901325 data communications & networking chapter 1 introduction introduction الصيفي 2012/2011

901325 Data Communications & Networking Chapter 1 Introduction Introduction 2012/2011

Data Communication & Networking Communication Sharing information. Sharing can be local (face to face) or remote ( over distance ) Tele communication (telephone, television, telegraphy) means communication at a distance remote communication. (tele: far) Data communication: exchange of data between two devices via transmission medium (wire cable) Communicating devices made up of : H.W( physical equipments )and S.W 2

3 Why Study Data Communication & Networking? Because Data Communication & Networking are changing the way we do business and the way we live Require immediate access to accurate information Database, online shopping Enable long distance communication Internet, IP phone Access variable of information (text, voice and image) Email, messenger, video conference

4 A Data Communication Model Protocol is a set of rules that governs data communications. It represents an agreement between the communicating devices. Without a protocol two devices may be connected but not communicating

5 Data Representation Text represented as a bit pattern; codes often used ASCII: 7-bit pattern (128 different symbols ) Extended ASCII: 8-bit pattern (with an extra 0 at left from 00000000 to 0111111 Unicode :32 bits pattern (65,536,216) symbols, which is definitely enough to represent any symbol in the world ISO Numbers represented by binary equivalent Images represented by matrix of pixels, small dot. The size of pixel represent the resolution One method to represent color images is RGB Audio Audio represent sound by continuous (analog) signal Video

6 Effectiveness of data communication depends on Delivery System must deliver data to correct destination. Data must be received by only intended device or user. Accuracy Data delivered accurately Altered data which left uncorrected are unusable. Timeliness Data delivered in timely manner without delay (real-time) Jitter variation in packet arrival time, It is the uneven delay in the delivery of audio or video packets

Direction of Data Flow Simplex communication is unidirectional. (one-way-street). Only one of the two devices on a link can transmit; the other can only receive, As Keyboard and monitors Half-duplex Each station can both transmit and receive, but not at the same time. When one device is sending the other can receive and vice versa. one-lane road with two direction) Full-duplex Both stations can transmit and receive simultaneously. ( telephone network) Like two way street with traffic flowing in both directions at the same time Signals going in either direction share the capacity of the link in two ways: Either the link must contain two physically separate transmission paths one for sending and other for receiving. Capacity of the channel is divided between signals traveling in both direction 7

Networks Network is a collection of computers and devices (Nodes) connected by communications channels that facilitates communications among users and allows users to share resources with other users A node can be a computer, printer, or any other device can capable of sending and/or receiving data generated by other nodes on the network. NIC Nodes attached to media through NIC (network interface card) Distributed Processing Most network uses distributed processing, in which a task is divided among multiple computers. Instead of a single machine responsible for all aspects of a process, separate 8

Network Components Software components Communication Protocols Network Operating System- NOS peer-to-peer (Windows Xp,Win7) Client-server (Windows server 2003 Linux) Hardware components Server Workstations Connecting Devices Cabling system Shared resource & peripherals 9

Connecting devices Divided into 5 different categories based on the layer in which they operate in a network 1. Below the physical layer: passive hub 2. At the physical layer: repeater or active hub 3. At the physical and data link layers : bridge or two-layer switch 4. At the physical, data link, network layers: router or three-layer switch 5. At all five layers: gateway 10

Passive Hub Passive hub is just a connector. In a star-topology Ethernet LAN, it is just a point where signals coming from different stations collide. The hub is the collision point. This type of hub is part of the media its location in the Internet model is below the physical layer. 11

Repeaters 12 Operates only in the physical layers Can extend the physical length of a LAN Receive the signal before it becomes too weak or corrupted and regenerates the original bit pattern Do not actually connect two LANs connects two segments of the same LAN Segments connected are still part of one single LAN A repeater cannot connect two LANs of different protocols

Repeaters 13 Operates only in the physical layers Can extend the physical length of a LAN Receive the signal before it becomes too weak or corrupted and regenerates the original bit pattern While, Amplifiers, Cannot discriminate between the intended signal and noise. It amplifies equally everything fed into I Do not actually connect two LANs connects two segments of the same LAN Segments connected are still part of one single LAN A repeater cannot connect two LANs of different protocols

Example repeater can overcome 10Base5 Ethernet length restriction the length of the cable is limited to 500 m divide the cable into (500 m) sections and connect them with repeaters The whole network is still considered one LAN Portions of the network separated by repeaters are called segments Repeaters acts as two-port node and has no filtering capability 14

Active Hubs Actually a multiport repeater Used to create connections between stations in a physical star topology Can also be used to create tree topology to removes the length limitation of 10Base -T (100 m) 15

Example repeater can overcome 10Base5 Ethernet length restriction the length of the cable is limited to 500 m divide the cable into (500 m) sections and connect them with repeaters The whole network is still considered one LAN Portions of the network separated by repeaters are called segments Repeaters acts as two-port node and has no filtering capability 16

Bridge device that connects two LAN segments together, which may be similar or dissimilar, such as Ethernet and Token Ring. A bridge is inserted in the network to keep traffic contained within the segments to improve performance Operates in both the physical and the data link layer Physical layer : regenerates the signal Data link layer : check the physical (MAC) addresses (source & destination) contained in the frame Bridge has filtering capability, but repeaters has not. Checks the MAC (physical) address of the destination when receives a frame, and decide if the frame should be forwarded or dropped forwards the new copy only to the segment (specific port) to which the address belongs Bridge has a table that maps addresses to the port. 17

Bridge Bridge has a table to Maps address to ports. Used in filtering decisions 18

Transparent Bridges Bridges in which the stations are completely unaware of the bridges existence. the stations does not reconfigured when a bridge is added or deleted A system equipped with transparent bridges must meet three criteria: Frame must be forwarded correctly one station to another. The forwarding table is automatically made by learning frame movements in the network. Loops in the system must be prevented. Learning: early bridges had static forwarding table Administrated manually enter each table entry simple, but not practical better solution dynamic table management that maps addresses to ports automatically bridge gradually learns from the frame movement 19

Transparent Bridges 20 Destination physical address: used for the forwarding decision (table lookup). Source physical address : used for adding entries to the table and for updating purposes. A sends frame to D: flooding E sends a frame to A: Forwarding B sends a frame to C : flooding

Transparent Bridges Loop problem bridges are normally installed redundantly to make the system more reliable Two LANs may be connected by more than one bridge they may create a loop packet may be going round and round 21

Bridges: Spanning Tree Is graph in which there is no loop Create a topology in which each LAN can be reached from any other LAN through one path only (no loop) Create a logical topology that overlays physical topology which can not be changed To find the spanning tree we need to Assign a cost (metric) to each LAN The interpretation of the cost is left up to network admin It may be the path with : Minimum hops, (shortest distance) Minimum delay, or maximum bandwidth 22

Spanning Tree with Minimum hops The hop count is normally 1 from a bridge to the LAN and 0 in the reverse direction 23

Connecting Devices Network Interface cards 24

Connecting Devices Wireless Bridge device that connects two LAN segments together via infrared or microwave transmission. A wireless bridge is often used to span buildings and provides a more economical method than laying cable or leasing a private line 25

26 Network Criteria Performance depends on Number of user Type of transmission media, Capabilities of connected H.W and the efficiency of software Reliability measured by Frequency of failure The time it takes to recover from failure Networks robustness in a catastrophe Security Protection from unauthorized access and Viruses

27 TYPE OF CONNECTION Point to point A dedicated link is provided between two devices Most of them uses an actual length of wire or cable to connect the two ends but other options,such as microwave satellite are possible Multipoint More than two devices share a single line. The capacity is shared either spatially or temporally. Spatially : Several devices can use link simultaneously Temporally : Users take turns, it is a timeshared Point to point connection Multipoint connection

28 Topology Physical topology Is how the wires are run The way in which a network is laid out physically Logical topology is how the signal travels. A device can be wired to implement any logical topology. LANs are logical busses or rings, depending on how the hub is wired 4 basic types: mesh, star, bus, ring The most common physical topology is the star. All the wires come back to a central point May often see hybrid

29 Mesh Topology Every device has a dedicated point-to-point link to every other devices in network Mesh topology often used in MANs and WANs A fully connected mesh network has n(n-1)/2 physical channels to link n devices, Every device on the network must have n-1 I/O ports Advantage Privacy or security (every message travels along a dedicated line, only the intended recipient sees it. Physical boundaries prevents other user from gaining access the message eliminating the traffic problems. The use of dedicated links guarantees that each connection can carry its own data load; that can occur when links must be shared by multiple devices. A mesh is robust. If one link becomes unusable, it does not incapacitate the entire system. Fault identification and fault isolation easy. This enables the network manager to discover the precise location of fault and aids in finding its cause and solution. Disadvantage Need more resource (cable & ports) Expensive to implement

30 Star Topology Each device has a dedicated point-to-point link only to a central device (hub, switch, router) No direct traffic and link between devices Advantages of star topology Easy to install and reconfigure and less expensive Each device need only one link and I/O port to connect it to any other devices.) Robustness, If one link fails, only that link affected and other links remain active. Identification and fault isolation Disadvantages of star topology Failure of central device may cause network failure Requires more cable than (Ring,bus)

Tree topology Is a variation of star Not every device plugs directly into the central hub. The majority of devices connect to secondary hub that in turn is connected to the central hub The advantages and disadvantages of tree topology are generally the same as those of star. The addition of secondary hubs bring more advantage: Allow more devices to be attached to a single central hub, therefore increase the distance a signal can travel between devices. 31

32 Bus Topology A multipoint topology Consists of cables connecting PCs or file servers Terminator attached to each end of bus cable segment to absorb signal and prevent signal reflection back on to covered path Transmitting packet across bus Detected by all nodes on segment Given time limit to reach destination Advantages of bus design Requires less cable than other topologies Easy to install and extend bus with a workstation Disadvantages of bus topology Not secured Can become quickly congested with network traffic A fault in bus cable stops all transmissions even between devices on the same side of the problem. The damaged area reflects signals back the direction of origin, creating noise in both directions It can difficult to add new devices (adding more require modification of the backbone).

33 Ring Topology Each device is dedicated point-to-point connection only with the two devices on either side of it Signal is passed from device to device until it reaches destination Each device functions as a repeater Advantage Relatively easy to install and reconfigure Fault isolation is simplified Disadvantage Unidirectional traffic A break in the ring can disable the entire network. This can be solved by use dual ring Hybrid topology

34 Networks Categories Network category is determined by its size, ownership, the distance it cover and its physical architecture

35 LAN Privately owned and links the devices in a single office, building or campus LANs designed to allow resources to be shared between PCs or workstations. The resources may be H.W or S.W or data. In LANs one of the computers has a large capacity drive and becomes a server to other clients. SW stored on server and used as needed by the whole group. LAN size determined by licensing restrictions( No of users per copy of SW) LAN use only one type of transmission medium. The most common LAN topologies are bus, ring and star. Today, LAN speed can be 100Mbps or 1000MBps(1G)

36 MAN Owned by private company or it may be a service provided by public company ( such as local tel.-company) Extended over an entire city. May be single network such as a cable television network, or it may be connected number of LANs into a large network so that resources may be shared LAN-TO-LAN. Examples: Company can use MAN to connect the LANs in all its offices throughout the city. A part of the telephone line network that can provide DSL line to the customer

37 WAN Provides long distance transmission of data, voice, image and video information over large areas ( country or whole world) In contrast to LAN, WAN may utilize public or private communication equipment's or combination

Switched and a Point-to-point WAN 38

Categories of Networks Based on Control Peer-to-Peer Network No single computer controls the network. Each computer is the same (a peer) to all others It is suitable for small offices. Server-Based Network The network is controlled by a special high-powered server. The server is dedicated to running the network. Print and file servers, application servers, communication servers, and directory service servers are common. 39

40 Interconnections of networks : internetwork An internet (small i) is two or more networks that can communicate with each other

41 The Internet Collaboration of more than 100s of thousands of interconnected networks In mid of 1960 The A dvanced R esearch P rojects A gency (ARPA) in the department of defense was interested in finding a way to connect computers so that the researchers they funded could share their findings, to reduce costs and eliminating duplication of effort. 1n1967 ARPA presented its ideas for ARPANET, small network of connected computers 1n 1969 ARPANET was reality. Four nodes at the University Of California (at los angles and Santa Barba), University of Utah and Stand ford Research Institute connected via IMPs computers to form a network. Software called N etwork C ontrol P rotocol (NCP) provided communication between the hosts. 1n 1972, Protocol to achieve end -to-end delivery of packets, TCP. Authorities made decision to split TCP into 2 protocols: IP : Internetworking protocol to handle datagram routing and TCP : responsible for higher-level-functions such as error detection, segmentation and reassembly

42 Protocols Protocols are set of rules that govern data communication to define What is communicated? How it communicated? When it is communicated? Key elements Syntax Structure or format of the data, meaning the order in which they are presented Example: A simple protocol might expect the first byte of data to be the address of the sender, the second byte to be the address of the receiver and the reset of the stream to be the message itself. Semantics Refers to the meaning of each section of bits. Example: does an address identify the route to be taken or the final destination of the message Timing When data to should be sent? How fast they can be sent? If a sender produces data at 100Mpbs but the receiver can process data at only 1Mpbs, transmission will overload the receiver and data will be largely lost

43 Standards Standard provides a model for development allows for interoperability Types De jure/Formal legislated by an officially recognized body De facto Have been adopted as standers through widespread use Established by manufacturers that define the functionality of a new product or technology Standards Organizations International Organization for Standardization ( ISO ) International Telecommunication Union Telecommunication standard sector ( ITU-T ) American National Standards Institute ( ANSI ) Institute of Electrical and Electronics Engineers ( IEEE ) Electronic Industries Association ( EIA )

901325 data communications & networking chapter 1 introduction introduction الصيفي 2012/2011

Documents

altered data

exchange of data

timeliness data

accuracy data

data representation

distance remote communication

communicating devices

video conference slide