RFC3064 - MGCP CAS Packages

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.

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.

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

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.

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.

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

--------------------------------------------------

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-startBi-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.

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,

- "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.

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

---------------------------------------------------------------------

CodeDescription EventSignal 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

---------------------------------------------------------------------

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

---------------------------------------------------------------------

CodeDescription EventSignal 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

---------------------------------------------------------------------

CodeDescription EventSignal 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 -

relRelease - 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

---------------------------------------------------------------------

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

---------------------------------------------------------------------

CodeDescription EventSignal 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

---------------------------------------------------------------------

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

---------------------------------------------------------------------

CodeDescription EventSignal 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 -

---------------------------------------------------------------------

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

---------------------------------------------------------------------

CodeDescription EventSignal Additional Info

---------------------------------------------------------------------

ans Call Answer !Note P -

oc Operation Complete x -

of Operation Fail x -

orbkOperator 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

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.

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:

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)

O: bl/oc(bl/rg)

When the operation complete event is requested, it cannot be

parameterized with any event parameters.

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)

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.

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).

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.

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.

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

------------------------------------------------------------------

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.

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.

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.

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.

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.

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.

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)

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)

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

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

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

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.

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).

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)

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

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

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.

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.

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.

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

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]

---------------------------------------------------------------------

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

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.

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.

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

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

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

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

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".

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)

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

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

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

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.

References

[1] Arango, M., Dugan, A., Elliott, I., Huitema, C. and S. Pickett,

"Media Gateway Control Protocol (MGCP) Version 1.0", RFC2705,

October 1999.

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

RFC2327, 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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