Internet DRAFT - draft-burger-imap-chanuse
draft-burger-imap-chanuse
Network Working Group E. Burger
Internet Draft SnowShore Networks, Inc.
Document: draft-burger-imap-chanuse-00.txt February 2002
Category: Informational
Expires: August 2002
IMAP CHANNEL Use Cases
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026 [1].
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1. Abstract
This document describes different use cases for using the IMAP
CHANNEL facility.
Discussion of this and related drafts are on the IMAP Voice list.
To subscribe, send the message "subscribe" to
ietf-imap-voice-request@imc.org .
2. Conventions used in this document
This document refers generically to the sender of a message in the
masculine (he/him/his) and the recipient of the message in the
feminine (she/her/hers). This convention is purely for convenience
and makes no assumption about the gender of a message sender or
recipient.
FORMATTING NOTE: Notes, such at this one, provide additional
nonessential information that the reader may skip without missing
anything essential. The primary purpose of these non-essential
notes is to convey information about the rationale of this document,
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or to place this document in the proper historical or evolutionary
context. Readers whose sole purpose is to construct a conformant
implementation may skip such information. However, it may be of use
to those who wish to understand why we made certain design choices.
2.1. Definitions
2.1.1. Keywords
The keywords "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].
2.1.2. Jitter
Jitter is the variation of inter-arrival times for a packet stream.
Say a source generates a stream at a constant rate, such as one
packet every 20ms. Then the jitter is the variation away from 20ms
per packet from the packet inter-arrival time at the destination.
2.1.3. Latency
Latency is the amount of time a packet takes to transit an
operation. An operation can be transport, such as the terrestrial
transmission delay and router queue delays. An operation can also
be transformation, such as transcoding a stream from one format to
another or mixing a set of streams to create a new stream.
2.1.4. Real-Time Stream
A real-time stream is a packet flow characterized by having hard
requirements for latency, jitter, or both. For example, a
unidirectional voice flow requires almost no jitter. A bi-
directional voice flow requires almost no jitter and an end-to-end
latency of ideally less than 150ms and absolutely less than 200ms.
2.1.5. IMAP Store
2.1.6. Client Device
2.1.7. Media Server
3. Introduction
This document describes different use cases for using the IMAP
CHANNEL [3] facility.
4. Use Cases
Here is a set of useful use cases.
4.1. Conventional Message Store in Real-Time Network
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Conventional message stores typically run on general-purpose
computing hardware. Such platforms are very good at general storage
management and the data base management needed for keeping track of
user's profiles and messages. In addition, most general-purpose
computing platforms are rather efficient at retrieving large disk
blocks and transmitting and receiving relatively large network
packets (e.g. 8KB blocks).
For a variety of architectural reasons, general-purpose platforms
are rather inefficient for streaming low-latency, low-jitter
streams. Not only is the jitter unpredictable, the number of
simultaneous streams such a platform can support may be unacceptably
small.
The IMAP CHANNEL facility allows the network a mechanism for serving
IMAP messages with real-time delivery constraints. Here is an
exemplary configuration.
imap.sp.net
+---------+
IMAP | IMAP |
+--------+ ------------------------------>| Store |
| Client |/ ms.sp.net +---------+
| Device |<---\ SIP +--------+ ^
+--------+ \=============| Media | __| HTTP
| Server |---/
+--------+
In this example, the client issues a request to the IMAP store for
an object. The client knows that it needs real-time playback. The
client can know this, for example, if it knows the object is a
multimedia object. The client can determine this by convention
(e.g., the only message types stored are multimedia objects) or from
examining the content-type of the body part. Since the client
requires real-time playback of the object, it issues an IMAP CHANNEL
request, requesting an appropriate protocol, such as SIP [4] or RTSP
[5], for control of the object transport. In the example above, the
client asks for a SIP stream by issuing the following IMAP CHANNEL
request.
C: 927 CHANNEL (sip:) (2 3.2)
This requests the server to fetch section 3.2 from body part 2. The
client requests SIP as the return mechanism.
The server responds with a URI that is opaque to the client. Here
is an example using SIP netann [6].
S: * 1 CHANNEL 2 \
sip:annc@ms.sp.net;play=http://imap.sp.net/cgi-bin/get-obj?1af4e92
S: 927 OK done
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4.2. Clients Configured With "Close" Hosts
Clients, such as 3G wireless mobile terminals, can retrieve RTSP,
but may have limitations on which servers they can communicate with.
Likewise, the client may have a preferred set of hosts. Here is an
exemplary configuration.
imap.sp.net
IMAP
Store
Client close.sp.net
Device Close
Media far.other.com
Server Very
Far
far.sp.net Media
Far Server
Media
Server
In this example, the client issues a request to the IMAP for the
object. The client, through means outside IMAP, knows the
"distance" to the relevant media servers. The client issues the
following IMAP CHANNEL request.
C: 1023 CHANNEL (rtsp://close.sp.net
rtsp://far.sp.net
rtsp: imap:) (2 3.2) (9 1) (11 4.5)
This requests the server to fetch section 3.2 from message 2,
section 1 from message 9, and section 4.5 from message 11, with the
preferred order of servers for retrieving the object. Note the
listing of the partial-URI is for readability. An actual request
would have a space-separated list.
The server responds with (a set of) URI. Here is an example
response.
S: * 2 CHANNEL 3.2 rtsp://far.sp.net/playback/431987
S: * 9 CHANNEL 1 rtsp://close.sp.net/v531hn034f
S: * 11 CHANNEL 4.5 rtsp://far.other.com/m11p4e5.gsm \
rtsp://imap.sp.net/m11p4e5.au
S: 1023 OK done
The first response shows that the server could not satisfy the
request at the close media server, but could at the far one. The
second response shows that the server could satisfy the request from
the close media server. The third response show a copy available in
another domain and a copy on the IMAP server itself. Note that the
determination of whether to send a list or not is up to the IMAP
server.
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4.3. Transcoding Service
A description of a transcoding service, for example, from MS-GSM to
G.726, goes here.
4.4. Cluster Server
A description of using a proxy server and a media server to front
end a cluster of message stores goes here.
5. Security Considerations
Security will be a very important part of unified messaging. In
addition to the security issues present in Internet Mail, people
have higher expectations for Voice and Fax messaging. The goal,
wherever possible, is to preserve the semantics of existing
messaging systems and meet the expectations of users with respect to
security and reliability.
6. References
1 Bradner, S., "The Internet Standards Process -- Revision 3", BCP
9, RFC 2026, October 1996.
2 Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997
3 Hole, S., Nerenberg, L., and Leiba, B., "IMAP4 Channel Transport
Mechanism", draft-nerenberg-imap-channel-01.txt, November 2001,
work in progress
4 Rosenberg , J., et. al., "SIP: Session Initiation Protocol",
draft-ietf-sip-rfc2543bis-07.txt, February 2002, work in progress
5 Schulzrinne, H., Rau, A., and Lanphier, R., "Real Time Streaming
Protocol (RTSP)", RFC 2326, April 1998
6 O'Connor, W., Burger, E., and Van Dyke, J., "Networks
Announcements with SIP", draft-burger-sipping-netann-01.txt,
November 2001, work in progress
7. Acknowledgments
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I would like to thank Greg Vaudreuil and Glen Parsons for convincing
me this is a worthwhile effort. Also to Lyndon Nerenberg for
reminding me to get this draft out!
8. Author's Address
Eric Burger
SnowShore Networks, Inc.
Chelmsford, MA
USA
Phone: +1 978/367-8403
Email: eburger@snowshore.com
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