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

Ch1 - Client-Server Systems Flashcards

(48 cards)

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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?

21
Q

The Application Layer protocol: DNS uses which transport protocol?

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A

DNS is a router protocol, so it uses UDP

22
Q

What kind of transfers use the user datagram protocol?

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A

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

23
Q

What kind of transfers use the transmission control protocol?

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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?

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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
What are the two main characteristics of TCP and why is it used?
1. Reliable, but; 2. Slow Used when integrity of data transferred is essential.
26
Which transport layer protocol uses handshaking?
TCP
27
Which transport layer protocol uses IP packets and sequencing?
TCP
28
What kind of packets does UDP break info into?
Datagram packets
29
Which has the shorter header - TCP or UDP?
UDP
30
Which transport layer protocol uses acknowledgements?
TCP
31
Which transport layer protocol does not use congestion control?
UDP
32
What OSI layer is is http
Application
33
Application Layer protocols are typically built on which transport protocols?
TCP & UDP
34
Give three types of Application Layer protocols
- Request - Request-Reply - Request-Reply-Acknowledge
35
Describe an http request
A Series of ASCII strings containing method details and data
36
Describe http GET method
Used to retrieve a resource as specified in the URL
37
Describe http POST method
Used to retrieve a resource as specified in the method body
38
Give the 7 http methods
GET -- DELETE POST -- OPTIONS PUT -- TRACE HEAD
39
Where is info placed in an http GET method, and what is the advantage of this?
Info from forms is placed into the URL - placed after a ? Character - "variable=value" format
40
Where is info placed in an http POST method and what is the advantage?
Info is placed in the method body, making it more difficult to access. This is both an advantage and a disadvantage.
41
2 disadvantages of http being STATELESS
- doesn't maintain info about each connection | - can't tell if request is from an earlier or new client (IP addresses are temporary)
42
Why are cookies used in http
Http is stateless | Cookies hold a unique ID for the client, held by the client
43
What are 3 solutions for http's STATELESS disadvantages?
- Cookies - URL rewriting - Hidden Form Fields
44
What protocol is RMI typically built on?
TCP
45
What is the purpose of RMI?
Hides network protocols such as sockets and streams, allowing it to appear as though processes are running on the same machine
46
What is a proxy stub and what does it do?
An RMI component which represents a remote Object, it forwards serialised messages to the actual object for processing
47
Describe the RMI Registry
- Stores available remote objects, - Can look them up via a unique String identifier - listens on port 1099
48
Give the 8 steps for RMI implementation
``` 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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