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Kommunikatsiooniteenuste arendusIRT0080Loeng 8

Avo Otstelekommunikatsiooni õppetool,

TTÜ raadio- ja sidetehnika inst.avo.ots@ttu.ee

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• A signaling protocol for setting up multimedia sessions between endpoints

• Fundamental shift from PSTN : infrastructure consists of software on standard servers

– SIP designed in line with other Internet protocols by the IETF

– Uses overlay control network consisting of SIP Proxies to route SIP messages : Media path (RTP/UDP) decoupled from signaling

– name@domain addressing; message syntax similar to HTTP

SIP (Session Initiation Protocol)

SIP proxy SIP proxy

V V V V

SIP

signaling

RTP/UDP packets

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Protocols• Session Initiation Protocol – for signaling• Reservation Protocol – for reserving network

resources• Real-Time protocol – Transporting real-time

data and providing QoS feedback• Real-Time Streaming protocol – for controlling

delivery of streaming media• Session Advertising Protocol – advertising

multimedia sessions via multicast• Session Description Protocol – to describe

multimedia sessions

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Session Initiation Protocol

• Application layer protocol for creating, modifying and terminating multimedia sessions

• Supports unicast, mesh and multicast conferences, and combination of these modes

• Similar to HTTP, Client-Server protocol, and text-based

• Provides reliability without assuming anything about the lower layer transport protocols

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Components

• User Agents– User Agent Client– User Agent Server

• Network Servers– Registration Servers– Proxy Servers

• Stateful Proxy Server

• Stateless Proxy Servers

– Redirect Servers

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Parser

• Sip messages are sent as text (Unicode characters)• The Sip message grammar is given in the

augmented BNF-form (RFC 2543)• Syntax tree builder (JTBGJ)• Parser Generator (Javacc)

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Protocol Building blocks

User Agent A

RegistrationServer

User Agent BProxy Server

Location Server

B’s current location

RegistrationServer

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Registration

• SIP Client sends REGISTER message to the Registration server.

• Indicates the physical location• REGISTER messages can be multicast

(“sip.mcast.net” – 224.0.1.75)• Serves as a simple locator service.

REGISTER sip:belltell.com SIP/2.0Via: SIP/2.0/UDP saturn.belltell.comFrom: sip:watson@belltell.comTo: sip:watson@belltel.comCSeq: 1 REGISTERCall-ID: 70710@saturn.belltell.comContact: sip:watson@globe..belltell.com:3890Expires: 7200

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Name Translation, UserLocation

• SIP Addressing by a Sip URL (user@host:port)

• Resolves host name through – DNS server

– Checks if domain name refers to a host

– Mail exchange host

• User at a specific host derived through zero or more translations

• If called party is not at SIP server, can be directed or proxied (personal mobility)

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Session invitation

• Caller sends the request directly to UAS or to the nearest proxy server

• Proxy server uses the locator service to determine the next hop server

• Proxy forwards the request towards the callee• Redirect server simply returns the alternate

addressesINVITE sip:watson@ieee.org SIP/2.0

Via: SIP/2.0/UDP c.belltell.com

From: sip:a.g.bell@belltell.com

To: sip:watson@ieee.org

Call-ID: 23534@c.belltell.com

Cseq: 1 INVITE

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Session Invitation (cont.)

• If there are more than one locations to be contacted, the proxy forks the requests to all the locations.

• The callee’s response is propagated backwards the servers ( uses the Via header )

• Stateful Proxy maintains the state according to the Call-ID. So forwards responses accordingly

• The caller sends ACK request following the response.

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Feature negotiation

• Allows a group of end systems to agree on the media to exchange and their respective parameters such as encodings.

• INVITE request has a listing of media types and associated encodings that the calling party is willing

• Called party responds with a subset of media types and encodings that it is willing to use

• Feature changes– Subsequent INVITE request– OPTIONS request

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200 (OK)

INVITE

180 (Ringing)180 (Ringing)

200 (OK)

ACK ACK

RTP MEDIA PATH

BYE BYE

200 (OK) 200 (OK)

Call Teardown

MediaPath

Call Setup

INVITE

Proxy

200 (OK)

INVITE

180 (Ringing)

ACK

BYE

200 (OK)

Proxy User AgentUser Agent

VoIP Call setup : SIP message flow

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Motivation

Collaborative AppsCollaborative Apps

SameTimeSameTime

Notes Calendar/emailNotes Calendar/email

(SIP-enabled) (SIP-enabled) Services/ InfrastructureServices/ Infrastructure

Corporate VoIP/dataCorporate VoIP/data networknetwork(VoIP trial)(VoIP trial)

VoIP infrastructureVoIP infrastructureEnhancements Enhancements (conferencing, context)(conferencing, context)

Web BrowserWeb Browser

VoIP enabled portalsVoIP enabled portals

Client-side SIP serviceClient-side SIP service

In-house conferencing service In-house conferencing service (IP/ PSTN phones)(IP/ PSTN phones)

Distributed application scenarios, Distributed application scenarios, e.g. networked gamese.g. networked games

Game servers, IM serversGame servers, IM servers

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Applic

ati

on Inte

rface

SIP ServiceSIP Service

Web Browser

IM Agent

Email Client

Other Apps(Multi-player Games, …)

Wrapper 1

Wrapper 2

Wrapper 3

SIPSIPStackStackwith with

pub/subpub/sub

Client Laptop

IP Phone

SoftPhone

PSTN/ cell phone

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LINGID

http://www.wifi.ee/foorum2/viewtopic.php?t=1083

http://www.packetizer.com/voip/sip/

http://www.tech-invite.com/

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Lingid (1)http://www.eventhelix.com/RealtimeMantra/

CongestionControl/queueing_theory.htm

http://www.tmcnet.com/voip/conference/m05/sip-workshop.

aspx

http://en.wikipedia.org/wiki/SIP_trunking

http://en.wikipedia.org/wiki/Session_Initiation_Protocol

http://en.wikipedia.org/wiki/IP_Multimedia_Subsystem

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Lingid (2)http://www.ietf.org/rfc/rfc4740.txt?number=4740

http://www.cisco.com/en/US/products/ps6638/products_data_sheet09186a00804fe332.html

http://www1.cs.columbia.edu/~kns10/talks/belllabs.ppt

http://www1.cs.columbia.edu/~kns10/talks/