COSC 350 Midterm Exam Questions And
Answers
What is a communication protocol? what two aspects of communication does a
protocol specify?
1) Protocols specify the details of network communication.
2) A protocol specifies the format (syntax) and meaning (semantics) of messages
how headers are added and removed as data passes through a layered protocol
stack?
Each layer adds/removes its header to/from the packet and passes the resulting packet
to the layer below/above
If the maximum frequency audible to a human ear is 20,000 Hz, at what rate must
the analog signal from a microphone be sampled when converting it to digital?
The sampling rate = 2×fmax, so 2x20,000 = 40,000 Hz (i.e. 40,000 samples/sec)
Describe the difference between lossy and lossless compression.
Tell when each might be used.
Lossy compression: some data is lost when compressing (for loss-tolerant streams e.g.
video/audio).
Lossless compression: original data is preserved and recovered on decompression (for
loss-intolerant streams e.g. data files)
what three types of wiring are used to reduce interference form noise?
1)Coax, 2) unshielded/shielded twisted pair (UTP/STP),
3) optical fiber (carries light waves; is immune to electrical noise).
Can laser communication be used from a moving vehicle? Explain
Difficult since line-of-sight and precise alignment is needed
, How does one compute the minimum number of bit changes that can transform a
valid codeword into another valid codeword?
Hamming distance=# of bits in which two codewords differ. Compute dmin=min
Hamming distance among all pairs of codewords=min # of errors that can change a
valid codeword into another. Can detect at most (dmin-1) error
What is the chief characteristic of asynchronous transmission?
Data can arrive at any time with an arbitrary gap between data items
When using a synchronous transmission scheme, what happens when a sender
does not have data to send?
Start frame with a special sequence of bits for synchronization and transmit an idle byte
when there is no data.
In phase shift keying, is it possible to have a phase shift of 90°? of 270°? of 360°?
When modulating data, any phase shift can be used; 360-degree and 0-degree shifts
are the same (see slides).
Explain how a range of frequencies can be used to increase data rate.
Divide the frequency range into K carriers and send 1/K of the data on each carrier.
What type of multiplexing does ADSL use?
ADSL combines FDM with inverse multiplexing in a scheme known as DMT (Discrete
Multi Tone).
In the OSI 7-layer model, layer 3 is the network layer
(true or false)
T
UDP is a connection-oriented protocol
(true or false)
F
Voice packets in typical VoIP traffic use TCP instead of UDP
(true or false
)
F
TCP provides many-to-many communication
(true or false)
Answers
What is a communication protocol? what two aspects of communication does a
protocol specify?
1) Protocols specify the details of network communication.
2) A protocol specifies the format (syntax) and meaning (semantics) of messages
how headers are added and removed as data passes through a layered protocol
stack?
Each layer adds/removes its header to/from the packet and passes the resulting packet
to the layer below/above
If the maximum frequency audible to a human ear is 20,000 Hz, at what rate must
the analog signal from a microphone be sampled when converting it to digital?
The sampling rate = 2×fmax, so 2x20,000 = 40,000 Hz (i.e. 40,000 samples/sec)
Describe the difference between lossy and lossless compression.
Tell when each might be used.
Lossy compression: some data is lost when compressing (for loss-tolerant streams e.g.
video/audio).
Lossless compression: original data is preserved and recovered on decompression (for
loss-intolerant streams e.g. data files)
what three types of wiring are used to reduce interference form noise?
1)Coax, 2) unshielded/shielded twisted pair (UTP/STP),
3) optical fiber (carries light waves; is immune to electrical noise).
Can laser communication be used from a moving vehicle? Explain
Difficult since line-of-sight and precise alignment is needed
, How does one compute the minimum number of bit changes that can transform a
valid codeword into another valid codeword?
Hamming distance=# of bits in which two codewords differ. Compute dmin=min
Hamming distance among all pairs of codewords=min # of errors that can change a
valid codeword into another. Can detect at most (dmin-1) error
What is the chief characteristic of asynchronous transmission?
Data can arrive at any time with an arbitrary gap between data items
When using a synchronous transmission scheme, what happens when a sender
does not have data to send?
Start frame with a special sequence of bits for synchronization and transmit an idle byte
when there is no data.
In phase shift keying, is it possible to have a phase shift of 90°? of 270°? of 360°?
When modulating data, any phase shift can be used; 360-degree and 0-degree shifts
are the same (see slides).
Explain how a range of frequencies can be used to increase data rate.
Divide the frequency range into K carriers and send 1/K of the data on each carrier.
What type of multiplexing does ADSL use?
ADSL combines FDM with inverse multiplexing in a scheme known as DMT (Discrete
Multi Tone).
In the OSI 7-layer model, layer 3 is the network layer
(true or false)
T
UDP is a connection-oriented protocol
(true or false)
F
Voice packets in typical VoIP traffic use TCP instead of UDP
(true or false
)
F
TCP provides many-to-many communication
(true or false)
