Logical and Physical Network Design

Logical and physical network designs, while possessing some overlap, in reality are two different documents. While a good physical network design must encompass the goals and strictures as set forth in the logical design, the logical design itself may also include factors that are unrepresented by the physical plan.

For example, one of the aforementioned logical design factors that most plans will include is cost, both in time and money. While logically planning, the budgetary burden of materials and labor can be vitally important. Should the new network segments be constructed of Category 5e twisted pair cables, Category 6, fiber lines, wireless, or some combination of many different transport media? If planning for physical wires rather than wireless, who will perform the installation of the cables? Can the company’s network administrators afford the time away from maintaining the existing network to pull cables through walls, or under raised flooring? If a wireless network is decided upon, new security concerns arise. Also, wireless networks will likely require signal repeaters at various points in the facility, and this equipment must be placed based on a variety of further cascading concerns like signal strength, ease of maintenance, ensuring that the equipment is not in the way of office staff trying to perform their own job duties, etc.

Another crucial piece (or pieces) of information regarding the logical design is how, exactly, will the network be utilized. The designer must determine and account for who the clients of the network will be and provide for their needs. Services being operated on the network will fall within this realm. Will the network provide simple email and web browsing services, or will the applications in question use the network resources much more intensively? This will, as expected, affect the size and speed of the Internet connection. A busy data center, for example, would be unable to function properly if the only Internet connection available was a fractional T1 line. And a small accounting office would have no need of a 12 megabit T3 line, and in fact would be throwing money away if it were equipped with such a large connection.

An extension of the above concerns lies in what applications will actually be utilized. A requirement for an email solution, while seeming simple on the surface, may encompass further layers of complexity, for example. If all the clients are doing is sending and receiving basic text, then the network will not be taxed to its limits in providing this service. However, if the emails being transferred involve large files, like huge graphics of the type commonly employed by artists or architects, then there will be a much higher bandwidth requirement if the clients