ISO/IEC TR 15410:1998 情報技術—システム間のテレコミュニケーションと情報交換—PISNモビリティ-一般原則とサービスの側面 | ページ 5

4 Introduction

This clause provides some background and gives an overview of the concepts covered in this Technical Report by describing the basic structure of a PISN and explaining the key areas related to mobile users and terminals.

4.1 Private Integrated Services Network environment

As seen in this Technical Report, the telecommunications environment of a PISN consists of PINXs radio exchanges (RE), radio base stations (RBS), wired terminals, wireless terminals and users of these terminals. See Figure 1 for an illustration.

4.2 PISN mobility concept

As the PINX itself is not mobile, mobility with respect to the access side of the PINX can apply to the terminal, to the user of the terminal, or to both. This means that the relationship can be dynamic either between the access point and the terminal, or between the terminal and the user. See Figure 2 for an illustration.

WTM is applicable only to wireless terminals whilst PPM is applicable both to wired and wireless terminals, as well as to a mixed environment utilising both terminal types.

Three different levels are identified in order to describe a PISN mobility model for this study:

• access level;
• terminal level;
• user level.

Two mobility concepts are identified and generally described in this subclause. The two concepts are at this stage considered to be independent. This means that one of the concepts may be standardised/implemented without the other. The concepts are called Private Personal Mobility (PPM) and Wireless Terminal Mobility (WTM) and are briefly described below.

In this report mobility for users and terminals is limited to a single PISN. Referring to Figure 1, the mobility of a user/terminal is either within or between the PINXes. Mobility between two or more PISNs is outside the scope of this Technical Report.

4.2.1 Private Personal Mobility (PPM)

With PPM, the static relationship between the user and the terminal providing his telecommunications services is abandoned.

In PPM it is possible for the user to change terminal, wired or wireless, between calls while retaining his telecommunications services.

The intent of PPM is to associate services with users and not terminals. However, the services provided may be limited by the capabilities of the particular terminal at which the user registers.

The update of the users location shall be performed or initiated by the user. This can be done by the user manually (e.g. a key sequence), but, if the terminal permits, it can also be accomplished through more advanced and automatic means (e.g. use of smart cards).

4.2.2 Wireless Terminal Mobility (WTM)

With WTM, there is no fixed relation between the wireless terminal and the PISN access and the terminal can also change access points as it is moving. This can occur between calls or during an established call.

Wherever possible, services should be provided to a wireless terminal in the same way as to a wired terminal. However, some existing services may need modification and new services may be required. From the users point of view, the same level of service quality is desired from wireless terminals as from wired terminals.

Location information concerning the wireless terminal may be available in the network and used for call handling (e.g. routeing, charging, etc.). This location information may be updated automatically by the wireless terminal or manually by the user of the wireless terminal.

4.2.3 Database architecture

An architecture based on the Home Data Base/Visitor Data Base (HDB/VDB) concept has been assumed for mobility management in this Technical Report. This architecture is considered mature for mobile telecommunication applications. Furthermore the introduction of mobility based upon this approach is considered to minimise the impact on the current standards applicable to PISNs.

One consequence of the choice of the HDB/VDB concept is that the practical application of mobility with multiple HDBs in a PISN which allows a user to permanently change his location without changing his number (free numbering), is not covered in this Technical Report.

The interface between the PINX and the databases HDB/VDB is out of the scope of this Technical Report.

4.3 Relation between PPM and WTM

4.3.1 Mobility seen as a dynamic linking of identities

PPM gives the user freedom to use any terminal in the PISN whilst WTM allows a WT to be used at any compatible PISN radio access.

Each form of mobility requires a dynamic linking of two identities. PPM requires a dynamic linking between the PPM number and the terminal (access address in the case of a wired terminal). WTM requires a dynamic linking between the WT address and a PISN access address.

To the extent that each of these dynamic linkings are similar - in each of them one identity represents the mobile entity and the other identity represents its"location" - it should be possible to use the same addressing and routeing principles for both PPM and WTM.

It should then be possible to use the same HDB and VDB concept for both PPM and WTM, though different data structures may be required for the two forms of mobility.

There is no intention to standardise an interface between the PINX and the databases (HDB/VDB).

4.3.2 Similarities of processes

The following procedures should be defined as generic as possible for both PPM and WTM:

• Registration;
• Authentication;
• Handling of incoming calls to the mobile user;
• Handling of outgoing calls from the mobile user.

This would minimise the differences between the procedures for PPM and WTM while allowing the specific characteristics of each to be taken into account.

• a) WTM
  • Terminals can perform actions automatically.

• b) PPM

  • The PPM concept involves actions to be performed by the users. These procedures differ from the terminal procedures in that they have to be adapted to human actions.

4.3.3 Location Area

This report uses the term Location Area (LA) only in relation with WTM and not for the PPM case.

4.3.4 The use of PPM and WTM together

WTM is independent of PPM in the sense that WTM and PPM together allow mobility of the terminal while maintaining the PPM user's registration on the terminal. This is likely to require a complex procedure which the service standards must accomodate. The details are discussed further in chapter 7, «PPM on top of WTM».

4.4 Mobility between calls and during an established call

Two fundamental situations should be covered when discussing mobility;

• the ability to change access (WTM) or terminal (PPM) between calls, and
• the ability to change access (WTM) during an established call.

4.5 Services to be supported

When mobility is introduced, it is desirable that a full range of basic and supplementary services is made available to mobile users with the same quality of service as would be expected by fixed users. The operation of some existing supplementary services may need to be modified if they are to be available to mobile users.

4.5.1 Bearer services and Teleservices

Standards for mobility in the private network should be capable of supporting all circuit mode basic services as defined in ISO/IEC 11574.

4.5.2 Supplementary Services

All supplementary services defined for PISNs should be considered and made applicable if this can be done without undue difficulty. In addition the following mobility specific supplementary services and Additional Network Features (ANFs) should be standardized.

• WTM Location registration;
• WTM incoming call handling;
• WTM outgoing call handling;
• WTM authentication of the terminal by the network;
• WTM authentication of the network by the terminal;
• WTM Handover
• PPM registration;
• PPM incoming call handling;
• PPM outgoing call handling.

4.5.2.1 Access to supplementary services

The provision of standardised supplementary services where one or more of the involved users are either a WTM or PPM user can present a number of problems in implementation.

One of the most obvious problems likely to be encountered by mobile users as they roam from one PINX to another is the difference in supplementary service access methods implemented by the various manufacturers.

Careful network planning and management can, in many cases, be used to provide unified user procedures throughout the network but this is likely to be more difficult where:

• a) mobility is introduced to an established PISN of fixed users as the co-ordination of user procedures is of considerably less importance when all user terminals are static. Also, there may be some resistance to change among the existing users;
• b) some terminals or PINXs within the network implement fixed user procedures set by the manufacturer and are not available for customisation;
• c) not all PINXs in a PISN have implemented the same set of supplementary services:

The rationalisation of user procedures is, however, a difficult problem to deal with. While complying with the Private Signalling System #1 (PSS1) standards for supplementary service signalling between PINXs, each manufacturer is likely to offer access to the services in slightly different ways because:

• a) firstly, there are three generic procedures for network access protocols (i.e., the protocol between network and terminal equipment): functional procedures, the keypad stimulus protocol and the feature key management stimulus protocol and;
• b) secondly, even if the same generic method is used, there is still scope for differences, since in the stimulus protocol case no specific procedures are standardised for individual supplementary services, and standardised functional procedures are so far defined for public Integrated Services Digital Network (ISDN) terminals only and for very few services.

This could cause confusion to roaming users as they try to invoke supplementary services at different points within the PISN.

One way to overcome this problem is to create a homogeneous environment for roaming users, e.g., by ensuring that all PINXs supporting PPM or WTM in a network, all fixed radio equipemt and all WTs are of the same type and from a single manufacturer (in many instances this will not be considered as a practical or feasible solution), or by specifing standards for the access procedures (which is a long term goal rather than a practical alternative for the near future).

Another option is to ensure that the user's Home PINX is always accessed to provide supplementary services (i.e., always route incoming and outgoing calls via the Home PINX). For many services this would be quite acceptable and a very practical solution but for others, the processintg, signalling and transmission overheads necessary for maintaining user status at the Home PINX would be intolerable.

A further option is to make use of the functional protocols defined for public ISDN. The WTs and radio fixed parts would need to be upgraded whenever the functional protocols for a new service are published. The cost of keeping these up-to-date could be unacceptably high unless or until a method of downloadintg a WT on-line can be devised.

4.5.2.2 Service options

PISN standards specify in many cases the mandatory core of a supplementary service and optional features, which an implementation may support in addition to the basic core. A manufacturer may provide further proprietary enhancement of the supplementary service. For instance, the core of Call Forwarding Unconditional (CFU) is that all calls or calls associated with a specific basic service are diverted to another PISN address. Standard options are the provision of notifications, interrogation procedures, etc. A manufacturer may further offer the non-standardised possibility to specify different diverted-to numbers based on certain call criteria, e.g., external versus internal calls, while still complying with the basic core of CFU.

The consistent provision of standard and proprietary service options for roaming users faces similar difficulties as discussed in 4.5.2.1. Invoking the supplementary service at the Home PINX regardless of the user's actual location again seems a good solution in some cases.

4.5.2.3 Dynamic registration and service related data.

Some existing supplementary services allow the served user to register data that are then used in the invocation of the service. An example is the Diverted-to user's address in the Call Diversion (CD) services. Once registered, this information must continue to be associated with the mobile user regardless of the user's movements within the PISN.

Other supplementary services rely on data stored in association with a specific service invocation, which also must"follow" the roaming user when changing location. An example is the queue of outstanding call completion requests.

In both cases this may prove to be difficult in a multi-vendor envitonment where such data may be stored and processed in quite different ways. There seems to be no simple solution to this problem other than imposing constraints on the use of such services for mobile users.

4.5.2.4 Destination PINX: Home PINX versus Visitor PINX

Many supplementary services require actions from the destination PINX of a call. In the case of roaming users it is not so obvious what should be regarded the destination PINX, since the roaming user «exists» twice in the PISN. In a logical sense it would be the Home PINX as it holds the user's permanent «image». From a call termination point of view it would be the Visitor PINX as this is the user's current physical location. The determination of which interpretation is more suitable must be made on a case-by-case basis.

If the Visitor PINX is chosen, the following considerations are worthy of note in almost all cases:

• a) the service may not be available to a served user at all locations;
• b) the options subscribed to by the served user may not be offered at all Visitor PINXs:
• c) user procedures may differ from PINX to PINX.