Anastasia Silviani: Januari 2013

(Tugas Siskomber 2)
The Mobile Application Part (MAP) of GSM

J A N A A U D E S T A D

This is the story of how the Mobile Application Part was developed. MAP is the neural system interconnecting

the distributed computer infrastructure of GSM (VLRs, MSCs, HLRs and other entities). The work on MAP started as a study of the general architecture of mobile systems in ITU two years before the GSM group was established. In 1985 the work was taken over and later completed by the GSM group. MAP was the first protocol of its kind in telecommunications systems. After long and difficult negotiations with the community of switching and signalling experts, MAP got its final structure in 1988. This included the use of Signalling System No. 7 as carrier and the support of services such as roaming, call handling, non-interruptive handover, remote switching management and management of security functions. MAP is one of the real technological triumphs of GSM.

Interconnecting operators:

The three sausage model

This is the story of how the Mobile Application Part (MAP) was created and the problems and conflicts that this development caused between the communities of enthusiastic mobile communications experts and the conservative and preservative telephone switching engineers. The idea to design an international land mobile communications system came up in CCITT1) Study

Group XI (Switching) in late 1980, more than two years before GSM was established. The first document describing how mobility was achieved in the NMT system was presented to the Plenary Assembly of CCITT in 1981. The document was appended to a proposal for a new study question on land mobile systems. The authors were Bjørn Løken and myself. The Study Group found the proposal so interesting that they appointed Bjørn Løken as Interim Rapporteur so that work on land mobile systems could commence

immediately without awaiting the approval of the Plenary Assembly.

From mid 1981 the work on land mobile systems in CCITT took off at a violent speed and important results were obtained early. The three most important results obtained during the early years were a simple network model nicknamed the “tree sausage” model, a method for non-interrupt handover of calls betweendifferent switching centres, and the outline of a protocol supporting mobility within and between Public Land Mobile Networks (PLMN). The latter was later christened the Mobile Application Part (MAP). These achievements were all adopted and developed further by the GSM group.

Figure 1 shows the “three sausage” model of a land mobile system. The sausages are the two PLMNs and the fixed network. The significance of this model is that it is entirely abstract; that is, independent of the particular physical design of the network. The model can be used to describe all major activities taking place in the system and it is general enough to apply to every practical configuration of a mobile system. This allowed MAP to be developed independently of a particular network architecture: MAP is thus not specific for GSM.

The PLMN represents an entity of network ownership. The interaction between PLMNs is thus a cooperation of different mobile network operators allowing mobile subscribers to roam between networks independently of ownership and subscription.

The model shows two PLMNs together with the fixed network. MAP supports mobility between the PLMNs, that is, MAP offers to mobile terminals the capability to move from one PLMN to another PLMN retaining the capability to receive and make calls. Interconnectivity between a mobile terminal and a fixed terminal or between two mobile terminals takes place across the fixed network. The signalling protocol connecting the PLMN to the fixed network is Signalling System Number 7 (SS No 7). The plan was to implement SS No 7 in the telephone network during the 1980s so when an international mobile system was ready for operation around 1990, this would be the natural choice of interconnection method. When GSM was put in operation in 1991/92, SS No 7 was in place and mobile communications could commence immediately.

Kamis, 10 Januari 2013

The Mobile Application Part (MAP) of GSM