path: root/lib/megaco/doc/src/megaco.xml

<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE erlref SYSTEM "erlref.dtd">

<erlref>
  <header>
    <copyright>
      <year>2000</year><year>2016</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>megaco</title>
    <prepared>H&aring;kan Mattsson</prepared>
    <responsible>H&aring;kan Mattsson</responsible>
    <docno></docno>
    <approved>H&aring;kan Mattsson</approved>
    <checked></checked>
    <date>2007-06-15</date>
    <rev>%VSN%</rev>
    <file>megaco.xml</file>
  </header>
  <module>megaco</module>
  <modulesummary>Main API of the Megaco application</modulesummary>
  <description>
    <p>Interface module for the Megaco application</p>
  </description>

  <section>
    <title>DATA TYPES</title>
    <code type="none"><![CDATA[
megaco_mid() = ip4Address() | ip6Address() | 
               domainName() | deviceName() | 
               mtpAddress() 
ip4Address() = #'IP4Address'{}
ip6Address() = #'IP6Address'{}
domainName() = #'DomainName'{}
deviceName() = pathName() 
pathName()   = ia5String(1..64)
mtpAddress() = octetString(2..4)

action_request() = #'ActionRequest'{}
action_reply() = #'ActionReply'{}
error_desc() = #'ErrorDescriptor'{}
transaction_reply() = #'TransactionReply'{}
segment_no() = integer()

resend_indication() = flag | boolean()

property_parm() = #'PropertyParm'{}
property_group() = [property_parm()]
property_groups() = [property_group()]

sdp() = sdp_c() | sdp_o() | sdp_s() | sdp_i() | sdp_u() | 
        sdp_e() | sdp_p() | sdp_b() | sdp_z() | sdp_k() | 
        sdp_a() | sdp_a_rtpmap() | sdp_a_ptime() | 
        sdp_t() | sdp_r() | sdp_m()
sdp_v() = #megaco_sdp_v{} (Protocol version)
sdp_o() = #megaco_sdp_o{} (Owner/creator and session identifier)
sdp_s() = #megaco_sdp_s{} (Session name)
sdp_i() = #megaco_sdp_i{} (Session information)
sdp_u() = #megaco_sdp_u{} (URI of description)
sdp_e() = #megaco_sdp_e{} (Email address)
sdp_p() = #megaco_sdp_p{} (Phone number)
sdp_c() = #megaco_sdp_c{} (Connection information)
sdp_b() = #megaco_sdp_b{} (Bandwidth information)
sdp_k() = #megaco_sdp_k{} (Encryption key)
sdp_a() = #megaco_sdp_a{} (Session attribute)
sdp_a_rtpmap() = #megaco_sdp_a_rtpmap{}
sdp_a_ptime() = #megaco_sdp_a_ptime{}
sdp_a_quality() = #megaco_sdp_a_quality{}
sdp_a_fmtp() = #megaco_sdp_a_fmtp{}
sdp_z() = #megaco_sdp_z{} (Time zone adjustment)
sdp_t() = #megaco_sdp_t{} (Time the session is active)
sdp_r() = #megaco_sdp_r{} (Repeat times)
sdp_m() = #megaco_sdp_m{} (Media name and transport address)
sdp_property_parm() = sdp() | property_parm()
sdp_property_group() = [sdp_property_parm()]
sdp_property_groups() = [sdp_property_group()]

megaco_timer() = infinity | integer() >= 0 | megaco_incr_timer()
megaco_incr_timer() = #megaco_incr_timer{}
    ]]></code>
    <p>The record <c><![CDATA[megaco_incr_timer]]></c> contains the following fields: </p>
    <taglist>
      <tag><c><![CDATA[wait_for = integer() >= 0]]></c></tag>
      <item>
        <p>The actual timer time.</p>
      </item>
      <tag><c><![CDATA[factor = integer() >= 0]]></c></tag>
      <item>
        <p>The factor when calculating the new timer time 
          (<c><![CDATA[wait_for]]></c>).</p>
      </item>
      <tag><c><![CDATA[incr = integer()]]></c></tag>
      <item>
        <p>The increment value when calculating the new timer time 
          (<c><![CDATA[wait_for]]></c>). Note that this value <em>can</em> be negative
          and that a timer restart can therefor lead to a <c><![CDATA[wait_for]]></c>
          value of zero! It is up to the user to be aware of the 
          consequences of a <c><![CDATA[wait_for]]></c> value of zero. </p>
      </item>
      <tag><c><![CDATA[max_retries = infinity | infinity_restartable | integer() >= 0]]></c></tag>
      <item>
        <p>The maximum number of repetitions of the timer.</p>
        <p>There is a special case for this field. When the 
          <c><![CDATA[max_retries]]></c> has the value <c><![CDATA[infinity_restartable]]></c>, 
          it means that the timer is restartable as long as some 
          external event occurs (e.g. receipt of a pending 
          message for instance). But the timer will never be
          restarted "by itself", i.e. when the timer expires 
          (whatever the timeout time), so does the timer. 
          Whenever the timer is restarted, the timeout time will 
          be calculated in the usual way! Also, as mentioned 
          above, beware the consequences of setting the value to
          <c><![CDATA[infinity]]></c> if <em>incr</em> has been set to an 
          negative value.</p>
      </item>
    </taglist>

    <marker id="start"></marker>
  </section>

  <funcs>
    <func>
      <name>start() -> ok | {error, Reason}</name>
      <fsummary>Starts the Megaco application</fsummary>
      <type>
        <v>Reason = term()</v>
      </type>
      <desc>
        <p>Starts the Megaco application</p>
        <p>Users may either explicitly be registered with
          megaco:start_user/2 and/or be statically configured by
          setting the application environment variable 'users' to a
          list of {UserMid, Config} tuples. See the function
          megaco:start_user/2 for details.</p>

        <marker id="stop"></marker>
      </desc>
    </func>

    <func>
      <name>stop() -> ok | {error, Reason}</name>
      <fsummary>Stops the Megaco application</fsummary>
      <type>
        <v>Reason = term()</v>
      </type>
      <desc>
        <p>Stops the Megaco application</p>

        <marker id="start_user"></marker>
      </desc>
    </func>

    <func>
      <name>start_user(UserMid, Config) -> ok | {error, Reason}</name>
      <fsummary>Initial configuration of a user</fsummary>
      <type>
        <v>UserMid = megaco_mid()</v>
        <v>Config  = [{user_info_item(), user_info_value()}]</v>
        <v>Reason  = term()</v>
      </type>
      <desc>
        <p>Initial configuration of a user</p>
        <p>Requires the megaco application to be started. A user is
          either a Media Gateway (MG) or a Media Gateway Controller
          (MGC). One Erlang node may host many users.</p>
        <p>A user is identified by its UserMid, which must be a legal
          Megaco MID.</p>
        <p>Config is a list of {Item, Value} tuples.  See
          megaco:user_info/2 about which items and values that are valid.</p>

        <marker id="stop_user"></marker>
      </desc>
    </func>

    <func>
      <name>stop_user(UserMid) -> ok | {error, Reason}</name>
      <fsummary>Delete the configuration of a user</fsummary>
      <type>
        <v>UserMid = megaco_mid()</v>
        <v>Reason  = term()</v>
      </type>
      <desc>
        <p>Delete the configuration of a user</p>
        <p>Requires that the user does not have any active connection.</p>

        <marker id="user_info"></marker>
      </desc>
    </func>

    <func>
      <name>user_info(UserMid) -> [{Item, Value}]</name>
      <name>user_info(UserMid, Item) -> Value | exit(Reason)</name>
      <fsummary>Lookup user information</fsummary>
      <type>
        <v>Handle  = user_info_handle()</v>
        <v>UserMid = megaco_mid() </v>
        <v>Item    = user_info_item()</v>
        <v>Value   = user_info_value()</v>
        <v>Reason  = term()</v>
      </type>
      <desc>
        <p>Lookup user information</p>
        <p>The following Item's are valid:</p>
        <marker id="ui_connections"></marker>
        <taglist>
          <tag><c><![CDATA[connections]]></c></tag>
          <item>
            <p>Lists all active connections for this user. Returns a
              list of megaco_conn_handle records.</p>
            <marker id="ui_receive_handle"></marker>
          </item>

          <tag><c><![CDATA[receive_handle]]></c></tag>
          <item>
            <p>Construct a megaco_receive_handle record from user config</p>

            <marker id="ui_trans_id"></marker>
          </item>

          <tag><c><![CDATA[trans_id]]></c></tag>
          <item>
            <p>Current transaction id. </p>
            <p>A positive integer or the atom 
              <c><![CDATA[undefined_serial]]></c> (in case no messages has been sent).</p>

            <marker id="ui_min_trans_id"></marker>
          </item>

          <tag><c><![CDATA[min_trans_id]]></c></tag>
          <item>
            <p>First trans id. </p>
            <p>A positive integer, defaults to 1.</p>

            <marker id="ui_max_trans_id"></marker>
          </item>

          <tag><c><![CDATA[max_trans_id]]></c></tag>
          <item>
            <p>Last trans id. </p>
            <p>A positive integer or <c><![CDATA[infinity]]></c>, 
              defaults to <c><![CDATA[infinity]]></c>.</p>

            <marker id="ui_request_timer"></marker>
          </item>

          <tag><c><![CDATA[request_timer]]></c></tag>
          <item>
            <p>Wait for reply. </p>
            <p>The timer is cancelled when a reply is received. </p>
            <p>When a pending message is received, the timer is 
              cancelled and the <c><![CDATA[long_request_timer]]></c> is started instead 
              (see below). No resends will be performed from this point 
              (since we now know that the other side has received the 
              request). </p>
            <p>When the timer reaches an intermediate expire, the request
              is resent and the timer is restarted. </p>
            <p>When the timer reaches the final expire, either the function 
              <c><![CDATA[megaco:call]]></c> will return with <c><![CDATA[{error, timeout}]]></c>
              or the callback function <c><![CDATA[handle_trans_reply]]></c> will be 
              called with <c><![CDATA[UserReply = {error, timeout}]]></c> (if 
              <c><![CDATA[megaco:cast]]></c> was used).</p>
            <p>A Megaco Timer (see explanation above), 
              defaults to <c><![CDATA[#megaco_incr_timer{}]]></c>.</p>

            <marker id="ui_long_request_timer"></marker>
          </item>

          <tag><c><![CDATA[long_request_timer]]></c></tag>
          <item>
            <p>Wait for reply after having received a pending message. </p>
            <p>When the timer reaches an intermediate expire, the timer 
              is restarted. </p>
            <p>When a pending message is received, and the 
              <c><![CDATA[long_request_timer]]></c>  
              is <em>not</em> "on its final leg", the timer will be 
              restarted, and, if <c><![CDATA[long_request_resend = true]]></c>, the
              request will be re-sent. </p>
            <p>A Megaco Timer (see explanation above), 
              defaults to <c><![CDATA[60 seconds]]></c>.</p>

            <marker id="ui_long_request_resend"></marker>
          </item>

          <tag><c><![CDATA[long_request_resend]]></c></tag>
          <item>
            <p>This option indicates weather the request should be 
              resent until the reply is received,
              <em>even</em> though a pending message has been received. </p>
            <p>Normally, after a pending message has been received, 
              the request is not resent 
              (since a pending message is an indication that the
              request has been received). But since the reply (to the 
              request) can be lost, this behaviour has its values.</p>
            <p>It is of course pointless to set this value to <em>true</em>
              unless the <c><![CDATA[long_request_timer]]></c> (see above) is also set
              to an incremental timer (<c><![CDATA[#megaco_incr_timer{}]]></c>). </p>
            <p>A <c><![CDATA[boolean]]></c>, 
              defaults to <c><![CDATA[false]]></c>.</p>

            <marker id="ui_reply_timer"></marker>
          </item>

          <tag><c><![CDATA[reply_timer]]></c></tag>
          <item>
            <p>Wait for an ack. </p>
            <p>When a request is received, some info
              related to the reply is store internally (e.g. the
              binary of the reply). This info will live until either
              an ack is received or this timer expires. For instance,
              if the same request is received again (e.g. a request
              with the same transaction id), the (stored) reply will
              be (re-) sent automatically by megaco.</p>
            <p>If the timer is of type <c><![CDATA[#megaco_incr_timer{}]]></c>, 
              then for each intermediate timout, the reply will be resent
              (this is valid until the ack is received or 
              the timer expires). </p>
            <p>A Megaco Timer (see explanation above), defaults to 30000.</p>

            <marker id="ui_request_keep_alive_timeout"></marker>
          </item>

          <tag><c><![CDATA[request_keep_alive_timeout]]></c></tag>
          <item>
            <p>Specifies the timeout time for the request-keep-alive timer. </p>
            <p>This timer is started when the <em>first</em> reply to an asynchronous
              request (issued using the 
              <seealso marker="megaco#cast">megaco:cast/3</seealso> function)
              arrives. As long as this timer is running, replies will 
              be delivered via the 
              <seealso marker="megaco_user#trans_reply">handle_trans_reply/4,5</seealso> 
              callback function, with their "arrival number" 
              (see <c><![CDATA[UserReply]]></c> of the 
              <seealso marker="megaco_user#trans_reply">handle_trans_reply/4,5</seealso> 
              callback function). </p>
            <p>Replies arriving after the timer has expired, will be 
              delivered using the 
              <seealso marker="megaco_user#unexpected_trans">handle_unexpected_trans/3,4</seealso> 
              callback function. </p>
            <p>The timeout time can have the values: 
              <c><![CDATA[plain | integer() >= 0]]></c>. </p>
            <p>Defaults to <c><![CDATA[plain]]></c>.</p>

            <marker id="ui_call_proxy_gc_timeout"></marker>
          </item>

          <tag><c><![CDATA[call_proxy_gc_timeout]]></c></tag>
          <item>
            <p>Timeout time for the call proxy. </p>
            <p>When a request is sent using the 
              <seealso marker="megaco#call">call/3</seealso> function, 
              a proxy process is started to handle
              all replies. When the reply has been received and delivered 
              to the user, the proxy process continue to exist for as long
              as this option specifies. Any received messages, is passed on 
              to the user via the 
              <seealso marker="megaco_user#handle_unexpected_trans">handle_unexpected_trans</seealso> 
              callback function. </p>
            <p>The timeout time is in milliseconds. A value of 0 (zero) means
              that the proxy process will exit directly after the reply has 
              been delivered. </p>
            <p>An integer >= 0, defaults to 5000 (= 5 seconds).</p>

            <marker id="ui_auto_ack"></marker>
          </item>

          <tag><c><![CDATA[auto_ack]]></c></tag>
          <item>
            <p>Automatic send transaction ack when the transaction
              reply has been received (see <c><![CDATA[trans_ack]]></c> below). </p>
            <p>This is used for <em>three-way-handshake</em>.</p>
            <p>A <c><![CDATA[boolean]]></c>, defaults to <c><![CDATA[false]]></c>.</p>

            <marker id="ui_trans_ack"></marker>
          </item>

          <tag><c><![CDATA[trans_ack]]></c></tag>
          <item>
            <p>Shall ack's be accumulated or not. </p>
            <p>This property is only valid if <c><![CDATA[auto_ack]]></c> is true.</p>
            <p>If <c><![CDATA[auto_ack]]></c> is true, then if <c><![CDATA[trans_ack]]></c> is
              <c><![CDATA[false]]></c>, ack's will be sent immediately. 
              If <c><![CDATA[trans_ack]]></c> is <c><![CDATA[true]]></c>, then 
              ack's will instead be sent to the transaction 
              sender process for accumulation and later sending 
              (see <c><![CDATA[trans_ack_maxcount]]></c>, <c><![CDATA[trans_req_maxcount]]></c>, 
              <c><![CDATA[trans_req_maxsize]]></c>, <c><![CDATA[trans_ack_maxcount]]></c> and 
              <c><![CDATA[trans_timer]]></c>). </p>
            <p>See also <seealso marker="megaco_run#transaction_sender">transaction sender</seealso> for more info.</p>
            <p>An <c><![CDATA[boolean]]></c>, defaults to <c><![CDATA[false]]></c>.</p>

            <marker id="ui_trans_ack_maxcount"></marker>
          </item>

          <tag><c><![CDATA[trans_ack_maxcount]]></c></tag>
          <item>
            <p>Maximum number of accumulated ack's. At most this many ack's
              will be accumulated by the transaction sender (if started and 
              configured to accumulate ack's).</p>
            <p>See also <seealso marker="megaco_run#transaction_sender">transaction sender</seealso> for more info. </p>
            <p>An <c><![CDATA[integer]]></c>, defaults to 10.</p>

            <marker id="ui_trans_req"></marker>
          </item>

          <tag><c><![CDATA[trans_req]]></c></tag>
          <item>
            <p>Shall requests be accumulated or not. </p>
            <p>If <c><![CDATA[trans_req]]></c> is <c><![CDATA[false]]></c>, then request(s)
              will be sent immediately (in its own message).</p>
            <p>If <c><![CDATA[trans_req]]></c> is true, then request(s) will 
              instead be sent to the transaction sender process for 
              accumulation and later sending 
              (see <c><![CDATA[trans_ack_maxcount]]></c>, <c><![CDATA[trans_req_maxcount]]></c>, 
              <c><![CDATA[trans_req_maxsize]]></c>, <c><![CDATA[trans_ack_maxcount]]></c> and 
              <c><![CDATA[trans_timer]]></c>). </p>
            <p>See also <seealso marker="megaco_run#transaction_sender">transaction sender</seealso> for more info. </p>
            <p>An <c><![CDATA[boolean]]></c>, defaults to <c><![CDATA[false]]></c>.</p>

            <marker id="ui_trans_req_maxcount"></marker>
          </item>

          <tag><c><![CDATA[trans_req_maxcount]]></c></tag>
          <item>
            <p>Maximum number of accumulated requests. At most this many 
              requests will be accumulated by the transaction sender 
              (if started and configured to accumulate requests). </p>
            <p>See also <seealso marker="megaco_run#transaction_sender">transaction sender</seealso> for more info.</p>
            <p>An <c><![CDATA[integer]]></c>, defaults to 10.</p>
            <marker id="ui_trans_req_maxsize"></marker>
          </item>
          <tag><c><![CDATA[trans_req_maxsize]]></c></tag>
          <item>
            <p>Maximum size of the accumulated requests. At most this much
              requests will be accumulated by the transaction sender 
              (if started and configured to accumulate requests).</p>
            <p>See also <seealso marker="megaco_run#transaction_sender">transaction sender</seealso> for more info.</p>
            <p>An <c><![CDATA[integer]]></c>, defaults to 2048.</p>

            <marker id="ui_trans_timer"></marker>
          </item>

          <tag><c><![CDATA[trans_timer]]></c></tag>
          <item>
            <p>Transaction sender timeout time. Has two functions. First, if 
              the value is 0, then transactions will not be accumulated 
              (e.g. the transaction sender process will not be started). 
              Second, if the value is greater then 0 and <c><![CDATA[auto_ack]]></c> 
              and <c><![CDATA[trans_ack]]></c> are both true or 
              if <c><![CDATA[trans_req]]></c> is true, 
              then transaction sender will be started and transactions 
              (which is depending on the values of <c><![CDATA[auto_ack]]></c>, 
              <c><![CDATA[trans_ack]]></c> and <c><![CDATA[trans_req]]></c>) will be accumulated,
              for later sending. </p>
            <p>See also <seealso marker="megaco_run#transaction_sender">transaction sender</seealso> for more info. </p>
            <p>An <c><![CDATA[integer]]></c>, defaults to 0.</p>

            <marker id="ui_pending_timer"></marker>
          </item>

          <tag><c><![CDATA[pending_timer]]></c></tag>
          <item>
            <p>Automatically send pending if the timer expires before a
              transaction reply has been sent. This timer is also called 
              provisional response timer. </p>
            <p>A Megaco Timer (see explanation above), defaults to 30000.</p>

            <marker id="ui_sent_pending_limit"></marker>
          </item>

          <tag><c><![CDATA[sent_pending_limit]]></c></tag>
          <item>
            <p>Sent pending limit (see the MGOriginatedPendingLimit
              and the MGCOriginatedPendingLimit of the megaco root package).
              This parameter specifies how many pending messages that can
              be sent (for a given received transaction request).
              When the limit is exceeded, the transaction is aborted
              (see <seealso marker="megaco_user#request_abort">handle_trans_request_abort</seealso>) and an error message 
              is sent to the other side. </p>
            <p>Note that this has no effect on the actual sending of
              pending transactions. This is either implicit (e.g. when 
              receiving a re-sent transaction request for a request which
              is being processed) or controlled by the pending_timer,
              see above. </p>
            <p>A positive integer or <c><![CDATA[infinity]]></c>, 
              defaults to <c><![CDATA[infinity]]></c>.</p>

            <marker id="ui_recv_pending_limit"></marker>
          </item>

          <tag><c><![CDATA[recv_pending_limit]]></c></tag>
          <item>
            <p>Receive pending limit (see the MGOriginatedPendingLimit
              and the MGCOriginatedPendingLimit of the megaco root package).
              This parameter specifies how many pending messages that can
              be received (for a sent transaction request).
              When the limit is exceeded, the transaction is considered
              lost, and an error returned to the user (through the call-back
              function <em>handle_trans_reply</em>). </p>
            <p>A positive integer or <c><![CDATA[infinity]]></c>, 
              defaults to <c><![CDATA[infinity]]></c>. </p>

            <marker id="ui_send_mod"></marker>
          </item>

          <tag><c><![CDATA[send_mod]]></c></tag>
          <item>
            <p>Send callback module which exports send_message/2. The
              function SendMod:send_message(SendHandle, Binary) is
              invoked when the bytes needs to be transmitted to the
              remote user. </p>
            <p>An <c><![CDATA[atom]]></c>, defaults to <c><![CDATA[megaco_tcp]]></c>.</p>

            <marker id="ui_encoding_mod"></marker>
          </item>

          <tag><c><![CDATA[encoding_mod]]></c></tag>
          <item>
            <p>Encoding callback module which exports encode_message/2
              and decode_message/2. The function
              EncodingMod:encode_message(EncodingConfig,
              MegacoMessage) is invoked whenever a 'MegacoMessage'
              record needs to be translated into an Erlang binary. The
              function EncodingMod:decode_message(EncodingConfig,
              Binary) is invoked whenever an Erlang binary needs to be
              translated into a 'MegacoMessage' record. </p>
            <p>An <c><![CDATA[atom]]></c>, defaults to <c><![CDATA[megaco_pretty_text_encoder]]></c>.</p>

            <marker id="ui_encoding_config"></marker>
          </item>

          <tag><c><![CDATA[encoding_config]]></c></tag>
          <item>
            <p>Encoding module config. </p>
            <p>A <c><![CDATA[list]]></c>, defaults to <c><![CDATA[[]]]></c>.</p>

            <marker id="ui_protocol_version"></marker>
          </item>

          <tag><c><![CDATA[protocol_version]]></c></tag>
          <item>
            <p>Actual protocol version. </p>
            <p>An <c><![CDATA[integer]]></c>, default is 1.</p>

            <marker id="ui_strict_version"></marker>
          </item>

          <tag><c><![CDATA[strict_version]]></c></tag>
          <item>
            <p>Strict version control, i.e. when a message is received,
              verify that the version is that which was negotiated. </p>
            <p>An <c><![CDATA[boolean]]></c>, default is true.</p>

            <marker id="ui_reply_data"></marker>
          </item>

          <tag><c><![CDATA[reply_data]]></c></tag>
          <item>
            <p>Default reply data. </p>
            <p>Any term, defaults to the atom <c><![CDATA[undefined]]></c>.</p>

            <marker id="ui_user_mod"></marker>
          </item>

          <tag><c><![CDATA[user_mod]]></c></tag>
          <item>
            <p>Name of the user callback module. See the the reference
              manual for megaco_user for more info.</p>

            <marker id="ui_user_args"></marker>
          </item>

          <tag><c><![CDATA[user_args]]></c></tag>
          <item>
            <p>List of extra arguments to the user callback
              functions. See the the reference manual for megaco_user
              for more info.</p>

            <marker id="ui_threaded"></marker>
          </item>

          <tag><c><![CDATA[threaded]]></c></tag>
          <item>
            <p>If a received message contains several transaction requests, 
              this option indicates whether the requests should be handled
              sequentially in the same process (<c><![CDATA[false]]></c>), or if each 
              request should be handled by its own process (<c><![CDATA[true]]></c>
              i.e. a separate process is spawned for each request). </p>
            <p>An <c><![CDATA[boolean]]></c>, defaults to <c><![CDATA[false]]></c>. </p>

            <marker id="ui_resend_indication"></marker>
          </item>

          <tag><c><![CDATA[resend_indication]]></c></tag>
          <item>
            <p>This option indicates weather the transport module
              should be told if a message send is a resend or not. </p>
            <p>If <em>false</em>, megaco messages are sent using the
              <seealso marker="megaco_transport#send_message">send_message</seealso> 
              function. </p>
            <p>If <em>true</em>, megaco message <em>re-sends</em> are made using the
              <seealso marker="megaco_transport#resend_message">resend_message</seealso> 
              function. The initial message send is still done using the
              <seealso marker="megaco_transport#send_message">send_message</seealso> 
              function. </p>
            <p>The special value <em>flag</em> instead indicates that the 
              function 
              <seealso marker="megaco_transport#send_message">send_message/3</seealso> 
              shall be used. </p>
            <p>A <c>resend_indication()</c>, 
              defaults to <c><![CDATA[false]]></c>.</p>

            <marker id="ui_segment_reply_ind"></marker>
          </item>

          <tag><c><![CDATA[segment_reply_ind]]></c></tag>
          <item>
            <p>This option specifies if the user shall be notified of received
              segment replies or not. </p>
            <p>See 
              <seealso marker="megaco_user#segment_reply">handle_segment_reply</seealso> 
              callback function for more information. </p>
            <p>A <c><![CDATA[boolean]]></c>, 
              defaults to <c><![CDATA[false]]></c>. </p>

            <marker id="ui_segment_recv_timer"></marker>
          </item>

          <tag><c><![CDATA[segment_recv_timer]]></c></tag>
          <item>
            <p>This timer is started when the segment indicated by the
              <c><![CDATA[segmentation complete token]]></c> is received, but all 
              segments has not yet been received.</p>
            <p>When the timer finally expires, a "megaco segments not
              received" (459) error message is sent to the other side
              and the user is notified with a <c><![CDATA[segment timeout]]></c> <c><![CDATA[UserReply]]></c> in either the
              <seealso marker="megaco_user#trans_reply">handle_trans_reply</seealso> callback function or 
              the return value of the 
              <seealso marker="megaco#call">call</seealso> function. </p>
            <p>A Megaco Timer (see explanation above),
              defaults to <c><![CDATA[10000]]></c>. </p>

            <marker id="ui_segment_send"></marker>
          </item>

          <tag><c><![CDATA[segment_send]]></c></tag>
          <item>
            <p>Shall outgoing messages be segmented or not: </p>
            <taglist>
              <tag><c><![CDATA[none]]></c></tag>
              <item>
                <p>Do not segment outgoing reply messages. This is useful when
                  either it is known that messages are never to large or
                  that the transport protocol can handle such things
                  on its own (e.g. TCP or SCTP).</p>
              </item>
              <tag><c><![CDATA[integer() > 0]]></c></tag>
              <item>
                <p>Outgoing reply messages will be segmented as needed 
                  (see <c><![CDATA[max_pdu_size]]></c> below). This value, K, indicate 
                  the outstanding window, i.e. how many segments can be 
                  outstanding (not acknowledged) at any given time. </p>
              </item>
              <tag><c><![CDATA[infinity]]></c></tag>
              <item>
                <p>Outgoing reply messages will be segmented as needed 
                  (see <c><![CDATA[max_pdu_size]]></c> below). Segment messages 
                  are sent all at once (i.e. no acknowledgement awaited 
                  before sending the next segment). </p>
              </item>
            </taglist>
            <p>Defaults to <c><![CDATA[none]]></c>. </p>

            <marker id="ui_max_pdu_size"></marker>
          </item>

          <tag><c><![CDATA[max_pdu_size]]></c></tag>
          <item>
            <p>Max message size. If the encoded message (PDU) exceeds 
              this size, the message should be segmented, and then 
              encoded. </p>
            <p>A positive integer or <c><![CDATA[infinity]]></c>,
              defaults to <c><![CDATA[infinity]]></c>. </p>
          </item>
        </taglist>

        <marker id="update_user_info"></marker>
      </desc>
    </func>

    <func>
      <name>update_user_info(UserMid, Item, Value) -> ok | {error, Reason}</name>
      <fsummary>Update information about a user</fsummary>
      <type>
        <v>UserMid = megaco_mid() </v>
        <v>Item    = user_info_item()</v>
        <v>Value   = user_info_value()</v>
        <v>Reason  = term()</v>
      </type>
      <desc>
        <p>Update information about a user</p>
        <p>Requires that the user is started. See megaco:user_info/2
          about which items and values that are valid.</p>

        <marker id="conn_info"></marker>
      </desc>
    </func>

    <func>
      <name>conn_info(ConnHandle) -> [{Item, Value}]</name>
      <name>conn_info(ConnHandle, Item) -> Value | exit(Reason)</name>
      <fsummary>Lookup information about an active connection</fsummary>
      <type>
        <v>ConnHandle = #megaco_conn_handle{}</v>
        <v>Item       = conn_info_item()</v>
        <v>Value      = conn_info_value()</v>
        <v>Reason     = {no_such_connection, ConnHandle} | term()</v>
      </type>
      <desc>
        <p>Lookup information about an active connection</p>
        <p>Requires that the connection is active.</p>
        <marker id="ci_control_pid"></marker>
        <taglist>

          <tag><c><![CDATA[control_pid]]></c></tag>
          <item>
            <p>The process identifier of the controlling process for a
              connection.</p>

            <marker id="ci_send_handle"></marker>
          </item>

          <tag><c><![CDATA[send_handle]]></c></tag>
          <item>
            <p>Opaque send handle whose contents is internal for the
              send module. May be any term.</p>

            <marker id="ci_local_mid"></marker>
          </item>

          <tag><c><![CDATA[local_mid]]></c></tag>
          <item>
            <p>The local mid (of the connection, i.e. the own mid). 
              <c><![CDATA[megaco_mid()]]></c>.</p>

            <marker id="ci_remote_mid"></marker>
          </item>

          <tag><c><![CDATA[remote_mid]]></c></tag>
          <item>
            <p>The remote mid (of the connection). 
              <c><![CDATA[megaco_mid()]]></c>.</p>

            <marker id="ci_receive_handle"></marker>
          </item>

          <tag><c><![CDATA[receive_handle]]></c></tag>
          <item>
            <p>Construct a megaco_receive_handle record.</p>

            <marker id="ci_trans_id"></marker>
          </item>

          <tag><c><![CDATA[trans_id]]></c></tag>
          <item>
            <p>Next transaction id. A positive integer or the atom 
              <c><![CDATA[undefined_serial]]></c> (only in case of error). </p>
            <p>Note that transaction id's are (currently) maintained 
              on a per user basis so there is no way to be sure that 
              the value returned will actually be used for a transaction 
              sent on this connection (in case a user has several 
              connections, which is not at all unlikely). </p>

            <marker id="ci_max_trans_id"></marker>
          </item>

          <tag><c><![CDATA[max_trans_id]]></c></tag>
          <item>
            <p>Last trans id. </p>
            <p>A positive integer or <c><![CDATA[infinity]]></c>, 
              defaults to <c><![CDATA[infinity]]></c>.</p>

            <marker id="ci_request_time"></marker>
          </item>

          <tag><c><![CDATA[request_timer]]></c></tag>
          <item>
            <p>Wait for reply. </p>
            <p>The timer is cancelled when a reply is received. </p>
            <p>When a pending message is received, the timer is 
              cancelled and the <c><![CDATA[long_request_timer]]></c> is started instead 
              (see below). No resends will be performed from this point 
              (since we now know that the other side has received the 
              request). </p>
            <p>When the timer reaches an intermediate expire, the request
              is resent and the timer is restarted. </p>
            <p>When the timer reaches the final expire, either the function 
              <c><![CDATA[megaco:call]]></c> will return with <c><![CDATA[{error, timeout}]]></c>
              or the callback function <c><![CDATA[handle_trans_reply]]></c> will be 
              called with <c><![CDATA[UserReply = {error, timeout}]]></c> (if 
              <c><![CDATA[megaco:cast]]></c> was used).</p>
            <p>A Megaco Timer (see explanation above), 
              defaults to #megaco_incr_timer{}.</p>

            <marker id="ci_long_request_timer"></marker>
          </item>

          <tag><c><![CDATA[long_request_timer]]></c></tag>
          <item>
            <p>Wait for reply after having received a pending message. </p>
            <p>When the timer reaches an intermediate expire, the timer 
              restarted. </p>
            <p>When a pending message is received, and the 
              <c><![CDATA[long_request_timer]]></c> 
              is <em>not</em> "on its final leg", the timer will be 
              restarted, and, if <c><![CDATA[long_request_resend = true]]></c>, the
              request will be re-sent. </p>
            <p>A Megaco Timer (see explanation above), 
              defaults to <c><![CDATA[60 seconds]]></c>.</p>

            <marker id="ci_request_keep_alive_timeout"></marker>
          </item>

          <tag><c><![CDATA[request_keep_alive_timeout]]></c></tag>
          <item>
            <p>Specifies the timeout time for the request-keep-alive timer. </p>
            <p>This timer is started when the <em>first</em> reply to an asynchronous
              request (issued using the 
              <seealso marker="megaco#cast">megaco:cast/3</seealso> function)
              arrives. As long as this timer is running, replies will 
              be delivered via the 
              <seealso marker="megaco_user#trans_reply">handle_trans_reply/4,5</seealso> 
              callback function, with their "arrival number" 
              (see <c><![CDATA[UserReply]]></c> of the 
              <seealso marker="megaco_user#trans_reply">handle_trans_reply/4,5</seealso> 
              callback function). </p>
            <p>Replies arriving after the timer has expired, will be 
              delivered using the 
              <seealso marker="megaco_user#unexpected_trans">handle_unexpected_trans/3,4</seealso> 
              callback function. </p>
            <p>The timeout time can have the values: 
              <c><![CDATA[plain | integer() >= 0]]></c>. </p>
            <p>Defaults to <c><![CDATA[plain]]></c>.</p>

            <marker id="ci_long_request_resend"></marker>
          </item>

          <tag><c><![CDATA[long_request_resend]]></c></tag>
          <item>
            <p>This option indicates weather the request should be 
              resent until the reply is received,
              <em>even</em> though a pending message has been received. </p>
            <p>Normally, after a pending message has been received, 
              the request is not resent 
              (since a pending message is an indication that the
              request has been received). But since the reply (to the 
              request) can be
              lost, this behaviour has its values.</p>
            <p>It is of course pointless to set this value to <em>true</em>
              unless the <c><![CDATA[long_request_timer]]></c> (see above) is also set
              to an incremental timer (<c><![CDATA[#megaco_incr_timer{}]]></c>). </p>
            <p>A <c><![CDATA[boolean]]></c>, 
              defaults to <c><![CDATA[false]]></c>.</p>

            <marker id="ci_reply_timer"></marker>
          </item>

          <tag><c><![CDATA[reply_timer]]></c></tag>
          <item>
            <p>Wait for an ack. </p>
            <p>When a request is received, some info
              related to the reply is store internally (e.g. the
              binary of the reply). This info will live until either
              an ack is received or this timer expires. For instance,
              if the same request is received again (e.g. a request
              with the same transaction id), the (stored) reply will
              be (re-) sent automatically by megaco.</p>
            <p>If the timer is of type <c><![CDATA[#megaco_incr_timer{}]]></c>, 
              then for each intermediate timout, the reply will be resent
              (this is valid until the ack is received or 
              the timer expires). </p>
            <p>A Megaco Timer (see explanation above), defaults to 30000.</p>

            <marker id="ci_call_proxy_gc_timeout"></marker>
          </item>

          <tag><c><![CDATA[call_proxy_gc_timeout]]></c></tag>
          <item>
            <p>Timeout time for the call proxy. </p>
            <p>When a request is sent using the 
              <seealso marker="megaco#call">call/3</seealso> function, 
              a proxy process is started to handle
              all replies. When the reply has been received and delivered 
              to the user, the proxy process continue to exist for as long
              as this option specifies. Any received messages, is passed on 
              to the user via the 
              <seealso marker="megaco_user#handle_unexpected_trans">handle_unexpected_trans</seealso> 
              callback function. </p>
            <p>The timeout time is in milliseconds. A value of 0 (zero) means
              that the proxy process will exit directly after the reply has 
              been delivered. </p>
            <p>An integer >= 0, defaults to 5000 (= 5 seconds).</p>
            <marker id="ci_auto_ack"></marker>
          </item>

          <tag><c><![CDATA[auto_ack]]></c></tag>
          <item>
            <p>Automatic send transaction ack when the transaction
              reply has been received (see <c><![CDATA[trans_ack]]></c> below). </p>
            <p>This is used for <em>three-way-handshake</em>. </p>
            <p>A <c><![CDATA[boolean]]></c>, defaults to <c><![CDATA[false]]></c>.</p>

            <marker id="ci_trans_ack"></marker>
          </item>

          <tag><c><![CDATA[trans_ack]]></c></tag>
          <item>
            <p>Shall ack's be accumulated or not. </p>
            <p>This property is only valid if <c><![CDATA[auto_ack]]></c> is true. </p>
            <p>If <c><![CDATA[auto_ack]]></c> is true, then if <c><![CDATA[trans_ack]]></c> is
              <c><![CDATA[false]]></c>, ack's will be sent immediately. 
              If <c><![CDATA[trans_ack]]></c> is
              <c><![CDATA[true]]></c>, then ack's will instead be sent to the transaction 
              sender process for accumulation and later sending 
              (see <c><![CDATA[trans_ack_maxcount]]></c>, <c><![CDATA[trans_req_maxcount]]></c>, 
              <c><![CDATA[trans_req_maxsize]]></c>, <c><![CDATA[trans_ack_maxcount]]></c> and 
              <c><![CDATA[trans_timer]]></c>). </p>
            <p>See also <seealso marker="megaco_run#transaction_sender">transaction sender</seealso> for more info. </p>
            <p>An <c><![CDATA[boolean]]></c>, defaults to <c><![CDATA[false]]></c>.</p>

            <marker id="ci_trans_ack_maxcount"></marker>
          </item>

          <tag><c><![CDATA[trans_ack_maxcount]]></c></tag>
          <item>
            <p>Maximum number of accumulated ack's. At most this many ack's
              will be accumulated by the transaction sender (if started and 
              configured to accumulate ack's).</p>
            <p>See also <seealso marker="megaco_run#transaction_sender">transaction sender</seealso> for more info.</p>
            <p>An integer, defaults to 10.</p>

            <marker id="ci_trans_req"></marker>
          </item>

          <tag><c><![CDATA[trans_req]]></c></tag>
          <item>
            <p>Shall requests be accumulated or not. </p>
            <p>If <c><![CDATA[trans_req]]></c> is <c><![CDATA[false]]></c>, then request(s)
              will be sent immediately (in its own message). </p>
            <p>If <c><![CDATA[trans_req]]></c> is true, then request(s) will 
              instead be sent to the transaction sender process for 
              accumulation and later sending 
              (see <c><![CDATA[trans_ack_maxcount]]></c>, <c><![CDATA[trans_req_maxcount]]></c>, 
              <c><![CDATA[trans_req_maxsize]]></c>, <c><![CDATA[trans_ack_maxcount]]></c> and 
              <c><![CDATA[trans_timer]]></c>). </p>
            <p>See also <seealso marker="megaco_run#transaction_sender">transaction sender</seealso> for more info. </p>
            <p>An <c><![CDATA[boolean]]></c>, defaults to <c><![CDATA[false]]></c>.</p>

            <marker id="ci_trans_req_maxcount"></marker>
          </item>

          <tag><c><![CDATA[trans_req_maxcount]]></c></tag>
          <item>
            <p>Maximum number of accumulated requests. At most this many 
              requests will be accumulated by the transaction sender 
              (if started and configured to accumulate requests). </p>
            <p>See also <seealso marker="megaco_run#transaction_sender">transaction sender</seealso> for more info. </p>
            <p>An <c><![CDATA[integer]]></c>, defaults to 10.</p>

            <marker id="ci_trans_req_maxsize"></marker>
          </item>

          <tag><c><![CDATA[trans_req_maxsize]]></c></tag>
          <item>
            <p>Maximum size of the accumulated requests. At most this much
              requests will be accumulated by the transaction sender 
              (if started and configured to accumulate requests). </p>
            <p>See also <seealso marker="megaco_run#transaction_sender">transaction sender</seealso> for more info. </p>
            <p>An <c><![CDATA[integer]]></c>, defaults to 2048.</p>

            <marker id="ci_trans_timer"></marker>
          </item>

          <tag><c><![CDATA[trans_timer]]></c></tag>
          <item>
            <p>Transaction sender timeout time. Has two functions. First, if 
              the value is 0, then transactions will not be accumulated 
              (e.g. the transaction sender process will not be started). 
              Second, if the value is greater then 0 and <c><![CDATA[auto_ack]]></c> 
              and <c><![CDATA[trans_ack]]></c> is true or if <c><![CDATA[trans_req]]></c> is true, 
              then transaction sender will be started and transactions 
              (which is depending on the values of <c><![CDATA[auto_ack]]></c>, 
              <c><![CDATA[trans_ack]]></c> and <c><![CDATA[trans_req]]></c>) will be accumulated,
              for later sending. </p>
            <p>See also <seealso marker="megaco_run#transaction_sender">transaction sender</seealso> for more info. </p>
            <p>An <c><![CDATA[integer]]></c>, defaults to 0.</p>

            <marker id="ci_pending_timer"></marker>
          </item>

          <tag><c><![CDATA[pending_timer]]></c></tag>
          <item>
            <p>Automatic send transaction pending if the timer expires
              before a transaction reply has been sent. This timer is
              also called provisional response timer. </p>
            <p>A Megaco Timer (see explanation above), defaults to 30000.</p>

            <marker id="ci_sent_pending_limit"></marker>
          </item>

          <tag><c><![CDATA[sent_pending_limit]]></c></tag>
          <item>
            <p>Sent pending limit (see the MGOriginatedPendingLimit
              and the MGCOriginatedPendingLimit of the megaco root package).
              This parameter specifies how many pending messages that can
              be sent (for a given received transaction request).
              When the limit is exceeded, the transaction is aborted
              (see <seealso marker="megaco_user#request_abort">handle_trans_request_abort</seealso>) and an error message 
              is sent to the other side. </p>
            <p>Note that this has no effect on the actual sending of
              pending transactions. This is either implicit (e.g. when 
              receiving a re-sent transaction request for a request which
              is being processed) or controlled by the pending_timer,
              see above. </p>
            <p>A positive integer or <c><![CDATA[infinity]]></c>, 
              defaults to <c><![CDATA[infinity]]></c>.</p>

            <marker id="ci_recv_pending_limit"></marker>
          </item>

          <tag><c><![CDATA[recv_pending_limit]]></c></tag>
          <item>
            <p>Receive pending limit (see the MGOriginatedPendingLimit
              and the MGCOriginatedPendingLimit of the megaco root package).
              This parameter specifies how many pending messages that can
              be received (for a sent transaction request).
              When the limit is exceeded, the transaction is considered
              lost, and an error returned to the user (through the call-back
              function <em>handle_trans_reply</em>). </p>
            <p>A positive integer or <c><![CDATA[infinity]]></c>, 
              defaults to <c><![CDATA[infinity]]></c>.</p>

            <marker id="ci_send_mod"></marker>
          </item>

          <tag><c><![CDATA[send_mod]]></c></tag>
          <item>
            <p>Send callback module which exports send_message/2. The
              function SendMod:send_message(SendHandle, Binary) is
              invoked when the bytes needs to be transmitted to
              the remote user. </p>
            <p>An <c><![CDATA[atom]]></c>, defaults to <c><![CDATA[megaco_tcp]]></c>.</p>

            <marker id="ci_encoding_mod"></marker>
          </item>

          <tag><c><![CDATA[encoding_mod]]></c></tag>
          <item>
            <p>Encoding callback module which exports encode_message/2
              and decode_message/2. The function
              EncodingMod:encode_message(EncodingConfig, MegacoMessage)
              is invoked whenever a 'MegacoMessage' record needs to be
              translated into an Erlang binary. The function
              EncodingMod:decode_message(EncodingConfig, Binary) is
              invoked whenever an Erlang binary needs to be translated
              into a 'MegacoMessage' record. </p>
            <p>An <c><![CDATA[atom]]></c>, 
              defaults to <c><![CDATA[megaco_pretty_text_encoder]]></c>.</p>

            <marker id="ci_encoding_confi"></marker>
          </item>

          <tag><c><![CDATA[encoding_config]]></c></tag>
          <item>
            <p>Encoding module config. </p>
            <p>A <c><![CDATA[list]]></c>, defaults to [].</p>

            <marker id="ci_protocol_version"></marker>
          </item>

          <tag><c><![CDATA[protocol_version]]></c></tag>
          <item>
            <p>Actual protocol version. </p>
            <p>An positive integer, Current default is 1.</p>
            <marker id="ci_strict_version"></marker>
          </item>
          <tag><c><![CDATA[strict_version]]></c></tag>
          <item>
            <p>Strict version control, i.e. when a message is received,
              verify that the version is that which was negotiated. </p>
            <p>An <c><![CDATA[boolean]]></c>, default is true.</p>
            <marker id="ci_reply_data"></marker>
          </item>
          <tag><c><![CDATA[reply_data]]></c></tag>
          <item>
            <p>Default reply data. </p>
            <p>Any term, defaults to the atom <c><![CDATA[undefined]]></c>.</p>

            <marker id="ci_threaded"></marker>
          </item>

          <tag><c><![CDATA[threaded]]></c></tag>
          <item>
            <p>If a received message contains several transaction requests, 
              this option indicates whether the requests should be handled
              sequentially in the same process (<c><![CDATA[false]]></c>), or if each 
              request should be handled by its own process (<c><![CDATA[true]]></c>
              i.e. a separate process is spawned for each request). </p>
            <p>An <c><![CDATA[boolean]]></c>, defaults to <c><![CDATA[false]]></c>. </p>
            <marker id="ci_resend_indication"></marker>
          </item>
          <tag><c><![CDATA[resend_indication]]></c></tag>
          <item>
            <p>This option indicates weather the transport module
              should be told if a message send is a resend or not. </p>
            <p>If <em>false</em>, megaco messages are sent using the
              <seealso marker="megaco_transport#send_message">send_message/2</seealso> 
              function. </p>
            <p>If <em>true</em>, megaco message <em>re-sends</em> are made using the
              <seealso marker="megaco_transport#resend_message">resend_message</seealso> 
              function. The initial message send is still done using the
              <seealso marker="megaco_transport#send_message">send_message</seealso> 
              function. </p>
            <p>The special value <em>flag</em> instead indicates that the 
              function 
              <seealso marker="megaco_transport#send_message">send_message/3</seealso> 
              shall be used. </p>
            <p>A <c>resend_indication()</c>, 
              defaults to <c><![CDATA[false]]></c>.</p>
            <marker id="ci_segment_reply_ind"></marker>
          </item>

          <tag><c><![CDATA[segment_reply_ind]]></c></tag>
          <item>
            <p>This option specifies if the user shall be notified of received
              segment replies or not. </p>
            <p>See 
              <seealso marker="megaco_user#segment_reply">handle_segment_reply</seealso> 
              callback function for more information. </p>
            <p>A <c><![CDATA[boolean]]></c>, 
              defaults to <c><![CDATA[false]]></c>. </p>

            <marker id="ci_segment_recv_timer"></marker>
          </item>

          <tag><c><![CDATA[segment_recv_timer]]></c></tag>
          <item>
            <p>This timer is started when the segment indicated by the
              <c><![CDATA[segmentation complete token]]></c> (e.g. the last of the segment
              which makes up the reply) is received, but all 
              segments has not yet been received.</p>
            <p>When the timer finally expires, a "megaco segments not
              received" (459) error message is sent to the other side
              and the user is notified with a 
              <c><![CDATA[segment timeout]]></c> <c><![CDATA[UserReply]]></c> in either the
              <seealso marker="megaco_user#trans_reply">handle_trans_reply</seealso> 
              callback function or 
              the return value of the 
              <seealso marker="megaco#call">call</seealso> function. </p>
            <p>A Megaco Timer (see explanation above),
              defaults to <c><![CDATA[10000]]></c>. </p>

            <marker id="ci_segment_send"></marker>
          </item>

          <tag><c><![CDATA[segment_send]]></c></tag>
          <item>
            <p>Shall outgoing messages be segmented or not: </p>
            <taglist>
              <tag><c><![CDATA[none]]></c></tag>
              <item>
                <p>Do not segment outgoing reply messages. This is useful when
                  either it is known that messages are never to large or
                  that the transport protocol can handle such things
                  on its own (e.g. TCP or SCTP).</p>
              </item>
              <tag><c><![CDATA[integer() > 0]]></c></tag>
              <item>
                <p>Outgoing reply messages will be segmented as needed 
                  (see <c><![CDATA[max_pdu_size]]></c> below). This value, K, indicate 
                  the outstanding window, i.e. how many segments can be 
                  outstanding (not acknowledged) at any given time. </p>
              </item>
              <tag><c><![CDATA[infinity]]></c></tag>
              <item>
                <p>Outgoing reply messages will be segmented as needed 
                  (see <c><![CDATA[max_pdu_size]]></c> below). Segment messages 
                  are sent all at once (i.e. no acknowledgement awaited 
                  before sending the next segment). </p>
              </item>
            </taglist>
            <p>Defaults to <c><![CDATA[none]]></c>. </p>
            <marker id="ci_max_pdu_size"></marker>
          </item>

          <tag><c><![CDATA[max_pdu_size]]></c></tag>
          <item>
            <p>Max message size. If the encoded message (PDU) exceeds 
              this size, the message should be segmented, and then 
              encoded. </p>
            <p>A positive integer or <c><![CDATA[infinity]]></c>,
              defaults to <c><![CDATA[infinity]]></c>. </p>
          </item>
        </taglist>

        <marker id="update_conn_info"></marker>
      </desc>
    </func>

    <func>
      <name>update_conn_info(ConnHandle, Item, Value) -> ok | {error, Reason}</name>
      <fsummary>Update information about an active connection</fsummary>
      <type>
        <v>ConnHandle = #megaco_conn_handle{}</v>
        <v>Item       = conn_info_item()</v>
        <v>Value      = conn_info_value()</v>
        <v>Reason     = term()</v>
      </type>
      <desc>
        <p>Update information about an active connection</p>
        <p>Requires that the connection is activated. See
          megaco:conn_info/2 about which items and values that are
          valid.</p>

        <marker id="system_info"></marker>
      </desc>
    </func>

    <func>
      <name>system_info() -> [{Item, Value}] | exit(Reason)</name>
      <name>system_info(Item) -> Value | exit(Reason)</name>
      <fsummary>Lookup system information</fsummary>
      <type>
        <v>Item = system_info_item()</v>
      </type>
      <desc>
        <p>Lookup system information</p>
        <p>The following items are valid:</p>
        <taglist>
          <tag><c><![CDATA[text_config]]></c></tag>
          <item>
            <p>The text encoding config.</p>
          </item>
          <tag><c><![CDATA[connections]]></c></tag>
          <item>
            <p>Lists all active connections. Returns a list of
              megaco_conn_handle records.</p>
          </item>
          <tag><c><![CDATA[users]]></c></tag>
          <item>
            <p>Lists all active users. Returns a list of
              megaco_mid()'s.</p>
          </item>
          <tag><c><![CDATA[n_active_requests]]></c></tag>
          <item>
            <p>Returns an integer representing the number of requests
              that has originated from this Erlang node and still are
              active (and therefore consumes system resources).</p>
          </item>
          <tag><c><![CDATA[n_active_replies]]></c></tag>
          <item>
            <p>Returns an integer representing the number of replies
              that has originated from this Erlang node and still are
              active (and therefore consumes system resources).</p>
          </item>
          <tag><c><![CDATA[n_active_connections]]></c></tag>
          <item>
            <p>Returns an integer representing the number of active
              connections.</p>
          </item>
        </taglist>

        <marker id="info"></marker>
      </desc>
    </func>

    <func>
      <name>info() -> Info</name>
      <fsummary>All the information of the application</fsummary>
      <type>
        <v>Info = [{Key, Value}]</v>
      </type>
      <desc>
        <p>This function produces a list of information about the megaco 
          application. Such as users and their config, connections 
          and their config, statistics and so on.</p>

        <p>This information can be produced by the functions 
          <seealso marker="#user_info">user_info</seealso>, 
          <seealso marker="#conn_info">conn_info</seealso>, 
          <seealso marker="#system_info">system_info</seealso> and 
          <seealso marker="#get_stats">get_stats</seealso> 
          but this is a simple way to get it all at once.</p>

        <marker id="connect"></marker> <!-- Belongs to NEXT function(s) -->
      </desc>
    </func>

    <func>
      <name>connect(ReceiveHandle, RemoteMid, SendHandle, ControlPid) -> {ok, ConnHandle} | {error, Reason}</name>
      <name>connect(ReceiveHandle, RemoteMid, SendHandle, ControlPid, Extra) -> {ok, ConnHandle} | {error, Reason}</name>
      <fsummary>Establish a "virtual" connection</fsummary>
      <type>
        <v>ReceiveHandle = #megaco_receive_handle{}</v>
        <v>RemoteMid     = preliminary_mid | megaco_mid()</v>
        <v>SendHandle    = term()</v>
        <v>ControlPid    = pid()</v>
        <v>ConnHandle    = #megaco_conn_handle{}</v>
        <v>Reason        = connect_reason() | handle_connect_reason() | term()</v>
	<v>connect_reason() = {no_such_user, LocalMid} | {already_connected, ConnHandle} | term()</v>
	<v>handle_connect_error() = {connection_refused, ConnData, ErrorInfo} | term()</v>
	<v>LocalMid      = megaco_mid()</v>
	<v>ConnData      = term()</v>
	<v>ErrorInfo     = term()</v>
        <v>Extra         = term()</v>
      </type>
      <desc>
        <p>Establish a "virtual" connection</p>
        <p>Activates a connection to a remote user. When this is done
          the connection can be used to send messages (with
          SendMod:send_message/2). The ControlPid is the identifier
          of a process that controls the connection. That process will
          be supervised and if it dies, this will be detected and the
          UserMod:handle_disconnect/2 callback function will be
          invoked. See the megaco_user module for more info about the
          callback arguments. The connection may also explicitly be
          deactivated by invoking megaco:disconnect/2.</p>
        <p>The ControlPid may be the identity of a process residing on
          another Erlang node. This is useful when you want to
          distribute a user over several Erlang nodes. In such a case
          one of the nodes has the physical connection. When a user
          residing on one of the other nodes needs to send a request
          (with megaco:call/3 or megaco:cast/3), the message will
          encoded on the originating Erlang node, and then be
          forwarded to the node with the physical connection. When the
          reply arrives, it will be forwarded back to the originator.
          The distributed connection may explicitly be deactivated by
          a local call to megaco:disconnect/2 or implicitly when
          the physical connection is deactivated (with megaco:disconnect/2,
          killing the controlling process, halting the other node, ...).</p>
        <p>The call of this function will trigger the callback
          function UserMod:handle_connect/2 to be invoked. See the
          megaco_user module for more info about the callback
          arguments.</p>
        <p>A connection may be established in several ways:</p>
        <taglist>
          <tag><c><![CDATA[provisioned MID]]></c></tag>
          <item>
            <p>The MG may explicitly invoke megaco:connect/4 and use
              a provisioned MID of the MGC as the RemoteMid.</p>
          </item>
          <tag><c><![CDATA[upgrade preliminary MID]]></c></tag>
          <item>
            <p>The MG may explicitly invoke megaco:connect/4 with the
              atom 'preliminary_mid' as a temporary MID of the MGC,
              send an intial message, the Service Change Request, to
              the MGC and then wait for an initial message, the
              Service Change Reply. When the reply arrives, the Megaco
              application will pick the MID of the MGC from the
              message header and automatically upgrade the connection
              to be a "normal" connection. By using this method of
              establishing the connection, the callback function
              UserMod:handle_connect/2 to be invoked twice. First with
              a ConnHandle with the remote_mid-field set to
              preliminary_mid, and then when the connection upgrade is
              done with the remote_mid-field set to the actual MID of
              the MGC.</p>
          </item>
          <tag><c><![CDATA[automatic]]></c></tag>
          <item>
            <p>When the MGC receives its first message, the Service
              Change Request, the Megaco application will
              automatically establish the connection by using the MG
              MID found in the message header as remote mid.</p>
          </item>
          <tag><c><![CDATA[distributed]]></c></tag>
          <item>
            <p>When a user (MG/MGC) is distributed over several nodes,
              it is required that the node hosting the connection
              already has activated the connection and that it is
              in the "normal" state. The RemoteMid must be a real
              Megaco MID and not a preliminary_mid.</p>
          </item>
        </taglist>
        <p>An initial megaco_receive_handle record may be obtained
          with megaco:user_info(UserMid, receive_handle)</p>
        <p>The send handle is provided by the preferred transport
          module, e.g. megaco_tcp, megaco_udp. Read the documentation
          about each transport module about the details.</p>

	<p>The connect is done in two steps: first an internal 
          <c>connection setup</c> and then by calling the user 
          <seealso marker="megaco_user#connect">handle_connect</seealso> 
          callback function. The first step could result in 
          an error with <c>Reason = connect_reason()</c> and the second 
          an error with <c>Reason = handle_connect_reason()</c>: </p>

	<taglist>
	  <tag><c>connect_reason()</c></tag>
	  <item>
	    <p>An error with this reason is generated by the 
              megaco application itself.</p>
	  </item>

	  <tag><c>handle_connect_reason()</c></tag>
	  <item>
	    <p>An error with this reason is caused by the user 
              <seealso marker="megaco_user#connect">handle_connect</seealso> 
              callback function either returning an error 
              or an invalid value.</p>
	  </item>

	</taglist>

        <p><c><![CDATA[Extra]]></c> can be any <c><![CDATA[term()]]></c> 
          except the atom <c><![CDATA[ignore_extra]]></c>. 
          It is passed (back) to the user via the callback function 
          <seealso marker="megaco_user#connect">handle_connect/3</seealso>. </p>

        <marker id="disconnect"></marker> <!-- Belongs to NEXT function(s) -->
      </desc>
    </func>

    <func>
      <name>disconnect(ConnHandle, DiscoReason) -> ok | {error, ErrReason}</name>
      <fsummary>Tear down a "virtual" connection</fsummary>
      <type>
        <v>ConnHandle  = conn_handle()</v>
        <v>DiscoReason =  term()</v>
        <v>ErrReason   =  term()</v>
      </type>
      <desc>
        <p>Tear down a "virtual" connection</p>
        <p>Causes the UserMod:handle_disconnect/2 callback function to
          be invoked. See the megaco_user module for more info about
          the callback arguments.</p>

        <marker id="call"></marker> <!-- Belongs to NEXT function(s) -->
      </desc>
    </func>

    <func>
      <name>call(ConnHandle, Actions, Options) -> {ProtocolVersion, UserReply}</name>
      <fsummary>Sends one or more transaction request(s) and waits for the reply</fsummary>
      <type>
        <v>ConnHandle     = conn_handle()</v>
        <v>Actions        = action_reqs() | [action_reqs()]</v>
        <v>action_reqs()  = binary() | [action_request()]</v>
        <v>Options        = [send_option()]</v>
        <v>send_option()  = {request_timer, megaco_timer()} | {long_request_timer, megaco_timer()} | {send_handle, term()} | {protocol_version, integer()} | {call_proxy_gc_timeout, call_proxy_gc_timeout()}</v>
        <v>ProtocolVersion = integer()</v>
        <v>UserReply       = user_reply() | [user_reply()]</v>
        <v>user_reply()    = success() | failure()</v>
        <v>success()       = {ok, result()} | {ok, result(), extra()}</v>
        <v>result()        = message_result() | segment_result()</v>
        <v>message_result() = action_reps()</v>
        <v>segment_result() = segments_ok()</v>
        <v>failure()        = {error, reason()} | {error, reason(), extra()}</v>
        <v>reason()         = message_reason() | segment_reason() | user_cancel_reason() | send_reason() | other_reason()</v>
        <v>message_reason() = error_desc()</v>
        <v>segment_reason() = {segment, segments_ok(), segments_err()} | {segment_timeout, missing_segments(), segments_ok(), segments_err()}</v>
        <v>segments_ok()   = [segment_ok()]</v>
        <v>segment_ok()    = {segment_no(), action_reps()}</v>
        <v>segments_err()  = [segment_err()]</v>
        <v>segment_err()   = {segment_no(), error_desc()}</v>
        <v>missing_segments() = [segment_no()]</v>
        <v>user_cancel_reason() = {user_cancel, reason_for_user_cancel()}</v>
        <v>reason_for_user_cancel() = term()</v>
        <v>send_reason() = send_cancelled_reason() | send_failed_reason()</v>
        <v>send_cancelled_reason() = {send_message_cancelled, reason_for_send_cancel()}</v>
        <v>reason_for_send_cancel() = term()</v>
        <v>send_failed_reason()    = {send_message_failed, reason_for_send_failure()}</v>
        <v>reason_for_send_failure() = term()</v>
        <v>other_reason()   = {wrong_mid, WrongMid, RightMid, TR} | term()</v>
        <v>WrongMid = mid()</v>
        <v>RightMid = mid()</v>
        <v>TR = transaction_reply()</v>
        <v>action_reps()    = [action_reply()]</v>
        <v>call_proxy_gc_timeout() = integer() >= 0</v>
        <v>extra()          = term()</v>
      </type>
      <desc>
        <p>Sends one or more transaction request(s) and waits for the 
          reply.</p>
        <p>When sending one transaction in a message, <c><![CDATA[Actions]]></c> should be 
          <c><![CDATA[action_reqs()]]></c> (<c><![CDATA[UserReply]]></c> will then be 
          <c><![CDATA[user_reply()]]></c>). When sending several transactions in a message,
          <c><![CDATA[Actions]]></c> should be <c><![CDATA[[action_reqs()]]]></c> (<c><![CDATA[UserReply]]></c> 
          will then be <c><![CDATA[[user_reply()]]]></c>). Each element of the list is 
          part of one transaction.</p>
        <p>For some of <em>our</em> codecs (not binary), it is also possible 
          to pre-encode the actions, in which case <c><![CDATA[Actions]]></c> will be 
          either a <c><![CDATA[binary()]]></c> or <c><![CDATA[[binary()]]]></c>.</p>
        <p>The function returns when the reply arrives, when the
          request timer eventually times out or when the outstanding
          requests are explicitly cancelled.</p>
        <p>The default values of the send options are obtained by
          <c><![CDATA[megaco:conn_info(ConnHandle, Item)]]></c>. But the send options 
          above, may explicitly be overridden.</p>
        <p>The <c><![CDATA[ProtocolVersion]]></c> version is the version actually encoded
          in the reply message.</p>
        <p>At <c><![CDATA[success()]]></c>, the <c><![CDATA[UserReply]]></c> contains a list of 
          'ActionReply' records possibly containing error indications.</p>
        <p>A <c><![CDATA[message_error()]]></c>, indicates that the remote user has
          replied with an explicit transactionError.</p>
        <p>A <c><![CDATA[user_cancel_error()]]></c>, indicates that the request has been
          canceled by the user. <c><![CDATA[reason_for_user_cancel()]]></c> is the reason
          given in the call to the <seealso marker="#cancel">cancel</seealso>
          function. </p>
        <p>A <c><![CDATA[send_error()]]></c>, indicates that the send function of the 
          megaco transport callback module failed to send the request. 
          There are two separate cases: <c><![CDATA[send_cancelled_reason()]]></c> and 
          <c><![CDATA[send_failed_reason()]]></c>. 
          The first is the result of the send function returning 
          <c><![CDATA[{cancel, Reason}]]></c> and the second is some other kind of 
          erroneous return value. See the 
          <seealso marker="megaco_transport#send_message">send_message</seealso>
          function for more info. </p>
        <p>An <c><![CDATA[other_error()]]></c>, indicates some other error such as 
          timeout.</p>

        <p>For more info about the <c>extra()</c> part of the 
          result, see the 
          <seealso marker="megaco_user#extra_argument">note</seealso>
          in the user callback module documentation. </p>



        <marker id="cast"></marker>
      </desc>
    </func>

    <func>
      <name>cast(ConnHandle, Actions, Options) -> ok | {error, Reason}</name>
      <fsummary>Sends one or more transaction request(s) but does NOT wait for a reply</fsummary>
      <type>
        <v>ConnHandle     = conn_handle()</v>
        <v>Actions        = action_reqs() | [action_reqs()]</v>
        <v>action_reqs()  = binary() | [action_request()]</v>
        <v>Options        = [send_option()]</v>
        <v>send_option()  = {request_keep_alive_timeout, request_keep_alive_timeout()} | {request_timer, megaco_timer()} | {long_request_timer, megaco_timer()} | {send_handle, term()} | {reply_data, reply_data()} | {protocol_version, integer()}</v>
        <v>request_keep_alive_timeout() = plain | integer() >= 0</v>
        <v>Reason         =  term()</v>
      </type>
      <desc>
        <p>Sends one or more transaction request(s) but does NOT wait for a reply</p>
        <p>When sending one transaction in a message, <c><![CDATA[Actions]]></c> should be 
          <c><![CDATA[action_reqs()]]></c>. When sending several transactions in a message,
          <c><![CDATA[Actions]]></c> should be <c><![CDATA[[action_reqs()]]]></c>. Each element of the 
          list is part of one transaction.</p>
        <p>For some of <em>our</em> codecs (not binary), it is also possible 
          to pre-encode the actions, in which case <c><![CDATA[Actions]]></c> will be 
          either a <c><![CDATA[binary()]]></c> or <c><![CDATA[[binary()]]]></c>.</p>
        <p>The default values of the send options are obtained by
          megaco:conn_info(ConnHandle, Item). But the send options above,
          may explicitly be overridden.</p>
        <p>The ProtocolVersion version is the version actually encoded
          in the reply message.</p>
        <p>The callback function UserMod:handle_trans_reply/4 is invoked
          when the reply arrives, when the request timer eventually
          times out or when the outstanding requests are explicitly
          cancelled. See the megaco_user module for more info about
          the callback arguments.</p>
        <p>Given as UserData argument to UserMod:handle_trans_reply/4.</p>

        <marker id="encode_actions"></marker>
      </desc>
    </func>

    <func>
      <name>encode_actions(ConnHandle, Actions, Options) -> {ok, BinOrBins} | {error, Reason}</name>
      <fsummary>Encode action requests for one or more transaction request(s)</fsummary>
      <type>
        <v>ConnHandle     = conn_handle()</v>
        <v>Actions        = action_reqs() | [action_reqs()]</v>
        <v>action_reqs()  = [#'ActionRequest'{}]</v>
        <v>Options        = [send_option()]</v>
        <v>send_option()  = {request_timer, megaco_timer()} | {long_request_timer, megaco_timer()} | {send_handle, term()} | {protocol_version, integer()}</v>
        <v>BinOrBins      = binary() | [binary()]</v>
        <v>Reason         = term()</v>
      </type>
      <desc>
        <p>Encodes lists of action requests for one or more transaction 
          request(s).</p>
        <p>When encoding action requests for one transaction, 
          <c><![CDATA[Actions]]></c> should be <c><![CDATA[action_reqs()]]></c>. 
          When encoding action requests for several transactions,
          <c><![CDATA[Actions]]></c> should be <c><![CDATA[[action_reqs()]]]></c>. Each element 
          of the list is part of one transaction.</p>

        <marker id="token_tag2string"></marker>
      </desc>
    </func>

    <func>
      <name>token_tag2string(Tag) -> Result</name>
      <name>token_tag2string(Tag, EncoderMod) -> Result</name>
      <name>token_tag2string(Tag, EncoderMod, Version) -> Result</name>
      <fsummary>Convert a token tag to a string</fsummary>
      <type>
        <v>Tag = atom()</v>
        <v>EncoderMod = pretty | compact | encoder_module()</v>
        <v>encoder_module() = megaco_pretty_text_encoder | megaco_compact_text_encoder | atom()</v>
        <v>Version = int_version() | atom_version()</v>
        <v>int_version() = 1 | 2 | 3</v>
        <v>atom_version() = v1 | v2 | v3 | prev3c | prev3b</v>
        <v>Result = string() | {error, Reason}</v>
        <v>Reason = term()</v>
      </type>
      <desc>
        <p>Convert a token tag to a string</p>
        <p>If no encoder module is given, the default is used 
          (which is pretty).</p>
        <p>If no or an unknown version is given, 
          the <em>best</em> version is used (which is v3).</p>
        <p>If no match is found for <c><![CDATA[Tag]]></c>, <c><![CDATA[Result]]></c> will be the 
          empty string (<c><![CDATA[[]]]></c>).</p>

        <marker id="cancel"></marker>
      </desc>
    </func>

    <func>
      <name>cancel(ConnHandle, CancelReason) -> ok | {error, ErrReason}</name>
      <fsummary>Cancel all outstanding messages for this connection</fsummary>
      <type>
        <v>ConnHandle   = conn_handle()</v>
        <v>CancelReason =  term()</v>
        <v>ErrReason    =  term()</v>
      </type>
      <desc>
        <p>Cancel all outstanding messages for this connection</p>
        <p>This causes outstanding megaco:call/3 requests to return.
          The callback functions UserMod:handle_reply/4 and
          UserMod:handle_trans_ack/4 are also invoked where it
          applies.  See the megaco_user module for more info about the
          callback arguments.</p>

        <marker id="process_received_message"></marker>
      </desc>
    </func>

    <func>
      <name>process_received_message(ReceiveHandle, ControlPid, SendHandle, BinMsg) -> ok</name>
      <name>process_received_message(ReceiveHandle, ControlPid, SendHandle, BinMsg, Extra) -> ok</name>
      <fsummary>Process a received message</fsummary>
      <type>
        <v>ReceiveHandle = #megaco_receive_handle{}</v>
        <v>ControlPid    = pid()</v>
        <v>SendHandle    = term()</v>
        <v>BinMsg        = binary()</v>
        <v>Extra         = term()</v>
      </type>
      <desc>
        <p>Process a received message</p>

        <p>This function is intended to be invoked by some
          transport modules when get an incoming message. Which
          transport that actually is used is up to the user to
          choose.</p>

        <p>The message is delivered as an Erlang binary and is decoded
          by the encoding module stated in the receive handle together
          with its encoding config (also in the receive
          handle). Depending of the outcome of the decoding various
          callback functions will be invoked. See megaco_user for more
          info about the callback arguments.</p>

        <p>The argument <c>Extra</c> is just an opaque data structure passed to the user 
          via the callback functions in the 
          <seealso marker="megaco_user">user callback module</seealso>. 
          Note however that if <c>Extra</c> has the value 
          <c>extra_undefined</c> the argument will be ignored (same as if 
          <c>process_received_message/4</c> had been called). 
          See the documentation for the behaviour of the callback module,
          <seealso marker="megaco_user">megaco_user</seealso>, for more info. </p> 
        <p>Note that all processing is done in the context of the calling 
          process. A transport module could call this function via one of the
          <c><![CDATA[spawn]]></c> functions (e.g. <c><![CDATA[spawn_opt]]></c>). See also 
          <c><![CDATA[receive_message/4,5]]></c>.
          </p>
        <p>If the message cannot be decoded the following callback
          function will be invoked:</p>
        <list type="bulleted">
          <item>
            <p>UserMod:handle_syntax_error/3</p>
          </item>
        </list>
        <p>If the decoded message instead of transactions contains a
          message error, the following callback function will be
          invoked:</p>
        <list type="bulleted">
          <item>
            <p>UserMod:handle_message_error/3</p>
          </item>
        </list>
        <p>If the decoded message happens to be received before the
          connection is established, a new "virtual" connection is
          established. This is typically the case for the Media
          Gateway Controller (MGC) upon the first Service Change.
          When this occurs the following callback function will be
          invoked:</p>
        <list type="bulleted">
          <item>
            <p>UserMod:handle_connect/2</p>
          </item>
        </list>
        <p>For each transaction request in the decoded message the
          following callback function will be invoked:</p>
        <list type="bulleted">
          <item>
            <p>UserMod:handle_trans_request/3</p>
          </item>
        </list>
        <p>For each transaction reply in the decoded message the reply
          is returned to the user. Either the originating function
          megaco:call/3 will return.  Or in case the originating
          function was megaco:case/3 the following callback function
          will be invoked:</p>
        <list type="bulleted">
          <item>
            <p>UserMod:handle_trans_reply/4</p>
          </item>
        </list>
        <p>When a transaction acknowledgement is received it is
          possible that user has decided not to bother about the
          acknowledgement. But in case the return value from
          UserMod:handle_trans_request/3 indicates that the
          acknowledgement is important the following callback function
          will be invoked:</p>
        <list type="bulleted">
          <item>
            <p>UserMod:handle_trans_ack/4</p>
          </item>
        </list>
        <p>See the megaco_user module for more info about the callback
          arguments.</p>

        <marker id="receive_message"></marker>
      </desc>
    </func>

    <func>
      <name>receive_message(ReceiveHandle, ControlPid, SendHandle, BinMsg) -> ok</name>
      <name>receive_message(ReceiveHandle, ControlPid, SendHandle, BinMsg, Extra) -> ok</name>
      <fsummary>Process a received message</fsummary>
      <type>
        <v>ReceiveHandle = #megaco_receive_handle{}</v>
        <v>ControlPid    = pid()</v>
        <v>SendHandle    = term()</v>
        <v>BinMsg        = binary()</v>
        <v>Extra         = term()</v>
      </type>
      <desc>
        <p>Process a received message</p>
        <p>This is a callback function intended to be invoked by some
          transport modules when get an incoming message. Which
          transport that actually is used is up to the user to
          choose.</p>
        <p>In principle, this function calls the 
          <c><![CDATA[process_received_message/4]]></c> function via a <c><![CDATA[spawn]]></c> to
          perform the actual processing.</p>
        <p>For further information see the 
          <seealso marker="#process_received_message">process_received_message/4</seealso> 
          function.</p>

        <marker id="parse_digit_map"></marker>
      </desc>
    </func>

    <func>
      <name>parse_digit_map(DigitMapBody) -> {ok, ParsedDigitMap} | {error, Reason}</name>
      <fsummary>Parses a digit map body</fsummary>
      <type>
        <v>DigitMapBody       = string()</v>
        <v>ParsedDigitMap     = parsed_digit_map()</v>
        <v>parsed_digit_map() = term()</v>
        <v>Reason             = term()</v>
      </type>
      <desc>
        <p>Parses a digit map body</p>
        <p>Parses a digit map body, represented as a list of
          characters, into a list of state transitions suited to
          be evaluated by megaco:eval_digit_map/1,2.</p>

        <marker id="eval_digit_map"></marker>
      </desc>
    </func>

    <func>
      <name>eval_digit_map(DigitMap) -> {ok, MatchResult} | {error, Reason}</name>
      <name>eval_digit_map(DigitMap, Timers) -> {ok, MatchResult} | {error, Reason}</name>
      <fsummary>Collect digit map letters according to the digit map</fsummary>
      <type>
        <v>DigitMap           = #'DigitMapValue'{} | parsed_digit_map()</v>
        <v>parsed_digit_map() = term()</v>
        <v>ParsedDigitMap     = term()</v>
        <v>Timers             = ignore() | reject()</v>
        <v>ignore()           = ignore | {ignore, digit_map_value()}</v>
        <v>reject()           = reject | {reject, digit_map_value()} | digit_map_value()</v>
        <v>MatchResult        = {Kind, Letters} | {Kind, Letters, Extra}</v>
        <v>Kind               = kind()</v>
        <v>kind()             = full | unambiguous</v>
        <v>Letters            = [letter()]</v>
        <v>letter()           = $0..$9 | $a .. $k</v>
        <v>Extra              = letter()</v>
        <v>Reason             = term()</v>
      </type>
      <desc>
        <p>Collect digit map letters according to the digit map.</p>
        <p>When evaluating a digit map, a state machine waits for
          timeouts and letters reported by
          megaco:report_digit_event/2. The length of the various
          timeouts are defined in the digit_map_value() record.</p>
        <p>When a complete sequence of valid events has been received,
          the result is returned as a list of letters.</p>
        <p>There are two options for handling syntax errors (that is
          when an unexpected event is received when the digit map
          evaluator is expecting some other event). The unexpected
          events may either be ignored or rejected. The latter means
          that the evaluation is aborted and an error is returned. </p>

        <marker id="report_digit_event"></marker>
      </desc>
    </func>

    <func>
      <name>report_digit_event(DigitMapEvalPid, Events) -> ok | {error, Reason}</name>
      <fsummary>Send one or more events to the event collector process</fsummary>
      <type>
        <v>DigitMapEvalPid = pid()</v>
        <v>Events          = Event | [Event]</v>
        <v>Event           = letter() | pause() | cancel()</v>
        <v>letter()        = $0..$9 | $a .. $k | $A .. $K</v>
        <v>pause()         = one_second() | ten_seconds()</v>
        <v>one_second()    = $s | $S</v>
        <v>ten_seconds()   = $l | $L</v>
        <v>cancel()        = $z | $Z | cancel</v>
        <v>Reason          = term()</v>
      </type>
      <desc>
        <p>Send one or more events to the event collector process.</p>
        <p>Send one or more events to a process that is evaluating a
          digit map, that is a process that is executing
          megaco:eval_digit_map/1,2.</p>
        <p>Note that the events <c><![CDATA[$s | $S]]></c>, <c><![CDATA[l | $L]]></c> and
          <c><![CDATA[$z | $Z]]></c> has nothing to do with the timers using
          the same characters.</p>

        <marker id="test_digit_event"></marker>
      </desc>
    </func>

    <func>
      <name>test_digit_event(DigitMap, Events) -> {ok, Kind, Letters} | {error, Reason}</name>
      <fsummary>Feed digit map collector with events and return the result</fsummary>
      <type>
        <v>DigitMap           = #'DigitMapValue'{} | parsed_digit_map()</v>
        <v>parsed_digit_map() = term()</v>
        <v>ParsedDigitMap     = term()</v>
        <v>Timers             = ignore() | reject()</v>
        <v>ignore()           = ignore | {ignore, digit_map_value()}</v>
        <v>reject()           = reject | {reject, digit_map_value()} | digit_map_value()</v>
        <v>DigitMapEvalPid    = pid()</v>
        <v>Events             = Event | [Event]</v>
        <v>Event              = letter() | pause() | cancel()</v>
        <v>Kind               = kind()</v>
        <v>kind()             = full | unambiguous</v>
        <v>Letters            = [letter()]</v>
        <v>letter()           = $0..$9 | $a .. $k | $A .. $K</v>
        <v>pause()            = one_second() | ten_seconds()</v>
        <v>one_second()       = $s | $S</v>
        <v>ten_seconds()      = $l | $L</v>
        <v>cancel    ()       = $z | $Z | cancel</v>
        <v>Reason             = term()</v>
      </type>
      <desc>
        <p>Feed digit map collector with events and return the result</p>
        <p>This function starts the evaluation of a digit map with
          megaco:eval_digit_map/1 and sends a sequence of events to it
          megaco:report_digit_event/2 in order to simplify testing of
          digit maps.</p>

        <marker id="encode_sdp"></marker>
      </desc>
    </func>

    <func>
      <name>encode_sdp(SDP) -> {ok, PP} | {error, Reason}</name>
      <fsummary>Encode an SDP construct</fsummary>
      <type>
        <v>SDP = sdp_property_parm() | sdp_property_group() | sdp_property_groups() | asn1_NOVALUE</v>
        <v>PP = property_parm() | property_group() | property_groups() | asn1_NOVALUE</v>
        <v>Reason = term()</v>
      </type>
      <desc>
        <p>Encode (generate) an SDP construct.</p>
        <p>If a <c><![CDATA[property_parm()]]></c> is found as part of the input
          (<c><![CDATA[SDP]]></c>) then it is left unchanged.</p>
        <p>This function performs the following transformation:</p>
        <list type="bulleted">
          <item>
            <p>sdp()                 -&gt; property_parm()</p>
          </item>
          <item>
            <p>sdp_property_group()  -&gt; property_group()</p>
          </item>
          <item>
            <p>sdp_property_groups() -&gt; property_groups()</p>
          </item>
        </list>

        <marker id="decode_sdp"></marker>
      </desc>
    </func>

    <func>
      <name>decode_sdp(PP) -> {ok, SDP} | {error, Reason}</name>
      <fsummary>Decode an property parameter construct</fsummary>
      <type>
	<v>PP = property_parm() | property_group() | property_groups() | asn1_NOVALUE</v>
	<v>SDP = sdp() | decode_sdp_property_group() | decode_sdp_property_groups() | asn1_NOVALUE</v>
	<v>decode_sdp() = sdp() | {property_parm(), DecodeError}</v>
	<v>decode_sdp_property_group() = [decode_sdp()]</v>
	<v>decode_sdp_property_groups() = [decode_sdp_property_group()]</v>
	<v>DecodeError = term()</v>
	<v>Reason = term()</v>
      </type>
      <desc>
        <p>Decode (parse) a property parameter construct.</p>
        <p>When decoding <c><![CDATA[property_group()]]></c> or 
          <c><![CDATA[property_groups()]]></c>, 
          those property parameter constructs that cannot be decoded
          (either because of decode error or because they are unknown),
          will be returned as a two-tuple. The first element of which 
          will be the (undecoded) property parameter and the other the 
          actual reason. 
          This means that the caller of this function has to expect not 
          only sdp-records, but also this two-tuple construct.</p>
        <p>This function performs the following transformation:</p>
        <list type="bulleted">
          <item>
            <p>property_parm()   -&gt; sdp()</p>
          </item>
          <item>
            <p>property_group()  -&gt; sdp_property_group()</p>
          </item>
          <item>
            <p>property_groups() -&gt; sdp_property_groups()</p>
          </item>
        </list>

	<marker id="get_sdp_record_from_PG"></marker>
      </desc>
    </func>

    <func>
      <name>get_sdp_record_from_PropertGroup(Type, PG) -> [sdp()]</name>
      <fsummary>Get all sdp records of a certain type from a property group</fsummary>
      <type>
        <v>Type = v | c | m | o | a | b | t | r | z | k | s | i | u | e | p</v>
        <v>PG = sdp_property_group()</v>
        <v>Reason = term()</v>
      </type>
      <desc>
        <p>Retreive all the sdp records of type <c>Type</c> from the
          property group <c>PG</c>.</p>

        <marker id="versions1"></marker>
        <marker id="versions2"></marker>
      </desc>
    </func>

    <func>
      <name>versions1() -> {ok, VersionInfo} | {error, Reason}</name>
      <name>versions2() -> {ok, Info} | {error, Reason}</name>
      <fsummary>Retreive various system and application info</fsummary>
      <type>
        <v>VersionInfo = [version_info()]</v>
        <v>version_info() = term()</v>
        <v>Reason = term()</v>
      </type>
      <desc>
        <p>Utility functions used to retrieve some system and
          application info.</p>
        <p>The difference between the two functions is in how they get
          the modules to check. <c><![CDATA[versions1]]></c> uses the 
          app-file and <c><![CDATA[versions2]]></c> uses the function 
          <c><![CDATA[application:get_key]]></c>.</p>

        <marker id="print_version_info"></marker>
      </desc>
    </func>

    <func>
      <name>print_version_info() -> void()</name>
      <name>print_version_info(VersionInfo) -> void()</name>
      <fsummary>Formated print of result of the versions functions</fsummary>
      <type>
        <v>VersionInfo = [version_info()]</v>
        <v>version_info() = term()</v>
      </type>
      <desc>
        <p>Utility function to produce a formated printout of the versions 
          info generated by the <c><![CDATA[versions1]]></c> and <c><![CDATA[versions2]]></c> 
          functions.</p>
        <p>The function print_version_info/0 uses the result of function
          version1/0 as <c><![CDATA[VersionInfo]]></c>.</p>
        <p>Example: </p>
        <pre>
           {ok, V} = megaco:versions1(), megaco:format_versions(V). 
        </pre>
        <marker id="enable_trace"></marker>
      </desc>
    </func>

    <func>
      <name>enable_trace(Level, Destination) -> void()</name>
      <fsummary>Start megaco tracing</fsummary>
      <type>
        <v>Level       = max | min | 0 &lt;= integer() &lt;= 100</v>
        <v>Destination = File | Port | HandlerSpec | io</v>
        <v>File        = string()</v>
        <v>Port        = integer()</v>
        <v>HandleSpec  = {HandlerFun, Data}</v>
        <v>HandleFun   = fun() (two arguments)</v>
        <v>Data        = term()</v>
      </type>
      <desc>
        <p>This function is used to start megaco tracing at a given 
          <c><![CDATA[Level]]></c> and direct result to the given <c><![CDATA[Destination]]></c>.</p>
        <p>It starts a tracer server and then sets the proper match spec 
          (according to <c><![CDATA[Level]]></c>).</p>
        <p>In the case when <c><![CDATA[Destination]]></c> is <c><![CDATA[File]]></c>, the printable 
          megaco trace events will be printed to the file <c><![CDATA[File]]></c> using
          plain <c><![CDATA[io:format/2]]></c>. </p>
        <p>In the case when <c><![CDATA[Destination]]></c> is <c><![CDATA[io]]></c>, the printable 
          megaco trace events will be printed on stdout using plain 
          <c><![CDATA[io:format/2]]></c>. </p>
        <p>See <c><![CDATA[dbg]]></c> for further information.</p>
        <marker id="disable_trace"></marker>
      </desc>
    </func>

    <func>
      <name>disable_trace() -> void()</name>
      <fsummary>Stop megaco tracing</fsummary>
      <desc>
        <p>This function is used to stop megaco tracing.</p>
        <marker id="set_trace"></marker>
      </desc>
    </func>
    <func>
      <name>set_trace(Level) -> void()</name>
      <fsummary>Change megaco trace level</fsummary>
      <type>
        <v>Level = max | min | 0 &lt;= integer() &lt;= 100</v>
      </type>
      <desc>
        <p>This function is used to change the megaco trace level.</p>
        <p>It is assumed that tracing has already been enabled (see 
          <c><![CDATA[enable_trace]]></c> above).</p>

        <marker id="stats"></marker>
        <marker id="get_stats"></marker>
      </desc>
    </func>

    <func>
      <name>get_stats() -> {ok, TotalStats} | {error, Reason}</name>
      <name>get_stats(GlobalCounter) -> {ok, CounterStats} | {error, Reason}</name>
      <name>get_stats(ConnHandle) -> {ok, ConnHandleStats} | {error, Reason}</name>
      <name>get_stats(ConnHandle, Counter) -> {ok, integer()} | {error, Reason}</name>
      <fsummary></fsummary>
      <type>
        <v>TotalStats = [total_stats()]</v>
        <v>total_stats() = {conn_handle(), [stats()]} | {global_counter(), integer()}</v>
        <v>GlobalCounter = global_counter()</v>
        <v>GlobalCounterStats = integer()</v>
        <v>ConnHandle = conn_handle()</v>
        <v>ConnHandleStats = [stats()]</v>
        <v>stats() = {counter(), integer()}</v>
        <v>Counter = counter()</v>
        <v>counter() = medGwyGatewayNumTimerRecovery |  medGwyGatewayNumErrors</v>
        <v>global_counter() = medGwyGatewayNumErrors</v>
        <v>Reason = term()</v>
      </type>
      <desc>
        <p>Retreive the (SNMP) statistic counters maintained by the 
          megaco application. The global
          counters handle events that cannot be attributed to 
          a single connection (e.g. protocol errors that occur 
          before the connection has been properly setup).</p>
        <marker id="reset_stats"></marker>
      </desc>
    </func>

    <func>
      <name>reset_stats() -> void()</name>
      <name>reset_stats(ConnHandle) -> void()</name>
      <fsummary></fsummary>
      <type>
        <v>ConnHandle = conn_handle()</v>
      </type>
      <desc>
        <p>Reset all related (SNMP) statistics counters.</p>
        <marker id="test_request"></marker>
      </desc>
    </func>

    <func>
      <name>test_request(ConnHandle, Version, EncodingMod, EncodingConfig, Actions) -> {MegaMsg, EncodeRes}</name>
      <fsummary>Tests if the Actions argument is correct</fsummary>
      <type>
        <v>ConnHandle     = conn_handle()</v>
        <v>Version        = integer()</v>
        <v>EncodingMod    = atom()</v>
        <v>EncodingConfig = Encoding configuration</v>
        <v>Actions        = A list</v>
        <v>MegaMsg        = #'MegacoMessage'{}</v>
        <v>EncodeRes      = {ok, Bin} | {error, Reason}</v>
        <v>Bin            = binary()</v>
        <v>Reason         = term()</v>
      </type>
      <desc>
        <p>Tests if the Actions argument is correctly composed.</p>
        <p>This function is only intended for testing purposes. It's
          supposed to have a same kind of interface as the <seealso marker="#call">call</seealso> or <seealso marker="#cast">cast</seealso> functions (with the additions
          of the <c><![CDATA[EncodingMod]]></c> and <c><![CDATA[EncodingConfig]]></c>
          arguments). It composes a complete megaco message end
          attempts to encode it. The return value, will be a tuple of
          the composed megaco message and the encode result. </p>

        <marker id="test_reply"></marker>
      </desc>
    </func>

    <func>
      <name>test_reply(ConnHandle, Version, EncodingMod, EncodingConfig, Reply) -> {MegaMsg, EncodeRes}</name>
      <fsummary>Tests if the Reply argument is correct</fsummary>
      <type>
        <v>ConnHandle     = conn_handle()</v>
        <v>Version        = integer()</v>
        <v>EncodingMod    = atom()</v>
        <v>EncodingConfig = A list</v>
        <v>Reply          = actual_reply()</v>
        <v>MegaMsg        = #'MegacoMessage'{}</v>
        <v>EncodeRes      = {ok, Bin} | {error, Reason}</v>
        <v>Bin            = binary()</v>
        <v>Reason         = term()</v>
      </type>
      <desc>
        <p>Tests if the Reply argument is correctly composed.</p>
        <p>This function is only intended for testing purposes. It's
          supposed to test the <c><![CDATA[actual_reply()]]></c> return value of
          the callback functions 
          <seealso marker="megaco_user#trans_request">handle_trans_request</seealso>
          and 
          <seealso marker="megaco_user#trans_long_request">handle_trans_long_request</seealso>
          functions (with the additions of the <c><![CDATA[EncodingMod]]></c> and
          <c><![CDATA[EncodingConfig]]></c> arguments). It composes a complete
          megaco message end attempts to encode it. The return value,
          will be a tuple of the composed megaco message and the
          encode result.</p>
      </desc>
    </func>
  </funcs>

</erlref>