In this file You are going to know about the basic understanding of the Ethernet

1. EthernetPushpa

2. Computer Networking
• A group of computer systems or any hardware device linked together
Through communication channel Facilitate communication and
resource sharing.

3. OSI Model
• There are n number of users who use computer network and are
located over the world.
• So to ensure national and worldwide data communication systems
can be developed and are compatible to each other.
• ISO has developed OSI model. ISO stands for international
organization of Standardization.
• This is called a model for open system interconnection(OSI) and is
normally called as OSI model.

4. 7-Layer Architecture

5. Physical Layer
• Representation of Bits: Data in this layer consist of stream of bits.
• Data Rate: This layer defines the rate of transmission which is the number of bits per
second.
• Synchronization: It deals with the synchronization of the transmitter and receiver.The
sender and receiver are synchronized at bit level.
• Interface: The physical layer defines the transmission interface between device and
transmission medium.
• Line configuration: This layer connects device with the medium: point to point
configuration and Multipoint configuration.
• Topologies: Device must be connected using the following topologies: Mesh,Star,Ring
and Bus.
• Transmission Modes: Physical layer defines the direction of transmission between two
devices: Simplex,Half Duplex,Full Duplex.
• Transmission: Deals with base band and broadband transmission.

6. Base Band and Broad Band
• Base Band:
• Data is sent as digital signals through the media as a single channel that uses
the entire bandwidth of the media.
• Base band comm is bi-directional, which means that the same channel can be
used to send and receive signals.
• In baseband, frequency division multiplexing is not possible.
• Broadband:
• Broad band sends information in the form of an analog signal.
• Each transmission is assigned to a portion of the bandwidth, hence multiple
transmissions are possible at the same time.
• Broadband communication is unidirectional, so in order to send and
receive,two pathways are needed.

7. Data Link Layer
• Framing: Frames are the stream of bits received from the network layer into
manageable data units. This division of stream of bits is done by Data link layer.
• Physical Addressing: The data link layer adds a header to the frame in order to
define physical address of the sender or receiver of the frame, if the frames are
to be distributed to different systems on the network.
• Flow control: A flow control mechanism for frames to be sent.
• Error control: Error control is achieved by adding a trailer at the end of the frame.
Duplication of frames are also prevented by using this mechanism.Data link layer
adds mechanism to prevent duplication of frames.
• Access control: Protocols of this layer determine which of the devices has control
over the link at any given time, when two or more devices are connected to the
same link.

8. Network Layer
• The main aim of this layer is to deliver packets from source to
destination across multiple links(networks).
• If two computers(system) are connected on the same link then there
is no need for a network layer.
• It routes the signal through different channels to the other end and
acts as a network controller.
• It also divides the outgoing messages into packets and to assemble
incoming packets into messages for higher levels.

9. Transport Layer
• Transport layer breaks the message (data)into small units so that they
are handled more efficiently by the network layer and ensures that
message arrives in order by checking error and flow control.
• Service point Addressing: Transport layer header includes service
point address which is port address. This layer gets the message to
the correct process on the computer unlike Network layer, which gets
each packet to the correct computer.
• Segmentation and Reassembling: A message is divided into segments,
each segment contains sequence number, which enables this layer in
reassembling the message. Message is reassembled correctly upon
arrival at the destination and replaces packets which were lost is
transmission.

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• Connection Control: It includes 2 types: Connectionless Transport
Layer and Connection Oriented Transport Layer.
• Flow Control: In this layer, flow control is performed end to end.
• Error Control: Error control is performed end to end in this layer to
ensure that the complete message arrives at the receiving transport
layer without any error. Error correction is done through
retransmission.

11. Session Layer
• Its main aim is to establish, maintain and synchronize the interaction
between communicating system. Session layer manages and synchronize the
conversation between two different applications.
• Transfer of data from one destination to another session layer stream of
data are marked and are resynchronized properly, so that the ends of the
messages are not cut prematurely and data loss is avoided.
• Dialog Control: This layer allows two system to start communication with
each other in half-duplex or full –duplex.
• Synchronization: This layer allows a process to add checkpoints which are
considered as synchronization points into stream of data.
• Example: If a system is sending a file of 800 pages, adding checkpoints after
every 50 pages is recommended. This ensures that 50 pages unit is
successfully received and acknowledged. This is beneficial at the time of
crash as if a crash happens att page number 110.there is no need to
retransmit 1to100 pages.

12. Presentation Layer
• The primary goal of this layer is to take care of the syntax and semantics of
the information exchanged between two communicating systems.
Presentation layer takes care that the data is sent in such a way that the
receiver will understand the information (data) and will be able to use the
data. Languages(syntax)can be differ of the two communication systems.
Under this condition presentation layer plays a role translator.
• Transaction: Before being transmitted, information in the form of
characters and numbers should be changed to bit stream. The presentation
layer is responsible for interoperability between encoding methods as
different computers use different encoding methods. It translates the data
between the formats the network requires and the format the computer.

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• Encryption: It carries out encryption at the transmitter and
decryption at the receiver.
• Compression: It carries out data compression to reduce the
bandwidth of the data to be transmitted. The primary role of Data
compression is to reduce the number of bits to be transmitted. It is
important in transmitting multimedia such as audio, video,text etc.

14. Application Layer
• It is the top most layer of OSI Model. Manipulation of data(information)in
various ways is done in this layer which enables user or software to get
access to the network. Some services provided by this layer includes:E-
mail, transferring of files, distributing the result to user, directory services,
network resource etc.
• Mail services: This layer provides the basic for E-mail forwarding and
storage.
• Network Virtual Terminal: It allows a user to log on to a remote host. The
application creates software emulation of a terminal at the remote host.
Users computer talks to the software terminal which in turn talks to the
host and vice versa. Then the remote host believes it is communicating
with one of its own terminals and allows user to log on.

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• Directory Services: This layer provides access for global information
about various services.
• File Transfer, Access and Management(FTAM):It is a standard
mechanism to access files and manages it. Users can access files in a
remote computer and manage it. They can also retrieve files from a
remote computer.

16. IEEE Standards

17. Topologies
• Bus network topology -- Also known as backbone network topology, this configuration
connects all devices to a main cable via drop lines. The advantages of bus network
topology lie in its simplicity, as there is less cable required than in alternative topologies,
which makes for easy installation.
• Mesh network topology -- A dedicated point-to-point link connects each device on the
network to another device on the network, only carrying data between two devices.
• Ring network topology -- Two dedicated point-to-point links connect a device to the two
devices located on either side of it, creating a ring of devices through which data is
forwarded via repeaters until it reaches the target device.
• Star network topology -- The most common network topology, star topology connects
each device in the network to a central hub. Devices can only communicate with each
other indirectly through the central hub.
• Hybrid network topology -- Any combination of two or more topologies is a hybrid
topology.
• Tree network topology -- This topology consists of a parent-child hierarchy in which star
networks are interconnected via bus networks. Nodes branch out linearly from one root
node, and two connected nodes only share one mutual connection

18. Ethernet
• Standard for connecting computer to computer or other digital device
• The term Ethernet refers to the family of local-area-
network(LAN)Products covered by the IEEE 802.3 standard that
defines what is commonly known as the CSMA/CD protocol.
• Ethernet LAN consist of network nodes and interconnecting media.

19. Ethernet Network Elements
• Data terminal equipment(DTE)
--Source/destination of data
--PC
• Data communication equipment (DCE)
--Receive/forward the information
--Repeater ,routers

20. Ethernet and OSI

22. Ethernet MAC Layer
• Data encapsulation, including frame assembly before transmission,
and frame parsing/error detection during and after reception.
• Media access control, including initiation of frame transmission and
recovery from transmission failure

23. Ethernet MAC Client
• LLC(Logic Link Control):
• If the units is DTE
• If provides the interface between MAC and Upper layers
• Bridge entity:
• If the unit is DCE
• LAN to LAN interface

24. CSMA/CD
• Carrier Sense:
• Each station continuously listens for traffic on the medium to determine when
gaps between frame transmission occur.
• Multiple access:
• Stations may begin transmitting any time they detect that the network is
quite.
• Collision detect:
• If two or more station in the same CSMA/CD network (collision domain)begin
transmitting at approximately the same time,the bit stream from the
transmitting stations will interfere (collide)with each other,and both
transmissions will be unreable

25. Half Duplex Full Duplex
• Half Duplex:
• Transmission only in one direction
• Employs CSMA/CD and retransmits if collision is detected
• Not efficient
• Full Duplex:
• Two pairs of wires
• Fast data transmission than half duplex
• Collision does not happen in full duplex

26. Frame and Packet
• Frame :Data unit at data link layer
• Packet: Data unit at network layer and above.

27. Ethernet Frames

28. Ethernet Frame

29. Destination Address
• A destination MAC address of ff:ff:ff:ff:ff:ff indicates a broadcast,
meaning the packet is sent from one host to any other on that
network.
• A destination MAC address where the low-order bit of the first byte is
set indicates a Multicast, meaning the packet is sent from one host to
all hosts on the network interested in packets sent to that MAC
address.

30. Type/Length
• The field is interpreted as a length field if it has a value <=1500
• A type field if it has a value > 1500
• 0-1500 length field

31. Pad
• The minimum length of ethernet frame is 64 bytes
• If the frames has lesser number of bytes then extra bits are added to
the frame, those are called padding

32. Jumbo Frames
• JUMBO frames are introduced in order to increase the maximum size
of the MAC client Data field, larger frames would provide more
efficient use of the network Bandwidth while reducing the number of
frames that have to be processed.
• JUMBO frames has the capacity to carry bytes from 64bytes(min
size)to 9000bytes(max size).
• The 8870 value is actually a reserved Length/Type field assignment
that indicates frames as JUMBO.

33. Pause frames
• Flow control operation known as “PAUSE” frames are includes in
10GBE as it supports the full duplex mode.
• The 8808 value is actually a reserved Length/Type field. Length/Type
field is followed by 2 bytes of MAC control Opcode(00-01)and 2bytes
of MAC control parameter(timer=00-00 to FF-FF)with a unique DA(01-
80-C2-00-00-01)in MAC DA field.
• PAUSE frames considers 64bytes as Minimum size and 1518 bytes as
Maximum size for Normal frames and 1522 bytes when tagged.
• Transmitter MAC should not transmit the frames once it receives
pause frames from receiver until the time duration specified in the
pause timer.

34. Thank you