Sip básico

Session Initiation Protocol (SIP)
陳懷恩 博士 助理教授兼計算機中心資訊網路組組長 國立宜蘭大學資工系 Email: wechen@niu.edu.tw TEL: 03-9357400 # 340

Outline
Session Initiation Protocol SIP Extensions SIP Operation Examples References Q&A

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Session Initiation Protocol

Introduction [1/2]
SIP: Session Initiation Protocol
Originally developed in the MMUSIC working group of the IETF Great interest led to a separateSIP working Group RFC 2543 RFC 3261

SIP is used in conjunction with several other IETF protocols, such as SDP and RTP. SIP has been selected as the interfaces between the IP Multimedia Core Network elements.
※ MMUSIC: Multiparty Multimedia Session Control IETF: Internet Engineering Task Force

RFC: Request for Comments SDP: Session Description Protocol RTP: Real-time Transport Protocol
4Introduction [2/2]
SIP is a powerful alternative to H.323.
More flexible Simpler Easier to implement Better suited to the support of intelligent user devices Better suited to the implementation of advanced features

SIP+MGCP/MEGACO will be the dominant VoIP signaling architecture of the future.

※MGCP/MEGACO: Media Gateway Control Protocol VoIP: Voice over IP
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Architecture
SIP is asignaling protocol.
Setup a session
Find user’s current location Use SDP to carry session information

Modify a session Teardown a session

SIP signaling is separate from the media.
SIP Messages RTP Streams SIP User Agent IP Network SIP User Agent
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Network Entities [1/5]
SIP User Agent (UA)
User Agent Client (UAC)
Application that sends requests The calling party

User AgentServer (UAS)
Application that receives requests and sends responses The called party

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Network Entities [2/5]
Location Server (Registrar)
A database that maintains users’ location information
Receive REGISTER requests Record who is at where now Support user mobility

Generally combined with a proxy or redirect server

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Network Entities [3/5]
Proxy Server
Receive requests Forwardrequests or send responses back to originator or both
ex. 100 Trying

Used for call forwarding, time-of-day routing or follow-me services

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Network Entities [4/5]
Redirect Server
Receive requests Send responses Map the destination address to zero or more new addresses
302 Moved Temporarily 404 Not Found

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Network Entities [5/5]

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Registration Flow

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Call Flow[1/3]
UA to UA

INVITE Transaction

BYE Transaction
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Call Flow [2/3]
Through Proxy Server
Location Server (3) Bob@BobHost

NotHere.org

UA Alice@Here.org (1) INVITE Bob@NotHere.org

(2) Bob

Proxy Server

UA Bob@BobHost

(4) INVITE Bob@BobHost (5) 200 OK (6) 200 OK (7) ACK (8) ACK (9) RTP Media Stream

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Call Flow [3/3]
Through Redirect Server
Location ServerNotHere.org

UA Alice@Here.org (1) INVITE Bob@NotHere.org

Proxy Server

UA Bob@BobHost

(4) 302 Moved temprarily Contact: Bob@BobHost (5) ACK (6) INVITE Bob@BobHost (7) 200 OK (8) ACK (9) RTP Media Stream

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Message Syntax [1/2]
Text-based
Similar to HTTP More bandwidth consumption

Two type
Request message Response message

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Message Syntax [2/2]
Format
Start-lineRequest: request-line
Method SP Request-URI SP SIP-version CRLF Specify the type of request

Response: status-line
SIP-version SP Status-code SP Reason-phrase CRLF Indicate the success of failure of a given request

Headers*
Additional information of the request or response

CRLF [Message body]
Describe the type of session Examined only at the two end SDP
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SIP Addressing
URI:Uniform Resource Identifiers
Format: user@host ex. sip:944021371@sip3.ipv6.club.tw ex. sip:bean@course.ccca.nctu.edu.tw ex. sip:bean@140.113.11.35:5060 ex. sip:bean@[3ffe:3600:2::1]:3600

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Request Messages [1/2]
Method SP Request-URI SP SIP-version CRLF Methods
REGISTER, INVITE, ACK, BYE, CANCEL, OPTIONS REGISTER
Create a mapping of public address and current address Can register to...