rfc1107.txt

<VC++网络游戏建摸与实现>源代码

         This includes delegation of authority over parts of the
         namespace and arbitrating the shape of the namespace
         (addressing the questions about who gets what sorts of names).
         This is in addition to the continued and extended data
         collection and management, distributing the data, placing the
         code, documentation and user education.

      - Standards participation is an important part of the program.

         It is critical as X.500 changes during the next 4 year study
         period that the United States take a strong stand on any



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RFC 1107         A Plan for Internet Directory Services        July 1989


         changes we envision.  It is encumbant on us to utilize
         effectively the results of the largest field trials of this
         work in the international arena.  The group agreed that this
         could take up to one half of one person's time in a year.

      - A task force or working group is necessary to provide a forum
        for communication and discussion.

   It is important to pursue this path now, both to architect a unified
   solution before a collection of ad hoc solutions is deployed, and to
   provide effective input into the X.500 standards work based on the
   field trials.

2. Goals and Requirements for a White Pages Service

   The requirements of a white pages service are the following:

      - Functionality:

         The simple form of a white pages service is straightforward;
         one should be able to query the service with the name of a
         person, and have returned attributes of the person such as
         network mail address and phone number.

      - Correctness of information:

         The information in a white pages service is useless and
         untrusted if it is not updated regularly.  A white pages
         service will not be used, if the information it provides is out
         of date or incorrect.  This will require a set of management
         tools.  Data integrity is an especially difficult challenge in
         this area, in contrast with information that is syntactically
         correct.

      - Size:

         The science and research community has been estimated at ten
         million users.  The number of organizations in the United
         States is on the order of ten to one hundred thousand.

      - Usage and query rate:

         In comparison with the typical telephone book pattern of about
         one lookup a week per person, users of electronic mail in the
         science and research community will send more electronic mail
         messages than they currently make phone calls, leading to an
         estimate of ten searches a week per user for electronic as well
         as paper mail and telephone information.  This leads to a query



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         rate of 10**8 queries per week or 170 per second on average,
         with much higher peak rates.  The average could probably be
         handled by a single server, but not the peak rates and this
         would leave little room for growth.  Therefore, a distributed,
         multiple server solution is the only one that make sense.

      - Response time:

         The issue of overall query behavior must be considered
         carefully.  The issue arises when queries, in particular
         searches, are not limited to tightly constrained sets of
         entries.  Since the number of queries generated will be
         proportional to the number of users (and the size of the
         system), the white pages design must avoid costs per query that
         are related to the size of the system.  The consequence,
         otherwise, will be quadratic behavior in response time.

         The response time of the service must also reflect the expected
         usage.  A phone book style query must respond in the waiting
         time tolerable to a user, perhaps ten seconds maximum, or one
         second desirable.  If the service is incorporated as a
         component of a larger service, then the needs of that service
         determine the response time.

      - Partitioned Authority:

         The white pages service under discussion would be used by a
         wide variety of organizations, ranging from small and large
         companies, to network service providers, to government
         agencies.  Many of these would find it unacceptable to delegate
         the authority over their namespaces to some other organization.
         Therefore, partitioned authority including some access control,
         name assignment, and information management must be possible.

      - Access Control:

         The access control required by the white pages falls into two
         categories, read access control, and write or modify access
         control.  There are at least two reasons that read access
         control must be available.  One is that organizations may
         require limiting the access to the actual entries or parts of
         them.  This would be comparable to organizations not being
         willing to distribute their corporate phone books or personnel
         records.  The other reason is that some organizations do not
         want to publicize or make public their organizational
         structure.  Write and modify access control is necessary
         because both individuals and organizations may want to prevent
         inadvertent or malicious creation or modification of



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         information.  Access control is an issue for both organizations
         wanting to retain local control of personnel information and
         individuals wanting to control access to private information
         about themselves.

      - Multiple Transport Protocol Support:

         Within the next three years, one cannot expect all the
         organizations in the USA to convert to the OSI protocols.  On
         the other hand, some will.  It is therefore important that any
         white pages service provide interfaces on top of both OSI
         protocols and TCP/IP.  There currently exists a partial OSI
         suite know as ISODE on top of TCP.  This is being distributed
         widely enough that perhaps this should also be supported.

   In addition to these requirements, there are a number of features
   that would make a white pages service more useful.  These are:

      - Additional Functionality:

         Descriptive naming with sophisticated searching based on
         attributes would support a more flexible human interface than
         simple name translation.  Descriptive naming also would support
         a general yellow pages style service.

         The form of a yellow pages service is less certain.  One
         definition of a yellow pages service is a directory that stores
         a number of pre-computed inversions of the directory database,
         so that entries can be retrieved very efficiently using these
         predetermined attributes of the data.  Another definition of a
         yellow pages service is one that provides a very powerful set
         of search primitives, somewhat in common with a relational
         query language, to support retrieval of entries that match
         complex attribute conditions.  In other words, one view of a
         yellow pages service is that it is constructed to avoid
         expensive searches, the other is that it is to facilitate
         general searches.

      - Accountability:

         Accountability is important both for allocation and recovery of
         costs.  Vendors may provide commercial directory services,
         therefore depending on accounting as part of their successful
         commercial ventures.

      - Multiple Interfaces:

         There should be both human and programming interfaces to the



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         white pages.  For example, in addition to human lookups, mail
         services could effectively use a naming service allow users to
         include human oriented names than the current electronic mail
         addresses that are required, such as full domain names.

      - Multiple Clients:

         Several different clients should exist both to provide for a
         variety of styles of human usage, and to support selection of
         the most commonly used computer environments (e.g., UNIX, VMS,
         MSDOS, OS2, MAC/OS).

3. Pre-existing Services

   This section identifies other naming services that have been proposed
   or implemented for naming people.  Implementations of all of these
   exist, although some are still only experimental.

      Internet Domain Naming Service

         The Internet Domain Name Service [6,1] is used today to name
         host machines.  It is implemented to address the query rates
         and database sizes consistent with looking up hosts as part of
         mail delivery.  It provides a hierarchy with delegation of
         authority within the hierarchy.  Aliases are also available.
         There is no access control, and the service is widely
         distributed throughout the Internet.  It supports management of
         distribution, replication and caching.  It is operational, and
         provides a rich base of practical experience.  It was
         originally intended to be extensible to cover naming of people.
         It runs on a variety of different operating systems and
         utilizes the TCP/IP protocol suite.

      The DECnet Network Architecture Naming Service (DNANS)

         There is a rather well developed specification [5,3] for a
         naming service that is part of the DECnet architecture, which
         in turn arose from work at the DEC SRC in Palo Alto.  This
         architecture addresses some problems not yet covered by X.500,
         such as access control, replication, and caching.  It was
         explicitly defined to have great scalability and management
         features.  It provides a global hierarchy of names, which are
         mapped into properties.  Therefore, operations of searching
         based on properties or attributes may be expensive and
         difficult.  At present it is only implemented on VMS using the
         DNA protocols, but will be moved to UNIX and TCP in the next
         year.




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      Clearinghouse

         This service [7,2] is part of the Xerox network environment.
         It operates today as a global service for Xerox.  They have
         considerable experience with its operation, including problems
         of scale.  Clearinghouse provides a three-level hierarchy of
         names that are mapped to sets of properties.  Loose consistency
         is provided through slow propagation of updates.  Both this
         service and the DEC service mentioned above are to some extent
         based on an earlier Xerox service called Grapevine.

      Profile

         A project at the University of Arizona run by Larry Peterson
         [8] has produced a white pages name service called Profile.  It
         supports descriptive naming and sophisticated lookup tools.
         Profile assumes the existence of some other service such as the
         DNS to navigate among Profile servers.  This navigation service
         need not restrict the relationship among Profile servers to a
         hierarchical organization; Profile supports a non-hierarchical
         global structure.  Names in Profile consist of sets of
         attributes.  Experimental implementations are in operation
         today, and the largest site currently contains about 10,000
         entries.  The Profile code has been available for long enough