Straight Through and Cross over Cable

This tutorial explains how to make the cross-over cable and straight-through cable in detail with picture examples. Learn how the UTP cable transfers data between two nodes or end devices.

Before we learn how to make a straight-through or cross-cable, let's understand how the UTP cable transfers the data.

How does the UTP cable work?

In UTP cable, electronic signals are used to transmit and receive the data. A UTP cable connects two nodes. In data transmission, one node sends data and another node receives that data. NIC of the sender node converts data stream into the electronic signals and places them into the copper wire of the UTP cable. NIC of the receiver node reads those signals from the wire and converts back them into the data stream.

Let’s understand this process in a little bit more detail.

Electronic signals or electric currents flow in a circuit. In an electric circuit, two wires are used. The first wire is used to carry the electrons or current from the source to the load. The second wire is used to complete the circuit between the load and the source. When electrons or current passes through the load, the load performs its functions.

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Let’s take a simple example. Suppose we have an LED bulb, two wires, and a battery. To light this bulb, we connect it from the battery using the wires. We connect the positive side and negative side of the battery to the bulb separately. The following image shows this example.

electric curcit

The same mechanism is used in UTP cable to transfer the data. Two wires of a UTP cable create an electric circuit between nodes.

In this circuit:-

  • The NIC of the node which sends the data is work as the source.
  • The NIC of the node which receives the data is work as the load.
  • The first wire carries the current from the sender node to the receiver node.
  • The second wire completes the electric circuit.

The following image shows how the electric circuit builds between the sender and receiver nodes.

electric circuit in utp cable

Once the electric circuit is built, both the sender and receiver nodes use this electric circuit to transfer the data.

End devices, usually PCs or Server, store and process data in digital or binary format. To transfer binary data through the electric circuit, NICs of both sender and receiver nodes use an encoding scheme.

An encoding scheme is a language that both NICs understand. In the encoding scheme, the sender node changes the electrical signal over time, while the receiver node interprets those changes as binary data.

For example, to transfer a binary digit 0, NIC of the sender node drops the voltage to the lower voltage during the middle of a 1/10,000,000th-of-a-second interval. NIC of the receiver node detects this change and interprets it as a binary digit 0. Just like this, to transfer binary digit 1, NIC of the sender node raises the voltage to the higher voltage.

Current in an electric circuit always flows in one direction; from the source to the load. For this reason, only the sender node (source) can send its data to the receiver node (load). If the receiver node wants to send its data, it must have to create its own circuit.

The following image shows how both nodes create and use their circuits to transfer the data.

two way data transfer in utp cable

Thus, for a two-way data transfer, two electrical circuits are required. To create two electrical circuits, four wires are required. In the below section, we will understand which wires of the UTP cable are used to the electric circuit between nodes.

UTP cable

A UTP cable contains 8 wires. These wires are grouped in four pairs. Each pair consist of two twisted wires. The first wire has a single color-coded plastic coating while the other wire has that color plus white color striped plastic coating. For example, for the brown wire pair, one wire’s coating is all brown, while the other wire’s coating is brown-and-white striped.

The following image shows a UTP cable.

a utp cable

Why are the wires twisted?

When electrical current passes through the copper wire, it creates electromagnetic interference (EMI). The EMI interferes with the electrical signals in nearby wires, including the wires in the same cable. It is known as the cross talk. Twisting the wires in pairs removes the effect of cross talk.

RJ-45 (UTP cable) connector

Both NIC and switch port have an eight pins slot. To connect these pins with the wires of a UTP cable, a connector known as the RJ-45 connector is used. The RJ-45 connector has eight physical locations, known as pin positions or simply pins, into which the eight wires of the UTP cable can be inserted. These pins create a place where the ends of the copper wires can touch the pins of NIC or switch port.

The following image shows an RJ-45 connector.

a rj-45 connector

Making a UTP cable

A NIC uses pins 1 and 2 to transmit the data. To receive data, it uses pins 3 and 6. A switch does the opposite of it. It receives data on pins 1 and 2 and transmits data from the pin 3 and 6. Based on the type of end devices, a UTP cable can be made in two ways. The first type of cable, known as the straight-through cable, connects two different types of end devices; such as PC to Switch. The second type of cable, known as the cross-over cable, connects two same type of end devices such as PC to PC or Switch to Switch.

Let’s understand how to make both types of cable in detail.

Ethernet straight-through cable

In this cable, wires are placed in the same position at both ends. The wire at pin 1 on one end of the cable connects to pin 1 at the other end of the cable. The wire at pin 2 connects to pin 2 on the other end of the cable; and so on.

The following table lists the wire positions of the straight-through cable on both sides.

Side A Side B
Green White Green White
Green Green
Orange White Orange White
Blue Blue
Blue White Blue White
Orange Orange
Brown White Brown White
Brown Brown

The following image shows the straight-through cable.

color coding of straight through cable

A straight-through cable is used to connect the following devices.

  • PC to Switch
  • PC to Hub
  • Router to Switch
  • Switch to Server
  • Hub to Server

devices which a straight through cable can connect

Ethernet cross-over cable

In this cable, transmitting pins of one side connect with the receiving pins of the other side.

The wire at pin 1 on one end of the cable connects to pin 3 at the other end of the cable. The wire at pin 2 connects to pin 6 on the other end of the cable. Remaining wires connect in the same positions at both ends.

The following table lists the wire positions of the cross-over cable on both sides.

Side A Side B
Green White Orange White
Green Orange
Orange White Green White
Blue Blue
Blue White Blue White
Orange Green
Brown White Brown White
Brown Brown

The following image shows the cross-over cable.

color coding of the cross over cable

The cross-over cable is used to connect the following devices.

  • Two computers
  • Two hubs
  • A hub to a switch
  • A cable modem to a router
  • Two router interfaces

devices which a cross over cable can connect

That’s all for this tutorial. If you like this tutorial, please don’t forget to share it with friends through your favorite social platform.

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ComputerNetworkingNotes CCNA Study Guide Straight Through and Cross over Cable