Cat5 Straight-Through Cable Pin Assignments

Ethernet Cable Types, Performance & Pinout: Cat 5, 5e, 6, 6a, 7, 8 etc

Various cables are used for carrying Ethernet: current common types include Cat 5, 5e, Cat 6, 6a, 7 and Cat 8 and the RJ45 connector is widely used

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There are many Ethernet cables that can be bought. Often these cables are supplied free with equipment that uses Ethernet connectivity in some way or another.

There are several different varieties of Ethernet cable that can be obtained: speed variations, crossover cables, Cat 5, Cat 5e, Cat6, etc..

Normally Ethernet cables will be bought and there is no major need to understand what is inside or on the connectors, although it can be both interesting and helpful on some occasions. Even so, an understanding of the different types of Ethernet cable and the maximum lengths that should be used is helpful.

The commonly used cables: Cat 5, Cat 5e, Cat 6 all have different levels of performance, and therefore to is necessary to buy or select the right cable for the right application.

Categories for Ethernet cables

A variety of different cables are available for Ethernet and other telecommunications and networking applications. These cables that are described by their different categories, e.g. Cat 5 cables, Cat-6 cables, etc, which are often recognised by the TIA (telecommunications Industries Association) and they are summarised below:

  • Cat-1:     This is not recognised by the TIA/EIA. It is the form of wiring that is used for standard telephone (POTS) wiring, or for ISDN.
  • Cat-2:     This is not recognised by theTIA/EIA. It was the form of wiring that was used for 4Mbit/s token ring networks.
  • Cat-3:     This cable is defined in TIA/EIA-568-B. It is used for data networks employing frequencies up to 16 MHz. It was popular for use with 10 Mbps Ethernet networks (100Base-T), but has now been superseded by Cat-5 cable.
  • Cat-4:     This cable is not recognised by the TIA/EIA. However it can be used for networks carrying frequencies up to 20 MHz. It was often used on 16Mbps token ring networks.
  • Cat-5:     This is not recognised by the TIA/EIA. It is the cable that is widely used for 100Base-T and 1000Base-T networks as it provides performance to allow data at 100 Mbps and slightly more (125 MHz for 1000Base-T) Ethernet. Cat 5 cable is now obsolete and therefore it is not recommended for new installations.
  • Cat-5e:     This form of cable is recognised by the TIA/EIA and is defined in TIA/EIA-568-B.. It has a slightly higher frequency specification that Cat-5 cable as the performance extends up to 125 Mbps. It can be used for 100Base-T and 1000Base-t (Gigabit Ethernet). Cat 5e or enhanced is a form of Cat 5 cable manufactured t0 higher specifications although physically the same as Cat 5. It is tested to a higher specification.
  • Cat-6:     This cable is defined in TIA/EIA-568-B provides a significant improvement in performance over Cat5 and Cat 5e. During manufacture Cat 6 cables are more tightly wound than either Cat 5 or Cat 5e and they often have an outer foil or braided shielding. The shielding protects the twisted pairs of wires inside the Ethernet cable, helping to prevent crosstalk and noise interference. Cat-6 cables can technically support speeds up to 10 Gbps, but can only do so for up to 55 metres.
  • Cat-6a:     The “a” in Cat 6a stands for “Augmented.” The Cat 6a cables are able to support twice the maximum bandwidth, and are capable of maintaining higher transmission speeds over longer cable lengths. Cat 6a cables utilise shielded which is sufficient to all but eliminate crosstalk. However this makes them less flexible than Cat 6 cable.
  • Cat-7:     This is an informal number for ISO/IEC 11801 Class F cabling. It comprises four individually shielded pairs inside an overall shield. It is aimed at applications where transmission of frequencies up to 600 Mbps is required.
  • Cat-8:     These cables are still in development, but will be released in the foreseeable future to provide further improvements in speed and general performance.

Further descriptions of Cat-5 and Cat-5e cables are given below as these are widely used for Ethernet networking applications today.

Ethernet Cable Performance Summary
CategoryShieldingMax Transmission Speed (at 100 meters)Max Bandwidth
Cat 3Unshielded10 Mbps16 MHz
Cat 5Unshielded10/100 Mbps100 MHz
Cat 5eUnshielded1000 Mbps / 1 Gbps100 MHz
Cat 6Shielded or Unshielded1000 Mbps / 1 Gbps>250 MHz
Cat 6aShielded10000 Mbps / 10 Gbps500 MHz
Cat 7Shielded10000 Mbps / 10 Gbps600 MHz
Cat 8Details to be released later

Ethernet Cat 5 cable & pinout

Cat 5 cables or to give them their full name category 5 cable is the current preferred cable type for LAN network and telephone wiring where twisted pair cabling is required. Cat 5 cables consist of an unshielded cable comprising four twisted pairs, typically of 24 gauge wire. The terminating connector is an RJ-45 jack. In view of this these Cat5 network cables are often referred to as RJ45 network cables or RJ45 patch cables. Certified Cat-5 cables will have the wording "Cat-5" written on the side. As they conform to EIA/TIA 568A-5, this is written on the outer sheath. It is always best to use the appropriate network cables when setting up a network as faulty or not to standard cables can cause problems that may be difficult to identify and trace.

Cat5 network cable is now the standard form of twisted pair cable and supersedes Cat 3. The Cat 5 cables can be used for data speeds up to 125 Mbps, thereby enabling them to support 100Base-T which has a maximum data speed of 100 Mbps whereas the Cat-3 cable was designed to be compatible with 10Base-T. The Cat5 cable is able to support working up to lengths of 100 metres at the full data rate.

Where it is necessary to operate at higher speeds, as in the case of Gigabit Ethernet, an enhanced version of Cat 5 cable known as Cat 5e is often recommended, although Cat 5 is specified to operate with Gigabit Ethernet, 1000Base-T. Alternatively Cat 5e can be used with 100Base-T to enable greater lengths (up to 350 metres) to be achieved.

The wires and connections within the Cat 5 or Cat 5e cable vary according to the applications. A summary of the signals carried and the relevant wires and connections is given in the table below:

RJ-45 / Cat 5 / Cat 5e Pinout & Wiring
Mode A
Mode B
1 White / green   +TX +TD +BI_DA 48 V out  
2 Green   -TX -TX -BI_DA 48 V out  
3 White / orange   +RX +RX +BI_DB 48 V return  
4 Blue Ring     +BI_DC   48 V out
5 Blue / white Tip     -BI_DC   48 V out
6 Orange   -RX -RX -BI_DB 48 V return  
7 White / brown       +BI_DD   48 V return
8 Brown       -BI_DD   48 V return

In the table, TX is transmitted data, and RX is received data. BI_Dn is bi-directional data, A, B, C, and D.

Ethernet Cat 5 crossover cables

There are a number of different configurations of cable that may be employed according to the equipment and the requirement. The most common type are the straight through cables which are wired in a 1 to 1 configuration. However Cat-5 crossover cables are also required on occasions.

Typically a Cat-5 cable used to connect a computer (PC) to a switch will be a straight through cable. However if two computers or two switches are connected together then a Cat5 crossover cable is used.

Many Ethernet interfaces in use today are able to detect the type of cable, whether it is a straight through or crossover cable, and they are able to adapt to the required format. This means that the requirement for Cat-5 crossover cables is less than it might otherwise be.

When using Cat-5 Ethernet crossover cables, they are not marked with the fact that they are crossover cables. Accordingly it is often wise to mark them to avoid confusion later.

A variety of different cables are seen connecting different Ethernet elements together. Cat5, Cat5e and Cat6 are all seen. The cables use the cost efficient but effective RJ45 patch connector and using this, these Ethernet cables are able to link or patch multiple items of Ethernet based equipment together. On some occasions where specialised connectivity is needed crossover cables may be required - these sold be clearly marked as such as they may get used elsewhere unknowingly and cause the connection not to work. Apart from this using Cat 5, Cat5e and Cat 6 Ethernet cables is very easy and there are normally very few issues.

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RJ-45 conductor data cable contains 4 pairs of wires each consists of a solid colored wire and a strip of the same color. There are two wiring standards for RJ-45 wiring: T-568A and T-568B. Although there are 4 pairs of wires, 10BaseT/100BaseT Ethernet uses only 2 pairs: Orange and Green. The other two colors (blue and brown) may be used for a second Ethernet line or for phone connections. The two wiring standards are used to create a cross-over cable (T-568A on one end, and T-568B on the other end), or a straight-through cable (T-568B or T-568A on both ends).

To create a straight-through cable, you'll have to use either T-568A or T-568B on both ends of the cable. The diagram depicted on the left and right shows clip of the RJ-45 connector down.

To create a cross-over cable, you'll wire T-568A on one end and T-568B on the other end of the cable.

The straight-through cables are used when connecting Data Terminating Equipment (DTE) to Data Communications Equipment (DCE), such as computers and routers to modems (gateways) or hubs (Ethernet Switches). The cross-over cables are used when connecting DTE to DTE, or DCE to DCE equipment; such as computer to computer, computer to router; or gateway to hub connections. The DTE equipment terminates the signal, while DCE equipment do not.

More on straight-through and cross-over connections

The RJ45 data cables we use to connect computers to a Ethernet switch is straight-through cables. As noted above, the RJ45 cable uses only 2-pairs of wires: Orange (pins 1 & 2) and Green (pins 3 & 6). Pins 4, 5 (Blue) and 7, 8 (Brown) are NOT used. Straight-through cable, as its name suggests, connects pin 1 to pin 1, pin 2 to pin 2, pin 3 to pin 3, and pin 6 to pin 6. Cross-over cables are used to connect TX+ to RX+, and TX- to RX-, which connects pin 1 to pin 3, pin 2 to pin 6, pin 3 to pin 1 and pin 6 to pin 2. The unused pins are generally connected straight-through in both straight-through and cross-over cables.

To network two computers without a hub, a cross-over cable is used. Cross-over cable is also used to connect a router to a computer, or ethernet switch (hub) to another ethernet switch without an uplink. Most ethernet switches today provide an uplink port, which prevents a use of cross-over cable to daisy chain another ethernet switch. Straight-through cables are used to connect a computer to an ethernet switch, or a router to an ethernet switch.

Pin Number Designations

There are pin number designations for each color in T-568B and T-568A.

T-568B T-568A -------------------------- ------------------------ Pin Color Pin Name Color Pin Name --- ------------- -------- ------------- -------- 1 Orange Stripe Tx+ Green Stripe Rx+ 2 Orange Tx- Green Rx- 3 Green Stripe Rx+ Orange Stripe Tx+ 4 Blue Not Used Blue Not Used 5 Blue Stripe Not Used Blue Stripe Not Used 6 Green Rx- Orange Tx- 7 Brown Stripe Not Used Brown Stripe Not Used 8 Brown Not Used Brown Not Used

RJ-45 Wiring FAQ

1. What are T-568A and T-568B wiring standards, and how are they different?

T-568A and T-568B are the two wiring standards for RJ-45 connector data cable specified by TIA/EIA-568-A wiring standards document. The difference between the two is the position of the orange and green wire pairs. It is preferable to wire to T-568B standards if there is no pre-existing pattern used within a building.

2. What is RJ stands for?

RJ stands for Registered Jacks. These are used in telephone and data jack wiring registered with FCC. RJ-11 is a 6-position, 4-conductor jack used in telephone wiring, and RJ-45 is a 8-position, 8-conductor jack used in 10BaseT and 100BaseT ethernet wiring.

3. What is the Category Rating System?

Electronic Industries Association (EIA) developed the TIA/EIA-568-A standard, which specifies wiring and performance standards for Unshielded Twisted Pair (UTP) cabling. Category Rating System specifies the definition of performance categories for 100 ohm UTP cabling system.

Category 3 specifies the twisted pair cable and connecting hardware that can support transmission frequency up to 16MHz, and data rates up to 10Mbps. This is primarily used in telephone wiring.

Category 4 specifies cables and connectors that supports up to 20MHz and data rates up to 16Mbps. With introduction of category 5, this is a rarely used category.

Category 5 specifies cables and connectors that supports up to 100MHz and data rates up to 100Mbps. With 100BaseT Ethernet today, Category 5 is a widely used cabling system that matches todays high-speed data requirements.

CategoryTIA/EIA StandardDescription
Cat 1NonePOTS, ISDN and doorbell wiring
Cat 2None4 Mbps token ring networks
Cat 3TIA/EIA 568-B10 Mbps Ethernet - frequency up to 16MHz
Cat 4None16 Mbps token ring networks - frequency up to 20MHz
Cat 5None100 Mbps Ethernet - frequency up to 100 MHz
Not suitable for GigE (1000BaseT)
Cat 5eTIA/EIA 568-B100 Mbps & GigE Ethernet - frequency up to 100 MHz
Cat 6TIA/EIA 568-B2x Performance of Cat 5 & 5e - frequency up to 250 MHz
Cat 6aNoneFuture specification for 10Gbps application
Cat 7ISO/IEC 11801 Class FDesigned for transmission at frequencies up to 600 MHz

4. What is UTP Cable?

UTP stands for Unshielded Twisted Pair. It is the cabling system with one or more pairs of twisted insulated copper wires contained in a single sheath. It is the most widely used cabling system in telecommunications and data communications environment today.

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