Data Communication and Networks

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

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.

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. 

Fiber optic is based on the principle of total internal reflection.

BUS topology provides a common path shared by many users.

Total connection between path sender and receiver information is also called CIRCUIT.

Bottom three layers of OSI model are implemented by MAN. MAN size is greater than LAN so bottom three layers have the capabilities of proper delivery of packets.

Sampling technique is used to remove redundancy from continuous signals and the amplitude signal is measured at equal intervals to generate a series of discrete pulses.

It is not a type of transmission.

Satellite communication suffers from propagation delays due to large distance travelled by signals.

In above condition only simplex is involved, i.e. only in one direction.

Satellite communication suffers from propagation delay due to large distance travelled by the signals. 

'M bit in a X.25 standard is set to 1' means there is more than one packet.

D channel is the lowest data rate because it is used for signaling with 16 kbps.

Amplifier is used to strengthen the analog signals because by travelling long distance analogs get weaker.

Firewall is a true network protector, which authenticates the external access to a network.

Synchronous and asynchronous are communication techniques.

By decreasing data rate, it can reduce bit error rate.

FDDI MAC protocol uses three timers.
Token holding timer - It determines duration for which a station can transmit after acquiring token. 
Token rotation timer - It restarts after every token is seen.
Valid transmission timer - It is used to time out and recover from certain transient ring errors.

FDDI ring uses two fiber rings, one transmits clockwise and other counter clockwise, if one breaks up other uses as backup.

ASK , FSK and PSK are modulation techniques to transform digital data to analog. ASK - Amplitude Shifting Key, PSK - Phase Shifting Key and FSK- Frequency Shifting Key.