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LAN design methodology

LAN design methodology 
5.1.3 For a LAN to be effective and serve the needs of its users, it should be designed and implemented based on a planned series of systematic steps. This page will describe the following steps:
  • Gather requirements and expectations
  • Analyze requirements and data
  • Design the Layer 1, 2, and 3 LAN structure, or topology 
  • Document the logical and physical network implementation
The process to gather information helps to clarify and identify any current network problems. This information includes the history of the organization and current status, their projected growth, operation policies and management procedures, office systems and procedures, and the viewpoints of the people who will use the LAN.
The following questions should be asked to gather information:
  • Who are the people that will use the network?
  • What is the skill level of these people?
  • What are their attitudes toward computers and computer applications?
  • How developed are the organizational documented policies?
  • Has some data been declared mission critical?
  • Have some operations been declared mission critical?
  • What protocols are allowed on the network?
  • Are only certain desktop hosts supported?
  • Who is responsible for LAN addresses, naming, topology design, and configuration?
  • What are the organizational human, hardware, and software resources?
  • How are these resources currently linked and shared?
  • What financial resources does the organization have available?
Documentation of the requirements allow for an informed estimate of costs and timelines for projected LAN design implementation. It is important to understand performance issues of any network.
Availability measures the usefulness of the network. The following are a few of the many things that affect availability:
  • Throughput
  • Response time
  • Access to resources
Every customer has a different definition of availability. For example, there may be a need to transport voice and video over the network. These services may require more bandwidth than is available on the network or backbone. To increase availability, more resources can be added, but that increases the cost of the network. Network designs should provide the greatest availability for the least cost.
The next step in the network design is to analyze the requirements of the network and its users. Network user needs constantly change. As more voice and video-based network applications become available, the necessity to increase network bandwidth grows too.
A LAN that is not able to provide prompt and accurate information to its users is useless. Steps must be taken to ensure that the information requirements of the organization and its workers are met.
The next step is to decide on an overall LAN topology that will satisfy the user requirements.   In this curriculum, concentration will be on the star topology and extended star topology. The star topology and extended star topology use Ethernet 802.3 CSMA/CD technology. CSMA/CD star topology is the dominant configuration in the industry.
LAN topology design can be broken into the following three unique categories of the OSI reference model:
  • Network layer
  • Data link layer
  • Physical layer
The final step in LAN design methodology is to document the physical and logical topology of the network. The physical topology of the network refers to the way in which various LAN components are connected together. The logical design of the network refers to the flow of data in a network. It also refers to the name and address schemes used in the implementation of the LAN design solution.
The following are important LAN design documentation:
  • OSI layer topology map
  • LAN logical map
  • LAN physical map
  • Cut sheets
  • VLAN logical map
  • Layer 3 logical map
  • Address maps
The next page will discuss Layer 1 design issues.

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