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.

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.