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Keywords: technical, infrastructure, swedish, access, gateways
Network Working Group T. Eklof
Request for Comments: 2969 L. Daigle
Category: Informational October 2000
Wide Area Directory Deployment - Experiences from TISDAG
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2000). All Rights Reserved.
Abstract
The TISDAG (Technical Infrastructure for Swedish Directory Access
Gateway) project provided valuable insight into the current reality
of deploying a wide-scale directory service. This document
catalogues some of the experiences gained in developing the necessary
infrastructure for a national (i.e., multi-organizational) directory
service and pilot deployment of the service in an environment with
off-the-shelf directory service products. A perspective on the
project's relationship to other directory deployment projects is
provided, along with some proposals for future extensions of the work
(larger scale deployment, other application areas).
These are our own observations, based on work done and general
project discussions. No doubt, other project participants have their
own list of project experiences; we don't claim this document is
exhaustive!
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RFC 2969 Wide Area Directory Deployment October 2000
Table of Contents
1.0 Introduction ................................................ 2
1.1 Overview of the TISDAG project .............................. 2
1.2 Organization of this document ............................... 3
2.0 The TISDAG project itself ................................... 3
2.1 TISDAG overview ............................................ 3
2.2 Some successes .............................................. 4
2.3 Some surprises .............................................. 5
2.3.1 LDAP objectclasses and the "o" attribute .................. 6
2.3.1 The Tagged Index Object ................................... 6
2.3.3 Handling Status Messages ................................. 7
2.3.4 Deployment with Commercial Software ...................... 7
2.4 Some observations ........................................... 7
2.4.1 Participation of the WDSPs ................................ 7
2.4.2 Index Objects and Referral Index size ..................... 8
2.4.3 Index Object and Query Performance ........................ 8
2.5 Some evolutions ............................................. 9
3.0 Related Projects ............................................ 11
3.1 The Norwegian Directory of Directories (NDD) ................ 11
3.2 DESIRE Directory Services ................................... 11
4.0 Some Directions for TISDAG Next Steps ....................... 12
4.1 Security support ............................................ 12
4.2 WDSPs attributes and schemas ............................... 12
5.0 Some conclusions ............................................ 13
6.0 Security Considerations ..................................... 13
7.0 Acknowledgements ............................................ 13
8.0 Authors' Addresses .......................................... 13
9.0 References .................................................. 14
Appendix -- Specific Software Issues and Deployment Experiences.. 15
Full Copyright Statement ........................................ 18
1.0 Introduction
1.1 Overview of the TISDAG project
As described in more detail in [TISDAG], the original intention of
the TISDAG project was to provide the infrastructure for a national
whitepages directory service. To be effective, such an
infrastructure needed to address the concrete realities of end-users'
existing client software, as well as the needs of information
providers ("Whitepages Directory Service Providers" -- WDSPs). These
realities include the existence of multiple protocols (so-called
directory service access protocols, as well as more general Internet
application protocols such as HTTP and SMTP). The project was also
sensitive to the fact that WDSPs have many good reasons for being
reluctant to relinquish copies of their subscribers' personal data.
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1.2 Organization of this document
In an effort to communicate the experiences with this project, from
conception through implementation and pilot deployment, this document
is divided into 3 major sections. The first section reviews specific
lessons learned by the authors through the TISDAG project and
implementation of one conformant system. Next, some perspectives are
offered on the relationship of the TISDAG work to other large-scale
directory projects that are currently on-going, to give a sense of
how these efforts might possibly interact. Finally, some preliminary
thoughts on applying the DAG system to other applications and
deployment environments are outlined. Further suggestions for
deploying networked DAG servers (meshes) can be found in [DAG-Mesh].
More discussion of useful development of architectural principles is
provided in a separate document ([DAG++]).
2.0 The TISDAG project itself
2.1 TISDAG overview
Briefly, the technical infrastructure proposed for the TISDAG project
(see [TISDAG] for the complete overview and technical specification)
provides end-user client software with connection points to perform
basic whitepages queries. Different connection points are provided
for the various protocols end-users are likely to wish to use to
access the information -- WWW (http), e-mail (SMTP), Whois++, LDAPv2
and LDAPv3. For each client, a transaction will be carried out
within the bounds of the protocol's syntax and semantics. However,
since the TISDAG system does not maintain a replicated copy of all
whitepages information, but rather an index over the data that allows
redirection (referrals) to services that are likely to contain
responses that match the client's query, a fair bit of background
work must be done by the DAG system in order to fulfill the client's
query.
The first, and most important step, is for the system to make a query
against the DAG Referral Index -- a server containing index
information (obtained by the Common Indexing Protocol (see [CIP1,
CIP2, CIP3]) in the Tagged Index Object format (see [TIO]). This
index contains sufficient information to indicate which of the many
participating WDSPs should be contacted to complete the query.
Wherever possible, these referrals are passed back to the querying
client so that it can contact relevant WDSPs directly. This
minimizes the amount of work done by the DAG system itself, and
allows WDSPs greater visibility (which is an incentive for
participating in the system). Protocols which support referrals
natively include Whois++ and LDAPv3 -- although these may only be
referred to servers of the same protocol.
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Since many protocols do not support referrals (e.g., LDAPv2), and in
order to address referrals to servers using a protocol other than the
calling client's own, a secondary step of "query chaining" is
provided to pursue these extra referrals within the DAG system
itself. For example, if an LDAPv2 client connects to the system, a
query is made against the Referral Index to determine which WDSPs may
have answers for the query, and then resources within the DAG system
are used to pursue the query at the designated WDSPs' servers. The
results from these different services are packaged into a single
response set for the client that made the query.
The architecture that was developed in order to support the required
functionality separated the system into distinct components to handle
incoming queries from client software ("Client Access Points", or
CAPs), a referral index (RI) to maintain an index over the collected
whitepages information and provide referrals, based on actual data
queries, to WDSPs that might have relevant information, and finally
components that mediate access to WDSP whitepages servers to perform
queries and retrieve results for the client's query ("Service Access
Points", or SAPs). Several CAPs and SAPs exist within the system --
at least one for every protocol supported for incoming queries and
WDSP servers, respectively.
Designed to be implementable as separate programs, these components
interact with each other through the use of an internal protocol --
the DAG/IP. Pragmatically, the use of the protocol means that
different components can reside on different machines, for reasons of
load-balancing and performance enhancement. It also acts as a
"common language" for the CAPs, SAPs and RI to express queries and
receive results.
This outlines the planned or ideal behaviour of the system; once
designed, a pilot phase was started for the project to compare
reality against expectations. Two independent implementations of the
software were created, and a test deployment was set up within the
Swedish University Network (SUNET). More detail on the project and
its current status can be found at http://tisdag.sunet.se/.
The rest of this section outlines some conclusions drawn from making
a reality of the proposed architecture -- both successes and
surprises.
2.2 Some successes
Implementation and pilot deployment of software meeting the TISDAG
technical specification did demonstrate some important successes of
the approach.
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Most notably, the system works pretty much as expected (see
exceptions below) to provide transparent middleware for whitepages
directory services. That is, client software and WDSP servers were
minimally affected -- from the point of view of behaviour and
configuration, the DAG system looked like a server to clients, and a
client to servers.
The goal of the TISDAG project, operationally, was to be able to
provide responses to end-user queries in reasonable response times
(although not "an addressbook replacement"). The prototype systems
demonstrated some success in achieving responses within 10 seconds,
at least with the limited testbed of a configuration with 10 WDSP's
providing directory service information. More observations on system
performance are provided below.
The DAG system does demonstrate that it is possible to build
referral-level services at a national level (although the deployment
has yet to prove conclusively that it can, in its current
formulation, operate as a transparent query-fulfillment proxy
service).
The success of the implementation demonstrated that it is possible,
in some sense, to do (semantic) protocol mapping with N+M complexity
instead of NxM mappings. That is, protocol translations had to be
defined for "N" allowable end-user query access protocols to/from the
DAG/IP, and "M" supported WDSP server protocols, instead of requiring
each of the N input components to individually map to the M output
protocols.
As a correlated issue, the prototype system demonstrated some
successes with mapping between schema representations in the
different protocol paradigms -- in a large part because system's
schemas were kept simple and focused on the minimal needs to support
the base service requirements.
2.3 Some surprises
Over the span of a dozen months from the first "final" document of
the specification through the implementation and first deployment of
the software system, a few surprises did surface. These fell into
two categories: those that surfaced when the theoretical
specification was put into practice, and others that became apparent
when the resulting system was put into operation with commercial
software clients and servers.
More detail is provided in the Appendix concerning specific software
issues encountered, but some of the larger issues that surfaced
during the implementation phase are describe below.
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2.3.1 LDAP objectclasses and the "o" attribute
It came as a considerable surprise, some months into the project,
that none of the "standard" LDAP person objectclasses included
organization ("o") as an attribute. The basic assumption seems to be
that "o" will be part of the distinguished name for an entry, and
therefore there is little (if any) cause to list it out separately.
This does make it trickier to store information for people across
multiple organizations (e.g., at an ISP's directory server) and use
the organization name in query refinement. (Roland Hedberg caught
this issue, and has flagged it to the authors of the "inetorgperson"
objectclass document).
2.3.1 The Tagged Index Object
The Tagged Index Object ("TIO"), used to carry indexes of WDSP
information to the RI, is designed to have record (entry) tags to
reduce the number of false positive referrals generated when doing a
search in the RI. One of the features of the first index object
type, Whois++'s centroid (see [centroid]) was the fact that the index
object size did not grow linearly with the size of data indexed --
i.e., at some point the growth of the index object slowed as compared
to that of the underlying data set. At first glance, this also seems
to be the case for the TIO. However, as the index grows in size the
compression factor of the TIO may not achieve the same efficiency as
the centroids. One reason for this is that the tagged lists can get
quite long, depending on the ordering of the assignment of tags to
the underlying data. That is, the tagging as defined allows for a
compressed expression of tag "ranges" -- e.g., "1-500" instead of
"1,2,3,[...]500". Thus, it might be interesting to explore an
optimal "sorting" of underlying data, before applying tags, in order
to arrange the most common tokens have consecutive tags (maximal
compression of the tag lists). It's not clear if this can be done
efficiently over the entire set of records, attributes, and tokens,
but it would bear some investigation, to produce the most compressed
TIO for transmission.
Additionally, in order to make (time) efficient use of the tags in
the RI in practice, it is almost necessary to "reinflate" the index
object to be able to do joins on tag lists associated with tokens
that match. Alternatively, the compressed tag list can be stored,
and there is an additional cost associated with comparing the tag
lists for matching tokens -- i.e., list comparison operations done
outside the scope of a base database management system. There was an
unexpected tradeoff to be made.
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2.3.3 Handling Status Messages
Mapping of status messages from multiple sub-transactions into a
single status communication for the end-user client software became
something of a challenge. When chaining a query to multiple WDSPs
(though the SAPs), it is not uncommon for at least one of the WDSP
servers to return an error code or be unavailable. If one WDSP
cannot be reached, out of several referrals, should the client
software be given the impression that the query was completed
successfully, or not? Most client protocol error handling models are
not sophisticated enough to make this level of distinction clear.
2.3.4 Deployment with Commercial Software
When it then was time to test the resulting software with standard
commercial client and server software, a few more surprises came to
light (primarily in terms of these softwares' expected worldview and
occasional implementation shortcuts). Again, more detail is provided
in the Appendix, but highlights included client software that could
only handle a very small subset of a protocol's defined status
message lexicon (e.g., 2 system messages supported), and client
software that automatically appended additional terms to a query
specified by the user (e.g., adding "or email=<what the user typed in
to the query>").
2.4 Some observations
2.4.1 Participation of the WDSPs
One of the things that came to light was that the nature of the index
object generated by the WDSPs has an important impact on performance
-- both in terms of integrating the index object into the Referral
Index, and in terms of efficiency of handling queries. A proposal
might be either to define more clearly how the WDSPs should generate
the CIP index object (currently left to their discretion), or to
alert individual WDSPs when their index objects are considered
substandard.
On another front, when chaining referrals to WDSP servers, some
servers perform more efficiently than others, affecting the overall
response time of the DAG system. From a service point of view, it
should also be possible to suggest to WDSP's that are consistently
slow (longer than some selected response time) that they are
substandard.
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2.4.2 Index Objects and Referral Index size
As described in more detail [complex], there are many factors that
can influence the growth factor of index objects (as more data is
indexed). That work dealt specifically with tokenized data for
Whois++ centroids, and is not immediately generalizable to all forms
of the Tagged Index Object. However, the particular structure of the
TIO used for the TISDAG project is similar enough in structure to a
centroid that the same "order of magnitude" and growth
characteristics are applicable.
Factors that affects the size of the data ("number of entries"):
. Number of generated tokens
The number of tokens generated from the directory data depends
on what is tokenized. If data is tokenized on names and
addresses (i.e. not unique data like phone numbers) a rough
estimation is that the number_of_tokens = 0.2 *
number_of_data_records. The growth is linear in the span from
a few thousand to at least 1.2 million records. The growth
should then level off since the sets of names and addresses
are finite, but the current tests have not shown a break
point.
If data is tokenized on something that is unique, e.g. phone
numbers, then a rough estimation is that the number_of_tokens
= number_of_data_records. Note that it is possible to tokenize
in different ways, for example divide the phone numbers in
parts. This would result in fewer tokens.
. Number of directories
Since the tokens are generated individually for each
directory, the data size depends on the number of directories.
10 directories with 100.000 records will generate the same
amount of tokens as one directory with 1.000.000 records.
2.4.3 Index Object and Query Performance
Factors that affects the performance ("queries/second"):
. Type of query (exact, substring, etc.)
A 'substring' query is slower than an 'exact' query due to:
1) somewhat slower look-up in the internal DAG database than
an exact query.
2) Mostly, a larger amount of data is fetched from the
internal DAG database due to more hits, which generates
more index processing.
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3) Substring queries are sent to the directory servers which
also results in more hits and more data fetched. The
directory servers may also be more or less effective in
handling substring queries.
. Number of search attributes
A query with one or few attributes will most of the time
result in many hits, which results in a lot of data, both
internally in DAG and from the directory servers. On the other
hand, a query with many attributes will result in a somewhat
slower look-up in the internal DAG database.
. Number of directories
A larger number of directories may result in many referrals,
but it depends on the query. A simple query will generate a
lot of referrals, which means a lot of data from the
directories has to be fetched. It will also result in a
somewhat slower look-up in the internal DAG database.
. Number of chained referrals
Queries that are not chained are faster, since the result data
does not have to be sent through the DAG system. Chained
queries to several directories can be processed in parallel in
the SAPs, but all data has to be processed in the CAP before
sent to the client.
. Response time in the directory servers
The response time from the directory servers are of course
critical. The total response time for DAG is never faster than
the slowest involved directory server.
. Number of tokens (size of Tagged Index Objects)
The number of tokens has little impact on the look-up time in
the internal DAG database.
2.5 Some evolutions
To date, the TISDAG project has been "alive" for just over two years.
During that time, there have been a number of evolutions -- in terms
of technologies and ideas outside the project (e.g., user and service
provider expectations, deployment of related software, etc) as well
as goals and understanding within the scope of the project.
Chief among these last is the fact that the project set out to
primarily fulfill the role of a national referral service, and
gradually evolved towards becoming more of a transparent protocol
proxy service, fulfilling client queries as completely as possible,
within the client protocol's semantics. This evolution was probably
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provoked by a number of reasons -- existing client & server software
has a narrower range of accepted (expected) behaviour than their
protocol specs may describe, once the technology was there for some
proxying, going all the way seemed to be within reach, etc.
>From the point of view of providing a national whitepages service,
this is a very positive evolution. However, it did place some
strains on the original system architecture, for which some
adjustments have been proposed (more detail below). What is less
clear is the impact this evolution will have on the flexibility of
the system architecture -- in terms of addressing other applications,
different protocols (and protocol paradigms), etc. That is, the
original intention of the system was to very simply fulfill an
unsophisticated role -- "find things that sort of match the input
query and let the client itself determine if the match is close
enough". As the requirements become more sophisticated, the
simplicity of the system is impacted, and perhaps more brittle.
(Some proposals for avoiding this are outlined in [DAG++], which
attempts to return to the underlying principles and propose steps
forward at that level).
In terms of impact within the TISDAG project, this evolution lead to
the following technical adjustments:
. The latest version of the technical specification makes a
distinction (in the internal protocol grammar) between queries
directed at the Referral Index, and those passed to SAPs to
fulfill a query. This distinction keeps the query-routing
queries simple, but allows more sophistication in expressing a
query designed to fulfill the client's original semantic
expression.
. The additional constraints in the SAP query language is still
not enough to allow the internal protocol to express very
sophisticated queries. Originally intended only for query-
routing queries, the DAG/IP expects all queries to be token-
based (whereas LDAP queries are phrase-oriented). This means
that SAPs have to do a good deal of "post-pruning" of WDSP
result sets to match the DAG/IP query sent by a CAP for query
fulfillment. And, CAPs must in turn do more post-pruning to
match the DAG/IP results (from the SAPs) to the original query
semantics.
The real strength of the TISDAG project was that it separated the
technical framework needed to support the service from the
configuration required in order to support a particular application
or service -- query & schema mapping, configuration for protocols,
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etc. Future improvements should focus on evolving that framework,
maintaining the separation from the specific applications, services,
and protocols that may use it.
3.0 Related Projects
The TISDAG project is not alone in attempting to solve the problems
of providing coordinated access to resources managed by multiple,
disparate services.
3.1 The Norwegian Directory of Directories (NDD)
Described in [NDD], the Norwegian Directory of Directories project
also aims to provide necessary infrastructure for a national
directory service. It assumes LDAP (v2 or v3) accessibility of WDSP
information (provided by the WDSP itself, or through other
arrangements), and aims to resolve some of the trickier issues
associated with hooking together already-operational LDAP servers
into a coherent network: uniform distinguished naming scheme, and
content-based referrals. It also addresses some of the pragmatic
realities of being compatible with different versions of LDAP clients
-- e.g., v2, which does not support referrals, and v3, which does.
At the heart of the system is the "Referral Index and Organizational
information" (RIO) server, which provides a searchable catalogue over
Norwegian organization. This facilitates the location of whitepages
servers for individual organizations (assuming the query includes
information about which organization(s) is(are) interesting).
This work can be seen as being complementary to the TISDAG work, in
that it provides a more focused service for integrating LDAP
directory servers. However, there is still some requirement that one
knows the organization to which a person belongs before doing a
search for their e-mail address. This may be reasonable for seeking
mail addresses associated with a person's work organization, but is
less often successful when it comes to finding a personal e-mail
address -- in an age where ISPs abound, a priori knowledge of a
user's ISP identification is unlikely.
3.2 DESIRE Directory Services
The EC funded project DESIRE II (http://www.desire.org) is developing
a distributed European indexing system for information on Research
and Education. The Directory Services work undertaken by DANTE and
SURFnet proposes an architecture applied to a server mesh structure
to create a wide-area directory service infrastructure.
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This service is intended to support both whitepages information with
LDAP servers at WDSPs, as well as a Web-search meshes at various
places using Whois++ for information about resources and routing of
queries to other index-based services.
Like the TISDAG project, the DESIRE directory services project aims
to act as a focal point for queries, allowing client software to
access appropriate resources from a wide range of disparate services.
There are architectural differences between the approach used in the
TISDAG project and the DESIRE directory service project, but many of
the driving needs are the same, and the approach of using content-
based indexing and referrals was also selected.
4.0 Some Directions for TISDAG Next Steps
The fun thing with technology is that there are always more tweaks
and changes that can be made. However, a service should evolve in
response to specific customer needs, and there are several ways in
which the TISDAG service itself could advance. Some of them are
outlined below, in terms of possibilities perceived at this time,
rather than specific recommendations for underlying technology
changes that would be necessary to fulfill them. A related topic,
networking DAG servers (meshes), is discussed in [DAG-Mesh].
4.1 Security support
There is a need for security considerations when making use of a
wide-scaled directory system in other application areas than the
public white-pages application of the TISDAG project. There are
issues whether the directory service is distributed across the
Internet, or even if it functions completely within an internal,
closed network.
4.2 WDSPs attributes and schemas
Today the DAG system makes use of 2 information schemas -- the
DAGPERSON schema for information about specific people, and the
DAGORGROLE schema for organizational roles. The technical
specification includes a definition of the schema, as well as an
understood mapping to (and from) some standard schemas used in the
supported protocols. Nevertheless, to include new WDSPs which may
not have all attributes in schemas, may use different schemas as well
as query attributes, it should be possible to provide creation and
use of new customized/standardized schemas and perform schema mapping
if it's necessary. It might also be possible to constrain queries to
desired query attributes, templates, or object classes.
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In practice, this means that different WDSP's may choose to use
different subparts of one defined schema, or even implement local
customizations.
5.0 Some conclusions
Although fewer people now hold out the hope of a unified global
directory service, based on standardize protocols, it is interesting
to see more projects providing infrastructure that permits unified
access to what is otherwise an unforgivingly diverse and dislocated
set of information servers. What cannot be dictated (in standardized
protocols and schemas) may yet be accommodated through service
infrastructure. The right approach seems to be to build better and
better frameworks for supporting such diversified services, without
making the framework architecture dependent on specific technologies.
6.0 Security Considerations
To date, the TISDAG project has focused on serving only publicly-
sharable information. As noted in Section 4.1, any future work will
have to provide additional facilities for providing authentication,
authorization, encryption, and otherwise handling sensitive data in
an open environment.
7.0 Acknowledgements
This document outlines the perspectives and opinions of the authors,
based on experience as well as many fruitful and enlightening
discussions with others: Roland Hedberg, Torbjorn Granat, Patrik
Granholm, Rikard Wessblad and Sandro Mazzucato.
The work described in this document was carried out as part of an
on-going project of Ericsson. For further information regarding that
project, contact:
Bjorn Larsson
bjorn.x.larsson@era.ericsson.se
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8.0 Authors' Addresses
Thommy Eklof
Hotsip AB
EMail: thommy.eklof@hotsip.com
Leslie L. Daigle
Thinking Cat Enterprises
EMail: leslie@thinkingcat.com
9.0 References
Request For Comments (RFC) and Internet Draft documents are available
from numerous mirror sites.
[CIP1] Allen, J. and M. Mealling, "The Architecture of the Common
Indexing Protocol (CIP)", RFC 2651, August 1999.
[CIP2] Allen, J. and M. Mealling, "MIME Object Definitions for
the Common Indexing Protocol (CIP)", RFC 2652, August
1999.
[CIP3] Allen, J., Leach, P. and R. Hedberg, "CIP Transport
Protocols", RFC 2653, August 1999.
[DAG++] Daigle, L. and T. Eklof, "An Architecture for Integrated
Directory Services", RFC 2970, October 2000.
[DAG-Mesh] Daigle, L. and T. Eklof, "Networking Multiple DAG servers:
Meshes", RFC 2968, October 2000.
[TISDAG] Daigle, L. and R. Hedberg "Technical Infrastructure for
Swedish Directory Access Gateways (TISDAG)," RFC 2967,
October 2000.
[centroid] Deutsch, P., Schoultz, R., Faltstrom, P. and C. Weider,
"Architecture of the WHOIS++ service", RFC 1835, August
1995.
[NDD] Hedberg, R. and H. Alvestrand, "Technical Specification,
The Norwegian Directory of Directories (NDD)", Work in
Progress.
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[TIO] Hedberg, R., Greenblatt, B., Moats, R. and M. Wahl, "A
Tagged Index Object for use in the Common Indexing
Protocol", RFC 2654, August 1999.
[complex] P. Panotzki, "Complexity of the Common Indexing Protocol:
Predicting Search Times in Index Server Meshes", Master's
Thesis, KTH, September 1996.
[WAP] The Wireless Application Protocol, http://www.wapforum.org
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Appendix -- Specific Software Issues and Deployment Experiences
The following paragraphs outline practical deployment experiences in
an anecdotal fashion. This is not meant to be construed as an
exhaustive, authoritative evaluation of existing client software, but
rather an indication of the types of challenges the average
implementation team may expect to encounter in a development and
deployment effort.
Character encoding
------------------
One client's addressbook sends iso-8859 encoding (depending on the
font configuration in the browser) when querying a directory server
but the directory server responds with Unicode (UTF-8) encoding.
This means that the LDAP CAP would have to handle different character
set encodings for request and response.
Referrals
---------
Today there appears to be only one commercial addressbook supporting
LDAPv3. All the others support only LDAPv2. However, this LDAPv3
client software does not handle referrals correctly -- the client
couldn't handle server the result contains "response code 10"
(designated for referrals). From what was observed, there was now
way for the client or the end-user to decide if, or which, referrals
to follow-up. It is therefore not clear how the LDAP clients handle
a combination of both referrals and results -- but the supposition
is that it doesn't work.
Objectclasses in LDAP
---------------------
No objectclass is defined in the query to the DAG-system from the
LDAP-clients. This means that the DAG-system doesn't see any
differences between "inetOrgPerson" and "organisationalRole" when
attribute "cn" is representing both "name" and "role". This is not
so much a problem as that it has interesting side effects. Namely,
although most directory user interfaces (found in browsers, mail
programs) claim only to support person-related queries, in practise a
user of the client could use the interface to send a query with role
in the name entry.
Query with attribute Organisation
---------------------------------
It is possible to send a query with attribute "organisation" but it
would result in no hits because of that the organisation attribute is
not included in the objectclass "inetOrgPerson". Roland Hedberg has
proposed a change for the latest release of the objectclass
definition document.
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RFC 2969 Wide Area Directory Deployment October 2000
To provide the desired ability to narrow search focus to some range
of organization names (attribute values), there are three possible
approaches with differing merits/detractions:
Recommend the use of the "locality" attribute -- although a more
standard definition would be required (locality is currently used
for everything from organization to county to map coordinates).
Recommend or require that the attribute organisation should be
inherited in objectclass "inetOrgPerson".
Build the LDAP DAG-SAP to submit 2 query to the WDSP. The second
is the same as the first, with only cn filters if the entire query
including "o" results in no hits (i.e., back off from the
organization filtering if it doesn't seem to be supported).
Configuration
-------------
It is not possible to see what character set a LDAP clients want to
use. The recommendation so far in he project has been to define a
unique port for each character set. This requires extra end-user
configuration of client software, and proper advertising of the port
number-charset mapping provided in the service.
DN
--
When the user wants to look-up more information about a person found
in a preliminary search, the LDAP client uses the entry's DN
together with host and port to the DAG system. Not only does that
mean that the client submits a non-compliant query to the DAG system,
as DNs are not part of any of the defined queries for the service, it
simply does not provide the desired effect of getting to the user's
entry.
Response Codes
--------------
The LDAPv3 client that was used does not support more than 2 response
codes -- "success" and "size limit exceeded". All the other response
codes are translated to "size limit exceeded", although no results
are returned. That is, if the error was in fact that the size limit
was exceeded, the results up to the size limit are presented. If it
was another response code mapped to that one, no results are
presented.
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RFC 2969 Wide Area Directory Deployment October 2000
Sending and loading CIP Index Objects
-------------------------------------
At least one server is quoting the CIP-object incorrectly for the
Swedish characters A-Ring, A-Umlaut and O-Umlaut. Sending quoted
printable CIP-objects with PINE mail software works.
Source - Labeled URI
--------------------
The original plan for the use of the labeled-URI attribute was to use
it to return a pointer to the WDSP that provided the user
information. However, the standard use of the labeled-URI attribute,
which may in fact be populated in the data returned by a WDSP, is to
contain the URI for more private related homepages.
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RFC 2969 Wide Area Directory Deployment October 2000
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