chapter 4 Flashcards
Due to the absence of shared memory in distributed systems, how does communication occur?
processes build messages in their own address space and then execute system calls to send them
what is the drawback of the OSI model?
- focuses on message passing only
- unneeded functionality
- violates access transparency
list and explain low-level layers?
- physical - bit implementation and transmission b/n sender and receiver.
- datalink - slices bits into frames for flow and error control
- network - describes packet routing
what is the lowest-level interface for many DS?
network layer
what is the transport layer in a DS?
- provides actual communication facilities [ TCP UDP ]
what is the middleware layer in a DS?
- provides common services and protocols to be used by d/t applications
give examples of services provided by the middleware layer?
- un marshaling
- naming - easy resource sharing
- security
- scaling - replication / caching
list types of communications.
- transient, persistent, synchronous, async
what is a transient comm?
comm server discards messages if not received by receiver
what is persistent comm?
comm server stores messages until they are delivered
what is a sync comm?
sender is blocked until its request is accepted
_____________ aims at a high level persistent async comm?
message oriented middleware
well engineered procedures operate in ___________?
isolation / blackbox
_____________ is used to hide comm b/n caller and callee?
procedure call methods
what does wrapping a parameter mean?
transforming a value into bytes
what does packing parameters into messages mean?
parameter marshaling
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
C
___________ is used to achieve access transparency?
remote reference mechanism
how can remote references be used in RPC?
passed in as parameters
what type of RPC comm gets rid of strict req / rep policy?
- async, allows the client to continue without a reply from server
what is a deferred sync RPC?
client can perform non blocking requests just like async RPC
what is the d/ce between async and deferred sync RPC?
async - a server reply is handled immediately when it arrives
deferred sync - the client can decide when it wants to poll the reply
what is the issue with client-to-server binding?
client having to locate the server
what is a message queueing system?
puts messages into and gets messages out of queues.
what function calls are used in message queuing technique?
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
what is a message broker?
a centralized component that homogenizes a MQ system.
transforms incoming msg to target format
what type of routing does message broker provide?
subject-based
message broker is considered a gateway to the application?
True
what is an example of MOM?
IBM’s WebSphere MQ
message transfer b/n queues is done through __________ ?
channels
what are the responsibilities of a message channel agent?
- (un) wrapping packets
- creating channel connections [ tcp/ip ]
- send / receive packets
channels are _________ ?
A. bidirectional
B. unidirectional
B
what type of comm exchange [ media ] do MOM, RMI and RPC support?
discreet, time independent
what are characteristics of a continuous media?
time dependency
- audio
- video
- animation
- sensory data [ temp, pressure ]
what is stream oriented comm [ SOC ]?
comm where timing plays a role
what are the transmission methods in SOC?
- async
- sync
- isochronous
which transmission method in SOC defines maximum end-to-end delay?
sync
which transmission method in SOC defines maximum and minimum end-to-end delay?
isochronous
what is a maximum and minimum end to end delay called?
bounded jitter
isochronous transmission mode is aka?
streams
what are common characteristics of streams?
- unidirectional
- has a single source and a 1 or more sinks
- either source or sink is a hardware wrapper
list and describe types of stream?
simple - 1 type of data flow [ vid or audio ]
complex - multiple types of data flow [ stereo audio …]
what is a jitter?
the maximum delay variance
what QoSs need to be specified in streams?
- max delay [ till session starts ]
- max end-to-end delay [ until data makes it to receiver ]
- jitter
- max round trip delay
- bit rate
stream QoS is about _________ ?
A. timelines
B. volume
C. reliability
what is link stress?
counts how often an application level multicasting msg crosses a physical link
what is stress?
the ratio between ALM and network path.
application level multicasting
what is an epidemic algorithm?
a protocol that spreads updates among peers
what are the 2 forms of epidemics?
- 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
what is the run time of a push-pull node update exchange?
O(log(n))
