Frank X. Mara
CommTran Consulting
The Telecommunications Industry Association task group that is working on the definition of a transmission channel and its parameters is close to producing a standard, to be known as Technical Systems Bulletin-67, transmission performance specifications for field-testing of unshielded twisted-pair cabling systems. This document, which will become part of TIA/EIA-568A, will provide the contractor and end user with a transmission specification to which the field-test measurements made on a cabling system can be compared. Despite claims previously made by some test-equipment vendors, there has been no agreed-upon specification available to date, and certification of an installed channel has not been possible.
TSB-67 will also address issues around the test equipment needed to test a channel. The accuracy of an instrument, the test procedure for measuring that accuracy and the tests required to specify the compliance of a channel or link will be covered. The probability of a testing unit being in error will also be discussed. This should minimize the uncertainty surrounding the interpretation of measured results, so that the contractor and end user will be able to make meaningful decisions.
Rewiring is an expensive option, but without a specification, accuracy statements about testers and an indication of the uncertainty of their measurements, contractors have been at risk of having to reinstall channels because of faulty equipment. Also, end users are not fully aware about the capability of their cabling systems.
Although TSB-67 will help ensure proper channel measurements, it still needs to deal with channels that do not match the specified channel configuration of the bulletin, as well as cover return loss measurements and ambient noise specifications. These issues are not addressed in the current TSB, but they will nevertheless affect channel performance.
Because of the highly technical nature of such transmission measurements, marketing hype will continue to confuse many users. The solution is to make vendors explain their product claims and ask for proof that the product meets all of the requirements of TSB-67, including following the test procedures for measuring the specifications of the product.
Frank X. Mara is the principal of CommTran Consulting, Sandwich, MA. He is active in the TIA and the Building Industry Consulting Service International.
