Networks and Communication Links

Normally, locations will have some form of electronic communications, which could range from a dial-up modem connected to a telephone system, a dedicated Wide-Area Network, the Internet or a satellite link. Normally the link should have a relatively high speed and reliable on-line communication channel with as many satellite locations as possible. However, line speeds as low as 48K are supported.

The communications network must be a tree structure, which means that there is a unique path between one location and another. The Hub is the root of the tree. It is possible to have links between one satellite and another, using Location Groups ‑ in this case there is more than one path between locations. Refer to Location Groups for further information.

The following diagram shows some of the different configurations possible, when Groups are not used. For a diagram showing the use of Groups, refer to Location Groups for further information.

Figure 3:1. Examples of tree structures for locations

The relationship between locations is described in terms of a family tree: there are parents, children, ancestors and descendants. For example, in , the relationships between locations A, B, C, D and E are described as follows:

• A is the parent of B and C.

• B and C are the children of A.

• B, C, D and E are the descendants of A.

• A, C and D are the ancestors of E.

Every location except the Hub has a parent. The parent of each location is stored in the Global database. The parent-child relationships define the connectivity of the communications network, and allow the Global daemons to find the path from one location to another.