Class 12 Computer Network Network Stack

Network Stack

A set of network protocol layers that work together. The term stack also refers to the actual software that processes the protocols. it is an implementation of a computer networking protocol suite or protocol family. The suite is the definition of the communication protocols and the stack is the software implementation of them.

Modulation

Mixing of low frequency signal with high frequency carrier signal is called modulation. Two signals are involved in modulation process. Messaging signals also known as baseband signals with low frequency and carrier signals with high frequency. The amplitude of baseband signals(low frequency ) is transferred to the high frequency carrier signals which can travel much farther than the baseband signals. There are various forms of modulation, each designed to alter a particular characteristic of the carrier wave.

Types of modulation are

* Amplitude
* Frequency modulation.

Amplitude modulation

A type of modulation where the amplitude of the carrier signal is modulated (changed) in proportion to the message signal while the frequency and phase are kept constant.

Frequency modulation

A type of modulation where the frequency of the carrier signal is modulated (changed) in proportion to the message signal while the amplitude and phase are kept constant.

Collision in Wireless Network

A network collision occurs when two or more devices attempt to transmit data over a network at the same time. For example, if two computers on an Ethernet network send data at the same moment, the data will “collide” and not finish transmitting. This is why most networking protocols confirm that packets has been received before transmitting additional data. Switches and routers can reduce collisions by checking if a transmission line is idle or “in use” before transmitting data. A common method is CSMA/CD or “Carrier-sense multiple access/collision detect with collision avoidance” which allows devices to take turns using signal carrier line. While it is possible to reduce collisions, they cannot be completely avoided. For example, if two systems determine a line is idle and then transmit data at exactly the same time, a collision may occur. This can be resolved by retransmitting the data after a random delay.

Error Checking

Error is a condition when an output information does not match with the input information. During transmission digital signals suffer from noise that can introduce some errors in the binary bits travelling from one system to another. This means the 0 bit may change to 1 and 1 bit may change to 0. In networking, error detection refers to the techniques used to detect noise or other impairments introduced into data while it is transmitted from source to destination.

Error detecting codes are used which are additional data added to a given digital message to help us detect if an error occurred during transmission of the message. Along with this some data is passed to figure out the original message from the corrupt message. This type of data is called as error-correcting code. Error correcting codes also detect the exact location of the corrupt bit. To detect and correct the errors, additional bits are added to the data bits at the time of transmission. These bits are called as Parity bits which allow detection and correction of the errors. The data bits along with the parity bits form a code word.

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