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Session Initiation Protocol

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Proxy Server. SIP Router. Receives SIP messages from a user ... Unlike Proxy server, Redirect server don't pass the request on to other servers. SIP messages ... – PowerPoint PPT presentation

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Title: Session Initiation Protocol


1
Session Initiation Protocol
  • Presenter Kideok Cho (kdcho_at_mmlab.snu.ac.kr)
  • 2005. 10. 19

2
Contents
  • Session Initiation Protocol
  • SIP Entities
  • SIP Messages
  • Message Flow in SIP
  • Extending SIP
  • Current Status of SIP
  • Conclusion

3
Session Initiation Protocol
  • Main goal
  • Originally designed to invite users to existing
    multimedia conference
  • Today, used to create, modify, and terminate
    multimedia sessions
  • To deliver a session description to a user at
    their current location
  • RFC3261 and some related RFCs
  • About 70 related-RFCs

4
Session Description
  • Contains
  • Information for the remote user to join the
    session
  • Such as, IP address, Port , codecs
  • Most common format
  • Session Description Protocol (SDP), RFC 2327

v0 oAlice 26764646 46734 IN IP4
192.0.01 sLets talk about swimming
techniques cIN IP4 192.0.0.1 t0 0 maudio 20000
RTP/AVP 0 asendrecv mvideo 20002 RTP/AVP
31 asendrecv
5
SIP Uniform Resource Identifier (URI)
  • SIP URI e-mail-like address
  • Consists of user name and domain
  • sipkdcho_at_mmlab.snu.ac.kr
  • To provide personal mobility
  • Public URI vs. Current URI
  • sipkdcho_at_yonsei.ac.kr
  • Need to map public URI to current URI
  • Registrar

6
SIP Entities (1/2)
  • User Agent
  • SIP endpoint usually handled by users
  • User Agent Client (UAC)
  • User Agent Server (UAS)
  • Registrar
  • Maintains public URI to current URI mappings
  • Accepts REGISTER requests
  • Update a location database with the contact
    information

7
SIP Entities (2/2)
  • Proxy Server
  • SIP Router
  • Receives SIP messages from a user agent or
    another proxy server
  • Routes it towards its destination
  • Redirect Server
  • Maps the SIP address of the called party into new
    address(es) and returns them
  • Unlike Proxy server, Redirect server dont pass
    the request on to other servers

8
SIP messages
  • Request Methods
  • INVITE, REGISTER, ACK, BYE, CANCEL, etc
  • Response type
  • Provisional 1xx class
  • Provisional, searching, ringing, queuing etc.
  • Final 2xx, 3xx, 4xx, 5xx, 6xx class
  • Success
  • Redirection, forwarding
  • Request failure, server failure, global failure

9
Message Format
  • SIP is a textual request-response protocol

Start line A number of header fields Empty
line Optional message body
INVITE siplaptop1_at_factoryA.com SIP/2.0 Via
SIP/2.0/UDP pc33.company.com branch33 Max-Forwar
ds 70 To siplatptop1_at_factoryA.com From
sipTN_at_company.com Call-id 1234_at_pc33.company.com
Cseq 1 INVITE Contact sipTN_at_pc33.company.com v
0 oAlice 26764646 46734 IN IP4 192.0.01 sLets
talk about swimming techniques cIN IP4
192.0.0.1 t0 0 maudio 20000 RTP/AVP 0 asendrecv
SIP/2.0 200 OK Via SIP/2.0/UDP pc33.company.com
branch33 Max-Forwards 70 To siplatptop1_at_factor
yA.com From sipTN_at_company.com Call-id
1234_at_pc33.company.com Cseq 1 200 OK Contact
sipTN_at_pc33.company.com v0 oAlice 26764646
46734 IN IP4 192.0.01 sLets talk about swimming
techniques cIN IP4 192.0.0.1 t0 0 maudio 30000
RTP/AVP 0 asendrecv
10
SIP Call Redirection
SIP proxy
Redirect Server
Location Server
Alice
Bob
11
Extending SIP (1/2)
  • Event Notification (RFC 3265)
  • To obtain the status of a given resource
  • To track changes in that status
  • E.g. online, offline

Alice
Alices Voicemail
SUBSCRIBE Event message-summary
200 OK
NOTIFY Message-Waiting yes Message-Account
sipalice_at_vmail.example.com Voice-Message 2/8
(0/2)
200 OK
12
Extending SIP (2/2)
  • User Agent Capability (RFC 3840)
  • SIP methods it supports
  • Video, audio, text communication
  • Business or personal communication, etc
  • Signaling Compression (RFC 3320)
  • Textual encoding makes SIP messages grow
    dramatically as soon as several extensions are
    used at the same time

13
2005.10.5.
14
2005.10.18.
15
IP Multimedia Subsystem (IMS)
  • To offer Internet services everywhere and at any
    time using cellular technologies
  • Session Control Protocol
  • SIP(RFC 3261) was chosen among the three
    candidates (BICC, H.323, SIP)

16
tElephone NUmber Mapping (ENUM)
  • Protocol to identify ordinary phones, fax
    machines, pagers, email clients, etc, by one
    E.164 number

From Jaeyoung Chois presentation
17
Conclusion
  • Session Initiation Protocol is new standard
  • Many advantages
  • Text-based encoding
  • Application layer protocol
  • Many extensions
  • Makes SIP more useful
  • VoIP, IMS, ENUM, etc

18
Any Question?
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