COMP212 - Distributed Systems UPDATED
ACTUAL Exam Questions and CORRECT
Answers
What is a distributed system? - CORRECT ANSWER - A collection of independent
computers that appears to its users as a single coherent system
What are some main goals of distributed systems? - CORRECT ANSWER - Transparency
Openness
Reliability
Performance
Scalability
Connect users & resources
What is a transparent distributed system? - CORRECT ANSWER - It appears to its users
as if it were only a single computer system
What is a scalable distributed system? - CORRECT ANSWER - One that is capable of
growing
List some graph topologies - CORRECT ANSWER - Ring
Tree
Complete network
What is an undirected network - CORRECT ANSWER - A network that you can go in
either direction down along an edge
What is a directed network - CORRECT ANSWER - A network that you can only go in the
specified direction down along an edge
,What are the 4 steps of a synchronous round? - CORRECT ANSWER - 1. all nodes read
incoming messages
2. all nodes update their state
3. all nodes generate new messages and put them in transit
4. all messages are transmitted over the channels and the next round begins
Which step(s) of a synchronous round are handled locally? - CORRECT ANSWER - 1, 2,
3
Which step(s) of a synchronous round are handled by the network? - CORRECT
ANSWER -4
What are two algorithms used for leader election in directed ring networks? - CORRECT
ANSWER - LCR
HS
What are a few ways we measure the performance of a distributed algorithm? - CORRECT
ANSWER - Time Complexity (#rounds required)
Space Complexity (memory used)
Communication Complexity ( total #messages transmitted, size of messages)
What is the time complexity of LCR? - CORRECT ANSWER - n rounds
What is the worst case communication complexity of LCR? - CORRECT ANSWER -
O(n^2) messages
What algorithm can we use to elect a leader in a general network? - CORRECT
ANSWER - Flooding/FloodMax
, How does LCR work? - CORRECT ANSWER - all nodes send their initial id clockwise
upon receiving an incoming id, compare it to your own
-if incomingID > ownID, forward incomingID
-if incomingID < ownID, discard incomingID
-if incomingID = ownID, declare self leader
What is the diameter of a network - CORRECT ANSWER - the greatest shortest path
between nodes
How does FloodMax work? - CORRECT ANSWER - diameter = D
all processors store the greatest id that they have seen
in every round send the greatest id to all out-neighbours
after D rounds compare the greatest stored id and own id, if the are equal declare self the leader
What is the time complexity of FloodMax? - CORRECT ANSWER - O(D+1)
What is the communication complexity of FloodMax? - CORRECT ANSWER - D*m
m is the number of direct links in the network
What type of protocol is IP? - CORRECT ANSWER - network protocol
What type of protocol is TCP? - CORRECT ANSWER - transport protocol
What type of protocol is HTTP? - CORRECT ANSWER - application protocol
ACTUAL Exam Questions and CORRECT
Answers
What is a distributed system? - CORRECT ANSWER - A collection of independent
computers that appears to its users as a single coherent system
What are some main goals of distributed systems? - CORRECT ANSWER - Transparency
Openness
Reliability
Performance
Scalability
Connect users & resources
What is a transparent distributed system? - CORRECT ANSWER - It appears to its users
as if it were only a single computer system
What is a scalable distributed system? - CORRECT ANSWER - One that is capable of
growing
List some graph topologies - CORRECT ANSWER - Ring
Tree
Complete network
What is an undirected network - CORRECT ANSWER - A network that you can go in
either direction down along an edge
What is a directed network - CORRECT ANSWER - A network that you can only go in the
specified direction down along an edge
,What are the 4 steps of a synchronous round? - CORRECT ANSWER - 1. all nodes read
incoming messages
2. all nodes update their state
3. all nodes generate new messages and put them in transit
4. all messages are transmitted over the channels and the next round begins
Which step(s) of a synchronous round are handled locally? - CORRECT ANSWER - 1, 2,
3
Which step(s) of a synchronous round are handled by the network? - CORRECT
ANSWER -4
What are two algorithms used for leader election in directed ring networks? - CORRECT
ANSWER - LCR
HS
What are a few ways we measure the performance of a distributed algorithm? - CORRECT
ANSWER - Time Complexity (#rounds required)
Space Complexity (memory used)
Communication Complexity ( total #messages transmitted, size of messages)
What is the time complexity of LCR? - CORRECT ANSWER - n rounds
What is the worst case communication complexity of LCR? - CORRECT ANSWER -
O(n^2) messages
What algorithm can we use to elect a leader in a general network? - CORRECT
ANSWER - Flooding/FloodMax
, How does LCR work? - CORRECT ANSWER - all nodes send their initial id clockwise
upon receiving an incoming id, compare it to your own
-if incomingID > ownID, forward incomingID
-if incomingID < ownID, discard incomingID
-if incomingID = ownID, declare self leader
What is the diameter of a network - CORRECT ANSWER - the greatest shortest path
between nodes
How does FloodMax work? - CORRECT ANSWER - diameter = D
all processors store the greatest id that they have seen
in every round send the greatest id to all out-neighbours
after D rounds compare the greatest stored id and own id, if the are equal declare self the leader
What is the time complexity of FloodMax? - CORRECT ANSWER - O(D+1)
What is the communication complexity of FloodMax? - CORRECT ANSWER - D*m
m is the number of direct links in the network
What type of protocol is IP? - CORRECT ANSWER - network protocol
What type of protocol is TCP? - CORRECT ANSWER - transport protocol
What type of protocol is HTTP? - CORRECT ANSWER - application protocol
