Guest Blog: Which Category cable? They all do Gigabit

by Felix Zayas
June 21, 2010

Once upon a time there was a technology called 10Base2. Alright, we won't start that far back. However, we will start by talking about bandwidth. Bandwidth is measured in either digital bits per second (bps) or analog hertz (Hz). 1000BaseT, IEEE 802.3ab - or Gigabit Ethernet as most call it - requires Category 5e or Category 6 cabling. Gigabit Ethernet has a maximum network segment of 100 meters (328 feet) and can operate at speeds of 1000 Mbps, or 1 Gbps.

The differences between Category 5e and Category 6 occur in the analog measurements. Category 5e must pass a number of tests at 100 MHz, such as return loss, insertion loss, PSNEXT loss, ACRF, PSACRF, propagation delay skew, PSANEXT loss, average PSANEXT loss, PSAACRF, average PSAACRF loss and NEXT. The results, being analog, are measured in decibels (dB). Category 6 cabling must pass the same tests at 250 MHz. For example, the requirements for ACRF using Category 5e cabling is 17.4 dB at 100 MHz and 15.3 dB with Category 6 at 250 MHz.

Cabling systems on the high end of Category 6 performance do not have a standard they can reference. Rather, their results will usually be in documentation showing how far above and beyond the current standards they perform. These analog, frequency-based performance requirements are set by the standard from the Telecommunications Industry Association (TIA) called ANSI/TIA-568-C.2.

The main argument is that the high-end Category 6 cabling has more "headroom" than lower-grade cabling, referring to the more stringent certification tests that must be passed. Now let's talk digital bandwidth. With all three types of cable run, terminated and tested in the same exact manner, sure, the higher-end Category 6 cable will outperform the others with the analog, frequency-based testers. If they outperform the lower-end cable in the digital world, does that mean there will be what is called a high bit error rate (BER) with the low-end cabling?

There are application-based testers you can run independently, or programs you can download, to test out actual digital bandwidth. You will find that there will be times when a high-end Category 6 cable performs similar to a Category 5e cable, and other times when the higher-end Category 6 cable outperforms all. The higher-end cables are engineered to deliver higher performance. The manufacturer takes steps such as putting a separator between the pairs, using a different style jacket, using a tighter twist rate, or incorporating any of the many other considerations that go into cable construction.

There are many obstacles and third-party items, over which we may not have complete control in the real world, that could degrade our cable's performance. These high-end cables may be our answer to keeping a low BER and maintaining an actual throughput worthy of Gigabit Ethernet.

Felix Zayas is a technology designer for BVH Integrated Services Inc., a multi-disciplined engineering firm based in Bloomfield, CT. BVH provides MEP, civil, structural, sustainable design, commissioning, and technology services to clients in the educational, health care, corporate, governmental and research markets. With more than seven years of telecommunications engineering experience, Felix designs voice/data systems, structured cabling, fiber, as well as A/V, paging, security, nurse-call, physiological monitoring, CATV and wireless systems.

He achieved his Registered Communications Distribution Designer (RCDD) and Network Transport Systems (NTS) designations from BICSI and is a Certified Technology Specialist (CTS) as designated by InfoComm as well as a licensed Telecommunications Layout Technician (TLT) in the state of Connecticut. Felix is also a LEED Green Associate as designated by the Green Building Certification Institute. He blogged about the process of achieving that designation as well. He can be reached at felixz@bvhis.com or 860-286-9171.