Everybody knows that the bigger number on category-rated unshielded-twisted pair (UTP) cables means higher performance. What does it really mean to the contractor? The Telecommunications Industry Association specification for Cat 6a cabling is a whopping 136 pages, with 32 diagrams of test configurations, 57 tables of test specs and 35 drawings of special test fixtures required to verify cabling performance. Fortunately, you don’t need to understand all that technical gibberish; you just need to buy a new Level 3e tester to certify it. But many of those specs affect how you install and troubleshoot Category 6a-rated cables. Let’s test your knowledge. Correct answers and explanations are in red.
1. Most of the performance specifications of a category-rated UTP cable depend on the consistency of the ________ of the wires in each pair.
C. Copper-clad conductor
D. Copper alloy
The consistency of the twists in UTP cable combined with the technique of balanced transmission provide the high performance of category-rated UTP cable.
2. Crosstalk occurs mainly at the connections on the ends of the cable, so that is where to look first if the link fails crosstalk.
Most crosstalk problems arise from installation processes at the termination on the ends of the cable.
3. Maintaining the twists in each pair to closer than ________ to the termination point is important to maintaining the cabling performance.
A. 1 inch (25 mm)
B. ½ inch (13 mm)
C. ¼ inch (6 mm)
D. Maintaining the twists is not important
Untwists of the wires in the pairs should be less than ½ inch (13 mm) at every termination point.
4. Since the introduction of gigabit Ethernet—which uses bidirectional transmission on all four pairs—a new specification, ________ , has become an important test for installed UTP cable.
C. Return loss
Since signals are going in both directions simultaneously, reflections from the far end (measured as return loss) must be minimized.
5. Since gigabit and 10 gigabit Ethernet use bidirectional transmission on all four pairs, testing ________ crosstalk has become important.
With signals being transmitted on all four pairs simultaneously, crosstalk from the three other pairs can affect any pair.
6. Ten gigabit Ethernet requires tighter control of the twists of all four pairs, but that causes new problems with ________ crosstalk.
The pairs in Cat 6a are so consistent that crosstalk can occur from a pair in one cable to the same pair in another cable because it has the same twist rate and is tuned to the same frequency.
7. Because of the time-consuming testing procedures, some manufacturers do not require testing ________ to certify cables for their warranty programs.
A. At all
B. Every cable
C. Power-sum, far-end crosstalk
D. Alien crosstalk
Alien crosstalk is hard to test, requiring testing multiple cables after completing all the installation so some manufacturers do not require testing it.
8. Most crosstalk problems can be solved by using ________.
A. Soldered connections
B. Connectors instead of punchdowns
C. Shielded UTP cable and connection hardware
D. A better tester
Shielded twisted pair cable has shields over every pair as well as the whole cable, preventing any crosstalk problems.
9. Alien crosstalk problems can often be solved by being less neat in bundling cable runs.
Bundling cables neatly can make alien crosstalk more likely.
10. If you run out of Cat 6a-recognized components, such as jacks or patchcords, you can use ________.
A. Cat 5e
B. Cat 6
C. Any shielded equivalents
D. No lower-rated components and still maintain Cat 6a performance
Maintaining Cat 6a performance requires using only Cat 6a rated components and installing them properly
HAYES is a VDV writer and educator and the president of The Fiber Optic Association. Find him at www.JimHayes.com.