Request for Comments: 3665 MCI
BCP: 75 S. Donovan
Category: Best Current Practice R. Sparks
C. Cunningham
dynamicsoft
K. Summers
Sonus
December 2003
Session Initiation Protocol (SIP) Basic Call Flow Examples
Status of this Memo
This document specifies an Internet Best Current Practices for the
Internet Community, and requests discussion and suggestions for
improvements. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This document gives examples of Session Initiation Protocol (SIP)
call flows. Elements in these call flows include SIP User Agents and
Clients, SIP Proxy and Redirect Servers. Scenarios include SIP
Registration and SIP session establishment. Call flow diagrams and
message details are shown.
Table of Contents
1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. General Assumptions. . . . . . . . . . . . . . . . . . . 3
1.2. Legend for Message Flows . . . . . . . . . . . . . . . . 3
1.3. SIP Protocol Assumptions . . . . . . . . . . . . . . . . 4
2. SIP Registration . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Successful New Registration. . . . . . . . . . . . . . . 5
2.2. Update of Contact List . . . . . . . . . . . . . . . . . 7
2.3. Request for Current Contact List . . . . . . . . . . . . 8
2.4. Cancellation of Registration . . . . . . . . . . . . . . 9
2.5. Unsuccessful Registration. . . . . . . . . . . . . . . . 10
3. SIP Session Establishment. . . . . . . . . . . . . . . . . . . 12
3.1. Successful Session Establishment . . . . . . . . . . . . 12
3.2. Session Establishment Through Two Proxies. . . . . . . . 15
3.3. Session with Multiple Proxy Authentication . . . . . . . 26
3.4. Successful Session with Proxy Failure. . . . . . . . . . 37
3.5. Session Through a SIP ALG. . . . . . . . . . . . . . . . 46
3.6. Session via Redirect and Proxy Servers with SDP in ACK . 54
3.7. Session with re-INVITE (IP Address Change) . . . . . . . 61
3.8. Unsuccessful No Answer . . . . . . . . . . . . . . . . . 67
3.9. Unsuccessful Busy. . . . . . . . . . . . . . . . . . . . 75
3.10. Unsuccessful No Response from User Agent . . . . . . . . 80
3.11. Unsuccessful Temporarily Unavailable . . . . . . . . . . 85
4. Security Considerations. . . . . . . . . . . . . . . . . . . . 91
5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 91
5.1. Normative References . . . . . . . . . . . . . . . . . . 91
5.2. Informative References . . . . . . . . . . . . . . . . . 91
6. Intellectual Property Statement. . . . . . . . . . . . . . . . 91
7. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . 92
8. Authors’ Addresses . . . . . . . . . . . . . . . . . . . . . . 93
9. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 94
1. Overview
The call flows shown in this document were developed in the design of
a SIP IP communications network. They represent an example minimum
set of functionality.
It is the hope of the authors that this document will be useful for
SIP implementers, designers, and protocol researchers alike and will
help further the goal of a standard implementation of RFC 3261 [1].
These flows represent carefully checked and working group reviewed
scenarios of the most basic examples as a companion to the
specifications.
These call flows are based on the current version 2.0 of SIP in RFC
3261 [1] with SDP usage described in RFC 3264 [2]. Other RFCs also
comprise the SIP standard but are not used in this set of basic call
flows.
Call flow examples of SIP interworking with the PSTN through gateways
are contained in a companion document, RFC 3666 [5].
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14, RFC 2119 [4].
1.1. General Assumptions
A number of architecture, network, and protocol assumptions underlie
the call flows in this document. Note that these assumptions are not
requirements. They are outlined in this section so that they may be
taken into consideration and to aid in the understanding of the call
flow examples.
The authentication of SIP User Agents in these example call flows is
performed using HTTP Digest as defined in [1] and [3].
Some Proxy Servers in these call flows insert Record-Route headers
into requests to ensure that they are in the signaling path for
future message exchanges.
These flows show TCP, TLS, and UDP for transport. See the discussion
in RFC 3261 for details on the transport issues for SIP.
1.2. Legend for Message Flows
Dashed lines (---) represent signaling messages that are mandatory to
the call scenario. These messages can be SIP or PSTN signaling. The
arrow indicates the direction of message flow.
Double dashed lines (===) represent media paths between network
elements.
Messages with parentheses around their name represent optional
messages.
Messages are identified in the Figures as F1, F2, etc. This
references the message details in the list that follows the Figure.
Comments in the message details are shown in the following form:
/* Comments. */
1.3. SIP Protocol Assumptions
This document does not prescribe the flows precisely as they are
shown, but rather the flows illustrate the principles for best
practice. They are best practices usages (orderings, syntax,
selection of features for the purpose, handling of error) of SIP
methods, headers and parameters. IMPORTANT: The exact flows here
must not be copied as is by an implementer due to specific incorrect
characteristics that were introduced into the document for
convenience and are listed below. To sum up, the basic flows
represent well-reviewed examples of SIP usage, which are best common
practice according to IETF consensus.
For simplicity in reading and editing the document, there are a
number of differences between some of the examples and actual SIP
messages. For example, the HTTP Digest responses are not actual MD5
encodings. Call-IDs are often repeated, and CSeq counts often begin
at 1. Header fields are usually shown in the same order. Usually
only the minimum required header field set is shown, others that
would normally be present such as Accept, Supported, Allow, etc are
not shown.
Actors:
Element Display Name URI IP Address
------- ------------ --- ----------
User Agent Alice alice@atlanta.example.com 192.0.2.101
User Agent Bob bob@biloxi.example.com 192.0.2.201
User Agent bob@chicago.example.com 192.0.2.100
Proxy Server ss1.atlanta.example.com 192.0.2.111
Proxy/Registrar ss2.biloxi.example.com 192.0.2.222
Proxy Server ss3.chicago.example.com 192.0.2.233
ALG alg1.atlanta.example.com 192.0.2.128
2. SIP Registration
Registration binds a particular device Contact URI with a SIP user
Address of Record (AOR).
2.1. Successful New Registration
Bob SIP Server
| |
| REGISTER F1 |
|------------------------------>|
| 401 Unauthorized F2 |
|<------------------------------|
| REGISTER F3 |
|------------------------------>|
| 200 OK F4 |
|<------------------------------|
| |
Bob sends a SIP REGISTER request to the SIP server. The request
includes the user’s contact list. This flow shows the use of HTTP
Digest for authentication using TLS transport. TLS transport is used
due to the lack of integrity protection in HTTP Digest and the danger
of registration hijacking without it, as described in RFC 3261 [1].
The SIP server provides a challenge to Bob. Bob enters her/his valid
user ID and password. Bob’s SIP client encrypts the user information
according to the challenge issued by the SIP server and sends the
response to the SIP server. The SIP server validates the user’s
credentials. It registers the user in its contact database and
returns a response (200 OK) to Bob’s SIP client. The response
includes the user’s current contact list in Contact headers. The
format of the authentication shown is HTTP digest. It is assumed
that Bob has not previously registered with this Server.
Message Details
F1 REGISTER Bob -> SIP Server
REGISTER sips:ss2.biloxi.example.com SIP/2.0
Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
Max-Forwards: 70
From: Bob <sips:bob@biloxi.example.com>;tag=a73kszlfl
To: Bob <sips:bob@biloxi.example.com>
Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com
CSeq: 1 REGISTER
Contact: <sips:bob@client.biloxi.example.com>
Content-Length: 0
F2 401 Unauthorized SIP Server -> Bob
SIP/2.0 401 Unauthorized
Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
;received=192.0.2.201
From: Bob <sips:bob@biloxi.example.com>;tag=a73kszlfl
To: Bob <sips:bob@biloxi.example.com>;tag=1410948204
Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com
CSeq: 1 REGISTER
WWW-Authenticate: Digest realm="atlanta.example.com", qop="auth",
nonce="ea9c8e88df84f1cec4341ae6cbe5a359",
opaque="", stale=FALSE, algorithm=MD5
Content-Length: 0
F3 REGISTER Bob -> SIP Server
REGISTER sips:ss2.biloxi.example.com SIP/2.0
Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashd92
Max-Forwards: 70
From: Bob <sips:bob@biloxi.example.com>;tag=ja743ks76zlflH
To: Bob <sips:bob@biloxi.example.com>
Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com
CSeq: 2 REGISTER
Contact: <sips:bob@client.biloxi.example.com>
Authorization: Digest username="bob", realm="atlanta.example.com"
nonce="ea9c8e88df84f1cec4341ae6cbe5a359", opaque="",
uri="sips:ss2.biloxi.example.com",
response="dfe56131d1958046689d83306477ecc"
Content-Length: 0
F4 200 OK SIP Server -> Bob
SIP/2.0 200 OK
Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashd92
;received=192.0.2.201
From: Bob <sips:bob@biloxi.example.com>;tag=ja743ks76zlflH
To: Bob <sips:bob@biloxi.example.com>;tag=37GkEhwl6
Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com
CSeq: 2 REGISTER
Contact: <sips:bob@client.biloxi.example.com>;expires=3600
Content-Length: 0
2.2. Update of Contact List
Bob SIP Server
| |
| REGISTER F1 |
|------------------------------>|
| 200 OK F2 |
|<------------------------------|
| |
Bob wishes to update the list of addresses where the SIP server will
redirect or forward INVITE requests.
Bob sends a SIP REGISTER request to the SIP server. Bob’s request
includes an updated contact list. Since the user already has
authenticated with the server, the user supplies authentication
credentials with the request and is not challenged by the server. The
SIP server validates the user’s credentials. It registers the user
in its contact database, updates the user’s contact list, and returns
a response (200 OK) to Bob’s SIP client. The response includes the
user’s current contact list in Contact headers.
Message Details
F1 REGISTER Bob -> SIP Server
REGISTER sips:ss2.biloxi.example.com SIP/2.0
Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
Max-Forwards: 70
From: Bob <sips:bob@biloxi.example.com>;tag=a73kszlfl
To: Bob <sips:bob@biloxi.example.com>
Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com
CSeq: 1 REGISTER
Contact: mailto:bob@biloxi.example.com
Authorization: Digest username="bob", realm="atlanta.example.com",
qop="auth", nonce="1cec4341ae6cbe5a359ea9c8e88df84f", opaque="",
uri="sips:ss2.biloxi.example.com",
response="71ba27c64bd01de719686aa4590d5824"
Content-Length: 0
F2 200 OK SIP Server -> Bob
SIP/2.0 200 OK
Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
;received=192.0.2.201
From: Bob <sips:bob@biloxi.example.com>;tag=a73kszlfl
To: Bob <sips:bob@biloxi.example.com>;tag=34095828jh
Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com
CSeq: 1 REGISTER
Contact: <sips:bob@client.biloxi.example.com>;expires=3600
Contact: <mailto:bob@biloxi.example.com>;expires=4294967295
Content-Length: 0
2.3. Request for Current Contact List
Bob SIP Server
| |
| REGISTER F1 |
|------------------------------>|
| 200 OK F2 |
|<------------------------------|
| |
Bob sends a register request to the Proxy Server containing no
Contact headers, indicating the user wishes to query the server for
the user’s current contact list. Since the user already has
authenticated with the server, the user supplies authentication
credentials with the request and is not challenged by the server.
The SIP server validates the user’s credentials. The server returns
a response (200 OK) which includes the user’s current registration
list in Contact headers.
Message Details
F1 REGISTER Bob -> SIP Server
REGISTER sips:ss2.biloxi.example.com SIP/2.0
Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
Max-Forwards: 70
From: Bob <sips:bob@biloxi.example.com>;tag=a73kszlfl
To: Bob <sips:bob@biloxi.example.com>
Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com
CSeq: 1 REGISTER
Authorization: Digest username="bob", realm="atlanta.example.com",
nonce="df84f1cec4341ae6cbe5ap359a9c8e88", opaque="",
uri="sips:ss2.biloxi.example.com",
response="aa7ab4678258377c6f7d4be6087e2f60"
Content-Length: 0
F2 200 OK SIP Server -> Bob
SIP/2.0 200 OK
Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
;received=192.0.2.201
From: Bob <sips:bob@biloxi.example.com>;tag=a73kszlfl
To: Bob <sips:bob@biloxi.example.com>;tag=jqoiweu75
Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com
CSeq: 1 REGISTER
Contact: <sips:bob@client.biloxi.example.com>;expires=3600
Contact: <mailto:bob@biloxi.example.com>;expires=4294967295
Content-Length: 0
2.4. Cancellation of Registration
Bob SIP Server
| |
| REGISTER F1 |
|------------------------------>|
| 200 OK F2 |
|<------------------------------|
| |
Bob wishes to cancel their registration with the SIP server. Bob
sends a SIP REGISTER request to the SIP server. The request has an
expiration period of 0 and applies to all existing contact locations.
Since the user already has authenticated with the server, the user
supplies authentication credentials with the request and is not
challenged by the server. The SIP server validates the user’s
credentials. It clears the user’s contact list, and returns a
response (200 OK) to Bob’s SIP client.
Message Details
F1 REGISTER Bob -> SIP Server
REGISTER sips:ss2.biloxi.example.com SIP/2.0
Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
Max-Forwards: 70
From: Bob <sips:bob@biloxi.example.com>;tag=a73kszlfl
To: Bob <sips:bob@biloxi.example.com>
Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com
CSeq: 1 REGISTER
Expires: 0
Contact: *
Authorization: Digest username="bob", realm="atlanta.example.com",
nonce="88df84f1cac4341aea9c8ee6cbe5a359", opaque="",
uri="sips:ss2.biloxi.example.com",
response="ff0437c51696f9a76244f0cf1dbabbea"
Content-Length: 0
F2 200 OK SIP Server -> Bob
SIP/2.0 200 OK
Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
;received=192.0.2.201
From: Bob <sips:bob@biloxi.example.com>;tag=a73kszlfl
To: Bob <sips:bob@biloxi.example.com>;tag=1418nmdsrf
Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com
CSeq: 1 REGISTER
Content-Length: 0
2.5. Unsuccessful Registration
Bob SIP Server
| |
| REGISTER F1 |
|------------------------------>|
| 401 Unauthorized F2 |
|<------------------------------|
| REGISTER F3 |
|------------------------------>|
| 401 Unauthorized F4 |
|<------------------------------|
| |
Bob sends a SIP REGISTER request to the SIP Server. The SIP server
provides a challenge to Bob. Bob enters her/his user ID and
password. Bob’s SIP client encrypts the user information according
to the challenge issued by the SIP server and sends the response to
the SIP server. The SIP server attempts to validate the user’s
credentials, but they are not valid (the user’s password does not
match the password established for the user’s account). The server
returns a response (401 Unauthorized) to Bob’s SIP client.
Message Details
F1 REGISTER Bob -> SIP Server
REGISTER sips:ss2.biloxi.example.com SIP/2.0
Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
;received=192.0.2.201
From: Bob <sips:bob@biloxi.example.com>;tag=a73kszlfl
To: Bob <sips:bob@biloxi.example.com>
Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com
CSeq: 1 REGISTER
Contact: <sips:bob@client.biloxi.example.com>
Content-Length: 0
F2 Unauthorized SIP Server -> Bob
SIP/2.0 401 Unauthorized
Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
;received=192.0.2.201
From: Bob <sips:bob@biloxi.example.com>;tag=a73kszlfl
To: Bob <sips:bob@biloxi.example.com>;tag=1410948204
Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com
CSeq: 1 REGISTER
WWW-Authenticate: Digest realm="atlanta.example.com", qop="auth",
nonce="f1cec4341ae6ca9c8e88df84be55a359",
opaque="", stale=FALSE, algorithm=MD5
Content-Length: 0
F3 REGISTER Bob -> SIP Server
REGISTER sips:ss2.biloxi.example.com SIP/2.0
Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashd92
Max-Forwards: 70
From: Bob <sips:bob@biloxi.example.com>;tag=JueHGuidj28dfga
To: Bob <sips:bob@biloxi.example.com>
Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com
CSeq: 2 REGISTER
Contact: <sips:bob@client.biloxi.example.com>
Authorization: Digest username="bob", realm="atlanta.example.com",
nonce="f1cec4341ae6ca9c8e88df84be55a359", opaque="",
uri="sips:ss2.biloxi.example.com",
response="61f8470ceb87d7ebf508220214ed438b"
Content-Length: 0
/* The response above encodes the incorrect password */
F4 401 Unauthorized SIP Server -> Bob
SIP/2.0 401 Unauthorized
Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashd92
;received=192.0.2.201
From: Bob <sips:bob@biloxi.example.com>;tag=JueHGuidj28dfga
To: Bob <sips:bob@biloxi.example.com>;tag=1410948204
Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com
CSeq: 2 REGISTER
WWW-Authenticate: Digest realm="atlanta.example.com", qop="auth",
nonce="84f1c1ae6cbe5ua9c8e88dfa3ecm3459",
opaque="", stale=FALSE, algorithm=MD5
Content-Length: 0
3. SIP Session Establishment
This section details session establishment between two SIP User
Agents (UAs): Alice and Bob. Alice (sip:alice@atlanta.example.com)
and Bob (sip:bob@biloxi.example.com) are assumed to be SIP phones or
SIP-enabled devices. The successful calls show the initial
signaling, the exchange of media information in the form of SDP
payloads, the establishment of the media session, then finally the
termination of the call.
HTTP Digest authentication is used by Proxy Servers to authenticate
the caller Alice. It is assumed that Bob has registered with Proxy
Server Proxy 2 as per Section 2 to be able to receive the calls via
the Proxy.
3.1. Successful Session Establishment
Alice Bob
| |
| INVITE F1 |
|----------------------->|
| 180 Ringing F2 |
|<-----------------------|
| |
| 200 OK F3 |
|<-----------------------|
| ACK F4 |
|----------------------->|
| Both Way RTP Media |
|<======================>|
| |
| BYE F5 |
|<-----------------------|
| 200 OK F6 |
|----------------------->|
| |
In this scenario, Alice completes a call to Bob directly.
Message Details
F1 INVITE Alice -> Bob
INVITE sip:bob@biloxi.example.com SIP/2.0
Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
Max-Forwards: 70
From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
To: Bob <sip:bob@biloxi.example.com>