Point to point communication can be carried out using 2-/4-wire twisted pair cables or fiber optic cables. Fiber optic cables can be used on parts of the network with high performance requirements, or where the risk of electrical and electromagnetic interference is high. It is also more difficult to tap into communications via a fiber optic cable. The communications principle is the same as for 2-/4-wire cable, except that special modems which transform the electrical signal into an optical signal are used.