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rfc:rfc1615

Network Working Group J. Houttuin Request for Comments: 1615 RARE Secretariat RARE Technical Report: 9 J. Craigie Category: Informational Joint Network Team

                                                              May 1994
               Migrating from X.400(84) to X.400(88)

Status of this Memo

 This memo provides information for the Internet community.  This memo
 does not specify an Internet standard of any kind.  Distribution of
 this memo is unlimited.

Scope

 In the context of a European pilot for an X.400(88) messaging
 service, this document compares such a service to its X.400(84)
 predecessor.  It is aimed at a technical audience with a knowledge of
 electronic mail in general and X.400 protocols in particular.

Abstract

 This document compares X.400(88) to X.400(84) and describes what
 problems can be anticipated in the migration, especially considering
 the migration from the existing X.400(84) infrastructure created by
 the COSINE MHS project to an X.400(88) infrastructure. It not only
 describes the technical complications, but also the effect the
 transition will have on the end users, especially concerning
 interworking between end users of the 84 and the 88 services.

Table of Contents

 1. New Functionality                                              2
 2. OSI Supporting Layers                                          3
 3. General Extension Mechanism                                    5
 4. Interworking                                                   5
    4.1. Mixed 84/88 Domains                                       5
    4.2. Generation of OR-Name Extensions from X.400(84)           6
    4.3. Distribution List Interworking with X.400(84)             8
    4.4. P2 Interworking                                          10
 5. Topology for Migration                                        11
 6. Conclusion                                                    12
 7. Security Considerations                                       13
 Appendix A - DL-expanded and Redirected Messages in X.400(84)    14
 Appendix B - Bibliography                                        14
 Appendix C - MHS Terminology                                     15

Houttuin & Craigie [Page 1] RFC 1615 Migrating from X.400(84) to X.400(88) May 1994

 Appendix D - Abbreviations                                       16
 Authors' Addresses                                               17

1. New Functionality

 Apart from the greater maturity of the standard and the fact that it
 makes proper use of the Presentation Layer, the principal features of
 most use to the European R&D world in X.400(88) not contained in
 X.400(84) are:
  1. A powerful mechanism for arbitrarily nested Distribution

Lists including the ability for DL owners to control access

    to their lists and to control the destination of nondelivery
    reports. The current endemic use of DLs in the research
    community makes this a fundamental requirement.
  1. The Message Store (MS) and its associated protocol, P7. The

Message Store provides a server for remote User Agents (UAs)

    on Workstations and PCs enabling messages to be held for
    their recipient, solving the problems of non-continuous
    availability and variability of network addresses of such
    UAs. It provides powerful selection mechanisms allowing the
    user to select messages from the store to be transferred to
    the workstation/PC. This facility is not catered for
    adequately by the P3 protocol of X.400(84) and provides a
    major incentive for transition.
  1. Use of X.500 Directories. Support for use of Directory Names

in MHS will allow a transition from use of O/R Addresses to

    Directory Names when X.500 Directories become widespread,
    thus removing the need for users to know about MHS
    topological addressing components.
  1. The provision of message Security services including

authentication, confidentiality, integrity and non-

    repudiation as well as secure access between MHS components
    may be important for a section of the research community.
  1. Redirection of messages, both by the recipient if

temporarily unable to receive them, and by the originator in

    the event of failure to deliver to the intended recipient.
  1. Use of additional message body encodings such as ISO 8613

ODA (Office Document Architecture) reformattable documents or

    proprietary word processor formats.

Houttuin & Craigie [Page 2] RFC 1615 Migrating from X.400(84) to X.400(88) May 1994

  1. Physical Delivery services that cater for the delivery of an

electronic message on a physical medium (such as paper)

    through the normal postal delivery services to a recipient
    who (presumably) does not use electronic mail.
  1. The use of different body parts. In addition to the

extensible externally defined body parts, the most common

    types are predefined in the standard.  In order to give end-
    users a real advantage as compared to other technologies, the
    following body-parts should be supported as a minimum:
  1. IA5
  2. Message
  3. G3FAX
  4. External
    1. General Text
    2. Others
    The last bullet should be interpreted as follows: all UAs
    should be configurable to use any type of externally defined
    body part, but as a minimum General Text can be generated and
    read.
  1. The use of extended character sets, both in O/R addresses

and in the General Text extended bodypart. As a minimum, the

    character sets as described in the European profiles will be
    supported. A management domain may choose as an internal
    matter which character sets it wants to support in
    generating, but all user agents must be able to copy (in
    local address books and in replies) any O/R address, even if
    it contains character sets it cannot interpret itself.

2. OSI Supporting Layers

 The development of OSI Upper Layer Architecture since 1984 allows the
 new MHS standards to sit on the complete OSI stack, unlike X.400(84).
 A new definition of the Reliable Transfer Service (RTS), ISO 9066,
 has a mode of operation, Normal-mode, which uses ACSE and the OSI
 Presentation Layer. It also defines another mode compatible with
 X.410(84) RTS that was intended only for interworking with X.400(84)
 systems.
 However, there are differences between the conformance requirements
 of ISO MOTIS and CCITT X.400(88) for mandatory support for the
 complete OSI stack. ISO specify use of Normal-mode RTS as a mandatory
 requirement with X.410-mode RTS as an additional option, whereas
 CCITT require X.410-mode and have Normal-mode optional. The ISO
 standard identifies three MTA types to provide options in RTS modes:

Houttuin & Craigie [Page 3] RFC 1615 Migrating from X.400(84) to X.400(88) May 1994

  1. MTA Type A supports only Normal-mode RTS, and provides

interworking within a PRMD and with other PRMDs (conforming

    to ISO 10021), and with ADMDs which have complete
    implementations of X.400(88) or which conform to ISO 10021.
  1. MTA Type B adds to the functionality of MTA type A the

ability to interwork with ADMDs implementing only the minimal

    requirements of X.400(88), by requiring support for X.410-
    mode RTS in addition to Normal-mode.
  1. MTA Type C adds to the functionality of MTA type B the

ability to interwork with external X.400(84) Management

    Domains (MDs, i.e., PRMDs and ADMDs), by requiring support for
    downgrading (see 5.1) to the X.400(84) P1 protocol.
 The interworking between ISO and CCITT conformant systems is
 summarised in the following table:
                                    CCITT
                          X.400(84)       X.400(88)
                                       minimal   complete
                                        implementation
 ISO 10021/   MTA Type A     N            N         Y
 MOTIS        MTA Type B     N            Y         Y
              MTA Type C     Y            Y         Y
          Table 1: Interworking ISO <-> CCITT systems
 The RTS conformance difference would totally prevent interworking
 between the two versions of the standard if implementations never
 contained more than the minimum requirements for conformance, but in
 practice many 88 implementations will be extensions of 84 systems,
 and will thus support both modes of RTS. (At the moment we are aware
 of only one product that doesn't support Normal mode.)
 Both ISO and CCITT standards require P7 (and P3) to be supported
 directly over the Remote Operations Service (ROS), ISO 9072, and use
 Normal-mode presentation (and not X.410-mode). Both allow optionally
 ROS over RTS (in case the Transport Service doesn't provide an
 adequately reliable service), again using Normal-mode and not X.410-
 mode.
 CCITT made both Normal and X.410 mode mandatory in its X.400(92)
 version, and it is expected that the 94 version will have the X.410
 mode as an option only.

Houttuin & Craigie [Page 4] RFC 1615 Migrating from X.400(84) to X.400(88) May 1994

3. General Extension Mechanism

 One of the major assets in ISO 10021/X.400(88) is the extension
 mechanism. This is used to carry most of the extensions defined in
 these standards, but its principal benefit will be in reducing the
 trauma of transitions to future versions of the standards. Provided
 that implementations of the 88 standards do not try to place
 restrictions on the values that may be present, any future extension
 will be relayed by these implementations when appropriate (i.e., when
 the extension is not critical), thus providing a painless migration
 to new versions of the standards.

4. Interworking

4.1. Mixed 84/88 Domains

 ISO 10021-6/X.419(88) defines rules for interworking with X.400(84),
 called downgrading. As X.400 specifies the interconnection of MDs,
 these rules define the actions necessary by an X.400(88) MD to
 communicate with an X.400(84) MD. The interworking rules thus apply
 at domain boundaries. Although it would not be difficult to extend
 these to rules to convert Internal Trace formats which might be
 thought a sufficient addition to allow mixed X.400(84)/X.400(88)
 domains, the problems involved in attempting to define mixed 84/88
 domains are not quite that simple.
 The principle problem is in precisely defining the standard that
 would be used between MTAs within an X.400(84) domain, as X.400(84)
 only defines the interconnection of MDs. In practice, MTA
 implementations either use X.400(84) unmodified, or X.400(84) with
 the addition of Internal Trace from the first MOTIS DIS (DIS 8883),
 or support MOTIS as defined in DIS 8505, DIS 8883, and DIS 9065. The
 second option is recommended in the NBS Implementors Agreements, and
 the third option is in conformance with the CEN/CENELEC MHS
 Functional Standard [1], which requires as a minimum tolerance of all
 "original MOTIS" protocol extensions. An 84 MD must decide which of
 these options it will adopt, and then require all its MTAs to adopt
 (or at least be compatible with) this choice. No doubt this is one of
 the reasons for the almost total absence currently of mixed- vendor
 X.400(84) MDs in the European R&D MHS community. The fact that none
 of these three options for communication between MTAs within a domain
 have any status within the standardisation bodies accounts for the
 absence from ISO 10021/X.400(88) of detailed rules for interworking
 within mixed 84/88 domains.
 Use of the first option, unmodified X.400(84), carries the danger of
 undetectable routing loops occurring. Although these can only occur
 if MTAs have inconsistent routing tables, the absence of standardised

Houttuin & Craigie [Page 5] RFC 1615 Migrating from X.400(84) to X.400(88) May 1994

 methods of disseminating routing information makes this a possibility
 which if it occurred might cause severe disruption before being
 detected. The only addition to the interworking rules needed for this
 case is the deletion of Internal Trace when downgrading a message.
 Use of the second option, X.400(84) plus Internal Trace, allows the
 detection and prevention of routing loops. Details of the mapping
 between original-MOTIS Internal Trace and the Internal Trace of ISO
 10021 can be found in Annex A. This should be applied not only when
 downgrading from 88 to 84, but also in reverse when an 84 MPDU is
 received by the 84/88 Interworking MTA. If the 84 domain properly
 implements routing loop detection algorithms, then this will allow
 completely consistent reception of messages by an 84 recipient even
 after DL expansion or Redirection within that domain (but see also
 section 5.3).  Unfortunately, the first DIS MOTIS like X.400(84) left
 far too much to inference, so not all implementors may have
 understood that routing loop detection algorithms must only consider
 that part of the trace after the last redirection flag in the trace
 sequence.
 Use of the third option, tolerance of all original-MOTIS extensions,
 would in principle allow a still higher level of interworking between
 the 84 and 88 systems. However, no implementations are known which do
 more than relay the syntax of original-MOTIS extensions: there is no
 capability to generate these protocol elements or ability to
 correctly interpret their semantics.
 The choice between the first two options for mixed domains can be
 left to individual management domains. It has no impact on other
 domains provided the topology recommended in section 5 is adopted.

4.2. Generation of OR-Name Extensions from X.400(84)

 The interworking rules defined in DIS 10021-6/X.419 Annex B allow for
 delivery of 88 messages to 84 recipients, but do not make any 88
 extensions available to 84 originators. In general this is an
 adequate strategy. Most 88 extensions provide optional services or
 have sensible defaults. The exception to this is the OR-Name
 extensions. These fall into three categories: the new CommonName
 attribute; fifteen new attributes for addressing physical delivery
 recipients; and alternative Teletex (T.61) encodings for all
 attributes that were defined as Printable Strings. Without some
 mechanism to generate these attributes, 84 originators are unable to
 address 88 recipients with OR-Addresses containing these attributes.
 Such a mechanism is defined in RARE Technical Report 3 ([2]), "X.400
 1988 to 1984 downgrading".

Houttuin & Craigie [Page 6] RFC 1615 Migrating from X.400(84) to X.400(88) May 1994

 Common-name appears likely to be a widely used attribute because it
 remedies a serious deficiency in the X.400(84) OR-Name: it provides
 an attribute suitable for naming Distribution Lists and roles, and
 even individuals where the constraints of the 84 personal-name
 structure are inappropriate or undesirable. As 84 originators will no
 doubt wish to be able to address 88 DLs (and roles), [2] defines a
 Domain Defined Attribute (DDA) to enable generation of common-name by
 84 originators. This consists of a DDA with its type set to "common-
 name" and its value containing the Printable String encoding to be
 set into the 88 common-name attribute.
 This requires that all European R&D MHS 88 MTAs capable of
 interworking with 84 systems shall be able to map the value of
 "common-name" DDA in OR-Names received from 84 systems to the 88
 standard attribute extension component common-name, and vice versa.
 X.400(84) originators will only be able to make use of this ability
 to address 88 common-name recipients if their system is capable of
 generating DDAs. Unfortunately, one of the many serious deficiencies
 with the CEN/CENELEC and CEPT 84 MHS Functional Standards ([1] and
 [3]), as originally published, is that this ability is not a
 requirement for all conformant systems. Thus if existing European R&D
 MHS X.400(84) users wish to be able to address a significant part of
 the ISO 10021/X.400(84) world they must explicitly ensure that their
 84 systems are capable of generating DDAs. However, this will be a
 requirement in the revised versions of ENV 41201 and ENV 41202, which
 are to be published soon. There is no alternative mechanism for
 providing this functionality to 84 users. It is estimated that
 currently 95% of all European R&D MHS users are able to generate
 DDAs.
 When messages are sent to both ISO 10021/X.400(88) and X.400(84)
 recipients outside the European R&D MHS community, this
 representation of common-name will not enable the external recipients
 to communicate directly unless their 84/88 interworking MTA also
 implements this mapping. However, use of this mapping within the
 European R&D MHS community has not reduced external connectivity, and
 provided RTR 3, RFC 1328 is universally implemented within this
 community it will enhance connectivity within the community.
 As for the new Physical Delivery address attributes in X.400(88), RTR
 3 (RFC1328) takes the following approach. A DDA with type "X400-88"
 is used, whose value is an std-or encoding of the address as defined
 in RARE Technical Report 2 ([4]), "Mapping between X.400(1988)/ISO
 10021 and RFC 822". This allows source routing through an appropriate
 gateway. Where the generated address is longer than 128 characters,
 up to three overflow DDAs are used: X400-C1; X400-C2; X400-C3. This
 solution is general, and does not require co-operation, i.e., it can

Houttuin & Craigie [Page 7] RFC 1615 Migrating from X.400(84) to X.400(88) May 1994

 be implemented in the gateways only.
 Note that the two DDA solutions mentioned above have the undesirable
 property that the P2 heading will still contain the DDA form, unless
 content upgrading is also done. In order to shield the user from
 cryptic DDAs, such content upgrading is in general recommended, also
 for nested forwarded messages, even though the available standards
 and profiles do not dictate this.

4.3. Distribution List Interworking with X.400(84)

 Before all X.400(84) systems are upgraded to ISO 10021, the
 interaction of Distribution Lists with X.400(84) merits special
 attention as DLs are already widely used.
 Nothing, apart perhaps from the inability to generate the DL's OR-
 Address if the DL uses the common-name attribute, prevents an
 X.400(84) originator from submitting a message to a DL.
 X.400(84) users can also be members (i.e., recipients) of a DL.
 However, if the X.400(84) systems involved correctly implement
 routing loop detection, the X.400(84) recipient may not receive all
 messages sent to the DL. X.400(84) routing loop detection involves a
 recipient MD in scanning previous entries in a message's trace
 sequence for an occurrence of its own domain, and if such an entry is
 found the message is non-delivered. The new standards extend the
 trace information to contain flags to indicate DL-expansion and
 redirection, and re-define the routing loop detection algorithm to
 only examine trace elements from the last occurrence of either of
 these flags. Thus 88 systems allow a message to re-traverse an MD (or
 be relayed again by an MTA) after either DL-expansion or redirection.
 However, these flags cannot be included in X.400(84) trace, so are
 deleted on downgrading. Therefore the 84 DL recipient will receive
 all messages sent to the DL except those which had a common point in
 the path to the DL expansion point with the path from the expansion
 points to his UA. This common point is an MD in the case of a DL in
 another MD or an MTA in the case of a DL in the same MD. Although
 this is quite deterministic behaviour, the user is unlikely to
 understand it and instead regard it as erratic or inconsistent
 behaviour.
 Another problem with X.400(84) DL members will be that delivery and
 non-delivery reports will be sent back directly to the originator of
 a message, rather than routed through the hierarchy of DL expansion
 points where they could have been routed to the DL administrator
 instead of (or as well as) the originator.

Houttuin & Craigie [Page 8] RFC 1615 Migrating from X.400(84) to X.400(88) May 1994

 No general solution to this problem has yet been devised, despite
 much thought from a number of experts. The nub of the problem is that
 changing the downgrading rules to enable 84 recipients to receive all
 such messages also allows the possibility of undetectable infinite DL
 or redirection looping where there is an 84 transit domain.
 A potential solution is to extend the DL expansion procedures to
 explicitly identify X.400(84) recipients and to treat them specially,
 at least by deleting all trace prior to the expansion point. This
 solution is only dangerous if another DL reached through an 84
 transit domain is inadvertently configured as an 84 recipient, when
 infinite looping could occur. It does however impose the problems of
 84 interworking into MHS components which need to know nothing even
 of the existence of X.400(84). It also requires changes to the
 Directory attribute mhs-dl-members to accommodate the indication that
 identifies the recipient as an X.400(84) user, unless European R&D
 MHS DLs are restricted to being implemented by local tables rather
 than making use of the Directory.
 A similar change would be required for Redirection. However, the
 change for Redirection would have substantially more impact as it
 would require European R&D MHS-specific MHS protocol extensions to
 identify the redirected recipient as an X.400(84) user. If the
 European R&D MHS adopts a reasonable quality of MHS(88) service, all
 its MTAs would be capable of Redirection and all UAs would be capable
 of requesting originator-specified-alternate-recipient and thus be
 required to incorporate these non-standard additions. A special
 European R&D MHS modification affecting all MTAs and UAs seems
 impractical, too!
 If the recommended European R&D MHS topology for MHS migration (See
 chapter 5) is adopted there will never be an X.400(84) transit domain
 (or MTA) between two ISO 10021 systems. This allows the deletion of
 trace prior to the last DL expansion or redirection to be performed
 as part of the downgrading, giving the X.400(84) user a consistent
 service. This solution has the advantage of only requiring changes at
 the convertors between X.400(84) and ISO 10021/X.400(88), where other
 European R&D MHS specific extensions have also been identified. A
 precise specification of this solution is given in Annex A.
 Finally, problems might occur because some X.400(84) MTAs could
 object to messages containing more than one recipient with the same
 extension-id (called originally-requested-recipient-number in the new
 standards), since this was not defined in X.400(84).  Note that
 X.400(84) only requires that all extension-id's be different at
 submission time, so 84 software that does not except messages with
 identical extension-id's for relaying or delivery must be considered
 broken.

Houttuin & Craigie [Page 9] RFC 1615 Migrating from X.400(84) to X.400(88) May 1994

4.4. P2 Interworking

 RTR 3, RFC 1328 also defines the downgrading rules for P2 (IPM)
 interworking: The IPM service in X.400(1984) is usually provided by
 content type 2. In many cases, it will be useful for a gateway to
 downgrade P2 from content type 22 to 2. This will clearly need to be
 made dependent on the destination, as it is quite possible to carry
 content type 22 over P1(1984). The decision to make this downgrade
 will be on the basis of gateway configuration.
 When a gateway downgrades from 22 to 2, the following should be done:
  1. Strip any 1988 specific headings (language indication, and
     partial message indication).
  2. Downgrade all O/R addresses, as described in Section 3.
  3. If a directory name is present, there is no method to
     preserve the semantics within a 1984 O/R Address. However, it
     is possible to pass the information across, so that the
     information in the Distinguished Name can be informally
     displayed to the end user. This is done by appending a text
     representation of the Distinguished Name to the Free Form
     Name enclosed in round brackets. It is recommended that the
     "User Friendly Name" syntax is used to represent the
     Distinguished Name [5]. For example:
        (Steve Hardcastle-Kille, Computer Science,
        University College London, GB)
  4. The issue of body part downgrade is discussed in Section 6.
 Note that a message represented as content type 22 may have
 originated from [6]. The downgrade for this type of message can be
 improved. This is discussed in RTR 2, RFC 1327.
 Note that the newer EWOS/ETSI recommendations specify further rules
 for downgrading, which are not all completely compatible with the
 rules in RTR 3, RFC 1328. This paper does not state which set of
 rules is preferred for the European R&D MHS, it only states that a
 choice will have to be made.
 As the transition topology recommended for the European R&D MHS is to
 never use 84 transit systems between 88 systems, it is possible to
 improve on the P2 originator downgrading and resending scenario. The
 absence of 84 transit systems means that the necessity for a P1
 downgrade implies that the recipient is on an 84 system, and thus
 that it is better to downgrade 88 P2 contents to 84 P2 rather than to

Houttuin & Craigie [Page 10] RFC 1615 Migrating from X.400(84) to X.400(88) May 1994

 relay it in the knowledge that it will not be delivered.

5. Topology for Migration

 Having decided that a transition from X.400(84) is appropriate, it is
 necessary to consider the degree of planning and co- ordination
 required to preserve interworking during the transition.
 It is assumed as a fundamental tenet that interworking must be
 preserved during the transition. This requires that one or more
 system in the European R&D MHS community must act as a protocol
 converter by implementing the rules for "Interworking with 1984
 Systems" listed in Annex B of ISO 10021-6/X.419.
 When downgrading from ISO 10021/X.400(88) to X.400(84) all extensions
 giving functionality beyond X.400(84) are discarded, or if a critical
 extension is present then downgrading fails and a non-delivery
 results. Thus, although it is possible to construct topologies of
 interconnected MTAs so that two 88 MTAs can only communicate by
 relaying through one or more 84 MTA, to maximise the quality of
 service which can be provided in the European R&D MHS community it is
 proposed that it require that no two European R&D MHS 88 MTAs shall
 need to communicate by relaying through a X.400(84) MTA. Furthermore,
 if this is extended to require that no two European R&D MHS 88 MTAs
 shall ever communicate by relaying through an X.400(84) MTA, then the
 European R&D MHS can provide enhanced interworking functionality to
 its X.400(84) users.
 If mixed vintage 88 and 84 Management Domains (MDs) are created, the
 routing loop detection rules, which specify that a message shall not
 re-enter an MD it has previously traversed, require that downgrading
 is performed within that mixed vintage MD. That MD therefore requires
 at least one MTA capable of downgrading from 88 to 84. It is unlikely
 that every MTA within an MD will be configured to act as an entry-
 point to that MD from other MDs. However, the proposed European R&D
 MHS migration topology requires that as soon as a domain has an 88
 MTA it shall also have an 88 entry point - this may, of course, be
 that same MTA.
 Even for MDs operating all the same MHS vintage internally, providing
 entry-points for both MHS vintages will give considerable advantage
 in maximising the connectivity to other MDs. Initially, it will be
 particularly important for 88 MDs to be able to communicate with 84
 only MDs, but as 88 becomes more widespread eventually the 84 MDs
 will become a minority for which the ability to support 88 will be
 important to maintain connectivity. For most practical MDs providing
 entry-points that implement options in the supporting layers will
 also be important. Support for at least the following is recommended

Houttuin & Craigie [Page 11] RFC 1615 Migrating from X.400(84) to X.400(88) May 1994

 at MD entry-points:
  88-P1/Normal-mode RTS/CONS/X.25(84)
  88-P1/Normal-mode RTS/RFC1006/TCP/IP
  84-P1/X.25(80)
  84-P1/RFC1006/TCP/IP
 The above table omits layers where the choice is obvious (e.g.,
 Transport class zero), or where no choice exists (e.g., RTS for 84-
 P1).
 The requirement for no intermediate 84 systems does require that the
 European R&D MHS use direct PRMD to PRMD routing between 88 PRMDs at
 least until such time as all ADMDs will relay the 88 MHS protocols.
 Finally, in order to keep routing co-ordination overhead to a
 minimum, an important requirement for the migration strategy is that
 only one common set of routing procedures is used for both 84 and 88
 systems in the European R&D MHS.

6. Conclusion

  1. The transition from X.400(84) to ISO 10021/X.400(88) is
     worthwhile for the European R&D MHS, to provide:
  1. P7 Message Store to support remote UAs.
  2. Distribution Lists.
  3. Support for Directory Names.
  4. Standardised external Body Part types.
  5. Redirection.
  6. Security.
  7. Future extensibility.
  8. Physical Delivery.
  2. To minimise the number of transitions the European R&D MHS
     target should be ISO 10021 rather than CCITT X.400(88) -
     i.e., straight to use of the full OSI stack with Normal-mode
     RTS.
  3. To give a useful quality of service, the European R&D MHS
     should not use minimal 88 MTAs which relay the syntax but
     understand none of the semantics of extensions. In
     particular, all European R&D MHS 88 MTAs should generate
     reports containing extensions copied from the subject message
     and route reports through the DL expansion hierarchy where
     appropriate.

Houttuin & Craigie [Page 12] RFC 1615 Migrating from X.400(84) to X.400(88) May 1994

  4. The European R&D MHS should carefully plan the transition so
     that it is never necessary to relay through an 84 system to
     provide connectivity between any two 88 systems.
  5. The European R&D MHS should consider the additional
     functionality that can be provided to X.400(84) users by
     adopting an enhanced specification of the interworking rules
     between X.400(84) and ISO 10021/X.400(88), and weigh this
     against the cost of building and maintaining its own
     convertors. The advantages to X.400(84) users are:
  1. Ability to generate 88 common-name attribute, likely to

be widely used for naming DLs.

  1. Consistent reception of DL-expanded and Redirected

messages.

  1. Ability to receive extended 88 P2 contents

automatically downgraded to 84 P2.

7. Security Considerations

 Security issues are not discussed in this memo.

Houttuin & Craigie [Page 13] RFC 1615 Migrating from X.400(84) to X.400(88) May 1994

Appendix A - DL-expanded and Redirected Messages in X.400(84)

 This Annex provides an additional to the rules for "Interworking with
 1984 Systems" contained in Annex B of ISO 10021-6/X.419,  to give
 X.400(84) recipients consistent reception of messages  that have been
 expanded by a DL or redirected.  It is applicable  only if the
 transition topology for the European R&D MHS  recommended in section
 3 is adopted.
 Replace the first paragraph of B.2.3 by:
 If an other-actions element is present in any trace- information-
 elements, that other-actions element and all preceding trace-
 information-elements shall be deleted. If an other-actions element is
 present in any subject-intermediate-trace-information- elements, that
 other-actions element shall be deleted.

Appendix B - Bibliography

 [1] ENV 41201, "Private MHS UA and MTA: PRMD to PRMD", CEN/CENELEC,
     1988.
 [2] Kille, S., "X.400 1988 to 1984 downgrading", RTR 3, RFC 1328,
     University College London, May 1992.
 [3] ENV 41202, "Protocol for InterPersonal Messaging between MTAs
     accessing the Public MHS", CEPT, 1988.
 [4] Kille, S.  "Mapping between X.400(1988)/ISO 10021 and RFC 822",
     RTR 2, RFC 1327; University College London. May 1992.
 [5] Kille, S., "Using the OSI Directory to achieve User Friendly
     Naming", RFC 1484, ISODE Consortium, July 1993.
 [6] Crocker, D., "Standard for the Format of ARPA Internet Text
     Messages", STD 11, RFC 822, University of Delaware, August 1982.
 [7] Craigie, J., "COSINE Study 8.2.2. Migration Strategy for
     X.400(84) to X.400(88)/MOTIS", Joint Network Team, 1988.
 [8] Craigie, J., "ISO 10021-X.400(88): A Tutorial for those familiar
     with X.400(84)", Computer Networks and ISDN systems 16, 153-160,
     North-Holland, 1988.
 [9] Manros, C.-U., "The X.400 Blue Book Companion", ISBN 1 871802 00
     8, Technology Appraisals Ltd, 1989.

Houttuin & Craigie [Page 14] RFC 1615 Migrating from X.400(84) to X.400(88) May 1994

[10] CCITT Recommendations X.400 - X.430, "Data Communication
     Networks: Message Handling Systems", CCITT Red Book, Vol. VIII -
     Fasc. VIII.7, Malaga-Torremolinos, 1984.
[11] CCITT Recommendations X.400 - X.420 (ISO IS-10021), "Data
     Communication Networks: Message Handling Systems", CCITT Blue
     Book, Vol. VIII - Fasc. VIII.7, Melbourne, 1988.

Appendix C - MHS Terminology

 Message Handling is performed by four types of functional entity:
 User Agents (UAs) which enable the user to compose, send, receive,
 read and otherwise process messages; Message Transfer Agents (MTAs)
 which provide store-and-forward relaying services; Message Stores
 (MSs) which act on behalf of UAs located remotely from their
 associated MTA (e.g., UAs on PCs or workstations); and Access Units
 (AUs) which interface MHS to other communications media (e.g., Telex,
 Teletex, Fax, Postal Services). Each UA (and MS, and AU) is served by
 a single MTA, which provides that user's interface into the Message
 Transfer Service (MTS).
 Collections of MTAs (and their associated UAs, MSs and AUs) which are
 operated by or under the aegis of a single management authority are
 termed a Management Domain (MD). Two types of MD are defined: an
 ADMD, which provides a global public message relaying service
 directly or indirectly to all other ADMDs; and a PRMD operated by a
 private concern to serve its own users.
 A Message is comprised of an envelope and its contents. Apart from
 the MTS content-conversion service, the content is not examined or
 modified by the MTS which uses the envelope alone to provide the
 information required to convey the message to its destination.
 The MTS is the store-and-forward message relay service provided by
 the set of all MTAs. MTAs communicate with each other using the P1
 Message Transfer protocol.

Houttuin & Craigie [Page 15] RFC 1615 Migrating from X.400(84) to X.400(88) May 1994

Appendix D - Abbreviations

    ACSE     Association Control Service Element
    ADMD     Administration Management Domain
    ASCII    American Standard Code for Information Exchange
    ASN.1    Abstract Syntax Notation One
    AU       Access Unit
    CCITT    Comite Consultatif International de Telegraphique et
             Telephonique
    CEN      Comite Europeen de Normalisation
    CENELEC  Comite Europeen de Normalisation Electrotechnique
    CEPT     Conference Europeene des Postes et Telecommunications
    CONS     Connection Oriented Network Service
    COSINE   Co-operation for OSI networking in Europe
    DL       Distribution List
    DIS      Draft International Standard
    EN       European Norm
    ENV      Draft EN, European functional standard
    IEC      International Electrotechnical Commission
    IPM      Inter-Personal Message
    IPMS     Inter-Personal Messaging Service
    IPN      Inter-Personal Notification
    ISO      International Organisation for Standardisation
    JNT      Joint Network Team (UK)
    JTC      Joint Technical Committee (ISO/IEC)
    MD       Management Domain (either an ADMD or a PRMD)
    MHS      Message Handling System
    MOTIS    Message-Oriented Text Interchange Systems
    MTA      Message Transfer Agent
    MTL      Message Transfer Layer
    MTS      Message Transfer System
    NBS      National Bureau of Standardization
    OSI      Open Systems Interconnection
    PRMD     Private Management Domain
    RARE     Reseaux Associes pour la Recherche Europeenne
    RFC      Request for Comments
    RTR      RARE Technical Report
    RTS      Reliable Transfer Service
    WG-MSG   RARE Working Group on Mail and Messaging

Houttuin & Craigie [Page 16] RFC 1615 Migrating from X.400(84) to X.400(88) May 1994

Authors' Addresses

 Jeroen Houttuin
 RARE Secretariat
 Singel 466-468
 NL-1017 AW Amsterdam
 Europe
 Phone: +31 20 6391131
 RFC 822: houttuin@rare.nl
 X.400: C=NL;ADMD=400net;PRMD=surf;
 O=rare;S=houttuin;
 Jim Craigie
 Joint Network Team
 Rutherford Appleton Laboratory
 UK-OX11 OQX Chilton
 Didcot, Oxfordshire
 Europe
 Phone: +44 235 44 5539
 RFC 822: J.Craigie@jnt.ac.uk
 X.400: C=GB;ADMD= ;PRMD=UK.AC;
 O=jnt;I=J;S=Craigie;

Houttuin & Craigie [Page 17]

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