Lectures

Question 1

What is the difference between packet-switched and circuit-switched networks?

Answer 1

Packet switching and circuit switching are two networking methods for transferring data between two nodes or hosts. For a packet-switched network, data is transferred by dividing the data into individual packets and passing it through the circuits to the other host. In packet-switched networks, the route is not exclusively determined when the packets hit the wire. Using routing algorithms, each packet may actually take a different route through the network to arrive at the destination host. Unlike a circuit-switched network where a static route is setup and pre-established prior to initializing connections to the host.

Question 2

What is the difference between a hub

and a switch?

Answer 2

The distinction seems to be that the hub is the place where data comes together and the switch is what determines how and where data is forwarded from the place where data comes together. Regarded in its switching aspects, a hub can also include a router.A router is often included as part of a network switch.The router is connected to at least two networks and decides which way to send each . A switch determines from the physical device (Media Access Control or MAC) address in each incoming message frame which output port to forward it to and out of.

Question 3

Completeness

Answer 3

Every crashed node is eventually suspected

by all correct nodes

Question 4

Accuracy

Answer 4

•strong
– no correct node is ever suspected by any node
• weak
– there exists a correct node that is never…
• eventually strong/weak:
– there is a time after which

Question 5

Call by Value

Answer 5

If data is passed by value, the data is copied from the variable used in for example main() to a variable used by the function. So if the data passed (that is stored in the function variable) is modified inside the function, the value is only changed in the variable used inside the function.

Question 6

Call by Reference

Answer 6

If data is passed by reference, a pointer to the data is copied instead of the actual variable as is done in a call by value. Because a pointer is copied, if the value at that pointers address is changed in the function, the value is also changed in main function

Question 7

A linearization or consistent run is

Answer 7

is a run 
that describes transitions between 
consistent global states.
• A state S' is reachable from state S if there 
is a linearization from S to S

Question 8

Global states predict stable

Answer 8

if a predicate is true it remains

true for all reachable states.

Question 9

Global states predict non stable

Answer 9

if a predicate can become

true and then later become false

Question 10

Mutual exclusion

Answer 10

Decide who is to enter a critical

section

Question 11

Leader election

Answer 11

Decide who is to be the new leader.

Question 12

Atomic multicast

Answer 12

Which messages, and in which

order, should be delivered.

Question 13

critical section

Answer 13

is a piece of code that accesses a shared resource that must not be concurrently accessed by more than one thread of execution

Question 14

Liveness

Answer 14

Something good eventually will happen

Question 15

Safety

Answer 15

Promise that nothing bad happens

Question 16

Completeness

Answer 16

if a node crashes then there
is a view that eventually is installed where the
node is not included

Question 17

Accuracy

Answer 17

if a node installs a view that does
not include a process then the process has
crashed (or will at least be treated as crashed)

Question 18

Agreements

Answer 18

If two nodes install their views at any moment, then these views are the same