Twisted pair cable is the simplest and oldest cable medium consisting of two insulated copper wires twisted around each other to reduce electrical interference. It is commonly used in telephone systems and comes in two main types - unshielded twisted pair (UTP) and shielded twisted pair (STP). UTP is the most common type used in networks today and comes in categories depending on the data transfer rate it supports, with category 5 cable providing up to 100 Mbps. STP cable has each pair of conductors encased in metal shielding to further prevent interference.