Crossover Cable is simply related to the connection of two devices of the same technology or systems like DCE-DCE or DTE-DTE, basically connecting asymmetrical devices like DTE-DCE cables are known as cross-link cables. IBM (International Business Machines Corporation) introduced such a distinction of all the devices.

In contrast, straight-through cables connect complimentary system devices by using direct wiring e.g. a computer to a switch plug but the crossing of cables in an adapter connection allows:

  • Connecting two or more routers or switches to work as one wider device.
  • Connecting the output of one device to the input of the other device.
  • Allowing two DTE devices to communicate without an interlinking cable or hub know e.g. PCs.

Straight through cables worked on most of the devices or applications, but crossover cable is also used sometimes. In straight-through, both pins of one and another end are matched like pin 1 or pin 1, Pin 2 or pin 2, etc. In straight-through cables, a particular color cable attached to a pin number at both ends yet.

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In crossover cables, all pins are not similar, all the transmitters are exchanged at the terminations. For example, if pin A on the first end goes to pin B on the other, then pin B on the first-hand goes to pin A on the other. Such cables of the crossover are electrically consistent, which means they can run identically nevertheless of which way you plug them in. In crossover cables, a particular color cable connects to one pin at one end and a different pin at the other.

Difference between Crossover and Straight through

As we come to the difference between both, in straight-through cables, when we talk about the cat5e cables patch, it is used to connect printers, computers and other client devices of the network to the hub. These cables are most repeatedly used to connect a host to the client. And, in crossover cables, these are much like straight through, expect that RX and TX are crossed. Taking 568-B standards as an example, you will see that pin A goes on the first connector to pin B on the second connector.

crossover and stright thorugh cable

Nowadays, many devices have auto switch technology of sensor that discerns the devices and cables and crosses pairs when required.

Introduction to ethernet

Ethernet is a wired technology where the usage of ethernet is the most widely used and popularly used across wired LAN technologies.

Ethernet is the communication standard in the local environment that is, LAN. where this ethernet helps to connect multiple devices so that they can create store, and share information. Ethernet operates in the data link layer and the physical layer. The family of networking technologies is defined in the IEEE 802.2 and 802.3 standards.

It supports the data bandwidth of 10, 100, 1000, 10000, 40000, and 100000Mbps or 100Gbps.

In layer2, ethernet is defined as a protocol called Ethernet protocols. Whereas in layer1, it is as an ethernet technology.

Ethernet technology deals with ethernet cables in the physical layer.

Ethernet has two separate sublayers of the data link layer to operate both the logical link control (LLC) and the MAC sublayers.

The evolution of ethernet is in four forms

1.Standard ethernet

2.Fast ethernet

3.Gigabit ethernet

4.Ten-Gigabit ethernet

The Standard Ethernet speeds up to 10Mbps, fast ethernet is 100Mbps, gigabit ethernet is 1Gbps and followed by ten-gigabit ethernet which speeds up to 10Gbps.

The Ethernet cabling can come in the form of a coaxial cable and then a twisted pair cable, fiber optics cable. The ethernet twisted pair cable will utilize the RJ-45 that is 8pin connectors at either end of the cable. This is a pin used for transferring the data either in half-duplex or in full-duplex mode.

The fiber optics cable will be consisting of either glass or plastic and these allow the transferring at distance with higher speed. The fiber optics cable uses various connectors such as SFP (small form plugged) and SC ( subscriber connector)

Frame format of IEEE 802.3

The above figure is the frame format of ethernet IEEE 802.3.

Each frame is associated with some bits along them.

The frame formats of ethernet are somewhat similar to the data link layer protocols and address.

Generally, frame formats start with the preamble. This preamble is of 7 bytes which are 56 bits of alternating 1’s and 0’s. The use of preamble was the synchronization of bits purpose and in preamble each byte of this field contains a bit pattern of 10101010.

SFD is a start frame delimiter which acts as a flag and also used for synchronization purpose.

The flag is fixed in SFD and this SFD is of 1 byte. 1byte of SFD is holding the information this can be of flag bits.

The main feature of SFD is, it acts as a flag at the same time the last two bits of the flag indicates that the upcoming field is a destination of the mac address.

The third field in the ethernet frame format is a destination address where it is holding of 6bytes. The destination address is a layer2 protocol where it is a data link layer. The layer2 protocol deals with the physical address that is the mac address.

The 6bytes of a destination address is 48bits.

So, whenever any frame is generated from the source, the packet should consist of both the mac addresses of source and destination. The upper layer of the data link layer is the network layer.

Whatever data received from the network layer needed to be encapsulated with both header and the trailer.

With the header, we can see where are the preamble, SFD, and destination mac addresses are. Suppose the sender is sending the data to the receiver it has to use both source and destination mac addresses. For suppose, the source and destination are occupying the same local area in the network it uses the source and destination mac address, and if the sender doesn’t know about the destination mac address it simply uses the ARP (address resolution protocol) to get the mac address of the destination IP address.

The destination address can be of 2 or 6 byte field where 1 is represented as group address and 0 is represented as ordinary address.The frame is sent to the grouped address it means the destination address is consisting of the value 1. All the stations will be listening to a single address so this type of sending frame or data to group of stations is known as multiplexing.

The length and data field type is of 2bytes which says about the type and length of the data.

Data and padding field, the data from the network layer will be stored in this field and the padding is used for making the frame into the fixed-size frame.

The data field can be in the range of 0 to 1500 and 802.3 suggests that the valid frame must be of 64 bytes long. The variable length data that belongs to the frame will be carried out by the data field itself.

CRC( cyclic redundancy check ), which is used for error detection purposes and its size is 4bytes.

Now, we are going to observe 3 types of cables.

1.cross over cable

2.straight-through cable

3.roll over cable

These 3 cables are consisting of pins where the connection between these pins of the 3 cables are different.

Cross over cable:-

For transmission of the data across a network, the cable acts as a common medium. The cross over the cable of the ethernet is the wiring format which makes it possible to only connects when there are two common or similar functionalities of devices like computer to computer have existed and then the one pc output is given to another pc input.

Straight through cable:-

It is also called a patch cable, where straight-through cables are commonly used in a local area network.

This replaces the wireless connections and the terminals will be accessing the routers and hubs. The terminal can be one or many in a network. The straight-through cable will be using the category 5e (cat5e) cable structure.

Rollover cable:

Rollover cable is used when the computer terminal console into a cisco router or a switch.

The pc or laptop is connected with a rollover cable and the other end of the cable is connected to the switch. The Rollover cable is having the rj45 connector and also DV9.

This DV9 is used to connect to the pc. The pinouts of the rollover cable are in the form of,

Rollover cable in networking

these pinouts are opposite to each other at both ends and like-wise one is connected to 8 and 3 to 6.

Difference between cross over cable and straight-through cable

Straight-through cable:

  • It is a single wire.
  • The straight-through cable will be going to the same pin on another end of the switch.
  • With the straight-through cable, a quick connection is possible.
  • It is simple to understand.
  • The connection is indirect with one and other devices.
  • This made the connection possible for 2, unlike devices like,
  • Switch to the router,
  • Hub to pc or server,
  • Switch to pc or server.

Cross over cable:

  • It is also a single wire.
  • The cross-over cable will not go to the same pin slot of another side, if it goes then the communication or transmission will not have happened.
  • it is somewhat complex to understand.
  • The connection is direct between two devices.
  • This makes connection possible for two likely devices such as,
  • switch to switch,
  • hub to hub,
  • router to router,
  • pc to pc.

To understand which type of cable we are following we need to see the rj45 connector. This will be saying if the connection is the same or different and by these, it will determine whether the cable is straight-through or cross over.

By making use of the rj45 pin connector the network can be formed.

Where each pin is associated with action in the form of,

pin1 with Transmit+

pin2 with Transmit-

pin3 with receive+

pin4 with reserved

pin5 with reserved

pin6 with receive-

pin7 with reserved

pin8 with reserved.

How the straight-through cable is used?

The straight-through cable is used to connect a host to switch or hub, or a router to switch or hub.

Consider 10 base-T and 100 Base-TX networks. The two networks are used along with pairs of transmitting and receiving.

The transmit pair from the PC is made-up of pins 1,2 and the receive pairs are made-up of 3,6.

Now if we are sending the data from pc or router the interface which we are plugging rj45 into is called MDI ( media-dependent interface).

If we are plugging into a switch or a hub that port is called a media-dependent cross over MDI-X.

If we would connect the pc to pc then we don’t want the transmit signal coming from pc-1 to go into the transmit pins of pc-2 so we need a receiving the transmission at another end.

And from the diagram, there are receive pins at one end and the other end has transmitted pins and transmit pins at one end with receive pins at another end.

That is, T+ pin 1 to R+ pin 1 and T+ pin 2 to R+ pin 1 in this form communication is possible.

The above diagram says, how the communication is not possible.

As there are fault occurrences in straight-through cable crossover cable came into exists.

The drawback is drawn when two PC’s want to connect, transmit, and to listen.

Eg, when pc-1 and pc-2 are connected with a straight-through cable. The pc-1 is started transmitting the data of 1,2 and listens with 3,6 while the pc-2 will be using the same for transmission and to listen.

If the pc-1 data reaches through the cable to pc-2 at 1,2 then communication is not possible as pc-2 is also transmitting from 1,2.

When to use cross-over cable? 

Crossover cables cab be used to connect to the same network devices.

We can use the crossover UTP (unshielded twisted pair)cable when connecting one computer with another computer eg., switch to switch to maintain transmission.

The connection is provided with a cross-over cable by plugging into a network interface card. And the auto-MDIX is used for adjusting the correct pinouts automatically.

In the crossover cable, we are having two transmit pins that are connected. Where the pin1 of T+ which is transmitted is going on to the pin2 to of R+ which receives and 2 to the 6. And when the 3rd pin of the left-hand side tries to send then the pin1 of the right-hand side will receive it. So the panel connections are interchanged in this form and make the connection possible. This makes the cross cable looks flexible to transfer between two devices.

Hardware loopback

Hardware loopback connectors are used in conjunction to solve diagnosing transmission problems with diagnosing software.

On the signal line, a hardware loopback plug loops the outgoing data signal wires back into the system which has an incoming signal.

Pros of ethernet

  • Ethernet is the most widely used wired LAN technology.
  • Ethernet is relatively inexpensive, this is another main reason for its popularity.
  • In ethernet, all the nodes have the same privileges. It does not follow client-server architecture.
  • The maintenance and administration are simple.
  • The cable used to connect systems in ethernet is robust to noise. So, ethernet is even reliable.
  • As it is robust to the noise, the quality of the data transfer does not degrade. The data transfer is good.
  • With the latest version such as gigabit ethernet, the transfer speeds in Gbps have become possible with more speed and performance and we are in the ethernet era can able to send data at the speed of 10gigabits per second and even more.

Cons of ethernet

Under heavy loads, due to collision too much of the network’s capacity is wasted. Ethernet supports collision detection it happens when two or more stations send or transmit data at a time at the start medium it leads to a collision.

  • It does not hold good for real-time applications and interactive applications.
  • As the network cannot set priority for the packets. It is not suitable for the client-server architecture.
  • For interactive applications, dummy data have to be fed to make the frame size 46B which is mandatory.
  • In real-time applications, small data can transfer between the sender and the receiver but this compulsory needs 46Bytes of the data so we may have between 1byte of the data to be transferred between the sender and the receiver.
  • Ethernet somehow has makes this 1byte information into 46byte information by adding padding bits to make it as a 46bytes because the minimum frame size in the ethernet is of 64bytes and the payload should be 46 bytes.
  • After receiving the packets receiver doesn’t send any acknowledgment. As ethernet uses CDMA/CS technology there is no chance for acknowledgment.

Ethernet Categories:-

  • Cat3, unshielded with a maximum transmission speed of 10Mbps.
  • Cat5, unshielded with a maximum transmission speed of 10 or 100Mbps.
  • Cat5e, unshielded with a maximum transmission speed of 1000Mbps or 1Gbps.
  • Cat6, unshielded or shielded with a maximum transmission speed of 1000Mbps or 1Gbps.
  • Cat6a shielded with a maximum transmission speed of 1000Mbps or 10Gbps.
  • Cat7 shielded with a maximum transmission speed of 1000Mbps or 10Gbps.
  • Cat8 shielded with a maximum transmission speed up to 40Gbps.

History of ethernet cable

The story of ethernet goes back to some 40 years ago. It is on May 22nd, 1973.

The inventor of ethernet was Dr. Robert M Metcalfe.

He was the first person in history to handle the job of networking and a building full of personal computers.

Building on the experience with the ARPANET the original internet and some heavy reading into the Aloha packet network at the University of Hawaii, Dr.Metcalfe set out to build a network of personal computers and Xerox David Boggs and Metcalf built the first ethernet in 1973.

Their first two driving applications were a laser printer which is shared among these hundreds of personal computers and they also had early internet access for the pcs to be able to access the Internet at high speed so they came up with ethernet.

Metcalf considered the coaxial as ethernet.

They thought to send packets into the ether and propagate them everywhere.

The word ether is taken from physics in the 19th century.

Physicists believed that there was some medium between the sun and the earth which they call the luminiferous ether, an omnipresent completely passive medium for the propagation of electromagnetic waves.

Metcalf felt that coax through the ceiling was going to go everywhere and it was going to be completely passive than it was going to be a medium for the propagation of electromagnetic namely the data packets to personal computers to exchange. So, this is the first Ethernet.

Metcalf started 3com corporation to build ethernet compatible products.

Xerox and digital equipment corporation and the intel corporation had decided to use ethernet as a standard for the interconnection of their products.

And Metcalf created a project of IEEE 802 to make the ethernet into a standard.

In September 1982, 3com shipped its first ethernet adapter for IBM personal computers.

And 3com successfully sold ethernet cards for pcs.

Metcalf says the ethernet faced the battle with the token ring from IBM and other local area networks that competed and ethernet won the battle by adapting market realities and shifting from coax to twisted pair ethernet and became a dominant local area network. Ethernet bears a little resemblance to the CSMA/cd technology which was developed by David Boggs and Metcalf developed in 1973.

Metcalf came up with five prepositions to describe the directions in which ethernet is now going those are,

Ethernet is going up, through, over, down, and across.

Each of that ethernet continues to go up started from 2.94 Mbps and then went to 10mbps, 100 Mbps and now ethernet standard runs at 10gbps and it’s going to be higher. It is also going to the wide-area network(WAN) is infused with ethernet equipment.

The old equipment the telephone companies used to use the TDM SONET infrastructure is gradually being replaced in the core by ethernet transport. So the ethernet is going up the land through the land and also goes through airwaves.

It is becoming wireless which is a little ironic in that ethernet was derived from the aloha packet radio network in 1970 which was wireless. It then went through the coaxial and the twisted pair and optical fibers and now the ethernet has come back to wireless again.

In  1983, IEEE satisfied ethernet as LAN standards which are IEEE 802.3.

In 1985, Thicknet was introduced with a speed of 10 Mbps. The thicknet was replaced soon by a much cheaper one 10 Base2, thinnet. Both thicknet and thinnet use coaxial cable and bus topology.

Later on, the thinnet was replaced by 10 Base-T, which used the twisted pair cable. It was as shielded twisted pair or unshielded twisted pair, or simply as STP or UTP.

In 1995, fast ethernet was introduced its maximum speed is up to 100 Mbps. Fast ethernet is not fast based upon today’s standards but in the 1990s 100 Mbps was fast indeed.

In 1999, 1gigabit ethernet has become ethernet standards.

In 2006, 10gigabit ethernet has hit the market for fiber transmission.

And it is having 40-gigabit ethernet and 100gigabit ethernet for transmission of frames.

In the year 2017, there is a terabit ethernet which includes 200 gigabit and 400 gigabits.

And at present in 2020 the new version of 800gigabit is announced which is a new version of ethernet speed and performance.


Ethernet is very popular for its framework of data transmission. It maintains a positive outcome by providing easy installations and ethernet speed and cost. Because of these advantages, there is wide acceptance in the market place.

By sticking to IEEE standards, the network protocols and equipment can communicate efficiently.

This ethernet cable is a tangible wire. Which made it possible for the transmission of information from one device to another.

Ethernet is less risky to disturbances and problems in comparison with wireless LAN (WLAN) technology. It provides network security so that, intruders cannot access network data or take over the bandwidth. This includes reliability and security.

Other Types of Cables

Basically, these cables are used for carrying Ethernet, some of them are cat8, 7, 6a, cat 6 and cat 5 and the RJ45 connector is used most widely. When we bought an Ethernet connection. Cables are free with equipment that uses the connectivity of Ethernet in some way or another. These cables are carrying with Ethernet in the twisted method. This method of twisting the cables together allows the balance of the currents.

In this method, a huge amount of data can be easily transmitted over the substantial lengths without requiring excessive provisions. Many different lengths of cables are available as patch cables in Ethernet cables or the cable own are available for integrating with buildings, systems, etc. This termination can be made for the required connector using a tool named the crimp tool.

Earlier, there is no shield in cables, but now these cables are shielded for improving performance. For example, an unshielded twisted pair (UTP) cable is not worked for a long run between the systems but foil shielded cables (FTP) are long run between these systems. As a result, FTP is better than UTP cables.

There are two types of basic Ethernet

  1. Solid Cables- This type of cables are not more flexible, but also more durable. This made it best for use for long time installation of cables under flooring or embedded in walls.
  2. Stranded Cables- This type of cables is more flexible than solid cables, but it is not used for Ethernet cables, often it is an idea of leads patch at the general connection to personal computers, etc.

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