Second Chapter

Question 1

Architecture of a System

Answer 1

Structure in terms of specified components aimed to be reliable, manageable, adaptable, and cost-effective.

Question 2

Middleware Layers

Answer 2

Includes Applications, OS, Middleware, Platform, and Hardware.

Question 3

Client-Server Model

Answer 3

Client requests services, server provides them.

Question 4

Two-Tier Architecture

Answer 4

UI and business logic on client, data layer on server.

Question 5

Three-Tier Architecture

Answer 5

Adds a middle server for translation, metering, or intelligent services.

Question 6

Null Client

Answer 6

Only captures input and forwards it to server, e.g., X-Terminal.

Question 7

Thin Client

Answer 7

UI separated from application logic, server handles most computation.

Question 8

Applet Client

Answer 8

Applets run on client, some business logic and data stored locally.

Question 9

Fat Client

Answer 9

Most or all application logic on client, server used mainly for storage.

Question 10

Mobile Code

Answer 10

Downloaded code executed locally, restricted in a sandbox.

Question 11

Transaction Monitor

Answer 11

Monitors and limits the number of simultaneous client requests.

Question 12

Proxy Server

Answer 12

Forwards client requests to the appropriate server.

Question 13

Broker

Answer 13

Returns address of a server offering a requested service.

Question 14

Trader

Answer 14

Selects server based on required service quality.

Question 15

Load Balancer

Answer 15

Distributes requests among multiple servers.

Question 16

Agent

Answer 16

Combines services from different servers for a client.

Question 17

Vertical Distribution

Answer 17

Different layers (UI, logic, data) on separate physical machines.

Question 18

Horizontal Distribution

Answer 18

Multiple replicas of services for load distribution.

Question 19

Peer-to-Peer Architecture

Answer 19

Nodes act as equals, sharing resources directly.

Question 20

Mobile Agent

Answer 20

Executable code that moves between systems to perform tasks.

Question 21

Mobile Devices

Answer 21

Devices that move across networks, causing dynamic associations.

Question 22

Responsiveness

Answer 22

How fast a system responds to user input.

Question 23

Throughput

Answer 23

How much work is done in a given time.

Question 24

Load Balancing

Answer 24

Distributing computational tasks across multiple nodes.

Question 25

Quality of Service (QoS)

Answer 25

Ensures timely and reliable service, e.g., for video streams.

Question 26

Caching and Replication

Answer 26

Improve performance and availability of data.

Question 27

Dependability

Answer 27

Includes correctness, fault tolerance, and security.

Question 28

Interaction Model

Answer 28

Describes process behavior and message passing.

Question 29

Latency

Answer 29

Time delay between message send and receive.

Question 30

Bandwidth

Answer 30

Amount of data that can be transferred over a network.

Question 31

Jitter

Answer 31

Variation in message delivery time.

Question 32

Clock Drift

Answer 32

Difference in clock time among computers.

Question 33

Synchronous System

Answer 33

Known bounds on processing and message delivery times.

Question 34

Asynchronous System

Answer 34

No assumptions about time or message delivery.

Question 35

Event Ordering

Answer 35

Tracking the order of events in distributed processes.

Question 36

Omission Failure

Answer 36

Missing messages or process crashes.

Question 37

Arbitrary Failure

Answer 37

Unexpected or incorrect behavior.

Question 38

Timing Failure

Answer 38

Response outside expected time.

Question 39

Masking Failure

Answer 39

Hiding or converting failures (e.g., with checksums).

Question 40

Security: Object Protection

Answer 40

Server checks user identity and access rights.

Question 41

Security Threats

Answer 41

Includes message spoofing, tampering, eavesdropping.

Question 42

Cryptography

Answer 42

Uses keys for secure communication and authentication.