751x mg (media gateway) fundamentals ed.02.ce

3FL 36201 AAAA WBZZA Ed. 02P01.02/2008Page 1

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All Rights Reserved Alcatel-Lucent 2008

3FL 36201 AAAA Edition 02 - 04/2008

751x MG (Media Gateway)Fundamentals



Media Gateway Basics

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Objectives

z This training document covers basic information ofmedia gateways in an NGN environment.




4

Objectives [cont.]





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Table of Contents

z Switch to notes view! Page1 NGN Overview 7

1.1 Voice over IP (VoIP) and NGN 81.2 IP Telephony (IPT) 91.3 Class 4 Application 101.4 Border Gateway 111.5 Class 5 Application 121.6 IP Multimedia Subsystem (IMS) 13

2 Gateway Functions 142.1 Classification of Gateways 152.2 Monolithic and Decomposed Gateway Concept 162.3 Codecs 172.4 Silence Supression 182.5 Fax Relay (T.38) 192.6 Hairpinning 202.7 Session Border Control 21

3 MEGACO Protocol 223.1 MEGACO Network Elements 233.2 Definitions and Commands 243.3 Call Setup Scenario 25

4 Signaling Transport (SIGTRAN) 274.1 Overview 284.2 SIGTRAN IUA Example 30

5 Summary 315.1 Gateway Applications 32




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Table of Contents [cont.]

z Switch to notes view!





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1 NGN Overview




8

1 NGN Overview

1.1 Voice over IP (VoIP) and NGN

Softphone / IP-Phone(H.323, SIP)


Data Network

Voice Communication between IP Devices


Data Network

Voice Communication between Networks

PSTN

POTS / ISDNGateway

Data Network

Data Networks to replace Local ExchangesPOTS / ISDNGatewayGatewayPOTS / ISDN

Data Network

Data Networks to replace Long Distance Exchanges

PSTN

POTS / ISDNGatewayGatewayPSTN

POTS / ISDN

Data Network-own network-

Border Gateway ApplicationBorder GatewayGateway

PSTN

POTS / ISDN

Data Network-other provider-




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1 NGN Overview

1.2 IP Telephony (IPT)

H.323,SIP

PSTN

VoiceGate-way

PRI

GatekeeperProxyServer

(IPT)

H.323, SIP

Softphone(H.323, SIP)

IP Telephone(H.323, SIP)

RTP

H.323,SIP

Softphone(H.323, SIP)

IP Telephone(H.323, SIP)

RTP RTP

ApplicationServer /Services

SIPData Network

IP Internet ProtocolIPT IP TelephonyMRF Media Resource FunctionPRI Primary Rate InterfacePSTN Public Switched Telephone NetworkRTP Real-Time Transport ProtocolSIP Session Initiating Protocol

RTP

MRF

SIP




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1 NGN Overview

1.3 Class 4 Application

Data Network

SignalingGateway

MediaGate-way

MediaGateway

Controller(Class 4)

SIGTRAN

ISUP

PSTN

N7

CCS N7(ISUP)

MediaGate-way

RTP

MEGACO MEGACO

MEGACO Media Gateway Control ProtocolRTP Real-Time Transport ProtocolSIGTRAN Signaling TransportSIP Session Initiating Protocol

ISUP




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1 NGN Overview

1.4 Border Gateway

Data Network

MediaGate-way

MediaGateway

Controller(IBCF)

ISUP

PSTN

BorderGate-way

RTPMEGACO

MEGACO

IBCF - Interconnection Border Control FunctionMEGACO Media Gateway Control ProtocolRTP Real-Time Transport ProtocolSIP Session Initiating Protocol

ISUP

Data Network

MediaGate-way

BorderGate-way

RTP

MEGACO

MediaGateway

Controller(IBCF)

PSTN

SIP / SIP-I SIP / SIP-I

Firewall Firewall




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1 NGN Overview

1.5 Class 5 Application

MediaGateway

Controller(Class 5)

MEGACO

AccessNode

AccessGate-way

ResidentialGateway

(MTA, IAD)

PABX

SIP, MGCP,MEGACO

CentralizedAccess

Gateway

MEGACOSIGTRAN

Data Network

RTP RTP

IAD Integrated Access DeviceMEGACO Media Gateway Control ProtocolMGCP - Media Gateway Control ProtocolMTA Media Terminal AdapterRTP Real-Time Transport ProtocolSIGTRAN Signaling TransportSIP Session Initiating Protocol

Access Network




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1 NGN Overview

1.6 IP Multimedia Subsystem (IMS)




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2 Gateway Functions




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AGW - Access GatewayAN - Access Nodec-AGW - centralized Access GatewayBGW - Border GatewayRGW - Residential GatewaySGW - Signaling GatewayTGW - Trunking Gateway

TDM Gateways

- convert TDM-voice to Packet-voice and vv.- Voice Coding, Echo Suppression, VAD, CNG- Special treatment for other traffic (Fax)

Signaling Gateways

- converts TDM Signaling (CCS N7, DSS, ...) to IP

Packet Gateways- Packet to Packet Gateways

- Voice Transcoding- Network Address Translation

- SLA Mapping of QoS-Levels

TransitBGW

Data Network other Provider

4,000..32,000EquivalentChannels

SignalingSGW

1...64CCS N7 Links

TGW

PSTN

250..32,000Channels

Data Network

Access

250..32,000Channels

1,500...100,000Subscriber

c-AGW

AN

1...8 Ports1 Subscriber+ Ethernet

RGW

250..1,500Subscriber

AGW BGW

4,000..16,000EquivalentChannels

2 Gateway Functions

2.1 Classification of Gateways

Classification of GatewaysA classification of gateways can be made via location of the gateway in the network. So we can decide between the following types of gateways:

Transit gateways Signaling gateways Access gateways

Transit GatewaysTransit gateways are gateways used between different networks. Beside border gateways (BGW), used between different packet networks, also trunking gateways (TGW) with a media conversion from circuit switched to packet switched networks and vice versa are possible.

Signaling GatewaysSignaling gateways (SGW) are used to transport TDM based signaling messages in a packet network. In an NGN environment signaling gateways are used for N7 signaling and DSS signaling (PRA interface)

Access GatewaysAccess gateways (AGW) are used to provide the access of subscribers to the telecommunication network. Depend on the function, size and physical location different types of access gateways are classified:

centralized Access Gateway (c-AGW)are used to connect TDM based concentrators to the data network

Access Gateways (AGW)contains subscriber interfaces and connect subscribers immediately the data network

Residential Gateways (RGW)are also used to connect subscribers immediately to the data network. In difference to an AGW the RGW is located on the subscriber premises and supports a small number of ports for analogue or ISDN telephone sets for one subscriber. Additionally an Ethernet interface can be supported.

Border Gateways (BGW)supports firewall functions in the access to a subscriber




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Voice Gateway

Call Control

Media

H.323 Terminal

Call Control

Media

Gatekeeper /Proxy Server

PSTN

ISDN

H.323SIP

H.323SIP

H.323, SIP

RTP

Monolithic Gateway

Media Gateway

Media

Media GatewayController

Call Control

PSTN

Media Gateway

Media PSTN

Signaling GWSignaling GW

ISUPCCS N7

ISUPSIGTRAN

ISUPSIGTRAN

ISUPCCS N7

MEGACO MEGACO

RTP

Decomposed Gateway

2 Gateway Functions

2.2 Monolithic and Decomposed Gateway Concept

Monolithic GatewayA monolithic gateway is used for example in an H.323 or SIP configuration. Here the terminal contains both the media handling (coding, packetization, ...) and the call control function. A Gatekeeper or Proxy Server is used for support functions only (Registration, address-translation, ...). The monolithic gateway contains also the media handling and the call control.

Monolithic gateways are used to connect a PABX or a VPN via an Primary Rate Interface (PRI) to an existing PSTN. Its also called a Voice Gateway.

Decomposed GatewayA decomposed gateway separates the media and call control function. So the call control function is located on a central instance, the Media Gateway Controller (MGC). The gateway covers only the media handling (coding, packetization, ...). Its also called a Media Gateway.




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DSP... 01101100 10110100 01010101 ... 010100 101010 011011

CODEC

i.e. 64 kBit/s PCM Bitstream (G.711) i.e. G.729 Packets (5,3/6,3kBit/s)

i.e.TDM Interface

i.e.Packet Interface

Codec Name Bitrate MOS

G.711 Pulse Code Modulation (PCM) 56 / 64 kBit/s 4.1

G.726 Adaptive Differential Pulse Code Modulation(ADPCM) 16 - 40 kBit/s 3.85

G.728 Low Delay Code Excited Linear Prediction (LD-CELP) 16 kBit/s 3.61

G.729 /G.729A

Conjugate Structure Algebraic Code Excited Linear Prediction(CS-ACELP) 8 kBit/s

3.92 /3.7

G.723.1 Multiple Maximum Likehood Quantizatition(MPMLQ) 6.3 kBit/s 3.9

G.723 Algebraic Code Excited Linear Prediction(ACELP) 5.3 kBit/s 3.65

2 Gateway Functions

2.3 Codecs

Codecs (COder/DECoder)A Codec is used for coding of a video or audio stream into packets used in the IP network.The codec works bi-directional. So the codec transforms also received IP packets into a video- or audio-stream.

G.711 PCM CodeThe ITU G.711 Standard is used in nearly all PSTNs world-wide. It describes the Pulse Code Modulation (PCM) with 64 kBit/s.

G723.1Low Bitrate Codec originally developed for video telephony.Silence suppression is possible.

G.729 / G.729ALow Bit Rate Codec used for integrated speech and data applications. It is similar to G.723.1 but less delay.Silence suppression is possible.

Mean Opinion Score (MOS)Usually technical procedures are used to measure the voice quality in a objective way. But these mechanisms cant describe the real perception. So additionally a Mean Opinion Score is defined as an average over a big number of individual opinions. The MOS ranges from 1 to 5.

Processor PowerThe reduction of bitrate required processor power. So this parameter describes the effort that has to be spend in the Digital Signal Processor (DSP).




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Data Network PSTN PSTN

1101 1010 0000 0000 1111 1010

1101 1010 1111 1010

without Voice Activity Detection

with Voice Activity Detection

2 Gateway Functions

2.4 Silence Supression

Voice Activity DetectionComfort Noise Generation

Voice Activity Detection (VAD)is a process used to identify presence or absence of speech data bits. The result can be used to reduce the bandwidth for a communication channel in a data network. So in case of no speech information only a no-information-but-still-alive indication is transmitted. This indication is send with one UDP packet i.e. all 300 ms. Compared with one UDP packet all i.e. 30 ms for speech data there is a reduction of up to 90% of bandwidth.

Comfort Noise Generation (CNG)To avoid the feeling of a dead line during a running Voice Activity Detection in a no-data-phase on the receiver side a quiet noise is generated.




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Data Network PSTN PSTN

DA

AD

AD

DA

0100 1011 1100

2 Gateway Functions

2.5 Fax Relay (T.38)

Fax Relay (T.38)




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TDM Hairpinning

IP Hairpinning (RTP Hairpinning)

AN - Access NetworkLEX - Local ExchangeTEX - Toll Exchange

AN

Media Gateway

TEX / LEX


AN

MediaGateway

MediaGateway

Controller

ANAN

MediaGateway

MediaGateway

Controller

Data Network 1 Data Network 2

IP Telephone Media Gateway

IP Telephone

Data Network

MediaGateway

IP Telephone IP Telephone

Subscriber withCall Forwarding

2 Gateway Functions

2.6 Hairpinning




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Data Center of Voice Application Service Providers

Hosted IP Based InteractiveCommunication Services (IC)

Peering Service Provider Networks

Serv

ice

Ass

uran

ce

Crit

ical

Sec

urit

y

Law

Enfo

rcem

ent

Requ

irem

ents

Applications for Session Border Control

2 Gateway Functions

2.7 Session Border Control

Session Border Controllers (SBC)is a new category of network equipment that provides critical control functions to enable high quality interactive communications across IP network borders.

SessionA "session" is any real-time, interactive voice, video or multimedia communication using layer 5 IP session signaling protocols such as SIP, H.323, MGCP or Megaco/H.248.

BorderThe "border" is any IP-IP network border such as those between service provider and customer/subscriber, or between two service providers.

ControlThe "control" functions span security, service assurance and law enforcement requirements.

Applications for Session Border Controllers (SBC) Peering service provider networks

Today many providers employ managed IP networks with softswitches and gateways. The next step in this network evolution entails connecting these softswitch -gateway islands to expand network reach and minimize PSTN termination costs. SBCs enable these VoIP providers to peer networks for PSTN origination and termination, IP transit and, ultimately, IP termination and origination.

Facilities-based providers offering hosted IP-based interactive communication (IC) services will also benefit from the use of SBCs at the borders to their business and residential customers.(voice, video, unified messaging, conferencing, gaming, IP-PBX transport)

Doorway to the data centers of voice applications service providers delivered to other retail providers or directly to users.(calling card, directory, messaging)

Across all of these applications, there are critical security, service assurance and law enforcement requirements that must be satisfied.




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3 MEGACO Protocol




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3 MEGACO Protocol

3.1 MEGACO Network Elements

PSTNPSTN

Ethernet

IP

TCP UDP

MEGACOH.248

MediaGateway

MediaGatewayController

Sign GW

#7ISUP

#7ISUP

MEGACO

Sign GWDataNetwork

MediaGateway

MediaGateway

MediaGateway

Media gateway Control Protocol (MEGACO)

Is a Protocol between a Media Gateway Controller (MGC) and a Media Gateway (MG). It is used to control Media Gateways (MG).

MEGACO covers thefunctionality to set up and release cross-connection between media streams in a circuit-switched and packed-based network.

official industry-standard for Media Gateway Control Protocol cooperation of IETF (Megaco RFC3015) and ITU-T (H.248 v1.0)

important component of Next Generation Network (decomposed model)

RFC-3015

Competitive protocols: MGCP IETF only (RFC-2705) Runs over TCP and UDP




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Gateway

Context

Termination

PSTN Data Network

Message

Add

Modify

Subtract

Move

AuditValue

AuditCapablities

Notify

Description

ServiceChange

Addition of a termination to a context. The first add-message creates a new context

Modification of features and signals of a termination.

Removal of a termination from a context. Removing the last termination causes the deletion of the context.

Removal of a termination from a context and addition of this termination to another context.

Requests information about features, events and signals of a termination

Requests information about all possible features, events and signals allowed for this termination

Notification on events.

Notification on changes in the status of a termination,also used for registration with an MGC

3 MEGACO Protocol

3.2 Definitions and Commands

TerminationA termination is a logical entity that sources and/or sinks media and/or control streams (virtual or logical)

ContextA context is an association between a number of terminations while a call is in progress.

PackageA package is a collection of properties, events, signals and statistics associated with a termination

Commands Add: to place a termination in a context Modify: to change the properties of a termination Subtract: to remove a termination from a context Move: to move a termination to another context (f.ex. Call Waiting) Audit value: a query for all information about a (set of) termination(s) Notify: allows the MG to inform MGC of the occurrence of an event (e.g. off-hook detected) Service change: to register with MGC and to report change to MGC (e.g. termination out of

service/in service)

Audit capabilities: to audit the capabilities of MG




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Data Network

MediaGateway

MediaGateway


PSTNPSTN

#7 ISUPMEGACOSpeech, VoIP

1 Initial Address Message (IAM)2 Add

3 Add-Reply4 Add

5 Add-Reply6 Modify

7 Modify-Reply

8 Initial Address Message (IAM)

10 Addr. Complete Message (ACM)9 Addr. Complete Message (ACM)

12 Answer Message (ANM)11 Answer Message (ANM)

LocalExchange

LocalExchange

Exchange of User Data

3 MEGACO Protocol

3.3 Call Setup Scenario

(1) The Media Gateway Controller (MGC) is notified by the Local Exchange (LEX) about a new call with the ss7 message - Initial Address Message (IAM). This message contains important parameters as Called Number, Calling Number, Circuit Identification Code (identification for the ds0 reserved for this call), ...

(2) Upon reception of this IAM, the MGC will generate an ADD REQUEST, requesting the Media Gateway (MG) to create a context for this new call, and add a TDM termination link (=the reserved ds0) to the newly created context. Physically, the MG will also allocate a DSP resource for the call. With the same or a second ADD message, the MGC will request the MG to add an RTP termination to the same context. When two terminations (a TDM and an RTP in this case) are placed in the same context, they have the potential to exchange media. The MG will add an RTP termination to the context, and set-up the DSP with the appropriate values (e.g. for codec, packetization time).

(3) The MG generates an ADD-REPLY to confirm that the TDM termination has been placed in the new context, and a DSP resource has been allocated for the call. Also the RTP termination (IP address and port number) are given back to the MGC.

(4) The routing in the MGC defines the terminating media gateway. Once determined, exactly the same procedure as on the origination gateway is repeated. So the MGC generates in the next step an ADD_REQUEST to request creation of a new context for this new call. This message contains a specific TDM termination that identifies the outgoing TDM termination link (outgoing ds0). The MG generates an RTP Termination, that is linked to the RTP IP address and port of the originating MG. For the incoming RTP traffic an own IP address and port number will be created. After allocation of an DSP both terminations are through connected.

(5)The ADD_REPLY message indicates the successful context allocation to the MGC. Furthermore the RTP address information is given back to the MGC.

(6) This information has to be forwarded to the originating MG. Now both terminations can be through connected.




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MediaGateway

MediaGateway


PSTNPSTN Data Network

#7 ISUPMEGACOSpeech, VoIP

1 Initial Address Message (IAM)2 Add

3 Add-Reply4 Add

5 Add-Reply6 Modify

7 Modify-Reply

8 Initial Address Message (IAM)

10 Addr. Complete Message (ACM)9 Addr. Complete Message (ACM)

12 Answer Message (ANM)11 Answer Message (ANM)

LocalExchange

LocalExchange

Exchange of User Data

3 MEGACO Protocol

3.3 Call Setup Scenario [cont.]

(7) The MG sends with the MODIFY-REPLY message a successful acknowledge back to the MGC.

(8) Now the MGC indicates to the terminating exchange the seizure of a trunk circuit with an INITIAL ADDRESS MESSAGE (IAM).

(9) (12) All further messages in the call setup scenario will be transmitted via the MGC without any messages to the gateways. So the ADDRESS COMPLETE MESSAGE (ACM) indicates the successful end to end call setup. With the ANSWER MESSAGE (ANM) the conversation phase starts.




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4 Signaling Transport (SIGTRAN)




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4.1 Overview

Ethernet, ATM, ...

IP

SCTP

M2UA M3UA IUA SUA V5UA

IUA - Q.921 User Adaptation Layer (ISDN)M2PA - MTP2 User Peer-to-Peer Adaptation LayerM2UA - MTP2 User Adaptation LayerM3UA - MTP3 User Adaptation LayerSCTP - Stream Control Transmission ProtocolSUA - SCCP User Adaptation LayerV5UA - V5 User Adaptation Layer

M2PA

SIGTRAN ModelSIGTRAN was developed by the IETF working group SIGTRAN and defines the control protocol between the Signaling Gateway, Media Gateway Controllers and IP based Signaling Points. The Sigtran protocol consists of a modular, extensible structure with a common reliable transport protocol used for all signaling transport. The protocol transports message based signaling protocols messages, usually SS7, transparently over IP networks.

Stream Control Transmission Protocol (SCTP)The Stream Control Transmission Protocol is a reliable transport protocol operating on top of a connectionless packet network such as IP. SCTP is designed to transport PSTN signaling messages over IP networks, but is capable of broader applications.It offers the following services to its users:

Acknowledged error-free non-duplicated transfer of user data.

Data fragmentation to conform to discovered path MTU size.

Sequenced delivery of user messages within multiple streams, with an option for order-of-arrival delivery of individual user messages.

Optional bundling of multiple-user messages into a single SCTP packet.

Network-level fault tolerance through supporting of multi-homing at either or both ends of an association.

Signaling Functions in SIGTRANOn top of SCTP there can be used different signaling applications depend on the network request. The most important signaling applications are the following:

- M2UA - MTP2 User Adaptation Layer- M3UA - MTP3 User Adaptation Layer- IUA - Q.921 User Adaptation Layer- SUA - SCCP User Adaptation Layer- V5UA - V5 User Adaptation Layer




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4.1 Overview [cont.]

ISDN User Adaptation (IUA)This layer provides functionality to transport ISDN signals from Switched Circuit Network (SCN) to IP network by back-hauling the Q.921 user messages over SCTP (Stream Control Transport Protocol) as per the IETF RFC 3057. IUA supports both ISDN Primary Rate access (PRA) as well as Basic Rate Access (BRA) including the support for both point-to-point and point-to-multi-point modes of communication.

MTP2 User Peer-to-Peer Adaptation Layer (M2PA)is a SIGTRAN protocol for transporting SS7 MTP Level 2 user part signaling messages (i.e. MTP Level 3) over IP using the Stream Control Transmission Protocol (SCTP). Unlike M2UA, M2PA is used to support full MTP Level 3 message handling and network management between any two SS7 nodes communicating over an IP network. IP signaling points function as traditional SS7 nodes using the IP network instead of the SS7 network. Each switched circuit or IP signaling point has an SS7 point code. The M2PA protocol layer provides the same set of services as MTP Level 2 provides to MTP Level 3.M2PA can be used between a signaling gateway and a media gateway controller, between a signaling gateway and an IP signaling point, and between two IP signaling points. Signaling points may use M2PA over IP or MTP Level 2 over standard SS7 links to send and receive MTP Level 3 messages.

MTP2 User Adaptation Layer (M2UA)is a protocol defined by the IETF Sigtran Working Group for transporting SS7 MTP Level 2 user (i.e. MTP Level 3) signaling messages over IP using the Stream Control Transmission Protocol (SCTP). The M2UA protocol layer provides the equivalent set of services to its users as MTP Level 2 provides to MTP Level 3.M2UA is used between the Signaling Gateway and Media Gateway Controller in VoIP networks. The signaling gateway receives SS7 messages over an MTP Level 1 and Level 2 interface from a signaling end point (SCP or SSP) or signal transfer point (STP) in the public switched telephone networks. The signaling gateway terminates the SS7 link at MTP Level 2 and transports MTP Level 3 and above to a Media Gateway Controller or other IP endpoint using M2UA over SCTP/IP. The signaling gateway maintains the Availability State of all media gateway controllers to manage signaling traffic flows across active SCTP associations.

MTP3 User Adaptation Layer (M3UA)is used for the transport of Signaling System 7 (SS7) MTP 3 user signaling messages over IP using the Stream




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Q.921 Q.921

SCTP

IP IP

SCTP

IUA

Q.931

IUA

Q.931

PABX

PABX

Media Gateway

Media Gatewaywith SIGTRAN

SoftswitchSoftswitch

DataNetwork

SIGTRAN(IUA)

PRI(30B+D)

ATM - Asynchronous Transfer ModeIP - Internet ProtocolIUA - Q.921 User Adaptation Layer (ISDN)SCTP - Stream Control Transmission ProtocolPABX - Private Automatic Branch ExchangePRI - Primary Rate InterfaceQ.921 - ISDN Layer 2 ProtocolQ.931 - ISDN Layer 3 Protocol

ATM, ... ATM, ...

E1E1


4.2 SIGTRAN IUA Example




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5 Summary




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5 Summary

5.1 Gateway Applications

VoPacketBackbone

PSTN PSTN

VoIP TrunkingVoIP TrunkingTDM-TDMHairpinningTDM-TDM

Hairpinning Alcatel7510 MG

Alcatel7510 MG

Alcatel7510 MG

Packet2PacketGateway

Packet2PacketGateway

LEX

LEXLEX

LEX

IP Phones

PBX

PBXAccessPBX

Access

Alcatel7510 MG

DLC

DLC AccessDLC Access

VoIPTermination

VoIPTermination

SCP/OSP Application Server3rd party Application Server

IP-PBX

VoPacketBackbone

Media gateway controller

DLC Digital Loop CarrierLEX Local ExchangePBX Private Branch ExchangePSTN Public Switched Telephone Network

SGWSGW

IP Hair-pinningIP Hair-pinning




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Abbreviations and Acronyms

z Switch to notes view!# A AGW Access Gateway AN Access Node ATM Asynchronous Transfer Mode B BGW Border Gateway C CNG Comfort Noise Generation CODEC CODer/DECoder D DLC Digital Loop Carrier DSP Digital Signal Processor DSS Digital Subscriber Signaling E F G H I IBCF Interconnection Border Control Function IETF Internet Engineering Task Force IP Internet Protocol IPT IP Telephony ISDN Integrated Services Digital Network ISUP ISDN User Part ITU-T International Telecommunications Union IUA ISDN User Adaptation Layer J K L LEX Local Exchange M M2PA MTP Level 2 Peer to Peer Adaptation Layer M2UA MTP Level 2 Adaptation Layer MEGACO Media Gateway Control Protocol MGC Media Gateway Controller MGW Media Gateway MOS Mean Opinion Score N NGN Next Generation Network O

P PABX Private Automatic Branch Exchange PCM Pulse Code Modulation PRI Primary Rate Interface PSTN Public Switched Telephone Network Q R RGW Residential Gateway RTP Real-Time Transport Protocol S SBC Session Border Control SGW Signaling Gateway SIGTRAN Signaling Transport SLA Service Level Agreement T TCP Transmission Control Protocol TDM Time Division Multiplex TEX Tall Exchange TGW Trunking Gateway U UDP User Datagram Protocol V VAD Voice Activity Detection VoIP Voice over IP W X Y Z

751x mg (media gateway) fundamentals ed.02.ce

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