Computer Networks Lecture 6 PDF

Lecture 6 Computer Networks  Learning Objectives 1. Networks Definition and Benefits 2. Area Networks 3. Networks Categories 4. Networks Elements 5. Networks Topologies 2  What is the Computer Network? Computer Ne...

Lecture 6 Computer Networks  Learning Objectives 1. Networks Definition and Benefits 2. Area Networks 3. Networks Categories 4. Networks Elements 5. Networks Topologies 2  What is the Computer Network? Computer Network means, a collection of Computers, and other devices, or peripherals connected together through connecting media 3  Benefits of Computer Networks Information sharing: Authorized users can use other computers on the network to access and share information and data. This could include special group projects, databases, etc. Hardware sharing: One device connected to a network, can be shared by many users. Software sharing: Instead of purchasing and installing a software program on each computer, it can be installed on the server. All of the users can then access the program from a single location. 4  Area Networks Local Area Networks (LANs) Metropolitan Area Networks (MANs) Wide Area Networks(WANs) Storage-Area Networks (SANS) Virtual Private Networks (VPNs) 5 Area Networks: LAN 6 Area Networks: WAN 7 Area Networks: MAN 8 Area Networks: SAN 9 Area Networks: VPN 10  Network Categories Two basic types of networks – Peer-to-Peer Networks – Client/Server Networks 11  Peer-to-Peer Networks In a peer-to-peer network, all computers are considered equal; they all have the same abilities to use the resources available on the network. Example : Windows Workgroup 12  Client/Server Networks Some nodes (SERVER) are dedicated to present services to other nodes (CLIENTS) Examples: – Mail Server – Web Server 13  Client Server Model Initiates a request Client Replies with a service Server Client Client 14  What do you need to build a computer network? Computers / Peripherals NICs Connecting Media Networking Device(s) – Routers – Switches – Bridges – Hubs Software Protocols – Communication rules that all entity must agree on 15  Networking Devices: Repeater A repeater does exactly that – It repeats any electric signals that come into one port out of its other port. Ethernet or WiFi data transmissions can only span a limited distance. Repeater helps to extend that distance. 16 Networking Devices 17  Networking Devices: HUB Center of a star network All nodes receive transmitted packets Slow and insecure It is a Half duplex Device. 18  Networking Devices: Switch A switch is an intelligent device. Replacement for hubs Only intended node receives transmission Fast and secure Switch can operate as full duplex or half duplex. 19  Networking Devices: Bridge – Connects two or more LANs together – Packets sent to remote LAN cross Other packets do not cross – Segments the network on MAC addresses 20  Networking Devices: Router Connects two or more LANs together Packets sent to remote LAN cross Network is segmented by IP address Connect internal networks to the Internet Need configured before installation 21  Networking Devices: Firewall Primary function of a Firewall is to protect a network from unauthorized users/hackers. Firewalls can be configured with "rules". Firewall rules can be used to allow/deny network traffic from/to the network. These rules can be based on Source/Destination network, Source/Destination IP Address, Source/Destination TCP/UDP port numbers, Protocols, Applications etc. 22  Networking Devices: Network interface cards Network interface cards – Network adapter – Connects node to the media – Unique Machine Access Code (MAC) 23  Network Topologies Topology refers to the shape of a network, or the network's layout. How different nodes in a network are connected to each other and how they communicate are determined by the network's topology. The choice of topology is dependent upon – Type and number of equipment being used – Cost 24 Network Topologies 25  Network Topologies Topology refers to the shape of a network, or the network's layout OR (how, and in what shape, network components are connected together). How different nodes in a network are connected to each other and how they communicate are determined by the network's topology. The choice of topology is dependent upon – Type and number of equipment being used – Cost 26  Network Topologies It is the structure, consisting of paths and switches, that provides the communications interconnection among nodes of a network. Computer networks topologies – Bus – Star – Ring – Mesh – Hybrid 27  Network Topologies: Packets – Pieces of data transmitted over a network Packets are created by sending node Data is reassembled by receiving node – Packet header Sending and receiving address – Packet payload Number and size of data Actual data – Packet error control 28  Network Topologies: Bus Topology All devices are connected to a central cable, called the bus or backbone. Both ends of the network must be terminated with a terminator. 29  Network Topologies: Bus Topology Bus Advantages and Disadvantages Advantages – Simple, easy to use and construct – Requires least amount of cable (less expensive) Disadvantages – A faulty cable will take the entire LAN down – Difficult to troubleshoot – Heavy network traffic can slow bus considerably 30  Network Topologies: Star Topology A physical Star topology connects the devices via a centralized unit such as a Hub or Switch. Nodes communicate across the network by passing data through the central device. 31  Network Topologies: Star Topology star hub Broadcasted Star Topology (Hubbed Star) – Through a hub which sends message out of all ports – Physical star, logically bus – Only one station can transmit at a time switch hub Switched Star Topology (Switched Star) – Through a switch which sends messages to only destination computer 32  Network Topologies: Bus Topology STAR Advantages and Disadvantages Advantages – Single computer failure doesn’t bring down whole network – Adding new devices to a Star network is very simple compared to any of the other topologies – No disruptions to the network when connecting or removing devices. – Centralized control – Centralized network/hub monitoring – Easy to troubleshoot Disadvantages – If central device fails, the whole network fails – Compared to the bus topology, a star network generally requires more cable – More expensive than linear bus topologies because of the cost of the central device 33  Network Topologies: RING Topology All devices are connected to one another in the shape of a closed loop, so that each device is connected directly to two other devices, one on either side of it. Data is passed one way from device to device. 34  Network Topologies: RING Topology A short message (called a token) is circulated around the ring, being passed from station to station. The token originates from a controller or master station which inserts it onto the ring. A station which wants to transmit waits for the token to arrive. When the token arrives, the station changes it from a token to a connector message, and appends its message. This new message is then placed on the outgoing side of the ring. 35  Network Topologies: RING Topology Each station passes on received tokens if they have nothing to transmit. They monitor connector messages to see if the message is addressed to them. If connector messages are addressed to them, they copy the message, modify it to signify its receipt, then send it on around the ring. Connector messages which are not addressed to them are passed directly on to the next station in the ring. When the connector message travels full circle and arrives at the original sending station, it checks the message to see if it's been received. It then discards the message and replaces it with a token. 36  Network Topologies: RING Topology Ring Advantages and Disadvantages Advantages – Equal access for all users – Perform well under heavy traffic Disadvantages – If one device/cable fails then the whole network goes down. – Difficult to troubleshoot – Adding/Removing computers disrupts the whole network. 37  Network Topologies: MESH Topology In a mesh topology each device/PC is connected to every other device/PC in the network by its own cable 38  Network Topologies: MESH Topology Mesh Advantages and Disadvantages Advantages – Mesh topology boasts the highest fault tolerance of all of the network topologies Disadvantages – Because each connection needs its own cable a Mesh topology can get very expensive. 39  Network Topologies: Hybrid Topology Hybrid means that there is more than one topology exist Stared Bus – Groups of star-configured networks are connected to a linear bus backbone 40  Network Transmission Media To transmit data, a medium must exist The medium can be in the form of cables or wireless medium Most common used media for data networks – Twisted pair cable – Coaxial cable – Fiber optic cable – Wireless media 41  Network Transmission Media: Bandwidth In computer networks, bandwidth is often used as a synonym for data transfer rate The amount of data that can be carried from one point to another in a given time period (usually a second). This kind of bandwidth is usually expressed in bits (of data) per second (bps) 42  Network Transmission Media Cable Media – Twisted Pair Cables STP UTP – Fiber Optic Cables – Coaxial Cables Wireless Media – Infrared – Microwave ( frequencies between 0.3 GHz and 300 GHz.) – Bluetooth 43  Network Transmission Media: Cable Media There are several types of cable which are commonly used with LANs. In some cases, a network will utilize only one type of cable, other networks will use a variety of cable types. The type of cable chosen for a network is related to the network's topology, protocol, and size. Understanding the characteristics of different types of cable and how they relate to other aspects of a network is necessary for the development of a successful network. 44  Cable Media:Twisted pair cable Most widely used (Ethernet networks) Three basic types Twisted pair cable has 7 categories Use RJ-45 connectors Crimper tool attach the twisted pair cable to RJ-45. 45  Cable Media:Twisted pair cable Image:Rj45plug-8p8c.png 46  Cable Media: Coaxial Cable Cost is Moderate Fairly Easy Installation Bandwidth ~ 10 Mbps Attenuation ~ few hundreds of meters 47  Cable Media: Fiber-optic ▪ glass fiber carrying light pulses, each pulse a bit ▪ high-speed operation: high-speed point-to-point transmission (10’s-100’s Gbps) ▪ low error rate: repeaters spaced far apart immune to electromagnetic noise 48  Wireless Media Flexible (Used in areas where it is hard to install cables ) Used in wireless LANs Hybrid environment is one which wireless components communicate with a network that use cables 49  IP Addresses An identifier for a computer or device on a TCP/IP network. Networks using the TCP/IP protocol route messages based on the IP address of the destination. The format of an IP address (V4) is a 32-bit numeric address written as four numbers separated by periods. Each number can be zero to 255. – For example, 1.160.10.240 could be an IP address. 50 IP Address Classes 51  IP Address Classes IP Address Class Class A Class B Class C First bit values (binary) 0 10 110 First byte value (decimal) 0–127 128–191 192–223 Number of network identifier bits 8 16 24 Number of host identifier bits 24 16 8 Number of possible networks 126 16,384 2,097,152 Number of possible hosts 16,777,214 65,534 254 52  IP Address Classes Class A 0–126.x.x.x , x can be between 0 and 255 The first octet is assigned to the owner, with the rest being freely distributable to the nodes Has a 24 bit address space supports 16 million hosts on each of 127 networks Class B 128 -191.x.x.x , x can be between 0 and 255 The first two octets are assigned to the address block owner, with the last two being freely distributable Class C 192-232.x.x.x , x can be between 0 and 255 The first three octets are assigned, with the last being freely distributable 53  IPv4 vs. IPv6 IPv4 – 32 bits used for address – 4,294,967,296 – Addresses not assigned by geographic region IPv6 – 128 bits used for address – 340,282,366,920,938,463,374,607,431,768,211,456 – That about 3.7x10^21 addresses per square inch of the earth’s surface – Addresses will be assigned by geographic region 54  IPv4 vs. IPv6 IPv4 addresses written as four octets (8 bits) separated by periods. – 134.129.67.235 IPv6 address written as eight 4-digit (16-bit) hexadecimal numbers separated by colons. – 1080:0:0:0:0:800:0:417A 55  Loopback address 127.0.0.0 – Network number that cannot be assigned to any network 127.0.0.1 – The loopback address – Used for diagnostic testing of the local TCP/IP installation 56  Loopback address 127.0.0.0 – Network number that cannot be assigned to any network 127.0.0.1 – The loopback address – Used for diagnostic testing of the local TCP/IP installation 57  Uniform Resource Locator http://www.ndsu.nodak.edu/pubweb/~latimer/index.html#events http:// communication protocol www.ndsu.nodak.edu web server hosting the page /ndsu/latimer/ path to the page on the host server index.html filename of the page #events anchor in the page 58  IP & Domain Name Examples IP: 134.129.67.85 URL: gdc.busad.ndsu.nodak.edu IP: 134.129.67.235 URL: dyn235.minard-67.ndsu.nodak.edu 59