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4.1 Wired LAN: Ethernet - Coggle Diagram
4.1 Wired LAN: Ethernet
INTRODUCTION
Although over a few decades many wired LAN protocols existed, only the Ethernet technology survives today.
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ETHERNET PROTOCOL
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This means that when we discuss these two layers, we are talking about networks that are using them.
As we see in this and the following two chapters, we can have wired or wireless networks
IEEE Project 802
In 1985, the Computer Society of the IEEE started a project, called Project 802, to set standards to enable intercommunication among equipment from a variety of manufacturers.
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Instead, it is a way of specifying functions of the physical layer and the data-link layer of major LAN protocols
has subdivided the data-link layer into two sublayers: logical link control (LLC) and media access control (MAC)
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ETHERNET EVOLUTION
Since then, it has gone through four generations: Standard Ethernet (10 Mbps), Fast Ethernet (100 Mbps), Gigabit Ethernet (1 Gbps), and 10 Gigabit Ethernet (10 Gbps),
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Addresing
Each station on an Ethernet network (such as a PC, workstation, or printer) has its own network interface card (NIC).
The NIC fits inside the station and provides the station with a link-layer address. The Ethernet address is 6 bytes (48 bits), normally written in hexadecimal notation, with a colon between the bytes.
Unicast, Multicast, and Broadcast Addresses
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The destination address, however, can be unicast, multicast, or broadcast. Figure 13.4 shows how to distinguish a unicast address from a multicast address.
If the least significant bit of the first byte in a destination address is 0, the address is unicast; otherwise, it is multicast.
Note that with the way the bits are transmitted, the unicast/multicast bit is the first bit which is transmitted or received.
The broadcast address is a special case of the multicast address: the recipients are all the stations on the LAN. A broadcast destination address is forty-eight 1s.
Standard Ethernet uses a coaxial cable (bus topology) or a set of twisted-pair cables with a hub (star topology)
We need to know that transmission in the standard Ethernet is always broadcast, no matter if the intention is unicast, multicast, or broadcast.
In the bus topology, when station A sends a frame to station B, all stations will receive it.
In the star topology, when station A sends a frame to station B, the hub will receive it. Since the hub is a passive element, it does not check the destination address of the frame; it regenerates the bits (if they have been weakened) and sends them to all stations except station A.
In fact, it floods the network with the frame.
FAST ETHERNET
In the 1990s, Ethernet made a big jump by increasing the transmission rate to 100 Mbps, and the new generation was called the Fast Ethernet.
The designers of the Fast Ethernet needed to make it compatible with the Standard Ethernet. The MAC sublayer was left unchanged.
But the features of the Standard Ethernet that depend on the transmission rate, had to be changed.
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GIGABIT ETHERNET
The need for an even higher data rate resulted in the design of the Gigabit Ethernet Protocol (1000 Mbps).
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The goals of the Gigabit Ethernet were to upgrade the data rate to 1 Gbps, but keep the address length, the frame format, and the maximum and minimum frame length the same.