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Distributed & Mobile Systems > Ch1 - Client-Server Systems > Flashcards

Ch1 - Client-Server Systems Flashcards

1
Q

Define a distributed system

A

A computer system consisting of multiple connected processors, where communication between them is achieved by passing messages.

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2
Q

What are three main issues which affect distributed systems?

A

DELAYS – No global clock
FAILURES – must be fail-safe
SECURITY ATTACKS

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3
Q

Distributed Systems require sophisticated tools, give 3 reasons why:

A

No global clock
Highly concurrent
Required to be fail-safe

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4
Q

Give 4 kinds of distributed system

A

Internet
Intranet
Mobile (nomadic) network
Pervasive (ubiquitous) network

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5
Q

What is the special-case distributed system?

A

Parallel Computing

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6
Q

What makes parallel computing different to mainstream distributed systems? (5 points)

A
  • Not geographically separated,
  • Share processors rather than resources,
  • Not flexible
  • Less scaleable
  • Communicate through shared memory instead of messages
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7
Q

List 9 challenges in making a distributed system:

A 
Heterogenous components (HW & SW)
Must conform to open standards
Maintain security
Be scaleable
Handle wide variety of workloads
Fail-safe
Asynchronous
Handle conflicts
Location transparency
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8
Q

What are the 2 main distributed system architecture models?

A

Client-server

Peer-to-peer

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9
Q

Describe the Client-server architecture model:

A

A server offers a service over the network to one or more clients. The (HW/SW) capabilities of the server usually exceed the client.

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10
Q

Describe tho Peer-to-peer architecture model:

A

There are no distinguishing differences in the SW between each process on the network. Peers work cooperatively to provide the service & may have different resources.

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11
Q

Give 7 D.S. architecture model variations:

A

Partitioning/Replicating data (fail-safe)
Proxy Servers (cache data)
Mobile/Client code (applets)
Thin Client
Fat Client
Spontaneous Interoperation (discover & connect)
Index/Coordination Servers (on P2P)

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12
Q

List 5 types of network:

A 
Personal Area Ntwk
Local Area Ntwk
Metro Area Ntwk
Wide Area Ntwk
Internetwork (internet)
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13
Q

Give 2 reasons why messages are broken into packets:

A
  • allows information to take multiple routes

- communications aren’t clogged by a single message

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14
Q

List the seven layers of the OSI model

A 
Application
Presentation
Transport
Session
Network
Data-link
Physical
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15
Q

Which OSI layer does internet protocol (IP) work on?

A

Network Layer

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16
Q

Which two protocols build on IP at the transport layer?

A

TCP

UDP

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17
Q

The Application Layer protocol: http uses which transport protocol?

A

TCP

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18
Q

The Application Layer protocol: smtp uses which transport protocol?

A

TCP

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19
Q

The Application Layer protocol: ftp uses which transport protocol?

A

TCP

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20
Q

The Application Layer protocol: VoIP uses which transport protocol?

A

UDP

21
Q

The Application Layer protocol: DNS uses which transport protocol?

A

DNS is a router protocol, so it uses UDP

22
Q

What kind of transfers use the user datagram protocol?

A

Video streaming, VoIP and router protocols such as DNS & ARP.

23
Q

What kind of transfers use the transmission control protocol?

A

file, email and web browser transfers (e.g. ftp, http, smtp)

24
Q

What are the two main characteristics of UDP and why is it used?

A
  1. Fast, but;
  2. unreliable data transfer
    Used where speed is essential (routers) or large files won’t miss small losses (video or voice).
25
Q

What are the two main characteristics of TCP and why is it used?

A
  1. Reliable, but;
  2. Slow
    Used when integrity of data transferred is essential.
26
Q

Which transport layer protocol uses handshaking?

A

TCP

27
Q

Which transport layer protocol uses IP packets and sequencing?

A

TCP

28
Q

What kind of packets does UDP break info into?

A

Datagram packets

29
Q

Which has the shorter header - TCP or UDP?

A

UDP

30
Q

Which transport layer protocol uses acknowledgements?

A

TCP

31
Q

Which transport layer protocol does not use congestion control?

A

UDP

32
Q

What OSI layer is is http

A

Application

33
Q

Application Layer protocols are typically built on which transport protocols?

A

TCP & UDP

34
Q

Give three types of Application Layer protocols

A
  • Request
  • Request-Reply
  • Request-Reply-Acknowledge
35
Q

Describe an http request

A

A Series of ASCII strings containing method details and data

36
Q

Describe http GET method

A

Used to retrieve a resource as specified in the URL

37
Q

Describe http POST method

A

Used to retrieve a resource as specified in the method body

38
Q

Give the 7 http methods

A

GET – DELETE
POST – OPTIONS
PUT – TRACE
HEAD

39
Q

Where is info placed in an http GET method, and what is the advantage of this?

A

Info from forms is placed into the URL

  • placed after a ? Character
  • “variable=value” format
40
Q

Where is info placed in an http POST method and what is the advantage?

A

Info is placed in the method body, making it more difficult to access. This is both an advantage and a disadvantage.

41
Q

2 disadvantages of http being STATELESS

A
  • doesn’t maintain info about each connection

- can’t tell if request is from an earlier or new client (IP addresses are temporary)

42
Q

Why are cookies used in http

A

Http is stateless

Cookies hold a unique ID for the client, held by the client

43
Q

What are 3 solutions for http’s STATELESS disadvantages?

A
  • Cookies
  • URL rewriting
  • Hidden Form Fields
44
Q

What protocol is RMI typically built on?

A

TCP

45
Q

What is the purpose of RMI?

A

Hides network protocols such as sockets and streams, allowing it to appear as though processes are running on the same machine

46
Q

What is a proxy stub and what does it do?

A

An RMI component which represents a remote Object, it forwards serialised messages to the actual object for processing

47
Q

Describe the RMI Registry

A
  • Stores available remote objects,
  • Can look them up via a unique String identifier
  • listens on port 1099
48
Q

Give the 8 steps for RMI implementation

A 
1 define remote interface
2 Implement remote object
3 (from server) export remote object
4 implement client
5 use proxy stub in client
6 start RMI Registry server
7 start server and code base
8 start clients

Distributed & Mobile Systems (2 decks)

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