1 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

2 Chapter 3: Networking and Internetworking From Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edition 3, © Addison-Wesley 2001

3 Networks – basics zA network consists of: yTransmission media (wire, cable, …). yHardware devices (routers, switches, …). ySoftware components (protocol stacks, drivers, …). zTerminology: yHost: Computers and other devices that use a network. yNode: Any computer or switching device attached to a network. ySubnet: Set of interconnected nodes. zDesign issues: Performance, scalability, reliability, security, mobility, quality of service, multicasting.

4 Networks – types RangeBandwidth (Mbps)Latency (ms) LAN1-2 kms WANworldwide MAN2-50 kms Wireless LAN km Wireless WANworldwide Internetworldwide

5 Networks – packet transmission zMessage: Sequence of data items of arbitrary length. zMessages subdivided into packets. zSwitching schemes: yBroadcast. yCircuit switching. yPacket switching. yATM / Frame relay.

6 Protocols – basics zProtocol: Set of rules and formats to be used for communication between processes in order to perform a given task. zShould include specification of: ySequence of messages that must be exchanged. yFormat of the data in the messages. zImplemented by a pair of software modules in the sending and receiving computers.

7 Protocols – layers Layer n Layer 2 Layer 1 Message sent Message received Communication medium SenderRecipient

8 Protocols – encapsulation and headers

9 Protocols – the ISO Open Systems Interconnection (OSI) model

10 Protocols – internetwork layers

11 Protocols – network layer routing (WAN) Hosts Links or local networks A DE B C Routers Routing algorithms, adaptive routing (congestion control) Packet delivery: Datagram or virtual circuit?

12 Internet protocols – Internetworking zInternetwork: Network which integrates a number of different subnets. zNeeds: yUnified internetwork addressing scheme (Internet: IP addresses) y Protocol defining format of internetwork packets and specifying rules for handling (Internet: IP protocol). yInterconnecting components that route packets to their destinations (Internet: Internet routers).

13 Internet protocols – the TCP/IP protocol suite Messages (UDP) or Streams (TCP) Application Transport Internet UDP or TCP packets IP datagrams Network-specific frames Message Layers Underlying network Network interface

14 Internet protocols – encapsulation and headers Application message TCP header IP header Ethernet header Ethernet frame port TCP IP

15 Internet protocols – IP zInternet Protocol. zTransmits datagrams from one host to another, if necessary via intermediate routers. zUnreliable, best-effort delivery semantics. zAddress resolution: Conversion of Internet addresses to network addresses (for a given network). zRouting: Each router in the Internet implements IP-layer software to provide a routing algorithm.

16 Internet protocols – IP packet layout and addressing

17 Internet protocols – TCP and UDP zUDP features: yTransport-level replica of IP. yNo guarantee of delivery. yNo setup cost, no acknowledgement messages. yMessage size up to 64 kbytes. zTCP features: yReliable delivery. yArbitrarily long sequences of bytes. yConnection-oriented. yMechanisms: Sequencing, flow control, retransmission, buffering, checksum.

18 Summary zNetworks. zProtocols. zInternet protocols (TCP/IP).