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                                                               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:
  1. Common DTE's which conform to current packet switching standards

should be able to operate between private and public data networks

    without modification.
  1. 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:
  1. select a data country code (DCC) in each zone to indicate

the location, or

  1. 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).
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