Ethernet is a widely used networking protocol for local area networks (LANs). It uses cables to connect multiple computers together to allow them to send data to each other. Common cable types are thick coaxial cable, thin coaxial cable, and twisted pair cables. Ethernet uses encoding schemes like Manchester encoding and differential Manchester encoding to transmit data over the cables. Ethernet has evolved over time to support higher speeds through standards like Fast Ethernet that supports 100 Mbps and Gigabit Ethernet that supports 1 Gbps, while maintaining compatibility with previous versions.

1. Ethernet
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2. Ethernet
 Ethernet is a way of connecting computers together in a local area network or
LAN.
 It has been the most widely used method of linking computers together in LANs
since the 1990s.
 The basic idea of its design is that multiple computers have access to it and can
send data at any time.
 describing how networked devices can format data for transmission to other
network devices on the same network segment, and how to put that data out on
the network connection.
 Ethernet is a network protocol that controls how data is transmitted over a LAN.
 Technically it is referred to as the IEEE 802.3 protocol.

3. Ethernet cabling
 Four types of cabling are commonly used in Ethernet.
 There are different Ethernet standards. Today, Ethernet cables look like thick
telephone cables. They connect to boxes called hubs or switches.

4. 10Base5
 Thick Ethernet.
 Up to 100 stations can be connected to the cable using vampire taps (bus)
 The system is difficult to install and maintain.
 The 10 refers to its transmission speed of 10 Mbit/s. The BASE is short for
baseband signaling as opposed to broadband,
 The 5 stands for the maximum segment length of 500 meters (1,600 ft.).
 It was the first Ethernet specification to use a bus topology with a external
transceiver connected via a tap to a thick coaxial cable.

5. 10Base2
 10BASE2 (also known as cheapernet, thin Ethernet, thinnet, and thinwire) is a
variant of Ethernet that uses thin coaxial cable, terminated with BNC connectors
 10BASE2 coax cables have a maximum length of 185 metres (607 ft).
 The maximum practical number of nodes that can be connected to a 10BASE2
segment is limited to 30 with a minimum distance of 50 cm.

6. 10Base-T
 Cables look like thick phone cables, but with 8 copper wires instead of 2 or 4, and
they go from each computer' to a Hub or a Switch.
 Supported speed is 10 MBit/second.
 It uses star topology and the station are connected via two pairs of twisted
cable(one for sending another for receiving)between the station and the hub.
 The maximum length of the twisted cable here is defined as 100m,to minimize the
effect of attenuation in the twisted cable.

7. 10Base-F
 Same as 10Base-T, but cables transmit light pulses, instead of electrical signals
 Using star topology.
 Expensive due to the cost of the connectors and terminators.

8. Manchester encoding
 Manchester coding is a very common data coding method, probably
the most common used today.
 With Manchester coding, we can encode both clock and signal into
one, and transmit the signal serially.
 Manchester encoding is also widely used in infrared data
transmissions, like for example the Phillips RC protocol.
 2 approaches
Manchester encoding
Differential Manchester encoding

9. Manchester encoding
 Here data are represented by logic 1 or 0, but with line transitions.
 A logic LOW (0) is represented by a transition from HIGH to LOW.
 And a logic HIGH (1) is represented by a transition from LOW to HIGH.
 Eg:. The data to encode is the binary number 10010, reading from left to right. The
coding occurs on every falling edge of the clock.
 On the first falling edge of the clock, the coded signal has a LOW to HIGH
transition, because the data is HIGH( ie, 1).
 On the second falling edge of the clock, the code has a HIGH to LOW transition
because the data is LOW (ie,0).
 The same algorithm is applied for the rest of the signal.

11. Differential Manchester Code
The Differential Manchester Code is a variation of the Manchester code.
The transmission line is kept HIGH when no data is sent (before Start and after End).
 There are 2 encoding methods:
The first is the "Transition on LOW"
the second is the "Transition on HIGH".
 Both methods work exactly the same.
 Eg: A data bit is send during each negative clock transition and the data bit is 0,
then a polarity transition occurs (if was HIGH it goes LOW, and if it was LOW it
goes HIGH), otherwise the line remains unchanged.

12.  A data bit is send during each negative clock transition. If the data bit is 0, then a
polarity transition occurs (if was HIGH it goes LOW, and if it was LOW it goes HIGH),
otherwise the line remains unchanged.
 the data that is transmitted is the binary '10011101' (starting from left to right).
 Each data bit is transmitted during negative transition of the clock.
 Between each bit transmission, the code line changes polarity. This is done to help the
receiver recreate the clock signal and synchronize with the transmitter.
 here use Transition on LOW”
 This means that when a bit is transmitted, if this bit is ZERO the data line changes
polarity. Otherwise, if the bit is 1 the data line polarity remains unchanged.
.

13.  we want to transmit this byte (10011101).
 The first bit is 1 (starting from left), so the code line polarity remains unchanged.
 After half a pulse, the code line polarity changes state and goes LOW.
 After one full pulse, the second bit is about to be transmitted. This bit is the 0, so
the code line changes polarity and goes HIGH.
 The same algorithm is used to transmit all 8 bits of the data. Finally, the code line
is pulled HIGH and the transmission ends.

14. "Transition on
LOW”

15. The Ethernet MAC Sublayer Protocol
 In standard Ethernet , the MAC sublayer ,governs the operation of the access method .
 And it also frames data received from the upper layer and passes them to the physical
layer.
 The Ethernet frames contains seven fields : preamble ,SFD ,DA ,SA ,length or type of
protocol data unit(PDU),upper-layer data ,the Checksum .
 Ethernet does not provide any mechanism for acknowledging received frames , making it
what is known as an unreliable medium.
 Acknowledgement must be implemented at the higher layers .

17.  Checksum: the last field contain error detection information.in
this case we use checksum.

18. Switched Ethernet

22. Fast Ethernet
 It was designed to compete with LAN protocols such as FDDI or Fiber channel .
 IEEE created Fast Ethernet under the name 802.3u.
 Fast Ethernet is backward-compatible with standard Ethernet , but it can transmit
data 10 times faster at rate of100Mbps.
 Goals of fast Ethernet:
 Upgrade the data rate to 100Mbps.
 Make it compatible with standard Ethernet.
 Keep the same 48 bit-address.
 Keep the same frame format.
 Keep the same minimum and maximum frame lengt

25. Gigabit Ethernet
 In computer networking, Gigabit Ethernet (Gb E or 1 GigE) is a term describing
various technologies for transmitting Ethernet frames at a rate of a gigabit per
second (1,000,000,000 bits per second), as defined by the IEEE 802.3-2008
standard.
 Fast Ethernet increased speed from 10 to 100 megabits per second (Mbit/s).
 Gigabit Ethernet was the next iteration, increasing the speed to 1000 Mbit/s. The
initial standard for Gigabit Ethernet was produced by the IEEE in June 1998 as IEEE
802.3z, and required optical fiber.
 Goals of Gigabit Ethernet
 Upgrade the data rate to 1Gbps.
 Make it compatible with standard or fast Ethernet.
 Use the same address ,frame format.
 Keep the same minimum and maximum frame length.
 To support auto negotiation as defined in Fast Ethernet.