draft-ietf-mmusic-kmgmt-ext-05.txt   draft-ietf-mmusic-kmgmt-ext-06.txt 
Internet Engineering Task Force J. Arkko Internet Engineering Task Force J. Arkko
MMUSIC Working Group E. Carrara MMUSIC Working Group E. Carrara
INTERNET-DRAFT F. Lindholm INTERNET-DRAFT F. Lindholm
Expires: December 2002 M. Naslund Expires: August 2003 M. Naslund
K. Norrman K. Norrman
Ericsson Ericsson
June, 2002 February, 2003
Key Management Extensions for SDP and RTSP Key Management Extensions for SDP and RTSP
<draft-ietf-mmusic-kmgmt-ext-05.txt> <draft-ietf-mmusic-kmgmt-ext-06.txt>
Status of this memo Status of this memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that other Task Force (IETF), its areas, and its working groups. Note that other
groups may also distribute working documents as Internet-Drafts. groups may also distribute working documents as Internet-Drafts.
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TABLE OF CONTENTS TABLE OF CONTENTS
1. Introduction.....................................................2 1. Introduction.....................................................2
1.1. Notational Conventions.........................................3 1.1. Notational Conventions.........................................3
2. Extensions to SDP and RTSP.......................................3 2. Extensions to SDP and RTSP.......................................3
2.1. SDP Extensions.................................................4 2.1. SDP Extensions.................................................4
2.2. RTSP Extensions................................................4 2.2. RTSP Extensions................................................4
3. Usage with SIP and RTSP..........................................5 3. Usage with SIP and RTSP..........................................5
3.1. General SDP processing.........................................5 3.1. General SDP processing.........................................5
3.2. SIP usage......................................................7 3.2. SIP usage......................................................6
3.3. RTSP usage.....................................................7 3.3. RTSP usage.....................................................7
3.4. Example scenarios..............................................8 3.4. Example scenarios..............................................7
4. Adding further Key management protocols.........................10 4. Adding further Key management protocols.........................10
5. Security Considerations.........................................10 5. Security Considerations.........................................10
6. IANA Considerations.............................................11 6. IANA Considerations.............................................11
7. Conclusions.....................................................11 7. Conclusions.....................................................11
8. Acknowledgments.................................................11 8. Acknowledgments.................................................11
9. Author's Addresses..............................................11 9. Author's Addresses..............................................11
10. References.....................................................12 10. References.....................................................12
10.1. Normative References.........................................12 10.1. Normative References.........................................12
10.2. Informative References.......................................12 10.2. Informative References.......................................12
1. Introduction 1. Introduction
There has recently been work to define a security framework for the There has recently been work to define a security framework for the
protection of real-time applications running over RTP, [SRTP]. protection of real-time applications running over RTP, [SRTP].
However, a security protocol needs a key management infrastructure to However, a security protocol needs a key management infrastructure to
exchange keys and security parameters, managing and refreshing keys, exchange keys and security parameters, managing and refreshing keys,
etc. etc.
A key management protocol is executed prior to the security protocol A key management protocol is executed prior to the security protocol
execution. The key management protocol's main goal is to, in a secure execution. The key management protocol's main goal is to, in a secure
and reliable way, establish a so called security association for the and reliable way, establish a so-called security association for the
security protocol. This includes one or several cryptographic keys security protocol. This includes one or several cryptographic keys
and a set of necessary parameters for the security protocol, e.g., and a set of necessary parameters for the security protocol, e.g.,
cipher and authentication algorithm to be used. The key management cipher and authentication algorithm to be used. The key management
protocol has similarities with, e.g., SIP [SIP] and RTSP [RTSP] in protocol has similarities with, e.g., SIP [SIP] and RTSP [RTSP] in
the sense that it negotiates necessary information in order to be the sense that it negotiates necessary information in order to be
able to setup the session. able to setup the session.
The focus in the following sections is to describe SDP attribute The focus in the following sections is to describe SDP attribute
extensions and RTSP header extensions to support key management, and extensions and RTSP header extensions to support key management, and
a possible integration within SIP and RTSP. A framework is therefore a possible integration within SIP and RTSP. A framework is therefore
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* The knowledge of the media at the session establishment makes it * The knowledge of the media at the session establishment makes it
easy to tie the key management to the multimedia sessions. easy to tie the key management to the multimedia sessions.
* This approach may be more efficient than setting up the security * This approach may be more efficient than setting up the security
later, as that approach might force extra roundtrips, possibly later, as that approach might force extra roundtrips, possibly
also a separate set-up for each stream, hence implying more delay also a separate set-up for each stream, hence implying more delay
to the actual setup of the media session. to the actual setup of the media session.
Currently in SDP [SDPnew], one field exists to transport keys, i.e. Currently in SDP [SDPnew], one field exists to transport keys, i.e.
the "key=" field. However, this is not enough for a key management the "key=" field. However, this is not enough for a key management
protocol. The approach here is to use and extend the SDP description protocol as there are many more parameters that need to be
to transport the key management offer/answer and also to associate it transported. The approach here is to use and extend the SDP
with the media sessions. SIP uses the offer/answer model [OAM] description to transport the key management offer/answer and also to
whereby extensions to SDP will be enough. However, RTSP [RTSP] does associate it with the media sessions. SIP uses the offer/answer model
not use the offer/answer model. This makes it impossible to send back [OAM] whereby extensions to SDP will be enough. However, RTSP [RTSP]
an answer to the server. To solve this, a new header is introduced in does not use the offer/answer model. This makes it impossible to send
which the key management data can be included. back an answer to the server. To solve this, a new header is
introduced in which the key management data can be included.
1.1. Notational Conventions 1.1. Notational Conventions
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 RFC-2119. document are to be interpreted as described in RFC-2119.
2. Extensions to SDP and RTSP 2. Extensions to SDP and RTSP
This section describes common attributes that are to be included in This section describes common attributes that are to be included in
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For the SDP description, the key management attributes MAY be defined For the SDP description, the key management attributes MAY be defined
at session level (i.e. before the media descriptor lines) and/or at at session level (i.e. before the media descriptor lines) and/or at
media level. If the key management attributes are defined at media media level. If the key management attributes are defined at media
level, they will only apply to that specific media. If the key level, they will only apply to that specific media. If the key
management attributes are defined at both session and media level, management attributes are defined at both session and media level,
the media level definition overrides the session level definition for the media level definition overrides the session level definition for
that specific media. that specific media.
The following SDP attribute is defined: The following SDP attribute is defined:
key-mgmt:<name> <opaque-data> key-mgmt:<identifier> <opaque-data>
<name> is the name of the key management protocol and the opaque-data
is a field to transport the key management protocol data. The key <identifier> is the name of the key management protocol and the
management protocol data contains the necessary information to opaque-data is a field to transport the key management protocol data.
establish the security protocol, e.g., keys and cryptographic The key management protocol data contains the necessary information
to establish the security protocol, e.g., keys and cryptographic
parameters. All parameters and keys are protected by the key parameters. All parameters and keys are protected by the key
management. Note that if the key management protocol fails, e.g., the management. Note that if the key management protocol fails, e.g., the
receiver does not accept any of the proposed security parameters, or receiver does not accept any of the proposed security parameters, or
simply does not understand the key management protocol, the security simply does not understand the key management protocol, the security
setup will fail. Consequently, it is impossible to establish a secure setup will fail. Consequently, it is impossible to establish a secure
session. So, if the key management fails, the offer must be rejected. session. So, if the key management fails, the offer must be rejected.
2.1. SDP Extensions 2.1. SDP Extensions
This section provides an Augmented Backus-Naur Form (ABNF) grammar This section provides an Augmented Backus-Naur Form (ABNF) grammar
(as used in [SDPnew]) for the key management extensions to SDP. (as used in [SDPnew]) for the key management extensions to SDP.
Note that the new definitions are compliant with the definition of an Note that the new definitions are compliant with the definition of an
attribute field, i.e. attribute field, i.e.
attribute = (att-field ":" att-value) | att-field attribute = (att-field ":" att-value) | att-field
One new attribute for SDP is defined: One new attribute for SDP is defined:
key-mgmt = "key-mgmt: " prtcl-name keymgmt-data key-mgmt = "key-mgmt: " prtcl-id keymgmt-data
prtcl-name = non-ws-string prtcl-id = non-ws-string
; e.g. "MIKEY" ; e.g. "mikey"
keymgmt-data = text keymgmt-data = text
where non-ws-string and text are as defined in SDP [SDPnew]. The where non-ws-string and text are as defined in SDP [SDPnew]. The
attribute may be used at session level, media level or at both attribute may be used at session level, media level or at both
levels. An attribute defined at media level overrides an attribute levels. An attribute defined at media level overrides an attribute
defined at session level. defined at session level.
2.2. RTSP Extensions 2.2. RTSP Extensions
To support the needed attribute described, the following RTSP header To support the needed attribute described, the following RTSP header
is defined: is defined:
KeyMgmt _ "keymgmt" ":" 1#key-mgmt-spec KeyMgmt = "keymgmt" ":" 1#key-mgmt-spec
key-mgmt-spec _ "prot" "=" token ";" "data" "=" quoted-string key-mgmt-spec = "prot" "=" token ";" "data" "=" quoted-string
token and quoted-string are as defined in the RTSP specification token and quoted-string are as defined in the RTSP specification
[RTSP]. [RTSP].
The KeyMgmt header should be possible to use in the messages The KeyMgmt header should be possible to use in the messages
described in the table below. described in the table below.
Method Direction Requirement Method Direction Requirement
DESCRIBE C->S required DESCRIBE C->S required
SETUP C->S required SETUP C->S required
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Today, the MIKEY protocol [MIKEY] has adopted the key management Today, the MIKEY protocol [MIKEY] has adopted the key management
extensions to work together with SIP and RTSP. Other protocols MAY extensions to work together with SIP and RTSP. Other protocols MAY
use the described attribute and header, e.g. Kerberos [KERB]. use the described attribute and header, e.g. Kerberos [KERB].
3.1. General SDP processing 3.1. General SDP processing
When an SDP message is created, the following procedure should be When an SDP message is created, the following procedure should be
applied: applied:
* The identifier of the key management protocol used (e.g. MIKEY or * The identifier of the key management protocol used (e.g. MIKEY or
Kerberos) MUST be put in the prtcl-name field. Kerberos) MUST be put in the prtcl-id field.
* The keymgmt-data field MUST be created with the data received from * The keymgmt-data field MUST be created with the data received from
the key management protocol (this data MUST be base64 encoded). the key management protocol (this data MUST be base64 encoded).
The data may e.g. be a MIKEY message or Kerberos ticket. The data may e.g. be a MIKEY message or Kerberos ticket.
A received SDP message that contains the key management attributes A received SDP message that contains the key management attributes
SHOULD process these attributes in the following manner: SHOULD process these attributes in the following manner:
* The key management protocol used MUST be identified by checking the * The key management protocol used MUST be identified by checking the
prtcl-name field in the key management attribute. prtcl-id field in the key management attribute.
* The key management data from the keymgmt-data field MUST be * The key management data from the keymgmt-data field MUST be
extracted and given to the key management protocol. Note that extracted and given to the key management protocol. Note that
depending on key management protocol, some extra parameters might depending on key management protocol, some extra parameters might
of course be requested, such as the source/destination network of course be requested, such as the source/destination network
address/port(s) for the specified media. address/port(s) for the specified media.
* Depending on the outcome of the key management processing (i.e. * Depending on the outcome of the key management processing (i.e.
whether it was accepted or not), the processing can proceed whether it was accepted or not), the processing can proceed
according to normal processing (e.g. according to the offer/answer according to normal processing (e.g. according to the offer/answer
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Note that the attribute MAY be repeated more than once (e.g., one at Note that the attribute MAY be repeated more than once (e.g., one at
session level and one at media level). Consequently, the process is session level and one at media level). Consequently, the process is
repeated for each key management attribute detected. repeated for each key management attribute detected.
If more than one key management protocol is supported, multiple If more than one key management protocol is supported, multiple
instances of the key management attribute MAY be included in the instances of the key management attribute MAY be included in the
initial offer, each transporting a different key management data, initial offer, each transporting a different key management data,
thus indicating alternatives supported. thus indicating alternatives supported.
If the sender includes more than one key management attributes at If the sender includes more than one key management protocol
session level (analogous for the media level), these SHOULD be listed attributes at session level (analogous for the media level), these
in order of preference (with the first being the preferred). The SHOULD be listed in order of preference (with the first being the
receiver chooses the key management protocol it supports. When preferred). The receiver chooses the key management protocol it
answering, only the accepted key management attribute MUST be supports. When answering, only the accepted key management protocol
included. If the receiver does not support any of the sender's attribute MUST be included. If the receiver does not support any of
suggested key management protocols, the receiver answers with an the sender's suggested key management protocols, the receiver answers
error message (see SIP and RTSP), possibly also listing the supported with an error message (see SIP and RTSP), whereby the sender MUST put
key management protocols (without any data included). down the current setup procedure.
However, the offerer is RECOMMENDED to include only one of the
protocols for a specific media. If the answerer cannot support the
proposed protocol, it rejects the offer.
Note that by placing multiple key management offers in a single Note that by placing multiple key management offers in a single
message has the disadvantage that the message expands and the message has the disadvantage that the message expands and the
computational workload for the offerer will increase drastically. It computational workload for the offerer will increase drastically. The
might be acceptable to use a trial and error approach if the number possibility to support multiple key management protocols may
of key management protocols supported are few. The possibility to introduce bidding down attacks. To avoid this, the list of
support multiple key management protocols may introduce bidding down identifiers of the proposed key management protocols MUST be
attacks. It is therefore important that the local policy considers authenticated, which MUST be done by each key management. This puts
this (e.g., only allows protocols that from a security point of view the requirement that it MUST be specified (in the key management
are equivalent, to be negotiated). protocol itself or in a companion document) how the protocol
identifiers could be authenticated from the offerer to the responder
What can be done to increase the likelihood for a successful setup is by the use of the specific key management protocol. Note that even if
to use a capability discovery mechanism (e.g., used in SIP when using only one key management protocol is used, that still must
the OPTION message). In this case, the key management protocols authenticate its own protocol identifier.
supported are expressed at session level without any data (i.e., a
list of only the key-mgmt:<name> part is used).
v=0 If more than one protocol is supported by the offerer, it is
o=alice 2891092738 2891092738 IN IP4 lost.somewhere.com RECOMMENDED that he offers all to him acceptable protocols in the
c=IN IP4 lost.somewhere.com first offer, rather than making single, subsequent alternative offers
a=key-mgmt:mikey in response to error messages, see "Security Considerations".
a=key-mgmt:coolxchg
m=audio 0 RTP/SAVP 98
a=rtpmap:98 AMR/8000
m=video 0 RTP/SAVP 31 34
a=rtpmap:31 H261/90000
a=rtpmap:34 H263/90000
3.2. SIP usage 3.2. SIP usage
The offerer SHOULD include the key management data within an offer The offerer SHOULD include the key management data within an offer
that contains the media description it should apply to. The answerer that contains the media description it should apply to. The answerer
MUST check with the key management protocol if the attribute values MUST check with the key management protocol if the attribute values
are valid, and then obtain from the key management the data to are valid, and then obtain from the key management the data to
include in the answer. include in the answer.
If the offer is not accepted, the answerer SHOULD return a "606 Not If the offer is not accepted, the answerer SHOULD return a "606 Not
Acceptable" message, including one or more Warning headers (at least Acceptable" message, including one or more Warning headers (at least
a 306). The offerer MAY then go out with a new (different) offer, a 306). The offer MUST then abort the security setup.
depending on the local security policy.
Re-keying can be handled as a new offer, i.e. a re-INVITE should be Re-keying can be handled as a new offer, i.e. a re-INVITE should be
sent with the new proposed parameters. The answerer treats this as a sent with the new proposed parameters. The answerer treats this as a
new offer where the key management is the issue of change. In new offer where the key management is the issue of change. In
general, the re-INVITE (and the key exchange) must be finalized general, the re-INVITE (and the key exchange) must be finalized
before the security protocol can change the keys. The synchronization before the security protocol can change the keys. The synchronization
method used when changing keys are dependent on the security and key method used when changing keys are dependent on the security and key
management protocol used. management protocol used.
3.3. RTSP usage 3.3. RTSP usage
RTSP does not use the offer/answer model, as SIP does. This causes RTSP does not use the offer/answer model, as SIP does. This causes
some problems as it is not possible (without abusing RTSP) to send some problems, as it is not possible (without abusing RTSP) to send
back an answer to the server (as the server will in most cases be the back an answer to the server (as the server will in most cases be the
one initiating the security parameter exchange). To solve this, a new one initiating the security parameter exchange). To solve this, a new
header has been introduced (Section 2.2). This also assumes that the header has been introduced (Section 2.2). This also assumes that the
key management also have some kind of binding to the media, so that key management also has some kind of binding to the media, so that
the response to the server will be processed as required. the response to the server will be processed as required.
The processing of a key management header in RTSP should be done The processing of a key management header in RTSP should be done
analogous of the SDP message processing. The initial key management analogous of the SDP message processing. The initial key management
message from a server should be sent to the client using SDP. When message from a server should be sent to the client using SDP. When
responding to this, the client uses the new RTSP header to send back responding to this, the client uses the new RTSP header to send back
an answer (included in the SETUP message). If a server receives a an answer (included in the SETUP message). If a server receives a
SETUP message in which it expects a key management message, but none SETUP message in which it expects a key management message, but none
is included, a 403 Forbidden SHOULD be returned to the client. is included, a 403 Forbidden SHOULD be returned to the client,
whereby the current setup MUST be aborted.
The server MAY provide re-keying/updating facilities by sending a new The server MAY provide re-keying/updating facilities by sending a new
key management message in an ANNOUNCE messages. The ANNOUNCE message key management message in an ANNOUNCE messages. The ANNOUNCE message
contains an SDP message including the key management parameters. The contains an SDP message including the key management parameters. The
response message is put in the new RTSP header in the response from response message is put in the new RTSP header in the response from
the client to the server. Note that the ANNOUNCE messages MUST be the client to the server. Note that the ANNOUNCE messages MUST be
supported if this feature is to be used. supported if this feature is to be used.
3.4. Example scenarios 3.4. Example scenarios
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The RTSP then proceeds as usual (with e.g. a SETUP message for the The RTSP then proceeds as usual (with e.g. a SETUP message for the
video followed by a PLAY message). video followed by a PLAY message).
4. Adding further Key management protocols 4. Adding further Key management protocols
This framework cannot be used with all key management protocols. The This framework cannot be used with all key management protocols. The
key management protocol needs to comply with the requirements key management protocol needs to comply with the requirements
described in Section 3. To be able to use a key management protocol described in Section 3. To be able to use a key management protocol
with this framework, the following MUST be specified: with this framework, the following MUST be specified:
* the key management protocol name that should be used in the * the key management protocol identifier that should be used in the
protocol name fields in both SDP and RTSP (e.g. "mikey" for protocol identifier fields in both SDP and RTSP (e.g. "mikey" for
MIKEY). MIKEY).
* the information the key management needs from SDP and RTSP (Section * the information the key management needs from SDP and RTSP (Section
3 gives a guideline of what SDP and RTSP needs from the key 3 gives a guideline of what SDP and RTSP needs from the key
management). The exact API is implementation specific, but it management). The exact API is implementation specific, but it
SHOULD at least support to exchange the specified information. SHOULD at least support to exchange the specified information.
Note that in particular, the key management MUST always be given
the protocol identifier(s) of the key management protocol(s)
included in the offer in the correct order as they appear.
The key management data MUST be base64 encoded in the SDP and RTSP The key management data MUST be base64 encoded in the SDP and RTSP
fields. Therefore, considerations of possible conversion from the fields. Therefore, considerations of possible conversion from the
normal key management representation to base64 SHOULD be taken into normal key management representation to base64 SHOULD be taken into
consideration. account.
5. Security Considerations 5. Security Considerations
The nature of this document is to allow SDP and RTSP to support The nature of this document is to allow SDP and RTSP to support
security of the media sessions. It is therefore not the intention of security of the media sessions. It is therefore not a primary
this document to describe possible security solutions or to define intention of this document to describe possible security solutions or
possible security problems. The defined SDP and RTSP extensions are to define possible security problems. The defined SDP and RTSP
not believed to introduce any new security risks to SDP and RTSP. extensions are not believed to introduce any new security risks to
SDP and RTSP, if used as specified.
Note that the purpose of the key management fields is to provide Note that the purpose of the key management fields is to provide
information to secure the media streams. Under the assumption that information to secure the media streams. Under the assumption that
the key management schemes are secure, the SDP can be passed along the key management schemes are secure, the SDP can be passed along
unprotected without affecting the key management, and the media unprotected without affecting the key management, and the media
streams will still be secure even if some attackers gained knowledge streams will still be secure even if some attackers gained knowledge
of the SDP contents. of the SDP contents.
However, if the SDP messages are not sent authenticated between the However, if the SDP messages are not sent authenticated between the
parties, it is possible for an active attacker to change attributes parties, it is possible for an active attacker to change attributes
without being detected. As the key management protocol may without being detected. As the key management protocol may
(indirectly) rely on some of the session information from SDP (e.g., (indirectly) rely on some of the session information from SDP (e.g.,
address information), an attack on SDP may have indirect consequences address information), an attack on SDP may have indirect consequences
on the key management. In general, it is therefore a good thing, not on the key management. In general, it is therefore a good thing, not
only to try to secure the session, but also to secure the session only to try to secure the session, but also to secure the session
setup. setup.
Note that it is impossible to assure the authenticity of a declined
offer, since even if it comes from the true respondent, the fact that
he/she declines the offer usually means that he/she does not support
the protocol(s) offered, and consequently cannot be expected to
authenticate the response either. This means that if the initiator is
unsure of which protocol(s) the responder supports, we RECOMMEND that
the initiator offers all acceptable protocols in a single offer. If
not, this opens up the possibility for a "man-in-the-middle" (MITM)
to affect the outcome of the eventually agreed upon protocol, by
faking unauthenticated error messages until the initiator eventually
offers a protocol "to the liking" of the MITM. This is not really a
security problem, but rather a mild form of denial of service that
can be avoided by following the above recommendation.
6. IANA Considerations 6. IANA Considerations
New attribute fields for SDP (see Section 2.1) and RTSP header are New attribute fields for SDP (see Section 2.1) and RTSP header are
registered (see Section 2.2). registered (see Section 2.2).
7. Conclusions 7. Conclusions
A security solution for real-time applications needs a key management A security solution for real-time applications needs a key management
infrastructure. Integrating the key management scheme with the infrastructure. Integrating the key management scheme with the
session establishment protocol could be done efficiently in most of session establishment protocol could be done efficiently in most of
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Karl Norrman Karl Norrman
Ericsson Research Ericsson Research
SE-16480 Stockholm Phone: +46 8 4044502 SE-16480 Stockholm Phone: +46 8 4044502
Sweden EMail: karl.norrman@era.ericsson.se Sweden EMail: karl.norrman@era.ericsson.se
10. References 10. References
10.1. Normative References 10.1. Normative References
[OAM] Rosenberg, J. and Schulzrinne, H., "An Offer/Answer Model with [OAM] Rosenberg, J. and Schulzrinne, H., "An Offer/Answer Model with
SDP", Internet Draft, IETF, Work in progress (MMUSIC). the Session Description Protocol (SDP)", IETF, 3264.
[RTSP] Schulzrinne, H., Rao, A., and Lanphier, R., "Real Time [RTSP] Schulzrinne, H., Rao, A., and Lanphier, R., "Real Time
Streaming Protocol (RTSP)", IETF, RFC 2326. Streaming Protocol (RTSP)", IETF, RFC 2326.
[SDPnew] Handley, M., Jacobson, V., and Perkins, C., "SDP: Session [SDPnew] Handley, M., Jacobson, V., and Perkins, C., "SDP: Session
Description Protocol", Internet Draft, IETF, Work in progress Description Protocol", Internet Draft, IETF, Work in progress
(MMUSIC). (MMUSIC).
[SIP] Handley, M., Schulzrinne, H., Schooler, E., and Rosenberg, J., [SIP] Handley, M., Schulzrinne, H., Schooler, E., and Rosenberg, J.,
"SIP: Session Initiation Protocol", IETF, RFC 2543. "SIP: Session Initiation Protocol", IETF, RFC 2543.
skipping to change at page 12, line 44 skipping to change at page 12, line 52
Service (V5)", IETF, RFC 1510. Service (V5)", IETF, RFC 1510.
[MIKEY] Arkko, J., Carrara, E., Lindholm, F., Naslund, M., and [MIKEY] Arkko, J., Carrara, E., Lindholm, F., Naslund, M., and
Norrman, K., "MIKEY: Multimedia Internet KEYing", Internet Draft, Norrman, K., "MIKEY: Multimedia Internet KEYing", Internet Draft,
IETF, Work in progress (MSEC). IETF, Work in progress (MSEC).
[SRTP] Baugher, M., Blom, R., Carrara, E., McGrew, D., Naslund, M, [SRTP] Baugher, M., Blom, R., Carrara, E., McGrew, D., Naslund, M,
Norrman, K., and Oran, D., "The Secure Real Time Transport Protocol", Norrman, K., and Oran, D., "The Secure Real Time Transport Protocol",
Internet Draft, IETF, Work in Progress (AVT). Internet Draft, IETF, Work in Progress (AVT).
This Internet-Draft expires in December 2002. This Internet-Draft expires in August 2003.
 End of changes. 

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