OSI Model and Network Layers

The X.25 protocol operate on all the three, i.e. physical, data link and network layers of OSI model.

 Data link layer provides a raw transmission facility on a reliable link.It is responsible for moving frames from one node to the next.The following are the responsibilities of data link layer:framing,error control,access control,flow  control and physical addressing. It delivers data on the data link layer by hop-to-hop and a bridge operates on this layer between two adjacent nodes, so this is the correct answer.

 Data link layer provides a raw transmission facility on a reliable link.It is responsible for moving frames from one node to the next.The following are the responsibilities of data link layer:framing,error control,access control,flow control and physical addressing. It delivers data on the data link layer by hop-to-hop(node-to-node) and a bridge operates on this layer between two adjacent nodes.it provides node to node delivery of data,so it is the correct answer.

This layer is responsible for movement of individual of bits from one node to the next.Physical layer deals with the mechanical and electrical specifications of the interface and transmission medium.The following are the functions of the 

the physical layer moves data in the form of electromagnetic signals across a transmission medium.whether you are collecting numerical statistics from computer,causing a bell to ring at a distant control center,sending animated pictures from a work station, you are working with transmission of data across network connections. this is the correct answer.

Full Duplex is communication in both directions, at a same time, like in the case of telecommunication, the user and the sender, comminicate with each other at a same time.

Increase in data transmission rate leads to a higher number of packets, being transmitted at the same time.

Presentation layer does the duty of encryption and decryption.

 Session layer is responsible for token management service. Tokens are used to identify the side, that may perform the critical operation.

Repeater is a device used to regenerate the electric signal, in order to extend the LAN segment beyond its physical limits. It works on the physical layer because of signals.

Usually traffic is measured in telephone network by erlangs. Erlangs is a measure of transmission, of the telephone network.

All of the above answers are incorrect because subnet usually comprises the Network layer. The Network Layer is known as the communication subnet layer, which controls operations of subnets by determining how packets are to be distributed /routed between the networks (subnets).

Layer -4 is a transport layer in which UDP (user datagram protocol ) and IP (internet protocol ) are present. There are five classes of standards for transport layer, which differ in degree of error recovery. 

TDR stands for Time Domain Reflectometry. It is a method for detecting fault and breaks in the cable. TDR measures the time it takes for signal, to travel down the cable and reflect back.

All the above answers are incorrect because frame format of CSMA/CD and Ethernet protocol, differ in size of preamble and address blocks.

Limited bandwidth limits the data rate, and leads to distortion, in the signal shape.

Network layer has duty for routing data packets from source to destination.

Switch is also called as fast Bridge. The common forwarding approaches include Cut through, Collision free and Fully buffered.

Bridges are network devices which work on first two layers of OSI model with filtering and forwading capabilities.