06.Softswitch and Media Gateway

Softswitch and Media Gateway(MGCP/MEGACO/SS7 over IP)

陳懷恩博士

助理教授兼資工所所長及

計算機中心資訊網路組組長

國立宜蘭大學

Email: [email protected]

TEL: 03-9357400 # 255

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Outline

Soft-switch Architecture

MGCP (Media Gateway Control Protocol)

MEGACO

SS7 over IP

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Separation of Media and Call Control

A network gateway has two related but separate

functions.

Signaling conversion

The call-control entities use signaling to communicate.

Media conversion

A slave function (mastered by call-control entities)

The following figure illustrates the separation of call

control and signaling from the media path.

MediaConversion

Media Conversion

Signalingand Call Control

Signalingand Call Control

Signaling over IP

Signaling over IP

Controland

Status

Controland

Status

External

Networks

External

Networks

Network Gateway Function Network Gateway Function

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Softswitch Architecture [1/2]

Media Gateway Controller Media Gateway Controller

Media Gateway

Media GatewayMedia Gateway

Media Gateway

Media Gateway

Call signaling over IP

Media over IP

Control and Status Signaling Control and

Status SignalingMGCP

SIP

RTP

MGCP

5

Softswitch Architecture [2/2]

SS7 Network

SCP

STP

COSwitch

TrunkingGatewayTrunking

GatewayTrunkingGateway

Signaling(SS7)

Gateway

CallAgent

MGCP/MEGACO

MGCP/MEGACO

ResidentialGatewayResidential

GatewayResidentialGateway

Internet

1 2 3

4 5 6

7 8 9

* 8 #

1 2 3

4 5 6

7 8 9

* 8 #

1 2 3

4 5 6

7 8 9

* 8 #

SIGTRAN

MGCP Calls and Connections

A connection

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

A call

A group of connections

The primary function of MGCP is to enable

The connections to be created

The session descriptions to be exchanged between the connections

1 2 3

4 5 6

7 8 9

* 8 #

1 2 3

4 5 6

7 8 9

* 8 #

Endpoint Endpoint

Gateway Gateway

Call

Media over IP

Connection ConnectionIP resource IP resource

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MGCP Connection Establishment

IP Network

iMac

(1) Call coming in !

(2) Select and RTP portand connect

(3) OK, port number xxx

Call Agent

Media Gateway

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9 commands to handle Connection/Endpoints

EndpointConfiguration (coding characteristics)

NotificationRequest (requested events)

Notify (GW: detected events)

CreateConnection

ModifyConnection

DeleteConnection

AuditEndpoint

AuditConnection

RestartInProgress (GW : taken in/out of service)

All commands are acknowledged.

EPCF

RQNT

NTFY

CRCX

MDCX

DLCX

AUEP

AUCX

RSIP

MGCP Commands

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Call Setup Using MGCP

iMac

Media Gateway Media GatewayCall Agent

Create Connection

ResponseSession description 1 (local)

Create ConnectionSession description 1 (remote)

ResponseSession description 2 (local)

Modify ConnectionSession description 2 (remote)

Media Transfer

a

b

c

d

e

f

iMac

Media Gateway Media GatewayCall Agent

CRCX 1111 [email protected] MGCP 1.0C:1234567M:recvonly

200 1111 OKI:AAAA

v=0c=IN IP4 123.45.6.7

m=audio 11000 RTP/AVP 0

CRCX 2222 [email protected] MGCP 1.0C:1234567M:sendrecv

v=0c=IN IP4 123.45.6.7


200 2222 OKI:BBBBM:recvonly

v=0c=IN IP4 123.45.8.9m=audio 22000 RTP/AVP 0

MDCX 1112 [email protected] MGCP 1.0I:1234567M:sendrecv


Media Transfer

a

b

c

d

e

f

200 1112 OKI: AAAA

g

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Interworking between MGCP and SIP

CRCX 11 [email protected] MGCP 1.0C:1234567M:recvonly

200 11 OKI:AAAA

v=0c=IN IP4 123.45.6.7


INVITE

v=0c-IN IP4 123.45.6.7

m=audio 11000 RTP/AVP 0CRCX 22 [email protected] MGCP 1.0

C:1234567M:sendrecv

v=0c=IN IP4 123.45.6.7


a

b

c

d

MG B MG ACall Agent B Call Agent A

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Interworking between MGCP and SIP

e

f

g

h

200 22 OKI:BBBBM:recvonly


SIP/2.0 200 OK


MDCX 12 [email protected] MGCP 1.0I:AAAAM:sendrecv


200 12 OKI:AAAA

ACK

Media Transfer

i

j

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MEGACO Command Naming

(9) EndpointConfiguration (Endpoint-encode) Add, Modify, Move

(8) NotificationRequest (Endpoint) Add, Modify, Move

(7) AuditConnection

(6) RestartInProgress (Endpoint) (8) ServiceChange (Termination)

(5) Notify (Endpoint) (7) Notify (Termination)

(NONE)(6) AuditCapability (Termination)

(4) AuditEndpoint(5) AuditValue (Termination-cur)

CreateConnection + DeleteConnection(4) Move (Termination)

(3) DeleteConnection (Endpoint) (3) Subtract (Termination)

(2) ModifyConnection (Endpoint) (2) Modify (Termination-descriptor)

(1) CreateConnection (Endpoint) (1) Add (Termination to Context)

Similar Commands in MGCPMEGACO

(NONE)

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MEGACO Connection Model

Media Gateway Controller

(MGC) Call Agent (CA)3

ContextConnection2

TerminationEndpoint1

MEGACOMGCP

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Concept of Context

MGCPCA

RGW RGW

MGCP

MEGACO

RTP

IP

MGC

MG MG

MEGACO

RTP

IP

Context

Connection

established

after CRCX

Termination

RTP Stream

Termination

SCN Channel

Add 2 Terminations into 1 context

Endpoint Endpoint

MG B

322.322.1.1

T4 T3

322.322.1.1MG A

311.311.1.1

T2 T1

a

b

c

d

e

f

Context = ${Add = T1, Add= $ {mode = receiveonly}}

Reply {Context = 1001{Add = T1, Add = T2{

Local Descriptor}}}

Context = ${Add = T4, Add= $ {Remot Descriptor}}

Reply {Context = 2002{Add = T4, Add= T3{Local Descriptor}}

Modify = 1001 {Modify = T2{Mode = sendreceive,Remote descriptor}}

Reply {Contex = 1001{modify = T2}}

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Introduction to SS7

Channel Associated Signaling

Still widely deployed today

Considered as old telephony

Common Channel Signaling

Separation of signaling and call paths

Signaling System 7 (SS7)

To enable a wide range of services to

be provided to the end-user

Caller ID, toll-free calling, call

screening, number portability, etc.

SS7 is the foundation for Intelligent

Network (IN) services.

Switch Switch

Speech and Signaling

Channel Associated Signaling

Switch Switch

Speech

Common Channel Signaling

Signaling

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The Telephone Network [2/2]

5 Basic Components in Intelligent Networks

SSP (Service Switching Point)

switching, service invocation

STP (Service Transfer Point)

signal routing

SCP (Service Control Point)

service logic execution

SDP (Service Data Point)

subscriber data storage, access

IP (Intelligent Peripheral)

resources such as customized voice announcement, voice

recognition, DTMF digit collection

SSP

SCP SDP

STPIP

SSP

STP

TCAP messages

ISUP messages

Voice

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SS7 Protocol Suite

ISUPTCAP

SCCP

MAP

MTP Level 3

MTP Level 2

MTP Level 1

OSI Layers

Application

Presentation

Session

Transport

Network

Data Link

Physical

INAP

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MTP Levels 1 & 2

Message Transfer Part

Level 1

Handling the issues related to the signals on the physical

links between one signaling node and another

Level 2

Dealing with the transfer of messages on a given link

from one node to another

Providing error detection/correction and sequenced

delivery of the SS7 messages

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MTP Level 3

Signaling message handling

Providing message routing between signaling points in

the SS7 network

Signaling network management

Rerouting traffic to other SS7 signaling links in the case

of link failure, congestion or node failure

Load-sharing

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ISUP

ISUP: ISDN User Part

Used as the protocol for setting up and tearing

down phone calls between switches

Initial Address Message (IAM)

To initiate a call between two switches

Answer Message (ANM)

To indicate that a call has been accepted by the called

party

Release Message (REL)

To initiate call disconnection

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SCCP

SCCP: Signaling Connection Control Part

Used as the transport layer for TCAP-based

services

freephone (800/888), calling card, wireless roaming

Both connection-oriented and connectionless

Mostly connectionless signaling

Global title translation (GTT) capabilities

The destination signaling point and subsystem number

is determined from the global title

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TCAP, MAP and INAP

TCAP: Transaction Capabilities Applications Part

Supporting the exchange of non-circuit related

information between signaling points

Queries and responses sent between SSPs and SCPs are

carried in TCAP messages

INAP (IN Application Part)

MAP (Mobile Application Part)

ISUP Call Establishment and Release

• A given circuit between two switches is identified by

OPC, DPC and CIC.

IAM

IAM

ACM

ACM

One-way audio

CPG

CPG

ANM

ANM

Two-way speech path

REL

REL

RLC

RLC

a

b

c

d

e

f

g

h

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k

l

m

n

•IAM (Initial Address Message)•ACM (Address Complete Message)•CFG (Call ProGress)•ANM (ANswer Message)•REL (RELease)•RLC (ReLease Complete)

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Softswitch Architecture

Signaling

(SS7)

Gateway

Trunking

Gateway

Call

Agent

SCP

Residential

Gateway

InternetSS7 Network

STP

Trunking

GatewayTrunking

Gateway

CO

Switch

Residential

GatewayResidential

Gateway

MGCP/

MEGACO

MGCP/

MEGACO

RTP

SIGTRAN

ISUP IAM

IP IAM

ADD

ADD Reply

SIP INVITE

ADD

ADD Reply

IP IAM

ISUP IAM

ISUP ACM

ISUP ACM

SIP 183

IP ACM

ISUP ACM

ISUP ANM

IP ANM

SIP 200

MODIFY

MODIFYReply

SIP ACK

IP ANM

ISUP ANM

Media Transfer

a

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m

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o

p

q

r

s

t

u

v

w

STP STPSignalingGateway

SignalingGateway

MediaGateway

MediaGateway

MGC MGC

06.Softswitch and Media Gateway

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