Media Gateway Control and the Softswitch Architecture

2IP Telephony

Outline

IntroductionSoftswitch

Softswitch ArchitectureSoftswitch Operations

Media Gateway Control ProtocolsMGCPMEGACO

3IP Telephony

Next Generation Network

Internet Telecom & Wireless Communication

IP

MGCF

CSCF

SGW MGWMGW

WLAN

GPRS

CSCFSIP

Server

PSTN

InternetWireless App.Server

3rd Parties App.

4IP Telephony

Gateways in Next Generation Networks

CO

SCP

STP

PBX

H.323GK

SS7/IN

PSTN IP Networks

SG

TGW

H.323MG

MGC

MGC : Media Gateway ControllerSG : Signaling GatewayTGW : Trunking GatewayRGW : Residential Gateway

MGCP/MEGACOH.323/SIPSIGTRANRTP/RTCP

Analog Line

TrunkMGCP/MEGACO

PhonesRGW

H.323 Phones

5IP Telephony

H323/SIP VS. MGCP/MEGACO [1/2]

GWGK

MCU

GW : GatewayGK : GatekeeperTN : TerminalMCU : Multipoint Control Unit

TN

PSTN CA

TGW RGW

CA : Call AgentTGW : Trunking GatewayRGW : Residential GatewaySG : Singling Gateway

SS7

PSTN CO

SG

RTP

MGCP

H.323

TNTN

GWGK

MCU

TN

TNTN

6IP Telephony

H323/SIP VS. MGCP/MEGACO [2/2]

H.323 , SIPpeer-to-peerinternet orientedintelligent endpoint

optional GK decentralized

Problemsmaintenance

cost & scalability of large systems

signaling & media control are coupledinteroperability with SS7

MGCP/MEGACOclient-servertraditional telephonyintelligent server

“dumb” terminalcentralized

Conceptgateway decomposed

separate call control from media portsCA (MGC), MG, SG

interoperability with PSTN

7IP Telephony

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 SignalingISUP MessagesINAP/TCAP Messages

8IP Telephony

The Telephone Network [2/2]

5 Basic Components in Intelligent NetworksSSP/Service Switching Point

switching, signaling, routing, service invocation

STP/Service Transfer Pointsignaling, routing

SCP/Service Control Pointservice logic execution

SDP/Service Data Pointsubscriber data storage, access

IP/Intelligent Peripheralresources such as customized voice announcement, voice recognition, DTMF digit collection

SSPSSP

SCPSCP SDPSDP

STPSTPIPIP

SSPSSP

STPSTP

TCAP messages

ISUP messages

Voice

9IP Telephony

Softswitch

The switching functions are handled by software.International Softswitch Consortium (ISC)

www.softswitch.orgTo promote the softswitch concept and related technologies

Why the softswitch approach is popular?A distributed architectureFor network operators

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

For equipment vendorsIt is possible to focus on one area.

10IP Telephony

Abstract Softswitch Architecture

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

11IP Telephony

Softswitch/PSTN Interworking

Modem Bank

12IP Telephony

Softswitch Overview [1/3]

Softswitch: Emulating Circuit Switching in Software

IN/SCPPSTNLocal Switch

PSTNLocal Switch STP SS7 Network

IP Network

RTP Streams

MGCMGC MGCMGC

Trunk Trunk GatewayGateway

Trunk Trunk GatewayGateway

SIP-T

SGSGSGSG

MEGACO

IP PhoneIP Phone

90009000 Personalized VoIPService System

Application ServerApplication Server

13IP Telephony

Softswitch Overview [2/3]

Softswitch Provides Open Layered Architecture

• Solutions in a proprietary box• Expensive• Little room for innovation

Circuit-Switched

TransportHardware

Call Control & Switching

Services & Applications

PROPRIETARY

• 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 Protocols APIs

Open APIs for 3rd Party App develop.

Best-in-class Access Devices.

Scalable, Open Interfaces for Comm.

14IP Telephony

Softswitch Overview [3/3]

Softswitch Changes the Telecom LandscapeIntegration/Incorporation

Convergence of voice and dataCombination of telecom & internet technologiesReuse PSTN database & IN services in packet networks Multiple sources for app development & deploymentDecreased operating costs

StandardizationStandard interfaces (protocols) for communicationsOpen standards (APIs) for service creationCustomized services created by users themselvesBetter scalability

15IP Telephony

Softswitch Architecture

COSwitch

STP

SCP

COSwitch

STP

SCP

Signaling Layer

Transport Layer

IP

SIP-T

MediaServer

RTP

SIP-?/MGCP

SIP-TSI

Media Gateway

Controller

MGCP/MEGACOPhones

App.Server

Media Gateway

Controller

SIGTRANSSA/SCTP

MGCP/MEGACOTrunkingGateway

Signaling(SS7)

Gateway

SS7 TCAP

ISUP/TCAP

16IP Telephony

LocalSwitch

STP

SCP

STP STP STP

LocalSwitch

STP

LocalSwitch

TrunkingGateway

Signaling(SS7)

GatewayMedia

GatewayController

TrunkingGateway

Signaling(SS7)

Gateway

RoutingDirectory 12 ISUP ACM

13 ISUP ANM

Softswitch Operations [1/3]

Basic Call Control

ISUP ACMISUP ANM

ISUP IAM ISUP IAM

1

23

4 5

6 7

8

910

14

11

SIGTRAN

MGCP/MEGACOVoice Voice

RTP

17IP Telephony

Softswitch Operations [2/3]

Inter-Softswitch Communications

LocalSwitch

STP

TrunkingGateway

Signaling(SS7)

GatewayMedia

GatewayController

STP

TrunkingGateway

STP

MediaGateway

Controller

Signaling(SS7)

Gateway

STP STP

Domain A Domain B

LocalSwitch

RoutingDirectory

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 ACM15 ISUP

ANM

ISUP ACMISUP ANM

18IP Telephony

Softswitch Operations [3/3]

IP-PSTN Interworking for IN Services

LocalSwitch

STP

SCP

STP STP STP

LocalSwitch

STP

LocalSwitch

TrunkingGateway

Signaling(SS7)

GatewayMedia

GatewayController

TrunkingGateway

Signaling(SS7)

Gateway

RoutingDirectory

ISUP IAM ISUP IAM

1

23

4

7

8 9

10

1112

13

SIGTRAN

MGCP/MEGACOVoice Voice

RTP

5

INAP/TCAP

16

6

14 ISUP ACM15 ISUP

ANM

ISUP ACMISUP ANM

19IP Telephony

Introduction

Voice over IPLower cost of network implementationIntegration of voice and data applicationsNew service featuresReduced bandwidth

Replacing all traditional circuit-switched networks is not feasible.VoIP and circuit-switching networks coexist

InteroperationSeamless interworking

20IP Telephony

Separation of Media and Call Control

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

Signaling path and media path are different in VoIP systems.

Media – directly (end-to-end)Signaling – through H.323 gatekeepers (or SIP proxies)

SS7, Signaling System 7The logical separation of signaling and media

21IP Telephony

Separation of Media and Call Control

A network gateway has two related but separate functions.

Signaling conversionThe call-control entities use signaling to communicate.

Media conversionA slave function (mastered by call-control entities)

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

22IP Telephony

Separation of Media and Call Control

Advantages of SeparationMedia conversion close to the traffic source and sinkThe call-handling functions is centralized.A call agent (media gateway controller - MGC) can control multiple gateways.New features can be added more quickly.

MGCP, Media Gateway Control ProtocolIETF

MEGACO/H.248IETF and ITU-T Study Group 16

23IP Telephony

Requirements for Media Gateway Control [1/2]

RFC 2895Media Gateway Control Protocol Architecture and Requirements

RequirementThe creation, modification and deletion of media streams

Including the capability to negotiate the media formatsThe specification of the transformations applied to media streamsRequest the MG to report the occurrence of specified events within the media streams, and the corresponding actions

24IP Telephony

Requirements for Media Gateway Control [2/2]

Request the MG to apply tones or announcementsThe establishment of media streams according to certain QoS requirementsReporting QoS and billing/accounting statistics from an MG to an MGCThe management of associations between an MG and an MGC

In the case of failure of a primary MGCA flexible and scalable architecture in which an MGC can control different MGsFacilitate the independent upgrade of MGs and MGCs

25IP Telephony

Protocols for Media Gateway Control

The first protocol is MGCPRFC 2705, informationalTo be succeeded by MEGACO/H.248Has be included in several product developments

MEGACO/H.248A standards-track protocolRFC 3015 is now the official version.

IPDC

SGCP

MGCP

MDCP

MEGACO

Telcodia (Bellcore)

Level 3 Communication

Lucent (by ITU-T)

IETF RFC 3015ITU-T H.248November 2000

IETF RFC 2705October 1999

MGCP 1.0

IETF RFC 3435January 2003

26IP Telephony

Relation with H.323/SIP Standards

27IP Telephony

MGCP/MEGACOPhones

TrunkingGateway

SignalingGateway

MGC

SIGTRANSSA/SCTP

RTP

MGCP/MEGACO

SS7 TCAP

ISUP/TCAP

Concept of MGCP/MEGACO

COSwitch

STP

SCP

PSTNPhones

Media Gateway

MGC

ConnectionCreateDeleteModify

Event NotificationRequest

StatusQuery

ResponseSuccessFailure

EventNotify

StatusReport

Dumb ClientStateless

Intelligent Server

28IP Telephony

MGCP

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

Call agents (MGCs) control the operation of MGsCall-control intelligenceRelated call signaling

MGsDo what the CA instructsA line or trunk on circuit-switched side to an RTP port on the IP side

Types of Media GatewayTrunking Gateway to CO/SwitchesResidential Gateway to PSTN PhonesAccess Gateway to analog/digital PBX

Communication between call agentsLikely to be the SIP

29IP Telephony

The MGCP Model

EndpointsSources or sinks of mediaTrunk interfacesPOTS line interfacesAnnouncement endpoint

ConnectionsAllocation of IP resources to an endpointAn ad hoc relationship is established from a circuited-switched line and an RTP port on the IP side.A single endpoint can have several connections

30IP Telephony

GW’s Domain Name + Local Name Local Name

A hierarchical form: X/Y/Z

trunk4/12/7@gateway.somenetwork.netTo identify DS0 number 7 within DS1 number 12 on DS3 number 4 at gateway.somenetwork.net

Wild-cards$, any; *, alle.g., trunk1/5/$@gateway.somenetwork.net

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

e.g., trunk1/5/*@gateway.somenetwork.netCA requests statistical information related to all endpoints on a gateway.

Endpoint Identifier

mailto:trunk4/12/7@gateway.somenetwork.netmailto:trunk1/5/$@gateway.somenetwork.netmailto:trunk1/5/*@gateway.somenetwork.net

31IP Telephony

MGCP Calls and Connections

A connectionRelationship established between a given endpoint and an RTP/IP session

A callA group of connections

The primary function of MGCP is to enableThe connections to be createdThe session descriptions to be exchanged between the connections

1 2 3

4 5 67 8 9

* 8 #

1 2 3

4 5 67 8 9

* 8 #

32IP Telephony

Call Identifier (Call ID)Created by CAUnique within CA Scope

Connection ID Created by GWUnique under Its GW

Calls and Connections

Endpoint Endpoint

CA1. CRCX3. MDCX2. CRCX

IP, Port, Packetization

RTP

33IP Telephony

9 commands to handle Connection/EndpointsEndpointConfiguration (coding characteristics)NotificationRequest (requested events)Notify (GW: detected events)CreateConnectionModifyConnectionDeleteConnectionAuditEndpointAuditConnectionRestartInProgress (GW : taken in/out of service)

All commands are acknowledged.

EPCF RQNTNTFYCRCXMDCXDLCXAUEPAUCXRSIP

MGCP Commands

34IP Telephony

Call Setup Using MGCP

iMac

iMac

Media Gateway Control and the Softswitch ArchitectureOutlineNext Generation NetworkGateways in Next Generation NetworksH323/SIP VS. MGCP/MEGACO [2/2]The Telephone Network [1/2]The Telephone Network [2/2]SoftswitchAbstract Softswitch ArchitectureSoftswitch/PSTN InterworkingSoftswitch Overview [1/3]Softswitch Overview [2/3]Softswitch Overview [3/3]Softswitch ArchitectureSoftswitch Operations [1/3]Softswitch Operations [2/3]Softswitch Operations [3/3]IntroductionSeparation of Media and Call ControlSeparation of Media and Call ControlSeparation of Media and Call ControlRequirements for Media Gateway Control [1/2]Requirements for Media Gateway Control [2/2]Protocols for Media Gateway ControlRelation with H.323/SIP StandardsConcept of MGCP/MEGACOMGCPThe MGCP ModelEndpoint IdentifierMGCP Calls and ConnectionsCalls and ConnectionsMGCP CommandsCall Setup Using MGCP