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Chapter 3 a

  1. 1. Slides for Chapter 3:Networking and InternetworkingFrom Coulouris, Dollimore, Kindberg and BlairDistributed Systems: Concepts and DesignEdition 5, © Addison-Wesley 2012
  2. 2. Network PerformanceThe main network performance parameters are those affecting the speed with which individual messages can be transferred between two interconnected computers.Latency is the delay that occurs after a send operation is executed and before data starts to arrive at the destination computer. It can be measured as the time required to transfer an empty message.Data transfer rate is the speed at which data can be transferred between two computers in the network once transmission has begun, usually quoted in bits per second.Message transmission time = latency + length ⁄ data transfer rateThe total system bandwidth of a network is a measure of throughput – the total volume of traffic that can be transferred across the network in a given time. 2
  3. 3. Figure 3.1Network performance km Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012
  4. 4. Figure 3.2Conceptual layering of protocol software Message sent Message receivedLayer nLayer 2Layer 1 Sender Communication Recipient medium Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012
  5. 5. Figure 3.3Encapsulation as it is applied in layered protocols Application-layer message Presentation header Session header Transport header Network header Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012
  6. 6. Figure 3.4Protocol layers in the ISO Open Systems Interconnection (OSI) model Message sent Message received Layers Application Presentation Session Transport Network Data link Physical Sender Communication Recipient medium Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012
  7. 7. Figure 3.5OSI protocol summary Layer Description Examples Application Protocols that are designed to meet the communication requirements of HTTP, FTP , SMTP, specific applications, often defining the interface to a service. CORBA IIOP Presentation Protocols at this level transmit data in a network representation that is Secure Sockets independent of the representations used in individual computers, which may (SSL),CORBA Data differ. Encryption is also performed in this layer, if required. Rep. Session At this level reliability and adaptation are performed, such as detection of failures and automatic recovery. Transport This is the lowest level at which messages (rather than packets) are handled. TCP, UDP Messages are addressed to communication ports attached to processes, Protocols in this layer may be connection-oriented or connectionless. Network Transfers data packets between computers in a specific network. In a WAN IP, ATM virtual or an internetwork this involves the generation of a route passing through circuits routers. In a single LAN no routing is required. Data link Responsible for transmission of packets between nodes that are directly Ethernet MAC, connected by a physical link. In a WAN transmission is between pairs of ATM cell transfer, routers or between routers and hosts. In a LAN it is between any pair of hosts. PPP Physical The circuits and hardware that drive the network. It transmits sequences of Ethernet base- band binary data by analogue signalling, using amplitude or frequency modulation signalling, ISDN of electrical signals (on cable circuits), light signals (on fibre optic circuits) or other electromagnetic signals (on radio and microwave circuits). Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012
  8. 8. Figure 3.6Internetwork layers Message Layers Application Internetwork Transport protocols Internetwork Internetwork packets Network interface Underlying Network-specific packets network protocols Underlying network Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012
  9. 9. Figure 3.7Routing in a wide area network A 1 B 2 Hosts Links or local 3 4 C networks 5 D 6 E Routers Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012
  10. 10. Figure 3.8Routing tables for the network in Figure 3.7 Routings from A Routings from B Routings from C To Link Cost To Link Cost To Link Cost A local 0 A 1 1 A 2 2 B 1 1 B local 0 B 2 1 C 1 2 C 2 1 C local 0 D 3 1 D 1 2 D 5 2 E 1 2 E 4 1 E 5 1 Routings from D Routings from E To Link Cost To Link Cost A 3 1 A 4 2 B 3 2 B 4 1 C 6 2 C 5 1 D local 0 D 6 1 E 6 1 E local 0 Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012
  11. 11. Figure 3.9Pseudo-code for RIP routing algorithm Send: Each t seconds or when Tl changes, send Tl on each non-faulty outgoing link. Receive: Whenever a routing table Tr is received on link n: for all rows Rr in Tr { if (Rr.link | n) { Rr.cost = Rr.cost + 1; Rr.link = n; if (Rr.destination is not in Tl) add Rr to Tl; // add new destination to Tl else for all rows Rl in Tl { if (Rr.destination = Rl.destination and (Rr.cost < Rl.cost or Rl.link = n)) Rl = Rr; // Rr.cost < Rl.cost : remote node has better route // Rl.link = n : remote node is more authoritative } } } Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012
  12. 12. InternetworkingTo build an integrated network (an internetwork) we must integrate many subnets. To make this possible, the following are needed: a unified internetwork addressing scheme that enables packets to be addressed to any host connected to any subnet; a protocol defining the format of internetwork packets and giving rules according to which they are handled; interconnecting components that route packets to their destinations in terms of internetwork addresses, transmitting the packets using subnets with a variety of network technologies. Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012
  13. 13. Figure 3.10Simplified view of part of a university campus network router/ Campus 138.37.95.240/29 138.37.95.241 firewallrouter subnet hammer Staff subnet Student subnet 138.37.88 138.37.88.251 138.37.94.251 138.37.94 compute file server/ server Eswitch Eswitch gateway bruno 138.37.88.249 custard 138.37.94.246 printers dialup server ☎ henry 138.37.88.230 other file servers server hotpoint 138.37.88.162 web server copper 138.37.88.248 hub hub desktop computers 138.37.88.xx desktop computers 138.37.94.xx Campus sickle 138.37.95.248/29 100 Mbps Ethernet router subnet router/ 138.37.95.249 firewall 1000 Mbps Ethernet Eswitch: Ethernet switch Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012
  14. 14. Figure 3.11Tunnelling for IPv6 migrationIPv6 encapsulated in IPv4 packets IPv4 network IPv6 IPv6 A B Encapsulators Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012
  15. 15. Figure 3.12TCP/IP layers TCP/IP, including the Web (HTTP), email (SMTP, POP), file transfer (FTP) and Telnet (telnet) Message Layers Application Messages (UDP) or Streams (TCP) Transport UDP or TCP packets Internet IP datagrams Network interface Network-specific frames Underlying network Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012
  16. 16. Figure 3.13Encapsulation in a message transmitted via TCP over an Ethernet Application message TCP header port IP header TCP Ethernet header IP Ethernet frame Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012
  17. 17. Figure 3.14The programmers conceptual view of a TCP/IP Internet Application Application TCP UDP IP Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012
  18. 18. IP Addressing Assigning host addresses to networks and the computers connected to them had to satisfy the following requirements:• It must be universal – any host must be able to send packets to any other host in the Internet.• It must be efficient in its use of the address space – it is impossible to predict the ultimate size of the Internet and the number of network and host addresses likely to be required. TCP/IP provision for 232 or approximately 4 billion addressable hosts. Short-sighted, for two reasons: – The rate of growth of the Internet has far outstripped all predictions. – The address space has been allocated and used much less efficiently than expected. 18
  19. 19. Figure 3.15Internet address structure, showing field sizes in bits 7 24 Class A: 0 Network ID Host ID 14 16 Class B: 1 0 Network ID Host ID 28 21 8 Class C: 1 1 0 Network ID Host ID 28 Class D (multicast): 1 1 1 0 Multicast address 27 Class E (reserved): 1 1 1 1 0 unused Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012
  20. 20. Figure 3.16Decimal representation of Internet addresses octet 1 octet 2 octet 3 Range of addresses Network ID Host ID 1.0.0.0 to Class A: 1 to 127 0 to 255 0 to 255 0 to 255 127.255.255.255 Network ID Host ID Class B: 128 to 191 0 to 255 0 to 255 0 to 255 128.0.0.0 to 191.255.255.255 Network ID Host ID 192.0.0.0 to Class C: 192 to 223 0 to 255 0 to 255 1 to 254 223.255.255.255 Multicast addressClass D (multicast): 224 to 239 0 to 255 0 to 255 1 to 254 224.0.0.0 to 239.255.255.255Class E (reserved): 240 to 255 0 to 255 0 to 255 1 to 254 240.0.0.0 to 255.255.255.255 Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012
  21. 21. Figure 3.17IP packet layout header IP address of source IP address of destination data up to 64 kilobytes Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012
  22. 22. Unregistered addresses and Network Address Translation (NAT) Not all of the computers and devices that access the Internet need to be assigned globally unique IP addresses. Computers that are attached to a local network and access to the Internet through a NAT-enabled router can rely upon the router to redirect incoming UDP and TCP packets for them. The network includes Internet-enabled computers that are connected to the router by a wired Ethernet connection as well as others that are connected through a WiFi access point. 22
  23. 23. Figure 3.18A typical NAT-based home network Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012
  24. 24. Figure 3.19IPv6 header layout Version (4bits) Traffic class Flow label (20bits) (8bits) Payload length (16 bits) Next header (8bits) Hop limit (8 bits) Source address (128 bits) Destination address (128 bits) Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012
  25. 25. Figure 3.20The MobileIP routing mechanism Sender Subsequent IP packets tunnelled to FA Mobile host MH Address of FA returned to sender First IP packet addressed to MH Internet Foreign agent FA Home agent First IP packet tunnelled to FA Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012
  26. 26. Figure 3.21Firewall configurations a) Filtering router Protected intranet Router/ filter Internet web/ftp server b) Filtering router and bastion R/filter Bastion Internet web/ftp server c) Screened subnet for bastion R/filter Bastion R/filter Internet web/ftp server Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012
  27. 27. Firewall IP packet filtering: This is a filter process examining individual IP packets. It may make decisions based on the destination and source addresses. It may also examine the service type field of IP packets and interpret the contents of the packets based on the type. For example, it may filter TCP packets based on the port number to which they are addressed, and since services are generally located at well-known ports, this enables packets to be filtered based on the service requested. For example, many sites prohibit the use of NFS servers by external clients. 27
  28. 28. Firewall TCP gateway: A TCP gateway process checks all TCP connection requests and segment transmissions. When a TCP gateway process is installed, the setting up of TCP connections can be controlled and TCP segments can be checked for correctness (some denial of service attacks use malformed TCP segments to disrupt client operating systems). When desired, they can be routed through an application- level gateway for content checking. 28
  29. 29. Firewall Application-level gateway: An application-level gateway process acts as a proxy for an application process. For example, a policy may be desired that allows certain internal users to make Telnet connections to certain external hosts. When a user runs a Telnet program on their local computer, it attempts to establish a TCP connection with a remote host. The request is intercepted by the TCP gateway. The TCP gateway starts a Telnet proxy process and the original TCP connection is routed to it. If the proxy approves the Telnet operation (i.e., if the user is authorized to use the requested host) it establishes another connection to the requested host and relays all of the TCP packets in both directions. A similar proxy process would run on behalf of each Telnet client, and similar proxies might be employed for FTP and other services. 29
  30. 30. Figure 3.22IEEE 802 network standards IEEE No. Name Title Reference 802.3 Ethernet CSMA/CD Networks (Ethernet) [IEEE 1985a] 802.4 Token Bus Networks [IEEE 1985b] 802.5 Token Ring Networks [IEEE 1985c] 802.6 Metropolitan Area Networks [IEEE 1994] 802.11 WiFi Wireless Local Area Networks [IEEE 1999] 802.15.1 Bluetooth Wireless Personal Area Networks [IEEE 2002] 802.15.4 ZigBee Wireless Sensor Networks [IEEE 2003] 802.16 WiMAX Wireless Metropolitan Area Networks [IEEE 2004a] Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012
  31. 31. Figure 3.23Ethernet ranges and speeds 10Base5 10BaseT 100BaseT 1000BaseT Data rate 10 Mbps 10 Mbps 100 Mbps 1000 Mbps Max. segment lengths: Twisted wire (UTP) 100 m 100 m 100 m 25 m Coaxial cable (STP) 500 m 500 m 500 m 25 m Multi-mode fibre 2000 m 2000 m 500 m 500 m Mono-mode fibre 25000 m 25000 m 20000 m 2000 m Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012
  32. 32. Figure 3.24Wireless LAN configuration A B C Laptops radio obstruction Wireless D LAN Palmtop E Server Base station/ access point LAN Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012
  33. 33. Issues Hidden stations: Carrier sensing may fail to detect that another station on the network is transmitting.If tablet D is transmitting to the base station E, laptop A may not be able to sense D’s signal because of the radio obstruction shown. A might then start transmitting, causing a collision at E unless steps are taken to prevent this. Fading: Due to the inverse square law of electromagnetic wave propagation, the strength of radio signals diminishes rapidly with the distance from the transmitter. Stations within a wireless LAN may be out of range of other stations in the same LAN.Thus laptop A may not be able to detect a transmission by C, although each of them can transmit successfully to B or E. Fading defeats both carrier sensing and collision detection. 33
  34. 34. Issues Collision masking: The ‘listening’ technique used in the Ethernet to detect collisions is not very effective in radio networks.Because of the inverse square law the locally generated signal will always be much stronger than any signal originating elsewhere, effectively drowning out the remote transmission.So, laptops A and C might both transmit simultaneously to E and neither would detect that collision, but E would receive only a garbled transmission. 34
  35. 35. Carrier Sensing, Multiple Access with Collision Avoidance (CSMA/CA).When a station is ready to transmit, it senses the medium. If it detects no carrier signal it may assume that one of the following conditions is true:1. The medium is available.2. An out-of-range station is in the process of requesting a slot.3. An out-of-range station is using a slot that it had previously reserved. 35
  36. 36. Figure 3.25Bluetooth frame structure bits: 72 18 18 18 0 - 2744 Access code Header Header Header Data for transmission copy 1 copy 2 copy 3 Header bits: 3 1 1 1 4 8 Destination Flow Ack Seq Type Header checksum Address within = ACL, SCO, Piconet poll, null SCO packets (e.g. for voice data) have a 240-bit payload containing 80 bits of data triplicated, filling exactly one timeslot. Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5 © Pearson Education 2012

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