Question 15/VII - Arrangements for interworking between networks other
than ISDNs and Telex, for the provision of data services
(amalgamations of Questions 15/VII, 16/VII, 17/VII and 18/VII
studied in 1985-88)

Considering

(a) that the provision of data services may require several networks to
interwork;

(b) the framework of X-Series Recommendations related to interworking
given in Recommendation X.300;

(c) that X.300-Series Recommendations define general principles and
arrangements for interworking between public networks or between public
networks and other networks for the provision of data services;

(d) that X.60 and X.70-Series Recommendations define detailed
internetwork signalling;

(e) that X.80-Series Recommendations define detailed interworking
functions,

1. What enhancements should be made to Recommendations:

X.322, X.324, X.326, X.327
X.350, X.351, X.352
X.82

2. What new Recommendation(s), if any, are necessary to describe
arrangements for interworking between networks of different types, other
than ISDNs and Telex, including CSPDN, PSPDN, CCSN, private networks and
mobile systems.

ANNEX 1

(to Question 15/VII)

Further details on the study of interworking between
public data networks (PDNs) and public mobile systems

Considering

(a) that administrations are currently operating PDNs (like circuit
switched and packet switched PDNs);

(b) that there is a need to define the specific requirements for
interworking between PDNs and Public Mobile Systems;

(c) that Recommendation X.300 defines general principles and
arrangements for interworking between PDNs and between PDNs and other
public networks for the provision of data transmission services;

(d) that Recommendation X.324 considers the general arrangements for
interworking between PSPDNs and public mobile systems for the provision
of data transmission services;

(e) that procedures for interworking between PDNs and the Maritime
Satellite Service are defined in Recommendations X.350, X.351, X.352,
and X.353;
(f) that Recommendation X.32 specifies the procedures for DTEs operating
in the packet mode and accessing a PSPDN through a public switched
network;

(g) that the mobility of the terminals connected to the Public Mobile
System may require specific functions within the PDNs (e.g. registration
of location, registration of desired facilities, transfer of charging
data between PDNs, etc.);

(h) that Recommendation X.213 specifies the OSI Network Service and that
the interworking between PDNs and Public Mobile Systems should enable
the provision to users of the OSI Network Service;

(i) that Recommendation E.212 contains an international identification
plan for land mobile stations;

(j) that Recommendation Q.1001 contains a comprehensive list of
definitions related to public land mobile networks (PLMNs),

What Recommendations, if any, are necessary to enable interworking
between PDNs and Public Mobile Systems?

What additions or modifications to existing Recommendations are
necessary?

Note 1 - The following liaisons should be maintained in this study:

a) the general principles and arrangements for interworking between PDNs
and between PDNs and other public networks are being studied under
Question 10/VII;

b) operational requirements, including routing numbering and
identification plans for public land mobile systems as studied by Study
Group II for interworking with the PSTN;

c) interworking between public land mobile systems and Signalling System
No.7 is studied by Study Group XI;

d) the study of DTEs accessing a PDN through a public switched network
is carried out under the relevant DTE interface Question 16/VII;

e) for interworking between Public Mobile Systems transfer of
registration and charging data could be required. The applicability of
using the Common Channel Signalling System for this purpose will be
studied by
Study Group XI.

Note 2 - The study should cover some possible specific requirements
related to the mobility of the terminals connected to the Public Mobile
System:

-call diversion to a number in the PDN;

-rerouting of calls when the mobile station roams between various Public
Mobile Systems;

-hand-over of calls when the mobile station moves from one base station
area to another within a Public Mobile System;

-procedures for obtaining routing information from the
Public Mobile System prior to setting up the call (interrogation
procedures).

Note 3 - The study should cover the possible specific requirements
related to new mobile satellite services such as Aeronautical and Land
mobile satellite services.

ANNEX 2

(to Question 15/VII)

Further details on the study of interworking between
Public Data Networks (PDNs) and private data networks

Considering

(a) that administrations are currently operating PDNs such as PSPDNs and
CSPDNs;

(b) that different interworking conditions may exist between private
networks and PDNs;

(c) that Recommendation X.25 defines the user interface to packet
switched PDNs and Recommendations X.21/X.21bis specify the user
interface to circuit switched PDNs. In this respect, it should be noted
that the suitability of such user interfaces for interworking with
private networks has already been considered by Study Group VII and will
still be taken into account;

(d) that PDNs operate a Network Address Extension mechanism which could
be applied in private networks connected to a PDN;

(e) that Recommendation X.300 defines general principles and
arrangements for interworking between public networks, and between
public networks and other networks for the provision of data
transmission services; and that these principles may apply in the case
of interworking between PDNs and private networks;

(f) that Recommendation X.213 specifies the OSI Network Service and that
interworking between Private Networks and PDNs should enable the
provision to users of the OSI Network Service;

(g) that Recommendation X.327 defines the general arrangements for
interworking between packet-switched public data networks (PDNs) and
private data networks for the provision of data transmission services,

1. What Recommendations, if any, are necessary to enable interworking
between PDNs and private networks?

2. What additions or modifications to existing Recommendations are
necessary for interworking between PDNs and private networks?

Note 1 - When studying this Question close liaison should be maintained
with Groups studying specific user interfaces to PDNs.

Note 2 - Different interworking conditions may exist between PDNs and
private networks. Study items identified in relation with such
conditions are documented in the annex.

Attachment

(to Annex 2 of Question 15/VII)

There is a need for general arrangements and principles of interworking
between private data networks and different types of public networks.

Different interworking conditions that may exist between private
networks and public networks are described in the appendix. Taking into
account that Recommendation X.300 already gives some guidance on this
kind of interworking, further study should consider in particular the
following aspects.

1. Bearing in mind the different interworking conditions with specific
arrangements, in addition to those provided for a simple DTE, are
required in the case the DTE is a private network equipment.

2. When considering a connection between a PDN or ISDN and a private
network equipment, what differences have to be considered between the
two types of networks (security, maintenance, ...)? Guidance from other
CCITT Groups would be of interest on this subject.

3. Which layers of the OSI Reference Model are involved in such a
connection between a PDN or ISDN and a private network equipment?

4. It is recognized that private networks, including several different
terminals and types of terminals will be connected to the public data
networks or ISDNs. In those private networks, the different terminals
may belong to different groups internally in the private networks and
may also have a need to communicate into different CUGs in the public
data network or ISDN.

This study should take into account the specific complete addressing
requirements for uniquely identifying a specific DTE as are defined in
Recommendations X.121 (International numbering plan for PDNs) and
I.320 (Numbering and addressing principles in ISDN).

Note - Study Group VII already considered the suitability of DTE/DCE
interfaces such as X.25 and X.21 for interworking with private networks.

These considerations should be taken into account.

Appendix

(to the Attachment to Annex 2 of Question 15/VII)

This appendix describes the different interworking conditions that may
exist between private networks and public data networks or ISDNs, for
the purpose of studying the technical aspects of this interworking.

Note - ISDN in this attachment is considered only for the provision of
data transmission services.

1. "Private PBX" type of interworking

In this case, the private equipment is linked by ONE CONNECTION TO ONE
PUBLIC DATA NETWORK OR ISDN IN ONE COUNTRY as illustrated in Figure 1.

FIGURE 1

"Private PBX" type of interworking

Note 1 - In the case the private equipment is having a second connection
to the same PDN or ISDN, e.g. for security or reliability, it may be of
interest to consider it also as a "Private PBX".

Note 2 - In a multi-services environment, the same PBX equipment may be
simultaneously connected to several dedicated public networks (e.g.
telephone, data, ...). In this case, such a PBX can be logically
considered as different "private PBXs", each one connected to one
dedicated public network.

2. "National private network" type of interworking

In this case, the private equipment is linked by SEVERAL CONNECTIONS TO
ONE OR SEVERAL NETWORKS IN ONE COUNTRY, as illustrated in Figure 2.

FIGURE 2

"National private network" type of interworking

Note - It may be interesting to distinguish in that category of private
equipment interworking, those which are connected to only one PDN or
ISDN.

3. "International private network" type of interworking

In this case, the private equipment is linked by SEVERAL CONNECTIONS TO
SEVERAL NATIONAL PUBLIC DATA NETWORKS IN SEVERAL COUNTRIES, as
illustrated in Figure 3.

FIGURE 3

"International private network" type of interworking

Note - In this case, it may be useful to recognize the different
national parts of the international private network.