Session Initiation Protocol (SIP) Basic Call Flow Examples :: RFC3665
Network Working Group A. Johnston
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.
Johnston, et al. Best Current Practice [Page 1]
RFC 3665 SIP Basic Call Flow Examples December 2003
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.
Johnston, et al. Best Current Practice [Page 2]
RFC 3665 SIP Basic Call Flow Examples December 2003
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. */
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RFC 3665 SIP Basic Call Flow Examples December 2003
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).
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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 ;tag=a73kszlfl
To: Bob
Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com
CSeq: 1 REGISTER
Contact:
Content-Length: 0
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RFC 3665 SIP Basic Call Flow Examples December 2003
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 ;tag=a73kszlfl
To: Bob ;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 ;tag=ja743ks76zlflH
To: Bob
Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com
CSeq: 2 REGISTER
Contact:
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 ;tag=ja743ks76zlflH
To: Bob ;tag=37GkEhwl6
Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com
CSeq: 2 REGISTER
Contact: ;expires=3600
Content-Length: 0
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RFC 3665 SIP Basic Call Flow Examples December 2003
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 ;tag=a73kszlfl
To: Bob
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 ;tag=a73kszlfl
To: Bob ;tag=34095828jh
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RFC 3665 SIP Basic Call Flow Examples December 2003
Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com
CSeq: 1 REGISTER
Contact: ;expires=3600
Contact: ;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 ;tag=a73kszlfl
To: Bob
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
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RFC 3665 SIP Basic Call Flow Examples December 2003
From: Bob ;tag=a73kszlfl
To: Bob ;tag=jqoiweu75
Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com
CSeq: 1 REGISTER
Contact: ;expires=3600
Contact: ;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 ;tag=a73kszlfl
To: Bob
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
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RFC 3665 SIP Basic Call Flow Examples December 2003
SIP/2.0 200 OK
Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
;received=192.0.2.201
From: Bob ;tag=a73kszlfl
To: Bob ;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 ;tag=a73kszlfl
To: Bob
Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com
CSeq: 1 REGISTER
Contact:
Content-Length: 0
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RFC 3665 SIP Basic Call Flow Examples December 2003
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 ;tag=a73kszlfl
To: Bob ;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 ;tag=JueHGuidj28dfga
To: Bob
Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com
CSeq: 2 REGISTER
Contact:
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 ;tag=JueHGuidj28dfga
To: Bob ;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
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RFC 3665 SIP Basic Call Flow Examples December 2003
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 ;tag=9fxced76sl
To: Bob
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RFC 3665 SIP Basic Call Flow Examples December 2003
Call-ID: 3848276298220188511@atlanta.example.com
CSeq: 1 INVITE
Contact:
Content-Type: application/sdp
Content-Length: 151
v=0
o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
s=-
c=IN IP4 192.0.2.101
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000
F2 180 Ringing Bob -> Alice
SIP/2.0 180 Ringing
Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
From: Alice ;tag=9fxced76sl
To: Bob ;tag=8321234356
Call-ID: 3848276298220188511@atlanta.example.com
CSeq: 1 INVITE
Contact:
Content-Length: 0
F3 200 OK Bob -> Alice
SIP/2.0 200 OK
Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
From: Alice ;tag=9fxced76sl
To: Bob ;tag=8321234356
Call-ID: 3848276298220188511@atlanta.example.com
CSeq: 1 INVITE
Contact:
Content-Type: application/sdp
Content-Length: 147
v=0
o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com
s=-
c=IN IP4 192.0.2.201
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000
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RFC 3665 SIP Basic Call Flow Examples December 2003
F4 ACK Alice -> Bob
ACK sip:bob@client.biloxi.example.com SIP/2.0
Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bd5
Max-Forwards: 70
From: Alice ;tag=9fxced76sl
To: Bob ;tag=8321234356
Call-ID: 3848276298220188511@atlanta.example.com
CSeq: 1 ACK
Content-Length: 0
/* RTP streams are established between Alice and Bob */
/* Bob Hangs Up with Alice. Note that the CSeq is NOT 2, since
Alice and Bob maintain their own independent CSeq counts.
(The INVITE was request 1 generated by Alice, and the BYE is
request 1 generated by Bob) */
F5 BYE Bob -> Alice
BYE sip:alice@client.atlanta.example.com SIP/2.0
Via: SIP/2.0/TCP client.biloxi.example.com:5060;branch=z9hG4bKnashds7
Max-Forwards: 70
From: Bob ;tag=8321234356
To: Alice ;tag=9fxced76sl
Call-ID: 3848276298220188511@atlanta.example.com
CSeq: 1 BYE
Content-Length: 0
F6 200 OK Alice -> Bob
SIP/2.0 200 OK
Via: SIP/2.0/TCP client.biloxi.example.com:5060;branch=z9hG4bKnashds7
;received=192.0.2.201
From: Bob ;tag=8321234356
To: Alice ;tag=9fxced76sl
Call-ID: 3848276298220188511@atlanta.example.com
CSeq: 1 BYE
Content-Length: 0
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RFC 3665 SIP Basic Call Flow Examples December 2003
3.2. Session Establishment Through Two Proxies
Alice Proxy 1 Proxy 2 Bob
| | | |
| INVITE F1 | | |
|--------------->| | |
| 407 F2 | | |
|<---------------| | |
| ACK F3 | | |
|--------------->| | |
| INVITE F4 | | |
|--------------->| INVITE F5 | |
| 100 F6 |--------------->| INVITE F7 |
|<---------------| 100 F8 |--------------->|
| |<---------------| |
| | | 180 F9 |
| | 180 F10 |<---------------|
| 180 F11 |<---------------| |
|<---------------| | 200 F12 |
| | 200 F13 |<---------------|
| 200 F14 |<---------------| |
|<---------------| | |
| ACK F15 | | |
|--------------->| ACK F16 | |
| |--------------->| ACK F17 |
| | |--------------->|
| Both Way RTP Media |
|<================================================>|
| | | BYE F18 |
| | BYE F19 |<---------------|
| BYE F20 |<---------------| |
|<---------------| | |
| 200 F21 | | |
|--------------->| 200 F22 | |
| |--------------->| 200 F23 |
| | |--------------->|
| | | |
In this scenario, Alice completes a call to Bob using two proxies
Proxy 1 and Proxy 2. The initial INVITE (F1) contains a pre-loaded
Route header with the address of Proxy 1 (Proxy 1 is configured as a
default outbound proxy for Alice). The request does not contain the
Authorization credentials Proxy 1 requires, so a 407 Proxy
Authorization response is sent containing the challenge information.
A new INVITE (F4) is then sent containing the correct credentials and
the call proceeds. The call terminates when Bob disconnects by
initiating a BYE message.
Johnston, et al. Best Current Practice [Page 15]
RFC 3665 SIP Basic Call Flow Examples December 2003
Proxy 1 inserts a Record-Route header into the INVITE message to
ensure that it is present in all subsequent message exchanges. Proxy
2 also inserts itself into the Record-Route header. The ACK (F15)
and BYE (F18) both have a Route header.
Message Details
F1 INVITE Alice -> Proxy 1
INVITE sip:bob@biloxi.example.com SIP/2.0
Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74b43
Max-Forwards: 70
Route:
From: Alice ;tag=9fxced76sl
To: Bob
Call-ID: 3848276298220188511@atlanta.example.com
CSeq: 1 INVITE
Contact:
Content-Type: application/sdp
Content-Length: 151
v=0
o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
s=-
c=IN IP4 192.0.2.101
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000
/* Proxy 1 challenges Alice for authentication */
F2 407 Proxy Authorization Required Proxy 1 -> Alice
SIP/2.0 407 Proxy Authorization Required
Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74b43
;received=192.0.2.101
From: Alice ;tag=9fxced76sl
To: Bob ;tag=3flal12sf
Call-ID: 3848276298220188511@atlanta.example.com
CSeq: 1 INVITE
Proxy-Authenticate: Digest realm="atlanta.example.com", qop="auth",
nonce="f84f1cec41e6cbe5aea9c8e88d359",
opaque="", stale=FALSE, algorithm=MD5
Content-Length: 0
Johnston, et al. Best Current Practice [Page 16]
RFC 3665 SIP Basic Call Flow Examples December 2003
F3 ACK Alice -> Proxy 1
ACK sip:bob@biloxi.example.com SIP/2.0
Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74b43
Max-Forwards: 70
From: Alice ;tag=9fxced76sl
To: Bob ;tag=3flal12sf
Call-ID: 3848276298220188511@atlanta.example.com
CSeq: 1 ACK
Content-Length: 0
/* Alice responds be re-sending the INVITE with authentication
credentials in it. */
F4 INVITE Alice -> Proxy 1
INVITE sip:bob@biloxi.example.com SIP/2.0
Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
Max-Forwards: 70
Route:
From: Alice ;tag=9fxced76sl
To: Bob
Call-ID: 3848276298220188511@atlanta.example.com
CSeq: 2 INVITE
Contact:
Proxy-Authorization: Digest username="alice",
realm="atlanta.example.com",
nonce="wf84f1ceczx41ae6cbe5aea9c8e88d359", opaque="",
uri="sip:bob@biloxi.example.com",
response="42ce3cef44b22f50c6a6071bc8"
Content-Type: application/sdp
Content-Length: 151
v=0
o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
s=-
c=IN IP4 192.0.2.101
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000
/* Proxy 1 accepts the credentials and forwards the INVITE to Proxy
2. Client for Alice prepares to receive data on port 49172 from the
network. */
Johnston, et al. Best Current Practice [Page 17]
RFC 3665 SIP Basic Call Flow Examples December 2003
F5 INVITE Proxy 1 -> Proxy 2
INVITE sip:bob@biloxi.example.com SIP/2.0
Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
Max-Forwards: 69
Record-Route:
From: Alice ;tag=9fxced76sl
To: Bob
Call-ID: 3848276298220188511@atlanta.example.com
CSeq: 2 INVITE
Contact:
Content-Type: application/sdp
Content-Length: 151
v=0
o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
s=-
c=IN IP4 192.0.2.101
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000
F6 100 Trying Proxy 1 -> Alice
SIP/2.0 100 Trying
Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
From: Alice ;tag=9fxced76sl
To: Bob
Call-ID: 3848276298220188511@atlanta.example.com
CSeq: 2 INVITE
Content-Length: 0
F7 INVITE Proxy 2 -> Bob
INVITE sip:bob@client.biloxi.example.com SIP/2.0
Via: SIP/2.0/TCP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1
Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
;received=192.0.2.111
Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
Max-Forwards: 68
Record-Route: ,
Johnston, et al. Best Current Practice [Page 18]
RFC 3665 SIP Basic Call Flow Examples December 2003
From: Alice ;tag=9fxced76sl
To: Bob
Call-ID: 3848276298220188511@atlanta.example.com
CSeq: 2 INVITE
Contact:
Content-Type: application/sdp
Content-Length: 151
v=0
o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
s=-
c=IN IP4 192.0.2.101
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000
F8 100 Trying Proxy 2 -> Proxy 1
SIP/2.0 100 Trying
Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
;received=192.0.2.111
Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
From: Alice ;tag=9fxced76sl
To: Bob
Call-ID: 3848276298220188511@atlanta.example.com
CSeq: 2 INVITE
Content-Length: 0
F9 180 Ringing Bob -> Proxy 2
SIP/2.0 180 Ringing
Via: SIP/2.0/TCP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1
;received=192.0.2.222
Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
;received=192.0.2.111
Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
Record-Route: ,
From: Alice ;tag=9fxced76sl
To: Bob ;tag=314159
Call-ID: 3848276298220188511@atlanta.example.com
Contact:
CSeq: 2 INVITE
Content-Length: 0
Johnston, et al. Best Current Practice [Page 19]
RFC 3665 SIP Basic Call Flow Examples December 2003
F10 180 Ringing Proxy 2 -> Proxy 1
SIP/2.0 180 Ringing
Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
;received=192.0.2.111
Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
Record-Route: ,
From: Alice ;tag=9fxced76sl
To: Bob ;tag=314159
Call-ID: 3848276298220188511@atlanta.example.com
Contact:
CSeq: 2 INVITE
Content-Length: 0
F11 180 Ringing Proxy 1 -> Alice
SIP/2.0 180 Ringing
Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
Record-Route: ,
From: Alice ;tag=9fxced76sl
To: Bob ;tag=314159
Call-ID: 3848276298220188511@atlanta.example.com
Contact:
CSeq: 2 INVITE
Content-Length: 0
F12 200 OK Bob -> Proxy 2
SIP/2.0 200 OK
Via: SIP/2.0/TCP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1
;received=192.0.2.222
Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
;received=192.0.2.111
Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
Record-Route: ,
From: Alice ;tag=9fxced76sl
To: Bob ;tag=314159
Call-ID: 3848276298220188511@atlanta.example.com
CSeq: 2 INVITE
Johnston, et al. Best Current Practice [Page 20]
RFC 3665 SIP Basic Call Flow Examples December 2003
Contact:
Content-Type: application/sdp
Content-Length: 147
v=0
o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com
s=-
c=IN IP4 192.0.2.201
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000
F13 200 OK Proxy 2 -> Proxy 1
SIP/2.0 200 OK
Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
;received=192.0.2.111
Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
Record-Route: ,
From: Alice ;tag=9fxced76sl
To: Bob ;tag=314159
Call-ID: 3848276298220188511@atlanta.example.com
CSeq: 2 INVITE
Contact:
Content-Type: application/sdp
Content-Length: 147
v=0
o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com
s=-
c=IN IP4 192.0.2.201
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000
F14 200 OK Proxy 1 -> Alice
SIP/2.0 200 OK
Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
Record-Route: ,
From: Alice ;tag=9fxced76sl
To: Bob ;tag=314159
Johnston, et al. Best Current Practice [Page 21]
RFC 3665 SIP Basic Call Flow Examples December 2003
Call-ID: 3848276298220188511@atlanta.example.com
CSeq: 2 INVITE
Contact:
Content-Type: application/sdp
Content-Length: 147
v=0
o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com
s=-
c=IN IP4 192.0.2.201
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000
F15 ACK Alice -> Proxy 1
ACK sip:bob@client.biloxi.example.com SIP/2.0
Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74b76
Max-Forwards: 70
Route: ,
From: Alice ;tag=9fxced76sl
To: Bob ;tag=314159
Call-ID: 3848276298220188511@atlanta.example.com
CSeq: 2 ACK
Content-Length: 0
F16 ACK Proxy 1 -> Proxy 2
ACK sip:bob@client.biloxi.example.com SIP/2.0
Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74b76
;received=192.0.2.101
Max-Forwards: 69
Route:
From: Alice ;tag=9fxced76sl
To: Bob ;tag=314159
Call-ID: 3848276298220188511@atlanta.example.com
CSeq: 2 ACK
Content-Length: 0
F17 ACK Proxy 2 -> Bob
ACK sip:bob@client.biloxi.example.com SIP/2.0
Via: SIP/2.0/TCP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1
Johnston, et al. Best Current Practice [Page 22]
RFC 3665 SIP Basic Call Flow Examples December 2003
Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
;received=192.0.2.111
Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74b76
;received=192.0.2.101
Max-Forwards: 68
From: Alice ;tag=9fxced76sl
To: Bob ;tag=314159
Call-ID: 3848276298220188511@atlanta.example.com
CSeq: 2 ACK
Content-Length: 0
/* RTP streams are established between Alice and Bob */
/* Bob Hangs Up with Alice. */
/* Again, note that the CSeq is NOT 3. Alice and Bob maintain
their own separate CSeq counts */
F18 BYE Bob -> Proxy 2
BYE sip:alice@client.atlanta.example.com SIP/2.0
Via: SIP/2.0/TCP client.biloxi.example.com:5060;branch=z9hG4bKnashds7
Max-Forwards: 70
Route: ,
From: Bob ;tag=314159
To: Alice ;tag=9fxced76sl
Call-ID: 3848276298220188511@atlanta.example.com
CSeq: 1 BYE
Content-Length: 0
F19 BYE Proxy 2 -> Proxy 1
BYE sip:alice@client.atlanta.example.com SIP/2.0
Via: SIP/2.0/TCP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1
Via: SIP/2.0/TCP client.biloxi.example.com:5060;branch=z9hG4bKnashds7
;received=192.0.2.201
Max-Forwards: 69
Route:
From: Bob ;tag=314159
To: Alice ;tag=9fxced76sl
Call-ID: 3848276298220188511@atlanta.example.com
CSeq: 1 BYE
Content-Length: 0
Johnston, et al. Best Current Practice [Page 23]
RFC 3665 SIP Basic Call Flow Examples December 2003
F20 BYE Proxy 1 -> Alice
BYE sip:alice@client.atlanta.example.com SIP/2.0
Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
Via: SIP/2.0/TCP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1
;received=192.0.2.222
Via: SIP/2.0/TCP client.biloxi.example.com:5060;branch=z9hG4bKnashds7
;received=192.0.2.201
Max-Forwards: 68
From: Bob ;tag=314159
To: Alice ;tag=9fxced76sl
Call-ID: 3848276298220188511@atlanta.example.com
CSeq: 1 BYE
Content-Length: 0
F21 200 OK Alice -> Proxy 1
SIP/2.0 200 OK
Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1
;received=192.0.2.111
Via: SIP/2.0/TCP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1
;received=192.0.2.222
Via: SIP/2.0/TCP client.biloxi.example.com:5060;branch=z9hG4bKnashds7
;received=192.0.2.201
From: Bob ;tag=314159
To: Alice ;tag=9fxced76sl
Call-ID: 3848276298220188511@atlanta.example.com
CSeq: 1 BYE
Content-Length: 0
F22 200 OK Proxy 1 -> Proxy 2
SIP/2.0 200 OK
Via: SIP/2.0/TCP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1
;received=192.0.2.222
Via: SIP/2.0/TCP client.biloxi.example.com:5060;branch=z9hG4bKnashds7
;received=192.0.2.101
From: Bob ;tag=314159
To: Alice ;tag=9fxced76sl
Call-ID: 3848276298220188511@atlanta.example.com
CSeq: 1 BYE
Content-Length: 0
Johnston, et al. Best Current Practice [Page 24]
RFC 3665 SIP Basic Call Flow Examples December 2003
F23 200 OK Proxy 2 -> Bob
SIP/2.0 200 OK
Via: SIP/2.0/TCP client.biloxi.example.com:5060;branch=z9hG4bKnashds7
;received=192.0.2.201
From: Bob ;tag=314159
To: Alice ;tag=9fxced76sl
Call-ID: 3848276298220188511@atlanta.example.com
CSeq: 1 BYE
Content-Length: 0
Johnston, et al. Best Current Practice [Page 25]
RFC 3665 SIP Basic Call Flow Examples December 2003
3.3. Session with Multiple Proxy Authentication
Alice Proxy 1 Proxy 2 Bob
| | | |
| INVITE F1 | | |
|----------->| | |
| 407 Proxy Authorization Required F2 |
|<-----------| | |
| ACK F3 | | |
|----------->| | |
| INVITE F4 | | |
|----------->| | |
| 100 F5 | | |
|<-----------| INVITE F6 | |
| |---------->| |
| | 407 Proxy Authorization Required F7
| |<----------| |
| | ACK F8 | |
| |---------->| |
| 407 Proxy Authorization Required F9 |
|<-----------| | |
| ACK F10 | | |
|----------->| | |
| INVITE F11| | |
|----------->| | |
| 100 F12 | | |
|<-----------| INVITE F13| |
| |---------->| |
| | 100 F14 | |
| |<----------| INVITE F15 |
| | |------------>|
| | | 200 OK F16 |
| | 200 OK F17|<------------|
| 200 OK F18 |<----------| |
|<-----------| | |
| ACK F19 | | |
|----------->| ACK F20 | |
| |---------->| ACK F21 |
| | |------------>|
| RTP Media Path |
|<====================================>|
In this scenario, Alice completes a call to Bob using two proxies
Proxy 1 and Proxy 2. Alice has valid credentials in both domains.
Since the initial INVITE (F1) does not contain the Authorization
credentials Proxy 1 requires, so a 407 Proxy Authorization response
is sent containing the challenge information. A new INVITE (F4) is
Johnston, et al. Best Current Practice [Page 26]
RFC 3665 SIP Basic Call Flow Examples December 2003
then sent containing the correct credentials and the call proceeds
after Proxy 2 challenges and receives valid credentials. The call
terminates when Bob disconnects by initiating a BYE message.
Proxy 1 inserts a Record-Route header into the INVITE message to
ensure that it is present in all subsequent message exchanges. Proxy
2 also inserts itself into the Record-Route header.
Message Details
F1 INVITE Alice -> Proxy 1
INVITE sip:bob@biloxi.example.com SIP/2.0
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b03
Max-Forwards: 70
Route:
From: Alice ;tag=9fxced76sl
To: Bob
Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
CSeq: 1 INVITE
Contact:
Content-Type: application/sdp
Content-Length: 151
v=0
o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
s=-
c=IN IP4 192.0.2.101
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000
/* Proxy 1 challenges Alice for authentication */
F2 407 Proxy Authorization Required Proxy 1 -> Alice
SIP/2.0 407 Proxy Authorization Required
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b03
;received=192.0.2.101
From: Alice ;tag=9fxced76sl
To: Bob ;tag=876321
Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
CSeq: 1 INVITE
Proxy-Authenticate: Digest realm="atlanta.example.com", qop="auth",
nonce="wf84f1cczx41ae6cbeaea9ce88d359",
opaque="", stale=FALSE, algorithm=MD5
Content-Length: 0
Johnston, et al. Best Current Practice [Page 27]
RFC 3665 SIP Basic Call Flow Examples December 2003
F3 ACK Alice -> Proxy 1
ACK sip:bob@biloxi.example.com SIP/2.0
Max-Forwards: 70
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b03
From: Alice ;tag=9fxced76sl
To: Bob ;tag=876321
Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
CSeq: 1 ACK
Content-Length: 0
/* Alice responds be re-sending the INVITE with authentication
credentials in it. The same Call-ID is used, so the CSeq is
increased. */
F4 INVITE Alice -> Proxy 1
INVITE sip:bob@biloxi.example.com SIP/2.0
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b21
Max-Forwards: 70
Route:
From: Alice ;tag=9fxced76sl
To: Bob
Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
CSeq: 2 INVITE
Contact:
Proxy-Authorization: Digest username="alice",
realm="atlanta.example.com",
nonce="wf84f1ceczx41ae6cbe5aea9c8e88d359", opaque="",
uri="sip:bob@biloxi.example.com",
response="42ce3cef44b22f50c6a6071bc8"
Content-Type: application/sdp
Content-Length: 151
v=0
o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
s=-
c=IN IP4 192.0.2.101
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000
/* Proxy 1 accepts the credentials and forwards the INVITE to Proxy
2. Client for Alice prepares to receive data on port 49172 from the
network. */
Johnston, et al. Best Current Practice [Page 28]
RFC 3665 SIP Basic Call Flow Examples December 2003
F5 100 Trying Proxy 1 -> Alice
SIP/2.0 100 Trying
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b21
;received=192.0.2.101
From: Alice ;tag=9fxced76sl
To: Bob
Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
CSeq: 2 INVITE
Content-Length: 0
F6 INVITE Proxy 1 -> Proxy 2
INVITE sip:bob@biloxi.example.com SIP/2.0
Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK230f2.1
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b21
;received=192.0.2.101
Max-Forwards: 69
Record-Route:
From: Alice ;tag=9fxced76sl
To: Bob
Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
CSeq: 2 INVITE
Contact:
Content-Type: application/sdp
Content-Length: 151
v=0
o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
s=-
c=IN IP4 192.0.2.101
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000
/* Proxy 2 challenges Alice for authentication */
F7 407 Proxy Authorization Required Proxy 2 -> Proxy 1
SIP/2.0 407 Proxy Authorization Required
Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK230f2.1
;received=192.0.2.111
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b21
;received=192.0.2.101
Johnston, et al. Best Current Practice [Page 29]
RFC 3665 SIP Basic Call Flow Examples December 2003
From: Alice ;tag=9fxced76sl
To: Bob ;tag=838209
Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
CSeq: 2 INVITE
Proxy-Authenticate: Digest realm="biloxi.example.com", qop="auth",
nonce="c1e22c41ae6cbe5ae983a9c8e88d359",
opaque="", stale=FALSE, algorithm=MD5
Content-Length: 0
F8 ACK Proxy 1 -> Proxy 2
ACK sip:bob@biloxi.example.com SIP/2.0
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b21
Max-Forwards: 70
From: Alice ;tag=9fxced76sl
To: Bob ;tag=838209
Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
CSeq: 2 ACK
Content-Length: 0
/* Proxy 1 forwards the challenge to Alice for authentication from
Proxy 2 */
F9 407 Proxy Authorization Required Proxy 1 -> Alice
SIP/2.0 407 Proxy Authorization Required
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b21
;received=192.0.2.101
From: Alice ;tag=9fxced76sl
To: Bob ;tag=838209
Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
CSeq: 2 INVITE
Proxy-Authenticate: Digest realm="biloxi.example.com", qop="auth",
nonce="c1e22c41ae6cbe5ae983a9c8e88d359",
opaque="", stale=FALSE, algorithm=MD5
Content-Length: 0
F10 ACK Alice -> Proxy 1
ACK sip:bob@biloxi.example.com SIP/2.0
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b21
Max-Forwards: 70
From: Alice ;tag=9fxced76sl
To: Bob ;tag=838209
Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
Johnston, et al. Best Current Practice [Page 30]
RFC 3665 SIP Basic Call Flow Examples December 2003
CSeq: 2 ACK
Proxy-Authorization: Digest username="alice",
realm="atlanta.example.com",
nonce="wf84f1ceczx41ae6cbe5aea9c8e88d359", opaque="",
uri="sip:bob@biloxi.example.com",
response="42ce3cef44b22f50c6a6071bc8"
Content-Length: 0
/* Alice responds be re-sending the INVITE with authentication
credentials for Proxy 1 AND Proxy 2. */
F11 INVITE Alice -> Proxy 1
INVITE sip:bob@biloxi.example.com SIP/2.0
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
Max-Forwards: 70
From: Alice ;tag=9fxced76sl
To: Bob
Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
CSeq: 3 INVITE
Contact:
Proxy-Authorization: Digest username="alice",
realm="atlanta.example.com",
nonce="wf84f1ceczx41ae6cbe5aea9c8e88d359", opaque="",
uri="sip:bob@biloxi.example.com",
response="42ce3cef44b22f50c6a6071bc8"
Proxy-Authorization: Digest username="alice",
realm="biloxi.example.com",
nonce="c1e22c41ae6cbe5ae983a9c8e88d359", opaque="",
uri="sip:bob@biloxi.example.com", response="f44ab22f150c6a56071bce8"
Content-Type: application/sdp
Content-Length: 151
v=0
o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
s=-
c=IN IP4 192.0.2.101
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000
/* Proxy 1 finds its credentials and authorizes Alice, forwarding the
INVITE to Proxy. */
Johnston, et al. Best Current Practice [Page 31]
RFC 3665 SIP Basic Call Flow Examples December 2003
F12 100 Trying Proxy 1 -> Alice
SIP/2.0 100 Trying
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
From: Alice ;tag=9fxced76sl
To: Bob
Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
CSeq: 3 INVITE
Content-Length: 0
F13 INVITE Proxy 1 -> Proxy 2
INVITE sip:bob@biloxi.example.com SIP/2.0
Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK230f2.1
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
Max-Forwards: 69
Record-Route:
From: Alice ;tag=9fxced76sl
To: Bob
Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
CSeq: 3 INVITE
Contact:
Proxy-Authorization: Digest username="alice",
realm="biloxi.example.com",
nonce="c1e22c41ae6cbe5ae983a9c8e88d359", opaque="",
uri="sip:bob@biloxi.example.com", response="f44ab22f150c6a56071bce8"
Content-Type: application/sdp
Content-Length: 151
v=0
o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
s=-
c=IN IP4 192.0.2.101
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000
/* Proxy 2 finds its credentials and authorizes Alice, forwarding the
INVITE to Bob. */
Johnston, et al. Best Current Practice [Page 32]
RFC 3665 SIP Basic Call Flow Examples December 2003
F14 100 Trying Proxy 2 -> Proxy 1
SIP/2.0 100 Trying
Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK230f2.1
;received=192.0.2.111
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
From: Alice ;tag=9fxced76sl
To: Bob
Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
CSeq: 3 INVITE
Content-Length: 0
F15 INVITE Proxy 2 -> Bob
INVITE sip:bob@client.biloxi.example.com SIP/2.0
Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK31972.1
Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK230f2.1
;received=192.0.2.111
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
Max-Forwards: 68
Record-Route: ,
From: Alice ;tag=9fxced76sl
To: Bob
Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
CSeq: 3 INVITE
Contact:
Content-Type: application/sdp
Content-Length: 151
v=0
o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
s=-
c=IN IP4 192.0.2.101
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000
/* Bob answers the call immediately */
Johnston, et al. Best Current Practice [Page 33]
RFC 3665 SIP Basic Call Flow Examples December 2003
F16 200 OK Bob -> Proxy 2
SIP/2.0 200 OK
Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK31972.1
;received=192.0.2.222
Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK230f2.1
;received=192.0.2.111
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
Record-Route: ,
From: Alice ;tag=9fxced76sl
To: Bob ;tag=9103874
Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
CSeq: 3 INVITE
Contact:
Content-Type: application/sdp
Content-Length: 147
v=0
o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com
s=-
c=IN IP4 192.0.2.201
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000
F17 200 OK Proxy 2 -> Proxy 1
SIP/2.0 200 OK
Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK230f2.1
;received=192.0.2.111
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
Record-Route: ,
From: Alice ;tag=9fxced76sl
To: Bob ;tag=9103874
Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
CSeq: 3 INVITE
Contact:
Content-Type: application/sdp
Content-Length: 147
v=0
o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com
s=-
Johnston, et al. Best Current Practice [Page 34]
RFC 3665 SIP Basic Call Flow Examples December 2003
c=IN IP4 192.0.2.201
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000
F18 200 OK Proxy 1 -> Alice
SIP/2.0 200 OK
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
Record-Route: ,
From: Alice ;tag=9fxced76sl
To: Bob ;tag=9103874
Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
CSeq: 3 INVITE
Contact:
Content-Type: application/sdp
Content-Length: 147
v=0
o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com
s=-
c=IN IP4 192.0.2.201
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000
F19 ACK Alice -> Proxy 1
ACK sip:bob@client.biloxi.example.com SIP/2.0
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b44
Max-Forwards: 70
Route: ,
From: Alice ;tag=9fxced76sl
To: Bob ;tag=9103874
Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
CSeq: 3 ACK
Proxy-Authorization: Digest username="alice",
realm="atlanta.example.com",
nonce="wf84f1ceczx41ae6cbe5aea9c8e88d359", opaque="",
uri="sip:bob@biloxi.example.com",
response="42ce3cef44b22f50c6a6071bc8"
Proxy-Authorization: Digest username="alice",
realm="biloxi.example.com",
Johnston, et al. Best Current Practice [Page 35]
RFC 3665 SIP Basic Call Flow Examples December 2003
nonce="c1e22c41ae6cbe5ae983a9c8e88d359", opaque="",
uri="sip:bob@biloxi.example.com", response="f44ab22f150c6a56071bce8"
Content-Length: 0
F20 ACK Proxy 1 -> Proxy 2
ACK sip:bob@client.biloxi.example.com SIP/2.0
Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK230f2.1
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b44
;received=192.0.2.101
Max-Forwards: 69
Route:
From: Alice ;tag=9fxced76sl
To: Bob ;tag=9103874
Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
CSeq: 3 ACK
Contact:
Proxy-Authorization: Digest username="alice",
realm="biloxi.example.com",
nonce="c1e22c41ae6cbe5ae983a9c8e88d359", opaque="",
uri="sip:bob@biloxi.example.com", response="f44ab22f150c6a56071bce8"
Content-Length: 0
F21 ACK Proxy 2 -> Bob
ACK sip:bob@client.biloxi.example.com SIP/2.0
Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK31972.1
Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK230f2.1
;received=192.0.2.111
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b44
;received=192.0.2.101
Max-Forwards: 68
From: Alice ;tag=9fxced76sl
To: Bob ;tag=9103874
Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
CSeq: 3 ACK
Contact:
Content-Length: 0
Johnston, et al. Best Current Practice [Page 36]
RFC 3665 SIP Basic Call Flow Examples December 2003
3.4. Successful Session with Proxy Failure
Alice Proxy 1 Proxy 2 Bob
| | | |
| INVITE F1 | | |
|--------------->| | |
| INVITE F2 | | |
|--------------->| | |
| INVITE F3 | | |
|--------------->| | |
| INVITE F4 | | |
|--------------->| | |
| INVITE F5 | | |
|--------------->| | |
| INVITE F6 | | |
|--------------->| | |
| INVITE F7 | | |
|--------------->| | |
| INVITE F8 | |
|-------------------------------->| |
| 407 F9 | |
|<--------------------------------| |
| ACK F10 | |
|-------------------------------->| |
| INVITE F11 | |
|-------------------------------->| INVITE F12 |
| 100 F13 |--------------->|
|<--------------------------------| |
| | 180 F14 |
| 180 F15 |<---------------|
|<--------------------------------| |
| | 200 F16 |
| 200 F17 |<---------------|
|<--------------------------------| |
| ACK F18 | |
|-------------------------------->| ACK F19 |
| |--------------->|
| Both Way RTP Media |
|<================================================>|
| | BYE F20 |
| BYE F21 |<---------------|
|<--------------------------------| |
| 200 F22 | |
|-------------------------------->| 200 F23 |
| |--------------->|
| | |
Johnston, et al. Best Current Practice [Page 37]
RFC 3665 SIP Basic Call Flow Examples December 2003
In this scenario, Alice completes a call to Bob via a Proxy Server.
Alice is configured for a primary SIP Proxy Server Proxy 1 and a
secondary SIP Proxy Server Proxy 2 (Or is able to use DNS SRV records
to locate Proxy 1 and Proxy 2). Alice has valid credentials for both
domains. Proxy 1 is out of service and does not respond to INVITEs
(it is reachable, but unresponsive). Alice then completes the call
to Bob using Proxy 2.
Message Details
F1 INVITE Alice -> Proxy 1
INVITE sip:bob@biloxi.example.com SIP/2.0
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK465b6d
Max-Forwards: 70
Route:
From: Alice ;tag=9fxced76sl
To: Bob
Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
CSeq: 1 INVITE
Contact:
Content-Type: application/sdp
Content-Length: 151
v=0
o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
s=-
c=IN IP4 192.0.2.101
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000
F2 INVITE Alice -> Proxy 1
Same as Message F1
F3 INVITE Alice -> Proxy 1
Same as Message F1
F4 INVITE Alice -> Proxy 1
Same as Message F1
Johnston, et al. Best Current Practice [Page 38]
RFC 3665 SIP Basic Call Flow Examples December 2003
F5 INVITE Alice -> Proxy 1
Same as Message F1
F6 INVITE Alice -> Proxy 1
Same as Message F1
F7 INVITE Alice -> Proxy 1
Same as Message F1
/* Alice gives up on the unresponsive proxy */
F8 INVITE Alice -> Proxy 2
INVITE sip:bob@biloxi.example.com SIP/2.0
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b8a
Max-Forwards: 70
From: Alice ;tag=9fxced76sl
To: Bob
Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com
CSeq: 1 INVITE
Contact:
Content-Type: application/sdp
Content-Length: 151
v=0
o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
s=-
c=IN IP4 192.0.2.101
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000
/* Proxy 2 challenges Alice for authentication */
F9 407 Proxy Authorization Required Proxy 2 -> Alice
SIP/2.0 407 Proxy Authorization Required
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b8a
;received=192.0.2.101
From: Alice ;tag=9fxced76sl
To: Bob ;tag=2421452
Johnston, et al. Best Current Practice [Page 39]
RFC 3665 SIP Basic Call Flow Examples December 2003
Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com
CSeq: 1 INVITE
Proxy-Authenticate: Digest realm="biloxi.example.com", qop="auth",
nonce="1ae6cbe5ea9c8e8df84fqnlec434a359",
opaque="", stale=FALSE, algorithm=MD5
Content-Length: 0
F10 ACK Alice -> Proxy 2
ACK sip:bob@biloxi.example.com SIP/2.0
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b8a
Max-Forwards: 70
From: Alice ;tag=9fxced76sl
To: Bob ;tag=2421452
Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com
CSeq: 1 ACK
Content-Length: 0
/* Alice responds by re-sending the INVITE with authentication
credentials in it. */
F11 INVITE Alice -> Proxy 2
INVITE sip:bob@biloxi.example.com SIP/2.0
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
Max-Forwards: 70
From: Alice ;tag=9fxced76sl
To: Bob
Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com
CSeq: 2 INVITE
Contact:
Proxy-Authorization: Digest username="alice",
realm="biloxi.example.com",
nonce="1ae6cbe5ea9c8e8df84fqnlec434a359", opaque="",
uri="sip:bob@biloxi.example.com",
response="8a880c919d1a52f20a1593e228adf599"
Content-Type: application/sdp
Content-Length: 151
v=0
o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
s=-
c=IN IP4 192.0.2.101
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000
Johnston, et al. Best Current Practice [Page 40]
RFC 3665 SIP Basic Call Flow Examples December 2003
/* Proxy 2 accepts the credentials and forwards the INVITE to Bob.
Client for Alice prepares to receive data on port 49172 from the
network.
*/
F12 INVITE Proxy 2 -> Bob
INVITE sip:bob@client.biloxi.example.com SIP/2.0
Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
Max-Forwards: 69
Record-Route:
From: Alice ;tag=9fxced76sl
To: Bob
Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com
CSeq: 2 INVITE
Contact:
Content-Type: application/sdp
Content-Length: 151
v=0
o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
s=-
c=IN IP4 192.0.2.101
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000
F13 100 Trying Proxy 2 -> Alice
SIP/2.0 100 Trying
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
From: Alice ;tag=9fxced76sl
To: Bob
Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com
CSeq: 2 INVITE
Content-Length: 0
F14 180 Ringing Bob -> Proxy 2
SIP/2.0 180 Ringing
Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1
;received=192.0.2.222
Johnston, et al. Best Current Practice [Page 41]
RFC 3665 SIP Basic Call Flow Examples December 2003
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
Record-Route:
From: Alice ;tag=9fxced76sl
To: Bob ;tag=314159
Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com
CSeq: 2 INVITE
Contact:
Content-Length: 0
F15 180 Ringing Proxy 2 -> Alice
SIP/2.0 180 Ringing
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
Record-Route:
From: Alice ;tag=9fxced76sl
To: Bob ;tag=314159
Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com
CSeq: 2 INVITE
Contact:
Content-Length: 0
F16 200 OK Bob -> Proxy 2
SIP/2.0 200 OK
Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1
;received=192.0.2.222
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
Record-Route:
From: Alice ;tag=9fxced76sl
To: Bob ;tag=314159
Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com
CSeq: 2 INVITE
Contact:
Content-Type: application/sdp
Content-Length: 147
v=0
o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com
s=-
c=IN IP4 192.0.2.201
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000
Johnston, et al. Best Current Practice [Page 42]
RFC 3665 SIP Basic Call Flow Examples December 2003
F17 200 OK Proxy 2 -> Alice
SIP/2.0 200 OK
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
Record-Route:
From: Alice ;tag=9fxced76sl
To: Bob ;tag=314159
Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com
CSeq: 2 INVITE
Contact:
Content-Type: application/sdp
Content-Length: 147
v=0
o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com
s=-
c=IN IP4 192.0.2.201
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000
F18 ACK Alice -> Proxy 2
ACK sip:bob@client.biloxi.example.com SIP/2.0
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b8g
Max-Forwards: 70
Route:
From: Alice ;tag=9fxced76sl
To: Bob ;tag=314159
Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com
CSeq: 2 ACK
Content-Length: 0
F19 ACK Proxy 2 -> Bob
ACK sip:bob@client.biloxi.example.com SIP/2.0
Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b8g
;received=192.0.2.101
Max-Forwards: 69
From: Alice ;tag=9fxced76sl
To: Bob ;tag=314159
Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com
Johnston, et al. Best Current Practice [Page 43]
RFC 3665 SIP Basic Call Flow Examples December 2003
CSeq: 2 ACK
Content-Length: 0
/* RTP streams are established between Alice and Bob */
/* Bob Hangs Up with Alice. */
F20 BYE Bob -> Proxy 2
BYE sip:alice@client.atlanta.example.com SIP/2.0
Via: SIP/2.0/UDP client.biloxi.example.com:5060;branch=z9hG4bKnashds7
Max-Forwards: 70
Route:
From: Bob ;tag=314159
To: Alice ;tag=9fxced76sl
Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com
CSeq: 1 BYE
Content-Length: 0
F21 BYE Proxy 2 -> Alice
BYE sip:alice@client.atlanta.example.com SIP/2.0
Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1
Via: SIP/2.0/UDP client.biloxi.example.com:5060;branch=z9hG4bKnashds7
;received=192.0.2.201
Max-Forwards: 69
From: Bob ;tag=314159
To: Alice ;tag=9fxced76sl
Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com
CSeq: 1 BYE
Content-Length: 0
F22 200 OK Alice -> Proxy 2
SIP/2.0 200 OK
Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1
;received=192.0.2.222
Via: SIP/2.0/UDP client.biloxi.example.com:5060;branch=z9hG4bKnashds7
;received=192.0.2.201
From: Bob ;tag=314159
To: Alice ;tag=9fxced76sl
Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com
CSeq: 1 BYE
Content-Length: 0
Johnston, et al. Best Current Practice [Page 44]
RFC 3665 SIP Basic Call Flow Examples December 2003
F23 200 OK Proxy 2 -> Bob
SIP/2.0 200 OK
Via: SIP/2.0/UDP client.biloxi.example.com:5060;branch=z9hG4bKnashds7
;received=192.0.2.201
From: Bob ;tag=314159
To: Alice ;tag=9fxced76sl
Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com
CSeq: 1 BYE
Content-Length: 0
Johnston, et al. Best Current Practice [Page 45]
RFC 3665 SIP Basic Call Flow Examples December 2003
3.5. Session Through a SIP ALG
Alice ALG Proxy 2 Bob
| | | |
| INVITE F1 | | |
|--------------->| INVITE F2 | |
| 100 F3 |--------------->| INVITE F4 |
|<---------------| 100 F5 |--------------->|
| |<---------------| 180 F6 |
| | 180 F7 |<---------------|
| 180 F8 |<---------------| |
|<---------------| | 200 F9 |
| | 200 F10 |<---------------|
| 200 F11 |<---------------| |
|<---------------| |
| ACK F12 | |
|--------------->| ACK F13 |
| |-------------------------------->|
| RTP Media | Both Way RTP Media |
|<==============>|<===============================>|
| BYE F14 | |
|--------------->| BYE F15 |
| |-------------------------------->|
| | 200 F16 |
| 200 F17 |<--------------------------------|
|<---------------| |
| | |
Alice completes a call to Bob through a ALG (Application Layer
Gateway) and a SIP Proxy. The routing through the ALG is
accomplished using a pre-loaded Route header in the INVITE F1. Note
that the media stream setup is not end-to-end - the ALG terminates
both media streams and bridges them. This is done by the ALG
modifying the SDP in the INVITE (F1) and 200 OK (F10) messages, and
possibly any 18x or ACK messages containing SDP.
In addition to firewall traversal, this Back-to-Back User Agent
(B2BUA) could be used as part of an anonymizer service (in which all
identifying information on Alice would be removed), or to perform
codec media conversion, such as mu-law to A-law conversion of PCM on
an international call.
Also note that Proxy 2 does not Record-Route in this call flow.
Johnston, et al. Best Current Practice [Page 46]
RFC 3665 SIP Basic Call Flow Examples December 2003
Message Details
F1 INVITE Alice -> SIP ALG
INVITE sip:bob@biloxi.example.com SIP/2.0
Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
Max-Forwards: 70
From: Alice ;tag=9fxced76sl
To: Bob
Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com
CSeq: 1 INVITE
Contact:
Route: 