3 - Communication

Question 1

What do communication protocols achieve?

Answer 1

• Formalises rules of communication
• Agreement on how data are transmitted

Question 2

Layered Protocol

Answer 2

• Each layer adds a header(/trailer)
• Virtually independent

Question 3

OSI Model stands for…?

Answer 3

Open Systems Interconnection

Question 4

What is the OSI model?

Answer 4

Communication organised in seven layers
Each layer has its own protocols

Question 5

What does the physical layer do?

Answer 5

How bits are transmitted over hardware.
Uses line codes

Question 6

Line codes

Answer 6

Return to zero
Manchester

Question 7

What is the data link layer responsibble for?

Answer 7

Data integrity

Question 8

Data link layer summary

Answer 8

• local delivery of frames
• Logical link control
• Media access control

Question 9

Data link layer protocols

Answer 9

• Ethernet,
• Address Resolution Protocol (ARP)

Question 10

What does Network layer do?

Answer 10

Route packets

Question 11

Network Layer summary

Answer 11

• Host addressing
• Routing, message forwarding

Question 12

Network Layer protocols

Answer 12

IP

Question 13

What does Transport Layer do?

Answer 13

Establlishes connection

Question 14

Transport layer summary

Answer 14

Connection-oriented or connectionless
Packet order, reliability, process addressing

Question 15

Transport layer protocols

Answer 15

Transmission Control Protocol
User Datagram Protocol
Real-time Transport Protocol

Question 16

What does Session layer manage?

Answer 16

Sessions between appplications

Question 17

Session layer summary

Answer 17

• Control and sync or message exchange
• Authentication/authorisation
• Checkpointing/recovery

Question 18

Session layer protocols

Answer 18

RPC
Password Authentication Protocol

Question 19

Presentation layer summary

Answer 19

• Encodings, definition of datasets
• Data conversion, compression, encryption

Question 20

Presentation layer protocols

Answer 20

External Data Representation (EDR)

Question 21

Application layer summary

Answer 21

• Data input/output
• Services for applications

Question 22

APplication layer protocols

Answer 22

FTP
HTTP
DNS
SMTP

Question 23

Middleware Protocol types

Answer 23

• Communication
• (Un)marshalling of data
• Naming
• Security
• Scaling mechanisms

Question 24

Transient vs Persistent

Answer 24

Transient - discarded if not delivered
Persistent - Buffered

Question 25

Async vs sync

Answer 25

Async - Sender continues immediately Sync - Sender blocked until response

Question 26

Discrete vs Streaming

Answer 26

Discrete - individual - not dependent on arrival time Streaming - Depends on arrival time - Intervals between packets important

Question 27

Message Passing Interface | What is it used in and why?

Answer 27

Parallel High Performance computing Sockets are not optimised enough

Question 28

What assumption is made with MPI?

Answer 28

All communication partners are known No fault tolerance

Question 29

RPC

Answer 29

Remote Procedure Call. Call as though it is local.

Question 30

RPC process

Answer 30

1. Client call. Handled by stub (alike to remote object) 2. stub builds message and calls local OS 3. OS sends message to remote 4. remote os gives to server stub 5. Server stub unpacks method call and parameters then calls. 6. Performs call and returns 7. Packs into message and calls OS 8. Server OS sends message back 9. back to client stub 10. CLient stub unpacks result and returns

Question 31

RPC Parameter passing issues

Answer 31

Must agree on encoding Pass by reference not possible - must be marshalled

Question 32

Solution to RPC interface description issue

Answer 32

Use generic language to describe interface - Interface Definition Langu

Question 33

IDL file

Answer 33

Contains unique interface ID and an interface description of the remote procedure and parameters

Question 34

IDL compiler

Answer 34

Outputs a header.h header file, the client stub and server stub code

Question 35

When binding RPC, the server must be...?

Answer 35

Server must be registered and prepared

Question 36

Message oriented middleware

Answer 36

Persistent async (compared to synchronous transient RPC) Messages in queues Transmission may take longer Additional features - Fault tolerance - Load balancing - Multicasting

Question 37

What separates a message broker from a simple queue?

Answer 37

Simple queues require agreement on messaging protocol. Broker can convert data

Question 38

Give some non-lecture examples of structured and attribute based names

Answer 38

Post addresses (structured). Students in a database (attribute)