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.
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When referring to a 'logical' network we are talking about the logical addressing used to describe the network itself or the networks it connects to. A logical network layout clearly shows the IP Addresses associated with each part of the network. One of the most important steps when designing a logical network is the future growth and expansion, a point that most people tend to overlook and face ...
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 compartment ed 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 inter connectivity of the four computer laboratories in which I work. The Advanced Concept Technology Demonstration (A CTD), 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 stimulator’s, access to analysis tools, and provided more space for work to get accomplished. There are two separate parts of the JCAN, the Defense Information System Network – Leading Edge Services (DISN-LES is basically a classified WAN that spans the United States) Extension (DE) and the Fast Mesh (FM).
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The main purpose of this project was to change the network architecture in such a way as to allow lab computers easier network access without being bound by lengthy network wiring. The lab computers are often moved around from project to project and easy network access was becoming a problem. After a detailed analysis of the current setup, it was determined that installing a wireless network in ...
All computers connected to the DISN-LES must be identified in a never ending paper trail called a system accreditation package.
For overall system security, a given computer or piece of instrumentation will be connected to either the DE or the FM, but not both simultaneously. The JCAN-DE can be viewed as a set of extension cords. Its primary purpose is to extend the reach of the DISN-LES physically into the other three labs. A patch panel is installed in each of the labs. The JDEP laboratory patch panel is connected to the others using 25-pair cables. Let us say that a test required connecting a Gateway Terminal Emulator (GTE) in the JTDL lab to the DISN-LES.
It is a simple matter to connect the GTE to the patch panel in the JTDL lab and use a patch cord in the JDEP lab to connect the other end of the cable to one of the DISN-LES Ethernet switches. The JCAN-FM can be viewed as a high-speed utility backbone. Its primary purposes are to provide a mechanism to connect Personal Computers (PC) to each other for day-to-day operations and ad how testing, and transfer data from lab to lab at high speed. Each lab is connected to every other lab via 1 Gbps 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.
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The History of The Internet Imagine talking about the latest elections with someone three thousand miles away without receiving a tremendous phone bill. Or sending a letter to a friend or relative and having it arrive one second later. How would it feel to know that any source of information is at your fingertips at the press of a button? All of these are possible and more with a system of ...
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.
