CS2302-COMPUTERNETWORKS

29. What is the purpose of hamming code?

A hamming code can be designed to correct burst errors of certain lengths. So the simple strategy used by the hamming code to correct single bit errors must be redesigned to be applicable for multiple bit correction.

30. What is redundancy?

It is the error detecting mechanism, which means a shorter group of bits or extra bits may be appended at the destination of each unit.

31. Define flow control?

Flow control refers to a set of procedures used to restrict the amount of data. The sender can send before waiting for acknowledgment.

32. Mention the categories of flow control?

There are 2 methods have been developed to control flow of data across communication links. a) Stop and wait- send one from at a time. b) Sliding window- send several frames at a time.

33. What is a buffer?

Each receiving device has a block of memory called a buffer, reserved for storing incoming data until they are processed.

34.What is the difference between a passive and an active hub?

An active hub contains a repeater that regenerates the received bit patterns before sending them out. A passive hub provides a simple physical connection between the attached devices.

35.  For n devices in a network, what is the number of cable links required for a

mesh and ring topology?

·         Mesh topology – n (n-1)/2

·         Ring topology – n

Computer Networks - Unit 1

11. Explain the two types of duplex?

·         Full duplex-two bit streams can be simultaneously transmitted over the links at the same time, one going in each direction.

·         Half duplex-it supports data flowing in only one direction at a time.

12. What is CODEC?

            A device that encodes analog voice into a digital ISDN link is called a CODEC, for coder/decoder.

13. What is spread spectrum and explain the two types of spread spectrum?

            Spread spectrum is to spread the signal over a wider frequency band than normal in such a way as to minimize the impact of interference from other devices.

·         Frequency Hopping

Direct sequence

14. What are the different encoding techniques?

·         NRZ

·         NRZI

·         Manchester

·         4B/5B

15.  How does NRZ-L differ from NRZ-I?

In the NRZ-L sequence, positive and negative voltages have specific meanings: positive for 0 and negative for 1. in the NRZ-I sequence, the voltages are meaningless.

Instead, the receiver looks for changes from one level to another as its basis for recognition of 1s.