Collisions and collision domain size are two factors that negatively affect the performance of a network. Microsegmentation of the network reduces the size of collision domains and reduces collisions.  Microsegmentation is implemented through the use of bridges and switches. The goal is to boost performance for a workgroup or a backbone. Switches can be used with hubs to provide the appropriate level of performance for different users and servers.

Another important characteristic of a LAN switch is how it can allocate bandwidth on a per-port basis. This will provide more bandwidth to vertical cabling, uplinks, and servers. This type of switching is referred to as asymmetric switching. Asymmetric switching provides switched connections between ports of unlike bandwidth, such as a combination of 10-Mbps and 100-Mbps ports.

The desired capacity of a vertical cable run is greater than that of a horizontal cable run. By installing a LAN switch at the MDF and IDF, the vertical cable run can manage the data traffic from the MDF to the IDF. The horizontal runs between the IDF and the workstations uses Category 5e UTP. No horizontal cable drop should be longer than 100 meters. In a normal environment, 10 Mbps is adequate for the horizontal drop. Use asymmetric LAN switches to allow for mixing 10-Mbps and 100-Mbps ports on a single switch.

The next task is to determine the number of 10 Mbps and 100 Mbps ports needed in the MDF and every IDF. This can be determined by reviewing the user requirements for the number of horizontal cable drops per room and the number of total drops in any catchment area. This includes the number of vertical cable runs. For example, suppose that user requirements dictate four horizontal cable runs to be installed to each room. The IDF services a catchment area of 18 rooms. Therefore, four drops in each of the 18 rooms will equal 72 LAN switch ports. (4x18=72)

The size of a collision domain is determined by how many hosts are physically connected to any single port on the switch. This also affects how much network bandwidth is available to any host. In an ideal situation, there is only one host connected on a LAN switch port. The collision domain would consist only of the source host and destination host. The size of the collision domain would be two. Because of the small size of this collision domain, there should be virtually no collisions when any two hosts are communicating with each other. Another way to implement LAN switching is to install shared LAN hubs on the switch ports, and connect multiple hosts to a single switch port. All hosts connected to the shared LAN hub share the same collision domain and bandwidth. Collisions would occur more frequently.

Some older switches, such as the Catalyst 1700, do not properly support sharing the same collision domain and bandwidth. The older switches do not maintain multiple MAC addresses mapped to each port. As a result, there are many broadcasts and ARP requests.

Shared media hubs are generally used in a LAN switch environment to create more connection points at the end of the horizontal cable runs. This is an acceptable solution, but care must be taken. Collision domains should be kept small and bandwidth requirements to the host must be provided according to the specifications gathered in the requirements phase of the network design process.