rfc1148.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

      3.   An IPM (MTA, MTS, and IPMS Services)

   Probes (MTA Service) must be processed by the gateway, as discussed
   in Chapter 5.  MTS Messages containing Content Types other than those
   defined by the IPMS are not mapped by the gateway, and should be
   rejected at the gateway.

1.5.4.  Repeated Mappings

   The mappings specified here are designed to work where a message
   traverses multiple times between X.400 and RFC 822.  This is often
   essential, particularly in the case of distribution lists.  However,
   in general, this will lead to a level of service which is the lowest
   common denominator (approximately the services offered by RFC 822).
   In particular, there is no expectation of additional X.400 services
   being mapped - although this may be possible in some cases.

1.6.  RFC 987

   Much of this work is based on the initial specification of RFC 987
   and in its addendum RFC 1026.  A basic decision is that the mapping
   will be to the full 1988 version of X.400, and not to a 1984
   compatible subset.  This is important, to give good support to
   communities which will utilise full X.400 at an early date.  This has



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   the following implications:

      -    This document does not obsolete RFC 987, as it has a
           different domain of application.

      -    If a gatewayed message is being transferred to a 1984
           system, then RFC 987 should be used.  If the X.400 side of
           the gateway is a 1988 system, then it should be operated in
           1984 compatibility mode.  There is no advantage and some
           disadvantage in using the new mapping, and later on applying
           X.400 downgrading rules.  Note that in an environment where
           RFC 822 is of major importance, it may be desirable for
           downgrading to consider the case where the message was
           originated in an RFC 822 system, and mapped according to
           this specification.

      -    New features of X.400 can be used to provide a much cleaner
           mapping than that defined in RFC 987.

   Unnecessary change is usually a bad idea.  Changes on the RFC 822
   side are avoided as far as possible, so that RFC 822 users do not see
   arbitrary differences between systems conforming to this
   specification, and those following RFC 987.  Changes on the X.400
   side are minimised, but are more acceptable, due to the mapping onto
   a new set of services and protocols.

   A summary of changes made is given in Appendix A.

1.7.  Aspects not covered

   There have been a number of cases where RFC 987 was used in a manner
   which was not intended.  This section is to make clear some
   limitations of scope.  In particular, this specification does not
   specify:

      -    Extensions of RFC 822 to provide access to all X.400
           services

      -    X.400 user interface definition

   These are really coupled.  To map the X.400 services, this
   specification defines a number of extensions to RFC 822.  As a side
   effect, these give the 822 user access to SOME X.400 services.
   However, the aim on the RFC 822 side is to preserve current service,
   and it is intentional that access is not given to all X.400 services.
   Thus, it will be a poor choice for X.400 implementors to use RFC
   987(88) as an interface - there are too many aspects of X.400 which
   cannot be accessed through it.  If a text interface is desired, a



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   specification targeted at X.400, without RFC 822 restrictions, would
   be more appropriate.

1.8.  Subsetting

   This proposal specifies a mapping which is appropriate to preserve
   services in existing RFC 822 communities.  Implementations and
   specifications which subset this specification are strongly
   discouraged.

1.9.  Document Structure

   This document has five chapters:

      1.   Overview - this chapter.

      2.   Service Elements - This describes the (end user) services
           mapped by a gateway.

      3.   Basic mappings - This describes some basic notation used in
           Chapters 3-5, the mappings between character sets, and some
           fundamental protocol elements.

      4.   Addressing - This considers the mapping between X.400 O/R
           names and RFC 822 addresses, which is a fundamental gateway
           component.

      5.   Detailed Mappings - This describes the details of all other
           mappings.

   There are also six appendices:

      A.   Differences with RFC 987

      B.   Mappings Specific to JNT Mail

      C.   Mappings Specific to UUCP Mail

      D.   Object Identifier Assignment

      E.   BNF Summary

      F.   Format of Address Tables

   WARNING:

      THE REMAINDER OF THIS SPECIFICATION IS TECHNICALLY DETAILED.
      IT WILL NOT MAKE SENSE, EXCEPT IN THE CONTEXT OF RFC 822 AND



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      X.400 (1988).  DO NOT ATTEMPT TO READ THIS DOCUMENT UNLESS
      YOU ARE FAMILIAR WITH THESE SPECIFICATIONS.

1.10.  Acknowledgements

   This work was partly sponsored by the Joint Network Team.  The
   workshop at UCL in June 1989 to work on this specification was also
   an IFIP WG 6.5 meeting.

   The work in this specification was substantially based on RFC 987,
   which had input from many people.

   Useful comments and suggestions were made by Pete Cowen (Nottingham
   Univ), Jim Craigie (JNT), Christian Huitema (Inria), Peter Lynch
   (Prime), Julian Onions (Nottingham Univ), Sandy Shaw (Edinburgh
   Univ), Einar Stefferud (NMA), and Peter Sylvester (GMD).

Chapter 2 -- Service Elements

   This chapter considers the services offered across a gateway built
   according to this specification.  It gives a view of the
   functionality provided by such a gateway for communication with users
   in the opposite domain.  This chapter considers service mappings in
   the context of SINGLE transfers only, and not repeated mappings
   through multiple gateways.

2.1.  The Notion of Service Across a Gateway

   RFC 822 and X.400 provide a number of services to the end user.  This
   chapter describes the extent to which each service can be supported
   across an X.400 <-> RFC 822 gateway.  The cases considered are single
   transfers across such a gateway, although the problems of multiple
   crossings are noted where appropriate.

2.1.1.  Origination of Messages

   When a user originates a message, a number of services are available.
   Some of these imply actions (e.g., delivery to a recipient), and some
   are insertion of known data (e.g., specification of a subject field).
   This chapter describes, for each offered service, to what extent it
   is supported for a recipient accessed through a gateway.  There are
   three levels of support:

      Supported
         The corresponding protocol elements map well, and so the
         service can be fully provided.





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      Not Supported
         The service cannot be provided, as there is a complete
         mismatch.

      Partial Support
         The service can be partially fulfilled.

   In the first two cases, the service is simply marked as "Supported"
   or "Not Supported".  Some explanation may be given if there are
   additional implications, or the (non) support is not intuitive.  For
   partial support, the level of partial support is summarised.  Where
   partial support is good, this will be described by a phrase such as
   "Supported by use of.....".  A common case of this is where the
   service is mapped onto a non- standard service on the other side of
   the gateway, and this would have lead to support if it had been a
   standard service.  In many cases, this is equivalent to support.  For
   partial support, an indication of the mechanism is given, in order to
   give a feel for the level of support provided.  Note that this is not
   a replacement for Chapter 5, where the mapping is fully specified.

   If a service is described as supported, this implies:

      -    Semantic correspondence.

      -    No (significant) loss of information.

      -    Any actions required by the service element.

   An example of a service gaining full support: If an RFC 822
   originator specifies a Subject: field, this is considered to be
   supported, as an X.400 recipient will get a subject indication.

   All RFC 822 services are supported or partially supported for
   origination.  The implications of non-supported X.400 services is
   described under X.400.

2.1.2.  Reception of Messages

   For reception, the list of service elements required to support this
   mapping is specified.  This is really an indication of what a
   recipient might expect to see in a message which has been remotely
   originated.

2.2.  RFC 822

   RFC 822 does not explicitly define service elements, as distinct from
   protocol elements.  However, all of the RFC 822 header fields, with
   the exception of trace, can be regarded as corresponding to implicit



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   RFC 822 service elements.

2.2.1.  Origination in RFC 822

   A mechanism of mapping, used in several cases, is to map the RFC 822
   header into a heading extension in the IPM (InterPersonal Message).
   This can be regarded as partial support, as it makes the information
   available to any X.400 implementations which are interested in these
   services. Communities which require significant RFC 822 interworking
   should require that their X.400 User Agents are able to display these
   heading extensions.  Support for the various service elements
   (headers) is now listed.

      Date:
           Supported.

      From:
           Supported.  For messages where there is also a sender field,
           the mapping is to "Authorising Users Indication", which has
           subtly different semantics to the general RFC 822 usage of
           From:.

      Sender:
           Supported.

      Reply-To:
           Supported.

      To:  Supported.

      Cc:  Supported.

      Bcc: Supported.

      Message-Id:
           Supported.

      In-Reply-To:
           Supported, for a single reference.  Where multiple
           references are given, partial support is given by mapping to
           "Cross Referencing Indication".  This gives similar
           semantics.

      References:
           Supported.

      Keywords:
           Supported by use of a heading extension.



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      Subject:
           Supported.

      Comments:
           Supported by use of an extra body part.

      Encrypted:
           Supported by use of a heading extension.

      Resent-*
           Supported by use of a heading extension.  Note that
           addresses in these fields are mapped onto text, and so are
           not accessible to the X.400 user as addresses.  In
           principle, fuller support would be possible by mapping onto
           a forwarded IP Message, but this is not suggested.

      Other Fields
           In particular X-* fields, and "illegal" fields in common
           usage (e.g., "Fruit-of-the-day:") are supported by use of
           heading extensions.

2.2.2.  Reception by RFC 822

   This considers reception by an RFC 822 User Agent of a message
   originated in an X.400 system and transferred across a gateway.  The
   following standard services (headers) may be present in such a
   message:

      Date:

      From:

      Sender:

      Reply-To:

      To:

      Cc:

      Bcc:

      Message-Id:

      In-Reply-To:

      References:




Kille                                                          [Page 13]