Mobile entity classes

In existing mobile system models mobile entities are grouped according to certain criteria. The grouping of mobile entities can be perceived as made according to their physical characteristics. For example, the grouping of m obile term inals refers to a group of entities with the physical characteristics of a terminal that can change point of attachment to the network (see mobile nodes in the Mobile IP architecture, chapter two). Similarly, there can be a group of m obile users who have the characteristics of persons who are able to change terminals.

Grouping mobile entities allows to associate certain common properties with them and to treat them in the same way. This assists in the design of mobile systems. For example, in the GSM architecture members of the group the m obile station s are identified and

distinguished by means of unique identifiers (the IMSI numbers), that comply with a certain format [GSM03.03].

Grouping mobile entities according the their physical characteristics cannot be acceptable on this framework. This is because if physical characteristics were employed for grouping mobile entities, this framework would not be generic. In this framework, the grouping of mobile entities is attempted according to their sharing the same absolute location space. For example, a number of mobile entities like mobile users who share the same absolute location space (e.g. a group of terminals) could be considered a group. This is not the only grouping we can make. However, as the following paragraphs show, this grouping allows us to express certain requirements for the scope of unique identifiers of mobile entities and to outline uniform solutions for locating/contacting entities that share the same absolute location space.

In this section we present different groups of network entities according to the absolute location space that they have. These groups are used when investigating the requirements for mobility in the FoT from the information and computational viewpoints in chapter four.

3.11.1 Mobile entity class (MEC)

We call a mobile entity class (MEC) a group of mobile entities that share an identical absolute location space.

A Mobile Entity Class is a complete set o f the mobile network entities that share an identical absolute location space.

Or:

Vmi, m2 € MEC, ALS(mi) - ALS(m2)

Let us consider for example a college that has a number of workstations in the laboratory for the undergraduate students. Every undergraduate student is allowed to use any workstation in the laboratory. If any of the postgraduates or undergraduates at the college needs to contact an undergraduate, they will have to use the Internet talk application, and they will be able to contact them on one of these workstations. The undergraduate students are not allowed to use any other workstation in the college.

In this case, the absolute location space for each undergraduate, is the set of the workstations in the laboratory. Since all the undergraduates share the same absolute location space, they consist a Mobile Entity Class.

3.11.2 Network entity class (NEC)

Every MEG can have a corresponding network entity class. A network entity class (NEC) is a group of network entities for which any member of a mobile entity class has the same relative location at a given point in time. It could be the case that a NEC includes members of the MEC too.

A Network Entity Class is the complete set o f the network entities for which the location o f any member o f a Mobile Entity Class is the same at

any given time. Or;

Vm E MEC I, Vnj, « 2 ^ NECp location„j(m) = location„2(m)

In the example of the previous section, we have a MEC that comprises the set of the undergraduate students. As already mentioned, both postgraduate and undergraduate students can contact the undergraduates. In this example, the location of an undergraduate student at any time will appear to be the same to any caller, and it will be the workstation that they are using at that time. Therefore, any undergraduate student will appear to have the same location to all the undergraduate and postgraduate students. In this case, the NEC that corresponds to the MEC of the undergraduates, is the union of the postgraduate and undergraduate students. In this example, the MEC is a subset of the NEC.

3.11.3 Complete Entity Class (CEC)

All the members of a Mobile Entity Class (MEC) share the same Absolute Location Space (ALS). We saw in the previous section that every MEC has a corresponding Network Entity Class (NEC). Here, we define that a MEC also has a corresponding Complete Entity Class (CEC). The CEC is the union of the corresponding NEC and the network entities of the ALS of the MEC. Therefore, the CEC of a mobile entity class includes all the network entities to which the location of any member of the MEC is the same at any given time, plus all the network entities of the absolute location space of the MEC. N.B. a CEC does not include the media that may be members of the ALS.

A Complete Entity Class is the union o f the Network Entity Class that corresponds to a Mobile Entity Class and the network entities o f the

Absolute Location Space o f that Mobile Entity Class. Or:

In the example of the previous section 3.11.2, the CEC is the union of all the undergraduate students, the postgraduate students and the workstations that the undergraduate students can use.

Let us now assume a mobile entity (M) and another network entity (A) that is having a message exchange with (M). Assume that (M) is a remote entity to (A). For this message exchange, a communications path (CPi) will have to be created between (A) and (M). Assume that (M) is a member of a mobile entity class (MECi), and (A) is a member of the corresponding network entity class (NECl). If we assume that (A) perceives the location of (M) as (L), then all the other network entities in (CP,) should perceive (M) at the same location. That is because, for that particular message exchange, the communications path (CP,) that was created determined (L) as the location of (M). Only the last entity in the CP from (A) to (M), which by definition is (L), perceives the location of (M) differently, and it identifies it by the medium, that connects (M) to (L). Therefore, all the entities of (CP,), except for (L), perceive (M) to be at the same location (L). And therefore, all the entities of (CP,), except for (L), belong to the same NEC with (A), that is (NEC,). We can therefore conclude that:

All the network entities in a CP from a network entity (A) to a mobile entity (M), except fo r the last one, belong to the same NEC with (A).

Now, the entity (L) of our example is part of the Absolute Location Space of the MEC of (M), MEC,. From the definition of a CEC, (L) is a member of the CEC of (A), CEC,. By definition, NEC, is also a subset of CEC,. Therefore:

All the network entities in a CP from a network entity (A) to a mobile entity (M) belong to the same CEC with (A).