Xerox Corporation had a second generation called Ethernet II. It was name DIX after its Corporate sponsors Digital, Intel and Xerox. Ethernet became the most widely used network system layouts. You can use many different types of system layouts, such as star or bus, as well as many different types of cable. Local Area Network can be linked together using a combination of cabling and system layouts. CSMA/CD which stands for Multiple Access with Collision Detection is the access method Ethernet uses.
CSMA/CD computer communications network over coaxial cabling, and published the “Blue Book Standard” for Ethernet Version 1. This standard was later enhanced, and in 1985 Ethernet II was released. The IEEEs (Institute of Electrical and Electronics Engineers’) Project 802 then used Ethernet Version 2 as the basis for the 802. 3 CSMA/CD network standard. The IEEE 802. 3 standard is generally interchangeable with Ethernet II, with the greatest difference being the construction of the network packet header.
This method consists of multiple workstation that accesses a transmission medium called Multiple Access. Here the medium listen until no signals are detected. This is known as Carrier Sense. After checking to see if more than one signal is present they transmit. This is called Collision Detection. When a collision occurs the station then has to retransmit. The most important part of CSMA/CD access method is collision detection. Workstation may simultaneous transmit causing a collision.
A method was needed to prevent this from happening. After a workstation transmit a signal within a matter of a second they can tell whether a collision has occurred because they do not receive their own transmission. When a collision has occurred each station must wait for a short period of time before they resubmit their signals. Two other types of network are the baseband and the broadband. A baseband network is one that provides a single channel for communications across the physical cable, so only one device can transmit at a time.
Devices on a baseband network, such as Ethernet, are permitted to use all the available bandwidth for transmission, and the signals they transmit do not need to be multiplexed onto a carrier frequency. An analogy is a single phone line such as you usually have to your house: Only one person can talk at a time–if more than one person wants to talk everyone has to take turns. Broadband physical cabling is virtually divided into several different channels; each with its own unique carrier frequency, using a technique called “frequency division modulation”.
These different frequencies are multiplexed onto the network cabling in such a way to allow multiple simultaneous “conversations to take place. The effect is similar to having several virtual networks traversing a single piece of wire. Network devices “tuned” to one frequency cant hear the “signal on other frequencies, and visa-versa. Cable-TV is an example of a broadband network: multiple conversations (channels) are transmitted simultaneously over a single cable; you pick which one you want to listen to by selecting one of the frequencies being broadcast.
