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  • Check in Tanenbaum times of cables <br /> T1 = 24 * 64Kbps <br /> T3 = 30 * T1 <br /> STS (Synchronous Transport Signal) or OC (Optical Carrier) <br />

Transcript

  • 1. Computer networks Dr. C.V. Suresh Babu Dr. C.V. Suresh Babu
  • 2. Topics • • • • • • • • • • • • • • Introduction to networks – network architecture – network performance – Direct link networks – encoding – framing – error detection – transmission – Ethernet – Rings – FDDI Wireless networks – Switched networks – bridges Dr. C.V. Suresh Babu
  • 3. Introduction to Computer Networks Computer Networks Computer network connects two or more autonomous computers. The computers geographically anywhere. can be located Dr. C.V. Suresh Babu
  • 4. Introduction to Computer Networks LAN, MAN & WAN Network in small geographical Area (Room, Building or a Campus) is called LAN (Local Area Network) Network in a City is call MAN (Metropolitan Area Network) Network spread geographically (Country or across Globe) is called WAN (Wide Area Network) Dr. C.V. Suresh Babu
  • 5. Introduction to Computer Networks Applications of Networks Resource Sharing Hardware (computing resources, disks, printers) Software (application software) Information Sharing Easy accessibility from anywhere (files, databases) Search Capability (WWW) Communication Email Message broadcast Remote computing Distributed processing (GRID Computing) Dr. C.V. Suresh Babu
  • 6. Introduction to Computer Networks Network Topology The network topology defines the way in which computers, printers, and other devices are connected. A network topology describes the layout of the wire and devices as well as the paths used by data transmissions. Dr. C.V. Suresh Babu
  • 7. Introduction to Computer Networks Bus Topology Commonly referred to as a linear bus, all the devices on a bus topology are connected by one single cable. Dr. C.V. Suresh Babu
  • 8. Introduction to Computer Networks Star & Tree Topology The star topology is the most commonly used architecture in Ethernet LANs. When installed, the star topology resembles spokes in a bicycle wheel. Larger networks use the extended star topology also called tree topology. When used with network devices that filter frames or packets, like bridges, switches, and routers, this topology significantly reduces the traffic on the wires by sending packets only to the wires of the destination host. Dr. C.V. Suresh Babu
  • 9. Introduction to Computer Networks Ring Topology A frame travels around the ring, stopping at each node. If a node wants to transmit data, it adds the data as well as the destination address to the frame. The frame then continues around the ring until it finds the destination node, which takes the data out of the frame. Single ring – All the devices on the network share a single cable Dual ring – The dual ring topology allows data to be sent in both directions. Dr. C.V. Suresh Babu
  • 10. Introduction to Computer Networks Mesh Topology The mesh topology connects all devices (nodes) to each other for redundancy and fault tolerance. It is used in WANs to interconnect LANs and for mission critical networks like those used by banks and financial institutions. Implementing the mesh topology is expensive and difficult. Dr. C.V. Suresh Babu
  • 11. Introduction to Computer Networks Network Components Physical Media Interconnecting Devices Computers Networking Software Applications Dr. C.V. Suresh Babu
  • 12. Introduction to Computer Networks Networking Media Networking media can be defined simply as the means by which signals (data) are sent from one computer to another (either by cable or wireless means). Dr. C.V. Suresh Babu
  • 13. Introduction to Computer Networks Networking Devices HUB, Switches, Wireless Access Modems etc. Routers, Points, Dr. C.V. Suresh Babu
  • 14. Introduction to Computer Networks Computers: Clients and Servers In a client/server network arrangement, network services are located in a dedicated computer whose only function is to respond to the requests of clients. The server contains the file, print, application, security, and other services in a central computer that is continuously available to respond to client requests. Dr. C.V. Suresh Babu
  • 15. Introduction to Computer Networks Networking Protocol: TCP/IP Dr. C.V. Suresh Babu
  • 16. Introduction to Computer Networks Applications E-mail Searchable Data (Web Sites) E-Commerce News Groups Internet Telephony (VoIP) Video Conferencing Chat Groups Instant Messengers Internet Radio Dr. C.V. Suresh Babu
  • 17. Network Architecture • Provides a general, effective, fair, and robust connectivity of computers • Provides a blueprint – Types • OSI Architecture • Internet Architecture Dr. C.V. Suresh Babu
  • 18. OSI ARCHITECTURE • Open Systems Interconnection (OSI) model is a reference model developed by ISO (International Organization for Standardization) in 1984 OSI model defines the communications process into Layers Provides a standards for communication in the network Primary architectural model for inter-computing and Inter networking communications. network communication protocols have a structure based on OSI Model Dr. C.V. Suresh Babu
  • 19. OSI Architecture Dr. C.V. Suresh Babu
  • 20. Ethernet 10 Mb/s LAN Architecture Summary Maximum Number of Transmission Types Notes Stations 1024 Category 3 UTP or better (10BASE- Replaced by Fast Ethernet; backward T), Thinnet RG-58 coax (10BASE- compatible with Fast or Gigabit Ethernet 2), Thicknet coax (10BASE-5), when using UTP. fiber-optic (10BASE-F) Fast Ethernet 100 Mb/s 1024 Category 5 UTP or better The most popular wired networking standard, rapidly being replaced by gigabit Ethernet. Gigabit Ethernet 1000 Mb/s 1024 Category 5 UTP or better Recommended for new installations; uses all four signal pairs in the cable. 10 000 Mb/s 1024 Category 6a UTP or better Uses all four signal pairs in the cable. 802.11a Wireless Ethernet Up to 54 Mb/s 1024 RF 5 GHz band with dual-band 802.11n Short range; interoperable with dual-band 802.11n. 802.11b Wireless Ethernet Up to 11 Mb/s 1024 RF 2.4 GHz band Interoperable with 802.11g/n. 802.11g Wireless Ethernet Up to 54 Mb/s 1024 RF 2.4 GHz band Interoperable with 802.11b/n. 802.11n Wireless Ethernet Up to 600 Mb/s 1,024 RF 2.4/5 GHz bands Longest range; interoperable with 802.11a/b/g; dual-band hardware needed to interoperate with 802.11a; recommended for new installations. Token-Ring 4/16/100 Mb/s 72 on UTP; 250–260 on UTP, Type 1 STP, and fiber-optic Type 1 STP Replaced by Ethernet; obsolete for new installations. 2.5 Mb/s 255 Replaced by Ethernet; obsolete for new installations; uses the same coax cable as IBM 3270 terminals. Network Type 10 Gigabit Ethernet ARCnet Speed RG-62 coax UTP, Type 1 STP Dr. C.V. Suresh Babu UTP = unshielded twisted pair, STP = shielded twisted pair, RF = Radio Frequency
  • 21. Direct Links: Outline • Physical Layer – Link technologies – Encoding • Link Layer – – – – Framing Error Detection Reliable Transmission (ARQ protocols) Medium Access Control: • Existing protocols: Ethernet, Token Rings, Wireless Dr. C.V. Suresh Babu
  • 22. Link Technologies • Cables: – – – – Cat 5 twisted pair, 10-100Mbps, 100m Thin-net coax, 10-100Mbps, 200m Thick-net coax, 10-100Mbps, 500m Fiber, 100Mbps-2.4Gbps, 2-40km • Leased Lines: – Copper based: T1 (1.544Mbps), T3 (44.736Mbps) – Optical fiber: STS-1 (51.84Mbps), STS-N (N*51.84Mbps) Dr. C.V. Suresh Babu
  • 23. Link Technologies • Last-Mile Links: – POTS (56Kbps), ISDN (2*64Kbps) – xDSL: ADSL (16-640Kbps, 1.554-8.448Mbps), VDSL (12.96Mbps55.2Mbps) – CATV: 40Mbps downstream, 20Mbps upstream • Wireless Links: Cellular, Satellite, Wireless Local Loop Dr. C.V. Suresh Babu
  • 24. FRAMING • An efficient data transmission technique • It is a message forwarding system in which data packets, called frames, are passed from one or many start-points to one Dr. C.V. Suresh Babu
  • 25. Dr. C.V. Suresh Babu
  • 26. Approaches • Byte oriented Protocol(PPP) BISYNC Binary Synchronous Communication DDCMP Digital Data Communication Message Protocol • Bit oriented Protocol(HDLC) • Clock based Framing(SONET) Dr. C.V. Suresh Babu
  • 27. Byte oriented Protocol(PPP) BISYNC FRAME FORMAT SYH SYH SOH Header STX Body ETX PPP Frame Format Flag Address Control Protocol Dr. C.V. Suresh Babu Payload Flag CRC
  • 28. DDCMP Frame Format SYN SYN Class Count Dr. C.V. Suresh Babu Header Body CRC
  • 29. Bit Oriented Protocol(HDLC) • Collection of Bits 1.HDLC High-Level Data Link Control 2.Closed Based Framing(SONET) Synchronous Optical Network Dr. C.V. Suresh Babu
  • 30. HDLC Frame Format Beginning sequence Header Body CRC Bit Stufffing After 5 consecutive 1s insert 0 Next bit is 0 – stuffed removed Next bit is 1 –end of frame or erorr Dr. C.V. Suresh Babu Ending sequence
  • 31. Closed Based Framing(SONET) • STS-1 Frame 9 rows of 90 byte each First 3 byte for overhead rest contains data Payload bytes scrambled- exclusive OR Supports Multiplexing Payloads 9 rows 90 columuns Dr. C.V. Suresh Babu
  • 32. ERROR DETECTION • Detecting Errors In Transmission Electrical Interference, thermal noise Approaches Two Dimensional Parity Internet Checksum Algorithm Cyclic Redundancy Check Dr. C.V. Suresh Babu
  • 33. Two Dimensional Parity 7 bits of data 8 bits including parity Number of 1s even odd 0000000 (0) 00000000 100000000 1010001 (3) 11010001 01010001 1101001 (4) 01101001 11101001 1111111 (7) 11111111 01111111 Dr. C.V. Suresh Babu
  • 34. Transmission sent using even parity: • A wants to transmit: 1001 • A computes parity bit value: 1^0^0^1 = 0 • A adds parity bit and sends: 10010 • B receives: 10010 B computes parity: 1^0^0^1^0 = 0 • B reports correct transmission after observing expected even result. Dr. C.V. Suresh Babu
  • 35. Transmission sent using odd parity: • • • • • • A wants to transmit: 1001 A computes parity bit value: ~(1^0^0^1) = 1 A adds parity bit and sends: 10011 B receives: 10011 B computes overall parity: 1^0^0^1^1 = 1 B reports correct transmission after observing expected odd result. Dr. C.V. Suresh Babu
  • 36. Reliable Transmission Deliver Frames Reliably Accomplished by Acknowledgements and Timeouts ARQ-Automatic Repeat Request Mechanism: Stop and Wait Sliding Window Concurrent Logical Channels Dr. C.V. Suresh Babu
  • 37. Stop And Wait ARQ • The source station transmits a single frame and then waits for an acknowledgement (ACK). • Data frames cannot be sent until the destination station’s reply arrives at the source station. • It discards the frame and sends a negative acknowledgement (NAK) back to the sender • causes the source to retransmit the damaged frame in case of error Dr. C.V. Suresh Babu
  • 38. Acknowledgements & Timeouts Sender Receiver Sender Timeout Timeout Fram e ACK ACK Timeout Fram e (a) Timeout Fram e Sender Timeout Receiver Fram e ACK (c) Timeout Sender Timeout Time Fram e Receiver Receiver Fram e ACK Fram e ACK ACK (b) Dr. C.V. Suresh Babu (d)
  • 39. Stop & wait sequence numbers Timeout Timeout Fram e 0 ACK Fram e 0 0 0 ACK (c) Sender Timeout Receiver Timeout Sender Receiver Fram e Sender 0 0 ACK Fram e 0 0 ACK Receiver Fram e0 0 ACK Fram e 1 ACK Fram e (d) 0 0 ACK (e) • Simple sequence numbers enable the client to discard duplicate copies of the same frame • Stop & wait allows one outstanding frame, requires two distinct sequence numbers Dr. C.V. Suresh Babu 1
  • 40. Stop And Wait Dr. C.V. Suresh Babu
  • 41. Sliding Window • bi-directional data transmission protocol used in the data link layer (OSI model) as well as in TCP • It is used to keep a record of the frame sequences sent • respective acknowledgements received by both the users. Dr. C.V. Suresh Babu
  • 42. Sliding Window: Sender • • • • • Assign sequence number to each frame (SeqNum) Maintain three state variables: – send window size (SWS) – last acknowledgment received (LAR) – last frame sent (LFS) Maintain invariant: LFS - LAR <= SWS Advance LAR when ACK arrives ≤ SWS Buffer up to SWS frames … LAR … LFS Dr. C.V. Suresh Babu
  • 43. Sequence Number Space • • • SeqNum field is finite; sequence numbers wrap around Sequence number space must be larger then number of outstanding frames SWS <= MaxSeqNum-1 is not sufficient – – – – – – • • suppose 3-bit SeqNum field (0..7) SWS=RWS=7 sender transmit frames 0..6 arrive successfully, but ACKs lost sender retransmits 0..6 receiver expecting 7, 0..5, but receives the original incarnation of 0..5 SWS < (MaxSeqNum+1)/2 is correct rule Intuitively, SeqNum “slides” between two halves of sequence number space Dr. C.V. Suresh Babu
  • 44. Sliding Window: Receiver • Maintain three state variables • – receive window size (RWS) – largest frame acceptable (LFA) – last frame received (LFR) Maintain invariant: LFA - LFRRWSRWS ≤ <= … … LFR LFA • Frame SeqNum arrives: • – if LFR < SeqNum < = LFA accept – if SeqNum < = LFR or SeqNum > LFA discarded Send cumulative ACKs – send ACK for largest frame such that all frames less than this have been received Dr. C.V. Suresh Babu
  • 45. Ehernet • local-area network (LAN) covered by the IEEE 802.3. • two modes of operation: – half-duplex – full-duplex modes. . Dr. C.V. Suresh Babu
  • 46. Three basic elements : 1. the physical medium used to carry Ethernet signals between computers, 2. a set of medium access control rules embedded in each Ethernet interface that allow multiple computers to fairly arbitrate access to the shared Ethernet channel, 3. an Ethernet frame that consists of a standardized set of bits used to carry data over the system Dr. C.V. Suresh Babu
  • 47. IEEE 802.5 Format Dr. C.V. Suresh Babu
  • 48. Frame Format IEEE 802.5 Dr. C.V. Suresh Babu
  • 49. IEEE 802.3 MAC Data Frame Format Dr. C.V. Suresh Babu
  • 50. Wireless • The process by which the radio waves are propagated through air and transmits data • Wireless technologies are differentiated by : • Protocol • Connection type—Point-to-Point (P2P) • Spectrum—Licensed or unlicensed Dr. C.V. Suresh Babu
  • 51. Types • Infrared Wireless Transmission – Tranmission of data signals using infrared-light waves • Microwave Radio – sends data over long distances (regions, states, countries) at up to 2 megabits per second (AM/FM Radio) • Communications Satellites – microwave relay stations in orbit around the earth. Dr. C.V. Suresh Babu
  • 52. Dr. C.V. Suresh Babu
  • 53. UNIT III Packet Switching • • • • • • Is a network communications method Groups all transmitted data, irrespective of content, type, or structure into suitably-sized blocks, called packets. Optimize utilization of available link capacity Increase the robustness of communication. When traversing network adapters, switches and other network nodes packets are buffered and queued, resulting in variable delay and throughput, depending on the traffic Dr. C.V. Suresh Babu
  • 54. Types • Connectionless • each packet is labeled with a connection ID rather than an address. • Example:Datagram packet switching • connection-oriented – each packet is labeled with a destination address – Example:X.25 vs. Frame Relay Dr. C.V. Suresh Babu
  • 55. Star Topology Dr. C.V. Suresh Babu
  • 56. Source Routing 0 Switch 1 3 0 1 2 Switch 2 2 3 0 1 3 3 1 2 1 3 0 0 Host A 0 1 3 1 0 Switch 3 3 2 Dr. C.V. Suresh Babu 1 Host B
  • 57. Virtual Circuit Switching • Explicit connection setup (and tear-down) phase • Subsequence packets follow same circuit • Sometimes called connection-oriented model 0 Switch 1 1 3 2 5   Analogy: phone call 3 11 2 Switch 2 1 0 Host A 7 Each switch maintains a VC table 1 0 Switch 3 3 2 Dr. C.V. Suresh Babu 4 Host B
  • 58. Datagram Switching • No connection setup phase • Each packet forwarded independently • Sometimes called connectionless model Host D   Analogy: postal system Each switch maintains a forwarding (routing) table 3 Host C Host E 0 Switch 1 1 2 Host F 3 2 Switch 2 1 0 Host A Host G 1 0 Switch 3 Host B 3 2 Host H Dr. C.V. Suresh Babu
  • 59. Virtual Circuit Model • Typically wait full RTT for connection setup before sending first data packet. • While the connection request contains the full address for destination • each data packet contains only a small identifier, making the per-packet header overhead small. • If a switch or a link in a connection fails, the connection is broken and a new one needs to be established. • Connection setup provides an opportunity to reserve resources. Dr. C.V. Suresh Babu
  • 60. Datagram Model • There is no round trip delay waiting for connection setup; a host can send data as soon as it is ready. • Source host has no way of knowing if the network is capable of delivering a packet or if the destination host is even up. • Since packets are treated independently, it is possible to route around link and node failures. • Since every packet must carry the full address of the destination, the overhead per packet is higher than for the connection-oriented model. Dr. C.V. Suresh Babu
  • 61. Bridges and Extended LANs • LANs have physical limitations (e.g., 2500m) • Connect two or more LANs with a bridge – accept and forward strategy – level 2 connection (does not add packet header) A B C Port 1 Bridge Port 2 • Ethernet Switch = Bridge on Steroids X Dr. C.V. Suresh Babu Y Z
  • 62. Spanning Tree Algorithm • Problem: loops A B B3 C B5 D B2 B7 E K F B1 G H B6 B4 I J • Bridges run a distributed spanning tree algorithm – select which bridges actively forward – developed by Radia Perlman – now IEEE 802.1 specification Dr. C.V. Suresh Babu
  • 63. Algorithm Details • Bridges exchange configuration messages – id for bridge sending the message – id for what the sending bridge believes to be root bridge – distance (hops) from sending bridge to root bridge • Each bridge records current best configuration message for each port • Initially, each bridge believes it is the root Dr. C.V. Suresh Babu
  • 64. Algorithm Details • Bridges exchange configuration messages – id for bridge sending the message – id for what the sending bridge believes to be root bridge – distance (hops) from sending bridge to root bridge • Each bridge records current best configuration message for each port • Initially, each bridge believes it is the root Dr. C.V. Suresh Babu
  • 65. FAQ 1. Explain the ISO-OSI model of computer network with a neat diagram. 2. Discuss the major functions performed by the Presentation layer and Application layer of the ISO OSI model. 3. Explain Transport Layer and Physical Layer. 4. What are the major components of an optical communication system? Discuss. 5. Distinguish between point to point links and multi point links. Give relevant diagrams. 6. Explain Data Link Layer and Network Layer. 7. Compare Connection oriented and connectionless service. 8. a) What is the need for data encoding and explain the various data encoding schemes and compare their features. (8) b) Explain how hamming code can be used to correct burst errors. (8) 9. Explain the operation of the bit-oriented protocol HDLC with the required frames 10.Explain the various error detection and correction Mechanisms used in computer network. 11. Write short notes on: a) Go back NARQ (8) b) Selective repeat ARQ (8) 12. a) Discuss the major functions performed by the Presentation layer and Application layer of the ISO - OSI model. (8) b) Compare Connection oriented and connectionless service. (4) c) What are the major components of an optical communication system? Discuss. (4) 13. a) A block of 32 bits has to be transmitted. Discuss how the thirty two bit block is transmitted to the receiver using Longitudinal Redundancy Check. (4) b) Consider a 32 bit block of data 11100111 11011101 00111001 10101001 that has to be transmitted. If Longitudinal Redundancy Check is used what is the transmitted bit stream?(4) c) In the Hamming code, for a data unit of 'm' bits how do you compute the number of redundant bits 'r' needed? (4) d) What kinds of errors can Vertical Redundancy check determine? What kinds of errors it cannot determine? (4) 14. Discuss stop and wait protocol 15. Discuss sliding window protocol using Go back n. 16. How does a Token Ring LAN operate? Discuss. Dr. C.V. Suresh Babu