the default parameters which this socket attempts
          to negotiate with its peer while establishing an association with it.
          Should be set after <c>open/*</c> but before the first
          <c>connect/*</c>. <c>#sctp_initmsg{}</c> can also be used
          as ancillary data with the first call of <c>send/*</c> to
          a new peer (when a new association is created).</p>
        <list type="bulleted">
          <item>
            <p><c>num_ostreams</c>: number of outbound streams;</p>
          </item>
          <item>
            <p><c>max_instreams</c>: max number of in-bound streams;</p>
          </item>
          <item>
            <p><c>max_attempts</c>: max re-transmissions while
              establishing an association;</p>
          </item>
          <item>
            <p><c>max_init_timeo</c>: time-out in milliseconds
              for establishing an association.</p>
          </item>
        </list>
      </item>
      <tag><c>{sctp_autoclose, integer() >= 0}</c></tag>
      <item>
        <p>Determines the time (in seconds) after which an idle association is
          automatically closed. <c>0</c> means that the association is
          never automatically closed.</p>
      </item>
      <tag><c>{sctp_nodelay, true|false}</c></tag>
      <item>
        <p>Turns on|off the Nagle algorithm for merging small packets
          into larger ones (which improves throughput at the expense
          of latency).</p>
      </item>
      <tag><c>{sctp_disable_fragments, true|false}</c></tag>
      <item>
        <p>If <c>true</c>, induces an error on an attempt to send
          a message which is larger than the current PMTU size
          (which would require fragmentation/re-assembling).
          Note that message fragmentation does not affect
          the logical atomicity of its delivery; this option
          is provided for performance reasons only.</p>
      </item>
      <tag><c>{sctp_i_want_mapped_v4_addr, true|false}</c></tag>
      <item>
        <p>Turns on|off automatic mapping of IPv4 addresses into IPv6 ones
          (if the socket address family is AF_INET6).</p>
      </item>
      <tag><c>{sctp_maxseg, integer()}</c></tag>
      <item>
        <p>Determines the maximum chunk size if message fragmentation is used.
          If <c>0</c>, the chunk size is limited by the Path MTU only.</p>
      </item>
      <tag><c>{sctp_primary_addr, #sctp_prim{}}</c></tag>
      <item>
<pre>  #sctp_prim{
        assoc_id = assoc_id(),
        addr     = {IP, Port}
  }
  IP = ip_address()
  Port = port_number()        </pre>
        <p>For the association given by <c>assoc_id</c>,
          <c>{IP,Port}</c> must be one of the peer's addresses.
          This option determines that the given address is
          treated by the local SCTP stack as the peer's primary address.</p>
      </item>
      <tag><c>{sctp_set_peer_primary_addr, #sctp_setpeerprim{}}</c></tag>
      <item>
<pre>  #sctp_setpeerprim{
        assoc_id = assoc_id(),
        addr     = {IP, Port}
  }
  IP = ip_address()
  Port = port_number()        </pre>
        <p>When set, informs the peer that it should use <c>{IP, Port}</c>
          as the primary address of the local endpoint for the association
          given by <c>assoc_id</c>.</p>
        <marker id="option-sctp_adaptation_layer"></marker>
      </item>
      <tag><c>{sctp_adaptation_layer, #sctp_setadaptation{}}</c></tag>
      <item>
        <marker id="record-sctp_setadaptation"></marker>
<pre>  #sctp_setadaptation{
        adaptation_ind = integer()
  }        </pre>
        <p>When set, requests that the local endpoint uses the value given by
          <c>adaptation_ind</c> as the Adaptation Indication parameter for
          establishing new associations. See
          <url href="http://www.rfc-archive.org/getrfc.php?rfc=2960">RFC2960</url> and
          <url href="http://tools.ietf.org/html/draft-ietf-tsvwg-sctpsocket-13">Sockets API Extenstions for SCTP</url> for more details.</p>
      </item>
      <tag><c>{sctp_peer_addr_params, #sctp_paddrparams{}}</c></tag>
      <item>
<pre>  #sctp_paddrparams{
        assoc_id   = assoc_id(),
        address    = {IP, Port},
        hbinterval = integer(),
        pathmaxrxt = integer(),
        pathmtu    = integer(),
        sackdelay  = integer(),
        flags      = list()
  }
  IP = ip_address()
  Port = port_number()        </pre>
        <p>This option determines various per-address parameters for
          the association given by <c>assoc_id</c> and the peer address
          <c>address</c> (the SCTP protocol supports multi-homing,
          so more than 1 address can correspond to a given association).</p>
        <list type="bulleted">
          <item>
            <p><c>hbinterval</c>: heartbeat interval, in milliseconds;</p>
          </item>
          <item>
            <p><c>pathmaxrxt</c>: max number of retransmissions
              before this address is considered unreachable (and an
              alternative address is selected);</p>
          </item>
          <item>
            <p><c>pathmtu</c>: fixed Path MTU, if automatic discovery is
              disabled (see <c>flags</c> below);</p>
          </item>
          <item>
            <p><c>sackdelay</c>: delay in milliseconds for SAC messages
              (if the delay is enabled, see <c>flags</c> below);</p>
          </item>
          <item>
            <p><c>flags</c>: the following flags are available:</p>
            <list type="bulleted">
              <item>
                <p><c>hb_enable</c>:  enable heartbeat; </p>
              </item>
              <item>
                <p><c>hb_disable</c>: disable heartbeat;</p>
              </item>
              <item>
                <p><c>hb_demand</c>: initiate heartbeat immediately;</p>
              </item>
              <item>
                <p><c>pmtud_enable</c>: enable automatic Path MTU discovery;</p>
              </item>
              <item>
                <p><c>pmtud_disable</c>: disable automatic Path MTU discovery;</p>
              </item>
              <item>
                <p><c>sackdelay_enable</c>: enable SAC delay;</p>
              </item>
              <item>
                <p><c>sackdelay_disable</c>: disable SAC delay.</p>
              </item>
            </list>
          </item>
        </list>
      </item>
      <tag><c>{sctp_default_send_param, #sctp_sndrcvinfo{}}</c></tag>
      <item>
        <marker id="record-sctp_sndrcvinfo"></marker>
<pre>  #sctp_sndrcvinfo{
        stream     = integer(),
        ssn        = integer(),
        flags      = list(),
        ppid       = integer(),
        context    = integer(),
        timetolive = integer(),
        tsn        = integer(),
        cumtsn     = integer(),
        assoc_id   = assoc_id()
  }        </pre>
        <p><c>#sctp_sndrcvinfo{}</c> is used both in this socket option, and as
          ancillary data while sending or receiving SCTP messages. When
          set as an option, it provides a default values for subsequent
          <c>gen_sctp:send</c>calls on the association given by
          <c>assoc_id</c>. <c>assoc_id = 0</c> (default) indicates
          the whole endpoint. The following fields typically need
          to be specified by the sender:</p>
        <list type="bulleted">
          <item>
            <p><c>sinfo_stream</c>: stream number (0-base) within the association
              to send the messages through;</p>
          </item>
          <item>
            <p><c>sinfo_flags</c>: the following flags are recognised:</p>
            <list type="bulleted">
              <item>
                <p><c>unordered</c>: the message is to be sent unordered;</p>
              </item>
              <item>
                <p><c>addr_over</c>: the address specified in
                  <c>gen_sctp:send</c> overwrites the primary peer address;</p>
              </item>
              <item>
                <p><c>abort</c>: abort the current association without
                  flushing any unsent data;</p>
              </item>
              <item>
                <p><c>eof</c>: gracefully shut down the current
                  association, with flushing of unsent data.</p>
              </item>
            </list>
            <p>Other fields are rarely used. See 
              <url href="http://www.rfc-archive.org/getrfc.php?rfc=2960">RFC2960</url> and 
              <url href="http://tools.ietf.org/html/draft-ietf-tsvwg-sctpsocket-13">Sockets API Extensions for SCTP</url> for full information.</p>
          </item>
        </list>
        <marker id="option-sctp_events"></marker>
      </item>
      <tag><c>{sctp_events, #sctp_event_subscribe{}}</c></tag>
      <item>
        <marker id="record-sctp_event_subscribe"></marker>
<pre>  #sctp_event_subscribe{
          data_io_event          = true | false,
          association_event      = true | false,
          address_event          = true | false,
          send_failure_event     = true | false,
          peer_error_event       = true | false,
          shutdown_event         = true | false,
          partial_delivery_event = true | false,
          adaptation_layer_event = true | false
    }        </pre>
        <p>This option determines which
          <seealso marker="#sctp_events">SCTP Events</seealso> are to be
          received (via <seealso marker="#recv/1">recv/*</seealso>)
          along with the data. The only
          exception is <c>data_io_event</c> which enables or disables
          receiving of 
          <seealso marker="#record-sctp_sndrcvinfo">#sctp_sndrcvinfo{}</seealso>
          ancillary data, not events.
          By default, all flags except <c>adaptation_layer_event</c> are
          enabled, although <c>sctp_data_io_event</c> and
          <c>association_event</c> are used by the driver itself and not
          exported to the user level.</p>
      </item>
      <tag><c>{sctp_delayed_ack_time, #sctp_assoc_value{}}</c></tag>
      <item>
<pre>  #sctp_assoc_value{
        assoc_id    = assoc_id(),
        assoc_value = integer()
  }        </pre>
        <p>Rarely used. Determines the ACK time
          (given by <c>assoc_value</c> in milliseconds) for
          the given association or the whole endpoint
          if <c>assoc_value = 0</c> (default).</p>
      </item>
      <tag><c>{sctp_status, #sctp_status{}}</c></tag>
      <item>
<pre>  #sctp_status{
        assoc_id            = assoc_id(),
        state               = atom(),
        rwnd                = integer(),
        unackdata           = integer(),
        penddata            = integer(),
        instrms             = integer(),
        outstrms            = integer(),
        fragmentation_point = integer(),
        primary             = #sctp_paddrinfo{}
  }        </pre>
        <p>This option is read-only. It determines the status of
          the SCTP association given by <c>assoc_id</c>. Possible values of
          <c>state</c> follows. The state designations are mostly
          self-explanatory. <c>state_empty</c> is the default which means
          that no other state is active:</p>
        <list type="bulleted">
          <item>
            <p><c>sctp_state_empty</c></p>
          </item>
          <item>
            <p><c>sctp_state_closed</c></p>
          </item>
          <item>
            <p><c>sctp_state_cookie_wait</c></p>
          </item>
          <item>
            <p><c>sctp_state_cookie_echoed</c></p>
          </item>
          <item>
            <p><c>sctp_state_established</c></p>
          </item>
          <item>
            <p><c>sctp_state_shutdown_pending</c></p>
          </item>
          <item>
            <p><c>sctp_state_shutdown_sent</c></p>
          </item>
          <item>
            <p><c>sctp_state_shutdown_received</c></p>
          </item>
          <item>
            <p><c>sctp_state_shutdown_ack_sent</c></p>
          </item>
        </list>
        <p>The semantics of other fields is the following:</p>
        <list type="bulleted">
          <item>
            <p><c>sstat_rwnd</c>: the association peer's current receiver
              window size;</p>
          </item>
          <item>
            <p><c>sstat_unackdata</c>: number of unacked data chunks;</p>
          </item>
          <item>
            <p><c>sstat_penddata</c>: number of data chunks pending receipt;</p>
          </item>
          <item>
            <p><c>sstat_instrms</c>: number of inbound streams;</p>
          </item>
          <item>
            <p><c>sstat_outstrms</c>: number of outbound streams;</p>
          </item>
          <item>
            <p><c>sstat_fragmentation_point</c>: message size at which SCTP
              fragmentation will occur;</p>
          </item>
          <item>
            <p><c>sstat_primary</c>: information on the current primary peer
              address (see below for the format of <c>#sctp_paddrinfo{}</c>).</p>
          </item>
        </list>
        <marker id="option-sctp_get_peer_addr_info"></marker>
      </item>
      <tag><c>{sctp_get_peer_addr_info, #sctp_paddrinfo{}}</c></tag>
      <item>
        <marker id="record-sctp_paddrinfo"></marker>
<pre>  #sctp_paddrinfo{
        assoc_id  = assoc_id(),
        address   = {IP, Port},
        state     = inactive | active | unconfirmed,
        cwnd      = integer(),
        srtt      = integer(),
        rto       = integer(),
        mtu       = integer()
  }
  IP = ip_address()
  Port = port_number()        </pre>
        <p>This option is read-only. It determines the parameters specific to
          the peer's address given by <c>address</c> within the association
          given by <c>assoc_id</c>. The <c>address</c> field must be set by the
          caller; all other fields are filled in on return.
          If <c>assoc_id = 0</c> (default), the <c>address</c>
          is automatically translated into the corresponding
          association ID. This option is rarely used; see
          <url href="http://www.rfc-archive.org/getrfc.php?rfc=2960">RFC2960</url> and
          <url href="http://tools.ietf.org/html/draft-ietf-tsvwg-sctpsocket-13">Sockets API Extensions for SCTP</url> for the semantics of all fields.</p>
      </item>
    </taglist>
  </section>

  <section>
    <marker id="examples"></marker>
    <title>SCTP EXAMPLES</title>
    <list type="bulleted">
      <item>
        <p>Example of an Erlang SCTP Server which receives SCTP messages and
          prints them on the standard output:</p>
<pre>  -module(sctp_server).
  
  -export([server/0,server/1,server/2]).
  -include_lib("kernel/include/inet.hrl").
  -include_lib("kernel/include/inet_sctp.hrl").
  
  server() -&gt;
      server(any, 2006).
  
  server([Host,Port]) when is_list(Host), is_list(Port) -&gt;
      {ok, #hostent{h_addr_list = [IP|_]}} = inet:gethostbyname(Host),
      io:format("~w -&gt; ~w~n", [Host, IP]),
      server([IP, list_to_integer(Port)]).
  
  server(IP, Port) when is_tuple(IP) orelse IP == any orelse IP == loopback,
                        is_integer(Port) -&gt;
      {ok,S} = gen_sctp:open(Port, [{recbuf,65536}, {ip,IP}]),
      io:format("Listening on ~w:~w. ~w~n", [IP,Port,S]),
      ok     = gen_sctp:listen(S, true),
      server_loop(S).
  
  server_loop(S) -&gt;
      case gen_sctp:recv(S) of
      {error, Error} -&gt;
          io:format("SCTP RECV ERROR: ~p~n", [Error]);
      Data -&gt;
          io:format("Received: ~p~n", [Data])
      end,
      server_loop(S).        </pre>
      </item>
      <item>
        <p>Example of an Erlang SCTP Client which interacts with the above Server.
          Note that in this example, the Client creates an association with
          the Server with 5 outbound streams. For this reason, sending of
          "Test 0" over Stream 0 succeeds, but sending of "Test 5"
          over Stream 5 fails. The client then <c>abort</c>s the association,
          which results in the corresponding Event being received on
          the Server side.</p>
<pre>  -module(sctp_client).
  
  -export([client/0, client/1, client/2]).
  -include_lib("kernel/include/inet.hrl").
  -include_lib("kernel/include/inet_sctp.hrl").
 
  client() -&gt;
      client([localhost]).
  
  client([Host]) -&gt;
      client(Host, 2006);
  
  client([Host, Port]) when is_list(Host), is_list(Port) -&gt;
      client(Host,list_to_integer(Port)),
      init:stop().
  
  client(Host, Port) when is_integer(Port) -&gt;
      {ok,S}     = gen_sctp:open(),
      {ok,Assoc} = gen_sctp:connect
          (S, Host, Port, [{sctp_initmsg,#sctp_initmsg{num_ostreams=5}}]),
      io:format("Connection Successful, Assoc=~p~n", [Assoc]),
      
      io:write(gen_sctp:send(S, Assoc, 0, &lt;&lt;"Test 0"&gt;&gt;)),
      io:nl(),
      timer:sleep(10000),
      io:write(gen_sctp:send(S, Assoc, 5, &lt;&lt;"Test 5"&gt;&gt;)),
      io:nl(),
      timer:sleep(10000),
      io:write(gen_sctp:abort(S, Assoc)),
      io:nl(),
      
      timer:sleep(1000),
      gen_sctp:close(S).        </pre>
      </item>
      <item>
        <p>A very simple Erlang SCTP Client which uses the
          connect_init API.</p>
<pre>-module(ex3).

-export([client/4]).
-include_lib("kernel/include/inet.hrl").
-include_lib("kernel/include/inet_sctp.hrl").

client(Peer1, Port1, Peer2, Port2)
  when is_tuple(Peer1), is_integer(Port1), is_tuple(Peer2), is_integer(Port2) -&gt;
    {ok,S}     = gen_sctp:open(),
    SctpInitMsgOpt = {sctp_initmsg,#sctp_initmsg{num_ostreams=5}},
    ActiveOpt = {active, true},
    Opts = [SctpInitMsgOpt, ActiveOpt],
    ok = gen_sctp:connect(S, Peer1, Port1, Opts),
    ok = gen_sctp:connect(S, Peer2, Port2, Opts),
    io:format("Connections initiated~n", []),
    client_loop(S, Peer1, Port1, undefined, Peer2, Port2, undefined).

client_loop(S, Peer1, Port1, AssocId1, Peer2, Port2, AssocId2) -&gt;
    receive
        {sctp, S, Peer1, Port1, {_Anc, SAC}}
          when is_record(SAC, sctp_assoc_change), AssocId1 == undefined -&gt;
            io:format("Association 1 connect result: ~p. AssocId: ~p~n",
                      [SAC#sctp_assoc_change.state,
                       SAC#sctp_assoc_change.assoc_id]),
            client_loop(S, Peer1, Port1, SAC#sctp_assoc_change.assoc_id,
                        Peer2, Port2, AssocId2);

        {sctp, S, Peer2, Port2, {_Anc, SAC}}
          when is_record(SAC, sctp_assoc_change), AssocId2 == undefined -&gt;
            io:format("Association 2 connect result: ~p. AssocId: ~p~n",
                      [SAC#sctp_assoc_change.state, SAC#sctp_assoc_change.assoc_id]),
            client_loop(S, Peer1, Port1, AssocId1, Peer2, Port2,
                        SAC#sctp_assoc_change.assoc_id);

        {sctp, S, Peer1, Port1, Data} -&gt;
            io:format("Association 1: received ~p~n", [Data]),
            client_loop(S, Peer1, Port1, AssocId1,
                        Peer2, Port2, AssocId2);

        {sctp, S, Peer2, Port2, Data} -&gt;
            io:format("Association 2: received ~p~n", [Data]),
            client_loop(S, Peer1, Port1, AssocId1,
                        Peer2, Port2, AssocId2);

        Other -&gt;
            io:format("Other ~p~n", [Other]),
            client_loop(S, Peer1, Port1, AssocId1,
                        Peer2, Port2, AssocId2)

    after 5000 -&gt;
            ok
    end.
</pre>
      </item>
    </list>
  </section>

  <section>
    <marker id="seealso"></marker>
    <title>SEE ALSO</title>
    <p><seealso marker="inet">inet(3)</seealso>,
      <seealso marker="gen_tcp">gen_tcp(3)</seealso>,
      <seealso marker="gen_udp">gen_udp(3)</seealso>,
      <url href="http://www.rfc-archive.org/getrfc.php?rfc=2960">RFC2960</url> (Stream Control Transmission Protocol),
      <url href="http://tools.ietf.org/html/draft-ietf-tsvwg-sctpsocket-13">Sockets API Extensions for SCTP.</url></p>
  </section>
</erlref>