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      Error detection techniques 1. Simple Parity check  Blocks of data from the source are subjected to a check bit or parity bit generator form, where a parity of : 1 is added to the block if it contains odd number of 1’s, and 0 is added if it contains even number of 1’s This scheme makes the total number of 1’s even, that is why it is called even parity checking. 2. Two-dimensional Parity check Parity check bits are calculated for each row, which is equivalent to a simple parity check bit. Parity check bits are also calculated for all columns, then both are sent along with the data. At the receiving end these are compared with the parity bits calculated on the received data. 3. Checksum In checksum error detection scheme, the data is divided into k segments each of m bits. In the sender’s end the segments are added using 1’s complement arithmetic to get the sum. The sum is complemented to get the checksum. The checksum segment is sent along with the data segme

Error Detection in Computer Networks Error A condition when the receiver’s information does not matches with the sender’s information. During transmission, digital signals suffer from noise that can introduce errors in the binary bits travelling from sender to receiver. That means a 0 bit may change to 1 or a 1 bit may change to 0. Error Detecting Codes (Implemented either at Data link layer or Transport Layer of OSI Model) Whenever a message is transmitted, it may get scrambled by noise or data may get corrupted. To avoid this, we use error-detecting codes which are additional data added to a given digital message to help us detect if any error has occurred during transmission of the message. Basic approach used for error detection is the use of redundancy bits, where additional bits are added to facilitate detection of errors. Some popular techniques for error detection are: 1. Simple Parity check 2. Two-dimensional Parity check 3. Checksum 4. Cyclic redundancy

Basics of Computer Networking Open system: A system which is connected to the network and is ready for communication. Closed system: A system which is not connected to the network and can’t be communicated with. Computer Network:  It is the interconnection of multiple devices, generally termed as Hosts connected using multiple paths for the purpose of sending/receiving data or media. There are also multiple devices or mediums which helps in the communication between two different devices which are known as  Network devices . Ex: Router, Switch, Hub, Bridge. The layout pattern using each device are interconnected is called as network topology such as bus ,star ,mesh, ring, daisy chain.

      Link state routing algorithm Link State Routing – Link state routing is the second family of routing protocols. While distance vector routers use a distributed algorithm to compute their routing tables, link-state routing uses link-state routers to exchange messages that allow each router to learn the entire network topology. Based on this learned topology, each router is then able to compute its routing table by using a shortest path computation. Features of link state routing protocols – Link state packet –  A small packet that contains routing information. Link state database –  A collection information gathered from link state packet. Shortest path first algorithm (Dijkstra algorithm) –  A calculation performed on the database results into shortest path Routing table –  A list of known paths and interfaces. Calculation of shortest path – To find shortest path, each node need to run the famous  Dijkstra algorithm . This famous algorithm uses the following step

    Distance vector routing protocols A distance vector routing protocol in data network determines the best route for data packet based on distance.   Distance vector routing protocol measure the distance by the number of routers a packet has to pass, one routers counts as one hop.   Distance vector routing protocols use the Bellmen- ford algorithm and fork - fulkerson algorithm to calculate the best route.   Distance vector routing protocol requires that a router inform it's neighbours of topology changes periodically.  Historically known as the old ARPANATE routing algorithm known as bellmen-ford algorithm.  Distance vector routing algorithm is distributed algorithm .   This routing algorithm is a iteration algorithm. Whenever a packet comes to router the neighbouring router will give the vector table and a new vector table is created at that router.          Distance Vector Routing Algorithm- Distance Vector Routing is a dynamic routing algorithm. I