draft-ietf-sipping-transc-conf-00.txt   draft-ietf-sipping-transc-conf-01.txt 
SIPPING Working Group G. Camarillo SIPPING Working Group G. Camarillo
Internet-Draft Ericsson Internet-Draft Ericsson
Expires: December 3, 2005 June 1, 2005 Expires: June 2, 2006 November 29, 2005
The Session Initiation Protocol (SIP) Conference Bridge Transcoding The Session Initiation Protocol (SIP) Conference Bridge Transcoding
Model Model
draft-ietf-sipping-transc-conf-00.txt draft-ietf-sipping-transc-conf-01.txt
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2005). Copyright (C) The Internet Society (2005).
Abstract Abstract
This document describes how to invoke transcoding services using the This document describes how to invoke transcoding services using the
conference bridge model. This way of invocation meets the conference bridge model. This way of invocation meets the
requirements for SIP regarding transcoding services invocation to requirements for SIP regarding transcoding services invocation to
support deaf, hard of hearing and speech-impaired individuals. support deaf, hard of hearing and speech-impaired individuals.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Caller's Invocation . . . . . . . . . . . . . . . . . . . . . 4 3. Caller's Invocation . . . . . . . . . . . . . . . . . . . . . 4
3.1 Unsuccessful Session Establishment . . . . . . . . . . . . 6 3.1. Procedures at the User Agent . . . . . . . . . . . . . . . 4
4. Callee's Invocation . . . . . . . . . . . . . . . . . . . . . 6 3.2. Procedures at the Transcoder . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7 3.3. Example . . . . . . . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 3.4. Unsuccessful Session Establishment . . . . . . . . . . . . 7
7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 8 4. Callee's Invocation . . . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 5. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8.1 Normative References . . . . . . . . . . . . . . . . . . . 8 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
8.2 Informational References . . . . . . . . . . . . . . . . . 9 7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 9 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Intellectual Property and Copyright Statements . . . . . . . . 10 8.1. Normative References . . . . . . . . . . . . . . . . . . . 10
8.2. Informational References . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 12
Intellectual Property and Copyright Statements . . . . . . . . . . 13
1. Introduction 1. Introduction
The Framework for Transcoding with SIP [6] describes how two SIP [4] The Framework for Transcoding with SIP [9] describes how two SIP [3]
UAs (User Agents) can discover imcompatibilities that prevent them UAs (User Agents) can discover imcompatibilities that prevent them
from establishing a session (e.g., lack of support for a common codec from establishing a session (e.g., lack of support for a common codec
or for a common media type). When such incompatibilities are found, or for a common media type). When such incompatibilities are found,
the UAs need to invoke transcoding services to successfully establish the UAs need to invoke transcoding services to successfully establish
the session. The transcoding framework introduces two models to the session. The transcoding framework introduces two models to
invoke transcoding services: the 3pcc (third-party call control) invoke transcoding services: the 3pcc (third-party call control)
model [7] and the conference bridge model. This document specifies model [8] and the conference bridge model. This document specifies
the conference bridge model. the conference bridge model.
In the conference bridge model for transcoding invocation, a In the conference bridge model for transcoding invocation, a
transcoding server that provides a particular transcoding service transcoding server that provides a particular transcoding service
(e.g., speech-to-text) behaves as a B2BUA (Back-to-Back User Agent) (e.g., speech-to-text) behaves as a B2BUA (Back-to-Back User Agent)
between both UAs and is identified by a URI. As shown in Figure 1, between both UAs and is identified by a URI. As shown in Figure 1,
both UAs, A and B, exchange signalling and media with the transcoder both UAs, A and B, exchange signalling and media with the transcoder
T. The UAs do not exchange any traffic (signalling or media) directly T. The UAs do not exchange any traffic (signalling or media) directly
between them. between them.
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Section 3 and Section 4 specify how the caller A or the callee B, Section 3 and Section 4 specify how the caller A or the callee B,
respectively, can use the conference bridge model to invoke respectively, can use the conference bridge model to invoke
transcoding services from T. transcoding services from T.
2. Terminology 2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED", In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
described in BCP 14, RFC 2119 [3] and indicate requirement levels for described in BCP 14, RFC 2119 [1] and indicate requirement levels for
compliant implementations. compliant implementations.
3. Caller's Invocation 3. Caller's Invocation
A needs to perform two operations to invoke transcoding services from User agent A needs to perform two operations to invoke transcoding
T for a session between A and B. A needs to establish a session with services from T for a session between user agent A and user agent B.
T and provide T with B's URI so that T can generate an INVITE towards User agent A needs to establish a session with T and provide T with
B. A uses the procedures for Conference Establishment Using Request- user agent B's URI so that T can generate an INVITE towards user
Contained Lists in SIP [9] to provide T with B's URI using the same agent B.
INVITE that establishes the session between A and T.
Figure 2 shows the message flow for the caller's invocation of a 3.1. Procedures at the User Agent
transcoder T. The caller (A) sends an INVITE (1) to the transcoder
(T) to establish the session A-T. Following the procedures in [9], A
adds a body part whose disposition type is recipient-list [8]. This
body part consists of a URI-list that MUST contain a single URI: B's
URI.
If a trancoder receives a URI-list with more than one URI, it SHOULD User agent A uses the procedures for Conference Establishment Using
return a 488 (Max 1 URI allowed in URI-list) response. Request-Contained Lists in SIP [11] to provide T with B's URI using
the same INVITE that establishes the session between A and T. That
is, user agent A adds to the INVITE a body part whose disposition
type is recipient-list [10]. This body part consists of a URI-list
that MUST contain a single URI: user agent B's URI.
3.2. Procedures at the Transcoder
On receiving an INVITE with a URI-list body, the transcoder follows
the procedures in [11] to generate an INVITE request towards the URI
contained in the URI-list body. Note that the transcoder acts as a
B2BUA, not as a proxy.
Additionally, the transcoder MUST generate the From header field of
the outgoing INVITE request using the same value as the From header
field included in the incoming INVITE request, subject to the privacy
requirements (see [5] and [6]) expressed in the incoming INVITE
request. Note that this does not apply to the "tag" parameter.
The session description the transcoder includes in the outgoing
INVITE request depends on the type of transcoding service that
particular transcoder provides. For example, a transcoder resolving
audio codec incompatibilities would generate a session description
listing the audio codecs the transcoder supports.
When the transcoder receives a final response for the outgoing INVITE
requests, it generates a new final response for the incoming INVITE
request. This new final response SHOULD have the same status code as
the one received in the response for the outgoing INVITE request.
If a trancoder receives an INVITE request with a URI-list with more
than one URI, it SHOULD return a 488 (Max 1 URI allowed in URI-list)
response.
3.3. Example
Figure 2 shows the message flow for the caller's invocation of a
transcoder T. The caller A sends an INVITE (1) to the transcoder (T)
to establish the session A-T. Following the procedures in [11], the
caller A adds a body part whose disposition type is recipient-list
[10].
A T B A T B
| | | | | |
|-----(1) INVITE SDP A----->| | |-----(1) INVITE SDP A----->| |
| | | | | |
|<-(2) 183 Session Progress-| | |<-(2) 183 Session Progress-| |
| |-----(3) INVITE SDP TB---->| | |-----(3) INVITE SDP TB---->|
| | | | | |
| |<-----(4) 200 OK SDP B-----| | |<-----(4) 200 OK SDP B-----|
| | | | | |
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|<----(6) 200 OK SDP TA-----| | |<----(6) 200 OK SDP TA-----| |
| | | | | |
|---------(7) ACK---------->| | |---------(7) ACK---------->| |
| | | | | |
| ************************* | ************************* | | ************************* | ************************* |
|** Media **|** Media **| |** Media **|** Media **|
| ************************* | ************************* | | ************************* | ************************* |
| | | | | |
Figure 2: Successful invocation of a transcoder by the caller Figure 2: Successful invocation of a transcoder by the caller
The following example shows an INVITE with two body parts: an SDP The following example shows an INVITE with two body parts: an SDP
[10] session description and a URI-list. [14] session description and a URI-list.
INVITE sip:transcoder@example.com SIP/2.0 INVITE sip:transcoder@example.com SIP/2.0
Via: SIP/2.0/TCP client.chicago.example.com Via: SIP/2.0/TCP client.chicago.example.com
;branch=z9hG4bKhjhs8ass83 ;branch=z9hG4bKhjhs8ass83
Max-Forwards: 70 Max-Forwards: 70
To: Transcoder <sip:transcoder@example.org> To: Transcoder <sip:transcoder@example.org>
From: A <sip:A@chicago.example.com>;tag=32331 From: A <sip:A@chicago.example.com>;tag=32331
Call-ID: d432fa84b4c76e66710 Call-ID: d432fa84b4c76e66710
CSeq: 1 INVITE CSeq: 1 INVITE
Contact: <sip:A@client.chicago.example.com> Contact: <sip:A@client.chicago.example.com>
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER,
SUBSCRIBE, NOTIFY SUBSCRIBE, NOTIFY
Allow-Events: dialog Allow-Events: dialog
Accept: application/sdp, message/sipfrag Accept: application/sdp, message/sipfrag
Require: recipient-list-invite Require: recipient-list-invite
Conten-Type: multipart/mixed;boundary="boundary1" Conten-Type: multipart/mixed;boundary="boundary1"
Content-Length: xxx Content-Length: 556
--boundary1 --boundary1
Content-Type: application/sdp Content-Type: application/sdp
v=0 v=0
o=example 2890844526 2890842807 IN IP4 chicago.example.com o=example 2890844526 2890842807 IN IP4 chicago.example.com
s=- s=-
c=IN IP4 192.0.2.1 c=IN IP4 192.0.2.1
t=0 0 t=0 0
m=audio 20000 RTP/AVP 0 m=audio 20000 RTP/AVP 0
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</resource-lists> </resource-lists>
--boundary1-- --boundary1--
On receiving the INVITE, the transcoder generates a new INVITE On receiving the INVITE, the transcoder generates a new INVITE
towards the callee. The transcoder acts as a B2BUA, not as a proxy. towards the callee. The transcoder acts as a B2BUA, not as a proxy.
Therefore, this new INVITE (3) belongs to a different transaction Therefore, this new INVITE (3) belongs to a different transaction
than the INVITE (1) received by the transcoder. than the INVITE (1) received by the transcoder.
When the transcoder receives a final response (4) from the callee, it When the transcoder receives a final response (4) from the callee, it
generates a new final response (6) for INVITE (1). This new final generates a new final response (6) for INVITE (1). This new final
response (6) SHOULD have the same status code as the one received in response (6) has the same status code as the one received in the
the response from the callee (4). response from the callee (4).
3.1 Unsuccessful Session Establishment 3.4. Unsuccessful Session Establishment
Figure 3 shows a similar message flow as the one in Figure 3. Figure 3 shows a similar message flow as the one in Figure 3.
Nevertheless, this time the callee generates a non-2xx final response Nevertheless, this time the callee generates a non-2xx final response
(4). Consequently, the transcoder generates a non-2xx final response (4). Consequently, the transcoder generates a non-2xx final response
(6) towards the caller as well. (6) towards the caller as well.
A T B A T B
| | | | | |
|-----(1) INVITE SDP A----->| | |-----(1) INVITE SDP A----->| |
| | | | | |
|<-(2) 183 Session Progress-| | |<-(2) 183 Session Progress-| |
| |-----(3) INVITE SDP TB---->| | |-----(3) INVITE SDP TB---->|
| | | | | |
| |<----(4) 404 Not Found-----| | |<----(4) 603 Decline-------|
| | | | | |
| |---------(5) ACK---------->| | |---------(5) ACK---------->|
|<----(6) 404 Not Found-----| | |<----(6) 603 Decline-------| |
| | | | | |
|---------(7) ACK---------->| | |---------(7) ACK---------->| |
| | | | | |
Figure 3: Unsuccessful session establishment Figure 3: Unsuccessful session establishment
The ambiguity in this flow is that, if the provisional response (2) The ambiguity in this flow is that, if the provisional response (2)
gets lost, the caller does not know whether the 404 (Not Found) gets lost, the caller does not know whether the 603 (Decline)
response means that the initial INVITE (1) did not reach the response means that the initial INVITE (1) was rejected by the
transcoder or that the INVITE generated by the transcoder (4) did not transcoder or that the INVITE generated by the transcoder (4) was
reach the callee. To resolve this ambiguity, the callee can either rejected by the callee. The use of the "History-Info" header field
require the use of the reliable provisional responses [5] SIP [12] between the transcoder and the caller resolves the previous
extension or send an OPTIONS request to the transcoder to check ambiguity.
whether it is reachable.
4. Callee's Invocation Callers that do not support the "History-Info" header field can,
alternatively, require the use of the reliable provisional responses
[4] SIP extension. If the caller receives a response reporting a
reachability problem, the caller can also send an OPTIONS request to
the transcoder to check whether or not the transcoder is reachable.
If the transcoder is reachable, the party that could not be reached
was the callee.
If a UA receives an INVITE with an offer that is not acceptable, it Note that this ambiguity problem could also have been resolved by
can redirect it to the transcoder by using a 302 (Moved Temporarily) having transcoders act as a pure conference bridge. The transcoder
response. The Contact header field of the 302 (Moved Temporarily) would respond with a 200 (OK) the INVITE request from the caller and
response contains the URI of the transcoder plus a "?body=" generate an outgoing INVITE request towards the callee. The caller
parameter. This parameter contains a recipient-list body with B's would get information about the result of the latter INVITE request
URI. Note that some escaping (e.g., for Carriage Returns and Line by subscribing to the conference event package [15] at the
Feeds) is needed to encode a recipient-list body in such a parameter. transcoder. Nevertheless, while this flow would have resolved the
Figure 4 shows the message flow for this scenario. ambiguity problem without requiring support for the "History-Info"
header field, it is more complex, requires a higher number on
messages, and introduces higher session setup delays. That is why it
was not chosen to implement transcoding services.
<t> 4. Callee's Invocation
Please view in a fixed-width font such as Courier.
If a UA receives an INVITE with a session description that is not
acceptable, it can redirect it to the transcoder by using a 302
(Moved Temporarily) response. The Contact header field of the 302
(Moved Temporarily) response contains the URI of the transcoder plus
a "?body=" parameter. This parameter contains a recipient-list body
with B's URI. Note that some escaping (e.g., for Carriage Returns
and Line Feeds) is needed to encode a recipient-list body in such a
parameter. Figure 4 shows the message flow for this scenario.
A T B A T B
| | | | | |
|-------------------(1) INVITE SDP A------------------->| |-------------------(1) INVITE SDP A------------------->|
| | | | | |
|<--------------(2) 302 Moved Temporarily---------------| |<--------------(2) 302 Moved Temporarily---------------|
| | | | | |
|-----------------------(3) ACK------------------------>| |-----------------------(3) ACK------------------------>|
| | | | | |
|-----(4) INVITE SDP A----->| | |-----(4) INVITE SDP A----->| |
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| | | | | |
| |---------(8) ACK---------->| | |---------(8) ACK---------->|
|<----(9) 200 OK SDP TA-----| | |<----(9) 200 OK SDP TA-----| |
| | | | | |
|--------(10) ACK---------->| | |--------(10) ACK---------->| |
| | | | | |
| ************************* | ************************* | | ************************* | ************************* |
|** Media **|** Media **| |** Media **|** Media **|
| ************************* | ************************* | | ************************* | ************************* |
Figure 4: \{Callee's invocation of a transcoder Figure 4: Callee's invocation of a transcoder
Note that A does not necessarily need to be the one performing the Note that A does not necessarily need to be the one performing the
recursion on the 302 (Moved Temporarily) response. Any proxy in the recursion on the 302 (Moved Temporarily) response. Any proxy in the
path between A and B may perform such a recursion. path between A and B may perform such a recursion.
5. Security Considerations 5. Security Considerations
TBD. Transcoders implementing this specification behave as a URI-list
service as described in [11]. Therefore, the security considerations
for URI-list services discussed in [10] apply here as well.
Need to mention how consent applies to this work when consent is more In particular, the requirements related to list integrity and
mature. unsolicited requests are important for transcoding services. User
agents SHOULD integrity protect URI-lists using mechanisms such as
S/MIME [7] or TLS [2], which can also provide URI-list
confidentiality if needed. Additionally, transcoders MUST
authenticate and authorize users and MAY provide information about
the identity of the original sender of the request in their outgoing
requests by using the SIP identity mechanism [13].
Need to mention TLS [1] and S/MIME [2]. The requirement in [10] to use opt-in lists (e.g., using the
Framework for Consent-Based Communications in SIP [16]) deserves
special discussion. The type of URI-list service implemented by
transcoders following this specification does not produce
amplification (only one INVITE request is generated by the transcoder
on receiving an INVITE request from a user agent) and does not
involve a translation to a URI that may be otherwise unknown to the
caller (the caller places the callee's URI in the body of its initial
INVITE request). Additionally, the identity of the caller is present
in the INVITE request generated by the transcoder. Therefore, there
is no requirement for transcoders implementing this specification to
use opt-in lists.
6. IANA Considerations 6. IANA Considerations
This document does not contain any IANA actions. This document does not contain any IANA actions.
7. Contributors 7. Contributors
This document is the result of discussions amongst the conferencing This document is the result of discussions amongst the conferencing
design team. The members of this team include Eric Burger, Henning design team. The members of this team include Eric Burger, Henning
Schulzrinne and Arnoud van Wijk. Schulzrinne, and Arnoud van Wijk.
8. References 8. References
8.1 Normative References 8.1. Normative References
[1] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
RFC 2246, January 1999.
[2] Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions
(S/MIME) Version 3.1 Certificate Handling", RFC 3850, July 2004.
[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
[4] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., [2] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
RFC 2246, January 1999.
[3] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002. Session Initiation Protocol", RFC 3261, June 2002.
[5] Rosenberg, J. and H. Schulzrinne, "Reliability of Provisional [4] Rosenberg, J. and H. Schulzrinne, "Reliability of Provisional
Responses in Session Initiation Protocol (SIP)", RFC 3262, Responses in Session Initiation Protocol (SIP)", RFC 3262,
June 2002. June 2002.
[6] Camarillo, G., "Framework for Transcoding with the Session [5] Peterson, J., "A Privacy Mechanism for the Session Initiation
Protocol (SIP)", RFC 3323, November 2002.
[6] Jennings, C., Peterson, J., and M. Watson, "Private Extensions
to the Session Initiation Protocol (SIP) for Asserted Identity
within Trusted Networks", RFC 3325, November 2002.
[7] Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions
(S/MIME) Version 3.1 Certificate Handling", RFC 3850,
July 2004.
[8] Camarillo, G., Burger, E., Schulzrinne, H., and A. van Wijk,
"Transcoding Services Invocation in the Session Initiation
Protocol (SIP) Using Third Party Call Control (3pcc)",
RFC 4117, June 2005.
[9] Camarillo, G., "Framework for Transcoding with the Session
Initiation Protocol", Initiation Protocol",
draft-camarillo-sipping-transc-framework-00 (work in progress), draft-camarillo-sipping-transc-framework-00 (work in progress),
August 2003. August 2003.
[7] Camarillo, G., "Transcoding Services Invocation in the Session [10] Camarillo, G. and A. Roach, "Framework and Security
Initiation Protocol (SIP) Using Third Party Call Control Considerations for Session Initiation Protocol (SIP) Uniform
(3pcc)", draft-ietf-sipping-transc-3pcc-02 (work in progress), Resource Identifier (URI)-List Services",
September 2004. draft-ietf-sipping-uri-services-04 (work in progress),
October 2005.
[8] Camarillo, G. and A. Roach, "Requirements and Framework for
Session Initiation Protocol (SIP)Uniform Resource Identifier
(URI)-List Services", draft-ietf-sipping-uri-services-02 (work
in progress), December 2004.
[9] Camarillo, G. and A. Johnston, "Conference Establishment Using [11] Camarillo, G. and A. Johnston, "Conference Establishment Using
Request-Contained Lists in the Session Initiation Protocol Request-Contained Lists in the Session Initiation Protocol
(SIP)", draft-ietf-sipping-uri-list-conferencing-02 (work in (SIP)", draft-ietf-sipping-uri-list-conferencing-04 (work in
progress), December 2004. progress), October 2005.
8.2 Informational References [12] Barnes, M., "An Extension to the Session Initiation Protocol
for Request History Information",
draft-ietf-sip-history-info-06 (work in progress),
January 2005.
[10] Handley, M., "SDP: Session Description Protocol", [13] Peterson, J. and C. Jennings, "Enhancements for Authenticated
draft-ietf-mmusic-sdp-new-24 (work in progress), February 2005. Identity Management in the Session Initiation Protocol (SIP)",
draft-ietf-sip-identity-06 (work in progress), October 2005.
8.2. Informational References
[14] Handley, M., "SDP: Session Description Protocol",
draft-ietf-mmusic-sdp-new-25 (work in progress), July 2005.
[15] Rosenberg, J., "A Session Initiation Protocol (SIP) Event
Package for Conference State",
draft-ietf-sipping-conference-package-12 (work in progress),
July 2005.
[16] Rosenberg, J., "A Framework for Consent-Based Communications in
the Session Initiation Protocol (SIP)",
draft-ietf-sipping-consent-framework-03 (work in progress),
October 2005.
Author's Address Author's Address
Gonzalo Camarillo Gonzalo Camarillo
Ericsson Ericsson
Hirsalantie 11 Hirsalantie 11
Jorvas 02420 Jorvas 02420
Finland Finland
Email: Gonzalo.Camarillo@ericsson.com Email: Gonzalo.Camarillo@ericsson.com
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