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What is the defference between Cross Cable and Straight Cable

Now days, LAN card has intelligence, so that both cables can work.

They have a feature on lots of switches and hubs etc called "auto-mdix" or "auto mdi/mdix", that is the new thing where it doesn’t matter what kind of cable you use, it will just auto detect the proper connection type no matter which cable you use.

The cable can be categorized as Cat 5, Cat 5e, and Cat 6 UTP cable. Cat 5 UTP cable can support 10/100 Mbps Ethernet network, whereas Cat 5e and Cat 6 UTP cable can support Ethernet network running at 10/100/1000 Mbps. You might hear about Cat 3 UTP cable, it's not popular anymore since it can only support 10 Mbps Ethernet network.

Straight and crossover cable can be Cat3, Cat 5, Cat 5e or Cat 6 UTP cable, the only difference is each type will have different wire arrangement in the cable for serving different purposes.

Ethernet network cables are straight and crossover cable. This Ethernet network cable is made of 4 pair high performance cable that consists of twisted pair conductors that used for data transmission. Both end of cable is called RJ45 connector.

There are two types of network cables commonly used in PC networks - Straight-through and cross-over.

 

Straight Cable

Usually use straight cable to connect different type of devices. This type of cable will be used most of the time and can be used to:

1) Connect a computer to a switch/hub's normal port.

2) Connect a computer to a cable/DSL modem's LAN port.

3) Connect a router's WAN port to a cable/DSL modem's LAN port.

4) Connect a router's LAN port to a switch/hub's uplink port. (Normally used for expanding network)

5) Connect two switches/hubs with one of the switch/hub using an uplink port and the other one using normal port.

If you need to check how straight cable looks like, it's easy. Both sides (side A and side B) of cable have wire arrangement with same color.


Crossover Cable

Sometimes you will use crossover cable, it's usually used to connect same type of devices. A crossover cable can be used to:

1) Connect two computers directly.

2) Connect a router's LAN port to a switch/hub's normal port. (Normally used for expanding network)

3) Connect two switches/hubs by using normal port in both switches/hubs.

In you need to check how crossover cable looks like, both side (side A and side B) of cable have wire arrangement with following different color.

This cable (either straight cable or cross cable) has total 8 wires (or we can say lines), i.e. four twisted pairs (4x2=8) with different color codes. Right now just forget about color codes. It doesn’t matter what color is given to the cable (but there is a standard).

In straight cable connectivity is like as follows

RJ451 Connected to RJ452

Pin1------------------------------------- Pin1

Pin2------------------------------------- Pin2

Pin3------------------------------------- Pin3

Pin4------------------------------------- Pin4

Pin5------------------------------------- Pin5

Pin6------------------------------------- Pin6

Pin7------------------------------------- Pin7

Pin8------------------------------------- Pin8

 

In cross cable connectivity is like as follows

RJ451 Connected to RJ452

Pin1------------------------------------- Pin3

Pin2------------------------------------- Pin6

Pin3------------------------------------- Pin1

Pin4------------------------------------- Pin4

Pin5------------------------------------- Pin5

Pin6------------------------------------- Pin2

Pin7------------------------------------- Pin7

Pin8------------------------------------- Pin8


Purpose of this cross cable is RX (receiving terminal) connects to TX (transmitting) of one pc to another PC and vice versa.

As we use two PCs (same devices), straight cable will connect TX to TX and RX to RX of two computers, so cross cable is required. If you use HUB or switch, then straight cable will work because it has internal arrangement like cross cable. So note that use cross cable to connect two similar devices.

A straight cable will not work to connect two computers together.

Crossover used to connect to PCs directly together, also used for connecting networking devices together like Switch to Switch etc.

Straight cables connect two DIFFERENT types of devices. Whereas crossover cables connect two of the SAME type


Now do this (if possible): connect cross cable between switch and PC and see what happens..!







  Hub SwitchRouter Workstation
 Hub Crossover Crossover Straight Straight
 Switch Crossover Crossover Straight Straight
 Router Straight Straight Crossover Crossover
 Workstation Straight Straight Crossover Crossover

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Communication between Switches and Workstations

When a workstation connects to a LAN, it transmits data independently of the other devices connected to the LAN media. The workstation simply transmits data frames from a NIC to the network medium.

If desired, the workstation can be attached directly to another workstation by using a crossover cable. Crossover cables connect the following devices:

  • Workstation to workstation
  • Switch to switch
  • Switch to hub
  • Hub to hub
  • Router to router
  • Router to PC 

Straight-through cables connect the following devices:

  • Switch to router
  • Switch to workstation or server
  • Hub to workstation or server 

Many modern switches now automatically adjust the port pinout to support the particular cable attached, whether it is a crossover or straight-through cable.

Switches, which are Layer 2 devices, use intelligence to learn the MAC addresses of the devices that are attached to its ports. This data is entered into a switching table. After the table is complete, the switch can read the destination MAC address of an incoming data frame on a port and immediately forward it. Until a device transmits, the switch does not know its MAC address.

Switches provide significant scalability on a network. Switches are normally connected to each other by way of trunk links.

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Mullaiselvan. M

Monday08June2009

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