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CSSE4004 - Lecture 5
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Questions in this quiz (16)
1Which of the following is false about the Repulsion forces approach in large scale coordinator election
- Aeach token is “repulsed” by nearby tokens (token holder sends token to another peer if too many tokens nearby)
- Btoken must be held by a node for a set time period before node can become superpeer
- Ceach node holding a token learns about other tokenholders
- Da superpeer which receives another token sends it to the lowest prime numbered neighbour
2How can a coordinator failure be addressed in a centralised mutual exclusion system?
- ABy using election algorithms to change the coordinator
- BBy using triple modular redundancy to compare the results of two coordinators
- CBy emitting a heartbeat that informs other nodes when the coordinator cannot provide a lock
- DBy moving the coordinator periodically to the next node in the token ring
3Which of these is not a drawback of a typical distributed mutual exclusion algorithm?
- Alarge number of messages required
- Bone slow process slows down others
- Cmore points of failure
- Dlocks may be granted unfairly
4Which of the following is true about Lamport's algorithm
- Awhen a message is received, its time is compared against the local clock. If the local clock is less than C(b), it is set to C(b) + 1
- Bmessages carry their sending time according to the receiver's clock e.g., C(b)
- Cbetween any two events, the clock must tick at least twice (i.e. one on the transmitting side, one on the receiving side)
- DEvents occurring in processes that do not interact (even indirectly through third parties) are said to be concurrent
5In the bully algorithm with nodes 1,2,3,4,5,6,7 if 7 is the coordinator and 4 notices the coordinator has crashed, who will be the new coordinator?
- A6
- B4
- C1
- D7 after it reboots
6Which of the following is false about wireless network clock synchronisation algorithms
- AClock synchronisation is difficult because nodes cannot always contact one another
- BNodes are resource-constrained
- CReceivers record difference between reference message timestamp and their own clock
- DThe coordinating node must transmit at a higher power level to ensure all nodes can receive clock broadcasts
7Which of the following is false about Lamport's algorithm?
- Aif a and b are events in the same process, and a occurs before b, then a - > b is true
- Bif a is the event of a message being sent by one process, and b is the receipt of that message in another process, then a ->b is also true
- Ca -> b and b -> c, then a -> c
- Dif a is the event of a message being sent by one process, and b is the receipt of that message in another process, then b -> a is also true
8Which of these are clock synchronisation protocols
- ANetwork Time Protocol, The Berkeley Algorithm
- BNetwork Time Protocol, Town Clock Algorithm, The Berkeley Algorithm
- CUTC lock algorithm, NTP
- DNetwork Time Protocol, Town Clock Algorithm
9Which is true about NTP?
- AStands for Numerical Time Protocol
- BDaemon calculates new time based on average of reported values
- CIn general, synchronising with stratum-k server makes you stratum-k+1
- DStratum-1 servers typically have direct access to a reference clock
10What issue is addressed by a vector clock?
- ALamport’s algorithm does not capture causality
- BSometimes messages are received out of order
- CSometimes messages are created at precisely the same time
- DSometimes events must be recorded before an event which occurred after it
11Which is true about the Berkeley algorithm?
- AUses averaging approach to correct clocks
- BDaemon tells each node how to adjust its clock
- CServers are divided into strata reflecting the accuracy of their clocks
- DLower stratum servers are assumed to be more accurate => A will try to synchronise with B’s clock
12Which of the following is false about superpeers
- ALarge-scale systems may require many local coordinators, creating the need for superpeers
- BShould offer low-latency access to other superpeers
- CServe no more than a set number of regular nodes
- DCan be selected by reserving a fraction of the identifier space in a distributed hash table containing all nodes
13In the ring election algorithm with nodes 1,2,3,4,5,6,7 if 7 is the coordinator and 5 and 2 both notice which node becomes the new coordinator?
- A6
- B5
- C5 or 2
- D2
14In a token ring mutual exclusion algorithm, how does a node respond if it currently holds the resource?
- AThe token is passed on to the next node in the ring when it is finished accessing the shared resource
- BIt sends a message in the opposite direction back to the requester stating that it holds the lock
- CIt sends a message in the forward direction to the requester stating that it holds the lock
- DThe previous node sends a message back to the requester when it doesn't get a response from the node holding the resource
15In a regular distributed mutual exclusion system, how does a node reply if it currently holds the resource?
- AIt ignores the message
- BIt sends a NACK response
- CIt queues the message until it is finished with the resource then replies OK
- DIt replies to the next node in the token ring
16Which of these is not an advantage of centralised mutual exclusion?
- Aeasy to implement
- Blow message overhead
- Cfair (access requests are processed in order)
- Dimproves performance with high message volumes
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- CSSE4004 - Lecture 5
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- tb22
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- English
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- Created on 7 Jun 2015 · updated on 4 Mar 2016
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