Network Working Group A. B. Roach
Internet-Draft dynamicsoft
Expires: December 19, 2003 June 20, 2003
SIMPLE Buddylist Configuration Problem Statement
draft-roach-simple-blconf-00
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Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This document contains a brief discussion of a particular challenge
that exists in making users' buddy list information available when a
SIMPLE client first starts up. It also provides a very brief
analysis of various solutions to the problem.
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1. Introduction
One of the formal deliverables of the SIMPLE working group is to
provide an architecture that allows multiple interoperable
implementations to provide a traditional buddylist-based instant
messaging presence application using SIP. An informal design goal of
the working group that stems from this deliverable is that such
solutions should enable at least the same set of features as the
currently available proprietary offerings. One of the keystones in
realizing this goal is allowing developers to provide a user
experience that is as good as or better than such offerings.
One stumbling block in allowing developers to create such a user
experience is the fact that there is currently no defined way, given
a user's address of record, to retrieve a list of contacts for the
purposes of displaying presence data and conveniently sending
messages. Without such an ability, creating a user experience that
is as straightforward as those currently available is frustrated.
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2. Problem Description
Imagine a typical internet user, known for the purposes of this
description as Bob, who wants to walk into a random Internet cafe and
log into an IM client so that he can see who of his friends are
online, and begin to send and receive messages. With currently
deployed proprietary systems, Bob would be able to fire up the
client, type in his user name and his password, and be finished.
With no further interaction, Bob's presence information is changed,
servers know how to route incoming messages to Bob, Bob's buddylist
is displayed to him, and client starts receiving updates which
indicate which of his buddies are online. The underlying proprietary
protocol knows, given a user name of, e.g., "bob1963", how to perform
all of these actions.
SIMPLE currently has a hole in this area. Client creators can
acheive almost all of the effects described above using mechanisms
already defined or under development within the IETF. Assuming that
Bob remembers his user ID (sip:bob@example.com, which is nicely
mnemonic and probably matches one of his e-mail addresses) and
password (used for responses to digest challenges), the client can
send a REGISTER [1] to sip:example.com (to route messages to him),
send a PUBLISH [5] to sip:bob@example.com (to update his presence),
and send an event-list [4] aware presence [3] SUBSCRIBE [2] to get
his buddy list and the status of each buddy. The complication arises
from the fact that the client doesn't have a URI to which this
SUBSCRIBE can be sent. So, without prompting Bob for an additional
URI -- that of his buddy list -- the client is unable to provide the
service.
A failure on part the of the IETF to define an adequate mechanism to
address this problem has a very high probability of causing
individual implementors to develop their own solution on an
implementation-by-implementation basis. Even if a sufficently large
critical mass of implementations begin using the same convention,
there will almost certainly be a substantial period of time before a
widespread pattern is established. Until such a de-facto standard is
established, interoperability between independant implementations
will suffer. Further, even if the convention for such a mechanism is
eventually established, older, non-interoperable conventions will
continue to exist side-by-side with it indefinitely for reasons of
backwards compatibility.
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3. Possible Solutions
3.1 Status Quo
Currently, the accepted solution to this problem is that such
information is manally entered into the client by the user. While
this invokes only a mild startup cost whenever Bob goes to set up his
home PC (not entirely unlike configuring the POP and SMTP servers for
an e-mail client), it adds an extra step to Bob's login process when
he's in an internet cafe, at a friends house, or at any other device
that he doesn't use on a regular basis.
Chances are very good that Bob isn't going to want to remember the
additional URI for his buddy list -- or, even if he can, probably
doesn't want to go through the trouble of typing it in (in addition
to his user ID) every time he logs in from a different location.
Requiring him to do so provides an experience that is clearly
inferior to those available from proprietary solutions today.
In short, while the approach of requiring the user to enter an
additional URI to access his buddy list is a solution to the problem
of where the information comes from, it does not do so in a way that
is, from a user perspective, as good as currently available products.
Because of this added inconvenience, implementors will likely attempt
to solve the problem in a variety of non-interoperable ways, as
discussed above.
3.2 Implicit URL Binding
One approach to solving this problem is to establish a convention
that indicates how to manipulate the URI in such a way that it
indicates the resource to which the SUBSCRIBE should be sent; for
example, appending "-buddies" to the user portion ("sip:bob-
buddies@example.com") would be one such transformation, as would
using the hostname portion (e.g. "sip:bob@buddies.example.com").
While acceptable from a technical perspective, this approach runs
afoul of several philosophical objections and has some suboptimal
characteristics. The prime philosophical objection is the supposed
property that URIs are (with certain well-defined exceptions) treated
as opaque by clients who use them. Establishing a convention that
describes specific transformations of the URI violates this property.
Suboptimal characteristics of any implicit approach include relics
such as requiring the user's registrar to handle buddy list services
and limiting users to having a single, centrally managed buddy list.
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3.3 User Configuration Retrieval
Another approach to solving the problem under discussion is to allow
the URI for the buddy list itself to be retrieved from the user's
home domain server (e.g. example.com). Doing so provides an
explicit way of indicating from where to retrieve the list. This
approach is, in spirit, similar to that defined for device
configuration [6]; specifically, a subscription would be sent to the
user's address-of-record for an event package that contains user
configuration data. One component of the user's configuration
information would be a URI (or possibly even URIs) that indicate from
where the user's buddy list could be retrieved.
In addition to providing a clear mechanism for unambiguously
identifying a user's buddy list, this mechanism has the additional
properties that it allows buddy lists to be hosted by a domain other
than that of the user's registrar, and that it allows users to have
multiple buddy lists configured. Finally, this approach can be
specified in such a way that it allows inclusion of additional user-
profile information if needed, such as a URI for message waiting
indication [7].
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4. Acknowledgements
Thanks to Paul Tidwell for first raising the issue discussed in this
document. Steve Donovan, Robert Sparks, and Dean Willis contributed
to early conversations on the topic.
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References
[1] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002.
[2] Roach, A.B., "Session Initiation Protocol (SIP)-Specific Event
Notification", RFC 3265, June 2002.
[3] Rosenberg, J., "Session Initiation Protocol (SIP) Extensions for
Presence", draft-ietf-simple-presence-07 (work in progress), May
2002.
[4] Roach, A.B., Rosenberg, J. and B. Campbell, "A Session Initiation
Protocol (SIP) Event Notification Extension for Resource Lists",
draft-ietf-simple-event-list-04 (work in progress), June 2003.
[5] Campbell, B., Olson, S., Peterson, J., Rosenberg, J. and B.
Stucker, "SIMPLE Presence Publication Mechanism", draft-ietf-
simple-publish-00 (work in progress), February 2003.
[6] Petrie, D., "A Framework for SIP User Agent Configuration",
draft-ietf-sipping-config-framework-00 (work in progress), Feb
2003.
[7] Mahy, R., "A Message Summary and Message Waiting Indication
Event Package for the Session Initiation Protocol (SIP)", draft-
ietf-sipping-mwi-02 (work in progress), March 2003.
Author's Address
Adam Roach
dynamicsoft
5100 Tennyson Pkwy
Suite 1200
Plano, TX 75024
US
EMail: adam@dynamicsoft.com
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