IEN 174

International Telegraph and Telephone        Com VII-No.____________
       Consultative Committee
               (CCITT)


      Period 1981-1984                       Original:  English

Question:  4/VII                             Date:  1981 February 12



                   STUDY GROUP VII - CONTRIBUTION NO.



SOURCE:  United States of America

TITLE:  Private Network DTE Addressing



1.  INTRODUCTION

   There is a need to allow interoperation between DTE's connected to a
   private data network and DTE's connected to or accessed through a
   public data network.  The number and sizes of private data networks
   are increasing, and further standardization in this area is urgently
   needed.

   The scope of this activity is to propose a standard addressing scheme
   to facilitate interoperation between DTE's in this environment.

   This document discusses several alternative addressing mechanisms to
   identify user devices connected to private networks.  The Annex
   contains a specific proposal for one alternative which seems to meet
   the objectives outlined below.

2.  OBJECTIVES

   The private network DTE addressing method chosen should satisfy the
   following objectives:

      - Common DTE's which conform to current packet switching standards
      should be able to operate between private and public data networks
      without modification.

      - Impact on public data networks in countries which do not allow
      private data networks should be avoided.

IEN 174                                                           Page 2



3.  ALTERNATIVES

   3.1  Shared Address Space.  Individual public data networks may
   allocate a portion of their X.121 address space to interconnected
   private networks, by subscription agreement.

   3.2  Extended X.121 Addressing.  Public data network X.121 addresses
   may be extended by providing additional address fields in the CALL
   REQUEST packet.  These fields could be contained within the
   facilities field or within the call user data field.

   3.3  Second Dial Tone.  The call may be established to the interface
   between a public network and the private network using a normal CALL
   REQUEST packet.  The call may then be extended either using a
   following special CALL REQUEST packet or by call request information
   contained in subsequent DATA packets.

   3.4  Private Network Identification Code.  A single private network
   DNIC may be allocated in each country which allows private networks.
   This DNIC would be shared among all private networks having public
   network connections in that country.  The remaining ten digits of the
   DTE numbering space for that DNIC would consist of a Private Network
   Identification Code (PNIC) followed by a network terminal number
   (NTN).

4.  CONSIDERATIONS

   4.1  Shared Address Space.  This approach has no impact on countries
   which do not allow private networks and has no impact on X.121
   numbering.  However, it may consume large amounts of address space in
   public networks, for example, if a private network supports a large
   number of terminals, or if a private network is directly connected to
   more than one public data network.

   4.2  Extended X.121 Addressing.  This alternative would consume
   potentially limited space in the facilities field or would require
   allocation of the call user data field.  Both current DTE
   implementations and public data networks in countries not allowing
   private networks would be impacted.

   4.3  Second Dial Tone.  For this approach, the user must know how to
   route all calls, and must construct a non-standard CALL REQUEST
   packet or specially formatted call request data in DATA packets.
   This impacts both current DTE implementations and public networks in
   countries not allowing private networks.

   4.4  Private Network Identification Code (PNIC).  Using this
   approach, the common private network DNIC may be used to specify the
   country for interconnection,  and PNIC and NTN addresses may be

IEN 174                                                           Page 3



   consistent between multiple public network interconnections.  Neither
   existing DTE implementations nor public networks in countries not
   permitting private networks are affected.  Figures 1 and 2 illustrate
   this.

   In Figure 1 an originating DTE on a private network placing a call to
   a normal DTE on a destination public data network requires no
   modification in either DTE, the transit public network, or the
   destination public network.  The called and calling DTE addresses
   both conform to X.121.  The calling address is composed of the shared
   private DNIC of the country of the originating public network,
   followed by the PNIC and the NTN.

   ORIG --> PRIVATE --> ORIG --> TRANSIT --> DEST --> DEST
   DTE      NETWORK     PDN        PDN       PDN      DTE


                                Figure 1

   In Figure 2, an originating DTE on a public network places a call to
   a DTE on a private network which is interconnected through another
   public data network.  This requires no modification to either DTE,
   the transit public network, or the originating public network.  The
   called and calling DTE addresses both conform to X.121.  The called
   address is composed of the shared private DNIC of the country of the
   destination public network, followed by the PNIC and the NTN.

   ORIG --> ORIG --> TRANSIT --> DEST --> PRIVATE --> DEST
   DTE      PDN        PDN       PDN      NETWORK     DTE

                                Figure 2

   Other combinations are possible, such as communication between DTE's,
   each on a separate private network, by means of one or more public
   data networks.

5.  CONCLUSIONS

   The shared address space and the private network identification code
   approaches meet the basic objectives outlined above.  Each has
   attributes that may make it more attractive for specific situations,
   taking into account characteristics such as the size of the private
   network.  Both approaches should be provided within the family of
   CCITT Recommendations.

IEN 174                                                           Page 4



                                 ANNEX

Draft Recommendation X.12x


         INTERNATIONAL NUMBERING PLAN FOR PRIVATE DATA NETWORKS


The purpose of this International Numbering Plan is to facilitate the
introduction of private data networks and provide for their interworking
on a worldwide basis.

   1.  Design considerations

   The design considerations that form the basis of this Plan are as
   follows:

      1.1  There could be a large number of private data networks in a
      country*;

      1.2  Where a number of private data networks are to be established
      in a country*, it should not be mandatory to integrate the
      numbering plans of the various networks;

      1.3  The International Numbering Plan should permit the
      identification of a called country* as well as a specific private
      data network in that country*;

      1.4  The number of digits comprising the code used to identify a
      country* should be the same for all countries*;

      1.5  The number of digits comprising the code used to identify a
      private data network should be inversely related to the number of
      data terminals to be suported on the private data network,
      resulting in efficient use of the numbering space;

      1.6  A network data number assigned to a data terminal should be
      unique within a particular private network.  This network data
      number should form part of the international data number which
      should also be unique on a worldwide basis;

      1.7  The number of digits to be used in an international data
      number should be governed by national and international
      requirements but a reasonable limit on the overall number of
      digits should be imposed;

      1.8  The Numbering Plan should make provision for the interworking
      of data terminals on private data networks with data terminals on
      public data, telephone, and telex networks;
      -----------------
      * Country or geographical area.

IEN 174                                                           Page 5



      Note - The term "telex" employed in this Recommendation, includes
      TWX networks.

      1.9  The International Numbering Plan should provide for
      substantial spare capacity to accommodate future requirements;

   2.  Characteristics and applications of the Numbering Plan

      2.1  Number system

         2.1.1  The 10 digit numeric character set 0-9 should be used
         for numbers (or addresses) assigned to data terminals on
         private data networks.  This principle should apply to both
         network data numbers and international data numbers.

         2.1.2  Use of the above number system will make it possible for
         data terminals on private data networks to interwork with data
         terminals on public data, telephone, and telex networks.

      2.2  Data network identification codes

         2.2.1  A data network identification code (DNIC) should be
         assigned to groups of private data networks within a country*.

         2.2.2  All data network identification codes (DNIC) should
         consist of four digits.  The first three digits should always
         identify a country* and could be regarded as a data country*
         code (DCC).  The fourth digit should identify a specific group
         of private data networks within a country*.

         2.2.3  Each country* should be assigned at least one 3-digit
         data country* code (DCC) in accordance with Recommendation
         X.121.  The data country* code (DCC) in conjunction with a
         specific fourth digit may identify a group of private data
         networks.  The format for data network identification codes
         (DNIC) should be as indicated in Figure 1/X.12x.

IEN 174                                                           Page 6



                   +---------Data network identification code (DNIC)
                   |
             +------------+
             | Z  X  X |X |
             +---------+--+
                  |     |
                  |     +----Private Network Group digit
                  |
                  +----------Data country code (DCC)

         X - denotes any digit from 0 through 9

         Z - denotes any digit from 2 through 7 as indicated in 2.2.4

                  TABLE 1/X.12x - First digit of data
                      network identification code

            0 -
            1 -   Reserved

            2 -
            3 -
            4 -   For data network identification codes (DNIC)
            5 -
            6 -
            7 -

            8 -   For interworking with telex networks
            9 -   For interworking with telephone networks


         Note 1 - The allocation of codes for non-zoned services, such
         as the marine satellite services, is for further study.  The
         following points could be considered:

            - select a data country code (DCC) in each zone to indicate
            the location, or

            - use an escape DNIC such as 11XX.

         Note 2 - Details on the Numbering Plan aspects of interworking
         between private data networks and public telephone and telex
         networks will be given in another Recommendation.

IEN 174                                                           Page 7



         2.2.6  The assignment of data country codes (DCC) is to be
         administered by the CCITT.  The assignment of private network
         group digits will be made nationally and the CCITT Secretariat
         notified.

         Assignments by the Director of the CCITT of data country* codes
         (DCC) as well as assignments by countries of the private
         network group digits will be published in the Operational
         Bulletin of the International Telecommunication Union.

      2.3  Private network identification codes

         2.3.1  A private network identification code (PNIC) should be
         assigned to each private data network contained within a group
         of private networks identified by a specific DNIC.

         2.3.2  The first digit of the private network identification
         code (PNIC) indicates the total number of digits comprising the
         private network identification code (PNIC).  In the system of
         private network identification codes, the first digit of such
         codes should be in accordance with Table 2/X.12x.

               TABLE 2/X.12x - Format of private network
            identification code and national terminal number

                                                        Maximum Number
         First Digit                                    of Networks
         of PNIC         PNIC + NTN                     per DNIC
         -------         ----------                     --------

         0
         1   reserved
         2               2X + 8 digit NTN maximum       10
         3               3XX + 7 digit NTN maximum      100
         4               4XXX + 6 digit NTN maximum     1,000
         5               5XXXX + 5 digit NTN maximum    10,000
         6               6XXXXX + 4 digit NTN maximum   100,000
         7
         8   reserved
         9

         NTN - denotes network terminal number
         X - denotes any digit from 0 through 9


         2.3.3  Should a country have more private data networks than
         can be grouped under one DNIC, another DNIC may be allocated
         for a new group of private data networks.

         2.3.4  The assignment of private network identification codes
         is to be administered nationally.

IEN 174                                                           Page 8



      2.4  International data number

         2.4.1  A data terminal on a private data network when called
         from another network should be addressed by its international
         data number.  Likewise, when a data terminal on a private data
         network calls a data terminal on any other network, the called
         data terminal should be addressed by its international data
         number.  The international data number for a data terminal on a
         private data network should consist of the data network
         identification code (DNIC) of the appropriate private network
         group, followed by the private network identification code
         (PNIC), followed by the network terminal number (NTN); i.e.,
         international data number = DNIC + PNIC + NTN.

         The network terminal number (NTN) should consist of all the
         digits necessary to uniquely identify the data terminal within
         the serving network and should not include any prefix (or
         access code) that might be employed for such calling.

      2.5  Maximum number of digits

         2.5.1  International data numbers could be of different lengths
         but should not consist of more than 14 digits.

         Note - The limit of 14 digits specified above applies
         exclusively to the address information.  Adequate register
         capacity should be made available at data switching exchanges
         to accommodate the above address digits as well as any
         additional digits that might be introduced for signalling, or
         other purposes.

      2.6  Prefix

         2.6.1  For outgoing calls from a private data network, a prefix
         (or access code) would generally be required to access
         appropriate facilities for network interworking.  The
         composition of this prefix is a network matter as the prefix
         does not form part of the international data number.  However,
         the possible need to accommodate such a prefix with regard to
         digit register capacity in the calling network should be noted.

      2.7  Number analysis - calls between data networks

         2.7.1  In the case of calls between data networks, provision
         should be made in originating networks to interpret the first
         three digits of the international data number.  These digits
         constitute the data country* code (DCC) component of the data
         network identification code (DNIC) and identify the terminal
         country*.  This information may be required in the originating
         network for routing purposes.

IEN 174                                                           Page 9



         2.7.2  In originating networks, it might also be necessary to
         interpret the fourth digit, of a DNIC.  Such interpretation may
         provide the identity of a specific public data network in a
         country* where several public data network are in service.
         This information might be required for the selection of
         specific routes to called public data networks.

         2.7.3  In networks connected to private data networks, it is
         necessary to interpret the private network identification code
         (PNIC).  Such interpretation provides the identity of a
         specific private data network in a country* where private data
         networks are in service.  This information is required for the
         selection of specific routes to called private data networks.

         2.7.4  Networks receiving calls for private data networks
         should receive the complete international data number including
         the data network identification code (DNIC).  However, where a
         country* of destination indicates that it does not wish to
         receive the data country* code (DCC) component of the DNIC,
         arrangements should be made to suppress the DCC.

         2.7.5  In transit countries*, the complete international data
         number including the data network identification code (DNIC)
         must always be received.  Interpretation of the first three
         digits would identify the called country*.  Interpretation of
         the fourth digit would identify a specific data network, a
         group of private data networks, or a service in the called
         country.  Interpretation of the fourth digit might be required
         for billing purposes or for route selection beyond the transit
         country*.

         2.7.6  Where a data call is to be routed beyond a transit
         country* through a second transit country*, the complete
         international data number, including the data network
         identification code (DNIC) should always be sent to the second
         transit country*.  Where the data call is to be routed by a
         transit country* to the country* of destination, the
         arrangements indicated in 2.6.4 above should apply.

      2.8  Directories and written international data number
      representation

         2.8.1  Directories for private data networks should include
         information on the procedures to be followed for making
         outgoing data calls.  A diagram could assist the customer in
         these procedures.

         2.8.2  With regard to the publication of international data
         numbers on letterheads or other written material, it is
         recommended that the network terminal number (NTN) and private
         network identification  code (PNIC) should be easily

IEN 174                                                          Page 10



         distinguished within the international number, i.e., that there
         be a space between the 4-digit DNIC, the PNIC, and the network
         terminal number (NTN).