Why did all category 6 cable used to have a spline, and now is offered without one?
Some category 6 cable designs have a spline to increase the separation between pairs and also to maintain the pair geometry. This additional separation improves NEXT performance and allows category 6 compliance to be achieved. With advances in technology, manufacturers have found other ways of meeting category 6 requirements. The bottom line is the internal construction of the cable does not matter, so long as it meets all the transmission and physical requirements of category 6. The standard does not dictate any particular method of cable construction.
