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Distribuerede systemer og sikkerhed – 21. februar 2002

From Coulouris, Dollimore and Kindberg

Distributed Systems: Concepts and Design

Edition 3, © Addison-Wesley 2001

Presentation based on slides for the book:

Slides modified by Jens B Jorgensen, University of Aarhus

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Chapter 3: Networking and Internetworking

From Coulouris, Dollimore and Kindberg

Distributed Systems: Concepts and Design

Edition 3, © Addison-Wesley 2001

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Networks – basics

A network consists of: Transmission media (wire, cable, …). Hardware devices (routers, switches, …). Software components (protocol stacks, drivers, …).

Terminology: Host: Computers and other devices that use a network. Node: Any computer or switching device attached to a network. Subnet: Set of interconnected nodes.

Design issues: Performance, scalability, reliability, security, mobility, quality of service, multicasting.

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Networks – types

Range Bandwidth (Mbps) Latency (ms)

LAN 1-2 kms 10-1000 1-10WAN worldwide 0.010-600 100-500MAN 2-50 kms 1-150 10Wireless LAN 0.15-1.5 km 2-11 5-20Wireless WAN worldwide 0.010-2 100-500Internet worldwide 0.010-2 100-500

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Networks – packet transmission

Message: Sequence of data items of arbitrary length.

Messages subdivided into packets.Switching schemes:

Broadcast. Circuit switching. Packet switching. ATM / Frame relay.

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Protocols – basics

Protocol: Set of rules and formats to be used for communication between processes in order to perform a given task.

Should include specification of: Sequence of messages that must be exchanged. Format of the data in the messages.

Implemented by a pair of software modules in the sending and receiving computers.

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Protocols – layers

Layer n

Layer 2

Layer 1

Message sent Message received

Communicationmedium

Sender Recipient

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Protocols – encapsulation and headers

Presentation header

Application-layer message

Session header

Transport header

Network header

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Protocols – the ISO Open Systems Interconnection (OSI) model

Application

Presentation

Session

Transport

Network

Data link

Physical

Message sent Message received

Sender Recipient

Layers

Communicationmedium

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Protocols – internetwork layers

Underlying network

Application

Network interface

Transport

Internetwork

Internetwork packets

Network-specific packets

MessageLayers

Internetworkprotocols

Underlyingnetworkprotocols

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Protocols – network layer routing (WAN)

Hosts Linksor local networks

A

D E

B

C

1

2

5

43

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Routers

Routing algorithms, adaptive routing (congestion control)

Packet delivery: Datagram or virtual circuit?

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Internet protocols – Internetworking

Internetwork: Network which integrates a number of different subnets.

Needs: Unified internetwork addressing scheme (Internet: IP

addresses) Protocol defining format of internetwork packets and

specifying rules for handling (Internet: IP protocol). Interconnecting components that route packets to

their destinations (Internet: Internet routers).

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Internet protocols – the TCP/IP protocol suite

Messages (UDP) or Streams (TCP)

Application

Transport

Internet

UDP or TCP packets

IP datagrams

Network-specific frames

MessageLayers

Underlying network

Network interface

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Internet protocols – encapsulation and headers

Application message

TCP header

IP header

Ethernet header

Ethernet frame

port

TCP

IP

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Internet protocols – IP

Internet Protocol.Transmits datagrams from one host to another,

if necessary via intermediate routers.Unreliable, best-effort delivery semantics.Address resolution: Conversion of Internet

addresses to network addresses (for a given network).

Routing: Each router in the Internet implements IP-layer software to provide a routing algorithm.

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Internet protocols – IP packet layout and addressing

7 24

Class A: 0 Network ID Host ID

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Class B: 1 0 Network ID Host ID

21 8

Class C: 1 1 0 Network ID Host ID

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Class D (multicast): 1 1 1 0 Multicast address

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Class E (reserved): 1 1 1 1 unused0

dataIP address of destinationIP address of source

header

up to 64 kilobytes

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Internet protocols – TCP and UDP

UDP features: Transport-level replica of IP. No guarantee of delivery. No setup cost, no acknowledgement messages. Message size up to 64 kbytes.

TCP features: Reliable delivery. Arbitrarily long sequences of bytes. Connection-oriented. Mechanisms: Sequencing, flow control,

retransmission, buffering, checksum.

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Summary

Networks.Protocols. Internet protocols (TCP/IP).