Unshiedled Twisted Pair Cable / Cat5E / RJ 45 / Ethernet at Physical Layer

Ethernet at Physical Layer:

           

The physical layer standards for Ethernet are defined by TIA/EIA. As per the TIA/EIA, Ethernet on copper can be implemented by using the Unshielded Twisted Pair cables.

What is TIA/EIA?

TIA (Telecommunications Industry Association) is a branch of EIA (Electronic Industries Alliance) that defines the wiring standards for the telecommunication devices.

The UTP cables we are using today  to interconnect our Ethernet network devices has been developed from the early telephone wiring standards which continuously evolved.

What is a Unshielded Twisted Pair cable?

           

            Now let’s take a look at a typical UTP cable seen in our Ethernet networks.

The name itself describes the cable: Every two wires (pair) inside the cable are twisted and the cable is not surrounded by any shielding, these are the two reasons for naming the cable as Unshielded Twisted Pair cable.

   Twisted pair cables come in two types: Solid and Stranded. 

Solid CAT5 cable supports longer lengths and works best in fixed wiring conditions like office buildings. 

Stranded CAT5 cable, on the other hand, can be easily influenced and better suited for shorter-distance, movable cabling such as on-the-fly patch cabling.

Why the wires are twisted?

            The wires/conductors inside a UTP cable are twisted to reduce the crosstalk with the adjacent pairs. And also to reduce the electromagnetic Induction, which can lower the performance of the conductor.

Why we are using Unshielded Twisted Pair cables?

           

    We are using them because actually those were the cables we had during the Ethernet evolution.  In the days before UTP Ethernet, we had a lot of UTP cabling in use for telephone connections, so it became easy to connect it for Ethernet as well. As we exceeded the capabilities of this cabling though, we have moved ahead to shielded, or fiber, or other media..

    But still we see a lot of UTP cables because it is very less expensive as compared to Shielded Twisted Pair cables. And also the UTP cables are easy to install and troubleshoot.

Which type of UTP cable are we using today?

            Actually there are few categories of UTP cables such as Category 3, Category 5, Category 5e, Category6 and Category7. The cables are categorized according to its data carrying ability which is again determined by the twist-rate (nothing but number of twists per meter).

            The type of cable seen mostly is Cat5e. The difference between Cat5 and Cat5e is that the Cat5e has more number of twists as compared to Cat5 cable. Both the cables are made to support 100Mbps (Fast Ethernet) and 1000Mbps (Gigabit Ethernet).

           

Now let’s take a look at the Cat5E cable.

Cat5E (or) Category5E cable:

            The specific category type of the cable can be identified by the printing on the side of the cable. The UTP Cat5e cable has 4pair of wires inside it, as shown above. It provides performance up to 100MHz and it is suitable for Ethernet (10Mbit/second), Fast Ethernet (100Mbit/second) and Gigabit Ethernet (1000 Mbit/second).

            The 10BaseT (Ethernet) & 100Base-TX (Fast Ethernet) connections require two pairs of wires. One pair is used for transmit and the other pair for receive.

            The 1000Base-T (Gigabit Ethernet) connections require four pairs. Two pair of wires is used for transmitting and the other two for receiving.

            The cable is connected using the 8pin modular connector called as RJ 45.

Pair Colors & Twists:

            There is a standard coloring for pairs:

           

            Pair one is Blue

            Pair two is Orange

            Pair three is Green

            Pair four is Brown

(I remember it as “Boss Of Google Browsing”)

            Each pair consists of a wire with a solid color and another wire with a stripped same color. For example, pair 1: One wire is in Solid blue color and the second wire will be in stripped Blue color.

           

            Each pair inside the cable has variable number of twists per meter to minimize cross talk between pairs. 

Pair	Turns per meter
Blue	64
Orange	56
Green	65
Brown	51

What is an RJ45 connector:

      The RJ stands for Registered Jack. A registered jack is an standardized interface used to connect the cabling in networks. There a various range of registered jacks, each with a slightly different design depending on the kind of cabling that is being connected.

    And the differences in these standards are described by the numbers after "RJ"; for example 'RJ11', or 'RJ45'.

     Originally the RJ45 connectors were used in telephone networks; it has a 8P2C array of pins, meaning that out of 8pins only two wires are used. As computer networks developed, an extremely similar standard physical interface is used for connection, the 8P8C.

8P8C Connector:

           

            The meaning of 8P8C is nothing but 8Position 8 Conductor/Wires/Connectors. The Electronics catalogs commonly advertised 8P8C modular connectors as "RJ45". Now let’s understand the working of an 8P8C connector (RJ45).

           

            These connectors are commonly used for Ethernet over twisted pair. There are two components of 8P8C, they are:

1.      The male plug

2.      The female socket/jack

Male plug:

Female Socket/Jack:

           

             Most commonly seen on the NIC cards where we can connect the RJ 45 male port.

 

So finally we’ve understood that Ethernet needs an Unshielded twisted pair cable with an RJ 45 connector to connect the devices. 

            But coming to interconnecting the devices, we may need to connect the like devices (PC to PC, Switch to Switch, Hub to Hub …etc.) and unlike devices (PC to Switch, Switch to Hub, Switch to Router …etc.).

            So there is a standard called T568 defined by TIA/EIA that defines the cabling methods to interconnect the devices.

            We will learn about them in the next post.