3-communication

Question 1

What is Latency?

Answer 1

Response time - affected by physical distance

Question 2

What is Bandwidth?

Answer 2

Volume of data transmitted per unit time. Important for large files.

Question 3

What is the formula for total transfer time?

Answer 3

Total transfer time = (size / bandwidth) + latency

Question 4

Name the 7 OSI layers top to bottom.

Answer 4

Application, Presentation, Session, Transport, Network, Data Link, Physical.

Question 5

What is the Application layer?

Answer 5

User-facing protocols: HTTP

Question 6

What is the Presentation layer?

Answer 6

Formatting and encryption: SSL

Question 7

What is the Session layer?

Answer 7

Connections: RPC.

Question 8

What is the Transport layer?

Answer 8

Delivery: TCP

Question 9

What is the Network layer?

Answer 9

Routing: IP.

Question 10

What is the Data Link layer?

Answer 10

Node-to-node transfer: Ethernet

Question 11

What is the Physical layer?

Answer 11

Medium: cables

Question 12

How does the OSI model work with messages?

Answer 12

Application creates message

Question 13

Why doesn’t OSI fit distributed systems well?

Answer 13

We need middleware layer between application and transport for location transparency and high-level communication.

Question 14

What is Synchronous communication?

Answer 14

Sender blocks/waits until reply. Tight coupling. Both must be active.

Question 15

What is Asynchronous communication?

Answer 15

Sender continues immediately. Loose coupling. Receiver processes when available.

Question 16

What is Transient communication?

Answer 16

Message only stored while sender and receiver running. Discarded if receiver not available.

Question 17

What is Persistent communication?

Answer 17

Message stored until delivered. Middleware stores in queue. Guaranteed delivery.

Question 18

Give example of Transient Synchronous.

Answer 18

RPC - both active

Question 19

Give example of Transient Asynchronous.

Answer 19

UDP - fire and forget

Question 20

Give example of Persistent Asynchronous.

Answer 20

Message queueing (MOM) - sender continues

Question 21

What is an RPC Stub?

Answer 21

A proxy that represents remote procedure and hides all networking from programmer.

Question 22

What are the steps of RPC?

Answer 22

1. Client calls stub, 2. Stub marshals params, 3. Client OS sends, 4. Server OS receives, 5. Server stub unmarshals, 6. Server executes, 7. Stub marshals result, 8. OS sends back, 9. Client stub unmarshals, 10. Returns to client.

Question 23

What is Marshalling?

Answer 23

Converting parameters into a byte stream for transmission.

Question 24

What is Big-Endian byte ordering?

Answer 24

Most significant byte first. Used by SPARC

Question 25

What is Little-Endian byte ordering?

Answer 25

Least significant byte first. Used by Intel x86.

Question 26

How do systems handle different byte ordering?

Answer 26

Agree on standard format (big-endian). Sender and receiver convert to/from this.

Question 27

What is Serialisation?

Answer 27

Converting object state into a format that can be transmitted. Binary (protobuf) or text (JSON

Question 28

What is Asynchronous RPC?

Answer 28

Client sends request and continues. Server processes in background. For when immediate result not needed.

Question 29

What is RMI?

Answer 29

Remote Method Invocation - RPC for object-oriented programming. Call methods

Question 30

How does RMI differ from RPC?

Answer 30

RPC: call functions, pass data, procedural. RMI: call object methods, pass object refs, OOP.

Question 31

What is a Socket?

Answer 31

Low-level communication endpoint for transient messaging.

Question 32

How do connection-oriented sockets work?

Answer 32

Client creates socket, server creates/binds/listens, client connects, server accepts, data exchanged, connections closed.

Question 33

What is MPI?

Answer 33

Message Passing Interface - standard interface for parallel computing

Question 34

Why was MPI created?

Answer 34

Many companies had proprietary libs - wasn't portable. MPI standardised it.

Question 35

What does MPI_bsend do?

Answer 35

Buffer send - copies to local buffer

Question 36

What does MPI_send do?

Answer 36

Standard send - blocks until message safely stored.

Question 37

What does MPI_recv do?

Answer 37

Receive - blocks until message arrives.

Question 38

What does MPI_irecv do?

Answer 38

Non-blocking receive - check without waiting.

Question 39

What is Message Queueing?

Answer 39

Messages stored in queues at communication servers. Persist until delivered. Solution to RPC limitations.

Question 40

What are the 4 Message Queue operations?

Answer 40

Put (add, non-blocking), Get (remove, blocks), Poll (check, don't block), Notify (register callback).

Question 41

What is AMQP?

Answer 41

Advanced Message Queueing Protocol - standard for message-oriented middleware.

Question 42

Name examples of message queue systems.

Answer 42

RabbitMQ, ActiveMQ, OpenStack.

Question 43

What is the hierarchy of communication technologies?

Answer 43

1. Sockets (lowest), 2. MPI (specialised for HPC), 3. RPC/RMI (mid-level, synchronous), 4. MOM (high-level, async, persistent).