Basics of Ethernet
- 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.
- 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.
- 10. Continue.. • 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.
- 13. Continue.. • 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.
- 15. Continue.. • 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