(c) Introduction to PLMN (c) Manzur Ashraf 2 Comparison of Fixed network & PLMN
(c) Introduction to PLMN (c) Manzur Ashraf 3 Hexagonal patterns are easy to work with
(c) Introduction to PLMN (c) Manzur Ashraf 4 GSM Network elements
(c) Introduction to PLMN (c) Manzur Ashraf 5 MS: A mobile station can be a mobile telephone, a fax having radio access or a laptop computer equipped with a radio modem. BTS: A base transceiver station contains equipment for transmission and reception, antennas for one or more cells, plus equipment for encryption/decryption and signal strength measurement and for communication with the BSC. BSC: A base station controller, also referred to as the radio switch, sets up the radio channels for traffic and for signaling to the MSC and monitors the access network portion of the connection. A BSC also performs traffic concentration and handles handover between the base stations that it controls. BSCs are only found in the GSM standard. In other standards, the MSC also handles radio switch functions.
(c) Introduction to PLMN (c) Manzur Ashraf 6 MSC: A mobile switching centre is a switching node having the specialised functions required by mobile networks, notably those relating to handover between MSCs and between different PLMNs. An MSC can be likened to the local exchange of a fixed network, although it does not have any fixed subscribers (at least not in the case of GSM). A PLMN can have one or several MSCs, depending on the size of the network and the number of subscribers. The cells whose base stations are controlled by a particular MSC constitute an MSC service area. A gateway MSC (GMSC) is a specialised MSC that serves as an interface to other networks. All connections to and from mobile networks pass through a GMSC (more than one unit can be found within one and the same network). A GMSC need not handle subscriber data but must be capable of handling different signalling standards for its communication with other networks. Charging and settlement of accounts between networks are also functions of the GMSC. A GMSC represents a mobile network vis-à-vis other networks. Fixed- network connections are performed at the national or international level of the PSTN/ISDN, where a PLMN can be identified in the same manner as any other operator network.
(c) Introduction to PLMN (c) Manzur Ashraf 7 Short message service centre (SMS-C): Messaging systems (in the form of voice mailboxes for short messages and fax mailboxes) are used to increase accessibility in a PLMN. HLR: Mobile subscribers must be permanently registered somewhere in the system. In a fixed network, every subscriber belongs to a local exchange; a mobile subscriber belongs to the network. That is why mobile networks include one or more databases (HLRs) for permanent storage of subscriber data. The HLR keeps continuous track of the location of the subscriber - whether he is in an MSC service area or in a different PLMN. This information is used by the GMSC when receiving a call from another network. An HLR can be a stand-alone network element or built into an MSC.
(c) Introduction to PLMN (c) Manzur Ashraf 8 VLR: An MSC only handles temporary subscribers, namely those who happen to be in the MSC service area at a given point in time. Data pertaining to these subscribers is stored in a VLR, which can be a stand-alone network element used by several MSCs. Ordinarily, though, each MSC has its own VLR. The VLR keeps track of the service area cells within which a mobile can be located and is constantly informed of whether the mobile is ON or OFF. AUC: The authentication centre stores security information - for example, encryption keys - for all subscribers of the network. The AUC is also used for encryption/decryption. EIR: The equipment identity register stores information on the identity of every mobile. The EIR is used to check that a mobile is not reported as stolen or barred for some other reason.
(c) Introduction to PLMN (c) Manzur Ashraf 9 Network elements for operation and maintenance The operation and maintenance centre (OMC) accommodates two network elements: an operations support system (OSS) and a network management system (NMS). Both are connected to other network elements in the core and access networks via a separate X.25 network.
(c) Introduction to PLMN (c) Manzur Ashraf 10 Data communication in digital mobile networks In the case of GSM, a number of different techniques are emerging: An increase of channel capacity, from 9.6 to 14.4 kbit/s, as a result of new channel coding. The use of data compression in accordance with ITU-T Recommendation V.42bis or V.42. This technique is most useful and effective when transferring text files. Concatenation of up to a maximum of eight time slots. This technique can be used for n9.6 kbit/s or n14.4 kbit/s. The concatenation technique is referred to as high-speed circuit switched data (HSCSD) and can also be used for video transmission.
(c) Introduction to PLMN (c) Manzur Ashraf 11 Parkerizing data in combination with the installation of a packet switch. This method is called general packet radio system (GPRS). The combination of GPRS and HSCSD can provide capacity exceeding 100 kbit/s.
(c) Introduction to PLMN (c) Manzur Ashraf 12
(c) Introduction to PLMN (c) Manzur Ashraf 13 Mobile data networks
(c) Introduction to PLMN (c) Manzur Ashraf 14 Future standards For several years, the ITU-T has been conducting a project aimed at setting future mobile standards: future public land mobile telecommunications systems (FPLMTS). The project, nowadays referred to as IMT 2000, addresses mobile systems having broadband characteristics. UMTS (which stands for universal mobile telecommunications system) is the designation used in Europe. UMTS should be regarded as an extension to GSM and not as a replacement.
(c) Introduction to PLMN (c) Manzur Ashraf 15 GSM/UMTS is structured into an access and a core network, having two different radio access systems - GSM radio access and UMTS radio access - and a common core. Using dual mode, mobiles can be adapted to GSM, UMTS or both. The interface between the core and the GSM radio access is referred to as A, while the interface between the core and the UMTS radio access is called generic radio access network (GRAN. The UMTS air interface is in the 2 GHz band. Three frequency alternatives - 900, 1800 and 1900 MHz - are available to the A-interface.