Introduction Modular
jacks typically are manufactured in four styles. Eight position, 8 position nonkeyed, 6 position and MMJ (modified modular jack). DEC introduced the MMJ and DEC hardware as its predominant application.
Ethernet 10BaseT 10BaseT wiring
specifies an 8 position jack using two pairs. These two pairs 2 & 3 of AT&T and TIA schemes.
IBM Token Ring Token Ring usually uses an 8 position jack. The wiring scheme is compatible with TIA, AT&T and USOC wiring
schemes because it uses the two center pairs. USOC The USOC wiring scheme has four versions supporting 1, 2, 3, and 4 pair systems. Pair1 is on the two center contacts, pair 2 is on the next two contacts out and so
forth. This scheme is popular because a six position plug configured with 1, 2, or 3 pairs can be inserted into an 8 position jack and maintain pair continuity. Note that pins 1 and 8 in the 8 position jack
may be damaged by the insertion of a 6 position plug Degraded transmissions quality has been reported by some users of the USOC wiring scheme. EIA/TIA and AT&T EIA/TIA-568 has adopted the EIA/TIA and AT&T wiring
schemes. They are similar, bit pairs 2 and 3 are reversed. The TIA scheme is popular because it is compatible with 1 or 2 pair USOC systems. Both schemes will support ISDN applications. Many Category 5
installations are using 568A. "RJ" Registered Jack Modular jacks should be referred to by their position count:;;8 position keyed, 6 position, 6 position modified (or MMJ). The RJ designations actually refer to
specfic wiring configurations called Universal Service Ordering Services Codes (USOC). The RJ designation means "registered jack". Each of the 8 position jacks and the 6 position jacks can be wired
as an RJ11C (1 pair), RJ14C (2 pair), or RJ25C (3 pair). The 8 position jacks can be wired as RJ4555, RJ45S and RJ47s. |
