TBE 2710

Chapter 12

Signaling

Signaling Functions

• Switch to switch communication

• Switch to station communication– Supervising

– Addressing

– Alerting

– Call Progress

Signaling Methods: In Band...

• Loop-Start Signaling

• Ground-Start Signaling

• Wink Start

General Call-State Model: In-Band

Signaling Methods: Out-of-Band or Clear Channel...

• ISDN – Primary Rate Interface (PRI)– Used for PBX and Business customers– Added features (CLID, RLT, etc.)– Quicker call setup than in-band

• System Signaling No. 7 (SS7)– Used for PSTN Carrier Networks– Enables multiple network services

Signaling System 7

• Standard Method for Linking Central Offices

• Supports CLASS Services

• Required for:– Local Number Portability (LNP)– E800 services– Calling Name/Number Delivery (CNAM)– Advanced Intelligent Networking (AIN)

Architecture of SS-7

STP=Signal Transfer Point

SCP=Service Control Point

SP=Signal Point

STP

STP

STP

STP

SCP

SP

SP

SPSP

SP

SP

User

User

Purposes of SS7

• Improves Call Management

• Enhances Network Management

• Separates Network Control From Hardware

• Supports User Database

• Handles Addressing And Supervision

• Supports 800 Number Portability

• Supports Local Number Portability

SS7 Vs OSI

Network Applications

TCAP

Presentation

Session

Transport

Presentation

Session

Transport

ISDNservice

userpart

(ISUP)

Signaling connection control point (SCCP)

Signaling Network

Signaling Link

Signaling Data Link

Application

Network

Datalink

Physical 1

2

3

4

5

6

7

1

2

3

4

OSILayer

SS7Layer

OAM&P

NetworkService

Part

MessageTransfer

Part

TelephoneUserPart

SS7 Messaging

• ISDN User Part – (ISUP)– Call Setup Messages

• IAM, ACK, DIS, etc…

• Transaction Capability User Part (TCAP)– Transports INAP messages

• SCP Database queries– E800, LNP, CNAM, etc.

SS7 Signaling Examples

• Call Setup– Global Title Translation– Point Code

• CNUM/CNAM

• E800

• LNP

IP Signaling

• IP traffic and PSTN traffic merging

• Gateways required for conversion

• Protocols– H.323– Media Gateway Control (Megaco)– SIP

H.323

• Large, open, flexible protocol with many options (good/bad), somewhat proprietary though

• H.225 – call control– Session master/slave

• H.245 – multimedia control– Negotiates capabilities of endpoints (intelligent or dumb).

• Gatekeeper– RAS – registration, admission, status

• Uses Q.931 messages (PSTN) over TCP/IP• Can be setup as peer to peer with intelligent endpoints

Media Gateway Control

• Megaco and H.248

• Controls interaction between Media Gateway and Media Gateway Controller (softswitch, ie. Gatekeeper in H.323)

• Call Control in central controller

SIP• Simple protocol for multimedia applications over IP• Text messaging between endpoints• Addresses are a URL• Decentralized – intelligent endpoints• Presence

– Servers keep track of users status and availability, and where to be reached (Instant Messaging uses SIP)

• Proxy server – routes information, locates users and stores their preferences

• Uses other protocols– SAP, SDP, TRIP, RSVP, AAA

SIP Advantages

• Operates over Any Network

• Provides Expanded User Choices

• Enables Developers to Create New Applications

• Supports Multimedia

• Allows User to Specify Best Way to Communicate

SIP Architecture

Eth

erne

t

Eth

erne

t

SIP Client

SIP Client

SIP Proxy

SIP Proxy

LocationServer

IPNetwork

RedirectServer

SIP Call SetupUser Agent A Proxy Server User Agent B

Invite

InviteTrying

Ringing

Ringing

OK

OK

ACKACK

ByeBye

OKOK