In manchester code, the bit duration is divided into the two halves. The voltage remains same at one level during first half and second half. It moves to the other level and the middle level to provide synchronization. It is like unipolar in which, the signal does not return zero at the middle of the bit and manchester is a combined feature of RZ and NRZ-L(polar). So, it is the correct option.

Trans-receiver is used for carrier detection and collision detection in LAN's. These detections are called CSMA/CD.

QAM is used in high speed modem. QAM - Quadrature Amplitude modulation is a combination of amplitude and phase modulation to obtain greater throughput in a given channel.

FDDI can spread over 200 kms. For large networks, it requires more repeaters.

In half duplex mode, each station can transmit and receive data but not at the same time. When one device is sending the data, the other can only receive, and vice versa. Radio is the example of half duplex, where at a time one can talk and other can listen, and vice versa.

All the above answers are wrong, because half duplex operations involves data flow in only one direction at a time. It is a two wire transmission with medium cost and efficiency.

Multiplexing allows several signals to travel in the same channel.

X.25 is a connection oriented protocol which supports both switched virtual circuits and permanent ones. X.25 is a popular packet switching protocol used in ISDN, consisting of physical, frame and packet levels.

Bit stuffing is a technique used to recover from occasional frame error.

X.25 is a popular packet switching protocol used in ISDN, consists of physical, frame and packet levels.

Frame relay uses connection oriented switching technique because synchronous frames of data are routed to different destinations depending on header information.

Switches are better than the hubs. Switches amplify the bandwidth, so that the same throughput is provided, to each of the machines, connected to the switch. On the other hand, hub simply divides the throughput equally among various nodes, connected to it.

The 10 base 5 permits five cable segments, multiple 10 base 5 segments may be connected through repeaters to form a larger network, that still consists of a single collision domain. A repeater regenerates the signals from receiving it from one cable segment, and transmitting to all cables.

Traffic in a network is usually measured by relative congestion, it is amount of data that flows.

X.21 is a state driven protocol running full dupex at 9600 bps to 64 kbps with subscriber networks. X.21 is a circuit-switching protocol using synchronous.