Rfc3261

SIP: Session Initiation Protocol June 2002

RFC: 3261 Network Dictionary
http://www.javvin.com/networkdiction-
ary.html

Network Protocols Map
Network Working Group J. Rosenberg http://www.javvin.com/map.html

Request for Comments: 326 dynamicsoft
Network Security Map
Obsoletes: 2543 H. Schulzrinne http://www.javvin.com/securitymap.
Category: Standards Track Columbia U. html
G. Camarillo Wireless Communications
Ericsson Technology Map
A. Johnston http://www.javvin.com/wirelessmap.
html
WorldCom
Network Protocols Hand-
J. Peterson
book
Neustar http://www.javvin.com/model.html
R. Sparks
TCP/IP Quick Guide
dynamicsoft http://www.javvin.com/tcpipguide.html
M. Handley
ICIR
Ethernet Quick Guide
E. Schooler http://www.javvin.com/ethernetguide.
ATT html
June 2002
Packet Analyzer
http://www.javvin.com/packet.html

DiskShare
http://www.javvin.com/diskshare.html
SIP: Session Initiation Protocol
DiskAccess
http://www.javvin.com/diskaccess.html

LANsurveyor
http://www.javvin.com/LANsurveyor.
html

CyberGauge
http://www.javvin.com/CyberGauge.
html

Easy Network Service
Monitor
http://www.javvin.com/easy.html

Business Card Scanner
http://www.javvin.com/businesscard-
scanner.html
Color Cards and Picture
Scanner
http://www.javvin.com/colorcardscan-
ner.html
Portable Document Scan-
ner
http://www.javvin.com/portablescan-
ner.html
www.javvin.com

www.networkdictionary.
com
[ Page ]


Status of this Memo Network Dictionary
This document specifies an Internet standards track protocol for the Internet community, and requests ary.html
discussion and suggestions for improvements. Please refer to the current edition of the Internet Official
Protocol Standards (STD ) for the standardization state and status of this protocol. Distribution of this Network Protocols Map
memo is unlimited. http://www.javvin.com/map.html

Copyright Notice http://www.javvin.com/securitymap.
html
Copyright (C) The Internet Society (2002). All Rights Reserved. Wireless Communications
Technology Map
Abstract http://www.javvin.com/wirelessmap.
html
This document describes Session Initiation Protocol (SIP), an application-layer control (signaling) protocol Network Protocols Hand-
for creating, modifying, and terminating sessions with one or more participants. These sessions include book
Internet telephone calls, multimedia distribution, and multimedia conferences. http://www.javvin.com/model.html
SIP invitations used to create sessions carry session descriptions that allow participants to agree on a set of TCP/IP Quick Guide
compatible media types. SIP makes use of elements called proxy servers to help route requests to the user's http://www.javvin.com/tcpipguide.html
current location, authenticate and authorize users for services, implement provider call-routing policies,
and provide features to users. SIP also provides a registration function that allows users to upload their cur-
rent locations for use by proxy servers. SIP runs on top of several different transport protocols. Ethernet Quick Guide
http://www.javvin.com/ethernetguide.
html

Packet Analyzer

DiskShare

DiskAccess

LANsurveyor
html

CyberGauge
html

Monitor

scanner.html
Scanner
ner.html
ner
ner.html
www.javvin.com

com
[ Page 2 ]


Table of Contents Network Dictionary
ary.html
Introduction ..................................................................................................0
http://www.javvin.com/map.html
2 Overview of SIP Functionality ....................................................................0
3 Terminology ................................................................................................. http://www.javvin.com/securitymap.
html
4 Overview of Operation ................................................................................ Wireless Communications
Technology Map
5 Structure of the Protocol ..............................................................................5 http://www.javvin.com/wirelessmap.
html
6 Definitions ....................................................................................................6 Network Protocols Hand-
book
http://www.javvin.com/model.html
7 SIP Messages ...............................................................................................9
7. Requests ...............................................................................................20 TCP/IP Quick Guide
http://www.javvin.com/tcpipguide.html
7.2 Responses .............................................................................................20
7.3 Header Fields .......................................................................................2
7.3. Header Field Format .........................................................................2 Ethernet Quick Guide
7.3.2 Header Field Classification ...............................................................23 html
7.3.3 Compact Form ...................................................................................23
7.4 Bodies ...................................................................................................23 Packet Analyzer
7.4. Message Body Type ..........................................................................23
7.4.2 Message Body Length .......................................................................23 DiskShare
7.5 Framing SIP Messages .........................................................................23 http://www.javvin.com/diskshare.html

8 General User Agent Behavior ......................................................................24 DiskAccess
8. UAC Behavior ......................................................................................24
8.. Generating the Request .....................................................................24
LANsurveyor
8... Request-URI ...................................................................................24 http://www.javvin.com/LANsurveyor.
8...2 To ....................................................................................................24 html
8...3 From ...............................................................................................25
CyberGauge
8...4 Call-ID ............................................................................................25 http://www.javvin.com/CyberGauge.
8...5 CSeq ...............................................................................................26 html
8...6 Max-Forwards ................................................................................26
8...7 Via ..................................................................................................26
Monitor
8...8 Contact ...........................................................................................27 http://www.javvin.com/easy.html
8...9 Supported and Require ...................................................................27
8...0 Additional Message Components .................................................27 http://www.javvin.com/businesscard-
8..2 Sending the Request ..........................................................................27 scanner.html
8..3 Processing Responses ........................................................................28 Color Cards and Picture
8..3. Transaction Layer Errors ................................................................28 Scanner
8..3.2 Unrecognized Responses ...............................................................28
ner.html
8..3.3 Vias .................................................................................................28
8..3.4 Processing 3xx Responses ..............................................................28
ner
8..3.5 Processing 4xx Responses ..............................................................29 http://www.javvin.com/portablescan-
8.2 UAS Behavior ......................................................................................30 ner.html
8.2. Method Inspection .............................................................................30 www.javvin.com
8.2.2 Header Inspection ..............................................................................30
8.2.2. To and Request-URI .......................................................................30 www.networkdictionary.
com
[ Page 3 ]


8.2.2.2 Merged Requests ............................................................................3 Network Dictionary
8.2.2.3 Require ...........................................................................................3 http://www.javvin.com/networkdiction-
ary.html
8.2.3 Content Processing ............................................................................3
8.2.4 Applying Extensions .........................................................................32 Network Protocols Map
8.2.5 Processing the Request ......................................................................32 http://www.javvin.com/map.html
8.2.6 Generating the Response ...................................................................32
8.2.6. Sending a Provisional Response ....................................................32 http://www.javvin.com/securitymap.
8.2.6.2 Headers and Tags ...........................................................................32 html
8.2.7 Stateless UAS Behavior ....................................................................32 Wireless Communications
8.3 Redirect Servers ...................................................................................33 Technology Map
http://www.javvin.com/wirelessmap.
html
9 Canceling a Request .....................................................................................34
9. Client Behavior ....................................................................................34 Network Protocols Hand-
9.2 Server Behavior ....................................................................................35 book

0 Registrations ..............................................................................................35 TCP/IP Quick Guide
0. Overview ............................................................................................35
0.2 Constructing the REGISTER Request ...............................................36
0.2. Adding Bindings ..............................................................................37 Ethernet Quick Guide
0.2.. Setting the Expiration Interval of Contact Addresses ..................38 html
0.2..2 Preferences among Contact Addresses .........................................38
0.2.2 Removing Bindings .........................................................................38 Packet Analyzer
0.2.3 Fetching Bindings ...........................................................................38
0.2.4 Refreshing Bindings ........................................................................38 DiskShare
0.2.5 Setting the Internal Clock ................................................................39 http://www.javvin.com/diskshare.html
0.2.6 Discovering a Registrar ...................................................................39
0.2.7 Transmitting a Request ....................................................................39 DiskAccess
0.2.8 Error Responses ..............................................................................39
0.3 Processing REGISTER Requests .......................................................39 LANsurveyor
Querying for Capabilities ...........................................................................4 html
. Construction of OPTIONS Request ...................................................4 CyberGauge
.2 Processing of OPTIONS Request ......................................................42 http://www.javvin.com/CyberGauge.
html
2 Dialogs .......................................................................................................42 Easy Network Service
2. Creation of a Dialog ...........................................................................43 Monitor
2.. UAS behavior ..................................................................................43 http://www.javvin.com/easy.html
2..2 UAC Behavior .................................................................................44 Business Card Scanner
2.2 Requests within a Dialog ...................................................................44 http://www.javvin.com/businesscard-
2.2. UAC Behavior .................................................................................44 scanner.html
2.2.. Generating the Request ................................................................44 Color Cards and Picture
2.2..2 Processing the Responses .............................................................46 Scanner
2.2.2 UAS Behavior .................................................................................46 ner.html
2.3 Termination of a Dialog .....................................................................47 Portable Document Scan-
ner
3 Initiating a Session .....................................................................................47 http://www.javvin.com/portablescan-
3. Overview ............................................................................................47 ner.html
3.2 UAC Processing .................................................................................47 www.javvin.com
3.2. Creating the Initial INVITE ............................................................47
3.2.2 Processing INVITE Responses .......................................................49 www.networkdictionary.
com
[ Page 4 ]


3.2.2. xx Responses ..............................................................................49 Network Dictionary
3.2.2.2 3xx Responses ..............................................................................49 http://www.javvin.com/networkdiction-
ary.html
13.2.2.3 4xx, 5xx and 6xx Responses ........................................................49
3.2.2.4 2xx Responses ..............................................................................49 Network Protocols Map
3.3 UAS Processing .................................................................................50 http://www.javvin.com/map.html
3.3. Processing of the INVITE ...............................................................50
3.3.. Progress ........................................................................................50 http://www.javvin.com/securitymap.
3.3..2 The INVITE is Redirected ...........................................................5 html
3.3..3 The INVITE is Rejected ...............................................................5 Wireless Communications
3.3..4 The INVITE is Accepted ..............................................................5 Technology Map
html
4 Modifying an Existing Session ..................................................................5
4. UAC Behavior ....................................................................................52 Network Protocols Hand-
4.2 UAS Behavior ....................................................................................53 book

5 Terminating a Session ................................................................................53 TCP/IP Quick Guide
5. Terminating a Session with a BYE Request .......................................54
5.. UAC Behavior .................................................................................54
5..2 UAS Behavior .................................................................................54 Ethernet Quick Guide
html
6 Proxy Behavior ..........................................................................................54
6. Overview ............................................................................................54 Packet Analyzer
6.2 Stateful Proxy .....................................................................................55
6.3 Request Validation .............................................................................56 DiskShare
6.4 Route Information Preprocessing .......................................................57 http://www.javvin.com/diskshare.html
6.5 Determining Request Targets .............................................................58
6.6 Request Forwarding ...........................................................................59 DiskAccess
6.7 Response Processing ..........................................................................63
6.8 Processing Timer C ............................................................................67 LANsurveyor
6.9 Handling Transport Errors ..................................................................67 http://www.javvin.com/LANsurveyor.
6.0 CANCEL Processing ........................................................................67 html
6. Stateless Proxy .................................................................................67 CyberGauge
6.2 Summary of Proxy Route Processing ..............................................68 http://www.javvin.com/CyberGauge.
6.2. Examples .......................................................................................69 html
6.2.. Basic SIP Trapezoid ...................................................................69 Easy Network Service
6.2..2 Traversing a Strict-Routing Proxy ..............................................70 Monitor
6.2..3 Rewriting Record-Route Header Field Values ............................7 http://www.javvin.com/easy.html

7 Transactions ...............................................................................................7 http://www.javvin.com/businesscard-
7. Client Transaction ..............................................................................72 scanner.html
7.. INVITE Client Transaction .............................................................72 Color Cards and Picture
7... Overview of INVITE Transaction ................................................73 Scanner
7...2 Formal Description .......................................................................73 ner.html
7...3 Construction of the ACK Request ................................................74 Portable Document Scan-
7..2 Non-INVITE Client Transaction .....................................................75 ner
7..2. Overview of the non-INVITE Transaction ..................................75 http://www.javvin.com/portablescan-
7..2.2 Formal Description .......................................................................75 ner.html
7..3 Matching Responses to Client Transactions ...................................76 www.javvin.com
7..4 Handling Transport Errors................................................................76
7.2 Server Transaction ..............................................................................77 www.networkdictionary.
com
[ Page 5 ]


7.2. INVITE Server Transaction ............................................................77 Network Dictionary
7.2.2 Non-INVITE Server Transaction ....................................................79 http://www.javvin.com/networkdiction-
ary.html
7.2.3 Matching Requests to Server Transactions .....................................80
7.2.4 Handling Transport Errors ...............................................................8 Network Protocols Map
8 Transport ....................................................................................................8
8. Clients ................................................................................................82 Network Security Map
http://www.javvin.com/securitymap.
8.. Sending Requests ............................................................................82 html
8..2 Receiving Responses .......................................................................83 Wireless Communications
8.2 Servers ................................................................................................83 Technology Map
8.2. Receiving Requests .........................................................................83 http://www.javvin.com/wirelessmap.
html
8.2.2 Sending Responses ..........................................................................84
8.3 Framing ..............................................................................................84 Network Protocols Hand-
8.4 Error Handling ...................................................................................84 book

9 Common Message Components ................................................................85 TCP/IP Quick Guide
9. SIP and SIPS Uniform Resource Indicators .......................................85
9.. SIP and SIPS URI Components ......................................................85
9..2 Character Escaping Requirements ..................................................87 Ethernet Quick Guide
9..3 Example SIP and SIPS URIs ...........................................................88 html
9..4 URI Comparison .............................................................................88
9..5 Forming Requests from a URI ........................................................89 Packet Analyzer
9..6 Relating SIP URIs and tel URLs .....................................................90
9.2 Option Tags ........................................................................................9 DiskShare
9.3 Tags ....................................................................................................9 http://www.javvin.com/diskshare.html

20 Header Fields .............................................................................................92 DiskAccess
20. Accept .................................................................................................93
20.2 Accept-Encoding ................................................................................94 LANsurveyor
20.3 Accept-Language ................................................................................94 http://www.javvin.com/LANsurveyor.
20.4 Alert-Info ............................................................................................94 html
20.5 Allow ..................................................................................................95 CyberGauge
20.6 Authentication-Info ............................................................................95 http://www.javvin.com/CyberGauge.
20.7 Authorization ......................................................................................95 html
20.8 Call-ID ................................................................................................95 Easy Network Service
20.9 Call-Info .............................................................................................96 Monitor
20.0 Contact .............................................................................................96 http://www.javvin.com/easy.html
20. Content-Disposition .........................................................................97 Business Card Scanner
20.2 Content-Encoding ............................................................................97 http://www.javvin.com/businesscard-
20.3 Content-Language ............................................................................97 scanner.html
20.4 Content-Length ................................................................................98 Color Cards and Picture
20.5 Content-Type ....................................................................................98 Scanner
20.6 CSeq .................................................................................................98 ner.html
20.7 Date ..................................................................................................98 Portable Document Scan-
20.8 Error-Info .........................................................................................98 ner
20.9 Expires ..............................................................................................99 http://www.javvin.com/portablescan-
20.20 From .................................................................................................99 ner.html
20.2 In-Reply-To ......................................................................................99 www.javvin.com
20.22 Max-Forwards ................................................................................00
20.23 Min-Expires ....................................................................................00
com
[ Page 6 ]


20.24 MIME-Version ...............................................................................00 Network Dictionary
20.25 Organization ...................................................................................00 http://www.javvin.com/networkdiction-
ary.html
20.26 Priority ............................................................................................00
20.27 Proxy-Authenticate ........................................................................0 Network Protocols Map
20.28 Proxy-Authorization .......................................................................0 http://www.javvin.com/map.html
20.29 Proxy-Require ................................................................................0
20.30 Record-Route .................................................................................0 http://www.javvin.com/securitymap.
20.3 Reply-To .........................................................................................0 html
20.32 Require ...........................................................................................02 Wireless Communications
20.33 Retry-After .....................................................................................02 Technology Map
20.34 Route ..............................................................................................02 http://www.javvin.com/wirelessmap.
html
20.35 Server .............................................................................................02
20.36 Subject ............................................................................................03
book
20.37 Supported .......................................................................................03 http://www.javvin.com/model.html
20.38 Timestamp ......................................................................................03
TCP/IP Quick Guide
20.39 To ....................................................................................................03 http://www.javvin.com/tcpipguide.html
20.40 Unsupported ...................................................................................03
20.4 User-Agent .....................................................................................04
20.42 Via ..................................................................................................04 http://www.javvin.com/ethernetguide.
20.43 Warning ..........................................................................................04 html
20.44 WWW-Authenticate .......................................................................05
Packet Analyzer
2 Response Codes .......................................................................................06
2. Provisional xx .................................................................................06 DiskShare
2.. 00 Trying .....................................................................................06 http://www.javvin.com/diskshare.html
2..2 80 Ringing ...................................................................................06
2..3 8 Call Is Being Forwarded ........................................................06 DiskAccess
2..4 82 Queued ...................................................................................06
2..5 83 Session Progress .....................................................................06 LANsurveyor
2.2 Successful 2xx ..................................................................................06 http://www.javvin.com/LANsurveyor.
html
2.2. 200 OK ..........................................................................................06
2.3 Redirection 3xx ................................................................................06 CyberGauge
2.3. 300 Multiple Choices ....................................................................06 http://www.javvin.com/CyberGauge.
html
2.3.2 30 Moved Permanently ...............................................................07
2.3.3 302 Moved Temporarily ................................................................07 Easy Network Service
2.3.4 305 Use Proxy ...............................................................................07 Monitor
2.3.5 380 Alternative Service .................................................................07 http://www.javvin.com/easy.html
2.4 Request Failure 4xx ..........................................................................07 Business Card Scanner
2.4. 400 Bad Request ...........................................................................07 http://www.javvin.com/businesscard-
scanner.html
2.4.2 40 Unauthorized ..........................................................................08
2.4.3 402 Payment Required ..................................................................08 Color Cards and Picture
2.4.4 403 Forbidden ...............................................................................08 Scanner
2.4.5 404 Not Found ...............................................................................08 ner.html
2.4.6 405 Method Not Allowed ..............................................................08 Portable Document Scan-
2.4.7 406 Not Acceptable .......................................................................08 ner
2.4.8 407 Proxy Authentication Required ..............................................08 http://www.javvin.com/portablescan-
ner.html
2.4.9 408 Request Timeout .....................................................................08
2.4.0 40 Gone .....................................................................................08 www.javvin.com
2.4. 43 Request Entity Too Large .....................................................08 www.networkdictionary.
2.4.2 44 Request-URI Too Long ........................................................09 com
[ Page 7 ]


2.4.3 45 Unsupported Media Type .....................................................09 Network Dictionary
2.4.4 46 Unsupported URI Scheme ....................................................09 http://www.javvin.com/networkdiction-
ary.html
2.4.5 420 Bad Extension ......................................................................09
2.4.6 42 Extension Required ..............................................................09 Network Protocols Map
2.4.7 423 Interval Too Brief .................................................................09 http://www.javvin.com/map.html
2.4.8 480 Temporarily Unavailable ......................................................09
2.4.9 48 Call/Transaction Does Not Exist ..........................................09 http://www.javvin.com/securitymap.
2.4.20 482 Loop Detected ......................................................................09 html
2.4.2 483 Too Many Hops ....................................................................0 Wireless Communications
2.4.22 484 Address Incomplete ..............................................................0 Technology Map
2.4.23 485 Ambiguous ...........................................................................0 http://www.javvin.com/wirelessmap.
html
2.4.24 486 Busy Here .............................................................................0
2.4.25 487 Request Terminated ..............................................................0
book
2.4.26 488 Not Acceptable Here ............................................................0 http://www.javvin.com/model.html
2.4.27 49 Request Pending ...................................................................0
TCP/IP Quick Guide
2.4.28 493 Undecipherable .................................................................... http://www.javvin.com/tcpipguide.html
2.5 Server Failure 5xx ............................................................................
2.5. 500 Server Internal Error ..............................................................
2.5.2 50 Not Implemented .................................................................... http://www.javvin.com/ethernetguide.
2.5.3 502 Bad Gateway .......................................................................... html
2.5.4 503 Service Unavailable ...............................................................
Packet Analyzer
2.5.5 504 Server Time-out ...................................................................... http://www.javvin.com/packet.html
2.5.6 505 Version Not Supported ...........................................................
2.5.7 53 Message Too Large ................................................................ DiskShare
2.6 Global Failures 6xx ..........................................................................2 http://www.javvin.com/diskshare.html
2.6. 600 Busy Everywhere ...................................................................2
DiskAccess
2.6.2 603 Decline ...................................................................................2 http://www.javvin.com/diskaccess.html
2.6.3 604 Does Not Exist Anywhere ......................................................2
2.6.4 606 Not Acceptable .......................................................................2 LANsurveyor
html
22 Usage of HTTP Authentication ................................................................2
22. Framework .......................................................................................2 CyberGauge
22.2 User-to-User Authentication ............................................................4 http://www.javvin.com/CyberGauge.
html
22.3 Proxy-to-User Authentication ..........................................................4
22.4 The Digest Authentication Scheme ..................................................6 Easy Network Service
Monitor
23 S/MIME ...................................................................................................7 http://www.javvin.com/easy.html
23.1 S/MIME Certificates ........................................................................7 Business Card Scanner
23.2 S/MIME Key Exchange ...................................................................8 http://www.javvin.com/businesscard-
23.3 Securing MIME bodies ....................................................................9 scanner.html

23.4 SIP Header Privacy and Integrity using S/MIME: Tunneling SIP ...20 Color Cards and Picture
23.4.1 Integrity and Confidentiality Properties of SIP Headers ...............2 Scanner
23.4.. Integrity ......................................................................................2 ner.html
23.4.1.2 Confidentiality ............................................................................2 Portable Document Scan-
23.4.2 Tunneling Integrity and Authentication ........................................2 ner
23.4.3 Tunneling Encryption ....................................................................23 http://www.javvin.com/portablescan-
ner.html
24 Examples ..................................................................................................24 www.javvin.com
24. Registration ......................................................................................24
24.2 Session Setup ...................................................................................25
com
[ Page 8 ]


25 Augmented BNF for the SIP Protocol ......................................................28 Network Dictionary
25. Basic Rules .......................................................................................28 http://www.javvin.com/networkdiction-
ary.html

26 Security Considerations: Threat Model and Security Usage Recommenda- Network Protocols Map
tions ...............................................................................................................37
26. Attacks and Threat Models ...............................................................37 Network Security Map
26.. Registration Hijacking ..................................................................38 html
26..2 Impersonating a Server .................................................................38 Wireless Communications
26..3 Tampering with Message Bodies ..................................................38 Technology Map
26..4 Tearing Down Sessions .................................................................39 http://www.javvin.com/wirelessmap.
26.1.5 Denial of Service and Amplification .............................................39 html

26.2 Security Mechanisms .......................................................................39 Network Protocols Hand-
26.2. Transport and Network Layer Security .........................................40 book
26.2.2 SIPS URI Scheme .........................................................................4
26.2.3 HTTP Authentication ....................................................................4 TCP/IP Quick Guide
26.2.4 S/MIME .........................................................................................4
26.3 Implementing Security Mechanisms ................................................4
26.3. Requirements for Implementers of SIP .........................................4 Ethernet Quick Guide
26.3.2 Security Solutions .........................................................................42 html
26.3.2. Registration ................................................................................42
26.3.2.2 Interdomain Requests .................................................................43 Packet Analyzer
26.3.2.3 Peer-to-Peer Requests ................................................................44
26.3.2.4 DoS Protection ...........................................................................44 DiskShare
26.4 Limitations .......................................................................................45 http://www.javvin.com/diskshare.html
26.4. HTTP Digest .................................................................................45
26.4.2 S/MIME .........................................................................................45 DiskAccess
26.4.3 TLS ................................................................................................46
26.4.4 SIPS URIs .....................................................................................46 LANsurveyor
26.5 Privacy ..............................................................................................47 http://www.javvin.com/LANsurveyor.
html
27 IANA Considerations ...............................................................................47 CyberGauge
27. Option Tags ......................................................................................47 http://www.javvin.com/CyberGauge.
27.2 Warn-Codes ......................................................................................48 html
27.3 Header Field Names .........................................................................48 Easy Network Service
27.4 Method and Response Codes ...........................................................48 Monitor
27.5 The message/sip MIME type. .......................................................49 http://www.javvin.com/easy.html
27.6 New Content-Disposition Parameter Registrations .........................49 Business Card Scanner
28 Changes From RFC 2543 .........................................................................49 scanner.html
28. Major Functional Changes ...............................................................49 Color Cards and Picture
28.2 Minor Functional Changes ...............................................................5 Scanner
ner.html
29 Normative References ..............................................................................52
ner
30 Informative References ............................................................................53 http://www.javvin.com/portablescan-
ner.html
A Table of Timer Values.................................................................................54 www.javvin.com

Acknowledgments .........................................................................................54 www.networkdictionary.
com
[ Page 9 ]


Authors' Addresses .........................................................................................55 Network Dictionary
ary.html
Full Copyright Statement ..............................................................................56
Acknowledgement ........................................................................................56 http://www.javvin.com/map.html

html
Wireless Communications
Technology Map
html
book

TCP/IP Quick Guide

html

Packet Analyzer

DiskShare

DiskAccess

LANsurveyor
html

CyberGauge
html

Monitor

scanner.html
Scanner
ner.html
ner
ner.html
www.javvin.com

com
[ Page 0 ]


1 Introduction Network Dictionary
There are many applications of the Internet that require the creation and management of a session, where ary.html
a session is considered an exchange of data between an association of participants. The implementation of
these applications is complicated by the practices of participants: users may move between endpoints, they Network Protocols Map
may be addressable by multiple names, and they may communicate in several different media - sometimes http://www.javvin.com/map.html
simultaneously. Numerous protocols have been authored that carry various forms of real-time multimedia
session data such as voice, video, or text messages. The Session Initiation Protocol (SIP) works in concert Network Security Map
with these protocols by enabling Internet endpoints (called user agents) to discover one another and to http://www.javvin.com/securitymap.
agree on a characterization of a session they would like to share. For locating prospective session partici- html
pants, and for other functions, SIP enables the creation of an infrastructure of network hosts (called proxy Wireless Communications
servers) to which user agents can send registrations, invitations to sessions, and other requests. SIP is an
agile, general-purpose tool for creating, modifying, and terminating sessions that works independently of Technology Map
underlying transport protocols and without dependency on the type of session that is being established. http://www.javvin.com/wirelessmap.
html
2 Overview of SIP Functionality book
SIP is an application-layer control protocol that can establish, modify, and terminate multimedia sessions
(conferences) such as Internet telephony calls. SIP can also invite participants to already existing sessions, TCP/IP Quick Guide
such as multicast conferences. Media can be added to (and removed from) an existing session. SIP transpar- http://www.javvin.com/tcpipguide.html
ently supports name mapping and redirection services, which supports personal mobility [27] - users can
maintain a single externally visible identifier regardless of their network location.
SIP supports five facets of establishing and terminating multimedia communications: http://www.javvin.com/ethernetguide.
html
User location: determination of the end system to be used for communication;
Packet Analyzer
User availability: determination of the willingness of the called party to engage in communications; http://www.javvin.com/packet.html

User capabilities: determination of the media and media parameters to be used; DiskShare
Session setup: ringing, establishment of session parameters at both called and calling party;

Session management: including transfer and termination of sessions, modifying session parameters, DiskAccess
and invoking services. http://www.javvin.com/diskaccess.html

SIP is not a vertically integrated communications system. SIP is rather a component that can be used with LANsurveyor
other IETF protocols to build a complete multimedia architecture. Typically, these architectures will in- http://www.javvin.com/LANsurveyor.
clude protocols such as the Real-time Transport Protocol (RTP) (RFC 889 [28]) for transporting real-time html
data and providing QoS feedback, the Real-Time streaming protocol (RTSP) (RFC 2326 [29]) for control-
ling delivery of streaming media, the Media Gateway Control Protocol (MEGACO) (RFC 3015 [30]) for CyberGauge
controlling gateways to the Public Switched Telephone Network (PSTN), and the Session Description http://www.javvin.com/CyberGauge.
Protocol (SDP) (RFC 2327 [1]) for describing multimedia sessions. Therefore, SIP should be used in html
conjunction with other protocols in order to provide complete services to the users. However, the basic
functionality and operation of SIP does not depend on any of these protocols. Easy Network Service
Monitor
SIP does not provide services. Rather, SIP provides primitives that can be used to implement different http://www.javvin.com/easy.html
services. For example, SIP can locate a user and deliver an opaque object to his current location. If this
primitive is used to deliver a session description written in SDP, for instance, the endpoints can agree on the Business Card Scanner
parameters of a session. If the same primitive is used to deliver a photo of the caller as well as the session http://www.javvin.com/businesscard-
description, a caller ID service can be easily implemented. As this example shows, a single primitive is scanner.html
typically used to provide several different services. Color Cards and Picture
SIP does not offer conference control services such as floor control or voting and does not prescribe how a Scanner
conference is to be managed. SIP can be used to initiate a session that uses some other conference control http://www.javvin.com/colorcardscan-
protocol. Since SIP messages and the sessions they establish can pass through entirely different networks, ner.html
SIP cannot, and does not, provide any kind of network resource reservation capabilities. Portable Document Scan-
ner
The nature of the services provided make security particularly important. To that end, SIP provides a http://www.javvin.com/portablescan-
suite of security services, which include denial-of-service prevention, authentication (both user to user and ner.html
proxy to user), integrity protection, and encryption and privacy services.
www.javvin.com
SIP works with both IPv4 and IPv6.
com
[ Page ]


3 Terminology Network Dictionary
In this document, the key words MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, ary.html
SHOULD, SHOULD NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OP-
TIONAL are to be interpreted as described in BCP 14, RFC 2119 [2] and indicate requirement levels for Network Protocols Map
compliant SIP implementations. http://www.javvin.com/map.html

4 Overview of Operation http://www.javvin.com/securitymap.
html
This section introduces the basic operations of SIP using simple examples. This section is tutorial in nature Wireless Communications
and does not contain any normative statements.
Technology Map
The first example shows the basic functions of SIP: location of an end point, signal of a desire to com- http://www.javvin.com/wirelessmap.
municate, negotiation of session parameters to establish the session, and teardown of the session once html
established. Network Protocols Hand-
book
Figure 1 shows a typical example of a SIP message exchange between two users, Alice and Bob. (Each http://www.javvin.com/model.html
message is labeled with the letter F and a number for reference by the text.) In this example, Alice uses a
SIP application on her PC (referred to as a softphone) to call Bob on his SIP phone over the Internet. Also TCP/IP Quick Guide
shown are two SIP proxy servers that act on behalf of Alice and Bob to facilitate the session establishment. http://www.javvin.com/tcpipguide.html
This typical arrangement is often referred to as the SIP trapezoid as shown by the geometric shape of the
dotted lines in Figure .
Alice calls Bob using his SIP identity, a type of Uniform Resource Identifier (URI) called a SIP URI. http://www.javvin.com/ethernetguide.
SIP URIs are defined in Section 19.1. It has a similar form to an email address, typically containing a html
username and a host name. In this case, it is sip:bob@biloxi.com, where biloxi.com is the domain of Bob's
SIP service provider. Alice has a SIP URI of sip:alice@atlanta.com. Alice might have typed in Bob's URI Packet Analyzer
or perhaps clicked on a hyperlink or an entry in an address book. SIP also provides a secure URI, called a http://www.javvin.com/packet.html
SIPS URI. An example would be sips:bob@biloxi.com. A call made to a SIPS URI guarantees that secure,
encrypted transport (namely TLS) is used to carry all SIP messages from the caller to the domain of the DiskShare
callee. From there, the request is sent securely to the callee, but with security mechanisms that depend on http://www.javvin.com/diskshare.html
the policy of the domain of the callee.

SIP is based on an HTTP-like request/response transaction model. Each transaction consists of a request DiskAccess
that invokes a particular method, or function, on the server and at least one response. In this example, the http://www.javvin.com/diskaccess.html
transaction begins with Alice's softphone sending an INVITE request addressed to Bob's SIP URI. INVITE
is an example of a SIP method that specifies the action that the requestor (Alice) wants the server (Bob) LANsurveyor
to take. The INVITE request contains a number of header fields. Header fields are named attributes that http://www.javvin.com/LANsurveyor.
provide additional information about a message. The ones present in an INVITE include a unique identifier html
for the call, the destination address, Alice's address, and information about the type of session that Alice
wishes to establish with Bob. The INVITE (message F in Figure ) might look like this: CyberGauge
html

Monitor

scanner.html
Scanner
ner.html
ner
ner.html
www.javvin.com

com
[ Page 2 ]


Network Dictionary
ary.html


html
Wireless Communications
Technology Map
html
book

TCP/IP Quick Guide

Figure : SIP session setup example with SIP trapezoid Ethernet Quick Guide
INVITE sip:bob@biloxi.com SIP/2.0 html
Via: SIP/2.0/UDP pc33.atlanta.com;branch=z9hG4bK776asdhds
Max-Forwards: 70 Packet Analyzer
To: Bob sip:bob@biloxi.com http://www.javvin.com/packet.html
From: Alice sip:alice@atlanta.com;tag=1928301774
Call-ID: a84b4c76e66710@pc33.atlanta.com DiskShare
CSeq: 3459 INVITE http://www.javvin.com/diskshare.html
Contact: sip:alice@pc33.atlanta.com
Content-Type: application/sdp DiskAccess
Content-Length: 42 http://www.javvin.com/diskaccess.html
(Alice's SDP not shown)
LANsurveyor
The first line of the text-encoded message contains the method name (INVITE). The lines that follow are a http://www.javvin.com/LANsurveyor.
list of header fields. This example contains a minimum required set. The header fields are briefly described html
below:
CyberGauge
Via contains the address (pc33.atlanta.com) at which Alice is expecting to receive responses to this request. http://www.javvin.com/CyberGauge.
It also contains a branch parameter that identifies this transaction. html

To contains a display name (Bob) and a SIP or SIPS URI (sip:bob@biloxi.com) towards which the request Easy Network Service
was originally directed. Display names are described in RFC 2822 [3]. Monitor
From also contains a display name (Alice) and a SIP or SIPS URI (sip:alice@atlanta.com) that indicate the
originator of the request. This header field also has a tag parameter containing a random string (1928301774) Business Card Scanner
that was added to the URI by the softphone. It is used for identification purposes. http://www.javvin.com/businesscard-
scanner.html
Call-ID contains a globally unique identifier for this call, generated by the combination of a random string Color Cards and Picture
and the softphone's host name or IP address. The combination of the To tag, From tag, and Call-ID com- Scanner
pletely defines a peer-to-peer SIP relationship between Alice and Bob and is referred to as a dialog. http://www.javvin.com/colorcardscan-
ner.html
CSeq or Command Sequence contains an integer and a method name. The CSeq number is incremented for
each new request within a dialog and is a traditional sequence number. Portable Document Scan-
ner
Contact contains a SIP or SIPS URI that represents a direct route to contact Alice, usually composed of a http://www.javvin.com/portablescan-
username at a fully qualified domain name (FQDN). While an FQDN is preferred, many end systems do ner.html
not have registered domain names, so IP addresses are permitted. While the Via header field tells other www.javvin.com
elements where to send the response, the Contact header field tells other elements where to send future
requests.
Max-Forwards serves to limit the number of hops a request can make on the way to its destination. It con- com
[ Page 3 ]

Rfc3261

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