Content Overview Designing a network can be a challenging task that involves more than just connecting computers together. A network requires many features in order to be reliable, manageable, and scalable. To design reliable, manageable, and scalable networks, a network designer must realize that each of the major components of a network has distinct design requirements. Network design is becoming more difficult despite improvements in equipment performance and media capabilities. Using multiple media types and interconnecting LANs with other external networks makes the networking environment complex. Good network design will improve performance and also reduce the difficulties associated with network growth and evolution. A LAN spans a single room, a building, or a set of buildings that are close together. A group of buildings that are on a site and belong to a single organization are referred to as a campus. The design of larger LANs includes identifying the following: Each of these LAN design layers requires switches that are best suited for specific tasks. The features, functions, and technical specifications for each switch vary depending on the LAN design layer for which the switch is intended. Understanding the role of each layer and then choosing the switches best suited for that layer ensures the best network performance for LAN users. Students completing this module should be able to:
Content 5.1 LAN Design 5.1.1 LAN design goals The first step in designing a LAN is to establish and document the goals of the design. These goals are unique to each organization or situation. The following requirements are usually seen in most network designs: Interactive Media Activity Matching: LAN Design Goals Matching When the student has completed this activity, the student will be able to understand the terms, definitions, and goals in network LAN design.
Content 5.1 LAN Design 5.1.2 LAN design considerations Many organizations have been upgrading existing LANs or planning, designing, and implementing new LANs. This expansion in LAN design is due to the development of high-speed technologies such as Asynchronous Transfer Mode (ATM). This expansion is also due to complex LAN architectures that use LAN switching and virtual LANs (VLANs).To maximize available LAN bandwidth and performance, the following LAN design considerations must be addressed: Servers provide file sharing, printing, communication, and application services. Servers typically do not function as workstations. Servers run specialized operating systems, such as NetWare, Windows NT, UNIX, and Linux. Each server is usually dedicated to one function, such as e-mail or file sharing. Servers can be categorized into two distinct classes: enterprise servers and workgroup servers. An enterprise server supports all the users on the network by offering services, such as e-mail or Domain Name System (DNS). E-mail or DNS is a service that everyone in an organization would need because it is a centralized function. However, a workgroup server supports a specific set of users, offering services such as word processing and file sharing. Enterprise servers should be placed in the main distribution facility (MDF). Traffic to the enterprise servers travels only to the MDF and is not transmitted across other networks. The reviewer's rewrite leaves out the important point about the traffic to the enterprise servers traveling only to the MDF. Ideally, workgroup servers should be placed in the intermediate distribution facilities (IDFs) closest to the users accessing the applications on these servers. By placing workgroup servers close to the users, traffic only has to travel the network infrastructure to an IDF, and does not affect other users on that network segment. Layer 2 LAN switches located in the MDF and IDFs should have 100 Mbps or more allocated to these servers. Ethernet nodes use CSMA/CD. Each node must contend with all other nodes to access the shared medium, or collision domain. If two nodes transmit at the same time, a collision occurs. When this occurs, the transmitted frame is destroyed, and a jam signal is sent to all nodes on the segment. The transmitting nodes wait a random period of time, and then resend the data. Excessive collisions can reduce the available bandwidth of a network segment to 35% or 40% of the bandwidth available. Segmentation is the process of splitting a single collision domain into smaller collision domains. Creating smaller collision domains reduces the number of collisions on a LAN segment, and allows for greater utilization of bandwidth. Layer 2 devices such as bridges and switches can be used to segment a LAN into smaller collision domains. Routers can achieve this at Layer 3. A broadcast occurs when the destination media access control (MAC) data frame address is set to FF-FF-FF-FF-FF-FF. A broadcast domain refers to the set of devices that receive a broadcast data frame originating from any device within that set. All hosts that receive a broadcast data frame must process it. Processing the broadcast data will consume the resources and available bandwidth of the host. Layer 2 devices such as bridges and switches reduce the size of a collision domain. These devices do not reduce the size of the broadcast domain. Routers reduce the size of the collision domain and the size of the broadcast domain at Layer 3.
Content 5.1 LAN Design 5.1.3 LAN design methodology For a LAN to be effective and serve the needs of its users, it should be designed and implemented according to a planned series of systematic steps. These steps include the following: The information gathering process helps clarify and identify any current network problems. This information includes the organization's history and current status, their projected growth, operating policies and management procedures, office systems and procedures, and the viewpoints of the people who will be using the LAN. The following questions should be asked when gathering information: