[Docs] [txt|pdf] [draft-foster-mgcp...] [Diff1] [Diff2]

INFORMATIONAL

Network Working Group                                          B. Foster
Request for Comments: 3064                                 Cisco Systems
Category: Informational                                    February 2001


                           MGCP CAS Packages

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

Abstract

   This document contains a collection of media gateway Channel
   Associated Signaling (CAS) packages for R1 CAS, North American CAS,
   CAS PBX interconnect as well as basic FXO support.  Included are six
   packages.  The "MS" package covers MF single stage dialing trunks.
   This includes wink start and immediate start PBX DID/DOD trunks as
   well as basic R1 and Feature Group D (FGD) Terminating protocol [3].
   The "DT "package covers immediate start and basic DTMF and dial-pulse
   trunks and the "BL" package covers the interface to a basic PBX
   (digital or FXS interface).  In addition to the Terminating protocol,
   there are three other FGD protocols described in [3].  These include
   EAIN and EANA which is covered by the enclosed "MD" package and the
   Operator Service Signaling protocol which is handled by the "MO"
   package.  Support for basic FXO interconnect is provided by "DO"
   package.

Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC-2119.

IESG Note:

   This document is being published for the information of the
   community.  It describes a protocol that is currently being deployed
   in a number of products.  Implementers should be aware of
   developments in the IETF Megaco Working Group and ITU SG16 who are
   currently working on a potential successor to this protocol.




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Table of Contents

   1.0.Introduction ................................................  3
   1.1. Functional Partitioning ....................................  3
   1.2. CAS Trunk Types ............................................  4
   1.2.1. "MS" Package .............................................  5
   1.2.2. "DT" Package .............................................  5
   1.2.3. "BL" Package .............................................  6
   1.2.4. "DO" Package .............................................  6
   1.2.5. "MD" Package .............................................  6
   1.2.6. "MO" Package .............................................  7
   2.0. Event Packages .............................................  7
   2.1. Events and Signals for the "MS" package ....................  9
   2.2. Events and Signals for the "DT" package .................... 10
   2.3. Events and Signals for the "BL" package (Basic PBX) ........ 10
   2.4. Events and Signals for the "DO" package .................... 11
   2.5. Events and Signals for the "MD" package .................... 12
   2.6. Events and Signals for the "MO" package .................... 13
   2.7. Event and Signal Descriptions .............................. 13
   3.0. Hook-State Signals and Events .............................. 23
   3.1. Overview of Approach ....................................... 23
   3.2. Suspend/Resume Processing .................................. 23
   3.3. Control over Disconnect for E911 ........................... 24
   3.3. Release and Release Complete ............................... 24
   3.4. Blocking CAS Trunks ........................................ 26
   3.5. Summary of Hook-State Events ............................... 26
   4.0. Glare Handling ............................................. 27
   4.1. Glare on MF Bi-directional Wink-start Trunks ............... 27
   4.2. Glare Handling - Basic PBX Trunks .......................... 27
   5.0. Example Call Flows ......................................... 28
   5.1. PBX to PBX ("MS", "DT, and "BL" packages)................... 28
   5.1.1. Call Setup Flows ......................................... 28
   5.1.2. Call Tear-Down ........................................... 34
   5.1.2.1. Origination End Initiates the Release .................. 35
   5.1.2.2. Termination End Initiates the Release .................. 38
   5.2. Example Call Flows - "DO" package .......................... 40
   5.2.1. Call Setup Flows ......................................... 40
   5.2.2. Call Tear-Down ........................................... 42
   5.3. Example Call Setup - "MD" Package .......................... 44
   5.4. Example Call Setup - "MO" Package .......................... 51
   Acknowledgements ................................................ 54
   References ...................................................... 55
   Author's Address ................................................ 55
   Full Copyright Statement ........................................ 56







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1.0.Introduction

1.1. Functional Partitioning

   There are a number of different possible approaches for partitioning
   the functional responsibility between the Call Agent and the Media
   Gateway:

    * The Call Agent takes all of the responsibility for the CAS state
      machine giving the media gateway detailed commands

    * The media gateway contains the CAS state machine and provides an
      abstract interface to the Call Agent

   Timing requirements of CAS protocols often involve reacting within
   time intervals measured in tens of milliseconds which makes direct
   control of timing impossible.  The approach used here is to allow the
   media gateway to handle low level CAS protocol and timing details
   where at all possible and have the Call Agent involved only whenever
   higher level processing is required.

   Taking this approach, the ideal situation would be to allow the Call
   Agent to treat as many CAS protocols in a similar way, leaving the
   details to the media gateway.  Example: for an incoming MF trunk that
   involves a single incoming digit string, the Call Agent should not
   care whether this is a wink start trunk or an immediate start trunk
   (media gateway should not have to provide the wink-start signal).

   Some goals in partitioning responsibility between the media gateway
   and media gateway:

    * Minimize the number of interactions between the Call Agent and the
      media gateway.

    * The media gateway should not have to do digit analysis (e.g., to
      determine that the incoming digits contain carrier access
      information).  This is a Call Agent's responsibility.

    * Provide some reasonable level of abstraction for the Call Agent so
      that it can reuse call flows when possible (e.g., Call Agent
      should not have to differentiate between wink start and immediate
      start interfaces when only one digit string is involved).

    * The media gateway should take care of the CAS protocol (and
      timeouts) where possible with the Call Agent taking over
      responsibility where the media gateway leaves off.





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   Use of Embedded Notifications: Rather than depending on the use of
   embedded notifications, signals and events were defined that had the
   specific semantics required.  There are two reasons for this:

   a) It allows an abstract interface for the Call Agent so that for
   example, the same incoming call-setup event can be used in the case
   of MF wink start and MF immediate start trunks, presenting a common
   interface to the Call Agent even though the semantics at the CAS
   state-machine level are slightly different (i.e., in the MF wink
   start case, a wink-start signal is provided reflexively as a result
   of an incoming seizure, where as in the immediate start case, this is
   not required).

   b) Potential events that might trigger an embedded notification
   (e.g., the incoming seizure mentioned above) typically needed to be
   visible to the Call Agent for billing anyway.

   This does not say that embedded notifications cannot be used.  It
   simply does not necessitate their use.

   Out-pulsing Approach: In order to provide the semantics for
   outpulsing, special higher level signals (e.g., "sup" for call set-up
   and "inf" for information) are included that contain the necessary
   semantics.

   Off-hook and On-hook Signals and Events: A higher level view of off-
   hook and on-hook events is taken in order to make the interface
   Q.931-like.  This provides the advantage that:

    * Similar call flows result when dealing with Q.931-based interfaces
      (e.g., PRI)

    * It's more evident (for ease in debug) when looking at message as
      to exactly what is going on without having to refer to previous
      events

1.2. CAS Trunk Types

   The following describes the types of trunks supported by the various
   packages.  Configuration of the specific trunk type (e.g., wink start
   versus immediate start) is done within the Media Gateway (MG) via
   provisioning facilities outside the scope of MGCP.  The Call Agent's
   responsibility is to support the particular package (i.e., in general
   the Call Agent does not have to differentiate between wink start and
   immediate start, since those differences are taken care of by the
   MG).  However, the Call Agent needs to know which trunks are
   incoming, outgoing or bi-directional.




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1.2.1. "MS" Package

   The "MS" package is used for PBX DID/DOD trunks as indicated in the
   following table.  It is also used for incoming or outgoing MF wink
   start trunks (R1 and FGD Terminating protocol [6]).

           Table 1 MF PBX Trunks

        --------------------------------------------------
       |  Trunk Type    |  Direction (w.r.t. the gateway) |
        --------------------------------------------------
       |MF, wink start  |Incoming - originate from PBX    |
       |                |(the same as FGD terminating     |
       |                | protocol)                       |
       |MF, wink start  |Outgoing - terminate on PBX      |
       |MF, wink start  |Bi-directional                   |
       |MF, Immediate   |Incoming (originate from PBX)    |
       |    start       |                                 |
       |MF, Immediate   |Outgoing (terminate on PBX)      |
       |    start       |                                 |
        --------------------------------------------------

1.2.2. "DT" Package

   DTMF and dial-pulse (DP) trunks (except basic PBX) are covered by the
   "DT" package along with the DTMF "D" package:

        Table 2 DTMF and DP Wink Start and Immediate Start Trunks

        --------------------------------------------------
       |  Trunk Type    |  Direction (w.r.t. the gateway) |
        --------------------------------------------------
       |DTMF, Immediate |Incoming (originate from PBX)    |
       | start, wink    |                                 |
       | start          |                                 |
       |DTMF, Immediate |Outgoing (terminate on PBX)      |
       | start, wink    |                                 |
       | start          |                                 |
        --------------------------------------------------












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1.2.3. "BL" Package

   DTMF and dial-pulse (DP) basic PBX trunks are covered by the "BL"
   package - along with the DTMF "D" package (essentially this is like a
   "basic line with no features") - either digital or FXS trunk
   interface:

          Table 3 Basic FXS Interface

         --------------------------------------
        | Trunk Type    |  Direction           |
        |               | (w.r.t. the gateway) |
         --------------------------------------
        |Basic, DTMF and |Bi-directional       |
        |DP, Loop Start  |                     |
        |Basic, DTMF and |Bi-directional       |
        |DP, Ground Start|                     |
         --------------------------------------

1.2.4. "DO" Package

   The "DO" package is used for analog FXO loop-start and ground-start
   analog trunks as indicated in the following table.

           Table 4 FXO analog PBX Trunks

         --------------------------------------
        | Trunk Type    |  Direction           |
        |               | (w.r.t. the gateway) |
         --------------------------------------
        |FXO, loop-start|Bi-directional        |
        |FXO, ground-   |Bi-directional        |
        |     start     |                      |
         --------------------------------------

1.2.5. "MD" Package

   The MD package provides support for North American MF Feature Group D
   EANA and EAIN [3], allowing the Media Gateway to be at either the end
   office, the carrier or the tandem side of the circuit.  The CAS
   Signaling Type column of the following tables is intended to indicate
   signaling differences that are of common interest to both the Call
   Agent and Media Gateway.  Configuration information that is only of
   interest to the Media Gateway is not identified.







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           Table 4 Feature Group D MF Trunks Supported

        --------------------------------------------------
       |  Trunk Type    |  Direction (w.r.t. the gateway) |
        --------------------------------------------------
       |FGD, EANA       |Outgoing (End Office to Carrier) |
       |FGD, EANA       |Incoming (Carrier to End Office) |
       |FGD, EAIN       |Outgoing (End Office to Carrier) |
       |FGD, EAIN       |Incoming (Carrier to End Office) |
        --------------------------------------------------

   Note that EANA and EAIN signaling may be requested on the same trunk
   on a call-by-call basis.

1.2.6. "MO" Package

   The "MO" package is used for FGD Operator Services Signaling,
   outgoing trunks only.  Feature Group C can also be supported by the
   same interface.

2.0. Event Packages

   This section defines the event packages.  The terms "signal" and
   "event" are used to differentiate a command from a Call Agent to a
   Media Gateway ("signal") from an "event" that  is detected by the
   Media Gateway and then is "Notified" to the Call Agent.

   Each package definition includes a package name, plus the event name
   codes and the definitions for each of the events in the package.  In
   the tables of events/signals for each package, there are five
   columns:

      * Code         The package unique event code used for the
                     event/signal.

      * Description  A short description of the event/signal.

      * Event        An "x" appears in this column if the event can be
                     Requested by the Call Agent.  Alternatively, one or
                     more of the following symbols may appear:

        - "P" indicating that the event is persistent,

        - "S" indicating that the event is an event-state that may be
              audited,






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        - "C" indicating that the event/signal may be detected/applied
              on a connection.  If "C" is associated with an event, this
              refers to an event that can occur on the media stream.
              However, "C" may also be associated with a signal (in the
              signal column), the signal can be requested to sent over a
              connection.

   Note that the intent of being able to audit state ("S") in an event
   in the following packages is to answer one of the two questions:

      1. Has a call been initiated on this line/trunk? For example in
      the packages that follow, call setup initiation is indicated by
      either a "sup" event or an "hd" (FXS - "BL" packages) or in the
      case of the "DO" package below (FXO), by the "rg" event so that
      those events have an "S" in the event column indicating that they
      are auditable.

      2. The other question of interest is to know whether the telephony
      leg of the call is in the idle state so that a new call can be
      initiated.  This is indicate by the "rlc" (release complete)
      event-state for packages that have that event.

       *  Signal     If nothing appears in this column then this event
                     cannot be signaled on request by the Call Agent.
                     Otherwise, one of the following symbols is provided
                     to identify the type of signal:

        - "OO" On/Off signal.  The signal is turned on until commanded
               by the Call Agent to turn it off, and vice versa.
        - "TO" Timeout signal.  The signal lasts for a given duration
               unless it is superseded by a new signal or terminated on
               detection of an event.  Default time-out values are
               supplied.  A value of zero indicates that the time-out
               period is infinite.  The provisioning process may alter
               these default values.
        - "BR" Brief signal.  The signal has a short, known duration.

       * Additional info Provides additional information about the
         event/signal, e.g., the default duration of TO signals.

   Unless otherwise stated, all of the events/signals are
   detected/applied on endpoints and audio generated by them is not
   forwarded on any connection the endpoint may have.  Audio generated
   by events/signals that are detected/applied on a connection will
   however be forwarded on the associated connection irrespective of the
   connection mode.





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2.1. Events and Signals for the "MS" package:

   The following codes are used to identify events and signals for the
   "MS" package:

      Table 5 "MS" Package Events and Signals
 ---------------------------------------------------------------------
|Code|Description       |Event|Signal |Additional Info                |
|---------------------------------------------------------------------|
|ans |Call Answer       |  P  |  BR   |                               |
| bl |Block             |  S  |  BR   |                               |
| bz |Busy tone         |  -  |  TO   |Time-out = 30 seconds          |
|inf |Information Digits|  x  |   -   |                               |
| oc |Operation Complete|  x  |   -   |                               |
| of |Operation Fail    |  x  |   -   |                               |
|rel |Release Call      |  P  |  BR   |                               |
|res |Resume call       |  P  |  BR   |                               |
|rlc |Release complete  | P,S |  BR   |                               |
| ro |Reorder tone      |  -  |  TO   |Time-out = 30 seconds          |
| rt |Ringback tone     |  -  |  TO   |Time-out = 180 seconds         |
|sup |Call Setup        | P,S |  TO   |Time-out when signal completes |
|    |                  |     |       |out-pulsing                    |
|sus |Suspend call      |  P  |  BR   |                               |
 ---------------------------------------------------------------------



























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2.2. Events and Signals for the "DT" package:

   The following codes are used to identify events and signals for the
   "DT" package:

     Table 6 "DT" Package Events and Signals
 ---------------------------------------------------------------------
|Code|Description       |Event|Signal |Additional Info                |
|---------------------------------------------------------------------|
|ans |Call Answer       |  P  |  BR   |                               |
| bl |Block             |  S  |  BR   |                               |
| bz |Busy tone         |  -  |  TO   |Time-out = 30 seconds          |
| dl |Dial tone         |  -  |  TO   |Time-out = 16 seconds          |
| oc |Operation Complete|  x  |  -    |                               |
| of |Operation Fail    |  x  |  -    |                               |
|rel |Release Call      |  P  |  BR   |                               |
|res |Resume call       |  P  |  BR   |                               |
|rlc |Release complete  | P,S |  BR   |                               |
| ro |Reorder tone      |  -  |  TO   |Time-out = 30 seconds          |
| rt |Ringback tone     |  -  |  TO   |Time-out = 180 seconds         |
|sup |Call Setup        | P,S |  TO   |Time-out when signals completed|
|    |                  |     |       |out-pulsing                    |
|sus |Suspend call      |  P  |  BR   |                               |
 ---------------------------------------------------------------------

2.3. Events and Signals for the "BL" package (Basic PBX)

   The following codes are used to identify events and signals for the
   "BL" package.  This package looks very much like a simplified line
   package:

          Table 7 "BL" Package Events and Signals
 ---------------------------------------------------------------------
|Code|Description       |Event|Signal |Additional Info                |
|---------------------------------------------------------------------|
| bz |Busy tone         |  -  |  TO   |Time-out = 30 seconds          |
| dl |Dial tone         |  -  |  TO   |Time-out = 16 seconds          |
| hd |Off-hook          | P,S |   -   |                               |
| hf |Flash hook        |  P  |   -   |                               |
| hu |On-hook           | P,S |   -   |                               |
| oc |Operation Complete|  x  |   -   |                               |
| of |Operation Fail    |  x  |   -   |                               |
| rel|Release           |  -  |  BR   |                               |
| rg |Ringing           |  -  |  TO   |Time-out = 180 seconds         |
| ro |Reorder tone      |  -  |  TO   |Time-out = 30 seconds          |
| rt |Ringback tone     |  -  | C,TO  |Time-out = 180 seconds         |
 ---------------------------------------------------------------------




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2.4. Events and Signals for the "DO" package:

   The following codes are used to identify events and signals for the
   "DO" package:

     Table 8 "DO" Package Events and Signals
 ---------------------------------------------------------------------
|Code|Description       |Event|Signal |Additional Info                |
|---------------------------------------------------------------------|
| ci |Caller id         |  x  |   -   |                               |
| hd |Offhook           |  -  |  BR   |                               |
| hf |Hook flash        |  -  |  BR   |                               |
| hu |Onhook            |  -  |  BR   |                               |
| oc |Operation Complete|  x  |   -   |                               |
| of |Operation Fail    |  x  |   -   |                               |
|rel |Release call      |  P  |   -   |                               |
| rg |Ringing           | P,S |   -   |                               |
|rlc |Release complete  | P,S |   -   |                               |
|sup |Call Setup        |  -  |  TO   |Time-out when signal completes |
|    |                  |     |       | out-pulsing                   |
 ---------------------------------------------------------------------






























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2.5. Events and Signals for the "MD" package:

   The following codes are used to identify events and signals for the
   "MD" package.

    Table 9 "MD" Package Events and Signals
 ---------------------------------------------------------------------
|Code|Description       |Event|Signal |Additional Info                |
|---------------------------------------------------------------------|
|ans |Call Answer       |  P  |  BR   |                               |
|awk |Acknowledge wink  |  P  |  BR   |                               |
| bl |Call Block        |  S  |  BR   |                               |
| bz |Busy tone         |  -  |  TO   |Time-out = 30 seconds          |
|cwk |Continue Wink     |  -  |  BR   |                               |
|inf |Information Digits|  x  |  TO   |Time-out when signals completed|
|    |                  |     |       | out-pulsing                   |
| oc |Operation Complete|  x  |   -   |                               |
| of |Operation Fail    |  x  |   -   |                               |
|rel |Release Call      |  P  |  BR   |                               |
|res |Resume call       |  P  |  BR   |                               |
|rlc |Release complete  | P,S |  BR   |                               |
| ro |Reorder tone      |  -  |  TO   |Time-out = 30 seconds          |
| rt |Ringback tone     |  -  |  TO   |Time-out = 180 seconds         |
|sup |Call Setup        | P,S |  TO   |Time-out when signals completed|
|    |                  |     |       | out-pulsing                   |
|sus |Suspend call      |  P  |  BR   |                               |
|swk |Start Wink        |  x  |   -   |                               |
 ---------------------------------------------------------------------























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2.6. Events and Signals for the "MO" package:

   The following codes are used to identify events and signals for the
   "MO" package.

    Table 10 "MO" Package Events and Signals

 ---------------------------------------------------------------------
|Code|Description       |Event|Signal |Additional Info                |
|---------------------------------------------------------------------|
|ans |Call Answer !Note |  P  |   -   |                               |
| oc |Operation Complete|  x  |   -   |                               |
| of |Operation Fail    |  x  |   -   |                               |
|orbk|Operator Ringback |  x  |   -   |                               |
|rbz |Reverse make busy | P,S |   -   |                               |
|rcl |Operator Recall   |  -  |  BR   |                               |
|rel |Release Call      |  P  |  BR   |                               |
|res |Resume Call       |  -  |  BR   |                               |
|rlc |Release complete  | P,S |  BR   |                               |
|sup |Call Setup        |  -  |  TO   |                               |
|sus |Suspend Call      |  -  |  BR   |                               |
|swk |Start Wink        |  x  |   -   |                               |
 ---------------------------------------------------------------------
!Note: There is no indication that the operator answered the call.
       The "ans" event is an indication that off-hook was received
       from the far end which simply indicates that the destination
       address was received properly and the calling number is in the
       process of being outpulsed.

2.7. Event and Signal Descriptions

   The following provides a list of the event and signal descriptions.

   The event/signal name appears in parenthesis followed by the
   corresponding Event + Signal attribute code plus a list of the
   packages in which the event/signal occurs.

   Call answer (ans; P + BR; DT,MD,MS,MO): Off-hook signal normally
   indicates that the call has been answered and that cut-through has
   been established.  The exception is the "MO" package where it simply
   indicates that off-hook was received and the calling number is in the
   process of being sent (i.e., there is no event available to indicate
   that the operator answered the call for operator services signaling).

   Acknowledgement Wink (awk; P + BR; MD): This event is only applicable
   to the "md" package.  It provides an indication that all digits have
   been received correctly.  In an outgoing trunk, the event is
   requested and when received indicates that the connecting switch



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   received all of the addressing information.  On an originating trunk,
   this signal is sent to inform the other end that all addressing
   information has been received.  If the Call Agent is providing a
   transit application for example, in which incoming and outgoing
   trunks are both EANA trunks, then after acknowledgement wink is
   received from the terminating trunk, it is passed to the originating
   side so that the originating side knows that addressing has passed to
   the destination switch.

   Call Block (bl; S + BR; DT,MS,MD): A steady off-hook signal applied
   to one-way incoming trunks to indicate that no further calls will be
   accepted.  When "bl" is used as a signal then the "rel" signal is
   used to release the blocking condition.

   A Call Agent should only request the "bl" event in a case where it
   knows that this is a one-way outgoing trunk, and it should never see
   an incoming call-setup request ("sup" event).  As such if "bl" is
   requested as an event, then "sup" is suppressed as a persistent
   event.

   Busy tone (bz ; - + TO; BL,DT,MD,MS): Refer to ITU E.180.  The
   definition of the tone is defined by the national characteristics and
   may be established via provisioning.  Station Busy is defined in GR-
   506-CORE - LSSGR, SIGNALING, Section 17.2.6. as a combination of two
   AC tones with frequencies of 480 and 620 Hertz and levels of -24 dBm
   each, to give a combined level of -21 dBm.  The cadence for Station
   Busy Tone is 0.5 seconds on followed by 0.5 seconds off, repeating.

   Caller Id (ci(time, number, name); x + -; DO): See TR-NWT-001188,
   GR-30-CORE, and TR-NWT-000031.  Each of the three fields are
   optional, however each of the commas will always be included.

      The time parameter is coded as "MM/DD/HH/MM", where MM is a two-
      digit value for Month between 01 and 12, DD is a two-digit value
      for Day between 1 and 31, and Hour and Minute are two-digit values
      coded according to military local time, e.g., 00 is midnight, 01
      is 1 a.m., and 13 is 1 p.m.

      The number parameter is coded as an ASCII character string of
      decimal digits that identify the calling line number.  White
      spaces are permitted if the string is quoted, however they
      will be ignored.

      The name parameter is coded as a string of ASCII characters that
      identify the calling line name.  White spaces are permitted if the
      string is quoted.





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   A "P" in the number or name field is used to indicate a private
   number or name, and an "O" is used to indicate an unavailable number
   or name.  The following example illustrates the use of the caller-id
   event:

      O: ci(10/14/17/26, "555 1212", somename)

   Continue Wink (cwk ; - + BR; MD): This signal is only applicable to
   the "md" package.  It provides an indication that digits sent have
   been accepted, and further digits must be sent in order to process
   the call.  For example, when using FGD EAIN signaling, this would
   correspond to sending a wink after the country access code had been
   received to indicate readiness to receive identification and address
   fields.

   Dial-tone (dl ; - + TO; BL,DT): Refer to ITU E.180.  The definition
   of the tone is defined by the national characteristics and may be
   established via provisioning.  In GR-506-CORE - LSSGR, SIGNALING,
   Section 17.2.1, sial Tone is defined as a combination of two
   continuous AC tones with frequencies of 350 and 440 Hertz and levels
   of -13dBm each to give a combined level of -10 dBm.  It is considered
   an error to try and play dial-tone on a phone that is on hook and an
   error should consequently be returned when such attempts are made
   (error code 402 - phone on hook).

   Information Digits (inf(<inf-digits>); x + TO; MS,MD): On an outgoing
   call ("md" package only) it is used as a signal to out-pulse the
   address information when doing overlapped sending.

   On an incoming call it is used as an event to indicate that an MF
   digit string has been received.  In this case, <inf-digits> are all
   of the digits accumulated up to and including the digit delimiters
   ST, ST', ST'', ST'''.  Multiple sequences of digits ending with one
   of the ST digits may be passed in a single "inf" event.  (Note that
   K0 is the same as KP, K1 is sometimes referred to as KP' etc.
   Similarly S0 is the same as ST, S1 is the same as ST' and so on.

   The value of <inf-digits> is a comma separated list of MF digits:
   MF1, MF2, ..., MFn

   where each of MFi will be one of the following MF digit symbols:










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             Table 11 MF Digit Symbols

             -------------------------
            | Symbol |MF digit         |
            |   0    |   MF 0          |
            |   1    |   MF 1          |
            |   2    |   MF 2          |
            |   3    |   MF 3          |
            |   4    |   MF 4          |
            |   5    |   MF 5          |
            |   6    |   MF 6          |
            |   7    |   MF 7          |
            |   8    |   MF 8          |
            |   9    |   MF 9          |
            |   K0   |   MF K0 or KP   |
            |   K1   |   MF K1         |
            |   K2   |   MF K2         |
            |   S0   |   MF S0 or ST   |
            |   S1   |   MF S1 or ST'  |
            |   S2   |   MF S2 or ST'' |
            |   S3   |   MF S3 or ST'''|
             --------------------------

   Thus, an example signal or event might look like:

      inf(k0, 5,5,5,1,2,3,4, s0)

   An example where the inter-digit timer expired after the 5,5,5 would
   appear as follows:

      inf(k0, 5,5,5)

   Operation Complete (oc ; x + -; all): The operation complete event is
   generated when the gateway was asked to apply one or several signals
   of type TO on the endpoint, and one or more of those signals
   completed without being stopped by the detection of a requested or
   persistent event such as setup.  The completion report may carry as a
   parameter the name of the signal that came to the end of its live
   time, as in:

      O: ms/oc(ms/sup)

   or

      O: bl/oc(bl/rg)

   When the operation complete event is requested, it cannot be
   parameterized with any event parameters.



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   Note that when requested at the same a signal for "sup" (out-pulsing
   - a TO event), the operation complete event will indicate when out-
   pulsing is complete.

   Operation failure (of; x + -; all):  In general, the operation
   failure event may be generated when the endpoint was asked to apply
   one or several signals of type TO on the endpoint, and one or more of
   those signals failed prior to timing out.  The completion report may
   carry as a parameter the name of the signal that failed, as in:

       O: ms/of(ms/sup)

   or

       O: bl/of(bl/rg)

   When the operation failure event is requested, it cannot be
   parameterized with any event parameters.

   Operator ringback (orbk; x + -; MO): The description of the signaling
   MF CAS signaling that results in this event is describe in the
   appendix of TR-NPL-000258 [3].  In brief, it is normally a wink-on
   signal which may or may not be followed by an MF tone.  This event
   will be generated when the operator service requests that the calling
   party be alerted ("mo" package only).

   Reverse make busy (rbz; P + -; MO): This event corresponds to a
   "blocking" (off-hook) generated by the other end of the one-way
   operator services trunk ("mo" package).  It has the same semantics as
   of the "bl" event in other packages.

   Operator recall (rcl; - + BR; MO): This signal may be applied to
   invoke operator recall, e.g., due to customer hook-flash to bring the
   operator back.

   Release call (rel; P,S + BR; BL,DT,MD,MO,MS,DO): A "rel" signal sent
   by the Call Agent to the Media Gateway is a request to release all of
   the resources associated with the telephony leg of the call.  This
   may also result in an off-hook signal being sent when appropriate.
   As a result of an "rel" signal, the gateway will respond with an
   "rcl" event, whenever the resources have been released.  Releasing
   resources associated with the telephony leg of the call does not
   affect existing connections (network legs).  It's up to the Call
   Agent to send the appropriate delete connection commands in order to
   release any network connections to that endpoint.






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   In the case of the FXS ("BL") package, the "rel" signal is used to
   provide a tip-ground release for ground-start trunks.  In the case of
   loop-start trunks, requesting to play this signal has no effect.

   The Media Gateway generates a "release call" event whenever a call is
   released as a result of an on-hook event from an originating end of a
   call (normal release) or due to abnormal event that resulted in
   releasing the call.  The event may be parameterized with one of the
   following cause codes indicating the reason for the release:

              Table 12 Release Reason Codes
      -----------------------------------------------------------------
     |Cause Code |Reason                                               |
     |-----------------------------------------------------------------
     |    0      |Normal release                                       |
     |    44     |Requested channel/circuit not available              |
     |           |(glare or incoming seizure detected during call      |
     |           | setup)                                              |
     |    111    |Protocol/signaling error, unspecified (e.g. timeout) |
      -----------------------------------------------------------------

   Note that a "rel" event with reason code "0" indicating normal
   release (due to an incoming on-hook) will only be "notified" by a
   gateway where a call origination occurred.  This behavior follows the
   rule that when an originator releases the call, all resources may be
   released.  The corresponding event for on-hook on the terminating end
   of a call is the "sus" event which only indicates hook-status and
   does not result in any resources being released.  It is always up to
   the Call Agent to release the call (by sending the "rel" signal) for
   the terminating end of a call.

   For FXO ground-start case ("DO" package), the Media Gateway generates
   a "release call" event whenever a call is released as a result of a
   tip-ground release event from the far end.

   Resume call (res ; P + BR; DT,MD,MS,MO): This indicates that the
   called party resumed the call, i.e., the party went off-hook after a
   previous suspend ("sus") but before the originating switch released
   ("rel") the trunk.  The "sus" and "res" events/signals are used to
   propagate on-hook and off-hook events without releasing the resources
   associated with the call.  In all but the operator services case
   ("MO" package), these events would normally be propagated from the
   terminating to the originating end (i.e., requested as events from
   the terminating end of the call and sent to the gateway as signals to
   a gateway on the originating side of the call).






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   However, it is up to the Call Agent to decide whether it wants to do
   "suspend"/"resume" processing.  If it doesn't, when it receives a
   "sup" event from the terminating end of the call it can simply go
   ahead and tear down the call immediately (send "rel" and delete
   connections to the endpoints on gateways at both originating and
   terminating end of the call).

   In the case of operator services and 911, "sus" and "res" are used to
   pass off-hook and on-hook signals to the operator without releasing
   any of the resources associated with the call.

   Ringing (rg; P,S + TO; BL,DO): This signal is used for outgoing basic
   trunks ("bl" package).  See GR-506-CORE - LSSGR: SIGNALING, Section
   14.  The provisioning process may define the ringing cadence.  It is
   considered an error to try and ring if the trunk indicates off hook
   and an error should consequently be returned when such attempts are
   made (error code 401 - phone off hook).

   In the case of the "DO" package, "rg" is defined as an event used to
   indicate detection of ringing.

   Release complete (rlc;P,S + BR; DO,DT,MD,MO,MS): The endpoint and
   Call Agent use the release complete event/signal to confirm the call
   has been released and the trunk is available for another call.  For
   FXO ground-start ("DO" package), this represents the release of the
   tip-ground event from the PBX after the gateway goes on-hook.

   Reorder tone (ro; - + TO; BL,DT,MD,MS): Reorder tone is a combination
   of two AC tones with frequencies of  480 and 620 Hertz and levels of
   -24 dBm each, to give a combined level of -21 dBm.  The cadence for
   reorder tone is 0.25 seconds on followed by 0.25 seconds off,
   repeating continuously.  See GR-506-CORE - LSSGR: SIGNALING, Section
   17.2.7.

   Ring back tone (rt; - + TO; BL,DT,MD,MS): Audible Ring Tone is a
   combination of two AC tones with frequencies of 440 and 480 Hertz and
   levels of -19 dBm each, to give a combined level of -16 dBm.  In the
   US the  cadence for Audible Ring Tone is defined to be 2 seconds on
   followed by 4 seconds off.  The definition of the tone is defined by
   the national characteristics of the Ring-back Tone, and MAY be
   established via provisioning.  See GR-506-CORE - LSSGR: SIGNALING,
   Section 17.2.5.

   Call Setup (sup ; P,S + TO; DO,DT,MD,MS,MO): The event/signal is used
   both for outgoing and incoming call setups.  Each will be described
   separately in the following.





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   Outgoing call setup:

   On an outgoing trunk, the "sup" signal is used to seize a trunk and
   out-pulse digits.  The "sup" signal is parameterized with up to four
   parameters sup(<ct>, <ca>, <id>, <addr>), depending on the package.
   The order of these parameters does not matter.  The following table
   indicates which ones are mandatory ("M"), optional ("O") or forbidden
   ("F") for the various packages.

               Table 13 "sup" parameters.

               ------------------------------------
              | Parameter | MS | DT | MO | MD | DO |
              |------------------------------------|
              |    <ct>   |  F |  F |  F |  M |  F |
              |    <ca>   |  F |  F |  F |  O |  F |
              |    <id>   |  F |  F |  M |  M |  F |
              |   <addr>  |  M |  M |  M |  O |  M |
               ------------------------------------

   The <ct> parameter is of the format ct(<ct-value>) where <ct-value>
   indicates the CAS signaling type and can have one of two values "nda"
   (North American Direct Access) for EANA and "nta" (North American
   Tandem Access) for EAIN.  The reason this parameter is needed in the
   case of trunks that handle the "MD" packages is because the same
   trunk can be used for both.  The <addr> field contains the
   destination number and when present will be on the form

         addr(dig1, dig2, ..., dign)

   The <id> field contains the identification of the caller and when
   present will be of the form:

        id(dig1, dig2, ..., dign)

   The <ca> field  contains the country address information and when
   present will be of the form:

        ca(dig1, dig2, ..., dign)

   When present, the <addr> field contains the destination number and
   will be of the form

       addr(dig1, dig2, ..., dign)

   where digi is an MF symbol as defined in table 11 in the case of
   "MS", "MO", and "MD" packages and digi is a DTMF symbol (0-9,
   *,#,A,B,C,D) in the case of the "DT" and "DO" packages.



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   The following table shows some interactions between the Media Gateway
   (MG) and the Switched Circuit Network (SCN) for single stage
   outpulsing applications ("DT", "MS" and "DO" packages):

    Table 14 SCN Sequencing during Call Setup (single stage outpulsing)

    ------------------------------------------------------------------
   |Interface Type |Setup                     |     Interactions      |
   |------------------------------------------------------------------|
   |wink start     |sup(add(<addrvalue>))     |MG|  off-hook ->   |SCN|
   |               |                          |MG|  <- wink       |SCN|
   |               |                          |MG| <addrvalue> -> |SCN|
   |------------------------------------------------------------------|
   |Immediate Start|(sup(addr(<addrvalue>))   |MG|  off-hook ->   |SCN|
   | or FXO)       |                          |MG| <addrvalue> -> |SCN|
    ------------------------------------------------------------------

   Call setup signal example for this case (MF signaling):

         sup(addr(s0,5,5,5,1,2,3,4,k0))

   The "MO" and "MD" packages involve multi-stage signaling and multiple
   parameters.  In the case of the "MD" package the following table
   shows some of the interactions:

      Table 15 SCN Sequencing during Call Setup (EANA and EAIN)

    ------------------------------------------------------------------
   |Setup                                     |      Interactions     |
   |------------------------------------------------------------------|
   | sup(ct(nda),addr(<addrvalue>),           |MG|  off-hook ->   |SCN|
   | id(<idvalue>))                           |MG|  <- wink       |SCN|
   |                                          |MG|  <idvalue> ->  |SCN|
   |                                          |MG| <addrvalue> -> |SCN|
   |------------------------------------------------------------------|
   | sup(ct(nta), ca(<cavalue>),              |MG|  off-hook ->   |SCN|
   | addr(<addrvalue>), id(<idvalue>))        |MG|  <- wink       |SCN|
   |                                          |MG|  <cavalue> ->  |SCN|
   |                                          |MG|  <- wink       |SCN|
   |                                          |MG|  <idvalue> ->  |SCN|
   |                                          |MG| <addrvalue> -> |SCN|
   |------------------------------------------------------------------|
   | sup(ct(nta), ca(<cavalue>),              |MG|  off-hook ->   |SCN|
   |    id(<idvalue>))                        |MG|  <- wink       |SCN|
   |                                          |MG|  <cavalue> ->  |SCN|
   |                                          |MG|  <- wink       |SCN|
   |                                          |MG|  <idvalue> ->  |SCN|
    ------------------------------------------------------------------



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   The last example is an overlapped sending example where the address
   value would be sent later using the "inf" signal.

   An example setup:

      sup(ct(nta),ca(k0,1,3,8,9,9,0,0,1,0,s0),id(k0,0,5,5,5,1,2,3,4,s0))

   In all of the above cases, the "ans" event is an indication of off-
   hook from the far end (the other end answered).  However, in the case
   of the operator service signaling (OSS) protocol of Feature Group D -
   shown in the following table, off-hook from the operator is part of
   the protocol (a request for the calling number) so that "ans" in this
   case does not indicate that the operator answered (only that off-
   hook/request for calling number was received).

   Table 16 SCN Sequencing during Call Setup OSS Protocol ("MO" Package)

    ------------------------------------------------------------------
   |Setup                                     |      Interactions     |
   |------------------------------------------------------------------|
   | sup(ct(nda),addr(<addrvalue>),           |MG|  off-hook ->   |SCN|
   | id(<idvalue>))                           |MG|  <- wink       |SCN|
   |                                          |MG| <- off-hook    |SCN|
   |                                          |MG| <addrvalue> -> |SCN|
   |                                          |MG|  <idvalue> ->  |SCN|
    ------------------------------------------------------------------

   Incoming Call Setup: A "sup" event is used to indicate when an
   incoming call arrives (corresponding to the incoming off-hook event).
   The event is provided without parameters.

   Suspend call (sus; P + BR; DT,MD,MS,MO): Suspend ("sus") is an on-
   hook event that is an indication that the called party went on-hook.

   An on-hook event will be "notified" to a Call Agent as a "sus" event
   for interfaces that use the "MS", "DT" and "MD" packages from an
   endpoint at a terminating end of a call (as compared to a "rel" event
   from the originating side).  The "sus" event from the terminating
   endpoint gives the Call Agent the option of doing "suspend/resume"
   processing or to simply release the call.

   The "sus" signal may be used to send an on-hook to the originating
   party without releasing the resources associated with the telephony
   leg of the call.  The "rel" signal on the other hand would send an
   on-hook and release the resources associated with the call.






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   Because of this "sus" can be followed by "res" (off-hook) and allow
   the call to resume, while "rel" cannot be followed by "res" because
   the call no longer exists.

   For E911 ("MO" package), the operator is normally in control of
   releasing the call so that, "sus" (on-hook), "res" (off-hook) and
   "rcl" (flash-hook) can be used to pass user hook events to the
   operator without releasing the call.

   Start Wink (swk; x + - MD,MO):.  An Call Agent can optionally request
   the MG to notify it when the wink start signal occurs.  Note that
   wink start ("swk") cannot be applied by the Call Agent as a signal.
   The occurrence of wink-start on an incoming trunk is a reflexive
   action that does not require Call Agent involvement.

3.0. Hook-State Signals and Events

3.1. Overview of Approach

   As mentioned in the introduction, a higher level view is taken for
   on-hook and off-hook events for many of the CAS packages to make the
   interface Q.931-like.  This provides the advantage that:

    * Similar call flows result as when dealing with Q.931-based
      interfaces (e.g., PRI)
    * It's more evident (for ease in debug) when looking at message as
      to exactly what is going on without having to refer to previous
      flows.

   This does require that media gateways maintain some state but this is
   a relatively small price to pay.

   One example of this is the "sup" signal which involves sending off-
   hook followed by digits as a high level signal.  The "ans" event is
   also used to represent off-hook but from the terminating end at the
   point where the call is answered.

3.2. Suspend/Resume Processing

   Other signals and events "sus" for suspend, "res" for resume and
   "rel" for release are based on the concept that one end (the
   originator) is in control of the call.  If the controlling end goes
   on-hook a "rel" is notified to the Call Agent, and results in a the
   call being released.  However, if the non-controlling (terminating)
   end goes on-hook, a "sus" event occurs (instead of the "rel" event).
   This gives the Call Agent the option of doing suspend/resume
   processing.




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   If the Call Agent decides not to do suspend/resume processing, it can
   simply send "rel" and delete connection commands to the endpoints
   after it receives "sus" from the non-controlling (terminating) end of
   the call.

   On the other hand, if it decides to do suspend/resume processing, it
   can start a timeout when it receives the "sus" event from the non-
   controlling (terminating) end of the call and continue the call if it
   receives a "res" (off-hook) event.  It also has the option of
   propagating the "sus" and "res" as signals back to the ingress
   gateway and allow it an opportunity to release the call ("rel" event)
   or not.  In any case the use of "sus" and "res" signals give another
   level of control over the "rel" signal which will not only send on-
   hook but also release the resources associated with the telephony leg
   of the call.

3.3. Control over Disconnect for E911

   Note that for E911 (the "MO" package) is a special case in that the
   operator (terminating end) is always the controlling end.  The "sus"
   and "res" signals are used to pass user hook state forward to the
   operator.  The "rel" event is passed back as a notify to the Call
   Agent when on-hook is received from the operator indicating that the
   Call should be released.  If the "rel" is not received the call
   should continue to stay up.

3.3. Release and Release Complete

   The "rel" signal/event generally means on-hook but more that that it
   also indicates "release of resources" for the telephony leg of the
   call.  If a Call Agent sends a "rel" signal instead of "sus" it is
   requesting the call to be abandoned (i.e., "rel" cannot be followed
   by "res").

   The "rel" signal does not also imply that connections should be
   deleted so that to completely release the call including connections
   would require a DLCX in addition to (or conjunction with) the signal
   "rel".

   In addition to being a signal, "rel" can also be an event triggered
   by either:

    * An on-hook from the controlling end of the call, or

    * Some abnormal event within the media gateway such that the
      telephony leg of the call can no longer be maintained.





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   In any case, "rel" (release) is generally followed by an "rlc"
   (release complete).  The release complete signal/event indicates that
   the trunk resources are now completely released and available for
   another call.  This is also an event state that can be audited as
   indicated by the "S" in the column for that event (allowing the Call
   Agent to check to see if that trunk is released and available).

   Examples of the use of "rel" and "rlc":

    * Call Agent sends a "rel" to release a trunk, resulting in an
      outgoing off-hook being sent for that trunk.  When the media
      gateway receives the on-hook from the other end, it returns an
      "rlc" event indicating that the trunk is released and available.
    * The media gateway receives a on-hook from the trunk at the
      controlling end of the call, resulting in a "rel" event being sent
      to the Call Agent.  The Call Agent then sends an "rlc" to the
      media gateway, resulting in on-hook being sent in the opposite
      direction.
    * An "rel" event is sent to the Call Agent in the event of some
      abnormal condition in which the media gateway is unable to sustain
      the telephony leg of the call (e.g., glare condition).  The Call
      Agent sends an "rlc" to the gateway to complete the release of the
      call. (note that "rlc may not correspond to on-hook but is
      generally sent anyway in response to a "rel".)
    * The Call Agent can send a "rel" (instead of "sus") signal to the
      controlling (originating) end of the call to abandon the call.
      The gateway will return with "rlc" when an off-hook has been
      received from the other end and all the resources have been
      released.
    * A "rel" can be sent on one-way incoming trunk to release a block
      ("bl") sent earlier.

   The "BL" (FXS) package is a simple line package, so does not have
   these events (uses "hd", "hf", and "hu" as the only hook state
   events).

   The "DO" (FXO) package, however, does have "rel" and "rlc" because in
   the ground-start case there is the ability to "release" the call as
   result of a tip-ground release.  The signal "rel" is used if the PBX
   releases the call first (followed by S: hu from the call Agent to
   complete the release).  Alternatively, the Call Agent can send the S:
   hu to initiate the release  - followed by an "rlc" event from the
   media gateway to Call Agent when the PBX does the tip ground release.
   Although the loop-start trunks would not normally have this behavior
   (only applies to ground-start), the media gateway should emulate the
   behavior in the case of loop-start in order to allow the Call Agent a
   common interface.




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3.4. Blocking CAS Trunks

   In addition to the above signals and events, there is the "bl"
   signal/event which is used for blocking one-way trunks (does not work
   for two way trunks) by providing a continuous off-hook.

3.5. Summary of Hook-State Events

   The following summarizes the use of the various events that involve
   off-hook and on-hook from call establishment to tear-down.  This
   applies mainly to "MS", "DT", "MD" and to a lesser extent the "DO"
   package.

    * The "sup" event represents off-hook origination.
    * The "sup" signal with parameters provides off-hook with digit
      outpulsing on the terminating side.
    * Once outpulsing is completed, an "ans" event indicates off-hook
      from the termination side (the called party has answered).
    * The call agent can then send an "ans" signal (off-hook) to the
      originating end to indicate to the caller that the called party
      has answered.
    * The Call Agent can send a "rel" to either end at any time to tear
      down the call (e.g., to abort the call).
    * The media gateway can send "rel" to indicate abnormal termination
      of the call (with a reason as a parameter).
    * However, under normal operation once a call is established, the
      Call Agent can expect a "sus" (suspend) event from the termination
      end to indicate that the caller went on-hook and a "res" if the
      called party goes off-hook again before the Call Agent tears down
      the call.  The Call Agent can send these same signals to the
      originating end to indicate off-hook and on-hook to the calling
      party without tearing down the call.
    * During normal operation, once the call is established, on-hook
      from the calling party (origination side) would result in a "rel"
      signal.  The Call Agent would then normally send the "rel" signal
      to the terminating end to terminate the call.  "rel is normally
      followed by "rlc" (e.g., media gateway indicates calling party on-
      hook with "rel" and the Call Agent responds with "rlc", which
      sends on on-hook back to the calling party to indicated release
      complete.

   The "MO" package is a bit different in that normally only the
   terminating side (the operator) can release the call ("rel" event).
   The "sus" and "res" are forward signals to the operator indicating
   user hook-status.






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4.0. Glare Handling

4.1. Glare on MF Bi-directional Wink-start Trunks

   Gateways may have a configurable glare bit on a per-DS0 basis that
   can be set to indicate whether the gateway is the controlling or
   non-controlling "switch".  However, in general, PBXs are either pre-
   configured or can be configured to behave as non-controlling
   switches.  In this case if they see an off-hook that exceeds
   allowable wink length, they will attach a receiver, go on-hook, and
   await digits for a new call.  Meanwhile the PBX will retry its
   original call on another trunk.

   If the gateway behaves like a controlling switch, when glare is
   detected, the gateway will wait for up to some timeout value (default
   value of 4 seconds) until the incoming off-hook changes to an on-hook
   state at which time it will start out-pulsing in the normal manner.
   If the timeout occurs before the state change to on-hook occurs, the
   gateway will send a release event to the Call Agent (a "rel(44)"
   event - cause code indicating glare).

   When "rel(44)" is sent by the gateway, that is an indication to the
   Call Agent that the call is in the process of being released and that
   the Call Agent should give up on that trunk.  However, the gateway
   may not actually want to send the on-hook at that time in order to
   avoid the possibility that the other end takes the on-hook as a wink.
   Instead, it may start a second timer and wait some longer period of
   time (e.g., 16 seconds or so) before releasing the trunk.  If it
   receives an on-hook prior the timeout, it completes the release by
   going on-hook.  If, on the other hand, the timer expires before the
   other end goes on-hook, it will simply go on-hook and wait for the
   other end to go on-hook.  In any case, once both ends have returned
   to the on-hook state, an "rlc" event is sent to the Call Agent.

4.2. Glare Handling - Basic PBX Trunks

   In order to reduce the chances of glare, the gateway should try a
   ringing pre-trip test prior to sending ringing on a basic ground
   start trunk.  If glare is detected on an outgoing seizure of a basic
   PBX trunk, the request for ringing should be "Nacked" (error code 401
   - phone off-hook) to the Call Agent.










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5.0. Example Call Flows

5.1. PBX to PBX ("MS", "DT, and "BL" packages).

   The following call flows involve a single Call Agent that handles
   both sides of the call (i.e., the inter-Call-Agent signaling is
   ignored).  The components involved in the call are:

   * The Call Agent (CA)

   * The originating Media Gateway (GW-o) and

   * The terminating Media Gateway (GW-t)

5.1.1. Call Setup Flows

   The following describes some PBX to PBX call.  The table gives an
   overview of the initial part of the call flow with details to follow.

    ---------------------------------------------------------------------
   | Steps |        GW-o        |         CA         |        GW-t       |
   |---------------------------------------------------------------------|
   |  A1   |       NTFY[seizure] ->                                      |
   |  A2   |                 <-  Ack                                     |
   |  A3   |                 <-  RQNT[request digits]                    |
   |  A4   |                 Ack ->                                      |
   |  A5   |       NTFY[digits]  ->                                      |
   |  A6   |                 <- Ack                                      |
   |  B1   |                 <- CRCX [M:recvonly, LCO]                   |
   |  B2   |          Ack[SDP1]  ->                                      |
   |  B3   |                     CRCX [M:sendrecv, LCO, SDP1] ->         |
   |  B4   |                                 <- Ack [SDP2]               |
   |  B5   |                 <-  MDCX [recvonly,SDP2]                    |
   |  B6   |                 Ack  ->                                     |
    ---------------------------------------------------------------------

   Step A1   PBX seizure results in a notify to the Call Agent
   indicating the start of a call setup:

         NTFY 3001 ds/ds1-3/6@gw-o.whatever.net MGCP 1.0
         X: 0123456789AF
         O: ms/sup (or dt/sup)









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       In the case of the "BL" package (basic PBX) the interface looks
       like a simplified line interface with the standard "hd" event for
       off-hook:

         NTFY 3001 ds/ds1-3/6@gw-o.whatever.net MGCP 1.0
         X: 0123456789AF
         O: bl/hd

   Another alternative would have been to use an embedded request in the
   RQNT that resulted in this notify and combine that request with step
   A3.  Example - "ms" package:

         RQNT 2001 ds/ds1-3/6@gw-o.whatever.net MGCP 1.0
         X: 0123456789AF
         R: ms/sup(E(R(ms/inf, ms/rel))

   Step 3 could also be eliminated by the use of "loop" mode e.g.:

         RQNT 2001 ds/ds1-3/6@gw-o.whatever.net MGCP 1.0
         X: 0123456789AF
         Q:loop
         R: ms/sup, ms/inf, ms/rel

   This would result in both notifies occurring without requiring the
   RQNT in step A3.

   Step A2   The Call Agent sends an Ack:

         200 3001 OK

   Step A3   The Call Agent requests that digits be collected.  The
   approach used here depends on the type of  PBX interface.  For an MF
   interface the Call Agent requests that information digits be
   collected as follows:

         RQNT 2001 ds/ds1-3/6@gw-o.whatever.net MGCP 1.0
         X: 0123456789B0
         R: ms/inf, ms/rel

       The Call Agent also asks to be told if the trunk gets released
       for some reason ("rel" event) in the process of call setup
       (release event may be due to some signaling error for example).
       For DTMF trunks (wink-start, immediate start and Basic PBX), the
       request is based on a digit map so looks a bit different:

         RQNT 2001 ds/ds1-3/6@gw-o.whatever.net MGCP 1.0
         X: 0123456789B0
         R: d/[0-9*#T](D), dt/rel (bl/hd in the case of Basic PBX)



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         D: (xxxxxxx | x.[T#])
         S: dt/dl

         Note: the request to signal dial-tone may or may not be here
         depending on PBX interface requirement - bl/dl  required for
         Basic PBX;  dt/dl for some Immediate Start interfaces.

   Step A4   The gateway responds with an ack:

         200 2001 OK

   Step A5   Once the digits are collected the gateway notifies the call
   agent.  In the case of an MF interface, the resulting notify will
   look like the following

         NTFY 3002 ds/ds1-3/6@gw-o.whatever.net MGCP 1.0
         X: 0123456789B0
         O: ms/inf(k0,5,5,5,1,2,3,4,s0)

       In the case of a DTMF interface (including Basic PBX), it will
       look like the following:

         NTFY 3002 ds/ds1-3/6@gw-o.whatever.net MGCP 1.0
         X: 0123456789B0
         O: d/5,d/5,d/5,d/1,d/2,d/3,d/4

   Step A6   The Call Agent responds with an ack:

         200 3002 OK

   Step B1   The Call Agent now requests that a receive-only connection
   be made.

         CRCX 2002 ds/ds1-3/6@gw-o.whatever.net MGCP 1.0
         C: A7453949499
         L: a:PCMU,s:off,e:on
         M: recvonly
         X: 0123456789B1
         R: ms/rel (or dt/rel or bl/hu).

   Step B2   The Gateway acks with a connection ID and provides the SDP
   information:

         200 2002 OK
         I: 23474FE






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         v=0
         o=- A7453949499 0 IN IP4 128.96.41.1
         s=-
         c=IN IP4 128.96.41.1
         t=0 0
         m= audio 3456 RTP/AVP 0

   Step B3   The Call Agent passes this SDP information to the
   terminating gateway (GW-t) as part of the connection request:

         CRCX 4001 ds/ds1-5/3@gw-t.whatever.net MGCP 1.0
         C: A7453949499
         X: 45375840
         L: a:PCMU,s:off,e:on
         M: sendrecv

         v=0
         o=- A7453949499 0 IN IP4 128.96.41.1
         s=-
         c=IN IP4 128.96.41.1
         t=0 0
         m=audio 3456 RTP/AVP 0

   Note that the call setup on the terminating trunk can be done with
   this CRCX, although in this call flow - it is shown later (step C1).

   Step B4   The terminating gateway, responds with an ack and its SDP
   information:

         200 4001 OK
         I: 34738A

         v=0
         o=- A7453949499 0 IN IP4 47.123.34.33
         s=-
         c=IN IP4 47.123.34.33
         t=0 0
         m= audio 3456 RTP/AVP 0

   Step B5   Call Agent sends a modify connection request with
   connection mode receive-only to the origination gateway and includes
   the SDP information with the selected profile from the termination
   gateway.

         MDCX 2003 ds/ds1-3/6@gw-o.whatever.net MGCP 1.0
         C: A7453949499
         I: 34738A
         M: recvonly



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         v=0
         o=- A7453949499 0 IN IP4 47.123.34.33
         s=-
         c=IN IP4 47.123.34.33
         t=0 0
         m= audio 3456 RTP/AVP 0

   Step B6   The Gateway Acks the modify connection request

         200 2003 OK

   The following table shows the remainder of the call flow to set up
   the call except for Basic PBX (Basic PBX shown in) with details to
   follow.

 ---------------------------------------------------------------------
| Steps |        GW-o        |         CA         |        GW-t       |
|---------------------------------------------------------------------|
|  C1   |                RQNT [S: ms/sup, R: ms/oc, ms/rel, ms/ans] ->|
|  C2   |                                    <-  Ack                  |
|  C3   |                                    <- NTFY [O:ms/oc(ms/sup)]|
|  C4   |                                    Ack  ->                  |
|  C5   |                                    <- NTFY [O: ms/ans]      |
|  C6   |                                    Ack  ->                  |
|  C7   |    <-  MDCX [M:sendrecv, S: ms/ans, R: ms/rel]              |
|  C8   |                Ack  ->                                      |
|  C9   |                        RQNT[R: ms/sus] ->                   |
|  C10  |                                   <-  Ack                   |
 ---------------------------------------------------------------------

   Step C1   The Call Agent does a setup request to the terminating
   gateway The setup request for an MF PBX interface (wink start or
   immediate start) will be the following:

         RQNT 4002 ds/ds1-5/3@gw-t.whatever.net MGCP 1.0
         X: 45375841
         Q: loop
         S: ms/sup(addr(ko,5,5,5,1,2,3,4,s0))
         R: ms/oc, ms/rel, ms/ans

       Note that the result of the "sup" signal is the following
       sequence on the interface to the PBX:

       * off-hook -> PBX
       * wink  -> PBX (for wink-start trunks; for immediate start this
         part of the sequence does is not included)
       * Digits sent to PBX




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       For DTMF PBX interface (except Basic PBX), the only difference is
       that the MF start and end delimiters (k0 and s0) are not
       included:

         RQNT 4002 ds/ds1-5/3@gw-t.whatever.net MGCP 1.0
         X: 45375841
         Q: loop
         S: dt/sup(addr(5,5,5,1,2,3,4))
         R: dt/oc, dt/rel, dt/ans

       Basic PBX requires ringing and ring-back instead i.e.:

         RQNT 4002 ds/ds1-5/3@gw-t.whatever.net MGCP 1.0
         X: 45375841
         Q: loop
         S: bl/rg,bl/rt@34738A
         R: bl/oc,bl/hd

       In this case ringback will come from the gateway and will start
       immediately with the signal request for rt@connectionID.  It will
       end as soon as an event occurs (off-hook representing answer
       event) In the case of other PBX's, the ringback tone comes from
       the PBX so does not have to be generated by the gateway.

       Note that these requests could be done as easily at the same time
       as the connection request (B3) saving some post-dial delay time.

   Step C2   The gateway responds with an ack:

           200 4002 OK

   Step C3   Except  for the basic PBX, case (where digits are not
   outpulsed) when the digits have completed being sent out, the gateway
   will notify the fact by indicate that the operation is complete.

         NTFY 1001 ds/ds1-5/3@gw-t.whatever.net MGCP 1.0
         X: 45375841
         O: ms/oc(ms/sup) (or dt/oc(dt/sup))

   Step C4   The Call Agent acks the notify

         200 1001 OK

       In the case of the BL package, steps C3 and C4 will not exist.







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   Step C5    When an answer is obtained from the other end (off-hook
   from the PBX), the gateway sends a notify to indicate:

         NTFY 1002 ds/ds1-5/3@gw-t.whatever.net MGCP 1.0
         X: 45375841
         O: ms/ans (or dt/ans or bl/hd)

   Step C6   The Call Agent acks

         200 1002 OK

   Step C7   The Call Agent now sends a request to make the connection
   full duplex and indicates that the other end has answered the phone.

         MDCX 2004 ds/ds1-3/6@gw-o.whatever.net MGCP 1.0
         C: A7453949499
         X: 45375842
         I: 34738A
         M: sendrecv
         S: ms/ans ( or dt/ans but S: not included in the case where the
         originating gateway uses the BL package)

   Step C8   The Gateway acks the request

         200 2004 OK

   Step C9   The Call Agent sends a notification request to be told
   when the trunk to be released.

         RQNT 4003 ds/ds1-5/3@gw-t.whatever.net MGCP 1.0
         X: 45375842
         R: ms/rel,ms/sus (or R: dt/rel,dt/sus or R: bl/hu)

   Step C10  The gateway acks the request

         200 4003 OK

       The call is now setup.

5.1.2. Call Tear-Down

   Two cases are included here, one where the origination end initiates
   the release (section 5.1.2.1) and one where the termination end
   initiates the release (section 5.1.2.2).







Foster                       Informational                     [Page 34]

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5.1.2.1. Origination End Initiates the Release

   The following call flow shows an example where the origination end
   initiates the release for the "MS" package (similar for "DT"
   Package).

    --------------------------------------------------------------------
   | Steps |        GW-o        |         CA         |        GW-t       |
   |-------------------------------------------------------------------- |
   |  A1   |    NTFY[O: ms/rel]  ->                                      |
   |  A2   |                 <-  Ack                                     |
   |  A3   |                       RQNT [S: ms/rel, R: ms/rlc]  ->       |
   |  A4   |                                       <-  Ack               |
   |  A5   |                                    <- NTFY [O: ms/rlc]      |
   |  A6   |                                    Ack  ->                  |
   |  A7   |              <-  DLCX [S: ms/rlc, R: ms/sup]                |
   |  A8   |              Ack [perf info] ->                             |
   |  A9   |                            DLCX [R: ms/sup]->               |
   |  A10  |                                   <-  Ack [perf info]       |
    ---------------------------------------------------------------------

   The same call flow for the "BL" package is shown below

    ---------------------------------------------------------------------
   | Steps |        GW-o        |         CA         |        GW-t       |
   |---------------------------------------------------------------------|
   |  A1   |    NTFY[O: bl/hu]  ->                                       |
   |  A2   |                 <-  Ack                                     |
   |  A3   |                       RQNT [S: bl/dl, R: bl/hu]  ->         |
   |  A4   |                                       <-  Ack               |
   |  A5   |                                    <- NTFY [O: bl/hu]       |
   |  A6   |                                    Ack  ->                  |
   |  A7   |              <- DLCX [R: bl/hd]                             |
   |  A8   |              Ack [perf info] ->                             |
   |  A9   |                            DLCX [R: bl/hd]->                |
   |  A10  |                                   <-  Ack [perf info]       |
    ---------------------------------------------------------------------

   Step A1   The originating user goes on-hook resulting in a Notify
   from the gateway to indicate that the trunk is being released (reason
   indicating normal release)

         NTFY 3005 ds/ds1-3/6@gw-o.whatever.net MGCP 1.0
         X: 45375842
         O: ms/rel(0) (or dt/rel(0) or bl/hu)






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   Step A2   The Call Agent Acks the Notify

         200 3005 OK

   Step A3   The Call Agent sends a request to release the trunk.  (For
   all but Basic PBX.)

         RQNT 4004 ds/ds1-5/3@gw-t.whatever.net MGCP 1.0
         X: 45375843
         S: ms/rel (or dt/rel)
         R: ms/rlc (or dt/rlc)

       For the Basic PBX ("BL" package), dial-tone is played

         RQNT 4004 ds/ds1-5/3@gw-t.whatever.net MGCP 1.0
         X: 45375843
         S: bl/dl
         R: bl/hu

   Step A4   The Gateways acks the request

         200 4004 OK

   Step A5   The other end releases the call by going on-hook and a
   Notify is sent to the Call Agent to indicate that release is
   complete.

         NTFY 1004 ds/ds1-5/3@gw-t.whatever.net MGCP 1.0
         X: 45375843
         O: ms/rlc (or dt/rlc)

       In the case of Basic PBX, this is:

         NTFY 1004 ds/ds1-5/3@gw-o.whatever.net MGCP 1.0
         X: 45375843
         O: bl/hu

   Step A6   The Call Agent returns an Ack

         200 1004 OK











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   Step A7   The Call Agent sends a delete connection to the originating
   gateway with a request to do a release complete (which results in
   sending on-hook to the PBX).

         DLCX 4005 ds/ds1-5/3@gw-o.whatever.net MGCP 1.0
         X: 45375844
         I: 34738A
         S: ms/rlc (or dt/rlc)
         R: ms/sup (or dt/sup)

       Or in the case of Basic PBX ("BL" package):

         DLCX 4005 ds/ds1-5/3@gw-o.whatever.net MGCP 1.0
         X: 45375844
         I: 34738A
         R: bl/hd

   Step A8   The Gateway  Acks and provides performance information.

         250 4005 OK
         P: PS=1245, OS=62345, PR=0, OR=0, PL=0, JI=0, LA=48

   Step A9   The Call Agent sends a DLCX to the terminating gateway.

         DLCX 2004 ds/ds1-5/3@gw-t.whatever.net MGCP 1.0
         X: 0123456789B3
         I: 23474FE
         R: ms/sup (or dt/sup or bl/hd)

   Step A10  The gateway acks with performance information

         250 2004 OK
         P: PS=1245, OS=62345, PR=0, OR=0, PL=0, JI=0, LA=48


















Foster                       Informational                     [Page 37]

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5.1.2.2. Termination End Initiates the Release

   The following call flow gives an example of the terminating end
   releasing a call for all but Basic PBX ("MS" package - "DT" package
   is similar).

 ---------------------------------------------------------------------
| Steps |        GW-o        |         CA         |        GW-t       |
|---------------------------------------------------------------------|
|  A1   |                                      <-  NTFY[O: ms/sus]    |
|  A2   |                                      Ack  ->                |
|  A3   |        <-  RQNT [S: ms/sus, R: ms/rel ]                     |
|  A4   |            Ack  ->                                          |
|  A5   |                        RQNT [R:  ms/res]  ->                |
|  A6   |                                       <-  Ack               |
|  A7   |    NTFY [O:  ms/rel]  ->                                    |
|  A8   |                   <-  Ack                                   |
|  A9   |                   DLCX [S:  ms/rel, R:  ms/rlc] ->          |
|  A10  |                                   <-  Ack [perf info]       |
|  A11  |                                   <-  Notify [O:  ms/rlc]   |
|  A12  |                                 Ack   ->                    |
|  A13  |   <- DLCX [S:  ms/rlc, R: ms/sup ]                          |
|  A14  |     Ack [perf info]  ->                                     |
 ---------------------------------------------------------------------

   The following shows the same call flow but for Basic PBX.  There is
   no equivalent to steps A3-A6 and A11-A12 - so these are not included.

 ---------------------------------------------------------------------
| Steps |        GW-o        |         CA         |        GW-t       |
|---------------------------------------------------------------------|
|  A1   |                                      <-  NTFY[O: bl/hu]     |
|  A2   |                                      Ack  ->                |
|  A7   |    NTFY [O: bl/hu]  ->                                      |
|  A8   |                   <-  Ack                                   |
|  A9   |                                 DLCX [R: bl/hd] ->          |
|  A10  |                                   <-  Ack [perf info]       |
|  A13  |         <- DLCX [bl/hd]                                     |
|  A14  |     Ack [perf info]  ->                                     |
 ---------------------------------------------------------------------

   Step A1   An on-hook is received from the PBX.  In the case of all
   but the "BL" package, this results in a notify with event "sus" for
   suspend.







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   Step A2   The Call Agent returns an acknowledge

       The Call Agent starts a timer at this point (typically 10
       seconds).  If an off-hook is received from the PBX connected to
       GW-t before the origination side releases, the call is continued
       (this would appear as a "res" event  or "hd" in the case of Basic
       PBX interface).  If the origination side goes on-hook or the
       timer expires, then the call is torn down.

       Note that for Basic PBX (the "BL" package), steps A3 - A6 are
       missing (these steps do not exist for basic PBX).

   Step A3   A "sus" signal is sent to the originating side resulting in
   a on-hook being sent to the originating PBX.

   Step A4   GW-o acks the request.

   Step A5   The Call Agent sends a request to see off-hook  or resume
   ("res") events.

   Note: this depends on whether the Call Agent wants to do
   suspend/resume processing.  If not, the Call Agent may simply send
   "rel" along with DLCX to both ends.

   Step A6   GW-t acks the request.

   Step A7   An on-hook is received from the originating PBX resulting
   in a notify from GW-o with event "rel" ("hu" for Basic PBX
   interface).

   Step A8   The Call Agent "acks"

   Step A9   A delete connection is sent to the terminating gateway with
   signal "rel" which results in on-hook being sent to the terminating
   PBX (except for basic PBX - where there is no such signal)

   Step A10  GW-t acks the DLCX and provides performance information

       Steps A11 and A12  do not exist for the basic PBX case.

   Step A11  GW-t returns an "rlc" event

   Step A12  The Call Agent "acks" the notify

   Step A13  A delete connection is sent to the originating side (with
   signal "rlc" except in the case of the "BL" package).

   Step A14  GW-o returns an "ack" with performance information.



Foster                       Informational                     [Page 39]

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5.2. Example Call Flows - "DO" package

5.2.1. Call Setup Flows

   The following describes some PBX to PBX call.  The table gives an
   overview of the initial part of the call flow with details to follow.

 ---------------------------------------------------------------------
| Steps |        GW-o        |         CA         |        GW-t       |
|---------------------------------------------------------------------|
|  A1   |       NTFY[O: do/rg] ->                                     |
|  A2   |                <-  Ack                                      |
|  B1   |              <- CRCX [S: do/hd, R: do/rel, M:recvonly, LCO] |
|  B2   |          Ack[SDP1]  ->                                      |
|  B3   |                     CRCX [M:sendrecv, LCO, SDP1] ->         |
|  B4   |                                 <- Ack [SDP2]               |
|  B5   |                 <-  MDCX [recvonly,SDP2]                    |
|  B6   |                 Ack  ->                                     |
|  C1   |                RQNT [S: do/sup, R: do/oc] ->                |
|  C2   |                                    <-  Ack                  |
|  C3   |                                    <- NTFY [O:do/oc(do/sup)]|
|  C4   |                                    Ack  ->                  |
|  C5   |    <-  MDCX [M:sendrecv, R: do/rel]                         |
|  C6   |                Ack  ->                                      |
|  C7   |                        RQNT[R: do/rel] ->                   |
|  C8   |                                   <-  Ack                   |
 ---------------------------------------------------------------------

   Step A1   PBX rings results in a notify to the Call Agent indicating
   the start of a call setup:

         NTFY 3001 aaln/0@gw-o.whatever.net MGCP 1.0
         X: 0123456789AF
         O: do/rg

   Step A2   The Call Agent sends an Ack:

   Step B1   The Call Agent now requests that a receive-only connection
   be made.

       If the endpoint is running FXO ground-start, the call would also
       request detection of disconnect supervision from the PBX (R:
       do/rel) and should send an off-hook (S: do/hd) in response to
       ringing.

   Step B2   The Gateway acks with a connection ID and provides the SDP
   information.




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   Step B3   The Call Agent passes this SDP information to the
   terminating gateway (GW-t) as part of the connection request.

   Step B4   The terminating gateway, responds with an ack and its SDP
   information.

   Step B5   Call Agent sends a modify connection request with
   connection mode receive-only to the origination gateway and includes
   the SDP information with the selected profile from the termination
   gateway.

   Step B6   The Gateway Acks the modify connection request

   Step C1   The Call Agent does a setup request to the terminating
   gateway The setup request will be the following:

         RQNT 4002 aaln/0@gw-t.whatever.net MGCP 1.0
         X: 45375841
         S: do/sup(addr(5,5,5,1,2,3,4))
         R: do/oc

       Note that the result of the "sup" signal is the following
       sequence on the interface to the PBX:

       * off-hook -> PBX
       * tip-ground <- PBX (for loop-start this step does not apply)
       * digits sent to PBX

   Step C2   The gateway responds with an ack:

         200 4002 OK

   Step C3   When the digits have been completely sent out, the gateway
   will notify the fact by indicate that the operation is complete.

         NTFY 1001 aaln/0@gw-t.whatever.net MGCP 1.0
         X: 45375841
         O: do/oc(do/sup)

   Step C4   The Call Agent acks the notify

         200 1001 OK









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   Step C5   The Call Agent now sends a request to make the connection
   full duplex and indicates that the other end has answered the phone.

       If the endpoint is running FXO ground-start, the call would also
       requests detection of disconnect supervision from the PBX
       (R:do/rel)

   Step C6   The Gateway acks the request

   Step C7   If the endpoint is running FXO ground-start, the Call Agent
   sends a notification request to be told  when the trunk to be
   released (R: do/rel).  This step and step C8 are not needed if the
   endpoint is running FXO loop-start.

   Step C8   The gateway acks the request and the call is now setup.

5.2.2. Call Tear-Down

   If the endpoint is running FXO loop-start, the PBX cannot
   initiate call release.  In this case, call release is always
   initiated by the Media Gateway by going onhook.  Disconnect
   supervision from the PBX is provided only for FXO ground-start.
   However, it does not matter whether the origination end or the
   termination end initiates the release.  The call flows for either
   case are the same.  Therefore, only the case where the origination
   end initiates the release is illustrated in this section.

 ---------------------------------------------------------------------
| Steps |        GW-o        |         CA         |        GW-t       |
|---------------------------------------------------------------------|
|  A1   |    NTFY[O: do/rel]  ->                                      |
|  A2   |                 <-  Ack                                     |
|  A3   |                       RQNT [S: do/hu, R: do/rlc]  ->        |
|  A4   |                                       <-  Ack               |
|  A5   |                                    <- NTFY [O: do/rlc]      |
|  A6   |                                    Ack  ->                  |
|  A7   |              <-  DLCX [S: hu, R: rg]                        |
|  A8   |              Ack [perf info] ->                             |
|  A9   |                            DLCX [R: do/rg]->                |
|  A10  |                                   <-  Ack [perf info]       |
 ---------------------------------------------------------------------










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   Step A1   The originating PBX goes on-hook resulting in a Notify from
   the gateway to indicate that the trunk is being released (reason
   indicating normal release).

         NTFY 3005 aaln/0@gw-o.whatever.net MGCP 1.0
         X: 45375842
         O: do/rel(0)

   Step A2   The Call Agent Acks the Notify

         200 3005 OK

   Step A3   The Call Agent sends a request to release the trunk.

   Step A4   The Gateways acks the request

   Step A5   PBX at the terminating end releases the call by releasing
   tip-ground and a Notify is then sent to the Call Agent to indicate
   that release is complete.

       Note that there is no ground signal in case of loop-start.
       However, this NTFY message is still generated as soon as hu
       signal is applied.

   Step A6   The Call Agent returns an Ack

   Step A7   The Call Agent sends a delete connection to the originating
   gateway with a request to go onhook.

   Step A8   The Gateway  Acks and provides performance information.

   Step A9   The Call Agent sends a DLCX to the terminating gateway.

   Step A10  The gateway acks with performance information

















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5.3. Example Call Setup - "MD" Package

   The following describes Feature Group D call setup  using the "MD"
   package.  The table gives an overview of the initial part of the call
   flow with details to follow.

 ---------------------------------------------------------------------
| Steps |        GW-o        |         CA         |        GW-t       |
|---------------------------------------------------------------------|
|  A1   |       NTFY[O:md/sup] ->                                     |
|  A2   |                 <-  Ack                                     |
|  A3   | NTFY[O:md/inf(<id>)] ->                                     |
|  A4   |                 <- Ack                                      |
|  A5   | NTFY[O:md/inf(<addr>)] ->                                   |
|  A6   |                <-  Ack                                      |
|  B1   |                <- CRCX [M:recvonly, LCO, R: md/rel]         |
|  B2   |          Ack[SDP1]  ->                                      |
|  B3   |                     CRCX [M:sendrecv, LCO, SDP1] ->         |
|  B4   |                                 <- Ack [SDP2]               |
|  B5   |                 <-  MDCX [recvonly,SDP2]                    |
|  B6   |                 Ack  ->                                     |
 ---------------------------------------------------------------------

   The assumption is that prior to the initial "notify", the Call Agent
   has sent a request to be informed of "sup" and "inf" events using
   quarantine handling "Q: loop".

   Step A1   Trunk seizure results in a notify to the Call Agent
   indicating the start of a call setup:

         NTFY 3001 ds/ds1-3/6@mgw45.whatever.net MGCP 1.0
         X: 0123456789B0
         O: md/sup

   Step A2   The Call Agent sends an Ack.

   Step A3   Once the digits for the identification field are collected
   the gateway notifies the call agent:

         NTFY 3002 ds/ds1-3/6@mgw45.whatever.net MGCP 1.0
         X: 0123456789B0
         O: md/inf(k0,0,0,4,0,8,5,5,5,1,2,3,4,s0)

   Step A4   The Call Agent responds with an ack.







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   Step A5   When the digits are collected for the address field,
   another notify is sent:

         NTFY 3003 ds/ds1-3/6@mgw45.whatever.net MGCP 1.0
         X: 0123456789B0
         O: md/inf(k0,5,1,2,5,5,5,4,5,6,7,s0)

   Step A6   The Call Agent "acks"

   Step B1   Create connection - receive only:

         CRCX 2002 ds/ds1-3/6@mgw45.whatever.net MGCP 1.0
         C: A3C47F21456789F1
         L: p:10, a:PCMU
         M: sendrecv
         X: 0123456789B1
         R: md/rel

   Step B2   The Gateway "acks" the request and provides connection ID
   and SDP information.

   Step B3   The Call Agent passes this SDP information to the
   terminating gateway (GW-t) as part of the connection request.

   Step B4   The terminating gateway, responds with an ack and its SDP
   information.

   Step B5   Call Agent sends a modify connection request with
   connection mode receive-only to the origination gateway and includes
   the SDP information with the selected profile from the termination
   gateway.

   Step B6   The Gateway Acks the modify connection request.


















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   In the case of EAIN signaling there is some additional information
   provided so that this initial part of the call setup looks slightly
   different:

 ---------------------------------------------------------------------
| Steps |        GW-o        |         CA         |        GW-t       |
|---------------------------------------------------------------------|
|  A1   |       NTFY[O:md/sup] ->                                     |
|  A2   |                 <-  Ack                                     |
|  A3   | NTFY[O:md/inf(<ca>)] ->                                     |
|  A4   |                 <- Ack                                      |
|  A5   |      <- RQNT[S:md/cwk, R:md/inf,md/rel]                     |
|  A6   |                <-  Ack                                      |
|  A7   | NTFY[O:md/inf(<id>)] ->                                     |
|  A8   |                 <- Ack                                      |
|  A9   | NTFY[O:md/inf(<addr>)] ->                                   |
|  A10  |                <-  Ack                                      |
|  B1   |                <- CRCX [M:recvonly, LCO, R: md/rel]         |
|  B2   |          Ack[SDP1]  ->                                      |
|  B3   |                     CRCX [M:sendrecv, LCO, SDP1] ->         |
|  B4   |                                 <- Ack [SDP2]               |
|  B5   |                 <-  MDCX [recvonly,SDP2]                    |
|  B6   |                 Ack  ->                                     |
 ---------------------------------------------------------------------

   The assumption is that prior to the initial "notify", the Call Agent
   has sent a request to be informed of "sup" and "inf" events using
   quarantine handling "Q: loop".

   Step A1   Trunk  seizure results in a notify to the Call Agent
   indicating the start of a call setup:

         NTFY 3001 ds/ds1-3/6@mgw45.whatever.net MGCP 1.0
         X: 0123456789B0
         O: md/sup

   Step A2   The Call Agent sends an Ack

   Step A3   The initial digit string contains the country address
   field:

         NTFY 3002 ds/ds1-3/6@mgw45.whatever.net MGCP 1.0
         X: 0123456789B0
         O: md/inf(k0,1,3,8,9,9,0,0,1,9,s0)

   Step A4   The Call Agent responds with an ack





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   Step A5   The Call Agent does processing on the country address field
   and sends a request to initiate further input (sends a continue
   wink):

         RQNT 2002 ds/*@mgw45.whatever.net MGCP 1.0
         X: 0123456789B1
         Q: loop
         R: md/inf,md/rel
         S: md/cwk

   Step A6   The Gateway "acks" the request.

   Step A7   Once the digits for the identification field are collected
   the gateway notifies the call agent:

         NTFY 3003 ds/ds1-3/6@mgw45.whatever.net MGCP 1.0
         X: 0123456789B0
         O: md/inf(k0,0,0,4,0,8,5,5,5,1,2,3,4,s0)

   Step A8   The Call Agent responds with an ack

   Step A9   When the digits are collected for the address field,
   another notify is sent:

         NTFY 3004 ds/ds1-3/6@mgw45.whatever.net MGCP 1.0
         X: 0123456789B0
         O: md/inf(k0,5,1,2,5,5,5,4,5,6,7,s0)

   Step A10  The Call Agent "acks"

   Step B1   Create connection - receive only:

         CRCX 2002 ds/ds1-3/6@mgw45.whatever.net MGCP 1.0
         C: A3C47F21456789F1
         L: p:10, a:PCMU
         M: sendrecv
         X: 0123456789B1
         R: md/rel

   Step B2   The Gateway "acks" the request and provides connection ID
   and SDP information

   Step B3   The Call Agent passes this SDP information to the
   terminating gateway (GW-t) as part of the connection request.

   Step B4   The terminating gateway, responds with an ack and its SDP
   information




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   Step B5   Call Agent sends a modify connection request with
   connection mode receive-only to the origination gateway and includes
   the SDP information with the selected profile from the termination
   gateway.

   Step B6   The Gateway Acks the modify connection request

   The following table shows the remainder of the call flow to set up
   the call for FGD EANA.

 ---------------------------------------------------------------------
| Steps |        GW-o        |         CA         |        GW-t       |
|---------------------------------------------------------------------|
|  C1   |       RQNT [S:sup, R:md/swk,md/oc, md/rel,md/awk, md/ans] ->|
|  C2   |                                    <-  Ack                  |
|  C3   |                                    <- NTFY [O:md/swk)]      |
|  C4   |                                    Ack  ->                  |
|  C5   |                                    <- NTFY [O:md/oc(md/sup)]|
|  C6   |                                    Ack  ->                  |
|  C7   |                                    <- NTFY [O:md/awk)]      |
|  C8   |                                    Ack  ->                  |
|  C9   |                  <- RQNT[S:md/awk]                          |
|  C10  |               Ack  ->                                       |
|  C11  |                                    <- NTFY [O: md/ans]      |
|  C12  |                                    Ack  ->                  |
|  C13  |    <-  MDCX [M:sendrecv, S: md/ans, R: md/rel]              |
|  C14  |                Ack  ->                                      |
|  C15  |                   RQNT [R: md/sus, md/rel] ->               |
|  C16  |                                    <-  Ack                  |
 ---------------------------------------------------------------------

   Step C1   The Call Agent does a setup request to the terminating
   gateway The setup request for an MF EANA FGD interface will be the
   following:

         RQNT 2001 ds/ds1-5/3@gw-t.whatever.net MGCP 1.0
         X: 45375841
         Q: loop
         S:
         md/sup(ct(nda),addr(k0,5,5,5,5,2,2,1,2,3,4,s0),id(k0,0,5,5,5,1,
         2,3,4,s2))
         R: md/swk,md/oc,md/rel,md/awk,md/ans









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       Note that the result of the "sup" signal is the following
       sequence on the interface to the PBX:

       * off-hook -> SCN
       * wink <- SCN
       * caller ID digits sent to SCN
       * address digits sent to SCN

   Step C2   The gateway responds with an ack

   Step C3   "Notify" the CA that the start of signaling has occurred
   (incoming wink start has occurred) i.e.:

         NTFY 3000 ds/ds1-3/6@mgw45.whatever.net MGCP 1.0
         X: 0123456789B0
         O: md/swk

   Step C4   The Call Agent "acks".

   Step C5   "Notify" that out-pulsing is complete:

         NTFY 3001 ds/ds1-3/6@mgw45.whatever.net MGCP 1.0
         X: 0123456789B0
         O: md/oc(md/sup)

   Step C6   The Call Agent "acks".

   Step C7   "Notify" that the acknowledgement wink has been received:

         NTFY 3002 ds/ds1-3/6@mgw45.whatever.net MGCP 1.0
         X: 0123456789B0
         O: md/awk

   Step C8   The Call Agent "acks".

   Step C9   The acknowledge wink is passed to the originating gateway:

         RQNT 2001 ds/ds1-5/3@gw-t.whatever.net MGCP 1.0
         X: 45375842
         S: md/awk
         R: md/rel

   Step C10  GW-o "acks".








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   Step C11  "Notify" off-hook event (the person at the other end has
   answered):

         NTFY 3003 ds/ds1-3/6@mgw45.whatever.net MGCP 1.0
         X: 0123456789B0
         O: md/ans

   Step C12  The Call Agent "acks".

   Step C13  The Call Agent now sends a request to make the connection
   full duplex and indicates that the other end has answered the phone
   (S: ans sent)

   Step C14  The Gateway acks the request

       In the case of FGD EAIN, there is an additional digits string
       (country address and/or carrier access code that has to be
       included so that step C1 looks like the following in a case where
       there is no overlapped sending:

         RQNT 2001 ds/ds1-5/3@gw-t.whatever.net MGCP 1.0
         X: 45375841
         Q: loop
         S:md/sup(ct(nta),ca(k0,1,3,8,9,9,0,0,1,0,s0),id(k0,
         0,5,5,5,1,2,3,4,s0),addr(ko,0,1,1,3,8,1,2,3,4,7,6,5,s0))
         R: md/swk,md/oc,md/rel,md/awk,md/ans

       If overlapped sending is done, only the country address and
       caller ID digit strings are sent out in step C1:

         RQNT 2001 ds/ds1-5/3@gw-t.whatever.net MGCP 1.0

         X: 45375841
         Q: loop
         S:md/sup(ct(nta),ca(k0,1,3,8,9,9,0,0,1,0,s0),id(k0,0,
         5,5,5,1,2,3,4,s0))
         R: md/swk,md/oc,md/rel,md/ans

       Then after these digits go out indicated by event "oc(sup)" in
       step C5, and as soon as the Call Agent has the address
       information, it sends it out using the "inf" signal:

         RQNT 2002 ds/ds1-3/6@mgw45.whatever.net MGCP 1.0
         X: 0123456789B1
         Q: loop
         R: md/oc,md/rel,md/awk,md/ans
         S: md/inf(ko,0,1,1,3,8,1,2,3,4,7,6,5,s0)




Foster                       Informational                     [Page 50]

RFC 3064                   MGCP CAS Packages               February 2001


       The Call Agent will then get a further "md/oc(md/sup)" event when
       these digits have gone out.

   Step C15  The Call Agent requests to be told of on-hook ("sus")
   events
           or abnormal release ("rel") events.

   Step C16  The gateway "acks" the request.

5.4. Example Call Setup - "MO" Package

   The following describes Feature Group D operator services signaling
   call setup (911 call) using the "MO" package.  The table gives an
   overview of the initial part of the call flow with details to follow.
   In this case GW-o is a residential gateway using the line package and
   GW-t connects to the E911 tandem.

 ---------------------------------------------------------------------
| Steps |        GW-o        |         CA         |        GW-t       |
|---------------------------------------------------------------------|
|  A1   |       NTFY[O:hd] ->                                         |
|  A2   |                 <-  Ack                                     |
|  A3   | <- RQNT S: dl, R: [0-9*#T](D)                               |
|  A4   |                 Ack ->                                      |
|  A5   |      NTFY[O: 9,1,1] ->                                      |
|  A6   |                <-  Ack                                      |
|  B1   |                <- CRCX [M:recvonly, R: hu]                  |
|  B2   |          Ack[SDP1]  ->                                      |
|  B3   |                  CRCX [M:sendrecv, LCO, SDP1, S: mo/sup] -> |
|  B4   |                                 <- Ack [SDP2]               |
|  B5   |                                 <- NTFY [O: oc(sup)]        |
|  B6   |                                 Ack  ->                     |
|  B5   |                 <-  MDCX [sendrecv,SDP2]                    |
|  B6   |                 Ack  ->                                     |
 ---------------------------------------------------------------------

  Note: the originating side in this case is a line-side gateway.

   Step A1   The user goes off-hook:

         NTFY 3001 aaln/1@gw-o.whatever.net MGCP 1.0
         X: 0123456789AF
         O: l/hd

   Step A2   The Call Agent sends an Ack:

         200 3001 OK




Foster                       Informational                     [Page 51]

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   Step A3   The Call Agent sends dial-tone and requests that digits be
   collected:

         RQNT 2001 aaln/1@gw-o.whatever.net MGCP 1.0
         X: 0123456789B0
         S: l/dl
         R: d/[0-9#*T](D), hu

   Step A4   The gateway responds with an ack:

         200 2001 OK

   Step A5   Once the digits are collected the gateway notifies the Call
   Agent.  In this case, it is a 911 call

         NTFY 3002 aaln/1@gw-o.whatever.net MGCP 1.0
         X: 0123456789B0
         O: d/9,d/1,d/1

   Step A6   The Call Agent responds with an ack:

         200 3002 OK

   Step B1   The Call Agent now requests that a receive-only connection
   be made.

         CRCX 2002 ds/ds1-3/6@gw-o.whatever.net MGCP 1.0
         C: A7453949499
         L: a:PCMU,s:off,e:on
         M: recvonly
         X: 0123456789B1
         R: l/hu.

   Step B2   The Gateway acks with a connection ID and provides the SDP
   information:

         200 2002 OK
         I: 23474FE

         v=0
         o=- A7453949499 0 IN IP4 128.96.41.1
         s=-
         c=IN IP4 128.96.41.1
         t=0 0
         m= audio 3456 RTP/AVP 0






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   Step B3   The Call Agent passes this SDP information to the
   terminating gateway (GW-t) as part of the connection request and does
   a call setup request at the same time:

         CRCX 4001 ds/ds1-5/3@gw-t.whatever.net MGCP 1.0
         C: A7453949499
         X: 45375840
         L: a:PCMU,s:off,e:on
         M: sendrecv
         Q: loop
         R: oc, rel, orbk
         S: sup(addr(k0,9,1,1,s2),id(k0,0,8,3,4,5,6,7,8,s0))

         v=0
         o=- A7453949499 0 IN IP4 128.96.41.1
         s=-
         c=IN IP4 128.96.41.1
         t=0 0
         m=audio 3456 RTP/AVP 0

   As a result of this request, the following signaling interactions
   will occur between GW-t and the Switched Circuit Network (SCN - in
   this case, the E911 tandem):

       * Off-hook -> SCN
       * Wink     <- SCN
       * k0,9,1,1,s2 -> SCN
       * Off-hook    <- SCN
       * k0,0,8,3,4,5,6,7,8,s0

       Note that off-hook from the SCN is part of the protocol (a
       request for the caller ID) and does not provide an indication of
       whether the operator answered or not.

   Step B4   The terminating gateway, responds with an ack and its SDP
   information:

         200 4001 OK
         I: 34738A

         v=0
         o=- A7453949499 0 IN IP4 47.123.34.33
         s=-
         c=IN IP4 47.123.34.33
         t=0 0
         m= audio 3456 RTP/AVP 0





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   Step B5   The Call Agent will get a further notify when outpulsing of
   all of the digits is complete.

         NTFY 3003 aaln/1@gw-o.whatever.net MGCP 1.0

         X: 45375840
         O: oc(sup)

   Step B6   The Call Agent returns an "ack"

         200 3003 OK

   Step B7   Call Agent sends a modify connection request with
   connection mode receive-only to the origination gateway and includes
   the SDP information with the selected profile from the termination
   gateway.

         MDCX 2003 ds/ds1-3/6@gw-o.whatever.net MGCP 1.0
         C: A7453949499
         I: 34738A
         M: sendrecv

         v=0
         o=- A7453949499 0 IN IP4 47.123.34.33
         s=-
         c=IN IP4 47.123.34.33
         t=0 0
         m= audio 3456 RTP/AVP 0

   Step B8   The Gateway Acks the modify connection request

         200 2003 OK

   The call is now established between the user and the operator.

Acknowledgements

   The source for some these packages are Flemming Andreasen, Wai-Tak
   Siu - Cisco Systems, and Don Stanwyck - IP Unity.  Special thanks to
   Joe Clark, Telcordia Technologies for his CAS interface expertise.
   Also thanks to all the reviewers for all their comments, including
   but not limited to the following people: Charles Eckel, Cisco
   Systems; Jerry Kamitses, Sonus Networks.








Foster                       Informational                     [Page 54]

RFC 3064                   MGCP CAS Packages               February 2001


References

   [1] Arango, M., Dugan, A., Elliott, I., Huitema, C. and S. Pickett,
       "Media Gateway Control Protocol (MGCP) Version 1.0", RFC 2705,
       October 1999.

   [2] Handley, M. and V. Jacobson, "SDP: Session Description Protocol",
       RFC 2327, April 1998.

   [3] Bellcore, Compatibility Information for Feature Group D Switched
       Access Service, TR-NPL-000258, Issue 1, October 1985.

   [4] Bellcore, Interoffice LATA Switching Systems Generic Requirements
       (LSSGR): Verification Connections (25-05-0903), TR-TSY-000531,
       Issue 2, July 1987.

   [5] Bellcore, LSSGR: Signaling for Analog Interfaces, GR-506-CORE,
       Issue 1, June 1996.

   [6] PacketCableTM PSTN Gateway Call Signaling Protocol Specification,
       Pkt-SP-TGCP-I01-991201

Author's Address

   Bill Foster
   170 West Tasman Dr
   San Jose, CA, 95134


   Phone: 408-527-8791
   EMail: bfoster@cisco.com




















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Full Copyright Statement

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
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   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
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   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















Foster                       Informational                     [Page 56]


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