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SIP. Session Initiation Protocol Short Introduction. Artur Hecker, ENST. SIP: Motivation. Need for a signalization protocol New applications with the same needs: IP telephony, video conferencing How can you: address the opponent? find the opponent? negotiate parameters?

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Sip

SIP

Session Initiation Protocol

Short Introduction

Artur Hecker, ENST


Sip motivation

SIP: Motivation

  • Need for a signalization protocol

  • New applications with the same needs:

    • IP telephony, video conferencing

  • How can you:

    • address the opponent?

    • find the opponent?

    • negotiate parameters?

    • manage the session?


Sip alternative visions

SIP: Alternative visions

  • ITU-T: H.323 recommendation

    • The first and most deployed vision

    • Different versions since 1996 (the recent - V3)

    • Defines the whole suite of components with the roles, codecs, interactions, etc. HEAVY!

  • Megaco: MGCP

    • Multimedia Gateway Control Protocol

    • RFC 2705


Sip rfc 2543

SIP: RFC 2543

  • Application-layer signaling protocol for:

    • Session creation/modification/termination

    • Parameter set agreement

    • User mobility by proxying and redirecting

    • Current location registration

  • SIP is:

    • Transport layer independent

    • Text-based and related to existent protocols (inheritance of SMTP and HTTP elements)


Sip main principles

SIP: Main principles

  • Internet-protocol: client-server

  • Messages and headers follow the HTTP and SMTP schemes

    • Client sends requests, server answers with state responses (HTTP-like)

    • Addressing uses the familiar format: sip:[email protected]

  • Simplicity, transparency

    • Designed to be an “easy protocol”


Sip components

SIP: Components

  • Listen at the default port UDP/5060

  • Can optionally use TCP

  • SIP-Clients:

    • UAC+UAS

  • SIP-Servers:

    • Proxy

    • Registration Server

    • Redirect Server


Sip simple call scenario

INVITE sip:[email protected] SIP/2.0

SIP/2.0 200 OK

ACK sip:[email protected] SIP/2.0

media session

BYE sip:[email protected] SIP/2.0

SIP: Simple call scenario

1

UAC

UAS

2

sip:[email protected]

sip:[email protected]

3

4


Sip messages 1

SIP: Messages (1)

INVITE sip:[email protected] SIP/2.0

Via: SIP/2.0/UDP rois.enst.fr

From: P. Chef <sip:[email protected]>

To: M. Pauvre <sip:[email protected]>

Call-ID: [email protected]

CSeq: 1 INVITE

Subject: Venez dans mon bureau

Content-Type: application/sdp

Content-Length: …

v=0

o=chef 5432 7654 IN IP4 10.1.1.1

s=Venez dans mon bureau

c=IN IP4 rois.enst.fr

m=audio 1050 RTP/AVP 0 3 4 5

2

SIP/2.0 200 OK

Via: SIP/2.0/UDP rois.enst.fr

From: P. Chef <sip:[email protected]>

To: <sip:[email protected]>

Call-ID: [email protected]

CSeq: 1 INVITE

Contact: sip:[email protected]

Content-Type: application/sdp

Content-Length: …

v=0

o=pauvre 14234 41322 IN IP4 …

s=Je suis en vacances

c=IN IP4 travail.enst.fr

m=audio 6043 RTP/AVP 0 3

1


Sip messages 2

SIP: Messages (2)

ACK sip:[email protected] SIP/2.0

Via: SIP/2.0/UDP rois.enst.fr

From: P. Chef <sip:[email protected]>

To: M. Pauvre <sip:[email protected]>

Call-ID: [email protected]

CSeq: 1 ACK

3

4

BYE sip:[email protected] SIP/2.0

Via: SIP/2.0/UDP rois.enst.fr

From: P. Chef <sip:[email protected]>

To: M. Pauvre <sip:[email protected]>

Call-ID: [email protected]

CSeq: 2 BYE


Sip methods

SIP: Methods

  • INVITE

    • invitation to a session, dialogue and session updates

  • ACK

    • response confirmation to INVITE

  • OPTIONS

    • query the server for its possibilities

  • BYE

    • release the call

  • CANCEL

    • Cancel the pending request

  • REGISTER

    • Registration of a new location at some registration server


Sip response classes

SIP: Response classes

  • 1xx: Informational

    • In-call-setup informational responses

  • 2xx: Success

    • Succeeded, done, accepted

  • 3xx: Redirection

    • Further action needed to complete request

  • 4xx: Client Error

    • Bad syntax or request can’t be fulfilled at the server

  • 5xx: Server Error

    • Server can’t fulfill a valid request

  • 6xx: Global Failure

    • The request can’t be fulfilled at any server


Sip headers

SIP: Headers

  • Usage and meaning depend on the method

  • Value according to syntax and current context

  • Different categories:

    • general, entity, request, response

    • end-to-end and hop-by-hop

  • Examples:

    • Hide

    • Encryption

    • Expires

    • Proxy-Authenticate

    • Proxy-Authorization

    • WWW-Authenticate


Sip components registration redirect servers

INVITE sip:[email protected]

302 Moved temporarily

Contact: [email protected]:3080;transport=udp

REGISTER sip:register.enst.fr SIP/2.0

Via: SIP/2.0/UDP travail.enst.fr

From: sip:[email protected]

To: sip:[email protected]

Call-ID: [email protected]

CSeq: 1 REGISTER

Contact: <sip:[email protected]:3080;transport=udp>

Expires: 3600

SIP: Components: Registration & Redirect Servers

enst.fr

register

travail


Sip components general proxy

INVITE sip:[email protected]

Via: SIP/2.0/UDP sip.lip6.fr

Via: SIP/2.0/UDP proxy.enst.fr

Via: SIP/2.0/UDP rois.enst.fr

INVITE sip:[email protected]

Via: SIP/2.0/UDP proxy.enst.fr

Via: SIP/2.0/UDP rois.enst.fr

INVITE sip:[email protected]

Via: SIP/2.0/UDP rois.enst.fr

SIP: Components:General proxy

sip

mobile

proxy

lip6.fr

enst.fr

SIP - trapezoid

rois


Sip security

SIP: Security

  • Authentication

    • Basic: clear text password

    • Digest: challenge/response with MD5

    • PGP: using PK cryptography

  • Encryption

    • e2e of the message body and some fields

    • hbh entire packet encryption

    • hbh of the Via: fields to hide the route


Sip presence future

SIP: Presence & Future

  • Problems:

    • Dialogue and session: no clear separation, INVITE used to adjust both states (will be changed in the new RFC)

    • No early media (UPDATE method)

    • Security problems: PGP hardly used, digest not proven to be secure, basic has severe problems (S/MIME, TLS, IPSec currently widely discussed, SIP-EAP draft released)

    • Routing: too strict (Loose Routing proposed in the new draft)

    • etc.

  • New RFC expected till the middle of March

    • It will be the largest RFC ever released… Simple?


Sip more

SIP: more…

  • Handley et al., Session Initiation Protocol, RFC 2543

  • S. Donovan, The INFO Method for SIP, RFC 2976

  • IETF, SIP Working Group Charter,http://www.ietf.org/html.charters/sip-charter.html

  • IETF, SIPPING Working Group Charter,http://www.ietf.org/html.charters/sipping-charter.html

  • J. Rosenberg et al., Session Initiation Protocol,draft-ietf-sip-rfc2543bis-09.txt

  • A. Johnston et al., SIP Call Flow Examples,draft-ietf-sip-call-flows-05.txt


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