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Development of Ethernet 
When the early days of Metcalfe develops Ethernet, a computer network created by connecting with a single copper cable. Physical limitations of a piece of copper wire record electrical signals is limited how far away from each other computers on an Ethernet. Repeater help ease the distance limitations. Repeater is a small tool that regenerates the electrical signals on the strength of the original signal. This process allows Ethernet to be able to extend across the floor of the office that may be beyond the reach of Ethernet limits. The addition or removal of devices on a wired Ethernet network, to all other connected devices. device called an Ethernet hub to solve this problem.
First, each port on the hub is actually a repeater.
Second, an Ethernet hub simplifies troubleshooting and administration. As the network grows larger, companies must comply more and more computers to an Ethernet.
Repeter hub and is working on the Physical Layer in the OSI model. Functions of Hub and Repeater is simple it is forwarding data packets sent from the PC without having the intelligence of a router that has a good destination IP filtering, MAC Address and others that only have the ability to forward it to the address that will be addressed.
Data sent by a computer will be delivered to the destination by spreading the news (broadcast) to all computers connected in a single terminal (Hub / Repeater), consequently all computers are connected to receive data packets, and if at the same time there is another computer that sends packets of data then there is the crush or collision data, and this will affect the smooth flow of data within the network. Computer-computers that are in the same LAN will have the same broadcast domain or so-called broadcast. Hub and Repeater does not have the ability to forward data to another computer that is in the broadcast domain or network ID of another, therefore the IP address given to computers that are in the same LAN usually have the same network.
For example is a single broadcast domain is: 
A PC that is in a network and a terminal with the IP 192.168.1.4 to 192.168.1.52 with subnet 255.255.255.0 and PC B is located in an other network and a terminal with the IP 192.168.2.6 to 192.168.2.70 with a subnet 255 255 .255.0 then A PC that is on network 192.168.1.4 is called a broadcast domain and PC B is located on the network 192.168.2.6 is in another broadcast domain.
The protocol used is IEEE 802.3 Ethernet uses a data-flow patterns Carrier Sense Multiple Access Collision Detection (CSMA-CD), by definition: that is a way of networking computers to check whether there is transmission of data by other parties. If there is no transmission of data, data by the other party will be sent. Ethernet networks are generally used only for half-duplex transmission, ie at a time can only send or receive only.
Hub and Repeater has only one collision domain, so that all computers are connected if one port is busy then the other ports will have to wait.
Why do we have to learn the Ethernet
Ethernet was developed in 1972 as a way to connect computers with laser printers which was newly created.
It was recognized even then as an outstanding technological breakthrough.
However, few people thought that the success of generating technology for connecting computers and devices will transform human communication on the same scale with the invention of the telephone business and change on the scale of the Industrial Revolution.
Several competing protocols have emerged since 1972, but remains the dominant standard Ethernet to connect computers to local area network (LAN). For many years the dominant Ethernet home networks as well.
Ethernet is a way of sharing resources in which the end stations (computers, servers, etc.) all have access to the transmission medium at the same time. The result is that only one device can transmit information at a time.
Given these limitations, there are two viable solutions:
• Use sharing mechanism: If all the end stations are forced to share the data via data cable, there must be rules to ensure that any end station to wait its turn before transmitting. In the case of simultaneous transmission, there must be rules to transmit.
• Divide the segment share, and protect them:
Another solution is the limitations of shared resources by using a device that reduces the number of stations to end the sharing of resources at any given time.

Ethernet Collisions 
In a traditional LAN, the user will all share the same ports on network devices and will fight for bandwidth.
The main limitation of such a setup is that only one device can transmit at a time. Segments that share resources in this way is called a collision domain, since if two or more devices transmit at the same time, information that "collide," and both end points must resend their information (at different times). Usually the device either to wait some random time before attempting to retransmit.
This method works well for a small number of user segments, where each has a relatively low bandwidth requirements. Due to the increasing number of users, the efficiency of collision domains decreased sharply, to the point where traffic will occur overhead (management and control) network.
Small segment
Segments can be divided to reduce the number of users and increase the bandwidth available to each user in this segment. Each new segment is created generating new collision domain.
Traffic from one segment or collision domain does not interfere with any other segment, thereby increasing the available bandwidth of each segment. In the following figure, each segment has a greater bandwidth, but all segments are on the same backbone and must share the available bandwidth.
This approach works best when care is taken to ensure that the largest users of bandwidth are placed in separate segments.
There are several basic methods for dividing an Ethernet LAN to a collision domains more:
• Use bridges to divide collision domains.
• Use the switch to provide a dedicated domain for each host.
• Use a router to route traffic between domains (and not route traffic that is not important to another domain).