– CEG3185[Z] Intro Data Comm. & Networking University of Ottawa
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Question 1
Using the following generator (1100101) or (x6+x5+x2+1) encode the following message: 101011. (Format: just use binary, e.g. 1010…)
Question 2
need to use synchronous TDM and combine 15 digital sources, each of 5
Mbps. Each output slot carries 1 bit from each digital source, but one
extra bit is added to each frame for synchronization.
1) What is the size of an output frame in bits? ____
2) What is the output frame rate? ____ frame/sec
3) What is the duration of an output frame? ____ sec
4) What is the output data rate? ____ bps
Answer for blank # 1: 16 (25 %)
Answer for blank # 2: 5,000,000 (5000000)
Answer for blank # 3: 0.000002 (.0000002, 0.0000002)
Answer for blank # 4: 8,000,000 (80000000, 80 Mbps)
Question 3 =
How many bits per baud can we send in case the signal constellation has 64 number of points?
Question 4
Selective Repeat algorithm is less efficient than Go-Back-N algorithm when the round trip delay of the network is very large
Question 5 1 / 2 points
Assume we need to design a Selective-Repeat sliding-window protocol for a network in which the bandwidth is 1 Gbps and the average distance between the sender and receiver is 1,000 km. Assume the average packet size is 10,000 bits and the propagation speed in the media is 2 × 108 m/s.
We can define the bandwidth-delay product in a network as the number of packets that can be in the pipe during the round-trip time (RTT).
1) The bandwidth-delay product of the average link is: ____ packets
2) The number of bits used for sequence number is: ____ bits (Hint: use the bandwidth-delay product to derive the max window size)
(Format: use plain numbers only)
Question 6 1 / 1 point
The size of the ARP packet is fixed.
Question 7 0 / 1 point
channels are multiplexed using Statistical Time-Division Multiplexing.
The channels bit rates is: 1, 1, 2, 2, 3, 3, 4, 4 Kbps. If channels
packs 12bit of data every time, followed by the channel ID., then the
effective data rate is given by: ____ Kbps.
Question 8 0 / 2 points
A CRC checker is using the generator 10011 (x4+x+1)
received the following message: 10111101. The syndrome (remainder) to
determine if the the message was OK is given by: ____. (Format: just use
binary, e.g. 10…)
Question 9 0 / 1 point
CSMA/CD, if the propagation delay in a broadcast network is 10 μs and
the frame transmission time is 5 μs, then the collision be detected no
matter where it occurs.
Question 10 0 / 1 point
A coding scheme has the following relationship between the number of redundant bits and the minimum distance between code words:
Extra Bits
The minimum number of extra bits required to guarantee detection of 2 bit errors is: ____
Question 11
in a slotted Aloha network send frames of size 5000 bits at the rate of
2 Mbps. The vulnerable time for this network is given by ____
milliseconds.
Question 12
a protocol that uses 6 bits for the sequence-number field, if a packet
has the sequence number x, how many packets need to be sent to see a
packet with the same sequence number x, assuming that each packet is
assigned one sequence number?
Question 13
a network using the Selective-Repeat protocol with m = 4 and the
sending window of size 8, the value of variables are Sf = 72, Sn = 77,
and Rn = 74. Packet 75 has already been acknowledged at the sender site;
packets 75 and 76 are received out-of-order at the receiver site.
Assume that the network does not duplicate the packets. Match the packet
sequence number with the packet state. Note: the sequence number provided is boundless counter, the counter field in the packet is modulo 16.
1. Not Sent
2. Sent, but not received
3. Sent, received, but pending Acknowledge
4. Sent, received and Acknowledged
Question 14
the Clear-to-send (CTS) message was lost, then the following sequence
of events will occur. (order the events in the proper order)
__3__ (4) Carrier Sense the medium
__2__ (1) Timeout will occur
__1__ (3) Wait for a back-off period TB
__4__ (2) Number of attempts (K) is incremented
Question 15
a wireless LAN, if station A is assigned IFS = 15 milliseconds and
station B is assigned IFS = 8 milliseconds, then station A has a higher
Question 16 1 / 1 point
We can say whether a signal is periodic or aperiodic by just looking at its frequency domain plot.
Question 17 1 / 1 point
CDMA system of 4 nodes are using the following chips {[1,1,1,1],
[1,-1,1,-1],[1,1,-1,-1], [1,-1,-1,1] for stations A, B, C, D,
respectively, If a receiver receives the sequence [0,0,4,0], then the
bit sent by station D is: ___
station is idle
Question 18 0 / 2 points
pure ALOHA network transmits 5000-bit frames on a shared channel of 20
Mbps. If the system produces 1000 frames per second, then the system
throughput is given by ____ frames/second (round to the nearest integer)
Answer: 338 (152, 151)
Question 19 1 / 1 point
The hamming distance between 0xF345 and 0xB215 is: ____
Question 20 1 / 1 point
The address resolution protocol (ARP) reply is a ____ message.
Overall Grade (highest attempt):
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