Session Initialization Protocol (SIP)

Presented by: Lei Luo

Computer & Information Science DepartmentUniversity of Delaware

Nov. 18, 2004

Some slides are borrowed from Dorgham Sisalem’s SIP Tutorial

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What Is SIP?

Phone Network

Alice

Alice’s Home Station

Bob

3

What is SIP?

A signaling protocol Set up Modify Multimedia Sessions Tear down Request/deliver presence and Instant messages

Enable Internet endpoints Discover one another Agree on a characterization of a session

4

What is NOT SIP?

Not a transport protocolNot a media transmission protocolNot a QoS Reservation ProtocolNot an integrated communications system

5

Internet Multimedia Protocol Stack

Source: Henning Schulzrinne,http://www.cs.columbia.edu/~hgs/internet/

SCTP

6

What can SIP Do?

User LocationUser AvailabilityUser CapabilitySession SetupSession Management

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What Else Can SIP Do?

Request/deliver presence information and instant message sessions: Publish and upload presence information Request delivery of presence information Notify presence and other events Transport instant messages

8

Tesla Marconi

INVITE

180 Ringing

200 OK

ACK

Media Session

BYE

200 OK

Simple SIP session establishment exampleSimple SIP session establishment example

9

AliceProxy Server

Bob

INVITE

180 Ringing

200 OK

ACK

Media Session

BYE

200 OK

INVITE

180 Ringing

200 OK

SIP call example with proxy serverSIP call example with proxy server

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Alice Registrar Server

REGISTERContact: sip:alice@128.175.13.16

200 OK

SIP registration exampleSIP registration example

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SUBSCRIBE

200 OK

NOTIFY

200 OK

…

NOTIFY

200 OK

MESSAGE

200 OK

MESSAGE

200 OK

SIP presence and instant message exampleSIP presence and instant message example

12

How does SIP Work?

Based on HTTP-like request/response modelText-based protocolUse the UTF-8 charsetSIP message

A request from a client to a server A response from a server to a client

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SIP User Agent (UA)

SIP-enabled end-devices Maintain states on calls

Local and remote tags Call-ID Local and remote CSeq header fields

Contain client (UAC) & server applications (UAS) Must support SDP for media description

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SIP User Agent Examples

Cisco Siemens

MIC

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Presence Agent

SIP devices Receive subscription requests Generate state notifications

Collect presence informationNeed to authenticate a subscription request

16

SIP Gateway

A special type of UA Interface a SIP network to a non-SIP network

Terminate the signaling pathMay or may not terminate the media pathSupport much more users than normal UA

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SIP Networks with Gateways

InternalTelephoneExtn: 7040

SIP/PSTN Gateway

Department PBX

Web based configuration

Web server

Telephoneswitch

SQLdatabase

Proxy, redirect, registrar server

Extn: 7134

xiaotaow@cs NetMeeting

H.323

rtspd: media server

sipum: Unified messaging

Quicktime

RTSP clients

RTSP

Extn: 7136

713x

Single machine

SNMP(Network Management)

sipconf: Conference server

SIP/H.323 Gateway

Local/long distance1-212-5551212

Borrowed from Xiaotao Wu’s slides (Columbia University, 2002)

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SIP Servers SIP Workhorses

Logical Entities Accept SIP requests Respond to requests

Types of Servers Proxy Server Redirect Server Registration Server

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SIP Message Format

Generic-message= Start-line

*message-header

CRLF

[ message-body ]

Start-line= Request-Line / Status-Line

Request-Line = Method SP Request-URI SP SIP-Version CRLF

Status-Line = SIP-Version SP Status-Code SP Reason-Phase CRLF

SP – blank space

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SIP Methods Sets

Basic Methods INVITE REGISTER BYE ACK CANCEL OPTIONS

Extended Methods REFER SUBSCRIBE NOTIFY MESSAGE etc.

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SIP Response Codes

Consistent with/extend HTTP/1.1 response codes 1xx – Informational 2xx – Success 3xx – Redirection 4xx – Client error 5xx – Server failure 6xx – Global Failure

600 – Busy Everywhere 603 – Decline 604 – Does Not Exist Anywhere etc.

Borrowed from HTTP

Created for SIP

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SIP Registration Server

Alice Registrar ServerSIP/2.0 200 OKVia: SIP/2.0/UDP 128.175.13.50:5060; branch=z9hG4bKus19To: Alice <sip:alice@eecis.udel.edu>From: Alice <sip:alice@eecis.udel.edu>;tag=3431Call-ID: 23@128.175.13.50CSeq: 1 REGISTERContact: <sip:alice@128.175.13.50>;expires=3600Content-Length: 0

REGISTER sip:registrar.udel.eduVia: SIP/2.0/UDP 128.175.13.50:5060; branch=z9hG4bKus19Max-Forwards: 70To: Alice <sip:alice@eecis.udel.edu>From: Alice <sip:alice@eecis.udel.edu>;tag=3431Call-ID: 23@128.175.13.50CSeq: 1 REGISTERContact: sip:alice@128.175.13.50Content-Length: 0

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SIP Proxy Server

Alice Bob

Outbound proxy server

Inbound proxy server

Location server

DNS server

Media (RTP)

INVITE sip:bob@yahoo.com SIP/2.0Via: SIP/2.0/UDP 100.101.102.103:5060; branch=z9hG4bKmp17aTo: Bob <sip:bob@yahoo.com>From: Alice <sip:alice@udel.edu>;tag=42Subject: Where are you exactly?Contact: <sip:alice@pc.udel.edu>

INVITE sip:bob@yahoo.com SIP/2.0Via: SIP/2.0/UDP proxy.yahoo.com:5060; branch=z9hG4bKtiop3Via: SIP/2.0/UDP proxy.udel.com:5060; branch=z9hG4bK83842.1Via: SIP/2.0/UDP 100.101.102.103:5060; branch=z9hG4bKmp17aTo: Bob <sip:bob@yahoo.com>From: Alice <sip:alice@udel.edu>;tag=42Subject: Where are you exactly?Contact: <sip:alice@pc.udel.edu>100 Trying

100 Trying

180 Ringing

180 Ringing

180 Ringing

200 OK

200 OK

200 OK

ACKBYE

200 OK

INVITE sip:bob@yahoo.com SIP/2.0Via: SIP/2.0/UDP proxy.udel.com:5060; branch=z9hG4bK83842.1Via: SIP/2.0/UDP 100.101.102.103:5060; branch=z9hG4bKmp17aTo: Bob <sip:bob@yahoo.com>From: Alice <sip:alice@udel.edu>;tag=42Subject: Where are you exactly?Contact: <sip:alice@pc.udel.edu>

SIP Trapezoid

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SIP Proxy Server

INVITE Bob

Alice

Bob’s voicemail

Bob’s Phone

INVITE Bob

486 Busy Here

INVITE Bob

Proxy servers can make flexible “routing decisions” to decide where to send a request.

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SIP Proxy Server

INVITE Bob

Alice

Bob’s Cell PhoneINVITE Bob

INVITE Bob

Bob’s Office Phone

INVITE Bob

Bob’s Home Phone

In parallel search, a proxy issues several requests to possible user locations upon receiving an incoming request.

200 OK

200 OKCANCEL

CANCEL

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SIP Redirect Server

INVITE sip:bob@yahoo.com SIP/2.0Via: SIP/2.0/UDP 100.101.102.103:5060; branch=z9hG4bKmp17aTo: Bob <sip:bob@yahoo.com>From: Alice <sip:alice@udel.edu>;tag=42Subject: Where are you exactly?Contact: <sip:alice@pc.udel.edu>

Alice

Bob

Redirect Server

SIP/2.0 302 Moved TemporarilyVia: SIP/2.0/UDP 100.101.102.103:5060; branch=z9hG4bKmp17aTo: Bob <sip:bob@yahoo.com>;tag=64From: Alice <sip:alice@udel.edu>;tag=42Subject: Where are you exactly?Contact: sip:alice@200.201.202.203ACK

INVITE sip:bob@200.201.202.203 SIP/2.0Via: SIP/2.0/UDP 100.101.102.103:5060; branch=z9hG4bKmp17aTo: Bob <sip:bob@yahoo.com>From: Alice <sip:alice@udel.edu>;tag=13473Subject: Where are you exactly?Contact: <sip:alice@pc.udel.edu>

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That’s It!

We have learned a lot about SIP!!

Did we really learn a lot of stuff about SIP?

No Way!!!

Then what are we gonna do?

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Key References

J. Rosenberg, SIP: Session Initialization Protocol, RFC 3261, 2002

A. Johnston, SIP: Understanding the Session Initialization Protocol, 2nd edition

J. Kuthan and D. Sisalem, SIP Tutorial http://iptel.org/sip/

SIP web site: http://www.cs.columbia.edu/sip/

Questions?