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Distributed Computing > 3 - Communication > Flashcards

3 - Communication Flashcards

1
Q

What do communication protocols achieve?

A
  • Formalises rules of communication
  • Agreement on how data are transmitted
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2
Q

Layered Protocol

A
  • Each layer adds a header(/trailer)
  • Virtually independent
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3
Q

OSI Model stands for…?

A

Open Systems Interconnection

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4
Q

What is the OSI model?

A

Communication organised in seven layers
Each layer has its own protocols

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5
Q

What does the physical layer do?

A

How bits are transmitted over hardware.
Uses line codes

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6
Q

Line codes

A

Return to zero
Manchester

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7
Q

What is the data link layer responsibble for?

A

Data integrity

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8
Q

Data link layer summary

A
  • local delivery of frames
  • Logical link control
  • Media access control
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9
Q

Data link layer protocols

A
  • Ethernet,
  • Address Resolution Protocol (ARP)
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10
Q

What does Network layer do?

A

Route packets

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11
Q

Network Layer summary

A
  • Host addressing
  • Routing, message forwarding
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12
Q

Network Layer protocols

A

IP

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13
Q

What does Transport Layer do?

A

Establlishes connection

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14
Q

Transport layer summary

A

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

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15
Q

Transport layer protocols

A

Transmission Control Protocol
User Datagram Protocol
Real-time Transport Protocol

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16
Q

What does Session layer manage?

A

Sessions between appplications

17
Q

Session layer summary

A
  • Control and sync or message exchange
  • Authentication/authorisation
  • Checkpointing/recovery
18
Q

Session layer protocols

A

RPC
Password Authentication Protocol

19
Q

Presentation layer summary

A
  • Encodings, definition of datasets
  • Data conversion, compression, encryption
20
Q

Presentation layer protocols

A

External Data Representation (EDR)

21
Q

Application layer summary

A
  • Data input/output
  • Services for applications
22
Q

APplication layer protocols

A

FTP
HTTP
DNS
SMTP

23
Q

Middleware Protocol types

A
  • Communication
  • (Un)marshalling of data
  • Naming
  • Security
  • Scaling mechanisms
24
Q

Transient vs Persistent

A

Transient - discarded if not delivered
Persistent - Buffered

25
Q

Async vs sync

A

Async - Sender continues immediately
Sync - Sender blocked until response

26
Q

Discrete vs Streaming

A

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

27
Q

Message Passing Interface

What is it used in and why?

A

Parallel High Performance computing

Sockets are not optimised enough

28
Q

What assumption is made with MPI?

A

All communication partners are known
No fault tolerance

29
Q

RPC

A

Remote Procedure Call. Call as though it is local.

30
Q

RPC process

A
  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
31
Q

RPC Parameter passing issues

A

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

32
Q

Solution to RPC interface description issue

A

Use generic language to describe interface - Interface Definition Langu

33
Q

IDL file

A

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

34
Q

IDL compiler

A

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

35
Q

When binding RPC, the server must be…?

A

Server must be registered and prepared

36
Q

Message oriented middleware

A

Persistent async (compared to synchronous transient RPC)

Messages in queues
Transmission may take longer
Additional features
- Fault tolerance
- Load balancing
- Multicasting

37
Q

What separates a message broker from a simple queue?

A

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

38
Q

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

A

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

Distributed Computing (13 decks)

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