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Data Communication Network Models

Data Communication Network Models. Behrouz A. Forouzan. LAYERED TASKS. Each layer at the sending site uses the services of the layer immediately below it. LAYERED TASKS. The layered model Introduced before 1990 was OSI model .

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Data Communication Network Models

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  1. Data CommunicationNetwork Models Behrouz A. Forouzan Data Communication - Network Models

  2. LAYERED TASKS Each layer at the sending site uses the services of the layer immediately below it Data Communication - Network Models

  3. LAYERED TASKS • The layered model Introduced before 1990 was OSI model. • The TCPIIPmodel became the dominant commercial architecture because it was used extensively in the Internet Data Communication - Network Models

  4. THE OSI MODEL Layer 7 Layer 6 Layer 5 Layer 4 Layer 3 Layer 2 Layer 1 Data Communication - Network Models

  5. THE OSI MODEL • Within a single machine, each layer calls upon the services of the layer just below it. • Between machines, layer x on one machine communicates with layer x on another machine (agreed-upon series of rules) Data Communication - Network Models

  6. THE OSI MODEL intermediate nodes usually involve only the first three layers of the OSI model Data Communication - Network Models

  7. THE OSI MODEL Data Communication - Network Models

  8. THE OSI MODEL • Encapsulation: the data portion of a packet at level N - 1 carries the whole packet (data and header and maybe trailer) from level N. • Layer N – 1 Encapsulate Layer N Packet Data Communication - Network Models

  9. OSI LayersPhysical Layer • coordinates to carry a bit stream (signal transfer) over a physical medium • mechanical and electrical specifications and procedures and functions of the interface and transmission medium Data Communication - Network Models

  10. OSI LayersPhysical Layer • Physical characteristics • interfaces and medium • Bits coding • how Os and I s are changed to signals • Data rate • number of bits sent each second • Clock Synchronization • The sender and receiver not only must use the same bit rate but also must be synchronized at the bit level Data Communication - Network Models

  11. OSI LayersPhysical Layer • Line configuration • connection of devices to the media • Point-to-point or multipoint connection • Physical topology • Bus, star, mesh, ring, hybrid • Transmission mode • simplex, half-duplex, or full-duplex Data Communication - Network Models

  12. OSI LayersData Link Layer • responsible for moving error-freeframes from one hop (node) to the next. Data Communication - Network Models

  13. OSI LayersData Link Layer • Framing • divides stream of bits received from network layer into units called frames • Physical addressing • adds address to the frame to define the sender and/or receiver of the frame. • If the frame destination is a system outside the sender's network, the receiver address is the address of the device that connects the network • Flow control • to avoid overwhelming the receiver (if sender speed is more than receiver) Data Communication - Network Models

  14. OSI LayersData Link Layer • Error control • detect and retransmit damaged or lost frames • Mechanism to recognize duplicate frames • achieved through a trailer added to end of frame • Access control • When two or more devices are connected to the same link, mechanism is necessary to determine which device has control over the link at a time Data Communication - Network Models

  15. OSI LayersData Link Layer • Note that the frames exchanged in every link between source and destination have different values in the headers and trailers • The source and Destination address is different in every link • The values of the trailers can also be different if error checking includes the header of the frame Data Communication - Network Models

  16. OSI LayersData Link Layer Data Communication - Network Models

  17. OSI Layers Network Layer • Data Link Layer: • delivery of the packet between two systems on the same network (links), • Network Layer: • responsible for the source-to-destination delivery of a packet Data Communication - Network Models

  18. OSI Layers Network Layer • Logical addressing • includes logical addresses of sender and receiver which don’t change in every hop through path opposite to physical address in data link layer which changes in every hop • Routing • Intermediate nodes route or switch the packets to their final destination based on logical address Data Communication - Network Models

  19. OSI Layers Network Layer Data Communication - Network Models

  20. OSI Layers Transport Layer • responsible for delivery of entire message not just packet • Network Layer: • source-to-destination delivery of individual packets, it does not recognize any relationship between those packets. I • Transport layer: • ensures that the whole message arrives intact and in-order, overseeing both error control and flow control at the source-to-destination level Data Communication - Network Models

  21. OSI Layers Transport Layer Data Communication - Network Models

  22. OSI Layers Transport Layer • Service-point addressing • Computers often run several programs at same time. • The network address gets each packet to the correct computer; • the transport address gets entire message to the correct process on that computer. • Segmentation and reassembly • A message is divided into transmittable segments, with each segment containing a sequence number • Sequence numbers enable to reassemble the message correctly upon arriving at the destination and to identify and replace lost packets • Flow control • Flow control at this layer is performed end to end rather than across a single link in data link layer Data Communication - Network Models

  23. OSI Layers Transport Layer • Connection control • can be connectionless or connection oriented • A connectionless transport layer treats each segment as an independent packet • A connection oriented transport layer makes a connection to destination first before delivering the packets. After all the data are transferred, the connection is terminated • Error control • responsible for error control. However, error control at this layer is performed process-to-process rather than across a single link as in data link layer. • makes sure that the entire message arrives at the receiver without error. • Error correction is usually achieved through retransmission. Data Communication - Network Models

  24. OSI Layers Transport Layer Data Communication - Network Models

  25. OSI Layers Session Layer • The session layer is responsible for dialog control and synchronization Data Communication - Network Models

  26. OSI Layers Session Layer • Dialog control • allows two systems to enter into a dialog • Half-duplex or full-duplex dialog • Synchronization • allows a process to add checkpoints, or synchronization points, to a stream of data • For example, if a system is sending a file of 2000 pages, it is advisable to insert checkpoints after every 100 pages to ensure that each 100-page unit is received and acknowledged independently. In this case, if a crash happens during the transmission of page 523, the only pages that need to be resent after system recovery are pages 501 to 523. Pages previous to 501 need not be resent. Data Communication - Network Models

  27. OSI Layers Presentation Layer • is concerned with the syntax and semantics of the information exchanged between two systems • responsible for translation, compression, and encryption. Data Communication - Network Models

  28. OSI Layers Presentation Layer • Translation • responsible for interoperability between different data encoding methods in different systems • Encryption • transforms the original information to another form • Decryption reverses the original process to transform the message back to its original form • Compression • Data compression reduces the number of bits contained in the information Data Communication - Network Models

  29. OSI Layers Application Layer • responsible for providing services to the user • Mail, File Transfer, Web Browsing, Directory Service Data Communication - Network Models

  30. OSI Layers Data Communication - Network Models

  31. TCP/IP Model • Physical and Data Link Layers • does not define any specific protocol • supports all the standard and protocols • Internetwork Protocol Layer • IP • ARP,RARP, ICMP, and IGMP. • Transport Layer • TCP , UDP and SCTP • Application Layer • combined session, presentation, and application layers in the OSI modeL Data Communication - Network Models

  32. TCP/IP Model Data Communication - Network Models

  33. ADDRESSING • physical (link) addresses • logical (IP) addresses • port addresses • Specific addresses Data Communication - Network Models

  34. ADDRESSING • Relation between addresses and layers Data Communication - Network Models

  35. Physical ADDRESSING • The physical address, also known as the link address, is the address of a node as defined by its LAN or WAN • Ethernet uses a 6-byte (48-bit) physical address that is imprinted on the network interface card (NIC). • 07:01:02:01 :2C:4B • LocalTalk (Apple), however, has a I-byte dynamic address that changes each time the station comes up Data Communication - Network Models

  36. Physical ADDRESSING Data Communication - Network Models

  37. Logical Addressing • are necessary for universal communications • independent of underlying physical networks. • Physical addresses are not adequate in an internetwork environment where different networks can have different address formats • Unique in universe • IP Address is Internet Logical Address • The physical addresses will change from hop to hop, but the logical addresses usually remain the same Data Communication - Network Models

  38. Logical Addressing Data Communication - Network Models

  39. Logical Addressing • in Every hop , routing table in consulted to find next-hop • ARP Protocol is used to translate Logical Address of next-hop to it’s physical Address Data Communication - Network Models

  40. Port Address • IP address and physical address are necessary for a data to travel from source to destination • Port address determines which services in destination host should data be delivered • port address is a 16-bit address represented by one decimal number Data Communication - Network Models

  41. Port Address Three process with A, B and C Addresses Two Processes with J and K Addresses Data Communication - Network Models

  42. Specific Addresses • Addresses in Application Layer • Email Address • URL Address in web Data Communication - Network Models

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