Question

1. What do you understand by The Hidden Node Problem? Describe 2 different spatial configurations which exemplify this issue.
2. What is the 4B/5B encoding for the 3-byte (ASCII) string “Sun”?
3. What is the 16-bit internet checksum for the 3-byte binary message 00110001 00110010 00110011?
4. Suppose a message is 11011000. What is the CRC checksum using the polynomial corresponding to 1011 to give a 3-bit answer? (Show the solution steps, not just the answer).
5. What is Time Domain Reflectometry?

Answer 1

1.

In wireless LANs ( wireless local area networks), the hidden terminal problem is a transmission problem that arises when two or more stations who are out of range of each other transmit simultaneously to a common recipient. This occurs when a station is visible from a wireless access point (AP), but is hidden from other stations that communicate with the AP.

2.

4B/5B encoding is a type of 'Block coding'. This processes groups of bits rather than outputting a signal for each individual bit . A group of 4 bits is encoded so that an extra 5th bit is added. Since the input data is taken 4-bits at a time, there are 2^4, or 16 different bit patterns. The encoded bits use 5-bit, and hence have 2^5 or 32 different bit patterns.

3. Checksum

4.

Cyclic Redundancy Check

5.

A Time Domain Reflectometry is a key diagnostic technique for high-speed digital circuit systems. It begins with system energy pulse signals transmitted to conductors. Subsequent reflected energy is then observed. Transmission variance detection is enabled by studying reflection shape, magnitude and duration.