NETWORKING NOTES BY AMP

Flow Control  Flow control coordinates the amount of data that can be sent before receiving an acknowledgment and is one of the most important duties of the data link layer. In most protocols, flow control is a set of procedures that tells the sender how much data it can transmit before it must wait for an acknowledgment from the receiver Error Control. Error control is both error detection and error correction. It allows the receiver to inform the sender of any frames lost or damaged in transmission and coordinates the re-transmission of those frames by the sender.In the data link layer, the term error control refers primarily to methods of error detection and re-transmission  Flow Control  Stop-and-wait Protocol- If data frames arrive at the receiver site faster than they can be processed, the frames must be stored until their use. Normally, the receiver does not have enough storage space, especially if it is receiving data from many sources. This may result...

Cyclic Redundancy Check-  Unlike checksum scheme, which is based on addition, CRC is based on binary division.   In CRC, a sequence of redundant bits, called cyclic redundancy check bits, are appended to the end of data unit so that the resulting data unit becomes exactly divisible by a second, predetermined binary number.   At the destination, the incoming data unit is divided by the same number. If at this step there is no remainder, the data unit is assumed to be correct and is therefore accepted.  A remainder indicates that the data unit has been damaged in transit and therefore must be rejected Hamming Code in Computer Network Hamming code is an error-correcting code used to ensure data accuracy during transmission or storage. Hamming code detects and corrects the errors that can occur when the data is moved or stored from the sender to the receiver. What is Redundant Bits? Redundant bits are extra binary bits that are generated and added to the ...

 Error Detection and Correction Data can be corrupted during transmission. Some applications require that errors be detected and corrected.  Types of Errors Single-Bit Error Burst Error Single-Bit Error In a single-bit error, only 1 bit in the data unit has changed. Burst Error A burst error means that 2 or more bits in the data unit have changed. Redundancy- The central concept in detecting or correcting errors is redundancy. To be able to detect or correct errors, we need to send some extra bits with our data. These redundant bits are added by the sender and removed by the receiver. Their presence allows the receiver to detect or correct corrupted bits. Detection Versus Correction The correction of errors is more difficult than the detection. In error detection, we are looking only to see if any error has occurred. The answer is a simple yes or no. We are not even interested in the number of errors. A single-bit error is the same for us as a burst error. In error correctio...

  Transmission medium- A transmission medium can be broadly defined as anything that can carry information from a source to a destination. Guided Media : Guided media, which are those that provide a medium from one device to another, include twisted-pair cable, coaxial cable, and fiber-optic cable.   Twisted-Pair Cable : A twisted pair consists of two conductors (normally copper), each with its own plastic insulation, twisted together. One of the wires is used to carry signals to the receiver, and the other is used only as a ground reference. Unshielded Versus Shielded Twisted-Pair Cable The most common twisted-pair cable used in communications is referred to as unshielded twisted-pair (UTP). STP cable has a metal foil or braided mesh covering that encases each pair of insulated conductors. Although metal casing improves the quality of cable by preventing the penetration of noise or crosstalk, it is bulkier and more expensive. Applications ·     ...

  OSI ·          OSI stands for Open Systems Interconnection ·          Created by International Standards Organization (ISO) ·          Was created as a framework and reference model to explain how different networking technologies work together and interact ·           Each layer has specific functions it is responsible for ·          All layers work together in the correct order to move data around a network  Physical Layer  The physical layer coordinates the functions required to carry a bit stream over a physical medium. It deals with the mechanical and electrical specifications of the interface and transmission medium. It also defines the procedures and functions that physical devices and interfaces have to perform for transmission to Occur.  The physical layer is al...

  LAN (Local Area Network) ·          Group of interconnected computers within a small area. (room, building, campus) ·          Two or more pc's can from a LAN to share files, folders, printers, applications and other devices. ·          Coaxial or CAT 5 cables are normally used for connections. ·          Due to short distances, errors and noise are minimum. ·          Data transfer rate is 10 to 100 mbps.      Example : A computer lab in a school.   MAN (Metropolitan Area Network) ·          Design to extend over a large area. ·          Connecting number of LAN's to form larger network, so that resources can be shared. ·        ...