Wiki1: http://en.wikipedia.org/wiki/RJ48The 8 Position 8 Contact (8P8C) (often called RJ45 see below)
People sometimes refer to the 10P10C modular connector as "RJ48." The origin of this misnomer is unknown; none of the RJ48 registered jacks use a 10P10C connector. However, it may be an outgrowth of the common misperception of the "RJ" USOCs as names of physical connectors. If one knew of the names RJ45 and RJ48 and knew of the 8P8C and 10P10C modular connectors, and believed (as explained in the RJ45 article) that RJ45 is the name of the 8P8C, one might conclude that RJ48 is the name of the larger 10P10C.
The RJ-48 connector may look very similar to an RJ-45 connector found on a typical CAT-5 cable, but don�t be fooled, they are very different in many ways.A RJ-48 connecter is fastened on to a STP (Shielded Twisted Pair) cable, not the standard UTP (Unshielded Twisted Pair) CAT-(1-5) cable.A RJ-48 also uses a different pin out arrangement, voltage level, and line capacitance then a RJ-45.See below for details on the RJ-48C, and RJ-48X connectors.