Computer Networks Lecture Notes PDF

Computer Networks Chandana Wimalarathne Dept. of Computer Science, 22/02/2022 University of Ruhuna 1  What is the Network ? We are familiar with several networks in our day-to-day work such as ; Radio Network A communication sy...

Computer Networks Chandana Wimalarathne Dept. of Computer Science, 22/02/2022 University of Ruhuna 1  What is the Network ? We are familiar with several networks in our day-to-day work such as ; Radio Network A communication system consisting of a group of broadcasting stations that transmit the same program Television Network Distributed network for television content whereby a central operation provides programming for many television station Rail road Network Telephone Network Dept. of Computer Science, 22/02/2022 University of Ruhuna 2  Computer Network A collection of two or more computers and related devices (printers, tape drivers, etc), connected in a way that allows them to share data, information, software, hardware devices and processing power. Dept. of Computer Science, 22/02/2022 University of Ruhuna 3  Problem… Dept. of Computer Science, 22/02/2022 University of Ruhuna 4  Analog and Digital Signals Digital Transmission— Analog Transmission— 1’s and 0’s Wires or wireless, On or Off Audio tones Computer-speak Info conveyed through signal amplitude, frequency, and phase 1 0 1 0 0 1 1 0 1 “1” bit “0” bit Start Stop Bit Bit Digital signals are seen as one’s and zero’s. The signal is either on or off. Whereas analog signals are like audio tones – for example, the high-pitched squeal you hear when you accidentally call a fax machine. So, in order for the computer world to use the services of the telephone system, a conversion of the signal had to occur. Dept. of Computer Science, 22/02/2022 University of Ruhuna 5  Birth of the Personal Computer  Applications  File storage  Processing power  Printing options  Smart terminals The birth of the personal computer in 1981 really fueled the explosion of the networking marketplace. No longer were people dependent on a mainframe for applications, file storage, processing, or printing. The PC gave users incredible freedom and power. Dept. of Computer Science, 22/02/2022 University of Ruhuna 6  Why we need Computer Network? Resource sharing ✓ File sharing ✓ Hardware sharing ✓ Program sharing ✓ Processing Power Communication ( Voice & video ) High reliability Centralized Administration Saving money Dept. of Computer Science, 22/02/2022 University of Ruhuna 7  Basic Requirements for Network Services Clients Protocol Communication Media Dept. of Computer Science, 22/02/2022 University of Ruhuna 8  Servers Computers that provide shared resources to network users. As a example :- File Server – Stores shared user files and provides space for users Communication Server – Provide communication service such as email Application Server – Provide access to a database or other application (SQL server database) Print Server – Provide the print queue and other services related to a network printer Dept. of Computer Science, 22/02/2022 University of Ruhuna 9  Workstation or Clients Computers that access shared network resources provided by a server. Dept. of Computer Science, 22/02/2022 University of Ruhuna 10  Protocol A protocol is an agreement (rules) between the communicating parties on how communication is proceed. Commonly used network protocols as follows : - NetBEUI (Simple and fast network protocol used with Microsoft and IBM’s – non routable protocol) - IPX/SPX (use for small and large networks used with Novell Netware) - TCP/IP (use for small and large networks and it can be run on a number of different software platforms such as Windows, Unix, and so on) - Apple Talk (use for corporate network used with Apple Macintoshes) Dept. of Computer Science, 22/02/2022 University of Ruhuna 11  Transmission Media The transmission of an electrical signal requires a transmission medium, which normally takes the form of a transmission line. Transmission physical media can be describe under two categories :- Cable (Wired/ Guided)Media Wireless (Unguided)Media - - Coaxial - Radio Wave - - Twisted Pair (UTP, STP) - Micro Wave - - Fiber Optic - Infrared Light Dept. of Computer Science, 22/02/2022 University of Ruhuna 12  Coaxial Cable Braided Copper Shielding Outer Jacket Plastic Insulation Copper Conductor Speed and throughput: 10/100 Mbps Relative cost: More than UTP, but still low Media and connector size: Medium Maximum cable length: 200/500 m Dept. of Computer Science, 22/02/2022 University of Ruhuna BNC Connector 13  Twisted-Pair (UTP and STP) Color-Coded STP only: Plastic Insulation Twisted-Pair Shielded Insulation to Reduce EMI Outer Jacket Speed and throughput: 10/100/1000 Mbps/10G RJ-45 Relative cost: Least costly Connector Media and connector size: Small Maximum cable length: 100 m Dept. of Computer Science, 22/02/2022 University of Ruhuna 14  Fiber-Optic Cable Plastic Kevlar Reinforcing Outer Jacket Shield Glass Fiber Material and Cladding Single mode: One stream of laser-generated light (100 km) Multimode: Multiple streams of LED-generated light (2 km) Multimode Speed and throughput: 100+ Mbps Connector Average cost per node: Most expensive Media and connector size: Small Maximum cable length: Up to 2 km Dept. of Computer Science, 22/02/2022 University of Ruhuna 15  Wireless Media Radio Wave Micro Wave Infrared Light UPLINK DOWNLINK Dept. of Computer Science, 22/02/2022 University of Ruhuna 16  Wireless Standards(IEEE 802.11) In 1997, the Institute of Electrical and Electronics Engineers (IEEE) created the first WLAN standard. They called it 802.11 Wireless standards collectively known as Wi-Fi technologies. Additionally, Bluetooth and various other non Wi-Fi technologies also exist, each also designed for specific networking applications. 802.11 only supported a maximum network bandwidth of 2 Mbps Dept. of Computer Science, 22/02/2022 University of Ruhuna 17  Bluetooth Bluetooth is an alternative wireless network technology that followed a different development path than the 802.11 family. Bluetooth supports a very short range (approximately 10 meters) Relatively low bandwidth (1-3 Mbps in practice) You can readily find Bluetooth in the networking of PDAs or cell phones with PCs. It is rarely used for general-purpose WLAN networking due to the range and speed considerations. 22/02/2022 Dept. of Computer Science, University of Ruhuna 18  WiMax WiMax is the industry term for a long-range wireless networking standard. (IEEE 802.16) WiMax technology has the potential to deliver high-speed Internet access to rural areas and other locations not serviced by cable or DSL technology. WiMax also offers an alternative to satellite Internet services. Data rates for WiMax can reach up to 75 megabits per second (Mb/s). A number of wireless signaling options exist ranging anywhere from the 2 GHz range up to 66 GHz. Dept. of Computer Science, 22/02/2022 University of Ruhuna 19  The choice of cable depends on Cost Distance Number of computers involves Speed Environment of cabling Dept. of Computer Science, 22/02/2022 University of Ruhuna 20  Network Technology A network technology is classified into one of three broad categories, depending on the size of networks that can be created: - LAN ( Local Area Network ) - MAN ( Metropolitan Area Network ) - WAN ( Wide Area Network ) Dept. of Computer Science, 22/02/2022 University of Ruhuna 21  Local Area Network—LAN What is a LAN? A collection of computers, printers, modems, and other devices that can communicate with each other in a small area What are the components? Computers Network operating system (NOS –Linux,WinNT,Win2000, etc.) Network Interface Card (NIC) Hubs, Switches How is a LAN controlled? Protocols—Formal descriptions of sets of rules and conventions that govern how devices on a network exchange information Dept. of Computer Science, 22/02/2022 University of Ruhuna 22  Network Operating System (NOS) Software that allows communicating and sharing of data and network resources Examples: Linux Win2000 WinNT AppleTalk NetWare PC or Workstation Loaded with NOS Dept. of Computer Science, 22/02/2022 University of Ruhuna 23  LAN Network Types Different networking models arose to fit different type of networking needs. Mainly networks are classified as follows, ◆ Peer-to-Peer networks ◆ Server-base networks Dept. of Computer Science, 22/02/2022 University of Ruhuna 24  Peer – to – Peer Networks In situations where a few computers needed to share a particular hardware or software, peer-to-peer networks provide an easy way to share resources, such as files and printers, without the need for an actual server computers. Peer computers act as both clients (the user of resources) and servers (the provide of resources). The only real requirements for building peer-to-peer network are installing an operating system on the PCs that support peer-to-peer networking and physically connecting the PCs. Examples :Windows workstation Dept. of Computer Science, 22/02/2022 University of Ruhuna 25  Peer – to – Peer Networks Dept. of Computer Science, 22/02/2022 University of Ruhuna 26  Server-based Networks Server-based networks provide greater centralized control of resources and expandability if required. A server computer is basically a special-purpose machine that logs in users and “serves” up resources to them. Because the server verifies users, this type of network makes it easier to manage resources by providing different access levels to the various users. Examples :- Linux, Unix, Windows Server, etc Servers Servers Dept. of Computer Science, 22/02/2022 University of Ruhuna 27  Server-based Networks Dept. of Computer Science, 22/02/2022 University of Ruhuna 28  Network Devices The connectivity devices that define the network topology. The most important being the network interface card. We will also take a look at Network Interface Card (NIC) Modems Hubs Bridges Switches Routers Dept. of Computer Science, 22/02/2022 University of Ruhuna 29  Network Interface Card Amplifies electronic signals Packages data for transmission Physically connects computer to transmission media (cable) Hardware or MAC address is burned into a ROM chip on the NIC. Dept. of Computer Science, 22/02/2022 University of Ruhuna 30  MAC Address 24 bits 24 bits Vendor Code Serial Number 00.00.0c.12. 34.56 ROM RAM MAC address is burned into ROM on a network interface card The MAC address is unique for each LAN interface Dept. of Computer Science, 22/02/2022 University of Ruhuna 31  Exercise Find out the MAC address of your NIC ipconfig/all Dept. of Computer Science, 22/02/2022 University of Ruhuna 32  The Hubs 123 126 124 127 Hub 125 128  Amplifies signals  Propagates signals through the network  Does not filter data packets based on destination  No path determination or switching  Unintelligent equipment Dept. of Computer Science, 22/02/2022 University of Ruhuna 33  Functionality of Hubs Dept. of Computer Science, 22/02/2022 University of Ruhuna 34  When multiple system try to communicate at the same time: System will try after a random delay again to transmit, resulting in network slowdown. This can be avoid using 'intelligent' device such a Switch Dept. of Computer Science, 22/02/2022 University of Ruhuna 35  The Switches Workstation 10-Mbps 31 UTP Cable “Dedicated” Switch 34 32 35 33 100 Mbps 100 Mbps 36 Corporate Intranet Uses bridging technology to forward traffic (i.e.maintains address tables, and can filter) Provides full dedicated transmission rate between stations that are connected to switch ports Used in both local-area and in wide-area networking Dept. of Computer Science, 22/02/2022 University of Ruhuna 36  Functionality of Switches handle more than 2 communications at the same time: Dept. of Computer Science, 22/02/2022 University of Ruhuna 37  Exercise Find out the ARP Table in your machine > arp -a Dept. of Computer Science, 22/02/2022 University of Ruhuna 38  LAN Topologies Define network device organization Three common types Bus topology Star topology Ring topology Topologies are logical architectures Actual devices need not be physically organized in these configurations Dept. of Computer Science, 22/02/2022 University of Ruhuna 39  Bus Topology Advantage Disadvantages s - Bus failure brings network - Less cable required - Flexible wiring scheme down - Simple - Troubleshooting is difficult - Low cost - Distance Limitation Dept. of Computer Science, 22/02/2022 University of Ruhuna 40  Star Topology Advantages Disadvantages - Fault tolerant - Requires more cable - Easy to maintain - Higher cost - Changes are easy - Distance imitation - Port limitation Dept. of Computer Science, 22/02/2022 University of Ruhuna 41  Ring Topology Advantages Disadvantages - Collisions free communication - Require more cable than BUS - Simple wiring scheme - Distance limitation - Good growth path - More difficult fault isolation Dept. of Computer Science, 22/02/2022 University of Ruhuna 42  What Is TCP/IP? A suite of protocols Rules that dictate how packets of information are sent across multiple networks Addressing Error checking Dept. of Computer Science, 22/02/2022 University of Ruhuna 43  IP Internet Protocol (IP) Determines where packets are routed based on their destination addresses Breaks packets into smaller packets and reassembles them Dept. of Computer Science, 22/02/2022 University of Ruhuna 44  IPv4 Addressing What is an IP Address ? ❖32 – bit Binary Number (Address) 11000000111110000011000000000001 Divided into 4, 8-bit Octal 11000000.11111000.00110000.00000001 Converted to Decimal Numbers 192.248.48.1 Decimal range of an Octal : 0-255 ❖ It Contains the device’s Network ID and Host ID Dept. of Computer Science, 22/02/2022 University of Ruhuna 45  Network ID and Host ID ❖ Host ID ❖ Network ID ▪ Shared with all ▪ Identifies a specific computers on the same device (Host) within a physical segment physical segment ▪ Unique on the entire ▪ Unique on the physical Network segment ▪ “Area Code” ▪ “Phone Number” 192.248.48.1 Dept. of Computer Science, 22/02/2022 University of Ruhuna 46  IP Addressing—Class A 10.222.135.17 Network # 10 Host # 222.135.17 Range of class A network IDs: 1–126 Number of available hosts: 16,777,214 Dept. of Computer Science, 22/02/2022 University of Ruhuna 47  IP Addressing—Class B 128.128.141.245 Network # 128.128 Host # 141.245 Range of class B network IDs: 128.1–191.254 Number of available hosts: 65,534 Dept. of Computer Science, 22/02/2022 University of Ruhuna 48  IP Addressing—Class C 192.150.12.1 Network # 192.150.12 Host # 1 Range of class C network IDs: 192.0.1–223.255.254 Number of available hosts: 254 Dept. of Computer Science, 22/02/2022 University of Ruhuna 49  IP Network Address Classes Class # Networks # Hosts Example A 126 16,777,214 01111111 00000000 00000000 00000000 B 16,384 65,534 10111111 11111111 00000000 00000000 C 2,097,152 254 11011111 11111111 11111111 00000000 Class A 35.0.0.0 Host Address Space Class B 128.5.0.0 Network Address Space Class C 192.33.33.0 Dept. of Computer Science, 22/02/2022 University of Ruhuna 50  Private IP Addresses Class A: 10.0.0.0 - 10.255.255.255 Class B: 172.16.0.0 - 172.31.255.255 Class C: 192.168.0.0 - 192.168.255.255 Dept. of Computer Science, 22/02/2022 University of Ruhuna 51  What is an Internet ? The internetwork is a collection of individual networks, connected by intermediate networking devices, that functions as a single large network and communicating via TCP/IP Various Services http (World Wide Web – WWW) Smtp (email) ftp telnet ….etc Dept. of Computer Science, 22/02/2022 University of Ruhuna 52  How it all works  Hierarchy of networks using TCP/IP  Addressing and routing – Your address identifies your host – Routing tells other networks “where you are” Reachability information  Domain Name System (DNS) – Map hostnames to ip addresses – Use alpha.ruh.ac.lk instead of 192.248.48.3 Dept. of Computer Science, 22/02/2022 University of Ruhuna 53  How it all works (cont..) Organizations buy connectivity from Internet Service Providers (ISPs) to connect to the Internet – Exchange routers – Know how to get to your network Dept. of Computer Science, 22/02/2022 University of Ruhuna 54  How it all works (cont..) ISPs buy service from larger ISPs for connectivity National Service Providers/International Service Providers – Tier 1 backbones do not need to buy connectivity from anyone else. Dept. of Computer Science, 22/02/2022 University of Ruhuna 55  How does it happen?  Connectivity – Dial-up via modem – Direct connection (leased line)  Need an ip address – Provider gives it to you – Get it from a Registry  Other networks need to know how to reach your network – Your provider routes your address space Dept. of Computer Science, 22/02/2022 University of Ruhuna 56  How DNS work / Root servers.com.edu.gov.mil Country code.lk.uk.ac.lk cintec.lk ruh.ac.lk pdn.ac.lk Dept. of Computer Science, 22/02/2022 University of Ruhuna 57  DNS server Domain Name System is an Internet-wide distributed database system that network-specific information, such as the associated IP address for a host name. Name resolution software that lets users locate computers on the Internet (TCP/IP network) by domain name. The DNS server maintains a database of domain names (host names) and their corresponding IP addresses. www.ruh.ac.lk or alpha.ruh.ac.lk presented to a DNS server, the IP address 192.248.48.3 would be 22/02/2022 returned. Dept. of Computer Science, University of Ruhuna 58  Server DNS Client Dept. of Computer Science, 22/02/2022 University of Ruhuna 59  The End Dept. of Computer Science, 22/02/2022 University of Ruhuna 60