|  | 1.3 | LAN Design
| 1.3.8 | Layer 2 switching
By installing LAN switching at the MDF and IDFs we can start to look at the size of our collision domains and the speed for each horizontal cable and vertical cable run. Since the vertical cable will be carrying all of the data traffic between the MDF and the IDFs, the capacity of this run must be larger. In the design of the Layer 1 structure we have installed fiber optic cable which will allow us to run at 100 Mbps. The horizontal cable runs are utilizing CAT 5 UTP and no cable drop is longer than 100 meters which will allow us to run these links at 10 Mbps or 100 Mbps. In a normal environment 10 Mbps is quite adequate for the horizontal cable drop. Since asymmetric LAN switches allow for mixing 10 Mbps and 100 Mbps ports on a single switch, the next task will be to determine the number of 10 Mbps and 100 Mbps ports needed in the MDF and every IDF. This can be determined by going back to the user requirements for the number of horizontal cable drops per room and how many drops total in any catchment area, along with the number of vertical cable runs. Example - User requirements dictate that 4 horizontal cable runs be installed to every room. The IDF that services a catchment area covers 18 rooms. 4 drops x 18 rooms =72 LAN switch ports.