3 Definitions and abbreviations

23.0023GPPNetwork architectureRelease 17TS

In addition to the abbreviations given in the remainder of this clause others are listed in TR 21.905 [1a].

The definitions of the entities of the mobile system are given in the next clause.

3.1 Public Land Mobile Network (PLMN)

A Public Land Mobile Network (PLMN) is established and operated by an administration or Recognized Private Operating Agency (RPOA) for the specific purpose of providing land mobile telecommunications service services to the public. A PLMN may be regarded as an extension of networks (e.g. ISDN, corporate and public PDNs, etc.); it is a collection of MSCs areas in CS domain and SGSN areas for GPRS and SGSN or MME areas for EPC in PS domain within a common numbering plan (e.g. same National Destination Code) and a common routing plan. The MSCs are the functional interfaces between the fixed networks and a PLMN for call set-up in CS domain. The GGSN and the SGSN are the functional interfaces between the fixed networks and a PLMN for packet transmission in GPRS PS domain. In case of EPC PS Domain, the PDN GW, Serving-GW and the SGSN and the MME are the functional interfaces between the fixed networks and a PLMN for packet transmission.

Functionally the PLMNs may be regarded as independent telecommunications entities even though different PLMNs may be interconnected through the ISDN/PSTN and PDNs for forwarding of calls or network information. A similar type of interconnection may exist for the interaction between the MSCs/SGSNs/MMEs of one PLMN.

3.2 Core Network (CN) and Access Network (AN)

The PLMN infrastructure is logically divided into a Core Network (CN) and an Access Network (AN) infrastructures, as defined in TS 23.101 [11a] and TS 23.110 [11b]. The CN is logically divided into a CS domain, a PS domain and an IM subsystem, as defined in next clause. The AN are GERAN (also called BSS for GSM), UTRAN (also called RNS), E-UTRAN, as defined in clause "The Access Network".

3.3 Circuit Switched (CS) and Packet Switched (PS) Domains

The CN is constituted of a Circuit Switched (CS) domain and a Packet Switched (PS) domain (which includes GPRS and EPC). These two domains differ by the way they support user traffic, as explained below.

These two domains are overlapping, i.e. they contain some common entities. A PLMN can implement only one domain or both domains.

3.3.1 CS Domain

The CS domain refers to the set of all the CN entities offering "CS type of connection" for user traffic as well as all the entities supporting the related signalling. A "CS type of connection" is a connection for which dedicated network resources are allocated at the connection establishment and released at the connection release.

The entities specific to the CS domain are: MSC, GMSC, VLR. All the other CN entities defined in clause 4 "The basic entities of the mobile system" and not defined as PS domain specific entities (see following clause) are common to the CS and to the PS domains. In case of E-UTRAN access, there is no support for CS Domain.

3.3.2 PS Domain

The PS domain refers to the set of all the CN entities offering "PS type of connection" for user traffic as well as all the entities supporting the related signalling. A "PS type of connection" transports the user information using autonomous concatenation of bits called packets: each packet can be routed independently from the previous one.

The entities specific to the PS domain are the GPRS specific entities, i.e. SGSN and GGSN and EPS specific entities, i.e. PDN GW, S-GW, MME, SGSN. All the other CN entities defined in clause "4 The basic entities of the mobile system" and not defined as CS domain specific entities (see previous clause) are common to the CS and to the PS domains.

3.3a IP Multimedia subsystem (IMS)

The IM subsystem comprises all CN elements for provision of IP multimedia services comprising audio, video, text, chat, etc. and a combination of them delivered over the PS domain. The entities related to IMS are CSCF, MGCF, MRF, etc. as defined in the stage 2 of the IM subsystem TS 23.228 [34]. See TS 22.228 [27] for some service examples of IMS.

3.4 Location register

To enable communication to a mobile station the network must know where this mobile station is located. This information is stored in a function named location register.

The location register is handled by the following entities.

– The Home Location Register (HLR).

The Home Location Register (HLR) is the location register to which a mobile subscriber is assigned for record purposes such as subscriber information. For EPS, the HLR functionality is provided via HSS.

– The Visitor Location Register (VLR).

The Visitor Location Register (VLR) is the location register for Circuit Switched (CS) services, other than the HLR, used by an MSC to retrieve information for, e.g. handling of calls to or from a roaming mobile station currently located in its area.

– The Serving GPRS Support Node (SGSN).

The location register function in the SGSN stores subscription information and location information for Packet Switched (PS) services for each subscriber registered in the SGSN.

The SGSN is needed only in a PLMN which supports PS Domain with GERAN or UTRAN access.

– The Gateway GPRS Support Node (GGSN).

The location register function in the GGSN stores subscriber information and routeing information (needed to tunnel packet data traffic destined for a GPRS MS to the SGSN where the MS is registered) for each subscriber for which the GGSN has at least one PDP context active.

The GGSN is needed only in a PLMN which supports GPRS with GERAN or UTRAN access.

– The Mobility Management Entity (MME).

The location register function in the MME stores subscription information and location information for Packet Switched (PS) services for each subscriber registered in the MME for EPS.

– The Packet Data Network Gateway (PDN GW).

The location register function in the PDN GW stores subscriber information and routeing information (needed to tunnel packet data traffic destined for an EPS UE to the Serving GW, where the UE is registered in the MME, in the SGSN or in the 3GPP AAA server in case of non-3GPP access) for each subscriber for which the PDN GW has at least one PDN connection active.

3.5 Cell

The cell is an area of radio coverage identified by a Base station identification as defined in TS 23.003 [3].

3.6 Base Station Controller (BSC) area

The Base Station Controller (BSC) area is an area of radio coverage consisting of one or more cells controlled by one BSC. The boundaries of a BSC area and a location area are independent; a location area may span the boundary between BSC area and a BSC area may span the boundary between location areas.

3.7 Radio Network Controller (RNC) area

The Radio Network Controller (RNC) area is an area of radio coverage consisting of one or more cells controlled by one RNC. The boundaries of a RNC area and a location area are independent; a location area may span the boundary between RNC area and a RNC area may span the boundary between location areas.

3.8 Location Area (LA)

The Location Area (LA) is defined as an area in which a mobile station may move freely without updating the VLR. A location area includes one or several GERAN/UTRAN cells.

3.9 Routing Area (RA)

The Routing Area (RA) is defined as an area in which a mobile station, in certain operation modes, may move freely without updating the SGSN. A routing area includes one or several GERAN/UTRAN cells. A RA is always contained within a location area.

3.9a Tracking Area (TA)

A Tracking Area (TA) includes one or several E-UTRAN cells. The network allocates a list with one or more TAs to the UE . In certain operation modes, the UE may move freely in all TAs of the list without updating the MME.

3.10 MSC area

The MSC area is the part of the network covered by an MSC. An MSC area may consist of one or several location areas. An MSC area may also consist of one or several BSC areas.

3.11 VLR area

The VLR area is the part of the network controlled by a VLR. A VLR area may consist of one or several MSC areas.

3.12 SGSN area

The SGSN area is the part of the network served by an SGSN. An SGSN area may consist of one or several routing areas. An SGSN area may also consist of one or several BSC areas. There need not be a one to one relationship between SGSN area and MSC/VLR area.

3.13 Zones for Regional Subscription

A PLMN operator may define a number of regional subscription areas, each of which is a subset of the service area for an unrestricted mobile subscriber. A regional subscription area may be contained within the service area of a single PLMN, or may lie within the service areas of two or more PLMNs. Each regional subscription area consists of one or more zones; each zone is contained within the service area of a PLMN.

The definition of a mobile subscriber’s regional subscription area is stored within the HLR/HSS per National Destination Code(s) (NDC) of a PLMN and is transferred to the VLRs and/or SGSNs/MMEs of that PLMN. The VLR and/or SGSN/MME evaluates this information to extract the restricted or accessible MSC and/or SGSN/MME areas and location areas to which the mobile subscriber is allowed to roam. The VLR and/or SGSN/MME inform the HLR/HSS if an entire MSC and/or SGSN/MME area is restricted.

Zones for Regional Subscription and their handling are defined in TS 23.003 [3], TS 23.008 [5] and TS 29.002 [26] and TS 29.272 [86] for EPC.

3.14 Service area

The service area is defined as an area in which a mobile subscriber can be reached by another (mobile or fixed) 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 include 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.

3.15 Group call area

The group call area is a predefined area composed of one or a number of cells to which a particular Voice Group Call Service (VGCS) or Voice Broadcast Service (VBS) call is distributed. The composition of a group call area is predefined in the network. The group call area may include cells of more than one MSC area and cells of more than one PLMN.

3.15a MME Area

The MME area is the part of the network served by an MME. An MME area consists of one or several Tracking Areas. All cells served by an eNodeB are included in an MME Area. There is no one to one relationship between an MME Area and an MSC/VLR area. Multiple MMEs may have the same MME Area as described in clause "Pool-area". MME Areas may overlap each other.

3.16 Pool-area

A pool area is an area where Intra Domain Connection of RAN Nodes to Multiple CN Nodes is applied. Within a pool-area an MS may roam without need to change the serving Core Network (CN) node. A pool-area is served by one or more CN nodes in parallel.

3.17 Serving GW Service Area

A Serving GW Service Area is the part of the network served by single Serving GW. Serving GW Service Areas consist of one or several complete Tracking Areas. All cells served by an eNodeB are included in an Serving GW Service Area .Serving GW Service Areas may overlap each other. There is no one to one relationship between an MME Area and a Serving GW Service Area.