Beyond Category 5

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Twisted-pair cables for the future

The news on bandwidth.
The need for increased bandwidth never ceases. Applications keep getting more complex, and it won’t be long before you need to increase your network’s speed. Doing so may mean upgrading your cable. Because twisted-pair copper cable is the most common networking cable, let’s take a brief look at current and pending standards for high-performance twisted-pair cable.

The limits of Category 5.
The Category 5 (CAT5) standard (for 100-Mbps LANs) has been around since 1991, so it’s well established.  If you have a lot of 10-Mbps equipment, CAT5 cabling will serve your needs. It also handles 100-Mbps Fast Ethernet transmissions very well.

But if you’re running up against the performance limits of a 100-Mbps network, you’ll probably want to upgrade at least parts of your system fairly soon.

Note that although some companies (including Black Box) still sell cable marked as CAT5, officially it is no longer recognised by the TIA/EIA and has been superceded by Cat5e.

Category 5e: the improved Category 5.
Ratified in 1999, Category 5e (CAT5e) is an incremental improvement designed to enable cabling to support full-duplex Fast Ethernet operation and Gigabit Ethernet.

The main differences between CAT5 and CAT5e can be found in the specifications. The CAT5e standard raises the performance requirements slightly.

CAT5e has stricter specifications for Power Sum Equal-Level Far-End Crosstalk (PS-ELFEXT), Near-End Crosstalk (NEXT), Attenuation and Return Loss (RL) than those for CAT5. Like CAT5, CAT5e is a 100-MHz standard, but it can handle bandwidth superior to that of CAT5. With these improvements, you can expect problem-free full-duplex, 4-pair Ethernet transmissions over your CAT5e UTP.

Category 6.
The next level in the cabling hierarchy is Category 6 (CAT6) (ANSI/TIA/EIA-568-B.2-1), which was ratified by the TIA/EIA in June 2002. CAT6 provides for much higher performance than CAT5e and features more stringent specifications for crosstalk and system noise.

The quality of the data transmission depends upon the performance of the components of the channel. So to transmit according to CAT6 specs, jacks, patch cables, patch panels, cross-connects and cabling must all meet CAT6 standards. (The channel basically includes everything from the wallplate to the wiring centre.) The CAT6 components are tested individually, and they are also tested together for performance. The standard also calls for generic system performance so that CAT6 components from any vendor can be used in the channel.

CAT6 channel transmission requirements should result in a Power Sum Attenuation-to-Crosstalk Ratio (PS-ACR) that is greater than or equal to zero at 200 MHz.

All CAT6 components must be backward compatible with CAT5e, CAT5 and CAT3.

If different category components are used with CAT6 components, then the channel will achieve the transmission performance of the lower category. For instance, if CAT6 cable is used with CAT5e jacks, the channel will perform at a CAT5e level.

Category 6a
Defined in 2008, Cat6a (augmented) is tested to 500 MHz. The CAT6 specification was highly susceptible to Alien Cross Talk (AXT) when bundled with other CAT6 cables. When transmitting 10Gig Ethernet, this meant that the maximum distance was restricted to 55m and this was only in situations where AXT was kept to a minimum.
As the 10Gbase-T standard aims for 100m transmission distance to keep in line with the other Ethernet standards, CAT6a was defined.

Category 7.
This standard specifies minimum performance standards for fully shielded cable (individually shielded pairs surrounded by an overall cable shield) transmitting data at rates up to 600 MHz. Although it is commonly referred to as CAT7, strictly speaking it is ‘Class F’ cable. It is defined by the ISO, not the EIA/TIA.

Category 7 aims to offer greater capacity for demanding applications such as broadband video but will have to compete with fibre optic cable. It is terminated by GG-45 or TERA connectors. GG45 is an 8P8C connector, similar to RJ-45 and TERA is a different style, developed by the Siemon company.

Category 7a
Although still a draft ISO standard, Cat7a is defined at frequencies of 1000Mhz. Tests have shown that it is possible to run 40 Gigabit Ethernet to 50m and 100 Gigabit Ethernet to 15m.

However, the IEEE is not looking at Cat7a for running 40 or 100 GigE so CAT7a may never be defined for use with any ethernet application.

Twisted-Pair Cable Specifications Comparison
	CAT5	CAT5e	CAT6	CAT6a (Proposed)	CAT7
Frequency	100 MHz	100 MHz	250 MHz	500 MHz	600 MHz
Attenuation (max. at 100MHz)	22.0 dB	22.0 dB	21.3 dB	19.1 dB	18.5 dB
Characteristic Impedance	100 ohms ± 15%	100 ohms ± 15%	100 ohms ± 15%	100 ohms ± 15%	100 ohms ± 15%
NEXT (max. at 100MHz)	-32.3 dB	-35.3 dB	-39.9 dB	-45.3 dB	-72.4 dB
PS-NEXT (max. at 100MHz)	-	-32.3 dB	-37.1 dB	-42.3 dB	-69.4 dB
EL-FEXT (max. at 100MHz)	-	-23.8 db	-23.3 db	-30.0 db	-54.0 db
PS-ELFEXT (max. at 100MHz)	-	-20.8 db	-20.3 db	-27.0 db	-51.0 db
PS-ANEXT (max. at 500MHz)	-	-	-	-24.2 db	-20.0 db
PS-AELFEXT (max. at 500MHz)	-	-	-	-23.0 db	-
Return Loss (max. at 100MHz)	-16.0 db	-20.1 db	-12.0 db	-20.1 db	-20.1 db
Delay Skew (max. at 100m)	-	45 ns	45 ns	40 ns	25 ns
Networks Supported	100BASE-T	1000BASE-T	1000BASE-TX	10GBASE-T	10GBASE-T +