Media Gateway Control and the Softswitch Architecture

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Media Gateway Control and the

Softswitch Architecture

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Outline

n

Introduction

n

Softswitch

n Softswitch Architecture

n Softswitch Operations

n

Media Gateway Control Protocols

n MGCP

n MEGACO

(3)

Next Generation Network

n Internet Telecom & Wireless Communication

IP

MGCF CSCF

T-SGW MGW MGW

WLAN GPRS

CSCF SIP

Server

PSTN

Internet

Wireless ^App.

Server 3rd Parties App.

(4)

Gateways in Next Generation Networks

MGC : Media Gateway Controller SG : Signaling Gateway

TGW : Trunking Gateway RGW : Residential Gateway

CO SCP STP

PBX

H.323 GK SS7/IN

PSTN IP Networks

SG

TGW

H.323 MG

MGC

MGCP/MEGACO H.323/SIP

SIGTRAN RTP/RTCP Analog Line

Trunk

MGCP/MEGACO Phones RGW

H.323 Phones

(5)

H323, SIP & MGCP, MEGACO

GK GW

MCU

GW : Gateway GK : Gatekeeper TN : Terminal

TN

PSTN CA

TGW RGW

CA : Call Agent

TGW : Trunking Gateway RGW : Residential Gateway SG : Singling Gateway

SS7

PSTN CO

SG

RTP MGCP

H.323 TN

TN

GW GK

MCU

TN

TN TN

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H323, SIP & MGCP/MEGACO

n H.323 , SIP

n peer-to-peer

n internet oriented

n intelligent endpoint

n optional GK

n decentralized

n Problems

n maintenance

n cost & scalability of large systems

n signaling & media control are coupled

n interoperability with

SS7

n MGCP/MEGACO

n client-server

n traditional telephony

n intelligent server

n “dumb” terminal

n centralized

n

Concept

n gateway decomposed

n separate call control from media ports

n CA (MGC), MG, SG

n interoperability with PSTN

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Class 5

End Office Switch

The Telephone Network [1/2]

Circuit Switched Network Intelligent

Peripheral

Signal Transfer Point

Service Control Point

Class 4

Tandem Switch

Service Data Point +

Transport Layer Control Layer SS7 Signaling

ISUP Messages

INAP/TCAP Messages

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The Telephone Network [2/2]

n

5 Basic Components in Intelligent Networks

n SSP/Service Switching Point

n switching, signaling, routing, service invocation

n STP/Service Transfer Point

n signaling, routing

n SCP/Service Control Point

n service logic execution

n SDP/Service Data Point

n subscriber data storage, access

n IP/Intelligent Peripheral

n resources such as customized voice announcement, voice recognition, DTMF digit collection

SSPSSP

SCPSCP

SDPSDP

STPSTP IPIP

SSPSSP STPSTP

TCAP messages

ISUP messages Voice

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Softswitch

n

The switching functions are handled by software

n

International Softswitch Consortium (ISC)

n www.softswitch.org

n To promote the softswitch concept and related technologies

n

Why the softswitch approach is popular?

n A distributed architecture

n For network operators

n It is possible to use different network components from different vendors.

n For equipment vendors

It is possible to focus on one area.

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Abstract Softswitch Architecture

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Softswitch/PSTN Interworking

n SIP is often used as the signaling protocol between the MGCs.

Mo d em Ban k

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Softswitch Overview [1/3]

n

Softswitch:

Emulating Circuit Switching in Software

IN/SCP

PSTN Local Switch PSTN

Local Switch

STP SS7 Network

IP Network

RTP Streams MGC

MGC MGCMGC

Trunk Trunk Gateway

Gateway Trunk Trunk

Gateway Gateway SIP-T

SG SG SG

SG SIGTRAN

MEGACO

IP Phone IP Phone

9000

9000 Personalized VoIP Service System

Application Server Application Server

(13)

Softswitch Overview [2/3]

n

Softswitch Provides Open Layered Architecture

• Solutions in a proprietary box

• Expensive

• Little room for innovation

Circuit-Switched

Transport Hardware Call Control

& Switching Services &

Applications

P R O P R I E T A R Y

• Solutions are open standards-based

• Customers choose best-in-class products

• Open standards enable lower cost for innovation

Soft-Switched

Transport Hardware Softswitch Call Control Services, Applications &

Features (Management, Provisioning and

Back Office)

Open Protocols APIs

Open APIs for 3rd Party App develop.

Best-in-class Access Devices.

Scalable,

Open Interfaces for Comm.

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Softswitch Overview [3/3]

n

Softswitch Changes the Telecom Landscape

n Integration/Incorporation

n Convergence of voice and data

n Combination of telecom & internet technologies

n Reuse PSTN database & IN services in packet networks

n Multiple sources for app development & deployment

n Decreased operating costs

n Standardization

n Standard interfaces (protocols) for communications

n Open standards (APIs) for service creation

n Customized services created by users themselves

n Better scalability

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Softswitch Architecture

CO Switch

STP SCP

CO Switch

STP SCP

Signaling Layer Transport Layer IP

SIP-T

Media Server

RTP SIP-?/

MGCP

SIP-TSI

Media Gateway Controller

MGCP/

MEGACO Phones

App.

Server

SIGTRAN SSA/SCTP

MGCP/MEGACO

Trunking Gateway Signaling

(SS7) Gateway

SS7 TCAP

ISUP/TCAP

(16)

Local Switch

STP

SCP

STP STP STP

Local Switch STP

Routing Directory

Softswitch Operations [1/3]

n

Basic Call Control

12 ISUP ACM 13 ISUP

ANM ISUP ACM

ISUP ANM

ISUP IAM ISUP IAM

1

2 3

4 5

6 7

8

9 10

14

11 SIGTRAN

MGCP/MEGACO

Voice Voice

RTP

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Softswitch Operations [2/3]

n

Inter-Softswitch Communications

STP

Trunking Gateway

STP

Signaling (SS7) Gateway

STP STP

Domain A Domain B

Local Switch Routing

Directory 3

1

5 2

ISUP IAM

4

SIGTRAN

MGCP/MEGACO

6 SIP-T

7

9

16 Voice

RTP

8

ISUP IAM 12

13 Voice

10

11

14 ISUP ACM 15 ISUP

ISUP ANM

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Softswitch Operations [3/3]

n

IP-PSTN Interworking for IN Services

STP

SCP

STP STP STP

Local Switch STP

Routing Directory

ISUP IAM ISUP IAM

1

2

3

4

7

8 9

10

11 12

13 SIGTRAN

MGCP/MEGACO

Voice Voice

RTP 5

INAP/TCAP

16 6

14 ISUP ACM 15 ISUP

ISUP ANM

(19)

Introduction

n

Voice over IP

n Lower cost of network implementation

n Integration of voice and data applications

n New service features

n Reduced bandwidth

n

Replacing all traditional circuit-switched networks is not feasible.

n

VoIP and circuit-switching networks coexist

n Interoperation

n Seamless interworking

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Separation of Media and Call Control

n

Gateways

n Interworking

n To make the VoIP network appear to the circuit switched network as a native circuit-switched system and vice versa

n

Signaling path and media path are different in VoIP systems.

n Media – directly (end-to-end)

n Signaling – through H.323 gatekeepers (or SIP proxies)

n

SS7, Signaling System 7

n The logical separation of signaling and media

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Separation of Media and Call Control

n A network gateway has two related but separate functions.

n Signaling conversion

n The call-control entities use signaling to communicate.

n Media conversion

n A slave function (mastered by call-control entities)

n Figure 6-1 illustrates the separation of call control and signaling from the media path.

(22)

Separation of Media and Call Control

n

Advantages of Separation

n Media conversion close to the traffic source and sink

n The call-handling functions is centralized.

n A call agent (media gateway controller - MGC) can control multiple gateways.

n New features can be added more quickly.

n

MGCP, Media Gateway Control Protocol

n IETF

n

MEGACO/H.248

n IETF and ITU-T Study Group 16

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Requirements for Media Gateway Control [1/2]

n

RFC 2895

n Media Gateway Control Protocol Architecture and Requirements

n

Requirement

n The creation, modification and deletion of media streams

n Including the capability to negotiate the media formats

n The specification of the transformations applied to media streams

n Request the MG to report the occurrence of

specified events within the media streams, and the corresponding actions

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Requirements for Media Gateway Control [2/2]

n Request the MG to apply tones or announcements

n The establishment of media streams according to certain QoS requirements

n Reporting QoS and billing/accounting statistics from an MG to an MGC

n The management of associations between an MG and an MGC

n In the case of failure of a primary MGC

n A flexible and scalable architecture in which an MGC can control different MGs

n Facilitate the independent upgrade of MGs and MGCs

(25)

Protocols for Media Gateway Control

n The first protocol is MGCP

n RFC 2705, informational

n To be succeeded by MEGACO/H.248

n Has be included in several product developments

n MEGACO/H.248

n A standards-track protocol

n RFC 3015 is now the official version.

IPDC SGCP

MGCP

MEGACO

Telcodia (Bellcore)

Level 3 Communication

Lucent (by ITU-T)

IETF RFC 3015 ITU-T H.248 November 2000 IETF RFC 2705

October 1999

MGCP 1.0

IETF RFC 3435 January 2003

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Relation with H.323/SIP Standards

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MGCP/

MEGACO Phones Trunking

Gateway Signaling

Gateway

MGC

SIGTRAN SSA/SCTP

RTP

MGCP/MEGACO

SS7 TCAP

ISUP/TCAP

Concept of MGCP/MEGACO

CO Switch

STP SCP

PhonesPSTN

Media Gateway

MGC Connection

Create Delete Modify

Event Notification Request

Status Query

Response Success Failure Event

Notify Status

Report Dumb Client

Stateless

Intelligent Server

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MGCP

n A master-slave protocol (A protocol for controlling media gateways)

n Call agents (MGCs) control the operation of MGs

n Call-control intelligence

n Related call signaling

n MGs

n Do what the CA instructs

n A line or trunk on circuit-switched side to an RTP port on the IP side

n Types of Media Gateway

n Trunking Gateway to CO/Switches

n Residential Gateway to PSTN Phones

n Access Gateway to analog/digital PBX

n Communication between call agents

n Likely to be the SIP

(29)

The MGCP Model

n

Endpoints

n Sources or sinks of media

n Trunk interfaces

n POTS line interfaces

n Announcement endpoint

n

Connections

n Allocation of IP resources to an endpoint

n An ad hoc relationship is established from a

circuited-switched line and an RTP port on the IP side.

n A single endpoint can have several connections

(30)

MGCP Endpoints [1/3]

n

DS0 channel

n A digital channel operates at 64kbps.

n Multiplexed within a larger transmission facility such as DS1 (1.544 Mbps) or E1 (2.048 Mbps)

n G.711 (u-law or A-law)

n

Analog line

n To a standard telephone line

n An analog voice stream

n Could also be audio-encoded data from a modem

n The gateway shall be required to extract the data and forward it as IP packets.

(31)

n

Announcement server access point

n Provide access to a single announcement

n One-way

n No external circuit-switched channels

n

Interactive voice response (IVR) access point

n Provide access to an IVR system

n

Conference bridge access point

n Media streams from multiple callers can be mixed

n

Packet relay

n A firewall between an open and a protected networks

MGCP Endpoints [2/3]

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MGCP Endpoints [3/3]

n

Wiretap access point

n For listening to the media transmitted

n One way

n

ATM trunk-side interface

n The termination of an ATM trunk

n May be an ATM virtual circuit

(33)

n GW’s Domain Name + Local Name

n Local Name

n A hierarchical form: X/Y/Z

n trunk4/12/7@gateway.somenetwork.net

n To identify DS0 number 7 within DS1 number 12 on DS3 number 4 at gateway.somenetwork.net

n Wild-cards

n $, any; *, all

n e.g., trunk1/5/$@gateway.somenetwork.net

n CA wants to create a connection on an endpoint in a gateway and does not really care which endpoint is used.

n e.g., trunk1/5/*@gateway.somenetwork.net

n CA requests statistical information related to all endpoints on

Endpoint Identifier

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MGCP Calls and Connections

n A connection

n Relationship established between a given endpoint and an RTP/IP session

n A call

n A group of connections

n The primary function of MGCP is to enable

n The connections to be created

n The session descriptions to be exchanged between the connections

123 456 789

*8#

123 456 789

*8#

(35)

n

Call Identifier (Call ID)

n Created by CA

n Unique within CA Scope

n

Connection ID

n Created by GW

n Unique under Its GW

n

CA Identifier (its domain name)

n Redundant CAs with a domain name: reliability

Calls, Connections and Call Agents

Endpoint Endpoint

1. CRCX CA

3. MDCX 2. CRCX

IP, Port, Packetization

RTP

(36)

n

9 commands to handle Connection/Endpoints

n EndpointConfiguration (coding characteristics)

n NotificationRequest (requested events)

n Notify (GW: detected events)

n CreateConnection

n ModifyConnection

n DeleteConnection

n AuditEndpoint

n AuditConnection

n RestartInProgress (GW : taken in/out of service)

n

All commands are acknowledged.

EPCF RQNT NTFY CRCX MDCX DLCX AUEP AUCX RSIP

MGCP Commands

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MGCP Command Format

n A command line

n Request verb (the name of the command)

n Transaction id

n Endpoint id (for which the command applies)

n Protocol version

n A number of parameter lines

n An optional session description (SDP)

n Separated by a single empty line

n Command Encapsulation

n One command can be included within another

n Only one level of encapsulation

n E.g., when instructing a gateway to create a connection, CA can simultaneously instruct the gateway to notify the CA of

(38)

MGCP Parameters [1/6]

n

BearInformation (B)

n The line-side encoding

n B:e:mu

n

CallId (C)

n Comprised of hexadecimal digits

n

Capabilities (A)

n In response to an audit

n

ConnectionId (I)

n Comprised of hexadecimal digits

n

ConnectionMode (M)

n Send only, receive only and send-receive

(39)

MGCP Parameters [2/6]

n ConnectionParameters (P)

n Connection-related statistical information

n Average latency, jitter, packets sent/received/lost

n GW -> CA

n DetectEvents (T)

n That an endpoint should detect during quarantine period

n E.g., off-hook, on-hook, hook-flash, DTMF digits…

n LocalConnectionDescripter (LC)

n An SDP session description

n LocalConnectionOptions (L)

n Bandwidth, packetization period, silence suppression, gain control, echo cancellation…

n L: e:off, s:on

n To turn echo cancellation off and to turn silence suppression on

(40)

MGCP Parameters [3/6]

n EventStates (ES)

n In response to an audit command

n A list of events associated with the current state

n MaxMGCPDatagram (MD)

n To indicate the maximum size MGCP packet supported by an MG

n Included in the response to an AUEP command

n NotifiedEntity (N)

n An address for the CA

n ObservedEvents (O)

n Detected by an endpoint

n PackageList (PL)

n Supported by an endpoint

n Events and signals are grouped into packages

n Analog line endpoint

(41)

n Events & Signals

n package name(o)/event or signal name (insensitive)

n L/hu = Hu (if L is the default package for the endpoint)

n packages: grouping of events & signals for a particular type of endpoints

n Generic Media (G)

n DTMF (D)

n MF (M)

n Trunk (T)

n Line (L)

n Handset (H)

n RTP (R)

n Script

n Network Access Server (N)

n Announcement Server (A)

n The experimental packages have names beginning

MGCP Packages

Gateway Supported packages Trunk GW (ISUP)

Trunk GW (MF)

Network Access Server Combined NAS/VOIP GW Access GW (VOIP)

Access GW (VOIP + NAS) Residential GW

Announcement GW

G, D, T, R G, M, D, T, R G, M, T, N

G, M, D, T, N, R G, M, D, R

G, M, D, N, R G, D, L, R A, R

(42)

MGCP Parameters [4/6]

n QuarantineHandling (Q)

n Events that occur during the

period in which the GW is waiting for a response to a Notify

command

n Process the events or discard them

n ReasonCode (E)

n When a GW deletes/restarts a connection

n RemoteConnectionDescripter (RC)

n An SDP session description

Q: process/discard step/loop (notify) T: events to detect

during quarantine Q: process/discard

step/loop (notify) T: events to detect

during quarantine

Request Response

Time

Quarantine Period

Notify

(43)

MGCP Parameters [5/6]

n RequestEvents (R)

n A list of events that an endpoint is to watch for

n Associated with each event, the endpoint can be instructed to perform actions

n E.g., collect digits, or apply a signal

n RequestInfo (F)

n In response to audit requests

n The current values of RequestEvents, DigitMap, NotifiedEntity

n RequestIdentifier (X)

n To correlate a given notification from a GW

n RestartDelay (RD)

n A number of seconds indicating when an endpoint will be brought back into service

(44)

MGCP Parameters [6/6]

n

RestartMethod (RM)

n Graceful or Forced

n

SecondConnectionId (I2)

n The connection on a second endpoint

n

SecondEndpointID (Z2)

n A connection between two endpoints on the same GW

n

SignalRequests (S)

n Signals to be applied by an endpoint

n

SpecificEndpointID (Z)

n Used to indicate a single endpoint

(45)

Inter-digit Timer n

CA ask GW to collect user dialed digits

n Created by CA

n

Usage

n Gateways detect a set of digits.

n e.g., (11x|080xxxxxx|03xxxxxxx|002x.T)

n Match accumulated digits

n under-qualified, do nothing further

n matched, send the collected digits to CA

n over-qualified, send the digits to CA

Digit Map

(46)

MGCP Response

n

Header

n A response line

n Return code + TransID + Commentary

n A set of parameter lines (optional)

n E.g., I: A3C47F21456789F0 (ConnectionId)

n

Session Description

n Session Description Protocol

n separated from header by an empty line

(47)

Return Code

n

100~199: provisional response

n current being executed

n

200~299: successful completion

n executed normally

n

400~499: transient error

n could not be executed because of no sufficient resources at this time

n phone already off/on hook

n

500~599: permanent error

n endpoint unknown

n protocol error

(48)

Protocol Description [1/2]

n

Transactions (simple text format)

n command

n header

n a command line (case insensitive)

n Action + TransId + Endpoint + Version

n a set of parameter lines

n parameter name (upper case): value

n Example

n RQNT 1201 endpoint/1@rgw.net MGCP 1.0

n X: 0123456789B1 (RequestIdentifier)

n R: hd (requestedEvent: hang down)

n S: rg (signalRequest: ring tone)

n session description

(49)

Protocol Description [2/2]

n

Transactions

n response

n header

n a response line

n Response code + TransId + Commentary

n a set of parameter lines (optional)

n Example

n 200 1201 OK

n after CRCX(/MDCX/DLCX/Audit/Restart)

n I: A3C47F21456789F0 (ConnectionId)

n session description

n Session Description Protocol (RFC 2327)

n separated from header by an empty line

(50)

Call Setup Using MGCP

i Ma c

(51)

i Mac