The Physical Layer and the Data Link Layer
University Of the People
CS 2204 Communications and Networking
Professor Charles Yaacoub
06 July 2022
, 1. What do you understand by The Hidden Node Problem? Describe 2 different
spatial configurations which exemplify this issue.
One popular transmission issue in networking is known as the Hidden Node Problem.
This happens when a one transmitter incorrectly determines a free channel because it
is physically unable to detect signals sent by other senders that are beyond its range. It
transmits to a third node despite its inability to distinguish other nodes (the ”hidden
nodes”), which leads to collision (The Hidden Terminal Problem, n.d.).
Let’s examine the following configurations to illustrate the issue:
In one instance, two distant stations are not within reach of each other.
Another station is located in the centre, which indicates that it is within the
range of both other stations. Due to their distance, the outside stations could
concurrently try to communicate with the central station. A hidden-node
collision occurs in this scenario, preventing the intermediate station from
receiving any useful communication.
In a separate situation, two stations become concealed when a physical barrier,
such as environmental variables, prohibits communication between them,
making them hidden.
2. What is the 4B/5B encoding for the 3-byte (ASCII) string “Sun”?
The 3-byte (ASCII) string “Sun” has the following 4B/5B encoding:
S 0101 0011 > 01011 10101
u 0111 0101 > 01111 01011
n 0110 1110 > 01110 11100
The complete Sun message will be: 01011 10101 0111101011 0111011100
University Of the People
CS 2204 Communications and Networking
Professor Charles Yaacoub
06 July 2022
, 1. What do you understand by The Hidden Node Problem? Describe 2 different
spatial configurations which exemplify this issue.
One popular transmission issue in networking is known as the Hidden Node Problem.
This happens when a one transmitter incorrectly determines a free channel because it
is physically unable to detect signals sent by other senders that are beyond its range. It
transmits to a third node despite its inability to distinguish other nodes (the ”hidden
nodes”), which leads to collision (The Hidden Terminal Problem, n.d.).
Let’s examine the following configurations to illustrate the issue:
In one instance, two distant stations are not within reach of each other.
Another station is located in the centre, which indicates that it is within the
range of both other stations. Due to their distance, the outside stations could
concurrently try to communicate with the central station. A hidden-node
collision occurs in this scenario, preventing the intermediate station from
receiving any useful communication.
In a separate situation, two stations become concealed when a physical barrier,
such as environmental variables, prohibits communication between them,
making them hidden.
2. What is the 4B/5B encoding for the 3-byte (ASCII) string “Sun”?
The 3-byte (ASCII) string “Sun” has the following 4B/5B encoding:
S 0101 0011 > 01011 10101
u 0111 0101 > 01111 01011
n 0110 1110 > 01110 11100
The complete Sun message will be: 01011 10101 0111101011 0111011100
