International Telegraph and Telephone Com VII-No.____________
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
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
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.
The private network DTE addressing method chosen should satisfy the
- Common DTE's which conform to current packet switching standards
should be able to operate between private and public data networks
- Impact on public data networks in countries which do not allow
private data networks should be avoided.
IEN 174 Page 2
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
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
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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
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
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
Other combinations are possible, such as communication between DTE's,
each on a separate private network, by means of one or more public
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
IEN 174 Page 4
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
1.1 There could be a large number of private data networks in a
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.
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Note - The term "telex" employed in this Recommendation, includes
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.
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+---------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
1 - Reserved
4 - For data network identification codes (DNIC)
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.
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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
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
First Digit of Networks
of PNIC PNIC + NTN per DNIC
------- ---------- --------
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
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.
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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
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
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
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
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
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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).