Data Link Layer Design Issues

Internet

Data Link Layer has a number of specific functions to carry out. These functions include:-

  1. Providing a well-defined service interface to the Network Layer.
  2. Determining how the bits of the Physical Layer are grouped into frames.
  3. Dealing with transmission errors.
  4. Regulating the flow of frames so that slow receivers are not overcome by a fast sender.

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Simplex Stop_and_Wait Protocol

Internet

This protocol also provides for a one-directional flow of data from sender to receiver. The communication channel is once again assumed to be error-free, as in protocol Unrestricted Simplex Protocol. However, in this case, the receiver has only a finite buffer capacity and a finite processing speed, so the protocol must explicitly prevent the sender from flooding the receiver with data faster than it can be handled.

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Unrestricted Simplex Protocol

It is the simplest though unrealistic protocol with the nickname “UTOPIA“. In this case, data is transmitted in one direction only. Both the transmitting and receiving Network Layer are always ready and the proceeding time can be ignored. Infinite buffer space is available and also communication between a Data Link Layer never damages or loses frames.

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Design Issues in Data Link Layer You Must Know

The design issues deal with how to make sure all frames are eventually delivered to the Network Layer at the destination and in the proper order. The usual way to ensure reliable delivery is to provide the sender with some feedback about whatever happening at the other end of the line. Typically the protocol calls for the receiver to send back special control frames bearing positive and negative acknowledgements about the incoming frames. If the sender receives a positive acknowledgement about a frame, it knows the frame has arrived safely. On the other hand, a negative acknowledgement means that something has gone wrong and the frame must be transmitted again.

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Switching

A network contains a large number of computers and various intermediate devices. All these devices and computers must be joined so as to transfer data from one computer of network to any other computer. This can be possible by using two methods:-

The first method is to create an individual wire link from every computer to every other computer (like fully connected topology) this method requires a lot of wiring and will increase the system cost and efficiency. The other method is to use a technique of switching. In a switched network, special devices called switches, are used to join two or more computers and intermediate devices with each other. Switches can create temporary connection between two devices attached to the switch. These devices are hardware devices that may have a software component in them. When a particular virtual path is to be set, the switch is set accordingly, to create a path between two nodes.

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A Guide to Multi-access Channels and Random Access Channels

Networks can be divided into two categories i.e., those using point-to-point connections and those using broadcast channels. Broadcast channels are sometimes referred to as multi-access channels or random access channels. The protocols used to determine who goes next on a multi-access channel belong to a sublayer of the data link layer called the MAC (Medium Access Control) sublayer. The MAC sublayer is especially important in LANs, nearly all of which use a multi-access channel to communicate. WAN, in contrast, uses point-to-point links except for satellite networks.

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Framing In Computer Network Data Link Layer With Types

In order to provide services to the Network Layer, the Data Link Layer must use the service provided to it by the Physical Layer. What the Physical Layer does is, accept a raw bit stream and attempt to deliver the data to the destination. The bit stream is not guaranteed to be error-free. the number of bits received may be less than or equal to or more than the number of bits that were transmitted and they have different values. It is the task of the Data Link Layer to provide the error-free transmission of the data. The usual approach is for the Data Link Layer to break the bitstream up into discrete frames and compute the checksum for each frame. When the frame arrives at the destination the checksum is recomputed. If the newly computed checksum is different from the one contained in the frame, the Data Link Layer knows that an error has occurred and takes the necessary steps to deal with it.

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Uses Of Internet

Common uses of internet are:-

(i). Transfer of data

(ii). Remote accessing

(iii). E-mailing

(iv). File sharing

(v). Audio, Video and Graphics

(vi). World Wide Web

(vii). FTP

(viii). Chat

(ix). Telnet

(x). Newsgroup

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Applications of Computer Network

Computer network applications are software programs that use the Internet or other network infrastructure technology to carry out useful tasks, including file transfers inside a network. They aid in the movement of data throughout the network from one location to another.

Some of the network applications in different fields are as follows:-

  1. Marketing and Sales:- Computer networks are used extensively in marketing and sales organizations. Marketing professionals use them to collect, exchange and analyze data relating to customer needs and product development cycles. Sales applications include Tele-Shopping, which uses Order-Entry Computers or telephones connected to order processing networks and online reservation services for hotels, airlines, and so on.

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Methods of Data Transmission

For data transmission various methods are used:-

  • Synchronous Transmission
  • Asynchronous Transmission

Synchronous Transmission

This method of data transmission involves block of characters that are transmitted at regular time sequences. Each of the block of characters is marked with synchronization characters. The receiving end, accepts the data block, till it detects the ending character or after a predefined number of characters are received, indicating end of a message.

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