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Distributed Systems > chapter 4 > Flashcards

chapter 4 Flashcards

1
Q

Due to the absence of shared memory in distributed systems, how does communication occur?

A

processes build messages in their own address space and then execute system calls to send them

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2
Q

what is the drawback of the OSI model?

A
  • focuses on message passing only
  • unneeded functionality
  • violates access transparency
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3
Q

list and explain low-level layers?

A
  1. physical - bit implementation and transmission b/n sender and receiver.
  2. datalink - slices bits into frames for flow and error control
  3. network - describes packet routing
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4
Q

what is the lowest-level interface for many DS?

A

network layer

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5
Q

what is the transport layer in a DS?

A
  • provides actual communication facilities [ TCP UDP ]
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6
Q

what is the middleware layer in a DS?

A
  • provides common services and protocols to be used by d/t applications
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7
Q

give examples of services provided by the middleware layer?

A
  • un marshaling
  • naming - easy resource sharing
  • security
  • scaling - replication / caching
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8
Q

list types of communications.

A
  • transient, persistent, synchronous, async
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9
Q

what is a transient comm?

A

comm server discards messages if not received by receiver

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10
Q

what is persistent comm?

A

comm server stores messages until they are delivered

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11
Q

what is a sync comm?

A

sender is blocked until its request is accepted

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12
Q

_____________ aims at a high level persistent async comm?

A

message oriented middleware

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13
Q

well engineered procedures operate in ___________?

A

isolation / blackbox

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14
Q

_____________ is used to hide comm b/n caller and callee?

A

procedure call methods

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15
Q

what does wrapping a parameter mean?

A

transforming a value into bytes

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16
Q

what does packing parameters into messages mean?

A

parameter marshaling

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17
Q

which of the f.f assumption is false?

A. while a procedure is executing, parameter values should not be assumed
B. any data operated on is passed in by parameters
C. global data references can not be operated on
D. none

A

C

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18
Q

___________ is used to achieve access transparency?

A

remote reference mechanism

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19
Q

how can remote references be used in RPC?

A

passed in as parameters

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20
Q

what type of RPC comm gets rid of strict req / rep policy?

A
  • async, allows the client to continue without a reply from server
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21
Q

what is a deferred sync RPC?

A

client can perform non blocking requests just like async RPC

22
Q

what is the d/ce between async and deferred sync RPC?

A

async - a server reply is handled immediately when it arrives
deferred sync - the client can decide when it wants to poll the reply

23
Q

what is the issue with client-to-server binding?

A

client having to locate the server

24
Q

what is a message queueing system?

A

puts messages into and gets messages out of queues.

25
Q

what function calls are used in message queuing technique?

A

put - appends a message
get - block until queue is !null and remove first msg
poll - remove first msg, but never block
notify - when a msg is put

26
Q

what is a message broker?

A

a centralized component that homogenizes a MQ system.
transforms incoming msg to target format

27
Q

what type of routing does message broker provide?

A

subject-based

28
Q

message broker is considered a gateway to the application?

A

True

29
Q

what is an example of MOM?

A

IBM’s WebSphere MQ

30
Q

message transfer b/n queues is done through __________ ?

A

channels

31
Q

what are the responsibilities of a message channel agent?

A
  • (un) wrapping packets
  • creating channel connections [ tcp/ip ]
  • send / receive packets
32
Q

channels are _________ ?
A. bidirectional
B. unidirectional

A

B

33
Q

what type of comm exchange [ media ] do MOM, RMI and RPC support?

A

discreet, time independent

34
Q

what are characteristics of a continuous media?

A

time dependency
- audio
- video
- animation
- sensory data [ temp, pressure ]

35
Q

what is stream oriented comm [ SOC ]?

A

comm where timing plays a role

36
Q

what are the transmission methods in SOC?

A
  • async
  • sync
  • isochronous
37
Q

which transmission method in SOC defines maximum end-to-end delay?

A

sync

38
Q

which transmission method in SOC defines maximum and minimum end-to-end delay?

A

isochronous

39
Q

what is a maximum and minimum end to end delay called?

A

bounded jitter

40
Q

isochronous transmission mode is aka?

A

streams

41
Q

what are common characteristics of streams?

A
  • unidirectional
  • has a single source and a 1 or more sinks
  • either source or sink is a hardware wrapper
42
Q

list and describe types of stream?

A

simple - 1 type of data flow [ vid or audio ]
complex - multiple types of data flow [ stereo audio …]

43
Q

what is a jitter?

A

the maximum delay variance

44
Q

what QoSs need to be specified in streams?

A
  • max delay [ till session starts ]
  • max end-to-end delay [ until data makes it to receiver ]
  • jitter
  • max round trip delay
  • bit rate
45
Q

stream QoS is about _________ ?

A

A. timelines
B. volume
C. reliability

46
Q

what is link stress?

A

counts how often an application level multicasting msg crosses a physical link

47
Q

what is stress?

A

the ratio between ALM and network path.
application level multicasting

48
Q

what is an epidemic algorithm?

A

a protocol that spreads updates among peers

49
Q

what are the 2 forms of epidemics?

A
  • anti-entropy : each replica regularly exchanges state updates with another replica at random, until both have identical states
  • gossip : a contaminated replica tells some ignorant replicas about its update and contaminates them as well
50
Q

what is the run time of a push-pull node update exchange?

A

O(log(n))

Distributed Systems (7 decks)

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