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network cable

Network Fault Finding - Cables

Cable problems are extremely common in networks and are one of the most basic to avoid. Use only cables from known sources, designed for the application intended. The number of times we've found phone grade cables used in patch panels for data networks, or connecting a PC to a wall point makes this our first check and so should also be yours.

Cable Category

Twisted pair cables come in a variety of categories and are given a 'Cat' value, such as Cat5e. Cat5e is the type used for connecting Ethernet network devices together running up to 1Gb or 1000Mb. Older Cat3 and Cat4 cables are commonly used for voice applications, but because they use the same plug (8P8C or also known as RJ45) they will fit into the connectors for networks. However these cables will not work reliably, especially not in a Gigabit network.

The table below gives an overview of different category cables and there common uses.
Cable Category Common Uses
1 Telephone Wiring Notes
10Base-T -> 10Mb or 'Standard' Ethernet
100Base-TX -> 100Mb or 'Fast' Ethernet
1000Base-T -> Gigabit Ethernet
10GBase-T -> 10 Gigabit Ethernet
2Telephone Wiring
3Telephone Wiring, 10Base-T
4Token-Ring, 10Base-T
5100Base-TX, 10Base-T
5e1000Base-T, 100Base-TX
61000Base-T, 100Base-TX
6a10GBase-T

The cable category on all 'good' network cables is printed on the cable. For example the cable pictured above has
'ETL Certified to TIA/EIA-568-B.2 Category 5e UTP 4 pairs 24AWG patch cable & AWM2835 30V 60°C'
written along its length every metre or so. This confirms that it has been certified to meet the category 5e rating and so is suitable for use in a Gigabit network.

Cable Type

Cables also come in different constructions, designed for different applications. Cable designed for infrastructure use, as used from the patch panel to a floor or wall socket is usually solid core, meaning each conductor in the cable has a single solid core of copper wire. This cable is stiff and will keep a shape when bent. Cables designed for patching connections and making connections between equipment and floor or wall sockets is stranded, meaning each conductor is made of multiple strands of thin copper wire. This cable is flexible and will not hold its shape as much when bent.
Using solid core cable for patching and connecting equipment will work for a while, but the regular movement typical in most environments will result in the cores breaking and lead to network reliability problems.
Likewise using flexible cable for infrastructure use will work, but it is not designed for the Krone push-down style connections and so can lead to connection issues. The flexible cable is also usually more costly, so it is a waste to use it for such applications.

connector pinout

Network Connectors

Modern Ethernet networks (and some others) use an 8P8C plastic connector to connect cable to equipment or floor/wall sockets. This connector is also often referred to as a RJ45 connector. Strictly speaking RJ45 connectors were designed for telephone use and were 8P2C (8 positions, 2 conductor/connector) plugs and jacks. However as this style of telephone connector was never widely used (most are RJ11 or RJ12) and the 8P8C connector used on networking looks very similar, the RJ45 name is widely used when referring to network connectors.

Connector Wiring

Two wiring configurations exist, known as T568A & T568B. Both connect the same pins together in a 'normal' straight through cable. i.e. pin 1 of the plug at one end of the cable is connected to pin 1 at the other end, 2 is connected 2 and so on. The difference is the pairs of wires used in the cable, or put another way the colour of the wires connected to each pin. Either configuration can be used for most applications, although ensure the same configuration is used through out the installation to reduce confusion and possible cross talk interference issues. Most installations and cables tend to use T568B, especially in North America. It is often recommended that business installations use T568B and residential use T568A; however this advice seems to rarely be followed. The important thing is to pick one configuration and use it consistently.

T568A connector wiring configuration
Pin #Wire Colour
(T568A)
Wire Diagram
(T568A)
10Base-T Signal
100Base-TX Signal
1000Base-T Signal
1White/Greenwhite/greenTransmit+BI_DA+
2GreengreenTransmit-BI_DA-
3White/Orangewhite/orangeReceive+BI_DB+
4BlueblueUnusedBI_DC+
5White/Bluewhite/blueUnusedBI_DC-
6OrangeorangeReceive-BI_DB-
7White/Brownwhite/brownUnusedBI_DD+
8BrownbrownUnusedBI_DD-

T568B connector wiring configuration
Pin #Wire Colour
(T568B)
Wire Diagram
(T568B)
10Base-T Signal
100Base-TX Signal
1000Base-T Signal
1White/Orangewhite/orangeTransmit+BI_DA+
2OrangeorangeTransmit-BI_DA-
3White/Greenwhite/greenReceive+BI_DB+
4BlueblueUnusedBI_DC+
5White/Bluewhite/blueUnusedBI_DC-
6GreengreenReceive-BI_DB-
7White/Brownwhite/brownUnusedBI_DD+
8BrownbrownUnusedBI_DD-

For straight through cables, which are used for normal connections between PCs and hubs/switches, the connections are the same at both ends of the cable, which results in a 1-1, 2-2, 3-3, 4-4, 5-5, 6-6, 7-7, 8-8 connected cable.

Cross over cables, which are usually used to connect to PCs directly together for peer-to-peer network use can exist in two different versions. Version 1 allows networks using 10Base-T (10Mb) and 100Base-TX (100Mb) connections only, whilst version 2 also allows 1000Base-T (Gigabit) connections. For version 1 the cable appears to be wired for T568A configuration at one end and T568B at the other. version 2 however can exist for T568A or T568B type pairing configuration when viewed from one end only. The other end appears to look to be incorrectly wired.

End 1
Pin #
Wire Colour
(T568A)
Wire Diagram
(T568A)
Wire Colour
(T568B)
Wire Diagram
(T568B)
End 2
Pin #
Version 1
End 2
Pin #
Version 2
1White/Greenwhite/green White/Orangewhite/orange33
2Greengreen Orangeorange66
3White/Orangewhite/orange White/Greenwhite/green11
4Blueblue Blueblue47
5White/Bluewhite/blue White/Bluewhite/blue58
6Orangeorange Greengreen22
7White/Brownwhite/brown White/Brownwhite/brown74
8BrownbrownBrown brown85

network cable tester

Basic Cable Testing

Basic cable testers are readily available from many suppliers. These allow all network cables and phone cables with RJ45 (8P8C) or RJ11 & RJ12 (6P6C & 6P4C)to be tested. Most low cost versions simply pass current down each conductor in turn to test for continuity. Models with indicators at both ends (as pictured), allow you to determine if the cable is straight through or crossed over.

In a straight through cable the same number indicators will show at both ends, i.e. 1&1, 2&2 etc.
In a cross over cable the indicators will show the end to end pattern as shown in the table above

These devices are useful to check correct wiring, but do not allow the 'quality' of the cable to verified. To certify an installation as meeting a category such as Cat5e requires a more sophisticated tester.