draft-ietf-mmusic-udptl-dtls-00.txt   draft-ietf-mmusic-udptl-dtls-01.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: April 21, 2014 G. Salgueiro Expires: May 25, 2014 G. Salgueiro
Cisco Cisco
October 18, 2013 November 21, 2013
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-00 draft-ietf-mmusic-udptl-dtls-01
Abstract Abstract
This document specifies how the UDP Transport Layer (UDPTL) protocol This document specifies how the UDP Transport Layer (UDPTL) protocol
can be transported over the Datagram Transport Layer Security (DTLS) can be transported over the Datagram Transport Layer Security (DTLS)
protocol, how the usage of UDPTL over DTLS is indicated in the protocol, how the usage of UDPTL over DTLS is indicated in the
Session Description Protocol (SDP), and how UDPTL over DTLS is Session Description Protocol (SDP), and how UDPTL over DTLS is
negotiated in a session established using the Session Initiation negotiated in a session established using the Session Initiation
Protocol (SIP). Protocol (SIP).
skipping to change at page 1, line 38 skipping to change at page 1, line 38
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 April 21, 2014. This Internet-Draft will expire on May 25, 2014.
Copyright Notice Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the Copyright (c) 2013 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
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
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 . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Secure Channel Establishment . . . . . . . . . . . . . . 5 3.1. Secure Channel Establishment . . . . . . . . . . . . . . 5
3.2. Secure Channel Usage . . . . . . . . . . . . . . . . . . 5 3.2. Secure Channel Usage . . . . . . . . . . . . . . . . . . 5
4. Miscellaneous Considerations . . . . . . . . . . . . . . . . 5 4. Miscellaneous Considerations . . . . . . . . . . . . . . . . 6
4.1. Anonymous Calls . . . . . . . . . . . . . . . . . . . . . 6 4.1. Anonymous Calls . . . . . . . . . . . . . . . . . . . . . 6
4.2. Middlebox Interaction . . . . . . . . . . . . . . . . . . 6 4.2. Middlebox Interaction . . . . . . . . . . . . . . . . . . 6
4.3. Rekeying . . . . . . . . . . . . . . . . . . . . . . . . 6 4.3. Rekeying . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6 5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7
8. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 7 8. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 7
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
9.1. Normative References . . . . . . . . . . . . . . . . . . 8 9.1. Normative References . . . . . . . . . . . . . . . . . . 8
9.2. Informative References . . . . . . . . . . . . . . . . . 9 9.2. Informative References . . . . . . . . . . . . . . . . . 10
Appendix A. Example . . . . . . . . . . . . . . . . . . . . . . 9 Appendix A. Example . . . . . . . . . . . . . . . . . . . . . . 10
A.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 9 A.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 10
A.2. Basic Message Flow with Identity . . . . . . . . . . . . 10 A.2. Basic Message Flow with Identity . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15 A.3. Message Flow Of T.38 Fax Replacing Audio Media Stream in
An Existing Audio-Only Session . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction 1. Introduction
While telephony encryption devices have been traditionally used for While telephony encryption devices have been traditionally used for
highly sensitive documents, secure fax on the Public Switched highly sensitive documents, secure fax on the Public Switched
Telephone Network (PSTN) was not as widely considered or prioritized Telephone Network (PSTN) was not as widely considered or prioritized
because of the challenges involved with physical access to telephony because of the challenges involved with physical access to telephony
equipment. As real-time communications transition to IP networks, equipment. As real-time communications transition to IP networks,
where information might potentially be intercepted or spoofed, an where information might potentially be intercepted or spoofed, an
appropriate level of security for fax that offers integrity and appropriate level of security for fax that offers integrity and
skipping to change at page 5, line 24 skipping to change at page 5, line 21
line) specified for UDPTL over the UDP, each SDP media description line) specified for UDPTL over the UDP, each SDP media description
for UDPTL over DTLS over the UDP will also contain several SDP for UDPTL over DTLS over the UDP will also contain several SDP
attributes, as specified in [RFC4145] and [RFC4572]. attributes, as specified in [RFC4145] and [RFC4572].
The SDP offer and SDP answer MUST conform to the following The SDP offer and SDP answer MUST conform to the following
requirements: requirements:
o The endpoint MUST set the "proto" field of the "m=" line to the o The endpoint MUST set the "proto" field of the "m=" line to the
token specified in Table 3. token specified in Table 3.
o The endpoint MUST use the SDP setup attribute [RFC4145]. The o The endpoint MUST use the SDP setup attribute [RFC4145]. The
offerer MUST assign the SDP setup attribute with setup:actpass offerer SHOULD assign the SDP setup attribute with a setup:actpass
value, and MUST be prepared to receive a DTLS client_hello message value, and MAY assign the SDP setup attribute with a setup:active
before it receives the SDP answer. The answerer MUST assign the value or setup:passive value. The offerer MUST NOT assign the SDP
SDP setup attribute with either setup:active value or setup attribute with a setup:holdconn value. If the offerer
setup:passive value. The answerer SHOULD assign the SDP setup assigns the SDP setup attribute with a setup:actpass value or
attribute with the setup:active value. Whichever party is active setup:passive value, it MUST be prepared to receive a DTLS
MUST initiate a DTLS handshake by sending a ClientHello over each client_hello message before it receives the SDP answer. If the
flow (host/port quartet). answerer accepts the media stream, then it MUST assign the 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. Whichever party is active, it MUST initiate a DTLS
handshake by sending a ClientHello over each flow (host/port
quartet).
o The endpoint MUST use the SDP certificate fingerprint attribute o The endpoint MUST use the SDP certificate fingerprint attribute
[RFC4572]. [RFC4572].
o The certificate presented during the DTLS handshake MUST match the o The certificate presented during the DTLS handshake MUST match the
fingerprint exchanged via the signaling path in the SDP. fingerprint exchanged via the signaling path in the SDP.
o If the fingerprint does not match the hashed certificate, then the o If the fingerprint does not match the hashed certificate, then the
endpoint MUST tear down the media session immediately. Note that endpoint MUST tear down the media session immediately. Note that
it is permissible to wait until the other side's fingerprint has it is permissible to wait until the other side's fingerprint has
been received before establishing the connection; however, this been received before establishing the connection; however, this
may have undesirable latency effects. may have undesirable latency effects.
o The endpoint MUST NOT use the SDP connection attribute [RFC4145].
Editor's note: FFS if connection attribute defined in RFC4145 is
needed.
3.2. Secure Channel Usage 3.2. Secure Channel Usage
DTLS is used as specified in [RFC6347]. Once the DTLS handshake is DTLS is used as specified in [RFC6347]. Once the DTLS handshake is
completed, the UDPTL packets SHALL be transported in DTLS record completed, the UDPTL packets SHALL be transported in DTLS record
layer "application_data" packets. layer "application_data" packets.
4. Miscellaneous Considerations 4. Miscellaneous Considerations
4.1. Anonymous Calls 4.1. 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 the content of the subjectAltName attribute used for each call and the content of the subjectAltName attribute
inside the certificate MUST NOT contain information that either inside the certificate MUST NOT contain information that either
allows correlation or identification of the user making anonymous allows correlation or identification of the user making anonymous
calls. calls.
4.2. Middlebox Interaction 4.2. Middlebox Interaction
skipping to change at page 7, line 47 skipping to change at page 7, line 51
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 and version of the draft, and to Paul E. Jones, James Rafferty and
Albrecht Schwarz who provided valuable feedback and input on the Albrecht Schwarz who provided valuable feedback and input on the
MMUSIC mailing list. MMUSIC mailing list.
8. Change Log 8. 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-00
o SDP offerer is allowed to assign an a=setup:active or
a=setup:passive value, in addition to the recommended
a=setup:actpass (http://www.ietf.org/mail-archive/web/mmusic/
current/msg12331.html).
o The example for secure fax replacing audio stream in audio-only
session added (http://www.ietf.org/mail-archive/web/mmusic/current
/msg12428.html).
o Editor's note on the connection attribute resolved by prohibiting
usage of the SDP connection attribute (http://www.ietf.org/mail-
archive/web/mmusic/current/msg12772.html).
o Editorial corrections.
Changes from draft-holmberg-mmusic-udptl-dtls-02 Changes from draft-holmberg-mmusic-udptl-dtls-02
o Milestone adopted - draft-ietf-mmusic version of the draft o Milestone adopted - draft-ietf-mmusic version of the draft
submitted. submitted.
Changes from draft-holmberg-mmusic-udptl-dtls-01 Changes from draft-holmberg-mmusic-udptl-dtls-01
o Gonzalo Salgueiro added as co-author. o Gonzalo Salgueiro added as co-author.
o PSTN comparison text and Introduction text modified. o PSTN comparison text and Introduction text modified.
skipping to change at page 10, line 44 skipping to change at page 11, line 16
|<----------------------------------------------->| |<----------------------------------------------->|
| | | | | |
Figure 1: Basic message flow with Identity Figure 1: Basic message flow with Identity
Message (1): Message (1):
Figure 2 shows the initial INVITE request sent by Alice to Alice's Figure 2 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:actpass attribute in the SDP offer indicates that
Alice has requested to be either the active or passive endpoint. Alice has requested to be either the active or passive endpoint.
The SDP fingerprint attribute in the SDP Offer indicates the The SDP fingerprint attribute in the SDP offer indicates 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
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, UPDATE Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, UPDATE
Max-Forwards: 70 Max-Forwards: 70
Content-Type: application/sdp Content-Type: application/sdp
Content-Length: xxxx Content-Length: xxxx
Supported: from-change Supported: from-change
v=0 v=0
o=- 1181923068 1181923196 IN IP4 ua1.example.com o=- 1181923068 1181923196 IN IP4 ua1.example.com
s=example1 s=-
c=IN IP4 ua1.example.com c=IN IP4 ua1.example.com
t=0 0 t=0 0
m=image 6056 UDP/TLS/UDPTL t38 m=image 6056 UDP/TLS/UDPTL t38
a=setup:actpass a=setup:actpass
a=fingerprint: SHA-1 \ a=fingerprint: SHA-1 \
4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB 4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
a=T38FaxRateManagement:transferredTCF a=T38FaxRateManagement:transferredTCF
Figure 2: Message (1) Figure 2: Message (1)
skipping to change at page 12, line 26 skipping to change at page 12, line 42
Identity: CyI4+nAkHrH3ntmaxgr01TMxTmtjP7MASwliNRdupRI1vpkXRvZXx1ja9k Identity: CyI4+nAkHrH3ntmaxgr01TMxTmtjP7MASwliNRdupRI1vpkXRvZXx1ja9k
3W+v1PDsy32MaqZi0M5WfEkXxbgTnPYW0jIoK8HMyY1VT7egt0kk4XrKFC 3W+v1PDsy32MaqZi0M5WfEkXxbgTnPYW0jIoK8HMyY1VT7egt0kk4XrKFC
HYWGCl0nB2sNsM9CG4hq+YJZTMaSROoMUBhikVIjnQ8ykeD6UXNOyfI= HYWGCl0nB2sNsM9CG4hq+YJZTMaSROoMUBhikVIjnQ8ykeD6UXNOyfI=
Identity-Info: https://example.com/cert Identity-Info: https://example.com/cert
Content-Type: application/sdp Content-Type: application/sdp
Content-Length: xxxx Content-Length: xxxx
Supported: from-change Supported: from-change
v=0 v=0
o=- 1181923068 1181923196 IN IP4 ua1.example.com o=- 1181923068 1181923196 IN IP4 ua1.example.com
s=example1 s=-
c=IN IP4 ua1.example.com c=IN IP4 ua1.example.com
t=0 0 t=0 0
m=image 6056 UDP/TLS/UDPTL t38 m=image 6056 UDP/TLS/UDPTL t38
a=setup:actpass a=setup:actpass
a=fingerprint: SHA-1 \ a=fingerprint: SHA-1 \
4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB 4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
a=T38FaxRateManagement:transferredTCF a=T38FaxRateManagement:transferredTCF
Figure 3: Message (2) Figure 3: Message (2)
skipping to change at page 13, line 11 skipping to change at page 13, line 31
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 the Alice's whether the certificate fingerprint calculated from the 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 3. In this received in the a=fingerprint SDP attribute of Figure 3. 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):
Figure 4 shows a 200 (OK) response to the initial SIP INVITE Figure 4 shows a SIP 200 (OK) response to the initial SIP INVITE
request, sent by Bob to Bob's proxy. The 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:active attribute in the SDP answer indicates that
Bob has requested to be the active endpoint. Bob has requested to be the active endpoint.
The SDP fingerprint attribute in the SDP Answer indicates the The SDP fingerprint attribute in the SDP answer indicates 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
CSeq: 1 INVITE CSeq: 1 INVITE
Contact: <sip:bob@ua2.example.com> Contact: <sip:bob@ua2.example.com>
Content-Type: application/sdp Content-Type: application/sdp
Content-Length: xxxx Content-Length: xxxx
Supported: from-change Supported: from-change
v=0 v=0
o=- 6418913922105372816 2105372818 IN IP4 ua2.example.com o=- 8965454521 2105372818 IN IP4 ua2.example.com
s=example2 s=-
c=IN IP4 ua2.example.com c=IN IP4 ua2.example.com
t=0 0 t=0 0
m=image 12000 UDP/TLS/UDPTL t38 m=image 12000 UDP/TLS/UDPTL t38
a=setup:active a=setup:active
a=fingerprint: SHA-1 \ a=fingerprint: SHA-1 \
FF:FF:FF:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB FF:FF:FF:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
a=T38FaxRateManagement:transferredTCF a=T38FaxRateManagement:transferredTCF
Figure 4: Message (6) Figure 4: Message (5)
Message (6): Message (6):
Figure 5 shows a 200 (OK) response to the initial SIP INVITE Figure 5 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 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.
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>
Content-Type: application/sdp Content-Type: application/sdp
Content-Length: xxxx Content-Length: xxxx
Supported: from-change Supported: from-change
v=0 v=0
o=- 6418913922105372816 2105372818 IN IP4 ua2.example.com o=- 8965454521 2105372818 IN IP4 ua2.example.com
s=example2 s=-
c=IN IP4 ua2.example.com c=IN IP4 ua2.example.com
t=0 0 t=0 0
m=image 12000 UDP/TLS/UDPTL t38 m=image 12000 UDP/TLS/UDPTL t38
a=setup:active a=setup:active
a=fingerprint: SHA-1 \ a=fingerprint: SHA-1 \
FF:FF:FF:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB FF:FF:FF:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
a=T38FaxRateManagement:transferredTCF a=T38FaxRateManagement:transferredTCF
Figure 5: Message (7) Figure 5: Message (6)
Message (7): Message (7):
Alice sends the SIP ACK request to Bob. Alice sends the SIP ACK request to Bob.
Message (8): Message (8):
At this point, Bob and Alice can exchange T.38 fax securely At this point, Bob and Alice can exchange T.38 fax securely
transported using UDPTL over DTLS. transported using UDPTL over DTLS.
A.3. Message Flow Of T.38 Fax Replacing Audio Media Stream in An
Existing Audio-Only Session
Figure 6 focuses on T.38 fax securely transported using UDPTL over
DTLS replacing audio media stream in an existing audio-only session.
In this example flow, Alice acts as the passive endpoint of DTLS
association and Bob acts as the active endpoint of DTLS association.
Alice Proxies Bob
| | |
| (1) Audio-only session initiation |
|<-----------------------+----------------------->|
| | |
| (2) SIP re-INVITE | |
|------------------------------------------------>|
| | (3) DTLS ClientHello |
|<------------------------------------------------|
| (4) remaining messages of DTLS handshake |
|<----------------------------------------------->|
| | |
| | |
| | (5) SIP 200 OK |
|<------------------------------------------------|
| (6) SIP ACK | |
|------------------------------------------------>|
| (7) T.38 message using UDPTL over DTLS |
|<----------------------------------------------->|
| | |
Figure 6: Message Flow Of T.38 Fax Replacing Audio Media Stream in An
Existing Audio-Only Session
Message (1):
Session establishment of audio-only session. The proxies decide
not to record-route.
Message (2):
Alice sends SIP re-INVITE request. SDP offer included in the SIP
re-INVITE request shown in Figure 7.
The first "m=" line in the SDP offer indicates audio media stream
being removed. The second "m=" line in the SDP offer indicates
T.38 fax using UDPTL over DTLS being added.
The SDP setup:actpass attribute in the SDP offer indicates that
Alice has requested to be either the active or passive endpoint.
The SDP fingerprint attribute in the SDP offer indicates the
certificate fingerprint computed from Alice's self-signed
certificate.
v=0
o=- 2465353433 3524244442 IN IP4 ua1.example.com
s=-
c=IN IP4 ua1.example.com
t=0 0
m=audio 0 UDP/TLS/RTP/SAVP 0
m=image 46056 UDP/TLS/UDPTL t38
a=setup:actpass
a=fingerprint: SHA-1 \
4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
a=T38FaxRateManagement:transferredTCF
Figure 7: SDP offer of message (2)
Message (3):
Bob sends a DTLS ClientHello directly to Alice.
Message (4):
Alice and Bob exchange further messages of DTLS handshake
(HelloVerifyRequest, ClientHello, ServerHello, Certificate,
ServerKeyExchange, CertificateRequest, ServerHelloDone,
Certificate, ClientKeyExchange, CertificateVerify,
ChangeCipherSpec, Finished).
When Bob receives Alice's certificate via DTLS, Bob checks whether
the certificate fingerprint calculated from Alice's certificate
received via DTLS matches the certificate fingerprint received in
the a=fingerprint SDP attribute of Figure 7. In this message
flow, the check is successful and thus session setup continues.
Message (5):
Bob sends a SIP 200 (OK) response to the SIP re-INVITE request.
The SIP 200 (OK) response contains an SDP answer shown in Figure
8.
The first "m=" line in the SDP offer indicates audio media stream
being removed. The second "m=" line in the SDP answer indicates
T.38 fax using UDPTL over DTLS being added.
The SDP setup:active attribute in the SDP answer indicates that
Bob has requested to be the active endpoint.
The SDP fingerprint attribute in the SDP answer indicates the
certificate fingerprint computed from Bob's self-signed
certificate.
v=0
o=- 4423478999 5424222292 IN IP4 ua2.example.com
s=-
c=IN IP4 ua2.example.com
t=0 0
m=audio 0 UDP/TLS/RTP/SAVP 0
m=image 32000 UDP/TLS/UDPTL t38
a=setup:active
a=fingerprint: SHA-1 \
FF:FF:FF:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
a=T38FaxRateManagement:transferredTCF
Figure 8: SDP answer of message (5)
Message (6):
Alice sends the SIP ACK request to Bob.
Message (7):
At this point, Bob and Alice can exchange T.38 fax securely
transported using UDPTL over DTLS.
Authors' Addresses Authors' Addresses
Christer Holmberg Christer Holmberg
Ericsson Ericsson
Hirsalantie 11 Hirsalantie 11
Jorvas 02420 Jorvas 02420
Finland Finland
Email: christer.holmberg@ericsson.com Email: christer.holmberg@ericsson.com
 End of changes. 27 change blocks. 
38 lines changed or deleted 185 lines changed or added

This html diff was produced by rfcdiff 1.41. The latest version is available from http://tools.ietf.org/tools/rfcdiff/