Week 9 - Reliable Links

Question 1

State the 3 properties of fair loss

Answer 1

If message m is sent an infinite amount of times then it will be delivered an infinite amount of times
If message m is sent a finite amount of times then it will be delivered a finite amount of times
No message is delivered unless it is sent

Question 2

State the 2 properties of stubborn links

Answer 2

If process i sends a message m to a correct process j and i does not crash then j takes delivery of m an infinite amount of times
No message is delivered unless it is sent

Question 3

State the 3 properties of a reliable link

Answer 3

Every message sent by i to j is eventually delivered to j
No message is delivered to a process more than once
No message is delivered unless it was sent

Question 4

What are the timing assumptions for a synchronous system?

Answer 4

The time it takes for a process to execute a step is bounded and known
There is a known upper bound on the time it takes for a message to be received
The drift between local clock and the global real time clock is bounded and known

Question 5

What are the timing assumptions for an asynchronous system?

Answer 5

There are none

Question 6

What are the timing assumptions for a partially synchronous system?

Answer 6

Timing bounds eventually hold (but you never know when)

Question 7

Failure detectors

Answer 7

A distributed oracle that provides processes with suspicions about crashed processes

Question 8

State the 2 properties of a perfect failure detector

Answer 8

Eventually every process that crashes is permanently detected by every correct process
No process is detected by any process before it crashes