Logical vs. Physical Design of a Network

Logical vs. Physical Design of a Network In the world of network design, there are two common design types; the logical network design and the physical network design. A logical network design can be described as how the network will be structured, basically all logical aspects of the network. According to Webopedia, "the logical topology is the way that the signals act on the network media, or the way that the data passes through the network from one device to the next without regard to the physical interconnection of the devices."
In a logical network layout, IP addresses are shown to be associated with different parts of the network. One such element of a logical network includes assigned IP addresses to devices such as routers, switches, servers, workstations and other devices utilized on a network. Logical design usually do not show the actual interfaces and physical cables in the diagrams; thus the term "logical". A logical network design is the design of a network as expressed in terms of its functionality and inter-relationship with different functions within the network. A logical network design document would demonstrate the functional inter-relationship abstract from the physical implementation as well as then mapping the functionality and interactions to the physical form. One of the most important steps in designing a logical network is planning for future growth and expansion. "When I design a network, I always leave room for an additional 50-60% growth of its current size," says Chris Partsenidis (2003). In essence, this means that if a network is originally designed to have 60 machines or devices, an additional 40 machines should be figured into the design. The logical network plainly shows the IP addresses associated with each part of the network. For example, many logical networks use a simple Class C network such as 192.168.0.0 with the default subnet mask of 255.255.255.0 (See Figure 1.). In this case, up to 254 hosts can be connected directly to it without the need of any routing. In addition to the logical design, there is also the physical design. The physical design of a network refers to the actual layout of the physical part of a network, the topology. It will show what type of technology will be utilized, such as Ethernet, fiber, ISDN, cable, or whatever will be used. The physical design will also show the network topology to be used. The different types of network topologies are as follows:
• Mesh topology
• Star topology
• Bus topology
• Ring topology
• Tree topology
The physical layout of the network shows the physical location of and the connections between devices participating on the network. In these diagrams, workstations are usually represented with small computer icons, servers with full tower cases, and switches and other similar devices are displayed as small rectangular boxes with the RJ-45 ports in the front. The physical design also defines the type of cable used to connect all devices. The type of cable that might be utilized could be Category 5, Category 5e, Category 6, coaxial cable, or fiber-optic cable. The physical design also shows the distance the devices will be located from other devices (See Figure 2.). The logical design and physical design of a network is essential in maintaining networks. They enable network administrators and engineers the ability to keep track of moves, adds, and changes in the network. They are also utilized to maintain security on a network. In addition, having a logical and physical design of a network can reduce unwanted headaches for network administrators.
References
Webopedia.com (n.d.) Retrieved May 1, 2005 from http://www.webopedia.com/TERM/L/logical_topology.html

TechTarget.com. (n.d.) Retrieved May 2, 2005, from
http://expertanswercenter.techtarget.com/eac/knowledgebaseAnswer/0,295199,sid63_gci975233,00.html

References: Webopedia.com (n.d.) Retrieved May 1, 2005 from http://www.webopedia.com/TERM/L/logical_topology.html TechTarget.com. (n.d.) Retrieved May 2, 2005, from http://expertanswercenter.techtarget.com/eac/knowledgebaseAnswer/0,295199,sid63_gci975233,00.html