Universal Services Ordering Code - USOC

Understanding USOC and what those RJ codes really mean.

The  Bell System Universal Service Ordering Code (USOC) system was developed to connect customer premises equipment to the public network.  These codes, adopted in part by the FCC, Part 68, Subpart F, Section 68.502, are a series of Registered Jack (RJ) wiring configurations for telephone jacks that remain in use today.


RJ11C & RJ11W
C= surface or flush-mounted
W=wall-mount                            

RJ-48C
C= surface or flush-mounted



RJ-45S
S=single-line jack


RJ-48X
X=complex multi-line or series-type jack



RJ-48S
S=single-line jack



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