HOWTO: Make a Network Cable
I recently had the opportunity to run some new network cables at one of our facilities. One of the requirements we ran into included creating new UTP cables and some fixing some old cables that had been run previously.
I quickly realized that I needed a primer on this as I hadn’t done it in ages. Needless to say we weren’t successful at first and some of the attempts were rather wrong (especially on my part). So, to remedy that and to allow some future notes to myself, here’s a quick tutorial on how to make network cables (including cross-over cables).
A Short History of UTP
In the early 1990’s coaxial cable was still the dominant network cable in use for both small and large computer networks. This is primarily due to the 10-Mbs Ethernet networks in place at the time. Since the advent of 100-Mbs networks and Gigabit networks coaxial cable has given way to Unshielded Twisted Pair cable (or UTP). Early UTP standards included CAT3 and CAT4. However, the 100Base-Tx (Fast Ethernet) networks required a newer standard, CAT5. Later uses of Gigabit Ethernet (100Base-T) generated yet another standard, CAT5e. The CAT5e standard has now been replaced by the CAT6 standard and is compatible with both CAT5 and CAT5e cabling.
In fact, for newer networks it is suggested that CAT6 be run in order to accomodate scalability for future network standards.
UTP Cable Rating Codes
In addition to the CAT standard for a cable, there are several rating codes to consider when running new cable. Generally, these indicate the fire-safety ratings and performance ratings for a specific type of CAT5/6 cable based on the quality of the cable jacket.
- UL - The National Electrical Code (NEC), published by the National Fire Protection Association (NFPA), details advisory safety considerations for electrical wiring.
- CMP (R-733, R-753) - Cables meeting type CMP requirements are suitable for installation in ducts and plenums without the use of conduit. These cables are designed for fire resistance and low-smoke and toxin producing characteristics. CMP is more expensive than the CMR or CM cable and is generally used for cable that must be run through ducts, suspended ceilings or other areas that act as an air passage in any way.
- CMR (R-731, R-751, R-756) - Riser type cables are engineered to prevent the spread of fire from floor to floor and are suitable for vertical shaft applications. CMR cable is generally acceptable for most indoor cabling requirements and is most likely the type of cable you will use for an office or home network.
- CM (R-732, R-752, R-757) - Cables for general building wiring. CM cables are used in areas other than plenums and risers. These cables are resistant to the spread of fire and pass the UL 1581 Vertical Tray Flame Test
UTP Specifications
Naturally, there are some industry standard specifications for the various CATx cable standards. The table below lists the standards for the most popular cable types, including the newer CAT7 standard.
| Category | CAT5 | CAT5e | CAT6 | CAT7 |
| Type | UTP | UTP | UTP | ScTP |
| Frequency | 100 Mhz | 100 Mhz | 250 Mhz | 600 Mhz |
| Max Length | 100m (328ft) | 100m (328ft) | 100m (328ft) | 100m (328ft) |
| LAN Applications | 100Base-Tx CDDI 52-155Mbps ATM | 100Base-T 52-155Mbps ATM | 100Base-T 155-622Mbps ATM | |
| Atten. dB/100m (MAX@100Mhz) | 22 dB | 22 dB | 19.8 dB | |
| Characteristic Impedance | 100 ohms +/-15% | 100 ohms +/-15% | 100 ohms +/-15% | 100 ohms +/-15% |
| NEXT dB (MIN@100Mhz) | 32 dB | 35 dB | 44 dB | |
| PS-NEXT dB (MIN@100Mhz) | – | 32 dB | 42 dB | |
| PS-ELFEXT dB (MIN@100Mhz) | – | 21 dB | 25 dB | |
| Return Loss dB (MIN@100Mhz) | 16 dB | 20 dB | 20 dB | |
| Delay Skew (MAX per 100m) | – | 45 ns | 45 ns |
Color Codes
Okay, now that the specifications are out of the way we can discuss the standard layouts for Ethernet Standards 568A and 568B.
Once you’ve got the color codes down the rest is pretty easy.
There are two color code layouts specificed by the Ethernet standard:
| 568A Standard | 568B Standard |
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Why two standards? The two standards are used to provide two different scenarios in which the UTP cable is used. That is, the need for Straight Through cables and Crossover cables.
A Straight Through cable arrangement must have both terminating ends of the cable use the same Ehternet standard (either 568A or 568B). It doesn’t matter which arrangement you use, as long as they are both the same on either end of the line.
A Crossover cable arrangement has both ends different. That is, one end of the cable will have a 568A layout while the opposite end will have a 568B layout. Essentially, crossover pairs are switching the send and recieve pairs.
If you look closely you’ll notice that the only difference between the two layouts is the arrangement of the green and orange pairs. By swapping the locations of the green and orange pairs you can obtain the opposite arrangement.
In fact, from what I understand pins 4,5,7,and 8 (the blue and brown pairs) are not used (or required) to implement 100Base-T duplexiing. They are essentially ignored for the purposes of these types of networks. They are needed to fulfill the standard though and are included in the concept of completing a “twisted” pair relationship, something that is far beyond the scope of this article.
Just remember this:
- 568A (green on left) for both terminating ends is a straight through cable
- 568B (orange on left) for both terminating ends is a straight through cable
- 568A on one end and 568B on the other end is a crossover cable
Straight through, Crossover, what the…?
Okay, it might be useful to describe what all this means.
For the most part, crossover cables are used to connect like equipment together, such as two computers, two hubs, two switches, etc.
On the other hand straight through cables are used to connect a computer to a hub, router, cable modem, etc. These are the most common types of cables you’ll use.
It might be interesting to also note that an uplink port (or WAN port) on a network device such as a switch or router acts as a crossover. That is, a straight through cable connected to an uplink port is essentially the same as connecting a crossover cable to a regular port.
Note also that some modern hubs and switches can automatically detect which type of port to use. That is, they can switch the port to an uplink if a crossover type is needed. You’ll have to refer to your products documentation to determine this though. If the switch or hub has a dedicated uplink port chances are it’s not going to be the type that can automatically detect.
Finally, How To Make a Network Patch Cable
It’s important to understand the standards described above in order to properly create the actual cable. Once you have the simple color codes down (remember A is green on left, B is orange on left) then the rest is just a matter of following the steps below:
- Make sure you purchase a good quality crimping tool. You will regret using cheap tools as they will always end up costing you time and patience.
- Make sure you have more RJ45 connectors than you will actually need. It’s a given that something always happens during the actual implementation (remember Murphy?). These connectors are relatively inexpensive so it’s not going to break the bank to plan ahead.
- Freshly cut the end of the cable.
- Strip no more than 1/2 inch of the insulating jacket. Make sure you only strip the jacket and NOT the insulation around the individual wires. Those need to stay intact. A good quality crimping tool will have a stripper built into it.
- Make sure the internal wires are cut in a straight line so that they fit uniformly within the RJ45 connector.
- Untwist the twisted pair wires just enough to line them up properly according to the illustrations above. Untwisting them too much could create unnecesary crosstalk, something you definitely want to avoid. Again, do not strip the individual wires.
- Once the wires are in the proper arrangement, insert them into the RJ45 connector, while keeping them in the same order.
- Before crimping, make sure the wires are still in the proper order and that all 8 of them are snug against the end of the plug.
- Finally, insert the connector into the crimping tool and squeeze hard. The tool will securely clamp down on to the connector inserting metal teeth through the individual wire jackets in order to make a good connection.
- Repeat this on the other end of the cable, with the same color code for a straight through arrangement and the opposite color code for a crossover cable arrangement.
General Suggestions
There are some general cautions and suggestions that are of use when running cable.
- Pay attention to the length of the cable and do not exceed 100 meters (or 328 feet). It’s probably best to not even get near that maximum length.
- Use a switch as opposed to a hub in most cases for better performance. Switches and routers can act as signal boosters while hubs cannot.
- Keep the cables from pinching or bending tighter than 1 inch. They should bend in smooth curves.
- To avoid crosstalk strip away only as much of the outer cable sheath (or jacket) as needed.
- Once they’ve been untwisted try not to retwist the cable ends as you may cuase “near end” crosstalk.
- Use onlyl CAT5 RJ45 connectors on CAT5 cables. That is don’t use CAT3 connectors or lower.
- Be careful when pulling on the cable and try not to exceed 25 lbs of pressure.