Computer Networks

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.

16. What are the responsibilities of data link layer?

Specific responsibilities of data link layer include the following. a) Framing b) Physical addressing c) Flow control d) Error control e) Access control.

17. What are the ways to address the framing problem?

·         Byte-Oriented Protocols(PPP)

·         Bit-Oriented Protocols(HDLC)

·         Clock-Based Framing(SONET)

18. Distinguish between peer-to-peer relationship and a primary-secondary relationship. peer -to- peer relationship?

            All the devices share the link equally.

Primary-secondary relationship: One device controls traffic and the others must transmit through it.

19. Mention the types of errors and define the terms?

            There are 2 types of errors

·         Single-bit error.

·         Burst-bit error.

Single bit error: The term single bit error means that only one bit of a given data unit (such as byte character/data unit or packet) is changed from 1 to 0 or from 0 to 1.

Burst error:  Means that 2 or more bits in the data unit have changed from 1 to 0 from 0 to 1.

20.  List out the available detection methods.

             There are 4 types of redundancy checks are used in data communication.

·         Vertical redundancy checks (VRC).

·         Longitudinal redundancy checks (LRC).

·         Cyclic redundancy checks (CRC).

                                    ·         Checksum.