Functionality

Functionality is the quality or state of being functional. It is the most essential element of network design. The primary function of network design is to meet the requirements of the users, and make the network deliver what was agreed with the users as requirements. If a network does not do what it is designed to do, it is a failed design regardless of whatever else it might have.

If a network was built to carry multiple types of traffic but ended up being capable of carrying only a certain type of traffic while the other types traffic could not be delivered either due to lack of support for the protocols or bandwidth, the network is not functional. Also, if the network can transfer data between the communicating nodes, but with significant delays such that the users cannot complete the business-critical transactions in a seamless manner, we would say that the network has failed the test of functionality. In most scenarios, the user experience is the best test of functionality of the network.

As an example, consider a network built to deliver high definition (HD) video to the end-points, but could deliver only standard definition (SD) video due to bandwidth limitations, this network has failed the functionality test.

The network might have all the other properties mentioned hereafter, but those are the icing on the cake. If there is no cake, the icing is useless.

All networks have a specific purpose, and the network design has to ensure that the purpose is catered for the network.