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Contents of Recommendation Q.1001
GENERAL ASPECTS OF PUBLIC LAND MOBILE NETWORKS
1. General
2. Definitions
3. Architecture of the Public Land Mobile Network
4. Services in the Public Land Mobile Network
5. List of acronyms Recommendation Q.1001
GENERAL ASPECTS OF PUBLIC LAND MOBILE NETWORKS
1. General
This Recommendation covers definitions, architectures and services in
Public Land Mobile Networks.
The definition section is subdivided into basic, roaming and handover
subheadings.
The architecture section covers examples of Public Land Mobile Network
architecture in roaming and handover situations.
The services section covers introductory descriptions of basic and
supplementary services that can be provided to the user.
2. Definitions
2.1 Basic definitions
2.1.1 Public Land Mobile Services
Telecommunications services provided to moving subscribers (terrestrial
applications).
2.1.2 Public Land Mobile Network
A Public Land Mobile Network (PLMN) is established and operated by an
administration or RPOA for the specific purpose of providing land mobile
telecommunication services to the public. A PLMN may be regarded as an extension of a
fixed network (e.g. PSTN) or as an integral part of the PSTN. In the first
case, it can be considered as a collection of mobile services switching centre
(MSC) areas within a common numbering plan (e.g. service access codes) and a common
routing plan (e.g. definition of crossover point); in this case the MSCs are
the functional interfaces between the fixed network and a PLMN for call set-up.
In the second case, it can be considered as an assemblage of special logic in
existing or future PSTN/ISDN stored program controlled digital local exchanges,
conceptually integrated within a common numbering and routing plan.
Functionally the PLMNs may be regarded as independent
telecommunications entities even though different PLMNs may be interconnected through the PSTN
and PDNs for forwarding of calls or network information. A similar type of
interconnection may exist for the interaction between the MSCs of one PLMN.
The location register system of a PLMN may be centralized, distributed
or segmented. So long as we are concerned with functions of a PLMN, such as
routing and interworking, the configuration and operation of the location register
system have no influence on external networks.
The use of the concept PLMN is illustrated in Figure 1/Q.1001 where
various PLMNs are shown with their interfaces to the fixed networks. It should be
noted that a PLMN may have several interfaces with the fixed network (e.g. one
for each MSC). Interworking between two PLMNs may be performed via an
international gateway.
Figure 1/Q.1001 also shows the information paths between a PSTN and a
PLMN and between two different PLMNs. The solid lines indicate a possible
physical path between the PLMNs through the PSTN. The dotted line indicates that, for
some interactions, an end-to-end information path (established through the
physical path) may exist between the two PLMNs.
FIGURE 1/Q.1001
The use of the concept PLMN for country A and country B
2.1.3 Mobile services switching centre
In an automatic system the Mobile Services Switching Centre (MSC)
constitutes the interface between the radio system and the public switched
telephone network. The MSC performs all necessary signalling functions in order to
establish calls to and from mobile stations.
In order to obtain radio coverage of a given geographical area a number
of base stations (radio transmitters/receivers) are normally required; i.e.
each MSC would thus have to interface several base stations. In addition several MSCs
may be required in order to cover a country. The definition of the MSC may be
prefixed by the terms "land" or "maritime" if that is more suitable in a specific
application.
2.1.4 Base station
The base station (BS) is the common name for all the radio equipment located
at one and the same place used for serving one or several cells.
2.1.5 Mobile station
The mobile station (MS) is the interface equipment used to terminate the
radio path at the user side. It includes terminal functions required to provide
services to the user, e.g. terminal equipment and terminal adaptors.
2.1.6 Cell
The area covered by a base station, or by a sub-system (sector antenna) of
that base station corresponding to a specific logical identification on the radio
path, whichever is smaller.
Every mobile station in a cell may be reached by the corresponding radio
equipment of the base station.
2.1.7 Base station area
The area covered by all the cells served by a base station.
2.1.8 Location area
The location area is defined as an area in which a mobile station may move
freely without updating the location register. A location area may comprise several
cells.
2.1.9 MSC area
The part of the network covered by an MSC. An MSC area may consist of
several location areas.
2.1.10 Service area
The service area is defined as an area in which a mobile station is
obtainable by another PLMN, PSTN or ISDN subscriber without the subscriber's knowledge of
the actual location of the mobile station within the area. A service area may consist
of several PLMNs. One service area may consist of one country, be a part of a
country or comprise several countries. The location registration system associated with
each service area must thus contain a list of all mobile stations located within that
service area.
Figure 2/Q.1001 shows an example of the composition of a service area.
Note - This definition does not take into account any constraints on routing
imposed by the international telephone network.
2.1.11 System area
The system area consists of one or more service areas with fully compatible
MS-BS interfaces.
Note - The location registers of the individual service areas remain autonomous;
updating of the location information is not performed when a roaming mobile station
moves from one service area to another. The overall composition of the international
land mobile system is shown in Figure 3/Q.1001.
2.1.12 Mobile Subscriber International ISDN Number
The Mobile Subscriber International ISDN Number is defined as the number
which has to be dialled in order to reach a mobile subscriber in a service area. See
also Recommendations E.164 and E.213.
2.1.13 International mobile station identity
The mobile station's identification uniquely identifies the MS
internationally. The identity is composed as defined in Recommendation E.212.
FIGURE 2/Q.1001
Use of the definitions.
In this example the service area consists of one PLMN
FIGURE 3/Q.1001
Composition of the system area
2.1.14 Radio traffic path
The radio communication facility between a mobile station and a base station
intended to carry a call and uniquely assigned to the mobile station during that
call.
2.1.15 Radio control path
The radio communication facility between a mobile station and a base station
intended to carry all the information transfer between the mobile station and the
MSC, in which area the mobile station currently is located, during the time that no
radio traffic path between that base station and that mobile station is assigned.
2.2 Roaming definitions
2.2.1 Location register
To establish a call to a mobile station the network must know where this
mobile station is located. This information is stored in a function named location
register. A mobile station is registered at one location register which functions as its
home centre for charging and billing purposes and for administering its subscriber
parameters.
2.2.2 Location information
The location register should as a minimum contain the following information
about a mobile station:
- international mobile station identity;
- actual location of the mobile station (e.g. PLMN, MSC area,
location area, as required).
2.2.3 Home PLMN
The PLMN in which a mobile station is permanently registered.
2.2.4 Home location register
The location register to which a mobile station is assigned for record
purposes such as subscriber information.
2.2.5 Home MSC
The term home MSC (HMSC) may be used in cases where the home location
register is implemented in an MSC.
2.2.6 Equipment Identity Register
The register to which an international mobile equipment identity is
assigned for record purposes.
2.2.7 Visited PLMN
The PLMN, other than the home PLMN, in which a roaming subscriber is
currently located.
2.2.8 Visitor location register
The location register, other than the home location register used by an
MSC to retrieve information for, for instance, handling of calls to or from a
roaming mobile station, currently located in its area.
2.2.9 Visited MSC
The term visited MSC (VMSC) may be used in cases where the visitor
location register is implemented in an MSC.
2.2.10 Gateway PLMN
The PLMN which receives a call from a fixed subscriber, via a public
switched network, for extension to a mobile station. The gateway PLMN may vary for
interconnection with different public networks.
The gateway PLMN could be the home PLMN or the visited PLMN or any
other.
2.2.11 Gateway MSC
The MSC which receives a call from a fixed subscriber, via a public
switched network, for extension to a mobile station. The gateway MSC may vary for
interconnection with different public networks.
The gateway MSC may be any MSC of the PLMN, including the HMSC or VMSC
if the home and visited location registers are implemented in the MSC.
2.2.12 Designation method
The calling subscriber must know the actual location area of any mobile
station. The call is established according to the dialled information only, i.e.
the call is not rerouted by the location register when the mobile station
currently is in another location area.
2.2.13 Non-designation method
The calling subscriber is not required to know the actual location area
of the mobile station. The call is routed according to the dialled information
and, if required, rerouted on additional information given by a location
register.
2.2.14 Mobile station roaming number
The network internal number used for routing of calls to the mobile
station. See Recommendation E.213.
2.3 Handover definitions
2.3.1 Handover
Handover is the action of switching a call in progress from one cell to
another (or between radio channels in the same cell). Handover is used to allow
established calls to continue when mobile stations move from one cell to another
(or as a method to minimize co-channel interference).
2.3.2 MSC-A (Controlling MSC)
The MSC which first established the radio connection to or from a mobile
station for mobile terminating or originating calls respectively. This MSC will
be the call controlling MSC for the duration of the call also in cases where a
call is handed over to another MSC.
2.3.3 MSC-B
The first MSC to which a call is handed over.
2.3.4 MSC-B'
The second (or subsequent) MSC to which a call is handed over.
Note - After the handover is completed and the circuit between MSC-A and MSC-B
has been released. MSC-B' will look, from the point of view of MSC-A and the
network, like MSC-B did before the handover.
2.3.5 Candidate MSC
A Candidate MSC is an MSC which controls cells that could be candidates
for receiving a call in case of a handover.
2.3.6 Target MSC
The Target MSC is the MSC controlling the cell(s) selected as target(s)
for a handover.
2.3.7 Serving MSC
The Serving MSC is the MSC which handles the call at the moment.
2.3.8 Old serving MSC
The old serving MSC is the MSC which was the serving MSC before a
handover, other than MSCA.
3. Architecture of the Public Land Mobile Network
3.1 Configuration of a Public Land Mobile Network
3.1.1 General
Figure 4/Q.1001 presents PLMN entities and the associated signalling
interfaces. The specific implementation in each country (or PLMN, if more than one
in each country) may be different; some of the functional entities may be
combined in the same equipment and this may result in some interfaces becoming
internal. The configuration of a PLMN must in any case have no impact on the
relationship with other PLMNs. Example: PLMN entities and associated signalling interfaces
are shown in Figure 5/Q.1001. To illustrate some implementation possibilities
three examples of configurations are presented in Figures 6/Q.1001, 7/Q.1001 and
8/Q.1001. In addition, it can be mentioned that HLR and VLR can be physically
implemented in the same equipment, as an integrated Location Register.
FIGURE 4/Q.1001
PLMN entities and associated signalling interfaces
Country A Country B
FIGURE 5/Q.1001
An example of interconnections of PLMNs and other networks
3.1.2 Configuration example No. 1 (No co-location of functional entities)
This configuration is presented in Figure 6/Q.1001. All functions are
implemented in dedicated equipment. The interfaces within the PLMN are equipment
external and therefore need the support of the Mobile Application Part (MAP) of
Signalling System No. 7 to exchange the data necessary to provide the mobile
service. All PLMN configurations can be deducted from this basic configuration. In
instances where some functions are contained in the same equipment, the relevant
interfaces become equipment internal to that equipment and the use of the MAP is
not necessary. Some examples are given in sections 3.1.3 and 3.1.4.
FIGURE 6/Q.1001
PLMN configuration example No. 1
3.1.3 Configuration example No. 2 (VLR co-located with VMSC)
This configuration is presented in Figure 7/Q.1001. The Visited Location
Register is co-located with or implemented in the VMSC for the following
reasons. The main type of data stored in the VLR is the practical location information
(i.e. location area) which has to be updated by the VMSC when the mobile station
moves from one location area to another. The VMSC also has to interrogate the
VLR at call set-up in order to know the relevant subscriber data (e.g.
restrictions and supplementary services).
FIGURE 7/Q.1001
PLMN configuration example No. 2
3.1.4 Configuration example No. 3 (HLR and VLR co-located with a MSC)
This configuration is presented in Figure 8/Q.1001. In cases where the
HLR is implemented in the MSC, this MSC will become the HMSC for the subscribers
managed by the Location Register. The two functions HLR and MSC are not of the
same type: the HLR is a pure network data base function, interrogated when needed
and the MSC is mainly in charge of call handling. The HMSC performs the call
handling function for all its subscribers, as defined by their allocation to the
HLR, when they are located in the HMSC area. Call set-up to mobile stations
handled by the HMSC uses only the international mobile subscriber ISDN/ PSTN number
and no roaming number is allocated to these mobile stations.
FIGURE 8/Q.1001
Configuration example No. 3
3.2 Interconnection between PLMNs
As the configuration of a PLMN does not have any impact on other PLMNs,
the specified signalling interfaces can be implemented between entities within a
PLMN or between PLMNs, with or without intermediate interface equipment
providing a gateway function at the application level.
A difference in the interface can be found at lower levels (SCCP), since
different signalling networks can be involved in the exchange of messages and
they are at least independent with respect to the signalling network addressing
plan.
A specific interconnection with a PLMN gateway may be needed in cases
where the organization and configuration of a PLMN does not meet the international
specifications. The specific interconnection is used in this case to mask, from
other PLMNs, a national configuration which is not in line with the
international specifications.
3.3 PLMN interfaces
3.3.1 General
The implementation of the public land mobile service with international
roaming and handover implies the exchange of mobile specific signalling
information between the equipment involved in the service. The introduction of
Signalling System No. 7 and its signalling network will be an opportunity to transfer the
data needed to support the Public Land Mobile Service. Signalling System No. 7
should be used to convey the information, where applicable. In addition some
parts of the equipment will have signalling interworking with the fixed network. The
descriptions given below are limited to the mobile application. The Mobile
Application Part will be supported by the Transaction Capabilities.
3.3.2 Interface between MSC and base station (A interface)
The exact definition of the interface between a base station and its MSC
depends on the division of functions between BS and MSC. Call handling as well
as mobile station management may be split between the two entities.
However, the BS - MSC interface will in any case carry information
concerning:
- Call handling
- Mobility management
- BS management
- Mobile station management
3.3.3 Interface between MSC and VLR (B interface)
The VLR is the location and management data base for the mobile stations
roaming in the area controlled by the associated MSC or MSCs. The MSC
interrogates the VLR whenever it needs information relating to a given mobile station
currently located in the MSC area. When a mobile station initiates a location
updating procedure with an MSC, the MSC informs its VLR which stores the relevant
information in its tables. This procedure occurs whenever a mobile station roams to
another location area. The MSC also informs the VLR when a subscriber for
instance activates a specific supplementary service or modifies some information
related to a service. The VLR stores these modifications and updates the HLR, if
required.
3.3.4 Interface between MSC and HLR (C interface)
This interface is used to exchange signalling information for
administrative and routing purposes.
In cases where charging information is transferred from an MSC, using
Signalling System No. 7, this interface will be used.
In cases where the fixed network is unable to interrogate the HLR, an
interrogation from a gateway MSC will be necessary in order to get the call
routing information from the HLR, for instance the roaming number (if the mobile
station is roaming).
3.3.5 Interface between HLR and VLR (D interface)
This interface is used to exchange the signalling information related to
the location of the mobile station and to the management of the subscriber. The
main service provided to the mobile subscriber is the capability to set-up or to
receive calls within the service area. To support this, the location registers
must exchange signalling information. The VLR informs the HLR of the location of
a mobile station managed by the HLR and provides the HLR with the roaming number
of that mobile station. The HLR sends to the VLR information needed to support
the service to the mobile station. The HLR also informs a VLR which previously
served the mobile station to delete all relevant information regarding a mobile
station, which has roamed to an MSC area served by another VLR. Exchange of
signalling information can also occur for instance when the mobile subscriber
activates a supplementary service, when the subscriber wants to change some information
related to his subscription or when the administration modifies some parameter
of the subscription.
3.3.6 Interface between MSCs (E interface)
This interface is used mainly for handover related information exchange
between MSCs. A handover is required when a mobile station moves from one MSC
area to another during a call in order to continue communication. The MSCs
exchange signalling information as a part of the process to determine the best cell for
handover and finally to perform the handover if the best cell is in another MSC
than the Serving MSC.
3.3.7 Interface between MSC and EIR (F interface)
This interface is used for information transfer between an MSC and the
equipment identity register, EIR, related to management of national and
international mobile equipment identities.
3.3.8 Interface between VLRs (G interface)
This interface is used for information transfer between VLRs when a
mobile station registers in a new VLR using a temporary mobile station identity,
TMSI, assigned by another VLR. This interface is used to retrieve the international
mobile subscriber identity, IMSI, from the VLR which assigned the TMSI.
3.3.9 Interface between BS and MS (Um interface)
The exact definitions of the interface between base station and mobile
station are not part of this specification.
However, the BS-MS interface is characterized by the Um reference point:
- the Um reference point is the traditional over-the-air radio-
interface that is RF technology dependent and
includes the physical aspects of the interface to the Base
Station.
3.3.10 Interface between user and network
The Digital PLMN User-Network interface provides:
The definition of the User-Network interface is for further study.
a) flexibility of user terminals with respect to Digital PLMN
network interconnection:
b) flexibility of separate user terminal evolution and PLMN
technology evolution; and
c) flexibility of definition and provisioning for PLMN basic bearer
services, teleservices and supplementary services.
4. Services in the public land mobile network
The services to be provided in a public land mobile network can be
described according to the ISDN service definition principles (see
Recommendation I.210) as basic services and supplementary services. Examples of these two types
of services are telephone service and call forwarding unconditional
respectively.
The basic services to be provided in the PLMN includes teleservices and
bearer services, e.g. telephone and data services (for further study) as well
as most other services provided in the ISDN (for further study).
The supplementary services to be provided are additional to one or more
basic services.
5. List of Acronyms (Additional acronyms will be included)
BS Base Station
EIR Equipment Identity Register
GMSC Gateway MSC
HLR Home Location Register
HPLMN Home PLMN
IMEI International Mobile Equipment Identity
IMSI International Mobile Station Identity
MAP Mobile Application Part
MCC Mobile Country Code
MNC Mobile Network Code
MS Mobile Station
MSC Mobile Services Switching Centre
MSC-A MSC with call control at handover
MSC-B MSC to which a handover is done
MSC-B' MSC to which a subsequent handover is done
MSIN Mobile Station Identity
MTP Message Transfer Part
NMSI National Mobile Station Identity
PLMN Public Land Mobile Network
SCCP Signalling Connection Control Part
SP Signalling Point
TMSI Temporary Mobile Station Identity
VLR Visitor Location Register
VPLMN Visited PLMN