Introduction to SIP

1
Introduction to SIP

• School of Electronics and Information
• Kyung Hee University
• Choong Seon HONG
• cshong_at_khu.ac.kr
• http//networking.khu.ac.kr

2
Overview of SIP

• Proposed standard released in 1999, current
  release in 2002
• Session-layer control-plane signaling protocol
  with support for establishing, modifying and
  terminating one-to-one or multiparty sessions.
• Light-weight, ASCII based generic signaling
  protocol to facilitate multimedia communications
  over IP
• Independent of media characteristics and
  transport protocol properties
• Work in IETF currently by SIP WG and SIPPING WG
• Related work by MMUSIC WG, AAA WG, GEOPRIV WG,
  SIMPLE WG, Internet Telephony WG
• 3GPP has decided to support it in IP multimedia
  services (IMS) domain.

3
Overview of SIP (contd)

• SIP is complimentary to SGCP/MGCP
• SIP Provides Session Control
• SGCP/MGCP Provides Device Control

4
The Big FAQ and SIP?

• Q You are too IP-centric, arent you?
• A Of course, we are.
• Internet telephony (which has Internet in its
  name) is about IP.
• IP telephony runs on top of IP and utilizes the
  IP service model.
• It is not about re-engineering PSTN -- PSTN is
  good enough.
• SIP is much more similar to HTTP rather than to
  legacy signaling both in terms of service model
  and protocol design.

5
Problem description

• Environment aging PSTN equipment, carrier fiber
  overcapacity and arrival of multimedia
  communications with preparation to millions of
  mobile hosts that are IP-aware. Additionally, the
  possibility of programming PSTN-services in a
  more open environment.
• Problem how to enable gradual deployment and
  transition to avoid the one-big-leap-for-mankind
  scenarios?
• Approach IETF multimedia architecture and
  interoperability schemes with PSTN and 3GPP.
  Signaling is one part of this. The multimedia
  architectures capabilities are related to Quality
  of Service architecture and IP multicast.

6
IETF Multimedia Architecture
7
What Protocols Are Needed?

• Signaling protocol to establish presence, locate
  users, set up, modify and teardown sessions
• Media Transport Protocols for transmission of
  packetized audio/video
• Supporting Protocols
• Gateway Location, QoS, interdomain AAA,
• address translation, IP, etc.

AAA Authentication, Authorization, Accounting
8
What Protocols Are There

• Signaling SIP/SDP (IETF), H.323 (ITU-T)
• Note SIP adopted by 3gpp lower production and
  operation costs reported
• Media RTP (IETFs, adopted by ITU-T)
• Transport UDP, TCP, (Stream Control
  Transmission Protocol RFC 2960)
• Supporting protocols
• DNS
• TRIP - Telephony Routing over IP - discovery and
  exchange of IP telephony gateway routing tables
  between providers
• RSVP - Resource Reservation Setup Protocol
• COPS - Common Open Policy Service - protocol for
  for supporting policy control over QoS
• Diameter - Authentication, Accounting,
  Authorization

9
SIP Signaling

• SIP is end-to-end, client-server session
  protocol
• SIPs primarily provides presence and mobility
• Protocol primitives Session setup, termination,
  changes
• Arbitrary services built on top of SIP, e.g.
• Redirect calls from unknown callers to secretary
• Reply with a webpage if unavailable
• Send a JPEG on invitation
• Features
• Textual encoding (telnet, tcpdump compatible)
• Programmability

10
SIP - General Purpose Presence Protocol

• SIP is not limited to Internet
• SIP establishes user presence
• SIP messages can convey arbitrary signaling
  payload session description, instant messages,
  JPEGs, any MIME types
• Suitable for applications having a notion of
  session
• distributed virtual reality systems,
• network games (Quake II/III implementations),
• video conferencing, etc.
• Applications may leverage SIP infrastructure
  (Call Processing, User Location, Authentication)
• Instant Messaging and Presence
• SIP for Appliances

11
Internet Multimedia

• Real Time Protocol (RTP) media packets
• Real Time Control Protocol (RTCP) monitor
  report
• Session Announcement Protocol (SAP)
• Session Description Protocol (SDP)
• Session Initiation Protocol (SIP)
• Real Time Stream Protocol (RTSP) play out
  control
• Synchronized Multimedia Integration Language
  (SMIL) mixes audio/video with text and graphics
  August 2001
• References Search keyword at http//www.rfc-edito
  r.org/rfc.html
• For SMIL - http//www.w3.org/AudioVideo/

12
Stages of IP Signaling Development

• Precommercial stage (1980-1995)
• Research in organizations and universities
• IETF Audio/Video Transport (AVT) WG - RTP
• IETF Multiparty Multimedia Session Control
  (MMUSIC) WG SIP
• PC-centric stage (1995-1998)
• First commercial VoIP software, proprietary
  software
• Calls from multimedia PC to another multimedia PC
• ITU May-June 1995 H.323v1
• Most commercial applications H.323 compliant by
  the end of 1996
• Carrier-grade stage (1998-)
• Service provider VoIP deployment
• First obstacle integration to PSTN signalling
  (gateway functionality)
• Development of media gateway controller protocols
  (MGCP and Megaco/H.248)
• Todays approach coexistence of SIP, H.323, MGCP
  and Megaco/H.248

13
SIP History

• Work began in 1995 in IETF mmusic WG
• 02/1996 draft-ietf-mmusic-sip-00 15 ASCII
  pages, one request type
• 12/1996 -01 30 ASCII pages, 2 request types
• 01/1999 -12 149 ASCII pages, 6 methods
• 03/1999 RFC 2543, 153 ASCII pages, 6 methods
• 11/1999 SIP WG formed
• 11/2000 draft-ietf-sip-rfc2543bis-02, 171 ASCII
  pages, 6 methods
• 12/2000 it was recognized that amount of work at
  SIP WG was becoming unmanageable 1 RFC 18 I-Ds
  on WGs agenda numerous individual submissions
• 04/2001 proposal for splitting SIP WG into SIP
  and SIPPING announced
• 2001 SIP implementations widely available
• http//www.cs.columbia.edu/hgs/sip/implementation
  s.html
• http//www.pulver.com/sip/products.html

14
SIP End-devices

• User Agent (user application)
• UA Client (originates calls)
• UA Server (listens for incoming calls)
• both SW and HW available

15
SIP Components

• SIP Proxy Server
• relays call signaling, i.e. acts as both client
  and server
• operates in a transactional manner, i.e., it
  keeps no session state
• SIP Redirect Server
• redirects callers to other servers
• SIP Registrar
• accept registration requests from users
• maintains users whereabouts at a Location
  Server (like GSM HLR)

16
Telephony on the Internet may not be a
stand-alone business, but part of IP services
SIP/RTP Media Architecture

• Public IP Backbone
• Goes everywhere
• End-to-end control
• Consistent for all services
• DNS mobility
• Messaging
• Web
• Directory
• Security
• QoS
• Media services
• Sessions
• Telephony

Telephone Gateway SIP client
CAS, Q.931, SS7
SIP
PCM
RTP
MGCP
CAS channel associated signaling
Any other sessions
17
Commercial Grade IP Telephony
Assure baseline PSTN features Leverage and
Commonality of telephony with the Web/Internet

• New services (new revenue)
• Scalability (Web-like)
• Baseline PSTNPBX features
• Client user authentication
• Accounting assured QoS
• QoS assured signaling
• Security assured signaling
• Hiding of caller ID location

• Better than PSTN features
• New fast service creation
• Internet (rapid) scalability
• Mobility
• Dynamic user preferences
• End-to-end control
• Service selection
• Feature control
• Mid-call control features
• Pre-call
• Mid-call

18
IP Communications
Complete integration of all services under full
user control

• PSTN/PBX-like
• POTS
• AIN CS-1, CS-2
• PBX Centrex
• User has control of
• All addressable devices
• Caller and called party preferences
• Better quality than 3.1 kHz

• Web-like
• Presence
• Voice and text chat
• Messaging
• Voice, data, video
• Multiparty
• Conferencing
• Education
• Games
• Any quality
• Most yet to be invented

19

• Development of SIP

• IETF - Internet Engineering Task Force
• MMUSIC - Multiparty Multimedia Session Control
  Working Group
• SIP developed by Handley, Schulzrinne, Schooler,
  and Rosenberg
• Submitted as Internet-Draft 7/97
• Assigned RFC 2543 in 3/99
• Internet Multimedia Conferencing Architecture.
• Alternative to ITUs H.323
• H.323 used for IP Telephony since 1994
• Problems No new services, addressing, features
• Concerns scalability, extensibility

20

• SIP Philosophy

• Internet Standard
• IETF - http//www.ietf.org
• Reuse Internet addressing (URLs, DNS, proxies)
• Utilizes rich Internet feature set
• Reuse HTTP coding
• Text based
• Makes no assumptions about underlying protocol
• TCP, UDP, X.25, frame, ATM, etc.
• Support of multicast

21

• SIP Clients and Servers - 1

• SIP uses client/server architecture
• Elements
• SIP User Agents (SIP Phones)
• SIP Servers (Proxy or Redirect - used to locate
  SIP users or to forward messages.)
• Can be stateless or stateful
• SIP Gateways
• To PSTN for telephony interworking
• To H.323 for IP Telephony interworking
• Client - originates message
• Server - responds to or forwards message

22

• SIP Clients and Servers - 2

• Logical SIP entities are
• User Agents
• User Agent Client (UAC) Initiates SIP requests
• User Agent Server (UAS) Returns SIP responses
• Network Servers
• Registrar Accepts REGISTER requests from clients
• Proxy Decides next hop and forwards request
• Redirect Sends address of next hop back to
  client
• The different network server types may be
  collocated

23

• SIP Addressing

• SIP gives you a globally reachable address
• Callees bind to this address using SIP REGISTER
  method.
• Callers use this address to establish real-time
  communication with callees.
• URLs used as address data format examples
• sipjiri_at_iptel.org
• sipvoicemail_at_iptel.org?subjectcallme
• sipsales_at_hotel.xy geo.position48.54_-123.84_1
  20

24
SIP Addressing (contd)

• must include host, may include user name, port
  number, parameters (e.g., transport), etc.
• may be embedded in Webpages, email signatures,
  printed on your business card, etc.
• address space unlimited
• non-SIP URLs can be used as well (mailto,
  http, ...)

25
SIP Registration
26

• SIP Session Setup Example

SIP User Agent Client
SIP User Agent Server
INVITE sippicard_at_uunet.com
200 OK
ACK
Media Stream
BYE
200 OK
host.wcom.com
sip.uunet.com
27

• Proxy Server Example

server.wcom.com
28
SIP Operation in Proxy Mode
29
Proxy Server Functionality

• Serve as rendezvous point at which callees are
  glabally reachable
• Perform routing function, i.e., determine to
  which hop (UA/proxy/redirect) signaling should be
  relayed
• Allow the routing function to be programmable.
  Arbitrary logic may be built on top of the
  protocol
• users signaling preferences
• AAA
• firewall control
• etc.
• Forking Several destinations may be tried for a
  request sequentially or in parallel.

30
Proxy Chaining

• There may be also cases when a local outbound
  proxy may be involved
• provides locally important call processing logic
  (e.g., identifying nearest 119)
• manages firewall
• provides least-gateway-cost routing service
• IP phones must know address of the proxymay be
  configured manually or with a configuration
  protocol (DHCP, TFTP, ... )
• In general, servers may be arbitrarily chained
• a central companys server may distribute
  signaling to departmental servers
• a user may want to forward incoming calls to her
  cell phone

31
Proxy Chaining an Example
Note signaling (in red) may take a completely
different path from media in blue)
32

• Redirect Server Example

33
SIP Operation in Redirect Mode
34
SIP Server - Proxy versus Redirection

• A SIP server may either proxy or redirect a
  request
• Which of the two method applies is a
  configuration issue. It may be statically
  configured or dynamically determined/
• Redirection useful if a user moves or changes
  her provider (PSTN The number you have dialed
  is not available.) -- caller does not need to
  try the original server next time. Stateless.
• Proxy useful if forking, AAA, firewall control
  needed. In general, proxying grants more control
  to the server.

35

• SIP Requests RFC2543 Methods

• SIP Requests (Messages) defined as
• Method SP Request-URI SP SIP-Version CRLF
  (SPSpace, CRLFCarriage Return and Line Feed)
• Example INVITE sippicard_at_wcom.com SIP/2.0

36

• SIP Requests Example

• Required Headers (fields)
• Via Shows route taken by request.
• Call-ID unique identifier generated by client.
• CSeq Command Sequence number
• generated by client
• Incremented for each successive request

INVITE sippicard_at_wcom.com SIP/2.0 Via
SIP/2.0/UDP host.wcom.com5060 From Alan
Johnston ltsipalan.johnston_at_wcom.comgt To Jean
Luc Picard ltsippicard_at_wcom.comgt Call-ID
314159_at_host.wcom.com CSeq 1 INVITE

Uniquely identify this session request
37

• SIP Requests Example

• Typical SIP Request

INVITE sippicard_at_wcom.com SIP/2.0 Via
SIP/2.0/UDP host.wcom.com5060 From Alan
Johnston ltsipalan.johnston_at_wcom.comgt To Jean
Luc Picard ltsippicard_at_wcom.comgt Call-ID
314159_at_host.wcom.com CSeq 1 INVITE Contact
sipalan.johnston_at_wcom.com Subject Where are you
these days? Content-Type application/sdp
Content-Length 124 v0 oajohnston 5462346
332134 IN IP4 host.wcom.com sLet's Talk t0
0 cIN IP4 10.64.1.1 maudio 49170 RTP/AVP 0 3
38

• SIP Responses

• SIP Responses defined as (HTTP-style)
• SIP-Version SP Status-Code SP Reason-Phrase CRLF
  (SPSpace, CRLFCarriage Return and Line Feed)
• Example SIP/2.0 404 Not Found
• First digit gives Class of response

39

• SIP Responses Example

• Required Headers
• Via, From, To, Call-ID, and CSeq are copied
  exactly from Request.
• To and From are NOT swapped!

SIP/2.0 200 OK Via SIP/2.0/UDP
host.wcom.com5060 From Alan Johnston
ltsipalan.johnston_at_wcom.comgt To Jean Luc Picard
ltsippicard_at_wcom.comgt Call-ID 314159_at_host.wcom.co
m CSeq 1 INVITE
40

• SIP Responses Example

• Typical SIP Response (containing SDP)

SIP/2.0 200 OK Via SIP/2.0/UDP
host.wcom.com From Alan Johnston
ltsipalan.johnston_at_wcom.comgt To Jean Luc Picard
ltsippicard_at_wcom.comgt Call-ID 314159_at_host.wcom.co
m CSeq 1 INVITE Contact sippicard_at_wcom.com Subj
ect Where are you these days? Content-Type
application/sdp Content-Length
107 v0 opicard 124333 67895 IN IP4
uunet.com sEngage! t0 0 cIN IP4
11.234.2.1 maudio 3456 RTP/AVP 0
41

• Forking Proxy Example

SIP User Agent Client
SIP Proxy Server
SIP User Agent Server 2
SIP User Agent Server 1
INVITE sippicard_at_wcom.com
INVITE
INVITE
100 Trying
404 Not Found
ACK
Fork
180 Ringing
180 Ringing
200 OK
200 OK
ACK
Media Stream
BYE
200 OK
sip.mci.com
proxy.wcom.com
host.wcom.com
sip.uunet.com
42

• SIP Headers - Partial List

43

• SIP Headers - Continued

44

• SIP Headers - Continued

45

• Via Headers and Routing

• Via headers are used for routing SIP messages
• Requests
• Request initiator puts address in Via header
• Servers check Via with senders address, then add
  own address, then forward. (if different, add
  received parameter)
• Responses
• Response initiator copies request Via headers.
• Servers check Via with own address, then forward
  to next Via address

46

• SIP Firewall Considerations

• Firewall Problem
• Can block SIP packets
• Can change IP addresses of packets
• TCP can be used instead of UDP
• Record-Route can be used
• ensures Firewall proxy stays in path
• A Firewall proxy adds Record-Route header
• Clients and Servers copy Record-Route and put in
  Route header for all messages

47

• SIP Message Body

• Message body can be any protocol
• Most implementations
• SDP - Session Description Protocol
• RFC 2327 4/98 by Handley and Jacobson
• http//www.ietf.org/rfc/rfc2327.txt
• Used to specify info about a multi-media session.
  
• SDP fields have a required order
• For RTP - Real Time Protocol Sessions
• RTP Audio/Video Profile (RTP/AVP) payload
  descriptions are often used

48
Session Description Protocol (SDP)

• Convey sufficient information to enable
  participation in a multimedia session
• SDP includes description of
• Media to use (codec, sampling rate)
• Media destination (IP address and port number)
• Session name and purpose
• Times the session is active
• Contact information
• Note indeed SDP is a data format rather than a
  protocol.

49
SDP Examples

• v0
• osisalem 28908044538 289080890 IN IP4
  193.175.132.118
• sSIP Tutorial
• esisalem_at_fokus.gmd.de
• cIN IP4 126.16.69.4
• t28908044900 28908045000
• maudio 49170 RTP/AVP 0 98
• artpmap98 L16/11025/2

50

• SDP Examples (contd)

SDP Example v0 oajohnston 1-613-555-1212 IN
IP4 host.wcom.com sLet's Talk t0 0 cIN IP4
101.64.4.1 maudio 49170 RTP/AVP 0 3
SDP Example v0 opicard 124333 67895 IN IP4
uunet.com sEngage! t0 0 cIN IP4
101.234.2.1 maudio 3456 RTP/AVP 0
51

• Another SDP Example (contd)

v0 oalan 1-613-1212 IN host.wcom.com sSSE
University Seminar - SIP iAudio, Listen
only uhttp//sse.mcit.com/university/ ealan_at_wcom
.com p1-329-342-7360 cIN IP4
10.64.5.246 bCT128 t2876565 2876599 maudio
3456 RTP/AVP 0 3 atyperecvonly
52

• Authentication Encryption

• SIP supports a variety of approaches
• end to end encryption
• hop by hop encryption
• Proxies can require authentication
• Responds to INVITEs with 407 Proxy-Authentication
  Required
• Client re-INVITEs with Proxy-Authorization
  header.
• SIP Users can require authentication
• Responds to INVITEs with 401 Unathorized
• Client re-INVITEs with Authorization header

53

• SIP Encryption Example

INVITE sippicard_at_wcom.com SIP/2.0 Via
SIP/2.0/UDP host.wcom.com5060 From Alan
Johnston ltsipalan_at_wcom.comgt To Jean Luc Picard
ltsippicard_at_wcom.comgt Call-ID 314159_at_host.wcom.co
m CSeq 1 INVITE Content-Length 224 Encryption
PGP version2.6.2, encodingascii q4aspdoCjh32a1_at_
WoiLuaE6erIgnqD3erDg8aFs8od7idf_at_
hWjasGdg,ddggfdgf_ggEOALewAKFeJqAFSeDlkjhasdfkj!
aJsdfasdfKlfghgasdfasdfaGsdfgta!sdasdf3w29451k45ms
er?we5y343.4kfj2ui2S8djGO4kPHk(Khujefjnjmbm.s
ddal12123awerwAo3529ofgk
54

• PSTN Features with SIP

• Features implemented by SIP Phone
• Call answering 200 OK sent
• Busy 483 Busy Here sent
• Call rejection 603 Declined sent
• Caller-ID present in From header
• Hold a re-INVITE is issued with IP Addr 0.0.0.0
• Selective Call Acceptance using From, Priority,
  and Subject headers
• Camp On 181 Call Queued responses are monitored
  until 200 OK is sent by the called party
• Call Waiting Receiving alerts during a call

55

• PSTN Features with SIP

• Features implemented by SIP Server
• Call Forwarding server issues 301 Moved
  Permanently or 302 Moved Temporarily response
  with Contact info
• Forward Dont Answer server issues 408 Request
  Timeout response
• Voicemail server 302 Moved Temporarily response
  with Contact of Voicemail Server
• Follow Me Service Use forking proxy to try
  multiple locations at the same time
• Caller-ID blocking - Privacy Server encrypts
  From information

56
SIP User Location Example
SIP supports mobility across networks and devices
Qquality gives preference SIP/2.0 302 Moved
temporarily Contact siphenry_at_wcom.com
serviceIP,voice mail mediaaudio
duplexfull q0.7 Contact phone
1-972-555-1212 serviceISDN
mobilityfixed languageen,es, q0.5 Contact
phone [phone] servicepager
mobilitymobile duplexsend-only
mediatext q0.1 priorityurgent
descriptionFor emergency only Contact
mailto henry_at_wcom.com
57
Programming SIP

• Examples
• discard all calls from Monica during my
  business hours
• redirect authenticated friends to my cell
  phone, anyone else to my secretary
• if busy, return my homepage and redirect to
  recorder
• Users and third parties may program
• SIP follows HTTP programming model
• Mechanisms suggested in IETF CGI, Call
  Processing Language (CPL), Servlets

58
Call Processing Logic Example
59
SIP Mobility Support
4
5
Foreign Network
Home Network
3
1
2
6
7
1 INVITE 2 302 moved temporarily 3, 4
INVITE 5, 6 OK 7 Data

• Global Wire and wireless
• No tunneling required
• No change to routing
• For fast hand-offs use
• Use Cellular IP or
• Use DRCP

Dynamic Registration and Configuration Protocol
60
SIP Mobility

• Pre-call mobility
• MH can find SIP server via multicast REGISTER
• MH acquires IP address via DHCP
• MH updates home SIP server

• Mid-call mobility
• MH-gtCH New INVITE with Contact and updated SDP
• Re-registers with home registrar

Need not bother home registrar Use multi-stage
registration Recovery from disconnects
61
Mobile IP Communications

• Mobile IP Requirements
• Transparency above L2
• Move but keep IP address and all sessions alive
• Mobility
• Within subnet
• Within domain
• Global
• AAA and NAIs
• Location privacy
• QoS for r.t. communications

• Evolution of Wireless Mobility
• Circuit Switched Mobility
• based on central INs
• LAN-MAN Cellular IP
• Wide Area Mobile IP
• Universal (any net) SIP

62
Presence, Instant Messaging and Voice
http//www.ietf.org/internet-drafts/draft-ietf-imp
p-model-03.txt
63
IP SIP Phones and Adaptors

• Are Internet hosts
• Choice of application
• Choice of server
• IP appliance
• Implementations
• 3Com (2)
• Cisco
• Columbia University
• Mediatrix (1)
• Nortel (3)
• Pingtel

1
2
3
64
H.323/SIP Comparison
65
H.323 vs. SIP Basic Call Control
66
H.323 vs. SIP Advanced features
67
H.323 vs. SIP Scalability
68
H.323 vs. SIP Extensibility of functionality
69
H.323 vs. SIP Ease of customization
70
H.323 vs. SIP Ease of customization
71
H.323 vs. SIP Ease of Implementation
72
Summary SIP vs H.323
73
Internet Drafts

• Session Timers in the Session Initiation Protocol
  (SIP)
• Caller Preferences for the Session Initiation
  Protocol (SIP)
• Guidelines for Authors of Extensions to the
  Session Initiation Protocol (SIP)
• The Stream Control Transmission Protocol as a
  Transport for for the Session Initiation Protocol
  
• The Session Inititation Protocol (SIP) 'Replaces'
  Header
• The SIP Referred-By Mechanism
• Compressing the Session Initiation Protocol
• Session Initiation Protocol Extension to Assure
  Congestion Safety
• A Mechanism for Content Indirection in Session
  Initiation Protocol (SIP) Messages
• The Session Inititation Protocol (SIP) 'Join'
  Header
• SIP Authenticated Identity Body (AIB) Format
• S/MIME AES Requirement for SIP
• An Extension to the Session Initiation Protocol
  for Request History Information
• Communications Resource Priority for the Session
  Initiation Protocol (SIP) Indicating User Agent
  Capabilities in the Session Initiation Protocol
  (SIP)
• Connection Reuse in the Session Initiation
  Protocol (SIP)
• The Internet Assigned Number Authority Universal
  Resource Identifier Parameter Registry for the
  Session Initiation Protocol
• The Internet Assigned Number Authority Header
  Field Parameter Registry for the Session
  Initiation Protocol
• Session Initiation Protocol (SIP) Extension for
  Event State Publication
• Interactions of Preconditions with Session
  Mobility in the Session Initiation Protocol (SIP)
  

74
RFCs

• The SIP INFO Method (RFC 2976)
• MIME media types for ISUP and QSIG Objects (RFC
  3204)
• SIP Session Initiation Protocol (RFC 3261)
• Reliability of Provisional Responses in SIP (RFC
  3262)
• SIP Locating SIP Servers (RFC 3263)
• SIP-Specific Event Notification (RFC 3265)
• DHCP Option for SIP Servers (RFC 3361)
• Hypertext Transfer Protocol (HTTP) Digest
  Authentication Using Authentication and Key
  Agreement (AKA) (RFC 3310)
• The Session Initiation Protocol UPDATE Method
  (RFC 3311)
• Integration of Resource Management and SIP (RFC
  3312)
• Internet Media Type message/sipfrag (RFC 3420)
• A Privacy Mechanism for the Session Initiation
  Protocol (SIP) (RFC 3323)
• Private Extensions to the Session Initiation
  Protocol (SIP) for Asserted Identity within
  Trusted Networks (RFC 3325)
• Session Initiation Protocol Extension for Instant
  Messaging (RFC 3428)
• The Reason Header Field for the Session
  Initiation Protocol (SIP) (RFC 3326)Session
  Initiation Protocol Extension for Registering
  Non-Adjacent Contacts (RFC 3327)
• Security Mechanism Agreement for the Session
  Initiation Protocol (SIP) Sessions (RFC 3329)
• Private Session Initiation Protocol
  (SIP)Extensions for Media Authorization (RFC
  3313)The Session Initiation Protocol (SIP) Refer
  Method (RFC 3515)
• Dynamic Host Configuration Protocol
  (DHCPv6)Options for Session Initiation Protocol
  (SIP) Servers (RFC 3319)
• An Extension to the Session Initiation Protocol
  (SIP) for Symmetric Response Routing (RFC 3581)

75
Relevant IETF Working Groups
http//ietf.org/html.charters/wg-dir.html

• Audio/Video Transport (avt) - RTP
• Differentiated Services (diffserv) QoS in
  backbone
• IP Telephony (iptel) CPL, GW location, TRIP
• Integrated Services (intserv) end-to-end QoS
• Media Gateway Control (megaco) IP telephony
  gateways
• Multiparty Multimedia Session Control (mmusic)
  SIP, SDP, conferencing
• PSTN and Internet Internetworking (pint) mixt
  services
• Resource Reservation Setup Protocol (rsvp)
• Service in the PSTN/IN Requesting InTernet
  Service (spirits)
• Session Initiation Protocol (sip) signaling for
  call setup
• Signaling Transport (sigtran) PSTN signaling
  over IP
• Telephone Number Mapping (enum) surprises !
• Instant Messaging and Presence Protocol (impp)

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• SIP Summary

• SIP is
• Relatively easy to implement
• Gaining vendor and carrier acceptance
• Very flexible in service creation
• Extensible and scaleable
• Appearing in products right now
• SIP is not
• Going to make PSTN interworking easy
• Going to solve all IP Telephony issues (QoS)

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References

• Book on Internetworking Multimedia
  by Jon Crowcroft, Mark Handley, Ian Wakeman, UCL
  Press, 1999 by Morgan Kaufman (USA) and Taylor
  Francis (UK)
• RFC 3261 SIP Session Initiation
  Protocol
• http//www.ietf.org/rfc/rfc3261.txt
• The IETF SIP Working Group home page
• http//www.ietf.org/html.charters/sip-cha
  rter.html
• SIP Home Page
• http//www.cs.columbia.edu/hgs/sip/
• Papers on IP Telephony
• http//www.cs.columbia.edu/sip/papers.html