LAN DESIGN
LAN design goals
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:
· Functionality – The network must work. The network must allow users to meet their job requirements. The network must provide user-to-user and user-to-application connectivity with reasonable speed and reliability.
· Scalability – The network must be able to grow. The initial design should grow without any major changes to the overall design.
· Adaptability – The network must be designed with a vision toward future technologies. The network should include no element that would limit implementation of new technologies as they becomeavailable.
· Manageability – The network should be designed to facilitate network monitoring and management to ensure ongoing stability of operation.
2.0 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:
· The function and placement of servers
· Collision detection issues
· Segmentation issues
· Broadcast domain issues
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.
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
