Frame Relay Components, part 2

Network Consultants Handbook - Frame Relay
by Matthew Castelli

Frame Relay Components (Cont'd)

As one would expect, determining the number of Virtual Circuits required for a network configuration is based on the number of end nodes, and the communication requirements, such as fully meshed (all-to-all), partial meshed (some-to-all), or hub-and-spoke (all-to-one), as illustrated by Figure 15-8.

Figure 15-8: Fully Meshed, Partially Meshed, and Hub-and-Spoke Networks

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In a fully meshed network environment, the number of VCs required can be represented by the following formula:

where N is the number of end nodes in the network. This formula is sometimes referred to as the "N² Formula" because it is derived from ((N²-N) / 2).

In a partial meshed network environment, the number of VCs required is not easily represented by a mathematical formula. You must consider many variables, the least of which is based on the determination of which end nodes require communication with which other end nodes. It is a fair assumption to estimate that the number of VCs required would fall between those of a fully meshed and those of a hub-and-spoke environment:

where N is the number of end nodes in the network and X is the number of VCs required to support a partially meshed configuration. The following formula can be used as an approximation to determine the number of VCs necessary to support a partial mesh configuration: , where N is the number of network nodes. This formula is useful from a network planning and cost-determination standpoint; however, because partial mesh connectivity is determined by application and user requirements at the end node, an exact number of partial-mesh VCs is almost impossible to determine.

In a hub-and-spoke network environment, the number of VCs required can be represented by the formula [N-1], where N is the number of end nodes in the network.