SIP( Session Initiation Protocol)

1
SIP( Session Initiation Protocol)

• 2006. 6. 8 (?)
• ? ? ?
• hufs96mk_at_hufs.ac.kr

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Contents

• SIP Introduction
• History of SIP
• SIP Overview
• Generating the Request
• Successful Session Establishment
• Skype P2p Overlay Network

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SIP Introduction

• Why SIP?
• SIP isnt simply voice
• It supports services that provide Integrated
  Personal Communications Environments that include
  voice
• SIP Session Initiation Protocol
• Signaling protocol for initiating, modifying, and
  terminating interactive sessions
• A session can be voice, video, data or any
  combination tied together by SIP
• SIP enables any kind of communication everywhere
  at any time

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History of SIP

• IETF MMSUIC WG
• ????? ????? ?? ??? ?? SIP ??
• 1999? 3? RFC 2543?? ??
• 1999? 9? SIP WG ??
• IETF SIP WG
• ??? ???? ???? ?? ? ?? ???? ????
• 2002.06 RFC 3261 ? 2006.1 RFC 3853,RFC 4320
• Real-time Applications and Infrastructure Area
  2006.1
• Avt, ecript, emun, geopriv, ieprep, iptel,
  megaco, mmusic, sigtran, simple, sip, sipping,
  speechs, sepeermint, xcon
• Top Issue
• Skype? voip? ???? ??????, ?? ????? ??? ??

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IETF WGs Related to SIP

• SIPPING WG
• Header or method? ?? ??? ????? ????.
• SIMPLE WG
• ??? ??? ??? ??
• P2P SIP BOF
• SKYPE? ???? ?? WG
• SPEERMINT WG
• ??? ??? ??
• ENUM

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SIP Overview

• ?? ?? ?? ????
• ????? ?? ??, ??, ??? ?? ??
• ?? ?? ?? ????? ???
• UDP, TCP, SCTP
• Secure transport TLS over TCP, IPSec
• HTTP ??
• ??? ?? ????
• URIs(Uniform Resource Indicators) ??
• SIP-URI ?? siphufs96mk_at_hufs.ac.kr
• Personal Mobility ??
• ??? SIP ??, ?? ??(??)
• ?? ???? ?? ??,??, ??, ?? ??
• ??? ??(forking)?? ??
• ??? ??? ?? ??
• Voice, video, gaming, instant messaging,
  presence, call control, etc

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Terminology Definitions

• Call
• Identified by a globally unique call-id
• Created with sending INVITE
• Dialog
• Peer-to-peer relationship between two UAs
• Call-ID, TO tag, FROM tag? ???? ??
• Transaction
• Client? Server?? Request? ?? Final Response? ??
  ???? ?? ?? ??
• Call-ID, CSeq, To tag, From Tag? ???? ??

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Loose Routing(1/2)

• Strict routing was too strict. Service logic
  could not affect routing of the initial request
• Strict routing conflates the request target with
  the next hop destination.
• Strict route processing throws away the
  information in the received Request-URI
• Behavior of UAs with default-outbound-proxies
  problematic.
• Brittle system failure if any element misroutes.

INVITE BRoute C,D
INVITE CRoute D
INVITE D
C
A
B
D
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Loose Routing(2/2)

• Define Routing the right way
• Keep request target and next route destination
  separate
• Allow each route destination to determine when it
  has been reached
• Then add mechanism to provide backwards-compatibil
  ity with strict routing SIP elements
• Support for loose routing is indicated through an
  lr parameter

INVITE DRoute B,C
INVITE DRoute C
INVITE D
A
C
B
D
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SIP Basic Flow
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SIP Elements (1/2)

• Proxy Server
• UAC? UAS ???? SIP ??? ???? ???? ??
• Example Outbound Proxy, Inbound Proxy
• UA (User Agent)
• UAC(User Agent Client)
• SIP ?? ???? ???? ??? ????
• SIP transaction? ????, ?? Transaction ???? ??
  UAC? ??
• UAS(User Agent Server)
• ??? SIP ?? ???? ???? ???? ???? ??? ????
• ?? ??? ??, ??, ?????
• Location Server (Registrar)
• SIP? Personal Mobility ??? ???? ?? ??
• Database of locations of SIP User Agents
• Queried by Proxies in routing
• Updated by User Agents by Registration
• DNS Server
• SRV(Service) Records used to located Inbound
  Proxy Servers

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SIP Elements (2/2)

• Redirect Server
• ?? ???? ?? 3XX ??? ???? UAS
• 3XX ??? ?? ????? ????? ???? ?? URIs ??
• Back-to-Back User Agent(B2BUA)
• ??? SIP ?? ???? ?? ?? ???? ???? ??? ????
• ?? ??? ??? ?? ??? ?? UAC?? ??
• Proxy ???? ??, ????? ???? ??

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SIP Architecture
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SIP Uniform Resource Indicators (URIs)

• E-Mail ??? ?? user_at_domain
• Two URI schemes
• SIP URI
• Sipsunok_at_etri.re.kr
• Secure SIP URI
• Sipssunok_at_etri.re.kr
• RFC 3261?? ??? ??? ??
• TLS over TCP
• Two types of SIP URIs
• Address of Record (AOR) (identifiers user)
• sipsunok_at_etri.re.kr
• etri.re.kr ???? SIP ??? ???? ?? DNS SRV record
  ??
• Contact ( identifies a device, FQDN)
• sipsunok_at_129.354.100.34 or sipsunok_at_pc233.etri.r
  e.kr
• SIP URI Addressing Example
• sipsunok_at_etri.re.kr3000transporttcp

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Dialog(1/2)

• Creation of a Dialog
• Created through the generation of specific
  responses to INVITE request
• Specific responses
• 2XX response Dialog
• 101199 response with a To tag Early Dialog
• Dialog State (in UAC, UAS)
• Example Media Session

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Dialog State
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SIP Message(1/2)

• Request Message UAC ? UAS
• Response Message UAC ? UAS

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SIP Message(2/2)

• Request Message
• Response Message

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SIP Response(1/3)
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SIP Response(2/3)
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SIP Response(3/3)
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Generating the Request(1/9)

• Mandatory Header
• From, To, CSeq, Call-ID, Max-Forwards, Via
• Content-Length TCP ??? MUST, UDP??? SHOULD
• UAC??? ??? ?? ??
• Dialog ?? ??(Outside of a Dialog)
• UAC?? ????? ??
• Dialog ?? ??(Within a Dialog)
• ???? ?? Dialog ?? ????? ???? ??? ??
• From
• Request ??? ??? SIP-URI
• Tag Parameter
• ??? ????? ??, tag? ???? ??
• Globally unique value 32bit ???
• To
• Request ??? ??? SIP-URI
• Tag Parameter
• Outside of a dialog ????? ??
• Within a Dialog
• ???? ?? Dialog ?? ?? ???? ??

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Generating the Request(2/9)

• CSeq
• Sequence number, Method
• 32bit unsigned integer
• Dialog ?? Transaction? ?? ? ??? ??? ? ??
• Outside of a Dialog
• 231?? ?? ? ??? ??? ?? (non-REGISTER Request)
• Within a Dialog
• MUST be incremented by one
• ???? ???? ?? ? ??
• UAS? Dialog?? ??? Request? ?? ?? CSeq? ??
• ?? ??? ?? ? ?? 4XX(Client Error) ?? ??
• ?? 1 ?? ??? ???? ??
• Call-ID
• Globally unique identifier
• NO Reuse
• ??? ????? ??
• ????? localid_at_host? ?? ??
• Within a dialog
• ???? ?? Call-ID ??? ??

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Generating the Request(3/9)

• MAX-Forwards
• Value 70
• If value is 0 before the request reaches its
  destination,
• 483(Too Many Hops) error response
• Proxy?? Max-Forwards ?? ??
• Contact
• INVITE/200(OK) ????? ??? ????? ?
• ???? ?? ?? ??? ????? ???
• SIP-URI? ???, ?? ?? ??? FQDN ??? SIP-URI
• INVITE/200(OK) ??? ??? ???? Proxy ?? ?? ??
  Contact?? ??? ???? ?? ?? ??
• Record-Route ??? ???? ?? ????? ?? ?? ??
• Content-Type
• Internet media type of Message Body
• May be used multipart MIME type

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Generating the Request(4/9)

• Via
• Request ???? ?? ??
• ? Transaction? Response/Request ?? ?? ??
• Branch parameter
• Mandatory??, Magic cookie(z9hG4bk)? ????? ?
  (Must)
• Branch Parameter ??? Request Processing? ??? ???
  ?? ???? ???? ???? ?
• To tag, From tag, Call-ID, Request-URI, CSeq,
  Proxy-Require, Proxy-Authorization, Route ?
• ??? Loop ??? ?? ???
• Loop ?? ??
• ??? ???? Via? ??? ??? ?? ?? ??
• ??? branch param? ?? ?? ??? branch param? ? ??
• ????, Loop
• ??? ???, Sprial
• Response ?? ?? ???(topmost) Via ?? ??
• ??? Via ??? ?? ?? Via ?? ?? ?? ?? ??

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Generating the Request(5/9)

• Record-Route
• Initial INVITE ???, Proxy ??? ???? ??
• Initial INVITE ???, Dialog ?? ???? ???? ????
  ????? ? ??, Proxy ??? ???? ??
• Proxy ??? ???, lr ???? ??(MUST)
• UAC ?? ??
• Initial INVITE? ?? Final response? 200 ??? ??? ??
• Record-Route ??? ???? Route set ??(in reverse
  order)
• UAS ?? ??
• Initial INVTE? Record-Route??? Response? ??
• Record-Route ??? ???? Route set ??(in order)
• Content-Length
• Body? ?? ??
• Header? Body? ???? CRLF? ??? ?? ?? ??
• 0??? ?? ??
• Body? ?? ???? 0
• Content-Length? ?? ???? ?? ???? ?
• ?? ?? Body? ??? ?? ?? 400 Bad Request ?? ??
• TCP ??? Mandatory

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Generating the Request(6/9)

• Request-URI, Route
• Outside of Dialog
• Initial Request-URI SHOULD be set value of To
  Header
• Route Pre-existing route set
• RECOMMAND Pre-existing route set? ???? Outband
  Proxy ??
• Within a Dialog route set ??
• Route set? Empty
• Request_URI remote target URI (MUST)
• Route Header empty(MUST)
• Route set? not empty??, route set? first URI? lr
  ????? ????,
• Request_URI remote target URI (MUST)
• Route header route set( in order, including all
  parameters) (MUST)
• Route set? not empty??, route set? first URI? lr
  ????? ???? ???,
• Request_URI route set? first URI (Request_URI??
  ???? ?? ?? ?????? ??) (MUST)
• Route header(MUST)
• First URI? ??? ??? route set
• Remote target URI? Route header? last value? ??

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Generating the Request(7/9)

• Request-URI, Route
• Strict Routing Example

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Generating the Request(8/9)

• Request-URI, Route
• SIP Loose Routing Example 1

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Generating the Request(9/9)

• Request-URI, Route
• SIP Loose Routing Example 2

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SIP Routing Mechanism(1/5)
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SIP Routing Mechanism(2/5)
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SIP Routing Mechanism(3/5)
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SIP Routing Mechanism(4/5)
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SIP Routing Mechanism(5/5)
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Successful Session Establishment(1/5)

• Alice completes a call to Bob directly

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Successful Session Establishment(2/5)
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Successful Session Establishment(3/5)
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Successful Session Establishment(4/5)
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Successful Session Establishment(5/5)
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Call Setup Attempt Scenario Successful
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?? ???? ?? ? ??
ltSession ??? ??gt
ltDB ??gt
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Skype P2p Overlay Network

• A peer-to-peer client developed by kaZaa in 2003
  in 2003
• Skype can
• Work almost seamlessly across NATS and firewalls
• Has better voice quality than the MSN and Yahoo
  IM application
• Encrypts calls end-to-end, and stores user
  information in a decentralized fashion

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SIP? ?? Peer-to-Peer SIP

• Two Layers
• SIP layer call processing
• P2P overlay layer location service