Data Communication & Computer Networks INFO

Transcription

1 Data Communication & Computer Networks INFO Instructor: Dr. A. SARI Department: Management Information Systems Course Code: MIS 305 Academic Term: 2013/2014 Fall Title: Data Communication & Computer Networks

2 Data Communication & Computer Networks Computer Networks Computer network connects two or more autonomous computers. The computers can be geographically located anywhere.

3 Data Communication & 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)

4 Data Communication & 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 Message broadcast Remote computing Distributed processing (GRID Computing)

5 Data Communication & 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.

6 Data Communication & Computer Networks Bus Topology Commonly referred to as a linear bus, all the devices on a bus topology are connected by one single cable.

7 Data Communication & 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.

8 Data Communication & 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, whichtakesthedataoutoftheframe. Singlering Allthedevicesonthe network share a single cable Dual ring The dual ring topology allows data to be sent in both directions.

9 Data Communication & 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.

10 Data Communication & Computer Networks Network Components Physical Media Interconnecting Devices Computers Networking Software Applications

11 Data Communication & 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).

12 Data Communication & Computer Networks Networking Devices HUB, Switches, Routers, Wireless Access Points, Modems etc.

13 Data Communication & 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.

14 Data Communication & Computer Networks Networking Protocol: TCP/IP

15 Data Communication & Computer Networks Applications Searchable Data (Web Sites) E-Commerce News Groups Internet Telephony (VoIP) Video Conferencing Chat Groups Instant Messengers Internet Radio

16 Network Architecture Provides a general, effective, fair, and robust connectivity of computers Provides a blueprint Types OSI Architecture Internet Architecture

17 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

18 OSI Architecture

19 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

20 Link Technologies Cables: Cat 5 twisted pair, Mbps, 100m Thin-net coax, Mbps, 200m Thick-net coax, Mbps, 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)

21 Link Technologies Last-Mile Links: POTS (56Kbps), ISDN (2*64Kbps) xdsl: ADSL (16-640Kbps, Mbps), VDSL (12.96Mbps- 55.2Mbps) CATV: 40Mbps downstream, 20Mbps upstream Wireless Links: Cellular, Satellite, Wireless Local Loop

22 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

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24 Approaches Byte oriented Protocol(PPP) BISYNC Binary Synchronous Communication DDCMP Digital Data Communication Message Protocol Bit oriented Protocol(HDLC) Clock based Framing(SONET)

25 Byte oriented Protocol(PPP) BISYNC FRAME FORMAT SYH SYH SOH Header STX Body ETX CRC PPP Frame Format Flag Address Control Protocol Payload Flag

26 DDCMP Frame Format SYN SYN Class Count Header Body CRC

27 Bit Oriented Protocol(HDLC) Collection of Bits 1.HDLC High-Level Data Link Control 2.Closed Based Framing(SONET) Synchronous Optical Network

28 HDLC Frame Format Beginning sequence Header Body CRC Ending sequence Bit Stufffing After 5 consecutive 1s insert 0 Next bit is 0 stuffed removed Next bit is 1 end of frame or erorr

29 Closed Based Framing(SONET) STS-1 Frame 9rowsof90byteeach First 3 byte for overhead rest contains data Payload bytes scrambled- exclusive OR Supports Multiplexing Payloads 9 rows 90 columuns

30 ERROR DETECTION Detecting Errors In Transmission Electrical Interference, thermal noise Approaches Two Dimensional Parity Internet Checksum Algorithm Cyclic Redundancy Check

31 Two Dimensional Parity 7 bits of data 8 bits including parity Number of 1s even odd (0) (3) (4) (7)

32 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: B receives: B computes parity: 1^0^0^1^0 = 0 B reports correct transmission after observing expected even result.

33 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: B receives: B computes overall parity: 1^0^0^1^1 = 1 B reports correct transmission after observing expected odd result.

34 Reliable Transmission Deliver Frames Reliably Accomplished by Acknowledgements and Timeouts ARQ-Automatic Repeat Request Mechanism: Stop and Wait Sliding Window Concurrent Logical Channels

35 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) backtothesender causes the source to retransmit the damaged frame in case of error

36 Acknowledgements & Timeouts Sender Receiver Sender Receiver Frame Frame ACK ACK Time Timeout Timeout Frame ACK Timeout (a) (c) Sender Receiver Sender Receiver Frame Frame Frame ACK ACK Timeout Timeout Timeout Timeout Frame ACK (b) (d)

37 Stop & wait sequence numbers Sender Receiver Sender Receiver Sender Receiver Timeout Timeout Timeout Timeout (c) (d) (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

38 Stop And Wait

39 Sliding Window bi-directional data transmission protocol used in the data link layer (OSImodel)aswellasinTCP Itisusedtokeeparecordoftheframesequencessent respective acknowledgements received by both the users.

40 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 LARwhen ACK arrives Buffer up to SWS frames SWS LAR LFS

41 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

42 Sliding Window: Receiver Maintain three state variables receive window size (RWS) largest frame acceptable (LFA) last frame received (LFR) Maintain invariant: LFA- LFR <= RWS RWS LFR LFA Frame SeqNum arrives: if LFR< SeqNum< = LFA accept if SeqNum< = LFRor SeqNum> LFA discarded Send cumulativeacks send ACK for largest frame such that all frames less than this have been received

43 Ethernet local-area network (LAN) covered by the IEEE two modes of operation: half-duplex full-duplex modes..

44 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 usedtocarrydataoverthesystem

45 IEEE Format

46 Frame Format IEEE 802.5

47 IEEE MAC Data Frame Format

48 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

49 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.

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51 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

52 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

53 Star Topology

54 Source Routing Switch Switch Host A Switch 3 2 Host B

55 Virtual Circuit Switching Explicit connection setup (and tear-down) phase Subsequence packets follow same circuit Sometimes called connection-oriented model Analogy: phone call Host A Switch Switch 2 1 Each switch maintains a VC table 7 0 Switch Host B

56 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 0 Switch Host C 2 Host A Host E Host F 2 Switch Host G 0 Switch 3Host B Host H

57 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.

58 Datagram Model There is no round trip delay waiting for connection setup; ahostcansenddataassoonasitisready. 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.

59 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 Bridge Port 1 Port 2 X Y Z Ethernet Switch = Bridge on Steroids

60 Spanning Tree Algorithm Problem: loops A B3 B C B5 B2 D B7 K E F B1 G H I B6 B4 J Bridges run a distributed spanning tree algorithm select which bridges actively forward developed by Radia Perlman now IEEE specification

61 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

62 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

63 Thank u