Network Design: Physical and Logical Design

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 ...

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...ses are to provide a mechanism to connect Personal Computers (PC) to each other for day-to-day operations and ad hoc testing, and transfer data from lab to lab at high speed. Each lab is connected to every other lab via 1Gbps Ethernet links running over Category 6 cables. This network is not part of the DISN-LES. System Administrators (SA) can reconfigure computers and network connectivity to suit mission requirements.

Some computers are used on both the DE and FM, but not simultaneously. An example of this would be a computer in the JDEP lab that is serving as the Data Extraction/Data Reduction (DX/DR) server during a test event. The computer is disconnected from the DISN-LES and connected to the FM. The data is then transferred at high speed to a computer in the TAMD laboratory. The computer is then disconnected from the FM and reconnected to the DISN-LES. Personnel in the TAMD laboratory can then back up the data and perform analysis.

The JCAN is actually a very simple network scheme. Although, it only serves approximately fifty users, is does so efficiently while maintaining a high degree of system/network security.