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Network Design: Physical and Logical Design

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Network Design:

Logical and Physical Design

In networking terminology, the term network topology refers to the entire structure of the network. There are two primary parts to the topology definition: the physical design, which is the actual layout of the wire (media), and the logical design, which defines how the media is accessed by the hosts. The physical designs that are commonly used in networks are the Bus, Ring, Star, Extended Star, Hierarchical, and Mesh.

A bus topology uses a single backbone segment (length of cable) that all the hosts connect to directly. A ring topology connects one host to the next and the last host to the first. This creates a physical ring of cable. A star topology connects all cables to a central point of concentration. This point is usually a hub or switch. An extended star topology uses the star topology to be created. It links individual stars together by linking the hubs/switches. This will extend the length and size of the network.

A hierarchical topology is created similar to an extended star but instead of linking the hubs/switches together, the system is linked to a computer that controls the traffic on the topology. A mesh topology is used when there can be absolutely no break in communications, for example the control systems of a nuclear power plant. Each host has its own connections to all other hosts. This also reflects the design of the Internet, which has multiple paths to any one location.

The logical topology design of a network is how the hosts communicate across a medium. The two most common types of logical designs are broadcast and Token-passing.

Broadcast topology simply means that each host sends its data to all other hosts on the network medium. There is no order the stations follow to use the network, it is first come, first serve. This is the way that Ethernet functions.

The second type is token-passing. Token-passing controls network access by passing an electronic token sequentially to each host. When a host receives the token that means that the host can send data on the network. If the host has no data to send, it passes the token to the next host and the process repeats itself.

In order to illustrate an example of a logical and physical design for a network, I have chosen to write about the creation of a network of which I was heavily involved with at my work. The Joint Interoperability Test Command (JITC) Joint Distributed Engineering Plant (JDEP) Division has numerous testing laboratories within their secure compartmented information facility. Due to the classified nature of my work environment, specifics of network or telecommunication designs will not be discussed in this document. The primary focus is on the interconnectivity of the four computer laboratories in which I work.

The Advanced Concept Technology Demonstration (ACTD), JDEP, and Theater Air Missile Defense (TAMD) labs all have extensive archives of test data, analysis capabilities, test results, etc. In the past, each of these labs has specialized in providing test support to the air defense mission but there was little to no synergy between the labs. JDEP was added to JITC with a new network approach to interoperability testing that would allow the sharing of resources between the Services and facilitate testing among these resources. Interconnecting these labs and the creation of the Joint Collaborative Analysis Network (JCAN) at JITC facilitated software development, access to simulators and stimulators,



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