Group05_Illuminati:Error Detection And Correction

CRC

In telecommunication, a redundancy check is extra data added to a message for the purposes of error detection.

A cyclic redundancy check (CRC) is a non-secure hash function designed to detect accidental changes to raw computer data, and is commonly used in digital networks and storage devices such as hard disk drives. A CRC-enabled device calculates a short, fixed-length binary sequence, known as the CRC code or just CRC, for each block of data and sends or stores them both together. When a block is read or received the device repeats the calculation; if the new CRC does not match the one calculated earlier, then the block contains a data error and the device may take corrective action such as rereading or requesting the block be sent again.

CRCs are so called because the check (data verification) code is a redundancy (it adds zero information) and the algorithm is based on cyclic codes. The term CRC may refer to the check code or to the function that calculates it, which accepts data streams of any length as input but always outputs a fixed-length code. CRCs are popular because they are simple to implement in binary hardware are easy to analyse mathematically, and are particularly good at detecting common errors caused by noise in transmission channels. The CRC was invented by W. Wesley Peterson, and published in his 1961 paper. The IEEE-recommended 32-bit CRC, used in Ethernet and elsewhere, appeared at a telecommunications conference in 1975.

 

Group 05 Illuminati:Error Detection and Correction ppt

Group_05 Illuminati:Mandatory Report

Team Name : Illuminati

Team Members : Munaff Ahmad Khan,   Dipesh Badlani,   Mohammad Ali,    Anil Mohanty

Group A Project Chosen : Transmission Media

Group B Project Chosen :Error Detection & Correction

Presentation Date of Group A Project : Completed, gave on September 9 2009

Presentation Date of Group B Project : Completed, gave on October 7 2009

Group A PPT Uploaded : Yes

Group B PPT Uploaded : Yes

Group A Project Report Made : No

Group B Project Report Made : No

Group A Project problems-faced-and-solved blog uploaded : No

Group B Project problems-faced-and-solved blog uploaded : No

Transmission Media PPT

Group05_Illuminati:How Internet Works?

Internet is a global network of computers. Every computer that is connected to the Internet is part of a network. For example, a modem can be used to dial a local number to connect to an Internet Service Provider (ISP). At work, a local area network might be used but still connection to the Internet is made using an ISP that the company has contracted with. When a connection to an ISP is made, we become part of their network. The ISP may then connect to a larger network and become part of their network. The Internet is simply a network of networks.
Each computer connected to the Internet must have a unique address. This address is known as an IP (Internet Protocol) address. Every computer needs one to communicate on the Internet and it is usually built into the computer’s operating system. The Internet uses a protocol stack referred to as the TCP/IP protocol stack because of the two major communication protocols used.The Internet backbone is made up of many large networks which interconnect with each other. These large networks are known as Network Service Providers or NSPs.These networks peer with each other to exchange packet traffic. Each NSP is required to connect to three Network Access Points or NAPs. At the NAPs, packet traffic may jump from one NSP’s backbone to another NSP’s backbone. NSPs also interconnect at Metropolitian Area Networks or MAEs. MAEs serve the same purpose as the NAPs but are privately owned. NAPs were the original Internet interconnect points. Both NAPs and MAEs are referred to as Internet Exchange Points or IXs. NSPs also sell bandwidth to smaller networks, such as ISPs and smaller bandwidth providers.The ISP maintains a pool of modems for their dial-in customers. This is managed by some form of computer (usually a dedicated one) which controls data flow from the modem pool to a backbone or dedicated line router. This setup may be referred to as a port server, as it ‘serves’ access to the network. Billing and usage information is usually collected here as well. No computer knows where any of the other computers are, and packets do not get sent to every computer. The information used to get packets to their destinations are contained in routing tables kept by each router connected to the Internet.. A router is usually connected between networks to route packets between them. Each router knows about it’s sub-networks and which IP addresses they use. When a packet arrives at a router, the router examines the IP address put there by the IP protocol layer on the originating computer. The router checks it’s routing table. If the network containing the IP address is found, the packet is sent to that network.After your packets traverse the phone network and your ISP’s local equipment, they are routed onto the ISP’s backbone or a backbone the ISP buys bandwidth from. From here the packets will usually journey through several routers and over several backbones, dedicated lines, and other networks until they find their destination,

Group05_Illuminati:Transmission Media

On any network, the various entities must communicate through some form of media. Just as humans can communicate through telephone wires or sound waves in the air, computers can communicate through cables, light, and radio waves. Transmission media enable computers to send and receive messages but do not guarantee that the messages will be understood. Our project will discuss some of the most common network transmission media, such as coaxial cable, shielded twisted-pair cable, and unshielded twisted-pair cable. We will also learn about network fiber-optic cable and wireless communications.