By a wide margin the most popular connector for Ethernet systems is the RJ45. This resembles the RJ11 connector that is very common in telephone systems. Comparing the two, the smaller RJ11 can handle, at most, two pairs of wires or four metallic connections. The larger RJ45 can handle up to four pairs or eight metallic conductors. Some of the earliest Ethernet configurations used what is called a “10Base-T” scheme. This system can deliver up to ten megabits of data per second. The 10Base-T only used two of the four pairs of wires and could employ a lower grade “Category 3 Unshielded Twisted Pair Cable”, or Cat-3 UTP cable for short. Each of the two pairs operated in a “Simplex” scheme which means each pair carried information in a single direction, one transmitting and the other receiving the signals. Similarly, 100Base-TX systems also use just two of the four pairs in the RJ45 in a simplex scheme.  However, the 100Base-TX can deliver up to 100 megabits of data per second and must use higher quality Cat-5 UPT cabling at a minimum.