Computer Networks Lecture Notes PDF

Computer Networks Dr. Rabab Emad Saudy  Computer Network A computer network: is a group of computers/devices(Nodes) that use a set of common communication protocols over digital interconnections for the purpose of sharing resources located on or provi...

Computer Networks Dr. Rabab Emad Saudy  Computer Network A computer network: is a group of computers/devices(Nodes) that use a set of common communication protocols over digital interconnections for the purpose of sharing resources located on or provided by the network nodes.  Network Elements The nodes of a computer network may include personal computers, servers, networking hardware, or other specialised or general-purpose hosts. The interconnections between nodes are formed from a broad spectrum of telecommunication network technologies, based on physically wired, optical, and wireless technologies. A communication protocol is a set of rules for exchanging information over a network. physically wired, optical, and wireless  Network Elements  Nodes  Medium  Protocol  Operating System (OS)  Software (SW)  Network Elements Nodes The nodes of a computer network may include personal computers, servers, networking hardware, or other specialised or general-purpose hosts. Medium The interconnections between nodes are formed from a broad spectrum of telecommunication network technologies, based on physically wired, optical, and wireless technologies. Protocol A communication protocol is a set of rules for exchanging information over a network. physically wired, optical, and wireless  Network Elements  Nodes: Special purpose devices PC server switch bridge router  Links: Connections between nodes 6 Optical fiber Coaxial cable wireless  Network Elements Network Software (SW) Computers need network software to issue the requests and responses that let them take the roles of client and servers. is used to provide remote access to systems and exchange files and messages in text, audio and/or video formats between different computers or users. Network Operating System is an operating system that manages network resources: essentially, an operating system that includes special functions for connecting computers and devices into a local area network (LAN). The NOS manages multiple requests (inputs) concurrently and provides the security necessary in a multiuser environment.  Ways of Transmitting Data Simplex:  In this mode the communication can take place in one direction. Half-duplex:  Communication channel is used in both directions, but only in one direction at a time. Full-duplex:  In full duplex the communication channel is used in both directions at the same time. Use of full-duplex line improves the efficiency. Example of this mode of transmission is the telephone line.  Types of Networks 1. Personal Area Network (PAN) 2. Local Area Network (LAN) 3. Campus Area Network (CAN) 4. Metropolitan Area Network (MAN) 5. Wide Area Network (WAN) 6. Storage-Area Network (SAN) 7. Virtual Private Network (VPN) 8. Client Server Network 9. Peer to Peer Network (P2P)  1. Personal Area Network 1. Personal Area Network (PAN) is a computer network used for data transmission amongst devices such as computers, telephones, tablets and personal digital assistants. 2. Also Known as HAN (Home Area Network) 3. PANs can be used for communication amongst the personal devices themselves (interpersonal communication), or for connecting to a higher level network and the Internet (an uplink) where one "master" device takes up the role as internet router.  2. Local Area Network Spans a small geographic area such as a home, school, office building, or campus. Usually administered by a single organization or individual. Provides high speed bandwidth to end and intermediary devices within the network. High throughput is the rate of successful message delivery over a communication channel.(productivity) An upside of a LAN is fast data transfer with data speed that can reach up to 10Gbps. Other significant LAN technologies are Fiber Distributed Data Interface (FDDI) and token ring. LAN Characteristics Mirror Server Clustering Load balancing Web caching  Mirror Server  Mirror server Utilizing a backup server that duplicates all the processes and transactions of the primary server. If, for any reason, the primary server fails, the backup server can immediately take its place without any down –time.  Server mirroring is an expensive but effective strategy for achieving fault tolerance. It's expensive because each server must be mirrored by an identical server whose only purpose is to be there in the event of a failure. A less expensive technique that is becoming more and more popular is clustering.  Clustering  Connecting two or more computers together in such a way that they behave like a single computer. Clustering is used for parallel processing, load balancing and fault tolerance.  Clustering is a popular strategy for implementing parallel processing applications because it enables companies to leverage the investment already made in PCs and workstations. In addition, it's relatively easy to add new CPUs simply by adding a new PC to the network.  Load balancing is dividing the amount of work that a computer has to do between two or more computers so that more work gets done in the same amount of time and, in general, all users get served faster. In load balancing, we distribute computing tasks over the cluster such that one single machine is not burdened with heavy processing that it can’t do.  Web Cache  A computer system in a network that keeps copies of the most-recently requested Web pages in memory or on disk in order to speed up retrieval. If the next page requested has already been stored in the cache, it is retrieved locally rather than from the Internet.  Web caching servers sit inside the company's firewall and enable all popular pages retrieved by users to be instantly available.  Since the content of Web pages can change, the caching software is always checking for newer versions of the page and downloading them. Pages will be deleted from the cache after a set amount of non-activity.  3. Campus Area Network Larger than LANs, but smaller than metropolitan area networks these types of networks are typically seen in universities. They can be spread across several buildings that are fairly close to each other so users can share resources  4. Metropolitan Area Network 1. A MAN is larger than a LAN but smaller than or equal in size to a WAN. 2. The size range anywhere from 5 to 50km in diameter. 3. MANs are typically owned and managed by a single entity. 4. This could be an ISP or telecommunications company that sells its services to end-users in that metropolitan area. 5. For all intents and purposes, a MAN has the same characteristics as a WAN with distance constraints.  5. Wide Area Network A Wide Area Network exist over a large area Data travels through telephone or cable lines Usually requires a Modem The world’s largest Wide Area Network in the Internet 5. Wide Area Network Technologies used include:  Circuit switching  Packet switching  Circuit switching  is a method of implementing a telecommunications network in which two network nodes establish a dedicated communications channel (circuit) through the network before the nodes may communicate.  Packet switching  Packet-switched networks move data in separate, small blocks -- packets -- based on the destination address in each packet. When received, packets are reassembled in the proper sequence to make up the message.  6. Storage Area Network SAN may be referred to as a Sub network or special purpose network. Its special purpose is to allow users on a larger network to connect various data storage devices with clusters of data servers. SANs can be accessed in the same fashion as a drive attached to a server.  7. Virtual Private Network VPN is a private network that can access public networks remotely. VPN uses encryption and security protocols to retain privacy while it accesses outside resources. When employed on a network, VPN enables an end user to create a virtual tunnel to a remote location. Typically, telecommuters use VPN to log in to their company networks from home. Authentication is provided to validate the identities of the two peers. Confidentiality provides encryption of the data to keep it private from prying eyes. Integrity is used to ensure that the data sent between the two devices or sites has not been tampered with.  8. Client/Server Network In a client/server arrangement, network services are located on a dedicated computer called a server. The server responds to the requests of clients. The server is a central computer that is continuously available to respond to requests from clients for file, print, application, and other services. Most network operating systems adopt the form of a client/server relationship. Typically, desktop computers function as clients, and one or more computers with additional processing power, memory, and specialized software function as servers.  9. Peer to Peer Network Usually very small networks Each workstation has equivalent capabilities and responsibilities Does not require a switch or a hub. These types of networks do not perform well under heavy data loads. Internet , Intranet & Extranet  The Internet  The Internet is a worldwide collection of interconnected LANs and WANs.  LANs are connected to each other using WANs.  WANs are then connected to each other using copper wires, fiber optic cables, and wireless transmissions.  The Internet is not owned by any individual or group, however, the following groups were developed to help maintain structure:  IETF  ICANN  IAB  Intranet & Extranet Intranet:  is a term often used to refer to a private connection of LANs and WANs that belongs to an organization and is designed to be accessible only by the organization’s members, employees, or others with authorization. Intranets are basically an internet that is usually only accessible from within the organization. Extranet:  An organization can use an extranet to provide secure and safe access to individuals who work for a different organization but require company data.  Examples of extranets include:  A company providing access to outside suppliers/contractors  A hospital providing a booking system to doctors so that they can make appointments for their patients