USOC vs. 568B
Since the early years of matrix intercoms systems, the McCurdy brand saw broad acceptance at the major broadcast networks in The United States. It is 2012 in London and I am working with an engineer that refers to the Telex ADAM key-panels as “the McCurdy”. Telex purchased the McCurdy intercom product line and in 1996, when the ADAM DSP/TDM product first appeared in the U.S, it was bound to a McCurdy 9500 controller frame. The software application was called CSEdit, a DOS program.
McCurdy featured the RJ-12 connector using the USOC (Universal Service Ordering
Code) wiring convention. Three unshielded twisted pairs: Audio talk (+/-), audio listen (+/-) and RS-485 data (+/-).
Enter computers and Ethernet. The now ubiquitous RJ-45 connector used in Ethernet data networks is everywhere. Intercom system which appeared on the market in later years featured the RJ-45 connector with the 568B wiring convention. This convention established a data-rate and pair usage that is quite different from the RJ-11/12 (USOC) standard. (disclaimer: this blog entry is not intended to be a tutorial on the FCC 47 Part 68. This is a pretty deep subject of nearly 160 pages)
Problems occur when the two wiring standards become intermingled. The DC-continuity can actually line-up pin-for-pin sometimes, but it is the “splitting of pairs” that wrecks havoc with proper noise immunity and data integrity. The twisting of the pairs may seem to some as insignificant, but it is a very critical element in the elimination of crosstalk and to the rejection of outside noise interference.
Since backward compatibility is a large part of the recipe for manufacturers to maintain customer loyalty, Telex developed the 1-RU, 32-port intercom system which they have named the “Zeus-III” with, RJ-45 connectors but still wired to the USOC standard. This allows an RJ-12 connector to plug into the Zeus using possibly pre-existing cables and key-panels. One other ADAM System product from Telex features an RJ-45; this is the KP-32-CLD. In an effort to remain compatible, the CLD is delivered from the factory as USOC but with internal jumpers it can be configured for 568B.
The problem is that Telex has not yet embraced the 568B as a complete option and the co-mingling of the two conventions, even within their own product line, is becoming a big problem.
1 Telex does not make any product that comes standard wired as 568B
2 That product uses an RJ-45 connector.
3 The use of an RJ-45 connector, in today’s world, that is not 568B is a problem waiting to happen
4 Since Telex is not presenting a solution in this area, other end-users and integrators are solving it with yet more incompatible schemes only adding to the confusion.
In conclusion, I would like to see Telex approach this situation proactively and establish a standard. Even if the standard is not yet ready, let the industry know that the situation is being addressed.