draft-ietf-mmusic-kmgmt-ext-00.txt   draft-ietf-mmusic-kmgmt-ext-01.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: May 2002 M. Naslund Expires: July 2002 M. Naslund
K. Norrman K. Norrman
Ericsson Ericsson
November, 2001 January, 2002
Key Management Extensions for SDP and RTSP Key Management Extensions for SDP and RTSP
<draft-ietf-mmusic-kmgmt-ext-00.txt> <draft-ietf-mmusic-kmgmt-ext-01.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
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skipping to change at page 1, line 36 skipping to change at page 1, line 36
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Abstract Abstract
Work for securing real-time applications have started. It has also
brought toward the need for a key management infrastructure to
support the security protocol.
This document defines extensions for SDP and RTSP to carry the This document defines extensions for SDP and RTSP to carry the
security information needed by a key management protocol, in order to security information needed by a key management protocol, in order to
secure the media stream itself. secure the media stream. Indications are also given on how it should
be used together with SIP and RTSP.
TABLE OF CONTENTS TABLE OF CONTENTS
1. Introduction..................................................2 1. Introduction..................................................2
1.1. Notational Conventions......................................3 1.1. Notational Conventions......................................3
2. SDP Attribute Fields for Key Management.......................3 2. Extensions to SDP and RTSP.................................... 3
2.1. SDP Grammar.................................................4 2.1. SDP Extensions.............................................. 3
2.2. SDP in SIP and RTSP.........................................5 2.2. RTSP Extensions............................................. 4
3. RTSP Header and Grammar.......................................5 3. Usage with SIP and RTSP....................................... 5
4. Security Considerations.......................................6 3.1. SIP usage................................................... 5
5. IANA Considerations...........................................6 3.2. RTSP usage.................................................. 5
6. Conclusions...................................................7 3.3. Example scenarios........................................... 6
7. Acknowledgments...............................................7 4. Security Considerations....................................... 8
8. Author's Addresses............................................7 5. IANA Considerations........................................... 9
9. References....................................................7 6. Conclusions................................................... 9
7. Acknowledgments............................................... 9
8. Author's Addresses............................................ 9
9. References....................................................10
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.
The Session Description Protocol [SDP] is used to convey The focus in the following sections is to describe SDP attribute
advertisements of conference sessions and communicate the relevant extensions and RTSP header extensions to support key management, and
conference setup information to prospective participants. SDP is a possible integration within SIP and RTSP.
intended to use different transport protocols as appropriate, e.g.
the Session Initiation Protocol [SIP] and the Real-Time Streaming
Protocol [RTSP].
An efficient way of performing key management is to integrate it into
SDP. This approach may reduce the number of roundtrips compared to a
standalone key management scheme (and in some cases it could also
reduce the total bandwidth consumption). However, to make it possible
to integrate the key management protocol (e.g. [MIKEY]) into SDP, a
set of attributes in SDP is needed. Such a set of attributes is
defined in this document to support integrated media stream key
management.
Currently in SDP, one field exists to transport keys, i.e. the "key="
field. However, this is not enough for a key management protocol.
There MUST exist the possibility to include not only the key, but
also the key encrypted, encryption parameters, security protocol
parameters, and at the same time have it all authenticated. This can
not be done with the "key=" field as specified today.
In RTSP, the SDP description is mainly used in the response to the
DESCRIBE method. This makes it hard to send key management messages
back from the client to the server. Therefore, this draft also
defines an RTSP header that may be used to carry additional key
management messages.
1.1. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in RFC-2119.
2. SDP Attributes for Key Management
This subsection describes common attributes that are to be included Some of the motivations to include the key management in the session
in the SDP description when an integrated key management protocol is establishment are:
used. All attribute values MUST follow the general SDP guidelines.
The attributes are designed to give a minimal impact on SDP, i.e. * Just as the codec information is a description of how to encode
only a minimal set of "knowledge" MUST be built into an existing SDP and decode the audio (or video) stream, the key management data
stack in order to support the key management. is a description of how to encrypt and decrypt the data.
Three SDP attributes are defined. * The possibility to negotiate the security for the entire
multimedia session at the same time.
To be able to detect the key management protocol applied, this MUST * The knowledge of the media at the session establishment makes it
be signaled by: easy to tie the key management to the multimedia sessions.
a=keymgmt-prot:<protocol> * This approach may be more efficient than setting up the security
later, as that approach might force extra roundtrips, possibly
also a separate set-up for each stream, hence implying more delay
to the actual setup of the media session.
The key management protocol data MUST be provided in the following Currently in SDP [SDP], one field exists to transport keys, i.e. the
field: "key=" field. However, this is not enough for a key management
protocol. The approach here is to use and extend the SDP description
to transport the key management offer/answer and also to associate it
with the media sessions. SIP uses the offer/answer model [OAM]
whereby extensions to SDP will be enough. An extra RTSP header is
also defined.
a=keymgmt-data:<key-transport-data> 1.1. Notational Conventions
Note that the data MUST be encoded in a way so that it complies with The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
the normal SDP rules. "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119.
In case the key management mechanism does not provide authentication 2. Extensions to SDP and RTSP
of the key management part, additional authentication data MAY be
provided in the "keymgmt-auth" field.
a=keymgmt-auth:<key-auth-data> This section describes common attributes that are to be included in
an SDP description or in an RTSP header when an integrated key
management protocol is used. All attribute values MUST follow the
general SDP or RTSP guideline.
The key management attributes may be defined both at the session For the SDP description, the key management attributes may be defined
level (i.e. before the media descriptor lines) and at the media level at session level (i.e. before the media descriptor lines) and/or at
of the SDP description. If the key management attributes are defined media level. If the key management attributes are defined at media
at media level, it 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.
Example 1 (session level) The extensions were defined in a way to:
a=keymgmt-prot:MIKEY * give a minimal impact on current SDP implementations, i.e. only
a=keymgmt-data:uiSDF9sdhs727ghsd/dhsoKkdOokdo7eWsnDSJD... minimal modifications MUST be built into an existing SDP stack in
m=audio 49000 RTP/SAVP 98 order to support the key management.
a=rtpmap:98 AMR/8000
m=video 2232 RTP/SAVP 31
In this example, MIKEY is negotiating the crypto suite for both * make it easy to use another key management protocol, or a new
streams at session level. It is recommended to use this approach if version, without having to redefine the attributes or add new
possible to save both bandwidth and computational resources. ones.
Example 2 (media level) The following set of attributes have been identified as necessary to
support:
m=audio 49000 RTP/SAVP 98 * key management protocol identifier, to indicate the key
a=keymgmt-prot:MIKEY management protocol used ('keymgmt-prtcl')
a=keymgmt-data:uiSDF9sdhs727ghsd/dhsoKkdOokdo7eWsnDSJD...
a=rtpmap:98 AMR/8000
m=video 2232 RTP/AVP 31
Note that the video part in this example is not protected by any * key management raw data field, to transport the key management
security protocol. protocol data ('keymgmt-data')
2.1. SDP Grammar * in the case of SDP, an extra (optional) authentication attribute
to be able to tie the key management data to the surrounding
media definitions ('key-extra-auth').
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 [SDP]) for the key management extensions to SDP. (as used in [SDP]) 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
Three new attributes are defined, keymgmt-prtcl, keymgmt-data, and Three new attributes are defined, keymgmt-prtcl, keymgmt-data, and
key-extra-auth. key-extra-auth.
keymgmt-prtcl = "keymgmt-prot:" prtcl-name keymgmt-prtcl = "keymgmt-prot:" prtcl-name
prtcl-name = 1*(alpha-numeric|SAFE) prtcl-name = 1*(safe)
; e.g. "MIKEY" ; e.g. "MIKEY"
keymgmt-data = "keymgmt-data:" byte-string keymgmt-data = "keymgmt-data:" byte-string
key-extra-auth = "keymgmt-auth:" byte-string key-extra-auth = "keymgmt-auth:" byte-string
byte-string = 1*(0x01..0x09|0x0b|0x0c|0x0e..0xff) where safe and byte-string are as defined in SDP [SDP].
;any byte except NUL, CR or LF
alpha-numeric = ALPHA | DIGIT
DIGIT = "0" | POS-DIGIT 2.2. RTSP Extensions
POS-DIGIT = "1"|"2"|"3"|"4"|"5"|"6"|"7"|"8"|"9" To support the three different attributes described, the following
RTSP header is defined:
ALPHA = "a"|"b"|"c"|"d"|"e"|"f"|"g"|"h"|"i"|"j"|"k"| KeyMgmt = "KeyMgmt" ":" [stream-url] protocol data
"l"|"m"|"n"|"o"|"p"|"q"|"r"|"s"|"t"|"u"|"v"|
"w"|"x"|"y"|"z"|"A"|"B"|"C"|"D"|"E"|"F"|"G"|
"H"|"I"|"J"|"K"|"L"|"M"|"N"|"O"|"P"|"Q"|"R"|
"S"|"T"|"U"|"V"|"W"|"X"|"Y"|"Z"
SAFE = "\$" | "-" | "_" | "." | "+" stream-url = "url" "=" url ";"
2.2. SDP in SIP and RTSP protocol = "Prot" "=" token ";"
Both SIP and RTSP provide means to transport SDP descriptions. This data = "Data" "=" quoted-string
section gives a recommendation of how/when to include key management
initiated SDP descriptions in SIP and RTSP.
For SIP, the recommendation is to use the Invite message (and the url, token and quoted-string are as defined in the RTSP specification
following response) to transport the SDP description with the key [RTSP]. The url indicates the stream URL, which the parameters
management parameters. correspond to.
For RTSP, the recommendation is to let the server include a SDP The KeyMgmt header should be possible to use in both request and
description with the key management parameters in the response to a response messages of the following methods:
DESCRIBE message. A problem with RTSP is that no SDP description can * DESCRIBE
be assumed to be sent back to the server. Therefore, other means to * ANNOUNCE
send key management messages between client and server is needed. * SETUP
This may be solved by using the new RTSP header defined in Section 3. * PLAY
* RECORD
* SET_PARAMETER
* GET_PARAMETER
* OPTIONS
In general, any key management protocol using SDP as a mean of 3. Usage with SIP and RTSP
transport, MUST not require a great number of exchange messages. It
is RECOMMENDED that the key management protocol does not use more
than one roundtrip. This is to create as small (if any) impact as
possible on the underlying transporting mechanism (e.g., SIP and
RTSP).
3. RTSP Header and Grammar This section gives recommendations of how/when to include the defined
key management attributes when SIP and/or RTSP are used together with
SDP.
To support the three different parameters described in Section 2, a Some general requirements MUST be set on the key management protocol
new RTSP header is defined. if it has to be suitable to work together with SIP and RTSP:
KeyMgmt = "KeyMgmt" ":" [stream-url] protocol data [auth] * It MUST be possible to execute the key management protocol in at
most one roundtrip in case the answerer accepts the offer.
stream-url = "url" "=" url ";" * The protocol MUST return, to SDP/RTSP, a valid answer whether the
provided offer was accepted or not.
protocol = "Prot" "=" prtcl-name * There MUST be a possibility for the key management protocol to
data = ";" "Data" "=" string tie the media sessions to the negotiated parameters (i.e. an
interface between the key management and the SDP and RTSP
implementation MUST exist).
auth = ";" "Auth" "=" string Today, the MIKEY protocol has adopted the key management extensions
to work together with SIP and RTSP. Other protocols may use the
described attributes and header, e.g. Kerberos.
string = 1*(alpha-numeric|SAFE|"=") 3.1. SIP usage
alpha-numeric, SAFE and prtcl-name are as defined in Section 2.1. The The offerer should include the key management data within an offer
url indicates the stream URL for which the parameters correspond to. that contains the media description it should apply to. The answerer
It is recommended that the string is a base64 encoded value. MUST check with the key management protocol if the attribute values
are valid, and then obtain from the key management the data to
include in the answer. If the offer is not accepted, the answerer
returns a notification message and the offerer may go out with a new
(different) offer, depending on the local security policy.
The new key management header should be possible to use in both Re-keying should be handled as a new offer, i.e. a re-INVITE should
request and response messages of the following methods: be sent with the new proposed parameters. The answerer treats this as
* ANNOUNCE a new offer where the key management is the issue of change.
* SETUP
* PLAY
* RECORD
* SET_PARAMETER
* GET_PARAMETER
* OPTIONS
When a key management protocol is enabled in the RTSP implementation, 3.2. RTSP usage
it MUST for each message to be sent (that may contain the KeyMgmt
header), check with the key management protocol if any parameters(s) RTSP does not use the offer/answer model, as SIP does. This causes
should be include in the header (i.e. the Data or Auth parameter). some problems as it is not possible (without abusing RTSP) to send
For each message received (that contains the KeyMgmt header), the key back an answer to the server (as the server will in most cases be the
management parameters (Data and Auth) are passed to the key one initiating the security parameter exchange). To solve this, a new
management protocol for processing. header has been introduced (Section 2.2).
The initial key management 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 an answer (included in either the SETUP
or the PLAY message).
The server may provide re-keying facilities by sending a new key
management message in a SET_PARAMETER or ANNOUNCE messages. In the
latter, the RTSP header is not used if the ANNOUNCE message includes
a SDP description where the data can be provided in. The response
message is then put in the new RTSP header in the response message
from the client to the server. Note that the SET PARAMETER and the
ANNOUNCE messages are not mandatory to support for the servers.
3.3. Example scenarios
Example 1 (SIP)
A SIP call is taking place between Alice and Bob. Alice sends an
Invite message consisting of the following offer:
v=0
o=alice 2891092738 2891092738 IN IP4 lost.somewhere.com
s=Cool stuff
e=alice@w-land.org
t=0 0
c=IN IP4 lost.somewhere.com
a=keymgmt-prot:MIKEY
a=keymgmt-data:uiSDF9sdhs727ghsd/dhsoKkdOokdo7eWsnDSJD...
m=audio 49000 RTP/SAVP 98
a=rtpmap:98 AMR/8000
m=video 52230 RTP/SAVP 31
a=rtpmap:31 H261/90000
i.e. Alice proposes to set up one audio stream and one video stream
that run over SRTP. To set up the security parameters for SRTP, she
uses MIKEY. Note that MIKEY is negotiating the crypto suite for both
streams (as it is placed at the session level).
Bob accepts the offer and sends an answer back to Alice:
v=0
o=bob 2891092897 2891092897 IN IP4 found.somewhere.com
s=Cool stuff
e=bob@null.org
t=0 0
c=IN IP4 found.somewhere.com
a=keymgmt-prot:MIKEY
a=keymgmt-data:skaoqDeMkdwRW278HjKVB...
m=audio 49030 RTP/SAVP 98
a=rtpmap:98 AMR/8000
m=video 52230 RTP/SAVP 31
a=rtpmap:31 H261/90000
Example 2 (SDP)
This example shows how Alice would have done in the previous example
if she wished to protect only the audio stream.
v=0
o=alice 2891092738 2891092738 IN IP4 lost.somewhere.com
s=Cool stuff
e=alice@w-land.org
t=0 0
c=IN IP4 lost.somewhere.com
m=audio 49000 RTP/SAVP 98
a=rtpmap:98 AMR/8000
a=keymgmt-prot:MIKEY
a=keymgmt-data:uiSDF9sdhs727ghsd/dhsoKkdOokdo7eWsnDSJD...
m=video 52230 RTP/AVP 31
a=rtpmap:31 H261/90000
Example 3 (RTSP)
A client wants to set up a streaming session and requests a media
description from the streaming server.
DESCRIBE rtsp://server.example.com/fizzle/foo RTSP/1.0
CSeq: 312
Accept: application/sdp
From: user@client.com
The server sends back an OK message including a SDP description. As
the server
RTSP/1.0 200 OK
CSeq: 312
Date: 23 Jan 1997 15:35:06 GMT
Content-Type: application/sdp
v=0
o=actionmovie 2891092738 2891092738 IN IP4 movie.somewhere.com
s=Action Movie
e=action@movie.somewhere.com
t=0 0
c=IN IP4 movie.somewhere.com
a=keymgmt-prot:MIKEY
a=keymgmt-data:uiSDF9sdhs727ghsd/dhsoKkdOokdo7eWsnDSJD...
m=audio 0 RTP/SAVP 98
a=rtpmap:98 AMR/8000
control:rtsp://movie.somewhere.com/action/audio
m=video 0 RTP/SAVP 31
a=rtpmap:31 H261/90000
control:rtsp://movie.somewhere.com/action/video
The client is now ready to setup the sessions. It includes the key
management data in the first message going back to the server (i.e.
the SETUP message).
SETUP rtsp://movie.somewhere.com/action/audio RTSP/1.0
CSeq: 313
Transport: RTP/SAVP/UDP;unicast;client_port=3056-3057
KeyMgmt: Prot=MIKEY;Data="skaoqDeMkdwRW278HjKVB..."
The server processes the request including checking the validity of
the key management header.
RTSP/1.0 200 OK
CSeq: 313
Session: 12345678
Transport: RTP/SAVP/UDP;unicast;client_port=3056-3057;
server_port=5000-5001
The RTSP is then proceeded as usual (with e.g. a SETUP message for
the video followed by a PLAY message).
4. Security Considerations 4. Security Considerations
The nature of this document is to allow SDP and RTSP support for 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 the intention of
this document to describe possible security solution nor define this document to describe possible security solution or to define
possible security problems. The defined SDP and RTSP extensions are possible security problems. The defined SDP and RTSP extensions are
not believed to introduce any new security risks to SDP and RTSP. not believed to introduce any new security risks to SDP and RTSP.
The 'key-extra-auth' attribute may be (optionally) used to guarantee
an authenticated binding between the session(s) and the security
parameters, e.g. authenticating both the key management lines and
(parts of) the surrounding SDP description. Each key management
specifies the coverage of such 'key-extra-auth' attribute. A denial-
of-service attack may be open if such authenticated binding is not
provided. Note however, the 'key-extra-auth' cannot work when NATs
are present.
Note that the purpose of the key management fields is to secure the Note that the purpose of the key management fields is to secure the
media streams themselves. Provided that the key management schemes media streams themselves. Under the assumption that the key
are secure, the SDP payloads can be passed along unprotected, and the management schemes are secure, the SDP payloads can be passed along
media streams will still be secure even if some attackers gained unprotected, and the media streams will still be secure even if some
knowledge of the SDP contents. There may, however, be other reasons attackers gained knowledge of the SDP contents. There may however, be
to protect the SDP payloads such as preventing attackers from gaining other reasons to protect the SDP payloads such as preventing
any information regarding the session or the used equipment. attackers from gaining any information regarding the session or the
used equipment.
5. IANA Considerations 5. IANA Considerations
Three new attributes fields for SDP (see Section 2) and one new RTSP Three new attributes fields for SDP (see Section 2.1) and one new
header are registered (see Section 3). RTSP header are registered (see Section 2.2).
6. Conclusions 6. 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
the scenarios. This document defines extensions to SDP and RTSP so the scenarios. A set of new attributes and headers have been defined
that it will be possible to integrate a key management protocol (e.g. in SDP and RTSP so that it will be possible to integrate a key
MIKEY) into protocol such as SIP and RTSP. management protocol (e.g. MIKEY) into SIP and RTSP.
7. Acknowledgments 7. Acknowledgments
Thanks to: Joerg Ott, Colin Perkins, Magnus Westerlund, and the rest Thanks to: Rolf Blom, Joerg Ott, Colin Perkins, Magnus Westerlund,
involved in the MMUSIC WG and the MSEC WG. and the rest involved in the MMUSIC WG and the MSEC WG.
8. Author's Addresses 8. Author's Addresses
Jari Arkko Jari Arkko
Ericsson Ericsson
02420 Jorvas Phone: +358 40 5079256 02420 Jorvas Phone: +358 40 5079256
Finland Email: jari.arkko@ericsson.com Finland Email: jari.arkko@ericsson.com
Elisabetta Carrara Elisabetta Carrara
Ericsson Research Ericsson Research
skipping to change at page 8, line 5 skipping to change at page 10, line 11
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
9. References 9. References
[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).
[OAM] Rosenberg, J. and Schulzrinne, H., "An Offer/Answer Model with
SDP", Internet Draft, IETF, Work in progress (MMUSIC).
[RTSP] Schulzrinne, H., Rao, A., and Lanphier, R., "Real Time [RTSP] Schulzrinne, H., Rao, A., and Lanphier, R., "Real Time
Streaming Protocol (RTSP)", RFC 2326, April 1998. Streaming Protocol (RTSP)", RFC 2326, April 1998.
[SDP] Handley, M., and Jacobson, V., "Session Description Protocol [SDP] Handley, M., and Jacobson, V., "Session Description Protocol
(SDP)", IETF, RFC2327 (SDP)", IETF, RFC2327
[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, RFC2543. "SIP: Session Initiation Protocol", IETF, RFC2543.
[SRTP] Blom, R., Carrara, E., McGrew, D., Naslund, M, Norrman, K., [SRTP] Blom, R., Carrara, E., McGrew, D., Naslund, M, Norrman, K.,
and Oran, D., "The Secure Real Time Transport Protocol", Internet and Oran, D., "The Secure Real Time Transport Protocol", Internet
Draft, IETF, Work in Progress (AVT). Draft, IETF, Work in Progress (AVT).
This Internet-Draft expires in May 2002. This Internet-Draft expires in July 2002.
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