SIP Overview

SIP 2

Contents What is Sip? SIP Benefits SIP message structure SIP components SIP mobility

SIP 3

What is SIP? Sip is signaling protocol defined by the Internet Engin

eering Task Force (IETF) for initiating, managing and terminating voice and video sessions across packet networks

A textual based client-server protocol Application layer protocol It’s not Transport Protocol It’s not QoS Reservation Protocol

SIP 4

SIP history Work began in 1995 in IETF mmusic WG 03/1999: RFC 2543, 153 pages, 6 methods 11/1999: SIP WG formed 11/2000: draft-ietf-sip-rfc2543bis-02, 171 pages, 6

methods

SIP 5

SIP benefits Integration with existing protocols

Integration well with Web(Http) and e-mail(Smtp) Simplicity Simple protocol vs H.323

Textual based, so parsing generation are simple Extensibility

HTTP and SMTP extensibility Modularity

Initiation,termination,change,user location, basic registration. Separating notion of a session to invite a user

Scalability Off DNS, BGP Server processing.

SIP 6

SIP Messages

SIP Requests: INVITE – Initiates a call by inviting user to

participate in session. ACK - Confirms that the client has received a

final response to an INVITE request. BYE - Indicates termination of the call. CANCEL - Cancels a pending request. REGISTER – bind a permanent address to current

location OPTIONS – Used to query the capabilities of a

server.

SIP 7

SIP Response Codes 1yz Informational

100 Trying 180 Ringing (processed

locally) 181 Call is Being

Forwarded 2yz Success

200 ok 3yz Redirection

300 Multiple Choices 301 Moved Permanently 302 Moved Temporarily

4yz Client error 400 Bad Request 401 Unauthorized 404 Not Found 405 Method not Allowed 407 Proxy Authentication Re

quired 415 Unsupported Media Typ

e 482 Loop Detected 486 Busy Here

5yz Server failure 500 Server Internal Error

6yz Global Failure 600 Busy Everywhere

SIP 8

Invite Message Example

INVITE sip:UserB@there.com SIP/2.0Via: SIP/2.0/UDP here.com:5060From: BigGuy <sip:UserA@here.com>To: LittleGuy <sip:UserB@there.com>Call-ID: 12345600@here.comCSeq: 1 INVITESubject: Happy ChristmasContact: BigGuy <sip:UserA@here.com>Content-Type: application/sdpContent-Length: 147

Response Status SIP/2.0 200 OKVia: SIP/2.0/UDP here.com:5060From: BigGuy <sip:UserA@here.com>To: LittleGuy <sip:UserB@there.com>;tag=65a35Call-ID: 12345601@here.comCSeq: 1 INVITE Subject: Happy ChristmasContact: LittleGuy <sip:UserB@there.com>Content-Type: application/sdpContent-Length: 134

Request Method

“receive RTP G.711-encoded audio at 100.101.102.103:49172”

v=0o=UserA 2890844526 2890844526 IN IP4 here.coms=Session SDPc=IN IP4 100.101.102.103t=0 0m=audio 49172 RTP/AVP 0a=rtpmap:0 PCMU/8000

v=0 o=UserB 2890844527 2890844527 IN IP4 there.com s=Session SDP c=IN IP4 110.111.112.113 t=0 0 m=audio 3456 RTP/AVP 0 a=rtpmap:0 PCMU/8000

Message Header Fields

Payload

SIP 9

Address Header Fields From: message originator To: final recipient Request-URI: current destination; may change along

signaling path Contact: appears in INVITE / OPTIONS / ACK / REGISTER

requests and in responses. It indicates direct response address to which subsequent transactions are sent.

A UA may send subsequent BYE or ACK to Contact: address (unless configured to use an outbound proxy).

It includes redirection address in 3xx and 485 responses. It includes additional error information in 4xx, 5xx, and 6xx

responses. It may include preference weights. It includes current location in REGISTER requests. Multiple Contact: header fields may be included.

SIP 10

Session Description Protocol (SDP)

Convey sufficient information to enable participation in a multimedia session

SDP includes description of: Session name and purpose Times the session is active Media to use Information where to send and

receive media Contact information

SIP 11

Session Description Protocol (SDP)

o=sisalem 28908044538 289080890 IN IP4 193.175.132.118

s=SIP Examplee=sisalem@fokus.gmd.dec=IN IP4 126.16.69.4v=0t=28908044900 28908045000m=audio 49170 RTP/AVP 0 a=rtpmap:0 PCMU/8000

SIP 12

SIP Distributed Architecture

Redirect Server

Location Server

Registrar Server

User Agent

Proxy Server

SIP/PSTN Gateway

PSTN

SIP Components

Proxy Server

H.323

SIP/H.323 Gateway

SIP 13

SIP Components User agent(user application)

UA Client(caller) UA Server(called party)

Proxy Server Redirect Server Register

SIP 14

User Agents An application that initiates,

receives and terminates calls. User Agent Clients (UAC) – An entity

that initiates a call. User Agent Server (UAS) – An entity

that receives a call.

Both UAC and UAS can terminate a call.

Both SW and HW available

SIP 15

Proxy Server An intermediary program that acts as both a server

and a client to make requests on behalf of other clients.

Requests are serviced internally or by passing them on, possibly after translation, to other servers.

Interprets, rewrites or translates a request message before forwarding it.

Stateless proxy server No information about the message is stored

Stateful proxy server Forking reliability

SIP 16

SIP Operation in Proxy Mode

User Caller@sip.com on left-hand side is initiating a call to Callee@example.comon right-hand side; Callee registered with his server previously

Caller@sip.com Callee@support.example.com

Location Server

Proxy/Registrar

INVITE sip:Callee@support.example.comFrom: sip:Caller@sip.comTo: sip: Callee@example.comCall-ID: 345678@sip.com

#4

INVITE sip:Callee@example.com From: sip:Caller@sip.com To: sip: Callee@example.com Call-ID: 345678@sip.com

#1

Callee@

support

#3

Cal

lee

#2

OK 200From: sip:Caller@sip.comTo: sip: Callee@example.comCall-ID: 345678@sip.com

#5OK 200 From: sip:Caller@sip.comTo: sip: Callee@example.comCall-ID: 345678@sip.com

#6

ACK Callee@example.com#7

Media stream #8

SIP 17

Location Server A location server is used by a SIP

redirect or proxy server to obtain information about a called party’s possible location(s).

Locating service LDAP SQL

SIP 18

Redirect Server

After location service to look up a user, location information is sent back to the caller in a redirection class response, which concludes the transaction.

Unlike a proxy server, the redirect server does not forward SIP request.

Unlike a user agent server, the redirect server does not accept or terminate calls.

SIP 19

SIP Operation in Redirect Mode

Caller@sip.com

Callee@home.com

Redirect Server/Location Server

Proxy

ACK Callee@home.com#8

Cal

lee

#2

INVITE Callee@example.com#1

302 moved temporarilyContact: Callee@home.com

#4

Callee@

home.com

#3

INVITE Callee@home.com#6

ACK Callee@example.com#5

OK 200#7

SIP 20

Registrer Server A server that accepts REGISTER requests. The register server may support authenticat

ion. A registrer server is typically co-located with

a proxy or redirect server and may offer location services.

SIP 21

SIP Registration

SIP 22

Simplified SIP Call Setup and Teardown

302 (Moved Temporarily)

INVITE

200 (OK)200 (OK)

ACK

INVITE302

(Moved Temporarily)ACK

INVITE

180 (Ringing)180 (Ringing)180 (Ringing)

200 (OK)ACKACK ACK

RTP MEDIA PATH

BYEBYE BYE

200 (OK)200 (OK) 200 (OK)Call Teardown

MediaPath

Call Setup

INVITE

Location/Redirect ServerProxy Server Proxy Server User AgentUser AgentINVITE

SIP 23

SIP and Terminal MobilitySIP and Terminal Mobility

Home Network

HP

Visited Network

FPSignalling

Cell 2

Cell 1REGISTER

#1

REGISTER #2

SIP 24

SIP and Terminal MobilitySIP and Terminal Mobility

Home Network

HP

Visited Network

FPSignallingData

Cell 2

Cell 1

INVITE#1

INVITE#2

INVITE#3

#4

SIP 25

SIP and Terminal MobilitySIP and Terminal Mobility

Home Network

HP

Visited Network

FPSignallingData

Cell 2

Cell 1

REGISTER#3

REGISTER

#2

#1

reINVITE #3

#4

SIP 26

Personal Mobility

Invest: bob@lucent.com

bob@lucent.com