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SIP: Session Initiation Protocol

1. Introduction

2. Overview of SIP Functionality

3. Terminology

4. Overview of Operation

5. Structure of the Protocol

7.3.1. Header Field Format

7.3.2. Header Field Classification

7.3.3. Compact Form

7.4. Bodies

7.4.1. Message Body Type

7.4.2. Message Body Length

7.5. Framing SIP Messages

8. General User Agent Behavior

8.1. UAC Behavior

8.1.1. Generating the Request

8.1.1.1. Request-URI

8.1.1.2. To

8.1.1.3. From

8.1.1.4. Call-ID

8.1.1.5. CSeq

8.1.1.6. Max-Forwards

8.1.1.7. Via

8.1.1.8. Contact

8.1.1.9. Supported and Require

8.1.1.10. Additional Message Components

8.1.2. Sending the Request

8.1.3. Processing Responses

8.1.3.1. Transaction Layer Errors

8.1.3.2. Unrecognized Responses

8.1.3.3. Vias

8.1.3.4. Processing 3xx Responses

8.1.3.5. Processing 4xx Responses

8.2. UAS Behavior

8.2.1. Method Inspection

8.2.2. Header Inspection

8.2.2.1. To and Request-URI

8.2.2.2. Merged Requests

8.2.2.3. Require

8.2.3. Content Processing

8.2.4. Applying Extensions

8.2.5. Processing the Request

8.2.6. Generating the Response

8.2.6.1. Sending a Provisional Response

8.2.6.2. Headers and Tags

8.2.7. Stateless UAS Behavior

8.3. Redirect Servers

9. Canceling a Request

10.2. Constructing the REGISTER Request

10.2.1. Adding Bindings

10.2.1.1. Setting the Expiration Interval of Contact Addresses

10.2.1.2. Preferences among Contact Addresses

10.2.2. Removing Bindings

10.2.3. Fetching Bindings

10.2.4. Refreshing Bindings

10.2.5. Setting the Internal Clock

10.2.6. Discovering a Registrar

10.2.7. Transmitting a Request

10.2.8. Error Responses

10.3. Processing REGISTER Requests

11. Querying for Capabilities

11.1. Construction of OPTIONS Request

11.2. Processing of OPTIONS Request

12. Dialogs

12.1. Creation of a Dialog

12.1.1. UAS behavior

12.1.2. UAC Behavior

12.2. Requests within a Dialog

12.2.1. UAC Behavior

12.2.1.1. Generating the Request

12.2.1.2. Processing the Responses

12.2.2. UAS Behavior

12.3. Termination of a Dialog

13. Initiating a Session

13.1. Overview

13.2. UAC Processing

13.2.1. Creating the Initial INVITE

13.2.2. Processing INVITE Responses

13.2.2.1. xx Responses

13.2.2.2. xx Responses

13.2.2.3. xx, 5xx and 6xx Responses

13.2.2.4. xx Responses

13.3. UAS Processing

13.3.1. Processing of the INVITE

13.3.1.1. Progress

13.3.1.2. The INVITE is Redirected

13.3.1.3. The INVITE is Rejected

13.3.1.4. The INVITE is Accepted

14. Modifying an Existing Session

14.1. UAC Behavior

14.2. UAS Behavior

15. Terminating a Session

15.1. Terminating a Session with a BYE Request

16.3. Request Validation

16.4. Route Information Preprocessing

16.5. Determining Request Targets

16.6. Request Forwarding

16.7. Response Processing

16.8. Processing Timer C

16.9. Handling Transport Errors

16.10. CANCEL Processing

16.11. Stateless Proxy

16.12. Summary of Proxy Route Processing

16.12.1. Examples

16.12.1.1. Basic SIP Trapezoid

16.12.1.2. Traversing a Strict-Routing Proxy

16.12.1.3. Rewriting Record-Route Header Field Values

17. Transactions

17.1. Client Transaction

17.1.1. INVITE Client Transaction

17.1.1.1. Overview of INVITE Transaction

17.1.1.2. Formal Description

17.1.1.3. Construction of the ACK Request

17.1.2. Non-INVITE Client Transaction

17.1.2.1. Overview of the non-INVITE Transaction

17.1.2.2. Formal Description

17.1.3. Matching Responses to Client Transactions

17.1.4. Handling Transport Errors

17.2. Server Transaction

17.2.1. INVITE Server Transaction

17.2.2. Non-INVITE Server Transaction

17.2.3. Matching Requests to Server Transactions

17.2.4. Handling Transport Errors

18. Transport

18.1. Clients

18.1.1. Sending Requests

18.1.2. Receiving Responses

18.2. Servers

18.2.1. Receiving Requests

18.2.2. Sending Responses

18.3. Framing

18.4. Error Handling

19. Common Message Components

19.1. SIP and SIPS Uniform Resource Indicators

19.1.1. SIP and SIPS URI Components

19.1.2. Character Escaping Requirements

19.1.3. Example SIP and SIPS URIs

19.1.4. URI Comparison

19.1.5. Forming Requests from a URI

19.1.6. Relating SIP URIs and tel URLs

20.2. Accept-Encoding

20.3. Accept-Language

20.4. Alert-Info

20.5. Allow

20.6. Authentication-Info

20.11. Content-Disposition

20.12. Content-Encoding

20.13. Content-Language

20.14. Content-Length

20.27. Proxy-Authenticate

20.28. Proxy-Authorization

20.44. WWW-Authenticate

21. Response Codes

21.1. Provisional 1xx

21.1.1. 100 Trying

21.1.2. 180 Ringing

21.1.3. 181 Call Is Being Forwarded

21.1.4. 182 Queued

21.1.5. 183 Session Progress

21.2. Successful 2xx

21.2.1. 200 OK

21.3. Redirection 3xx

21.3.1. 300 Multiple Choices

21.3.2. 301 Moved Permanently

21.3.3. 302 Moved Temporarily

21.3.4. 305 Use Proxy

21.3.5. 380 Alternative Service

21.4. Request Failure 4xx

21.4.1. 400 Bad Request

21.4.2. 401 Unauthorized

21.4.3. 402 Payment Required

21.4.4. 403 Forbidden

21.4.5. 404 Not Found

21.4.6. 405 Method Not Allowed

21.4.7. 406 Not Acceptable

21.4.8. 407 Proxy Authentication Required

21.4.9. 408 Request Timeout

21.4.10. 410 Gone

21.4.11. 413 Request Entity Too Large

21.4.12. 414 Request-URI Too Long

21.4.13. 415 Unsupported Media Type

21.4.14. 416 Unsupported URI Scheme

21.4.15. 420 Bad Extension

21.4.16. 421 Extension Required

21.4.17. 423 Interval Too Brief

21.4.18. 480 Temporarily Unavailable

21.4.19. 481 Call/Transaction Does Not Exist

21.4.20. 482 Loop Detected

21.4.21. 483 Too Many Hops

21.4.22. 484 Address Incomplete

21.4.23. 485 Ambiguous

21.4.24. 486 Busy Here

21.4.25. 487 Request Terminated

21.4.26. 488 Not Acceptable Here

21.4.27. 491 Request Pending

21.4.28. 493 Undecipherable

21.5. Server Failure 5xx

21.5.1. 500 Server Internal Error

21.5.2. 501 Not Implemented

21.5.3. 502 Bad Gateway

21.5.4. 503 Service Unavailable

21.5.5. 504 Server Time-out

21.5.6. 505 Version Not Supported

21.5.7. 513 Message Too Large

21.6. Global Failures 6xx

21.6.1. 600 Busy Everywhere

21.6.2. 603 Decline

21.6.3. 604 Does Not Exist Anywhere

21.6.4. 606 Not Acceptable

22. Usage of HTTP Authentication

22.1. Framework

22.2. User-to-User Authentication

22.3. Proxy-to-User Authentication

22.4. The Digest Authentication Scheme

23. S/MIME

23.1. S/MIME Certificates

23.2. S/MIME Key Exchange

23.3. Securing MIME bodies

23.4. SIP Header Privacy and Integrity using S/MIME: Tunneling SIP

23.4.1. Integrity and Confidentiality Properties of SIP Headers

23.4.1.1. Integrity

23.4.1.2. Confidentiality

23.4.2. Tunneling Integrity and Authentication

23.4.3. Tunneling Encryption

24. Examples

24.1. Registration

24.2. Session Setup

25. Augmented BNF for the SIP Protocol

25.1. Basic Rules

26. Security Considerations: Threat Model and Security Usage Recommendations

26.1. Attacks and Threat Models

26.1.1. Registration Hijacking

26.1.2. Impersonating a Server

26.1.3. Tampering with Message Bodies

26.1.4. Tearing Down Sessions

26.1.5. Denial of Service and Amplification

26.2. Security Mechanisms

26.2.1. Transport and Network Layer Security

26.2.2. SIPS URI Scheme

26.2.3. HTTP Authentication

26.2.4. S/MIME

26.3. Implementing Security Mechanisms

26.3.1. Requirements for Implementers of SIP

26.3.2. Security Solutions

26.3.2.1. Registration

26.3.2.2. Interdomain Requests

26.3.2.3. Peer-to-Peer Requests

26.3.2.4. DoS Protection

27. IANA Considerations

27.1. Option Tags

27.2. Warn-Codes

27.3. Header Field Names

27.4. Method and Response Codes

27.5. The "message/sip" MIME type.

27.6. New Content-Disposition Parameter Registrations

28. Changes From RFC 2543

28.1. Major Functional Changes

28.2. Minor Functional Changes

29. References

29.1. Normative References

29.2. Informative References

30. A Table of Timer Values

31. Acknowledgments

32. Authors' Addresses

33. Full Copyright Statement

34. Acknowledgement

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