draft-ietf-mmusic-sdp-cs-01.txt   draft-ietf-mmusic-sdp-cs-02.txt 
MMUSIC WG M. Garcia-Martin MMUSIC WG M. Garcia-Martin
Internet-Draft Ericsson Internet-Draft Ericsson
Intended status: Standards Track S. Veikkolainen Intended status: Standards Track S. Veikkolainen
Expires: December 19, 2009 Nokia Expires: April 25, 2010 Nokia
June 17, 2009 October 22, 2009
Session Description Protocol (SDP) Extension For Setting Up Audio Media Session Description Protocol (SDP) Extension For Setting Up Audio and
Streams Over Circuit-Switched Bearers In The Public Switched Telephone Video Media Streams Over Circuit-Switched Bearers In The Public
Network (PSTN) Switched Telephone Network (PSTN)
draft-ietf-mmusic-sdp-cs-01 draft-ietf-mmusic-sdp-cs-02
Status of this Memo Status of this Memo
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Copyright Notice Copyright Notice
Copyright (c) 2009 IETF Trust and the persons identified as the Copyright (c) 2009 IETF Trust and the persons identified as the
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and restrictions with respect to this document. and restrictions with respect to this document.
Abstract Abstract
This memo describes use cases, requirements, and protocol extensions This memo describes use cases, requirements, and protocol extensions
for using the Session Description Protocol (SDP) Offer/Answer model for using the Session Description Protocol (SDP) Offer/Answer model
for establishing audio media stream over circuit-switched bearers in for establishing audio and video media streams over circuit-switched
the Public Switched Telephone Network (PSTN). bearers in the Public Switched Telephone Network (PSTN).
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions Used in This Document . . . . . . . . . . . . . . 5 2. Conventions Used in This Document . . . . . . . . . . . . . . 5
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Overview of Operation . . . . . . . . . . . . . . . . . . . . 6 4. Overview of Operation . . . . . . . . . . . . . . . . . . . . 6
4.1. Example Call Flow . . . . . . . . . . . . . . . . . . . . 6 4.1. Example Call Flow . . . . . . . . . . . . . . . . . . . . 6
5. Protocol Description . . . . . . . . . . . . . . . . . . . . . 8 5. Protocol Description . . . . . . . . . . . . . . . . . . . . . 8
5.1. Level of Compliance . . . . . . . . . . . . . . . . . . . 8 5.1. Level of Compliance . . . . . . . . . . . . . . . . . . . 8
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5.2.3.5. Negotiating the used correlation mechanisms . . . 15 5.2.3.5. Negotiating the used correlation mechanisms . . . 15
5.3. Considerations for Usage of Existing SDP . . . . . . . . . 17 5.3. Considerations for Usage of Existing SDP . . . . . . . . . 17
5.3.1. Originator of the Session . . . . . . . . . . . . . . 17 5.3.1. Originator of the Session . . . . . . . . . . . . . . 17
5.3.2. Contact information . . . . . . . . . . . . . . . . . 17 5.3.2. Contact information . . . . . . . . . . . . . . . . . 17
5.3.3. Determining the Direction of the Circuit-Switched 5.3.3. Determining the Direction of the Circuit-Switched
Connection Setup . . . . . . . . . . . . . . . . . . . 17 Connection Setup . . . . . . . . . . . . . . . . . . . 17
5.4. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . 18 5.4. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . 18
6. SDP Examples . . . . . . . . . . . . . . . . . . . . . . . . . 19 6. SDP Examples . . . . . . . . . . . . . . . . . . . . . . . . . 19
6.1. Basic SDP example: Single Circuit-Switched Audio Stream . 19 6.1. Basic SDP example: Single Circuit-Switched Audio Stream . 19
6.2. Advanced SDP example: Alternative and IP 6.2. Advanced SDP example: Alternative and IP
Circuit-Switched Audio Streams . . . . . . . . . . . . . . 20 Circuit-Switched Audio and Video Streams . . . . . . . . . 20
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
7.1. Registration of new correlation SDP attribute . . . . . . 22 7.1. Registration of new correlation SDP attribute . . . . . . 22
7.2. Registration of a new "nettype" value . . . . . . . . . . 22 7.2. Registration of a new "nettype" value . . . . . . . . . . 22
7.3. Registration of new "addrtype" values . . . . . . . . . . 22 7.3. Registration of new "addrtype" values . . . . . . . . . . 22
7.4. Registration of a new "proto" value . . . . . . . . . . . 22 7.4. Registration of a new "proto" value . . . . . . . . . . . 22
8. Security Considerations . . . . . . . . . . . . . . . . . . . 23 8. Security Considerations . . . . . . . . . . . . . . . . . . . 23
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
10.1. Normative References . . . . . . . . . . . . . . . . . . . 23 10.1. Normative References . . . . . . . . . . . . . . . . . . . 23
10.2. Informative References . . . . . . . . . . . . . . . . . . 24 10.2. Informative References . . . . . . . . . . . . . . . . . . 24
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can exchange SDP media descriptions and come to an agreement as to can exchange SDP media descriptions and come to an agreement as to
which media streams should be used, along with the media related which media streams should be used, along with the media related
parameters. parameters.
In some scenarios it might be desirable to establish the media stream In some scenarios it might be desirable to establish the media stream
over a circuit-switched bearer connection even if the signaling for over a circuit-switched bearer connection even if the signaling for
the session is carried over an IP bearer. An example of such a the session is carried over an IP bearer. An example of such a
scenario is illustrated with two mobile devices capable of both scenario is illustrated with two mobile devices capable of both
circuit-switched and packet-switched communication over a low- circuit-switched and packet-switched communication over a low-
bandwidth radio bearer. The radio bearer may not be suitable for bandwidth radio bearer. The radio bearer may not be suitable for
carrying real-time audio media, and using a circuit-switched bearer carrying real-time audio or video media, and using a circuit-switched
would offer, however, a better perceived quality of service. So, bearer would offer, however, a better perceived quality of service.
according to this scenario, SDP and its higher layer session control So, according to this scenario, SDP and its higher layer session
protocol (e.g., the Session Initiation Protocol (SIP) [RFC3261]) are control protocol (e.g., the Session Initiation Protocol (SIP)
used over regular IP connectivity, while the audio is received [RFC3261]) are used over regular IP connectivity, while the audio or
through the classical circuit-switched bearer. video is received through the classical circuit-switched bearer.
Setting up a signaling relationship in the IP domain instead of just Setting up a signaling relationship in the IP domain instead of just
setting up a circuit-switched call offers also the possibility of setting up a circuit-switched call offers also the possibility of
negotiating in the same session other IP based media that is not negotiating in the same session other IP based media that is not
sensitive to jitter and delay, for example, text messaging or sensitive to jitter and delay, for example, text messaging or
presence information. presence information.
At a later point in time the mobile device might move to an area At a later point in time the mobile device might move to an area
where a high-bandwidth packet-switched bearer, for example a Wireless where a high-bandwidth packet-switched bearer, for example a Wireless
Local Area Network (WLAN) connection, is available. At this point Local Area Network (WLAN) connection, is available. At this point
the mobile device may perform a handover and move the audio media the mobile device may perform a handover and move the audio or video
streams over to the high-speed bearer. This implies a new exchange media streams over to the high-speed bearer. This implies a new
of SDP offer/answer that lead to a re-negotiation of the media exchange of SDP offer/answer that lead to a re-negotiation of the
streams. media streams.
Other use cases exists. For example, and endpoint might have at its Other use cases exists. For example, and endpoint might have at its
disposal circuit-switch and packet-switched connectivity, but the disposal circuit-switch and packet-switched connectivity, but the
audio codecs are not the same in both access networks. Consider that audio or video codecs are not the same in both access networks.
the circuit-switched audio stream supports narrow-bandwidth codecs, Consider that the circuit-switched audio or video stream supports
while the packet-switched access allows any other audio codec narrow-bandwidth codecs, while the packet-switched access allows any
implemented in the endpoint. In this case, it might be beneficial other audio or video codec implemented in the endpoint. In this
for the endpoint to describe different codecs for each access type case, it might be beneficial for the endpoint to describe different
and get an agreement on the bearer together with the remote endpoint. codecs for each access type and get an agreement on the bearer
together with the remote endpoint.
There are additional use cases related to third party call control There are additional use cases related to third party call control
where the session setup time is improved when the circuit-switched where the session setup time is improved when the circuit-switched
bearer in the PSTN is described together with one or more codecs. bearer in the PSTN is described together with one or more codecs.
The rest of the document is structured as follows: Section 2 provides The rest of the document is structured as follows: Section 2 provides
the document conventions, Section 3 introduces the requirements, the document conventions, Section 3 introduces the requirements,
Section 4 presents an overview of the proposed solutions, and Section 4 presents an overview of the proposed solutions, and
Section 5 contains the protocol description. Section 6 provides a Section 5 contains the protocol description. Section 6 provides a
few examples of descriptions of circuit-switched audio streams in few examples of descriptions of circuit-switched audio or video
SDP. Section 7 and Section 8 contain the IANA and Security streams in SDP. Section 7 and Section 8 contain the IANA and
considerations, respectively. Security considerations, respectively.
2. Conventions Used in This Document 2. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14, RFC 2119 document are to be interpreted as described in BCP 14, RFC 2119
[RFC2119] and indicate requirement levels for compliant [RFC2119] and indicate requirement levels for compliant
implementations. implementations.
3. Requirements 3. Requirements
This section presents the general requirements that are specific for This section presents the general requirements that are specific for
the audio media stream over circuit-switched bearers. the audio or video media stream over circuit-switched bearers.
REQ-1: A mechanism for endpoints to negotiate and agree on an audio REQ-1: A mechanism for endpoints to negotiate and agree on an audio
media stream established over a circuit-switched bearer MUST or video media stream established over a circuit-switched
be available. bearer MUST be available.
REQ-2: The mechanism MUST allow the endpoints to combine circuit- REQ-2: The mechanism MUST allow the endpoints to combine circuit-
switched audio media streams with other complementary media switched audio or video media streams with other
streams, for example, text messaging. complementary media streams, for example, text messaging.
REQ-3: The mechanism MUST allow the endpoint to negotiate the REQ-3: The mechanism MUST allow the endpoint to negotiate the
direction of the circuit-switched connection, i.e., which direction of the circuit-switched connection, i.e., which
endpoint is active when initiating the circuit-switched endpoint is active when initiating the circuit-switched
connection. connection.
REQ-4: The mechanism MUST be independent of the type of the circuit- REQ-4: The mechanism MUST be independent of the type of the circuit-
switched access (e.g., Integrated Services Digital Network switched access (e.g., Integrated Services Digital Network
(ISDN), Global System for Mobile Communication (GSM), etc.) (ISDN), Global System for Mobile Communication (GSM), etc.)
REQ-5: There MUST be a mechanism that helps an endpoint to correlate REQ-5: There MUST be a mechanism that helps an endpoint to correlate
an incoming circuit-switched bearer with the one negotiated an incoming circuit-switched bearer with the one negotiated
in SDP, as opposed to another incoming call that is not in SDP, as opposed to another incoming call that is not
related to that. related to that.
REQ-6: It must be possible for endpoints to advertise different list REQ-6: It must be possible for endpoints to advertise different list
of audio codecs in the circuit-switched audio stream from of audio or video codecs in the circuit-switched audio or
those used in a packet-switched audio stream. video stream from those used in a packet-switched audio or
video stream.
REQ-7: It must be possible for endpoints to not advertise the list REQ-7: It must be possible for endpoints to not advertise the list
of available codecs for circuit-switched audio streams. of available codecs for circuit-switched audio or video
streams.
4. Overview of Operation 4. Overview of Operation
The mechanism defined in this memo extends SDP and allows describing The mechanism defined in this memo extends SDP and allows describing
an audio media stream established over a circuit-switched bearer. an audio or video media stream established over a circuit-switched
New tokens are registered in the "c=" and "m=" lines to be able to bearer. New tokens are registered in the "c=" and "m=" lines to be
describe an audio media stream over a circuit-switched bearer. These able to describe a media stream over a circuit-switched bearer.
SDP extensions are described in Section 5.2. Since circuit-switched These SDP extensions are described in Section 5.2. Since circuit-
bearers are a sort of connection-oriented media streams, the switched bearers are a sort of connection-oriented media streams, the
mechanism re-uses the connection-oriented extensions defined in RFC mechanism re-uses the connection-oriented extensions defined in RFC
4145 [RFC4145] to negotiate the active and passive sides of a 4145 [RFC4145] to negotiate the active and passive sides of a
connection setup. This is further described in Section 5.3.3. connection setup. This is further described in Section 5.3.3.
4.1. Example Call Flow 4.1. Example Call Flow
Consider the example presented in Figure 1. In this example, Alice Consider the example presented in Figure 1. In this example, Alice
is located in an environment where she has access to both IP and is located in an environment where she has access to both IP and
circuit-switched bearers for communicating with other endpoints. circuit-switched bearers for communicating with other endpoints.
Alice decides that the circuit-switched bearer offers a better Alice decides that the circuit-switched bearer offers a better
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5.1. Level of Compliance 5.1. Level of Compliance
Implementations according to this specification MUST implement the Implementations according to this specification MUST implement the
SDP extensions described in Section 5.2, and MUST implement the SDP extensions described in Section 5.2, and MUST implement the
considerations discussed in Section 5.3. considerations discussed in Section 5.3.
5.2. Extensions to SDP 5.2. Extensions to SDP
This section provides the syntax and semantics of the extensions This section provides the syntax and semantics of the extensions
required for providing a description of audio media streams over required for providing a description of audio or video media streams
circuit-switched bearers in SDP. over circuit-switched bearers in SDP.
5.2.1. Connection Data 5.2.1. Connection Data
According to SDP [RFC4566], the connection data line in SDP has the According to SDP [RFC4566], the connection data line in SDP has the
following syntax: following syntax:
c=<nettype> <addrtype> <connection-address> c=<nettype> <addrtype> <connection-address>
where <nettype> indicates the network type, <addrtype> indicates the where <nettype> indicates the network type, <addrtype> indicates the
address type, and the <connection-address> is the connection address, address type, and the <connection-address> is the connection address,
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c=PSTN - - c=PSTN - -
5.2.2. Media Descriptions 5.2.2. Media Descriptions
According to SDP [RFC4566], the media descriptions line in SDP has According to SDP [RFC4566], the media descriptions line in SDP has
the following syntax: the following syntax:
m=<media> <port> <proto> <fmt> ... m=<media> <port> <proto> <fmt> ...
The <media> sub-field carries the media type. Since this document The <media> sub-field carries the media type. For establishing an
deals with establishing an audio bearer, the existing "audio" media audio bearer, the existing "audio" media type is used. For
type is used. establishing a video bearer, the existing "video" media type is used.
The <port> sub-field is the transport port to which the media stream The <port> sub-field is the transport port to which the media stream
is sent. Circuit-switched access lacks the concept of a port number, is sent. Circuit-switched access lacks the concept of a port number,
and therefore the <port> sub-field is set to the discard port "9". and therefore the <port> sub-field is set to the discard port "9".
According to RFC 3264 [RFC3264], a port number of zero in the offer According to RFC 3264 [RFC3264], a port number of zero in the offer
of a unicast stream indicates that the stream is offered but must not of a unicast stream indicates that the stream is offered but must not
be used. If a port number of zero is present in the answer of a be used. If a port number of zero is present in the answer of a
unicast stream, it indicates that the stream is rejected. These unicast stream, it indicates that the stream is rejected. These
rules are still valid when the media line in SDP represents a rules are still valid when the media line in SDP represents a
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syntactically correct with SDP [RFC4566] and to indicate the usage of syntactically correct with SDP [RFC4566] and to indicate the usage of
circuit-switched protocols in the PSTN. circuit-switched protocols in the PSTN.
The <fmt> sub-field is the media format description. In the The <fmt> sub-field is the media format description. In the
classical usage of SDP to describe RTP-based media streams, when the classical usage of SDP to describe RTP-based media streams, when the
<proto> sub-field is set to "RTP/AVP" or "RTP/SAVP", the <fmt> sub- <proto> sub-field is set to "RTP/AVP" or "RTP/SAVP", the <fmt> sub-
field contains the payload types as defined in the RTP audio profile field contains the payload types as defined in the RTP audio profile
[RFC3551]. [RFC3551].
In the case of circuit-switched descriptions, RTP is not really used. In the case of circuit-switched descriptions, RTP is not really used.
Rather than specifying the RTP audio profile payload type, we use the Rather than specifying the RTP audio/video profile payload type, we
<fmt> sub-field to indicate the list of available media types over use the <fmt> sub-field to indicate the list of available media types
the circuit-switched bearer. Therefore, the <fmt> sub-field MAY over the circuit-switched bearer. Therefore, the <fmt> sub-field MAY
indicate one or more available audio codecs for a circuit-switched indicate one or more available audio or video codecs for a circuit-
audio stream. We use the classical RTP audio media types, even when switched audio or video stream. We use the classical RTP audio and
applied to PSTN circuit-switched bearers, the media type merely video media types, even when applied to PSTN circuit-switched
represents an audio codec. bearers, the media type merely represents an audio or video codec.
However, in some cases, the endpoint is not able to determine the However, in some cases, the endpoint is not able to determine the
list of available codecs for circuit-switched audio streams. In this list of available codecs for circuit-switched media streams. In this
case, in order to be syntactically compliant with SDP [RFC4566], the case, in order to be syntactically compliant with SDP [RFC4566], the
endpoint MUST include a single dash "-" in the <fmt> sub-field. endpoint MUST include a single dash "-" in the <fmt> sub-field.
As per RFC 4566 [RFC4566], the media format descriptions are listed As per RFC 4566 [RFC4566], the media format descriptions are listed
in priority order. in priority order.
Example of a media description for circuit-switched audio streams is: Example of a media description for circuit-switched audio streams is:
m=audio 9 PSTN 3 0 8 m=audio 9 PSTN 3 0 8
m=audio 9 PSTN - m=audio 9 PSTN -
Similarly, an example of a media description for circuit-switched
video stream is:
m=video 9 PSTN 34
m=video 9 PSTN -
5.2.3. Correlating the PSTN Circuit-Switched Bearer with SDP 5.2.3. Correlating the PSTN Circuit-Switched Bearer with SDP
The endpoints should be able to correlate the circuit-switched bearer The endpoints should be able to correlate the circuit-switched bearer
with the session negotiated with SDP to avoid ringing for an incoming with the session negotiated with SDP to avoid ringing for an incoming
circuit-switched bearer that is related to the session controlled circuit-switched bearer that is related to the session controlled
with SDP (and SIP). with SDP (and SIP).
Several alternatives exist for performing this correlation. This Several alternatives exist for performing this correlation. This
memo provides three mutually non-exclusive correlation mechanisms. memo provides three mutually non-exclusive correlation mechanisms.
Other correlation mechanisms might exist as well, and their usage Other correlation mechanisms might exist as well, and their usage
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between the endpoints. The caller-ID is also available as the between the endpoints. The caller-ID is also available as the
Calling Party ID in the circuit-switched signaling. Calling Party ID in the circuit-switched signaling.
The second mechanism is based on the inclusion in SDP of a value that The second mechanism is based on the inclusion in SDP of a value that
is also sent in the User-to-User Information Element that is part of is also sent in the User-to-User Information Element that is part of
the bearer setup signaling in the PSTN. the bearer setup signaling in the PSTN.
The third mechanism is based on sending in SDP a string that The third mechanism is based on sending in SDP a string that
represents Dual Tone MultiFrequency (DTMF) digits that will be later represents Dual Tone MultiFrequency (DTMF) digits that will be later
sent right after the circuit-switched bearer is established. sent right after the circuit-switched bearer is established.
Implementations MAY use any of these mechanisms and MAY use two or Implementations MAY use any of these mechanisms and MAY use two or
more mechanisms simultaneously. more mechanisms simultaneously.
5.2.3.1. The "correlation" attribute 5.2.3.1. The "correlation" attribute
In order to provide support for the correlation mechanisms, we define In order to provide support for the correlation mechanisms, we define
a new SDP attribute called "correlation". This "correlation" a new SDP attribute called "cs-correlation". This "cs-correlation"
attribute can include any of the "callerid", "uuie", or "dtmf" attribute can include any of the "callerid", "uuie", or "dtmf"
parameters, which specify additional information required by the parameters, which specify additional information required by the
Caller-ID, User to User Information, or DTMF correlation mechanisms, Caller-ID, User to User Information, or DTMF correlation mechanisms,
respectively. respectively.
The following sections provide more detailed information of these The following sections provide more detailed information of these
parameters. The "correlation" attribute has the following format: parameters. The "cs-correlation" attribute has the following format:
"a=correlation: "callerid:<callerid-value>" | "a=cs-correlation: "callerid:<callerid-value>" |
"uuie:<uuie-value>" | "uuie:<uuie-value>" |
"dtmf:<dtmf-value>" "dtmf:<dtmf-value>"
The values "callerid", "uuie" and "dtmf" refer to the correlation The values "callerid", "uuie" and "dtmf" refer to the correlation
mechanisms defined in Section 5.2.3.2, Section 5.2.3.3, and mechanisms defined in Section 5.2.3.2, Section 5.2.3.3, and
Section 5.2.3.4, respectively. The formal Augmented Backus-Naur Section 5.2.3.4, respectively. The formal Augmented Backus-Naur
Format (ABNF) syntax of the "correlation" attribute is presented in Format (ABNF) syntax of the "cs-correlation" attribute is presented
Section 5.4. in Section 5.4.
5.2.3.2. Caller-ID Correlation Mechanism 5.2.3.2. Caller-ID Correlation Mechanism
The Caller-ID correlation mechanisms consists of an exchange of the The Caller-ID correlation mechanisms consists of an exchange of the
calling party number in E.164 format in SDP, followed by the calling party number in E.164 format in SDP, followed by the
availability of the Calling Party Number information element in the availability of the Calling Party Number information element in the
call setup signaling of the circuit switched connection. If both call setup signaling of the circuit switched connection. If both
pieces of information match, the circuit-switched bearer is pieces of information match, the circuit-switched bearer is
correlated to the session described in SDP. correlated to the session described in SDP.
An endpoint that is feasible to become the active party for setting An endpoint that is feasible to become the active party for setting
up the circuit-switched bearer and is willing to send the Calling up the circuit-switched bearer and is willing to send the Calling
Party Number in the PSTN signaling SHOULD add a "callerid" parameter Party Number in the PSTN signaling SHOULD add a "callerid" parameter
in the "correlation" attribute of the SDP offer or answer, and SHOULD in the "cs-correlation" attribute of the SDP offer or answer, and
include as the value the E.164 number that will be presented in the SHOULD include as the value the E.164 number that will be presented
Calling Party Number in the PSTN signaling. in the Calling Party Number in the PSTN signaling.
An endpoint that acts as the passive party for setting up the An endpoint that acts as the passive party for setting up the
circuit-switch bearer SHOULD add a "callerid" parameter in the circuit-switch bearer SHOULD add a "callerid" parameter in the "cs-
"correlation" attribute of the SDP if it supports the mechanism, and correlation" attribute of the SDP if it supports the mechanism, and
MAY include the E.164 number that will be presented in the circuit- MAY include the E.164 number that will be presented in the circuit-
switched bearer in the same corresponding lines, although these are switched bearer in the same corresponding lines, although these are
not used for correlation. not used for correlation.
Example of inclusion of E.164 number in the "correlation" attribute Example of inclusion of E.164 number in the "cs-correlation"
is: attribute is:
a=correlation:callerid:+15551234 a=cs-correlation:callerid:+15551234
Please note that there are no warranties that this correlation Please note that there are no warranties that this correlation
mechanism works or is even available, due a number of problems: mechanism works or is even available, due a number of problems:
o The endpoint might not be aware of its own E.164 number, in which o The endpoint might not be aware of its own E.164 number, in which
case it cannot populate the SDP appropriately. case it cannot populate the SDP appropriately.
o The Calling Party Number information element in the circuit- o The Calling Party Number information element in the circuit-
switched signaling might not be available, e.g., due to policy switched signaling might not be available, e.g., due to policy
restrictions of the network operator or caller restriction due to restrictions of the network operator or caller restriction due to
skipping to change at page 12, line 47 skipping to change at page 13, line 5
that represents the User-User Information Element that is part of the that represents the User-User Information Element that is part of the
call setup signaling of the circuit-switched bearer. The User-User call setup signaling of the circuit-switched bearer. The User-User
Information Element is specified in ITU-T Q.931 [ITU.Q931.1998] and Information Element is specified in ITU-T Q.931 [ITU.Q931.1998] and
3GPP TS 24.008 [3GPP.24.008], among others. The User-User 3GPP TS 24.008 [3GPP.24.008], among others. The User-User
Information Element has a maximum size of 35 or 131 octets, depending Information Element has a maximum size of 35 or 131 octets, depending
on the actual message of the PSTN protocol where it is included. on the actual message of the PSTN protocol where it is included.
The mechanism works as follows: An endpoint creates a User-User The mechanism works as follows: An endpoint creates a User-User
Information Element, according to the requirement of the call setup Information Element, according to the requirement of the call setup
signaling protocol. The same value is included in the SDP offer or signaling protocol. The same value is included in the SDP offer or
SDP answer, in a correlation:uuie attribute. When the SDP offer/ SDP answer, in a "cs-correlation:uuie" attribute. When the SDP
answer exchange is completed, each endpoint has become aware of the offer/answer exchange is completed, each endpoint has become aware of
value that will be used in the User-User Information Element of the the value that will be used in the User-User Information Element of
call setup message of the PSTN protocol. The endpoint that initiates the call setup message of the PSTN protocol. The endpoint that
the call setup attempt includes this value in the User-User initiates the call setup attempt includes this value in the User-User
Information Element. The recipient of the call setup attempt can Information Element. The recipient of the call setup attempt can
extract the User-User Information Element and correlate it with the extract the User-User Information Element and correlate it with the
value previously received in the SDP. If both values match, then the value previously received in the SDP. If both values match, then the
call setup attempt corresponds to that indicated in the SDP. call setup attempt corresponds to that indicated in the SDP.
Note that, for correlation purposes, the value of the User-User Note that, for correlation purposes, the value of the User-User
Information Element is considered as a opaque string and only used Information Element is considered as a opaque string and only used
for correlation purposes. Typically call signaling protocols impose for correlation purposes. Typically call signaling protocols impose
requirements on the creation of User-User Information Element for requirements on the creation of User-User Information Element for
end-user protocol exchange. The details regarding the generation of end-user protocol exchange. The details regarding the generation of
the User-User Information Element are outside the scope of this the User-User Information Element are outside the scope of this
specification. specification.
An endpoint that is feasible to become the active party for setting An endpoint that is feasible to become the active party for setting
up the PSTN call and is willing to send the User-User Information up the PSTN call and is willing to send the User-User Information
Element in the PSTN signaling SHOULD add a "uuie" parameter in the Element in the PSTN signaling SHOULD add a "uuie" parameter in the
"correlation" attribute of the SDP offer or answer. This "uuie" "cs-correlation" attribute of the SDP offer or answer. This "uuie"
parameter SHOULD include the value of the User-User Information parameter SHOULD include the value of the User-User Information
Element that will be used in the call setup attempt. Element that will be used in the call setup attempt.
An endpoint that takes the role of the passive party for setting up An endpoint that takes the role of the passive party for setting up
the circuit-switched bearer SHOULD include include a "uuie" parameter the circuit-switched bearer SHOULD include include a "uuie" parameter
in the "correlation" attribute in the SDP, if it supports the UUI in the "cs-correlation" attribute in the SDP, if it supports the UUI
mechanism. It MAY also add a value for the "uuie" parameter although mechanism. It MAY also add a value for the "uuie" parameter although
it is not used for correlation purposes. it is not used for correlation purposes.
Please note that there are no warranties that this correlation Please note that there are no warranties that this correlation
mechanism works. On one side, policy restrictions might not make the mechanism works. On one side, policy restrictions might not make the
User-User information available end to end in the PSTN. On the other User-User information available end to end in the PSTN. On the other
hand, the generation of the User-User Information Element is hand, the generation of the User-User Information Element is
controlled by the PSTN circuit-switched call protocol, which might controlled by the PSTN circuit-switched call protocol, which might
not offer enough freedom for generating different values from one not offer enough freedom for generating different values from one
endpoint to another one, or from one call to another in the same endpoint to another one, or from one call to another in the same
skipping to change at page 14, line 7 skipping to change at page 14, line 14
(DTMF)tones over the circuit-switched bearer once this bearer is (DTMF)tones over the circuit-switched bearer once this bearer is
established. If the DTMF digit sequence received through the established. If the DTMF digit sequence received through the
circuit-switched bearer matches the digit string negotiated in the circuit-switched bearer matches the digit string negotiated in the
SDP, the circuit-switched bearer is correlated with the session SDP, the circuit-switched bearer is correlated with the session
described in the SDP. The mechanism is similar to many voice described in the SDP. The mechanism is similar to many voice
conferencing systems which require the user to enter a PIN code using conferencing systems which require the user to enter a PIN code using
DTMF tones in order to be accepted in a voice conference. DTMF tones in order to be accepted in a voice conference.
The mechanism works as follows: An endpoint selects a DTMF digit The mechanism works as follows: An endpoint selects a DTMF digit
sequence. The same sequence is included in the SDP offer or SDP sequence. The same sequence is included in the SDP offer or SDP
answer, in a "correlation:dtmf" attribute. When the SDP offer/answer answer, in a "cs-correlation:dtmf" attribute. When the SDP offer/
exchange is completed, each endpoint has become aware of the DTMF answer exchange is completed, each endpoint has become aware of the
sequence that will be sent right after the circuit-switched bearer is DTMF sequence that will be sent right after the circuit-switched
set up. The endpoint that initiates the call setup attempt sends the bearer is set up. The endpoint that initiates the call setup attempt
DTMF digits as per the procedures defined for the circuit-switched sends the DTMF digits as per the procedures defined for the circuit-
bearer technology used. The recipient (passive side of the bearer switched bearer technology used. The recipient (passive side of the
setup) of the call setup attempt collects the digits and correlates bearer setup) of the call setup attempt collects the digits and
them with the value previously received in the SDP. If the digits correlates them with the value previously received in the SDP. If
match, then the call setup attempt corresponds to that indicated in the digits match, then the call setup attempt corresponds to that
the SDP. indicated in the SDP.
An endpoint that is feasible to become the active party for setting An endpoint that is feasible to become the active party for setting
up the PSTN call and is willing to send the DTMF digits after up the PSTN call and is willing to send the DTMF digits after
circuit-switched bearer cut-through SHOULD include a "dtmf" parameter circuit-switched bearer cut-through SHOULD include a "dtmf" parameter
in the "correlation" attribute of the SDP offer or answer. The value in the "cs-correlation" attribute of the SDP offer or answer. The
of the "dtmf" parameter SHOULD contain up to 32 randomly selected value of the "dtmf" parameter SHOULD contain up to 32 randomly
DTMF digits (numbers 0-9, characters A-D, "#" and "*"). selected DTMF digits (numbers 0-9, characters A-D, "#" and "*").
Implementations are advised to select a number of DTMF digits that Implementations are advised to select a number of DTMF digits that
provide enough assurance that the call is related, but on the provide enough assurance that the call is related, but on the
other hand do not prolong the bearer setup time unnecessarily. other hand do not prolong the bearer setup time unnecessarily.
As an example, an endpoint willing to send DTMF tone sequence "14D*3" As an example, an endpoint willing to send DTMF tone sequence "14D*3"
would include a "correlation" attribute line as follows: would include a "cs-correlation" attribute line as follows:
a=correlation:dtmf:14D*3 a=cs-correlation:dtmf:14D*3
An endpoint that takes the role of the passive party for setting up An endpoint that takes the role of the passive party for setting up
the circuit-switched bearer SHOULD include include a "dtmf" parameter the circuit-switched bearer SHOULD include include a "dtmf" parameter
in the "correlation" attribute in the SDP, if it supports the in the "cs-correlation" attribute in the SDP, if it supports the
mechanism. It MAY also add a value for the "dtmf" parameter although mechanism. It MAY also add a value for the "dtmf" parameter although
it is not used for correlation purposes. it is not used for correlation purposes.
Once the circuit-switched bearer is successfully set up, the active Once the circuit-switched bearer is successfully set up, the active
side MUST send DTMF digits according to the circuit-switched bearer side MUST send DTMF digits according to the circuit-switched bearer
technology used. The values and number of the DTMF digits MUST match technology used. The values and number of the DTMF digits MUST match
those that were agreed during SDP negotiation. those that were agreed during SDP negotiation.
The passive side of the circuit-switched connection setup MUST be The passive side of the circuit-switched connection setup MUST be
prepared to receive and collect DTMF digits once the circuit-switched prepared to receive and collect DTMF digits once the circuit-switched
bearer is set up. The received DTMF digits are compared to the value bearer is set up. The received DTMF digits are compared to the value
of the "dtmf" parameter of the "correlation" attribute that the the of the "dtmf" parameter of the "cs-correlation" attribute that the
active side sent during SDP offer/answer exchange. If the received the active side sent during SDP offer/answer exchange. If the
DTMF digits match the value of the "dtmf" parameter in the received DTMF digits match the value of the "dtmf" parameter in the
"correlation" attribute, the call SHOULD be treated as correlated to "cs-correlation" attribute, the call SHOULD be treated as correlated
the ongoing session. to the ongoing session.
If the offerer and answerer successfully agree on the usage of the If the offerer and answerer successfully agree on the usage of the
DTMF digit correlation mechanism, but the passive side does not DTMF digit correlation mechanism, but the passive side does not
receive any DTMF digits after successful circuit-switched bearer receive any DTMF digits after successful circuit-switched bearer
setup, or receives a set of DTMF digits that do not match the value setup, or receives a set of DTMF digits that do not match the value
of the "dtmf" attribute (including receving too many digits), the of the "dtmf" attribute (including receving too many digits), the
passive side SHOULD treat the circuit-switched bearer as not passive side SHOULD treat the circuit-switched bearer as not
correlated to the ongoing session. correlated to the ongoing session.
DTMF digits can only be sent once the circuit-switched bearer is DTMF digits can only be sent once the circuit-switched bearer is
skipping to change at page 15, line 35 skipping to change at page 15, line 44
In order to agree which correlation mechanisms are supported by each In order to agree which correlation mechanisms are supported by each
endpoint, we define a negotiation mechanism similar to the one endpoint, we define a negotiation mechanism similar to the one
defined for codec negotiation. defined for codec negotiation.
In some cases an endpoint may support the correlation mechanism, but In some cases an endpoint may support the correlation mechanism, but
it is not willing to become the active party in the circuit-switched it is not willing to become the active party in the circuit-switched
bearer establishment. bearer establishment.
If the offerer supports any of the correlation mechanisms defined in If the offerer supports any of the correlation mechanisms defined in
this memo, it SHOULD include an attribute line "a=correlation" in the this memo, it SHOULD include an attribute line "a=cs-correlation" in
SDP offer. The "a=correlation" line contains an enumeration of the the SDP offer. The "a=cs-correlation" line contains an enumeration
correlation mechanisms supported by the offerer, in the format of of the correlation mechanisms supported by the offerer, in the format
parameters. The current list of parameters include "callerid", of parameters. The current list of parameters include "callerid",
"uuie" and "dtmf" and they refer to the correlation mechanisms "uuie" and "dtmf" and they refer to the correlation mechanisms
defined in Section 5.2.3.2, Section 5.2.3.3, and Section 5.2.3.4, defined in Section 5.2.3.2, Section 5.2.3.3, and Section 5.2.3.4,
respectively. For example, if an endpoint is willing to use the respectively. For example, if an endpoint is willing to use the
User-User Information element and DTMF digit sending mechanisms, it User-User Information element and DTMF digit sending mechanisms, it
includes the following line to the SDP: includes the following line to the SDP:
a=correlation:uuie dtmf a=cs-correlation:uuie dtmf
The answerer, when generating the answer, SHOULD select those The answerer, when generating the answer, SHOULD select those
correlation mechanisms it supports, and include an "a=correlation" correlation mechanisms it supports, and include an "a=cs-correlation"
attribute line in the answer containing those mechanisms it supports. attribute line in the answer containing those mechanisms it supports.
The answerer MUST NOT add any mechanism which was not included in the The answerer MUST NOT add any mechanism which was not included in the
offer. offer.
If the answer does not contain an "a=correlation" attribute line, the If the answer does not contain an "a=cs-correlation" attribute line,
offerer MUST interpret this as an indication that the anwerer does the offerer MUST interpret this as an indication that the anwerer
not support any of the correlation mechanisms for this session. does not support any of the correlation mechanisms for this session.
If, in addition to supporting any of the correlation mechanisms, an If, in addition to supporting any of the correlation mechanisms, an
endpoint is willing to assume the role of the active party in endpoint is willing to assume the role of the active party in
establishing the circuit-switched bearer, it MUST add a parameter establishing the circuit-switched bearer, it MUST add a parameter
value to the supported mechanisms. For example, if the endpoint value to the supported mechanisms. For example, if the endpoint
supports and is willing to send the User-User Information element and supports and is willing to send the User-User Information element and
DTMF digits, it includes the following line to the SDP offer: DTMF digits, it includes the following line to the SDP offer:
a=correlation:uuie:2890W284hAT452612908awudfjang908 dtmf:14D*3 a=cs-correlation:uuie:2890W284hAT452612908awudfjang908 dtmf:14D*3
The answerer SHOULD select those correlation mechanisms it supports The answerer SHOULD select those correlation mechanisms it supports
and is willing to use, and include respective parameter values. If and is willing to use, and include respective parameter values. If
the answerer supports but is not willing to use some of the the answerer supports but is not willing to use some of the
mechanisms (for example, due to not being able to become the active mechanisms (for example, due to not being able to become the active
endpoint when setting up the circuit-switched bearer), it SHOULD endpoint when setting up the circuit-switched bearer), it SHOULD
include the respective parameter, but MUST NOT add a value to the include the respective parameter, but MUST NOT add a value to the
parameter. parameter.
Note that, as stated above, it cannot be guaranteed that any given Note that, as stated above, it cannot be guaranteed that any given
skipping to change at page 17, line 23 skipping to change at page 17, line 31
According to SDP [RFC4566], the origin line in SDP has the following According to SDP [RFC4566], the origin line in SDP has the following
syntax: syntax:
o=<username> <sess-id> <sess-version> <nettype> <addrtype> o=<username> <sess-id> <sess-version> <nettype> <addrtype>
<unicast-address> <unicast-address>
Of interest here are the <nettype> and <addrtype> fields, which Of interest here are the <nettype> and <addrtype> fields, which
indicate the type of network and type of address, respectively. indicate the type of network and type of address, respectively.
Typically, this field carries the IP address of the originator of the Typically, this field carries the IP address of the originator of the
session. Even if the SDP was used to negotiate an audio media stream session. Even if the SDP was used to negotiate an audio or video
transported over a circuit-switched bearer, the originator is using media stream transported over a circuit-switched bearer, the
SDP over an IP bearer. Therefore, <nettype> and <addrtype> fields in originator is using SDP over an IP bearer. Therefore, <nettype> and
the "o=" line should be populated with the IP address identifying the <addrtype> fields in the "o=" line should be populated with the IP
source of the signaling. address identifying the source of the signaling.
5.3.2. Contact information 5.3.2. Contact information
SDP [RFC4566] defines the "p=" line which may include the phone SDP [RFC4566] defines the "p=" line which may include the phone
number of the person reponsible for the conference. Even though this number of the person reponsible for the conference. Even though this
line can carry a phone number, it is not suited for the purpose of line can carry a phone number, it is not suited for the purpose of
defining a connection address for the media. Therefore, we have defining a connection address for the media. Therefore, we have
selected to define the PSTN specific connection addresses in the "c=" selected to define the PSTN specific connection addresses in the "c="
line. line.
skipping to change at page 19, line 17 skipping to change at page 19, line 17
connection-field = [%x63 "=" nettype SP addrtype SP connection-field = [%x63 "=" nettype SP addrtype SP
connection-address CRLF] connection-address CRLF]
;nettype and addrtype are defined in RFC 4566 ;nettype and addrtype are defined in RFC 4566
connection-address /= e164-address / "-" connection-address /= e164-address / "-"
e164-address = ["+"] 1*15DIGIT e164-address = ["+"] 1*15DIGIT
; DIGIT is specified in RFC 5234 ; DIGIT is specified in RFC 5234
;subrules for correlation attribute ;subrules for correlation attribute
attribute /= correlation-attr attribute /= cs-correlation-attr
; attribute defined in RFC 4566 ; attribute defined in RFC 4566
correlation-attr = "correlation:" corr-mechanisms cs-correlation-attr= "cs-correlation:" corr-mechanisms
corr-mechanisms = corr-mech *(SP corr-mech) corr-mechanisms = corr-mech *(SP corr-mech)
corr-mech = caller-id-mech / uuie-mech / dtmf-mech corr-mech = caller-id-mech / uuie-mech / dtmf-mech
caller-id-mech = "callerid" [":" caller-id-value] caller-id-mech = "callerid" [":" caller-id-value]
caller-id-value = ["+"] 1*DIGIT caller-id-value = ["+"] 1*DIGIT
uuie-mech = "uuie" [":" uuie-value] uuie-mech = "uuie" [":" uuie-value]
uuie-value = 1*32(ALPHA/DIGIT) uuie-value = 1*32(ALPHA/DIGIT)
dtmf-mech = "dtmf" [":" dtmf-value] dtmf-mech = "dtmf" [":" dtmf-value]
dtmf-value = 1*32(DIGIT / %x41-44 / %x23 / %x2A ) dtmf-value = 1*32(DIGIT / %x41-44 / %x23 / %x2A )
;0-9, A-D, '#' and '*' ;0-9, A-D, '#' and '*'
skipping to change at page 20, line 23 skipping to change at page 20, line 23
endpoint initiates the PSTN call. endpoint initiates the PSTN call.
v=0 v=0
o=jdoe 2890844526 2890842807 IN IP4 192.0.2.5 o=jdoe 2890844526 2890842807 IN IP4 192.0.2.5
s= s=
t=0 0 t=0 0
m=audio 9 PSTN - m=audio 9 PSTN -
c=PSTN E164 +15551234 c=PSTN E164 +15551234
a=setup:actpass a=setup:actpass
a=connection:new a=connection:new
a=correlation:uuie:2890W284hAT452612908awudfjang908 a=cs-correlation:uuie:2890W284hAT452612908awudfjang908
Figure 4: SDP offer (1) Figure 4: SDP offer (1)
6.2. Advanced SDP example: Alternative and IP Circuit-Switched Audio 6.2. Advanced SDP example: Alternative and IP Circuit-Switched Audio
Streams and Video Streams
Alice Bob Alice Bob
| | | |
| (1) SDP Offer (IP and PSTN audio)| | (1) SDP Offer (IP and PSTN audio and video)|
|--------------------------------->| |------------------------------------------->|
| | | |
| (2) SDP Answer (PSTN audio) | | (2) SDP Answer (PSTN audio and video) |
|<---------------------------------| |<-------------------------------------------|
| | | |
| PSTN call setup | | PSTN call setup |
|<---------------------------------| |<-------------------------------------------|
| | | |
|<==== media over PSTN bearer ====>| |<======== media over PSTN bearer ==========>|
| | | |
Figure 5: Alternative media Figure 5: Alternative media
Figure 5 shows an example of negotiating audio media streams over IP Figure 5 shows an example of negotiating audio and video media
or circuit-switched bearers. Using the mechanisms described in SDP streams over IP or circuit-switched bearers. Using the mechanisms
Capability Negotiation Framework described in SDP Capability Negotiation Framework
[I-D.ietf-mmusic-sdp-capability-negotiation] and extensions thereof [I-D.ietf-mmusic-sdp-capability-negotiation] and extensions thereof
(SDP media capabilities Negotiation (SDP media capabilities Negotiation
[I-D.ietf-mmusic-sdp-media-capabilities] and SDP Miscellaneous [I-D.ietf-mmusic-sdp-media-capabilities] and SDP Miscellaneous
Capabilities [I-D.garcia-mmusic-sdp-misc-cap]) it is possible to Capabilities [I-D.garcia-mmusic-sdp-misc-cap]) it is possible to
construct an SDP offer where audio media can be offered alternatively construct an SDP offer where audio and video media can be offered
over IP or circuit-switched bearer. alternatively over IP or circuit-switched bearer.
v=0 v=0
o=jdoe 2890844526 2890842807 IN IP4 192.0.2.5 o=jdoe 2890844526 2890842807 IN IP4 192.0.2.5
s= s=
t=0 0 t=0 0
m=audio 49170 RTP/AVP 0 8 3
c=IN IP4 192.0.2.5 c=IN IP4 192.0.2.5
a=sescap:1 1,3
a=sescap:2 2,4
a=creq:med-v0,ccap-v0 a=creq:med-v0,ccap-v0
a=mcap:1 PCMU/8000/1 a=acap:1 cs-correlation:uuie:2890W284hAT452612908awudfjang908
a=mcap:2 PCMA/8000/1
a=mcap:3 GSM/8000/1
a=mcap:4 -
a=tcap:1 RTP/AVP PSTN
a=ccap:1 IN IP4 192.0.2.1
a=ccap:2 PSTN E164 +15551234
a=acap:1 correlation:uuie:2890W284hAT452612908awudfjang908
a=acap:2 setup:actpass a=acap:2 setup:actpass
a=acap:3 connection:new a=acap:3 connection:new
a=pcfg:1 t=1 m=1,2,3 c=1 a=tcap:1 PSTN
a=pcfg:2 t=2 m=4 c=2 a=1,2,3 m=audio 49170 RTP/AVP 0 8 3
a=mcap:1 -
a=ccap:1 PSTN E164 +15551234
a=pcfg:1
a=pcfg:2 m=1 t=1 c=1 a=1,2,3
m=video 49174 RTP/AVP 34
a=mcap:2 -
a=ccap:2 PSTN E164 +15551234
a=pcfg:3
a=pcfg:4 m=2 t=1 c=2 a=1,2,3
Figure 6: SDP offer with alternative media (1) Figure 6: SDP offer with alternative media (1)
Upon receiving the SDP offer descibed in Figure 6, Bob decided to Upon receiving the SDP offer descibed in Figure 6, Bob decided to
select the circuit-switched bearer and generates the answer described select the circuit-switched bearer and generates the answer described
in Figure 7 in Figure 7
v=0 v=0
o=- 2890973824 2890987289 IN IP4 192.0.2.7 o=- 2890973824 2890987289 IN IP4 192.0.2.7
s= s=
t=0 0 t=0 0
m=audio - PSTN -
c=PSTN - -
a=acfg:2
a=setup:active a=setup:active
a=connection:new a=connection:new
a=correlation:uuie:2890W284hAT452612908awudfjang908 a=cs-correlation:uuie:2890W284hAT452612908awudfjang908
m=audio - PSTN -
c= PSTN E164 +1551234
m=video - PSTN -
c=PSTN E164 +1551234
a=acfg:2
Figure 7: SDP answer with circuit-switched media (2) Figure 7: SDP answer with circuit-switched media (2)
7. IANA Considerations 7. IANA Considerations
This document instructs IANA to register a number of SDP tokens This document instructs IANA to register a number of SDP tokens
according to the following data. according to the following data.
7.1. Registration of new correlation SDP attribute 7.1. Registration of new correlation SDP attribute
Contact: Miguel Garcia <miguel.a.garcia@ericsson.com> Contact: Miguel Garcia <miguel.a.garcia@ericsson.com>
Attribute name: correlation Attribute name: cs-correlation
Long-form attribute name: PSTN Correlation Identifier Long-form attribute name: PSTN Correlation Identifier
Type of attribute: media level only Type of attribute: media level only
This attribute is subject to the charset attribute This attribute is subject to the charset attribute
Description: This attribute provides the Correlation Identifier Description: This attribute provides the Correlation Identifier
used in PSTN signaling used in PSTN signaling
skipping to change at page 23, line 21 skipping to change at page 23, line 25
This memo provides mechanisms to agree on a correlation identifier or This memo provides mechanisms to agree on a correlation identifier or
identifiers that are used to evaluate whether an incoming circuit- identifiers that are used to evaluate whether an incoming circuit-
switched call is related to an ongoing session in the IP domain. If switched call is related to an ongoing session in the IP domain. If
an attacker replicates the correlation identifer and establishes a an attacker replicates the correlation identifer and establishes a
call within the time window the receiving endpoint is expecting a call within the time window the receiving endpoint is expecting a
call, the attacker may be able to hijack the circuit-switched call. call, the attacker may be able to hijack the circuit-switched call.
These types of attacks are not specific to the mechanisms presented These types of attacks are not specific to the mechanisms presented
in this memo. For example, caller ID spoofing is a well known attack in this memo. For example, caller ID spoofing is a well known attack
in the PSTN. Users are advised to use the same caution before in the PSTN. Users are advised to use the same caution before
revealing sensitive information as they would on any other phone revealing sensitive information as they would on any other phone
call. call. Furthermore, users are advised that mechanisms that may be in
use in the IP domain for securing the media, like Secure RTP (SRTP)
[RFC3711], are not available in the CS domain.
9. Acknowledgments 9. Acknowledgments
The authors want to thank Flemming Andreasen, Thomas Belling, Jari The authors want to thank Flemming Andreasen, Thomas Belling, John
Mutikainen, Miikka Poikselka, Jonathan Rosenberg, Ingemar Johansson, Elwell, Jari Mutikainen, Miikka Poikselka, Jonathan Rosenberg,
Christer Holmberg, and Alf Heidermark for providing their insight and Ingemar Johansson, Christer Holmberg, and Alf Heidermark for
comments on this document. providing their insight and comments on this document.
10. References 10. References
10.1. Normative References 10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3108] Kumar, R. and M. Mostafa, "Conventions for the use of the [RFC3108] Kumar, R. and M. Mostafa, "Conventions for the use of the
Session Description Protocol (SDP) for ATM Bearer Session Description Protocol (SDP) for ATM Bearer
skipping to change at page 24, line 19 skipping to change at page 24, line 26
[3GPP.24.008] [3GPP.24.008]
3GPP, "Mobile radio interface Layer 3 specification; Core 3GPP, "Mobile radio interface Layer 3 specification; Core
network protocols; Stage 3", 3GPP TS 24.008 3.20.0, network protocols; Stage 3", 3GPP TS 24.008 3.20.0,
December 2005. December 2005.
[I-D.garcia-mmusic-sdp-misc-cap] [I-D.garcia-mmusic-sdp-misc-cap]
Garcia, M., Veikkolainen, S., and R. Gilman, Garcia, M., Veikkolainen, S., and R. Gilman,
"Miscellaneous Capabilities Negotiation in the Session "Miscellaneous Capabilities Negotiation in the Session
Description Protocol (SDP)", Description Protocol (SDP)",
draft-garcia-mmusic-sdp-misc-cap-00 (work in progress), draft-garcia-mmusic-sdp-misc-cap-01 (work in progress),
October 2008. July 2009.
[I-D.ietf-mmusic-sdp-capability-negotiation] [I-D.ietf-mmusic-sdp-capability-negotiation]
Andreasen, F., "SDP Capability Negotiation", Andreasen, F., "SDP Capability Negotiation",
draft-ietf-mmusic-sdp-capability-negotiation-10 (work in draft-ietf-mmusic-sdp-capability-negotiation-10 (work in
progress), May 2009. progress), May 2009.
[I-D.ietf-mmusic-sdp-media-capabilities] [I-D.ietf-mmusic-sdp-media-capabilities]
Gilman, R., Even, R., and F. Andreasen, "SDP media Gilman, R., Even, R., and F. Andreasen, "SDP media
capabilities Negotiation", capabilities Negotiation",
draft-ietf-mmusic-sdp-media-capabilities-07 (work in draft-ietf-mmusic-sdp-media-capabilities-08 (work in
progress), February 2009. progress), July 2009.
[ITU.E164.1991] [ITU.E164.1991]
International Telecommunications Union, "The International International Telecommunications Union, "The International
Public Telecommunication Numbering Plan", ITU- Public Telecommunication Numbering Plan", ITU-
T Recommendation E.164, 1991. T Recommendation E.164, 1991.
[ITU.Q931.1998] [ITU.Q931.1998]
"Digital Subscriber Signalling System No. 1 (DSS 1) - ISDN "Digital Subscriber Signalling System No. 1 (DSS 1) - ISDN
User - Network Interface Layer 3 Specification for Basic User - Network Interface Layer 3 Specification for Basic
Call Control", ISO Standard 9594-1, May 1998. Call Control", ISO Standard 9594-1, May 1998.
skipping to change at page 25, line 7 skipping to change at page 25, line 14
June 2002. June 2002.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003. Applications", STD 64, RFC 3550, July 2003.
[RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and [RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and
Video Conferences with Minimal Control", STD 65, RFC 3551, Video Conferences with Minimal Control", STD 65, RFC 3551,
July 2003. July 2003.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, March 2004.
[RFC4975] Campbell, B., Mahy, R., and C. Jennings, "The Message [RFC4975] Campbell, B., Mahy, R., and C. Jennings, "The Message
Session Relay Protocol (MSRP)", RFC 4975, September 2007. Session Relay Protocol (MSRP)", RFC 4975, September 2007.
URIs URIs
[1] <http://www.iana.org/assignments/sdp-parameters> [1] <http://www.iana.org/assignments/sdp-parameters>
Authors' Addresses Authors' Addresses
Miguel A. Garcia-Martin Miguel A. Garcia-Martin
 End of changes. 63 change blocks. 
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