Ethernet, defined as protocol 802.3 by the Institute of Electrical and Electronics Engineers (IEEE), refers to the family of wired networking technologies used in data networks ranging from Local Area Networks (LAN), up to Wide Area Networks (WAN).
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It has been in use since the early 1970s when it was rated for 10 megabits per second (Mb/s), but didn’t become commercially available until 1980. Since then, it has undergone a number of developments and enhancements allowing it to achieve speeds into the gigabit range.
The first Ethernet networks used coaxial cable as the transmission medium, with computers connected in series in a bus topology. This had many drawbacks, including if the connection was disrupted at any one point, then all computers on the bus would also lose connectivity.
In 1985, category 1 unshielded twisted-pair cable was introduced with a data rate of one Mb/s. It was followed by category 2 which upped the speed to 4 Mb/s. However, it wasn’t until the introduction of category 3 cable that four twisted pairs were used, supporting 10 Mb/s with a 16 MHz bandwidth.
In 1990, Ethernet shifted from coaxial to category 3 10BASE-T, unshielded telephone twisted wire pairs, in the more stable star topology.
Starting with category 3, Ethernet cables were able to carry voice, data, and video signals over a single cable.
With twisted pairs having now become the preferred medium, the next generation 100BASE-T, saw a ten times increase in speed at 100 Mb/s with the introduction of category 5, which is still in use today, and can accommodate speeds in the gigabit range.
Increased speeds though, yield more problems with crosstalk, which can adversely affect performance, and so category 6 cable with added shielding was introduced.
CAT 5 vs CAT 6
CAT5 and CAT6 series cables comprise 4 twisted pairs of copper wire, used primarily in computer networks. The main difference between them is to be found in the physical structure of the cables themselves, where extra shielding and separation of twisted pairs offer greater protection from crosstalk.
CAT5
Category 5 or CAT5 was introduced in 1995. CAT5 is rated for frequencies up to 100 Mhz:
| Physical Layer | Speed | Pairs Used | Bandwidth | Maximum Distance |
| 10BASE-T | 10 Mb/s | 2 | 10 MHz | 100m |
| 100BASE-TX | 100 Mb/s | 2 | 31.25 MHz | 100m |
| 1000BASE-T | 1000 Mb/s | 4 | 62.5 MHz | 100m |
In 2001, CAT5 was superseded by CAT5e (enhanced Category 5), with stricter specifications allowing for an increase in bandwidth (350Mhz compared to 100MHz) and hence greater speeds, as well as elevated protection against crosstalk.
CAT5e is rated to handle frequencies up to 350 Mhz. It is backward compatible with CAT5:
| Physical Layer | Speed | Pairs Used | Bandwidth | Maximum Distance |
| 10BASE-T | 10 Mb/s | 2 | 10 MHz | 100m |
| 100BASE-TX | 100 Mb/s | 2 | 31.25 MHz | 100m |
| 1000BASE-T | 1000 Mb/s | 4 | 62.5 MHz | 100m |
| 2.5GBASE-T | 2500 Mb/s | 4 | 100 MHz | 100m |
| 5GBASE-T | 5000 Mb/s | 4 | 200 MHz | 100m |
Apart from network data, CAT5 and CAT5e are also capable of carrying telephone and video signals.
CAT6
Category 6 or CAT6, and Category 6A or CAT6A (augmented Category 6), are backward compatible with CAT5 and CAT5e, and are rated at 250 Mhz and 500 Mhz respectively. CAT6 and CAT6a cables use a thicker gauge copper wire with increased shielding and more twists per inch compared to CAT5 and CAT5E.
There is also a longitudinal spline separator which isolates each of the four cable pairs from each other, helping to further reduce crosstalk. This allows CAT6 and CAT6A to reach speeds of 5Gb/s and 10Gb/s respectively, over a maximum distance of 100 meters.
CAT6 is rated for frequencies up to 250Mhz and is backward compatible with CAT5e:
| Physical Layer | Speed | Pairs Used | Bandwidth | Maximum Distance |
| 10BASE-T | 10 Mb/s | 2 | 10 MHz | 100m |
| 100BASE-TX | 100 Mb/s | 2 | 31.25 MHz | 100m |
| 1000BASE-T | 1000 Mb/s | 4 | 62.5 MHz | 100m |
| 1000BASE-T1 | 1000 Mb/s | 1 | 375 MHz | 40m |
| 2.5GBASE-T | 2500 Mb/s | 4 | 100 MHz | 100m |
| 5GBASE-T | 5000 Mb/s | 4 | 200 MHz | 100m |
| 10GBASE-T | 10000 Mb/s | 4 | 250 MHz | 50m |
CAT6a is rated for frequencies up to 500Mhz and is backward compatible with CAT6:
| Physical Layer | Speed | Pairs Used | Bandwidth | Maximum Distance |
| 10BASE-T | 10 Mb/s | 2 | 10 MHz | 100m |
| 100BASE-TX | 100 Mb/s | 2 | 31.25 MHz | 100m |
| 1000BASE-T | 1000 Mb/s | 4 | 62.5 MHz | 100m |
| 1000BASE-T1 | 1000 Mb/s | 1 | 375 MHz | 40m |
| 2.5GBASE-T | 2500 Mb/s | 4 | 100 MHz | 100m |
| 5GBASE-T | 5000 Mb/s | 4 | 200 MHz | 100m |
| 10GBASE-T | 25000 Mb/s | 4 | 1000 MHz | 100m |
Networking Cable Terminology
UTP vs SCTP
With respect to CAT5 and CAT6 series cables, both unshielded twisted-pair (UTP) and screened twisted-pair (SCTP) comprise four twisted pair, 100 ohm, 24 awg solid copper conductors with a thermoplastic jacket.
Compared to UTP, SCTP offers enhanced construction, consisting of the four twisted pairs of copper wire, within a foil laminate shield and drain wire. This offers superior immunity to Radio-frequency interference (RFI) and Electromagnetic interference (EMI), as well as reduced crosstalk.
UTP is widely used in the U.S., while SCTP is used in Europe.
Stranded vs Solid Copper Wire
Solid copper wire has one solid strand per conductor, whereas stranded is made from many, thin copper wires twisted together to form a single conductor. The main difference between the two is that stranded wire is more flexible.
Stranded cables are better for short cable connections, such as from a workstation to a RJ45 Ethernet port on a switch or wall jack. Solid cables are better for long runs, being able to withstand corrosion far better which makes them ideal for outdoor installations.
Twisted-pair
Twisted pair refers to cabling where two conductors are twisted together in order to minimize the effects of RFI and EMI, and reduce emitted electromagnetic radiation, which can create crosstalk with neighboring cable pairs.
One of the main differences and enhancements of CAT6 over CAT5, is that CAT6 cables have more twists per inch.
Crosstalk
Crosstalk, as it applies to CAT5 and CAT6 series computer cable (and copper cable in general), refers to a phenomenon where the signal transmitted on one pair of wires adversely affects the signal on another pair or pairs.
In the days of analog telephony, this could be observed when the voices from another call could be heard at very low level. On computer networks, it causes data errors which can slow down the effective bitrate.
Crosstalk is caused when coupling – be it capacitive crosstalk caused by the electrical field, or inductive crosstalk caused by the magnetic field – occurs between adjacent cable pairs. Additionally, crosstalk can be further classified as near end crosstalk (NEXT), far end crosstalk (FEXT), and alien crosstalk (AXT).
NEXT is a measure of how much of a signal leaving at the source of transmission on one pair of wires, leaks into an incoming signal on an adjacent pair of wires. NEXT is measured in decibels (dB), and the higher the dB value, the less crosstalk imparted onto the affected adjacent wire pair.
FEXT is similar to NEXT except that the measurement is made at the far end from the source of the transmitted signal. Since the signal will have traveled the length of the cable, the signal will have been attenuated.
While NEXT and FEXT measure interference on twisted pairs within the same cable, AXT measures the interference caused by neighboring cables.
Conclusion
While both CAT5 and CAT6 series cables comprise 4 twisted copper wire pairs, and both use RJ45 end-connectors, they differ in their cable construction, the aim being to reduce EMI and RFI interference, and crosstalk, especially since CAT6 and CAT6a are rated at higher bitrates.
CAT6 and CAT6a cables typically have better insulation, with more twists per inch for each wire pair, and a thicker cable diameter of around 0.250-inches maximum, compared to 0.204-inches for CAT5e.
One of the major factors in helping reduce crosstalk, is the longitudinal spline separating each of the four twisted pairs from each other in CAT6 and CAT6a cables.
CAT6 and CAT6a cables have bandwidth capacities of 250 Mhz and 500 Mhz respectively, compared to 100 MHz and 350 MHz for CAT5 and CAT5e. CAT5e has a maximum bitrate of 5000 Mb/s over a maximum length of 100m, while CAT6a boasts of 25000 Mb/s over 100m maximum length.
Finally, CAT6 series cables must conform to stricter standards with regard to crosstalk and external noise mitigation.
It is worth mentioning that Cat8 (shielded only) is also available, which supports 2000 Mhz bandwidth and offers data rates of 25 Gb/s and 40 Gb/s. It incorporates even more shielding, individual wire insulation, as well as foil and braided shielding.
