draft-ietf-mmusic-udptl-dtls-05.txt   draft-ietf-mmusic-udptl-dtls-06.txt 
MMUSIC Working Group C. Holmberg MMUSIC Working Group C. Holmberg
Internet-Draft I. Sedlacek Internet-Draft I. Sedlacek
Intended status: Standards Track Ericsson Intended status: Standards Track Ericsson
Expires: August 18, 2014 G. Salgueiro Expires: September 26, 2014 G. Salgueiro
Cisco Cisco
February 14, 2014 March 25, 2014
UDP Transport Layer (UDPTL) over Datagram Transport Layer Security UDP Transport Layer (UDPTL) over Datagram Transport Layer Security
(DTLS) (DTLS)
draft-ietf-mmusic-udptl-dtls-05 draft-ietf-mmusic-udptl-dtls-06
Abstract Abstract
This document specifies how the UDP Transport Layer (UDPTL) protocol, This document specifies how the UDP Transport Layer (UDPTL) protocol,
the predominant transport protocol for T.38 fax, can be transported the predominant transport protocol for T.38 fax, can be transported
over the Datagram Transport Layer Security (DTLS) protocol, how the over the Datagram Transport Layer Security (DTLS) protocol, how the
usage of UDPTL over DTLS is indicated in the Session Description usage of UDPTL over DTLS is indicated in the Session Description
Protocol (SDP), and how UDPTL over DTLS is negotiated in a session Protocol (SDP), and how UDPTL over DTLS is negotiated in a session
established using the Session Initiation Protocol (SIP). established using the Session Initiation Protocol (SIP).
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 18, 2014. This Internet-Draft will expire on September 26, 2014.
Copyright Notice Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Secure Channel . . . . . . . . . . . . . . . . . . . . . . . 5 3. Secure Channel . . . . . . . . . . . . . . . . . . . . . . . 5
4. SDP Offerer/Answerer Procedures . . . . . . . . . . . . . . . 5 4. SDP Offerer/Answerer Procedures . . . . . . . . . . . . . . . 5
4.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.2. SDP Offerer Procedures . . . . . . . . . . . . . . . . . 6 4.2. Generating the Initial Offer . . . . . . . . . . . . . . 6
4.3. SDP Answerer Procedures . . . . . . . . . . . . . . . . . 6 4.3. Generating the Answer . . . . . . . . . . . . . . . . . . 6
4.4. Offerer Processing of the Answer . . . . . . . . . . . . 6
4.5. Modifying the Session . . . . . . . . . . . . . . . . . . 7
5. Miscellaneous Considerations . . . . . . . . . . . . . . . . 7 5. Miscellaneous Considerations . . . . . . . . . . . . . . . . 7
5.1. Anonymous Calls . . . . . . . . . . . . . . . . . . . . . 7 5.1. Anonymous Calls . . . . . . . . . . . . . . . . . . . . . 7
5.2. NAT Traversal . . . . . . . . . . . . . . . . . . . . . . 7 5.2. NAT Traversal . . . . . . . . . . . . . . . . . . . . . . 7
5.2.1. ICE Usage . . . . . . . . . . . . . . . . . . . . . . 7 5.2.1. ICE Usage . . . . . . . . . . . . . . . . . . . . . . 7
5.2.2. STUN Interaction . . . . . . . . . . . . . . . . . . 7 5.2.2. STUN Interaction . . . . . . . . . . . . . . . . . . 7
5.3. Rekeying . . . . . . . . . . . . . . . . . . . . . . . . 7 5.3. Rekeying . . . . . . . . . . . . . . . . . . . . . . . . 8
5.4. Compatibility With UDPTL over UDP . . . . . . . . . . . . 8 5.4. Compatibility With UDPTL over UDP . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9
9. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 9 9. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 10
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
10.1. Normative References . . . . . . . . . . . . . . . . . . 11 10.1. Normative References . . . . . . . . . . . . . . . . . . 12
10.2. Informative References . . . . . . . . . . . . . . . . . 12 10.2. Informative References . . . . . . . . . . . . . . . . . 13
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 13 Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 13
A.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 13 A.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 13
A.2. Basic Message Flow . . . . . . . . . . . . . . . . . . . 13 A.2. Basic Message Flow . . . . . . . . . . . . . . . . . . . 13
A.3. Message Flow Of T.38 Fax Replacing Audio Media Stream in A.3. Message Flow Of T.38 Fax Replacing Audio Media Stream in
An Existing Audio-Only Session . . . . . . . . . . . . . 19 An Existing Audio-Only Session . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
1. Introduction 1. Introduction
While it is possible to transmit highly sensitive documents using While it is possible to transmit highly sensitive documents using
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a UDPTL over DTLS media stream. a UDPTL over DTLS media stream.
In order to negotiate a UDPTL over DTLS media stream, the following In order to negotiate a UDPTL over DTLS media stream, the following
SDP attributes are used: SDP attributes are used:
o The SDP attributes defined for UDPTL over UDP, as described in o The SDP attributes defined for UDPTL over UDP, as described in
[ITU.T38.2010]; and [ITU.T38.2010]; and
o The SDP attributes, defined in [RFC4145] and [RFC4572], as o The SDP attributes, defined in [RFC4145] and [RFC4572], as
described in this section. described in this section.
The endpoint MUST NOT use the SDP connection attribute [RFC4145]. The endpoint MUST NOT use the SDP "connection" attribute [RFC4145].
In order to negotiate the TLS roles for the UDPTL over DTLS transport In order to negotiate the TLS roles for the UDPTL over DTLS transport
connection, the endpoint MUST use the SDP setup attribute [RFC4145]. connection, the endpoint MUST use the SDP "setup" attribute
[RFC4145].
If the endpoint supports, and is willing to use, a cipher suite with If the endpoint supports, and is willing to use, a cipher suite with
an associated certificate, the endpoint MUST include an SDP an associated certificate, the endpoint MUST include an SDP
fingerprint attribute [RFC4572]. "fingerprint" attribute [RFC4572].
If a cipher suite with an associated certificate is selected during If a cipher suite with an associated certificate is selected during
the DTLS handshake, the certificate received during the DTLS the DTLS handshake, the certificate received during the DTLS
handshake MUST match the fingerprint received in the SDP fingerprint handshake MUST match the fingerprint received in the SDP
attribute. If the fingerprint does not match the hashed certificate, "fingerprint" attribute. If the fingerprint does not match the
then the endpoint MUST tear down the media session immediately. Note hashed certificate, then the endpoint MUST tear down the media
that it is permissible to wait until the other side's fingerprint has session immediately. Note that it is permissible to wait until the
been received before establishing the connection; however, this may other side's fingerprint has been received before establishing the
have undesirable latency effects. connection; however, this may have undesirable latency effects.
4.2. SDP Offerer Procedures 4.2. Generating the Initial Offer
The offerer SHOULD assign the SDP setup attribute with a The offerer SHOULD assign the SDP "setup" attribute with a value of
setup:actpass value. Alternatively, the offerer MAY assign the SDP "actpass". Alternatively, the offerer MAY assign the SDP "setup"
setup attribute with a setup:active value or setup:passive value. attribute with a value of "active" or "passive". The offerer MUST
The offerer MUST NOT assign an SDP setup attribute with a NOT assign an SDP "setup" attribute with a "holdconn" value.
setup:holdconn value.
If the offerer assigns the SDP setup attribute with a setup:actpass If the offerer assigns the SDP "setup" attribute with a value of
value or setup:passive value, the offerer MUST be prepared to receive "actpass" or "passive", the offerer MUST be prepared to receive a
a DTLS client_hello message before it receives the SDP answer. DTLS ClientHello message before it receives the SDP answer.
When the offerer receives the associated answer, if the offerer ends 4.3. Generating the Answer
up being active it MUST initiate a DTLS handshake by sending a
If the answerer accepts the offered UDPTL over DTLS transport
connection, in the associated SDP answer the answerer MUST assign an
SDP "setup" attribute with a value of either "active" or "passive",
according to the procedures in [RFC4145]. The answerer MUST NOT
assign an SDP "setup" attribute with a value of "holdconn".
If the answerer assigns an SDP "setup" attribute with a value of
"active" value, the answerer MUST initiate a DTLS handshake by
sending a DTLS ClientHello message on the negotiated media stream,
towards the IP address and port of the offerer.
4.4. Offerer Processing of the Answer
When the offerer receives an SDP answer and, if the offerer ends up
being active it MUST initiate a DTLS handshake by sending a DTLS
ClientHello message on the negotiated media stream, towards the IP ClientHello message on the negotiated media stream, towards the IP
address and port of the answerer. address and port of the answerer.
4.3. SDP Answerer Procedures 4.5. Modifying the Session
If the answerer accepts the offered UDPTL over DTLS transport
connection, in the associated answer the answerer MUST assign an SDP
setup attribute with either a setup:active value or setup:passive
value, according to the procedures in [RFC4145]. The answerer MUST
NOT assign an SDP setup attribute with a setup:holdconn value.
If the answerer assigns a setup:active value, the answerer MUST Once an offer/answer exchange has been completed, either endpoint MAY
initiate a DTLS handshake by sending a ClientHello message on the send a new offer in order to modify the session. The endpoints can
negotiated media stream, towards the IP address and port of the reuse the existing DTLS association if the key fingerprint values and
offerer. transport parameters indicated by each endpoint are unchanged are
unchanged. Otherwise, following the rules as for the initial offer/
answer exchange, the endpoints can negotiate and create a new DTLS
association and, once created, delete the previous DTLS association,
following the same rules of for the initial offer/answer exchange.
5. Miscellaneous Considerations 5. Miscellaneous Considerations
5.1. Anonymous Calls 5.1. Anonymous Calls
When making anonymous calls, a new self-signed certificate SHOULD be When making anonymous calls, a new self-signed certificate SHOULD be
used for each call and attributes inside the certificate SHALL NOT used for each call and attributes inside the certificate SHALL NOT
contain information that either allows correlation or identification contain information that either allows correlation or identification
of the user making anonymous calls. This is particularly important of the user making anonymous calls. This is particularly important
for the subjectAltName and commonName attributes. for the subjectAltName and commonName attributes.
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When ICE [RFC5245] is being used, the ICE connectivity checks are When ICE [RFC5245] is being used, the ICE connectivity checks are
performed before the DTLS handshake begins. Note that if aggressive performed before the DTLS handshake begins. Note that if aggressive
nomination mode is used, multiple candidate pairs may be marked valid nomination mode is used, multiple candidate pairs may be marked valid
before ICE finally converges on a single candidate pair. UAs MUST before ICE finally converges on a single candidate pair. UAs MUST
treat all ICE candidate pairs associated with a single component as treat all ICE candidate pairs associated with a single component as
part of the same DTLS association. Thus, there will be only one DTLS part of the same DTLS association. Thus, there will be only one DTLS
handshake even if there are multiple valid candidate pairs. Note handshake even if there are multiple valid candidate pairs. Note
that this may mean adjusting the endpoint IP addresses if the that this may mean adjusting the endpoint IP addresses if the
selected candidate pair shifts, just as if the DTLS packets were an selected candidate pair shifts, just as if the DTLS packets were an
ordinary media stream. ordinary media stream. In case of an ICE restart, the DTLS handshake
procedure is repeated and a new DTLS association is created. Once
the DTLS handshake is completed ,and the new DTLS association has
been created, the previous DTLS association is deleted.
5.2.2. STUN Interaction 5.2.2. STUN Interaction
The UA SHALL send the STUN packets [RFC5389] directly over UDP, not The UA SHALL send the STUN packets [RFC5389] directly over UDP, not
over DTLS. over DTLS.
The UA MUST demultiplex packets arriving on the IP address and port The UA MUST demultiplex packets arriving on the IP address and port
associated with the DTLS association, e.g. as follows: associated with the DTLS association, e.g. as follows:
o If the value of the first byte of the packet is 0 or 1, then the o If the value of the first byte of the packet is 0 or 1, then the
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If a user requires fax to be transported securely using UDPTL over If a user requires fax to be transported securely using UDPTL over
DTLS, and if the remote user does not support UDPTL over DTLS, then a DTLS, and if the remote user does not support UDPTL over DTLS, then a
fax media stream cannot be established. fax media stream cannot be established.
If a user prefers fax to be transported securely using UDPTL over If a user prefers fax to be transported securely using UDPTL over
DTLS, but is willing to transport the fax insecurely in case the DTLS, but is willing to transport the fax insecurely in case the
remote user does not support UDPTL over DTLS, then the SDP Capability remote user does not support UDPTL over DTLS, then the SDP Capability
Negotiation mechanism [RFC5939] can be used to offer both UDPTL over Negotiation mechanism [RFC5939] can be used to offer both UDPTL over
DTLS and UDPTL over UDP. Alternatively, if the remote user rejects DTLS and UDPTL over UDP. Alternatively, if the remote user rejects
an offer for UDPTL over DTLS, a new offer for a UDPTL over UDP media an SDP offer for UDPTL over DTLS, a new SDP offer for a UDPTL over
stream can be sent. UDP media stream can be sent.
6. Security Considerations 6. Security Considerations
Fax may be used to transmit a wide range of sensitive data, including Fax may be used to transmit a wide range of sensitive data, including
personal, corporate, and governmental information. It is therefore personal, corporate, and governmental information. It is therefore
critical to be able to protect against threats to the confidentiality critical to be able to protect against threats to the confidentiality
and integrity of the transmitted data. and integrity of the transmitted data.
The mechanism in this document provides integrity and confidentiality The mechanism in this document provides integrity and confidentiality
protection for fax by specifying fax transport using UDPTL over DTLS protection for fax by specifying fax transport using UDPTL over DTLS
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plus an active attack on the media plane can allow an attacker to plus an active attack on the media plane can allow an attacker to
attack the connection (R-SIG-MEDIA in the notation of [RFC5479]). attack the connection (R-SIG-MEDIA in the notation of [RFC5479]).
7. IANA Considerations 7. IANA Considerations
This document updates the "Session Description Protocol (SDP) This document updates the "Session Description Protocol (SDP)
Parameters" registry as specified in Section 8.2.2 of [RFC4566]. Parameters" registry as specified in Section 8.2.2 of [RFC4566].
Specifically, it adds the values in Table 1 to the table for the SDP Specifically, it adds the values in Table 1 to the table for the SDP
"proto" field registry. "proto" field registry.
+-------+-----------------+------------+ +-------+---------------+------------+
| Type | SDP Name | Reference | | Type | SDP Name | Reference |
+-------+-----------------+------------+ +-------+---------------+------------+
| proto | "UDP/TLS/UDPTL" | [RFC-XXXX] | | proto | UDP/TLS/UDPTL | [RFC-XXXX] |
+-------+-----------------+------------+ +-------+---------------+------------+
Table 1: SDP "proto" field values Table 1: SDP "proto" field values
[RFC EDITOR NOTE: Please replace RFC-XXXX with the RFC number of this [RFC EDITOR NOTE: Please replace RFC-XXXX with the RFC number of this
document.] document.]
8. Acknowledgments 8. Acknowledgments
Special thanks to Peter Dawes, who provided comments on the initial Special thanks to Peter Dawes, who provided comments on the initial
version of the draft, and to Paul E. Jones, James Rafferty, Albrecht version of the draft, and to Paul E. Jones, James Rafferty, Albrecht
Schwarz, Oscar Ohlsson, David Hanes, Adam Gensler, Ari Keranen and Schwarz, Oscar Ohlsson, David Hanes, Adam Gensler, Ari Keranen and
Flemming Andreasen who provided valuable feedback and input on the Flemming Andreasen who provided valuable feedback and input on the
MMUSIC mailing list. MMUSIC mailing list.
9. Change Log 9. Change Log
[RFC EDITOR NOTE: Please remove this section when publishing] [RFC EDITOR NOTE: Please remove this section when publishing]
Changes from draft-ietf-mmusic-udptl-dtls-05
o Changes based on comments by Flemming Andreasen
o - SDP Offer/Answer sections structured according to RFC 3264.
o - Clarified that ICE considerations also apply to ICE restart.
o - Editorial changes.
Changes from draft-ietf-mmusic-udptl-dtls-04 Changes from draft-ietf-mmusic-udptl-dtls-04
o Changes based on comments by Flemming Andreasen o Changes based on comments by Flemming Andreasen
o - Addition of SDP Offer/Answer procedure section. o - Addition of SDP Offer/Answer procedure section.
o - Removal of non-ICE NAT traversal procedures. o - Removal of non-ICE NAT traversal procedures.
o - Addition of guidance regarding compatibility with UDPTL over o - Addition of guidance regarding compatibility with UDPTL over
UDP. UDP.
o - Editorial corrections. o - Editorial corrections.
o Minor editorial corrections o Minor editorial corrections
o -Spelling of Ari's family name. o -Spelling of Ari's family name.
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A.1. General A.1. General
Prior to establishing the session, both Alice and Bob generate self- Prior to establishing the session, both Alice and Bob generate self-
signed certificates which are used for a single session or, more signed certificates which are used for a single session or, more
likely, reused for multiple sessions. likely, reused for multiple sessions.
The SIP signaling from Alice to her proxy is transported over TLS to The SIP signaling from Alice to her proxy is transported over TLS to
ensure an integrity protected channel between Alice and her identity ensure an integrity protected channel between Alice and her identity
service. Alice's identity service asserts identity of Alice and service. Alice's identity service asserts identity of Alice and
protects the SIP message, e.g. using SIP Identity. Transport between protects the SIP message, e.g. using SIP Identity. Transport between
proxies should also be protected somehow. proxies should also be protected, e.g. by use of TLS.
Only one element is shown for Alice's and Bob's proxies for the In order to simplify the flow, only one element is shown for Alice's
purposes of simplification. and Bob's proxies.
For the sake of brevity and simplicity, only the mandatory SDP T.38 For the sake of brevity and simplicity, only the mandatory SDP T.38
attributes are shown. attributes are shown.
A.2. Basic Message Flow A.2. Basic Message Flow
Figure 3 shows an example message flow of session establishment for Figure 3 shows an example message flow of session establishment for
T.38 fax securely transported using UDPTL over DTLS. T.38 fax securely transported using UDPTL over DTLS.
In this example flow, Alice acts as the passive endpoint of the DTLS In this example flow, Alice acts as the passive endpoint of the DTLS
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Figure 3: Basic message flow Figure 3: Basic message flow
Message (1): Message (1):
Figure 4 shows the initial INVITE request sent by Alice to Alice's Figure 4 shows the initial INVITE request sent by Alice to Alice's
proxy. The initial INVITE request contains an SDP offer. proxy. The initial INVITE request contains an SDP offer.
The "m=" line in the SDP offer indicates T.38 fax using UDPTL over The "m=" line in the SDP offer indicates T.38 fax using UDPTL over
DTLS. DTLS.
The SDP setup:actpass attribute in the SDP offer indicates that The SDP "setup" attribute with a value of "actpass" in the SDP
Alice has requested to be either the active or passive endpoint. offer indicates that Alice has requested to be either the active
or passive endpoint.
The SDP fingerprint attribute in the SDP offer contains the The SDP "fingerprint" attribute in the SDP offer contains the
certificate fingerprint computed from Alice's self-signed certificate fingerprint computed from Alice's self-signed
certificate. certificate.
INVITE sip:bob@example.com SIP/2.0 INVITE sip:bob@example.com SIP/2.0
To: <sip:bob@example.com> To: <sip:bob@example.com>
From: "Alice"<sip:alice@example.com>;tag=843c7b0b From: "Alice"<sip:alice@example.com>;tag=843c7b0b
Via: SIP/2.0/TLS ua1.example.com;branch=z9hG4bK-0e53sadfkasldkfj Via: SIP/2.0/TLS ua1.example.com;branch=z9hG4bK-0e53sadfkasldkfj
Contact: <sip:alice@ua1.example.com> Contact: <sip:alice@ua1.example.com>
Call-ID: 6076913b1c39c212@REVMTEpG Call-ID: 6076913b1c39c212@REVMTEpG
CSeq: 1 INVITE CSeq: 1 INVITE
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Certificate, ClientKeyExchange, CertificateVerify, Certificate, ClientKeyExchange, CertificateVerify,
ChangeCipherSpec, Finished). ChangeCipherSpec, Finished).
When Bob receives the certificate of Alice via DTLS, Bob checks When Bob receives the certificate of Alice via DTLS, Bob checks
whether the certificate fingerprint calculated from Alice's whether the certificate fingerprint calculated from Alice's
certificate received via DTLS matches the certificate fingerprint certificate received via DTLS matches the certificate fingerprint
received in the a=fingerprint SDP attribute of Figure 5. In this received in the a=fingerprint SDP attribute of Figure 5. In this
message flow, the check is successful and thus session setup message flow, the check is successful and thus session setup
continues. continues.
Note that, unlike in this example, it is not necessary to wait for
the DTLS handshake to finish before the SDP answer is sent. If
Bob has sent the SIP 200 (OK) response and later detects that the
certificate fingerprints do not match, he will terminate the
session.
Message (5): Message (5):
Figure 6 shows a SIP 200 (OK) response to the initial SIP INVITE Figure 6 shows a SIP 200 (OK) response to the initial SIP INVITE
request, sent by Bob to Bob's proxy. The SIP 200 (OK) response request, sent by Bob to Bob's proxy. The SIP 200 (OK) response
contains an SDP answer. contains an SDP answer.
The "m=" line in the SDP answer indicates T.38 fax using UDPTL The "m=" line in the SDP answer indicates T.38 fax using UDPTL
over DTLS. over DTLS.
The SDP setup:active attribute in the SDP answer indicates that The SDP "setup" attribute with a value of "active" in the SDP
Bob has requested to be the active endpoint. answer indicates that Bob has requested to be the active endpoint.
The SDP fingerprint attribute in the SDP answer contains the The SDP "fingerprint" attribute in the SDP answer contains the
certificate fingerprint computed from Bob's self-signed certificate fingerprint computed from Bob's self-signed
certificate. certificate.
SIP/2.0 200 OK SIP/2.0 200 OK
To: <sip:bob@example.com>;tag=6418913922105372816 To: <sip:bob@example.com>;tag=6418913922105372816
From: "Alice" <sip:alice@example.com>;tag=843c7b0b From: "Alice" <sip:alice@example.com>;tag=843c7b0b
Via: SIP/2.0/TLS proxy.example.com:5061;branch=z9hG4bK-0e53sadfkasldk Via: SIP/2.0/TLS proxy.example.com:5061;branch=z9hG4bK-0e53sadfkasldk
Via: SIP/2.0/TLS ua1.example.com;branch=z9hG4bK-0e53sadfkasldkfj Via: SIP/2.0/TLS ua1.example.com;branch=z9hG4bK-0e53sadfkasldkfj
Record-Route: <sip:proxy.example.com;lr> Record-Route: <sip:proxy.example.com;lr>
Call-ID: 6076913b1c39c212@REVMTEpG Call-ID: 6076913b1c39c212@REVMTEpG
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Figure 6: Message (5) Figure 6: Message (5)
Message (6): Message (6):
Figure 7 shows a SIP 200 (OK) response to the initial SIP INVITE Figure 7 shows a SIP 200 (OK) response to the initial SIP INVITE
request, sent by Alice's proxy to Alice. Alice checks if the request, sent by Alice's proxy to Alice. Alice checks if the
certificate fingerprint calculated from the Bob's certificate certificate fingerprint calculated from the Bob's certificate
received via DTLS is the same as the certificate fingerprint received via DTLS is the same as the certificate fingerprint
received in the a=fingerprint SDP attribute of Figure 7. In this received in the a=fingerprint SDP attribute of Figure 7. In this
message flow, the check is successful and thus session setup message flow, the check is successful and thus the session setup
continues. continues.
SIP/2.0 200 OK SIP/2.0 200 OK
To: <sip:bob@example.com>;tag=6418913922105372816 To: <sip:bob@example.com>;tag=6418913922105372816
From: "Alice" <sip:alice@example.com>;tag=843c7b0b From: "Alice" <sip:alice@example.com>;tag=843c7b0b
Via: SIP/2.0/TLS ua1.example.com;branch=z9hG4bK-0e53sadfkasldkfj Via: SIP/2.0/TLS ua1.example.com;branch=z9hG4bK-0e53sadfkasldkfj
Record-Route: <sip:proxy.example.com;lr> Record-Route: <sip:proxy.example.com;lr>
Call-ID: 6076913b1c39c212@REVMTEpG Call-ID: 6076913b1c39c212@REVMTEpG
CSeq: 1 INVITE CSeq: 1 INVITE
Contact: <sip:bob@ua2.example.com> Contact: <sip:bob@ua2.example.com>
skipping to change at page 20, line 47 skipping to change at page 20, line 47
Message (2): Message (2):
Alice sends SIP re-INVITE request. The SDP offer included in the Alice sends SIP re-INVITE request. The SDP offer included in the
SIP re-INVITE request is shown in Figure 9. SIP re-INVITE request is shown in Figure 9.
The first "m=" line in the SDP offer indicates audio media stream The first "m=" line in the SDP offer indicates audio media stream
being removed. The second "m=" line in the SDP offer indicates being removed. The second "m=" line in the SDP offer indicates
T.38 fax using UDPTL over DTLS being added. T.38 fax using UDPTL over DTLS being added.
The SDP setup:actpass attribute in the SDP offer indicates that The SDP "setup" attribute with a value of "actpass" in the SDP
Alice has requested to be either the active or passive endpoint. offer indicates that Alice has requested to be either the active
or passive endpoint.
The SDP fingerprint attribute in the SDP offer contains the The SDP "fingerprint" attribute in the SDP offer contains the
certificate fingerprint computed from Alice's self-signed certificate fingerprint computed from Alice's self-signed
certificate. certificate.
v=0 v=0
o=- 2465353433 3524244442 IN IP4 ua1.example.com o=- 2465353433 3524244442 IN IP4 ua1.example.com
s=- s=-
c=IN IP4 ua1.example.com c=IN IP4 ua1.example.com
t=0 0 t=0 0
m=audio 0 UDP/TLS/RTP/SAVP 0 m=audio 0 UDP/TLS/RTP/SAVP 0
m=image 46056 UDP/TLS/UDPTL t38 m=image 46056 UDP/TLS/UDPTL t38
skipping to change at page 21, line 38 skipping to change at page 21, line 38
Alice and Bob exchange further messages of DTLS handshake Alice and Bob exchange further messages of DTLS handshake
(HelloVerifyRequest, ClientHello, ServerHello, Certificate, (HelloVerifyRequest, ClientHello, ServerHello, Certificate,
ServerKeyExchange, CertificateRequest, ServerHelloDone, ServerKeyExchange, CertificateRequest, ServerHelloDone,
Certificate, ClientKeyExchange, CertificateVerify, Certificate, ClientKeyExchange, CertificateVerify,
ChangeCipherSpec, Finished). ChangeCipherSpec, Finished).
When Bob receives the certificate of Alice via DTLS, Bob checks When Bob receives the certificate of Alice via DTLS, Bob checks
whether the certificate fingerprint calculated from Alice's whether the certificate fingerprint calculated from Alice's
certificate received via DTLS matches the certificate fingerprint certificate received via DTLS matches the certificate fingerprint
received in the a=fingerprint SDP attribute of Figure 9. In this received in the SDP "fingerprint" attribute of Figure 9. In this
message flow, the check is successful and thus session setup message flow, the check is successful and thus session setup
continues. continues.
Message (5): Message (5):
Bob sends a SIP 200 (OK) response to the SIP re-INVITE request. Bob sends a SIP 200 (OK) response to the SIP re-INVITE request.
The SIP 200 (OK) response contains an SDP answer shown in The SIP 200 (OK) response contains an SDP answer shown in
Figure 10. Figure 10.
The first "m=" line in the SDP offer indicates audio media stream The first "m=" line in the SDP offer indicates audio media stream
being removed. The second "m=" line in the SDP answer indicates being removed. The second "m=" line in the SDP answer indicates
T.38 fax using UDPTL over DTLS being added. T.38 fax using UDPTL over DTLS being added.
The SDP setup:active attribute in the SDP answer indicates that The SDP "setup" attribute with a value of "active" in the SDP
Bob has requested to be the active endpoint. answer indicates that Bob has requested to be the active endpoint.
The SDP fingerprint attribute in the SDP answer contains the The SDP "fingerprint" attribute in the SDP answer contains the
certificate fingerprint computed from Bob's self-signed certificate fingerprint computed from Bob's self-signed
certificate. certificate.
v=0 v=0
o=- 4423478999 5424222292 IN IP4 ua2.example.com o=- 4423478999 5424222292 IN IP4 ua2.example.com
s=- s=-
c=IN IP4 ua2.example.com c=IN IP4 ua2.example.com
t=0 0 t=0 0
m=audio 0 UDP/TLS/RTP/SAVP 0 m=audio 0 UDP/TLS/RTP/SAVP 0
m=image 32000 UDP/TLS/UDPTL t38 m=image 32000 UDP/TLS/UDPTL t38
 End of changes. 34 change blocks. 
67 lines changed or deleted 100 lines changed or added

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