rfc941.txt

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   d)  representing a binary syntax DSP as follows:

    Taking the octets in pairs, convert each octet of the pair to a
    number in the range 0-255; this generates six decimal digits,
    abcdef, of which digits a and d may take on only the values o, 1, or
    2. The pair of octets is represented by the sequence of five digits
    gbcef, where the value of digit g is given in Table 8-4:

    

                        Table 8-4:  Values of g.

                      _____________________________
                    |  \  a  |      |      |      |
                    | d \    |  0   |   1  |  2   |
                    |____\___|______|______|______|
                    |   0       0       1     2   |
                    |_____________________________|
                    |   1       3       4     5   |
                    |_____________________________|
                    |   2       6       7     8   |
                    |_____________________________|



    If the original binary field contained an odd number of octets,  the
    final  octet  is  converted  to  a  number  in  the  range 0-255 and
    represented as three decimal digits (000-255);

   e)  when the IDI format is "Local", representing an  ISO  646
       character syntax DSP using the technique described in Clause
       8.3.1 (e); and

   f)  when  the  IDI  format is "Local", representing a National
       Character syntax DSP using the technique described in Clause
       8.3.1 (f).

8.4  Maximum Network Address Length

 The maximum length of the NSAP address for each of the combinations of
 IDI abstract syntax is given in Table 8-5 both the decimal concrete
 syntax and the binary concrete syntax.









ISO/TC-97/SC-6                                                 [Page 26]
RFC 941                                                       April 1985
Network Layer Addressing


                                    

                Table 8-5:  Maximum NSAP Address Lengths

    ________________________________________________________________
    |             | DSP Abstract  |  Binary DSP     | Decimal DSP  |
    |  IDI Format |   syntax      | concrete syntax concrete syntax|
    |_____________|_______________|_________________|______________|
    |             |   Decimal     |   20 octets     |  40 digits   |
    |   X.121     |   Binary      |   17 octets     |  39 digits   |
    |             |               |                 |              |
    |             |   Decimal     |   20 octets     |  40 digits   |
    |  ISO DCC    |   Binary      |   17 octets     |  40 digits   |
    |             |               |                 |              |
    |             |   Decimal     |   20 octets     |  40 digits   |
    |    F.69     |   Binary      |   17 octets     |  40 digits   |
    |             |               |                 |              |
    |             |   Decimal     |   20 octets     |  40 digits   |
    |    E.163    |   Binary      |   17 octets     |  39 digits   |
    |             |               |                 |              |
    |             |   Decimal     |   20 octets     |  40 digits   |
    |    E.164    |    Binary     |   18 octets     |  40 digits   |
    |             |               |                 |              |
    |             |   Decimal     |   20 octets     |  40 digits   |
    | ISO 6523-ICD|   Binary      |   16 octets     |  39 digits   |
    |             |               |                 |              |
    |             |   Decimal     |   20 octets     |  40 digits   |
    |   LOCAL     |   Binary      |   16 octets     |  40 digits   |
    |             | Character     |   20 octets     |  40 digits   |
    |             |National Char. |   15 octets     |  37 digits   |
    |_____________|_______________|_________________|______________|

                                    

  Note:  These values assume a National Character representation of one
  character as two binary octets (see clause 8.2.3).

 From this table it is clear that:

 a)  the maximum length of an NSAP address in its binary concrete syntax
     is 20 octets; and

 b)  the maximum length of an NSAP address in its decimal concrete
     syntax is 40 digits.

 A Network Layer protocol which is capable of conveying a string of
 variable length with a maximum length of either 20 binary octets or 40
 decimal digits is capable of encoding the full semantic content of any
 Network Address.




ISO/TC-97/SC-6                                                 [Page 27]
RFC 941                                                       April 1985
Network Layer Addressing


9  CHARACTER BASED DSP ALLOCATION

An authority may choose to allocate NSAP addresses with the DSP in a
National Character syntax. In such cases, the allocating authority must
define and publish the mapping of the National Character syntax to
either a binary abstract syntax or a decimal abstract syntax.

 Note:  It is recommended that this mapping be done by reference to the
 ISO Register of Character Sets, which is maintained by the European
 Computer Manufacturers Association (ECMA) acting as a registration
 authority according to ISO 2375, "Procedure for the Registration of
 Escape Sequences".

In the case where the authority defines and publishes the mapping of the
National Character set to a binary abstract syntax, the result must be
representable in either one or two octets per National Character.  In
this case, the resulting DSP is considered to be based on the Binary
abstract syntax. AFI values from Table 8-2 and the mapping to binary and
decimal concrete syntaxes are based on the binary abstract syntax.

In the case where the authority defines and publishes the mapping of the
National Character set to a decimal abstract syntax, the result must be
representable in up to five decimal digits per National Character.  In
this case, the resulting DSP is considered to be based on the decimal
abstract syntax. AFI values from Table 8-2 and the mapping to binary and
decimal concrete syntaxes are based on the decimal abstract syntax.

 Note:  The ability to base DSP allocation on National Character sets
 allows DSP allocation based on international character sets. This may
 simplify address assignment in some cases, and may facilitate
 representation of NSAP address in humanly-readable form.  Nevertheless,
 NSAP addresses should not be confused with Application Layer entity
 titles.  NSAP addresses are not intended to provide the same degree of
 human-readable,  user-friendly  naming  and  addressing capabilities as
 may be expected in Application Layer entity titles.


















ISO/TC-97/SC-6                                                 [Page 28]
RFC 941                                                       April 1985
Network Layer Addressing


10  REFERENCE PUBLICATION FORMATS

Reference publication formats are defined  to  allow  unambiguous
representation of NSAP addresses in both written and oral communication.

10.1  Decimal Reference Publication Format

 The Decimal reference publication form (DRPF) consists of a string of
 up to 40 decimal digits.  The DRPF is the written inscription of the
 decimal concrete syntax defined in clause 8.3.2.

10.2  Hexadecimal Reference Publication Format

 The Hexadecimal reference publication format (HRPF) consists of the
 symbol "/" (solidus) followed by a string of up to 40 hexadecimal
 digits. The HRPF is the written inscription of the binary concrete
 syntax defined in clause 8.3.1, using two hexadecimal digits ranging
 from 00 through FF to represent each binary octet.



































ISO/TC-97/SC-6                                                 [Page 29]
RFC 941                                                       April 1985
Network Layer Addressing


ANNEX A - NETWORK ENTITY TITLES

This Annex is an integral part of the Addendum.

In order to perform routing functions and to distribute Network Layer
management information concerning routing among Network entities, it is
necessary to be able to unambiguously identify Network entities in end
systems and intermediate systems.  The Reference Model (ISO 7498)
provides a definition of the concept of an (N)-entity title, which may
be used to permanently and unambiguously identify a Network entity in an
end system or intermediate system.

Any authority responsible for allocating addresses to NSAPs may choose
also to allocate Network entity titles. One of the ways in which this
can be done is to use the principles and mechanisms defined in this
Addendum for allocating Network addresses. When this approach is taken,
a Network entity title has the same abstract syntax as an NSAP address.
A value may be allocated as a Network entity tile only if it has not
been allocated as an NSAP address.


































ISO/TC-97/SC-6                                                 [Page 30]
RFC 941                                                       April 1985
Network Layer Addressing


ANNEX B - NSAP ADDRESS ALLOCATION

This Annex is not an integral part of the Addendum.

The division of the global Network addressing domain according to the
IDI formats described in clause 8.2.1.2 may be illustrated by the
following figure.  The numbers adjacent to each line in the figure are
AFI values, as defined in Table 8-2 of clause 8.2.1.2.

         Figure B-1 - NSAP Address Allocation on attached page.

 00-09          Reserved - will not be allocated

 10-35          Reserved for future allocation by joint agreement of ISO
                and CCITT

 36-37          X.121

 38-39          ISO DCC

 40-41          F.69

 42-43          E.163

 44-45          E.164

 46-47          ISO ICD

 48-51          Local

 52-59          Reserved for future allocation by joint agreement of ISO
                and CCITT

 60-69          Allocated for assignment by ISO

 70-79          Allocated for assignment by CCITT

 80-99          Reserved for future allocation by joint agreement of ISO
                and CCITT

 












ISO/TC-97/SC-6                                                 [Page 31]
RFC 941                                                       April 1985
Network Layer Addressing


ANNEX C - RATIONALES

This annex contains tutorial and explanatory material, and is not an
integral part of the Addendum.

C.1  IDI FORMATS (Clause 8.2.1.2)

 The rationale for the use of the specific IDI formats identified in
 Clause 8.2.1.2 is to allow the allocation and assignment of NSAP
 addresses to be based on existing, well-established network numbering
 plans and organization-identification standards.

 The CCITT numbering plans are included so as to allow for the
 designation of the organization to which a number is assigned as an
 authority for the assignment of NSAP addresses. If the organization
 identified by a particular number from one of these plans chooses not
 to define any further sub-addressing beyond that number, then the
 number itself constitutes an NSAP