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Lecture 1: Internet Architecture

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  1. Lecture 1: Internet Architecture • Architecture of the Internet • Network • Internetwork • Router • Protocol • Accessing the Internet • Residential access • Dedicated access • Institutional access • Communicating over the Internet • Protocol layering (covers only BASIC idea) • Internet Addressing 1: Introduction

  2. 1. What’s the Internet • The Internet is a collection of networks connected by interconnectingdevices. • The connecting devices • are specialized computing devices, e.g. routers • forward data from one network to another. 1: Introduction

  3. Client-Server Model File Servers Workstations (Local Processing) Computer Network Application Servers 1.1 Computer network • An interconnected collection of computers 1: Introduction

  4. 1.1 Classifications of Networks • Based on size: • System/Storage area networks (SAN) • within the same room • Local area networks (LAN) • in a close proximity • Metropolitan area networks (MAN) • span a city • Wide area networks (WAN) • connecting computers situated anywhere • Connects many networks together 1: Introduction

  5. 1.2 internetwork • A collection of networks 1: Introduction

  6. 1.2 Internetwork: Another example Figure 15.3(text book) An example of internet with six networks and three computers attached. 1: Introduction

  7. 1.2 The Internet Topology See http://www.cybergeography.org/atlas/topology.html for more Internet topologies. 1: Introduction

  8. 1.2 The Illusion Of A Giant Network • Any computer can send data to any other computer providing they have IP software installed. • The Internet operates like a virtual network. Fig. 15.1 (text book) 1: Introduction

  9. 1.2 The Reality Of Internal Structure • The Internet contains a complex physical structure users never see • Interconnecting networks with routers Fig. 15.2 (text book) 1: Introduction

  10. communication infrastructure: enables distributed applications: WWW, email, games, e-commerce, database., cyberspace 1.2 Internet: a service view 1: Introduction

  11. millions of connected computing devices: hosts, end-systems pc’s workstations, servers PDA’s communication links fiber, copper, radio, satellite routers: forward packets (chunks of data) across networks router workstation server mobile local ISP regional ISP company network 1.2 Internet: “nuts & bolts” view 1: Introduction

  12. protocols: control sending, receiving of msgs e.g., TCP, IP, HTTP, FTP Internet: “network of networks” public Internet versus private intranet collection(s) of SAN, LAN, MAN, WAN 1.2 Internet: “nuts & bolts” view router workstation server mobile local ISP regional ISP company network 1: Introduction

  13. Cables connecting a computer to a LAN are usually short, but may be extended. Modems used to send data across wire, telephone system & optical fibres Fiber optic cable can provide connections across long distances. Requiring optical modems Using light instead of electricity to carry data 1.2 Connecting a Computer to a Remote Network Fig 13.1 (text book) 1: Introduction

  14. 1.3 Incompatible Network Technologies • Not all networks are compatible. • Networks: • Vary in speed • Vary in electrical voltages • Differ in addressing scheme • Each technology designed to meet speed, dist, cost constraints. • It is impractical to make computers in an enterprise use the same network technology. • Allow groups to select a network technology based on need 1: Introduction

  15. Special-purpose computers are used to interconnect networks Using standard hardware (CPU, memory, and network interfaces) Running special-purpose software Forwarding packets from one network to another Determining where to send packets Transforms packets as necessary to meet standards for each network Fig. 13.2 (text book) 1.3 Routers 1: Introduction

  16. 1.3 Routers • Interconnecting LAN to LAN • Interconnecting LAN to WAN Fig 13.3 (text book) 1: Introduction

  17. 1.4 Network Protocol • A common language computers use to exchange messages. • Specifying exact format and meaning of each message • specify actions taken during sending and receiving of data 1: Introduction

  18. a human protocol and a computer network protocol: TCP connection reply. Get http://gaia.cs.umass.edu/index.htm Got the time? 2:00 <file> time 1.4 Network Protocol Hi TCP connection req. Hi 1: Introduction

  19. human protocols: “what’s the time?” “I have a question” introductions … specific messages sent … specific actions taken when messages received, or other events network protocols: machines rather than humans all communication activity in Internet governed by network protocols 1.4 Network Protocol protocols define format, order of messages sent and received among network entities, and actions taken on message transmission, receipt 1: Introduction

  20. 1.4 Internet Protocol (IP) • IP defines computer communication details. • Specifying how packets are formed • Specifying how routers forward each packet • Computers connecting to the Internet must follow the IP rules. 1: Introduction

  21. 1.4 IP Software On Every Machine • Computer hardware does not understand IP. • Connecting a computer to the Internet does not mean it can use the Internet • Computers need IP software before using the Internet. 1: Introduction

  22. access network The Internet access network 2. Accessing the Internet • User’s computers or hosts connect to the Internet through an access network. • Residential access: • dial-up access vs. dedicated access. • dial-up access advantages: least expensive. • dedicated access advantages: higher speed of delivery and remains connected at all times. • instantaneous access • continuous availability • Institutional access • dedicated access. 1: Introduction

  23. 2.1. Access Network: Residential access • Residential access is normally through an ISP (Internet Service Provider) • Most ISPs offer dial-up access through a telephone-based system. • Requires a modem and software that uses the modem. • Speed: up to 56Kbps. Fig. 14.1 (text book) 1: Introduction

  24. 2.2. Access Network: dedicated access • Three newer technologies used by ISPs to offer inexpensive dedicated access: • Cable modems • use cable television wiring (most homes already have cable TV wiring). • Cable modems send data over coax cable but transmission does not interfere with TV signals • cable system is designed to carry many more signals than are currently available, cable modem use the unused bandwidth • advantages: • deliver data faster than a dial-up connection. • provide continuous connectivity. • use existing wiring system. • chief disadvantage: • customers share the wiring (share bandwidth) - data transmission may slow down if many customer send data at the same time; but even at the slowest speed it still operate faster than dial-up modem 1: Introduction

  25. 2.2. Access Network : dedicated access • DSL (Digital Subscriber Line) technology • use conventional telephone wiring • unlike dial-up modem (which encode data with sound), DSL does not use the telephone system. Instead DSL transfer data by using the underlying telephone wires to send electrical signals • does not affect normal telephone service • e.g. ADSL: asymmetric digital subscriber line. • 6.144 Mbps downstream (data flowing to user), 576Kbps upstream (data flowing from user). • advantages • use existing wiring • provide continuous connectivity. • does not share bandwidth with other subscribers (unlike cable modem) 1: Introduction

  26. 2.2. Access Network : dedicated access • Wireless access similar to cellular phones • use radio transmissions • a transmitter runs all the time to to provide continuous access • chief advantage is the ability to reach remote areas. 1: Introduction

  27. 2.3. Access Network: Institutional access • Institutional access is mainly through company/university local area network (LAN). • E.g. using Ethernet: • shared cable connects user computers • speeds: 10 Mbs, 100Mbps, Gigabit Ethernet Router 1: Introduction

  28. 3. Communicating over the Internet • To communicate over the Internet, the computers must: • use a common language or a protocol to govern the exchange of messages. • have a way to address one another. • Protocol: • specifies exact format, order of messages sent and received among network entities, and actions taken on message transmission and receipt. • Addressing: • defines where to deliver the messages. 1: Introduction

  29. 3.1 Protocol Layering • Internet has a large collections of protocols organized in a layering model. • Application: enables the user, whether human or software, to access the network. • Transport: responsible for reliable source-to-destination (end-to-end) delivery of the entire message. • Network: responsible for routing a packet (also called datagram) from source-to-dest (possibly) across multiple (different) networks. • Data link (also called network interface): specify how to organize data into frames and how to deliver a frame over a network. • Physical: coordinates the functions required to transmit a bit stream over a physical medium. 1: Introduction

  30. 3.1 Protocol Layering 1: Introduction

  31. 3.1 Protocol Layering 1: Introduction

  32. 3.1 Protocol Layering • TCP/IP Protocol Suite. 1: Introduction

  33. 3.1 Protocol Layering • Two key protocols are: • IP (Internet Protocol) • Oversee end-to-end delivery of individual packets • Does not recognize relationships among packets • Treats each packet independently, as if they belong to different message • TCP (Transport Control Protocol) • Ensure whole message arrive intact and in order • (eg, check if packets are missing or arrive out of order) 1: Introduction

  34. 3.1 Router Overrun with Datagrams • Router becomes overrun with datagrams • Eg, routers 1 & 2 each receives 5000 datagrams • both routers send all datagrams they received (5000+5000) across network d to router 3 • but router 3 can only handle 5000 datagrams • Analogy: traffic jam • Eg, cars from roads a and b attempt to merge into road d, causing traffic congestion 1: Introduction

  35. 3.1 Transmission Control Protocol • When a router is overrun with datagrams, some of them will be discarded. • As a result some datagrams will be lost • TCP checks for lost datagrams • When hardware in a router or network system fails, other routers start sending datagrams through new (alternative) paths. • As a result, some datagrams arrive in a different orderthan they were sent • TCP checks for out-of-order datagrams • Network hardware failure sometimes result in duplication of datagrams • TCP checks for duplication of datagrams 1: Introduction

  36. 3.1 Recovering Lost Datagrams: TCP Retransmission • TCP includes an identification of each datagram. • Ignores duplicate copies • Receiver uses identification (sequence numbers) to put out-of-order datagram back in order • Recovers lost datagrams • Uses timers • Sends an acknowledgementback to the source - this guarantees that all data arrives • If timer expires before an acknowledgement arrives, TCP assumes the datagram is lost and retransmit the datagram 1: Introduction

  37. 3.2 Internet Addresses • Every Computer Is Assigned A Unique Address • Each computer attached to the Internet must be assigned a unique address. • IP Addresses Are Not Random • Computers on the same network have the same prefix (Netid). 1: Introduction

  38. 3.2. Internet Addressing • IP or Internet address is a 32-bit (4 byte) address that uniquely defines every computing devices on the Internet. • Decimal notation to make it easier to read. 1: Introduction

  39. Designers chose a compromise - multiple address formats that allow both large and small prefixes Each format is called an address class Class of an address is identified by first four bits 3.2 Classes of IP addresses 1: Introduction

  40. 3.2 Dotted decimal notation • Class A, B and C all break between prefix and suffix on byte boundary • Dotted decimal notation is a convention for representing 32-bit internet addresses in decimal • Convert each byte of address into decimal; display separated by periods (``dots'') 1: Introduction

  41. 3.2 IP Address classes at a glance • Class A, B and C are primary classes • Used for ordinary host addressing • Class D is used for multicast, a limited form of broadcast • Class E is reserved 1: Introduction

  42. 3.2. Internet Addressing: An Example 1: Introduction

  43. Further Reading • Chapters 13, 14, 15, & 16 of the textbook. • Note: This lecture is designed with the objective of providing an introduction tothe architecture of the Internet and communicating over the internet. • Details of these topics are beyond the scope of this course and will NOT be taught or discussed. Students who wish to invest more time on studying more details for these topics are referred to: • Forouzan Chapter 2. • Doug Comer, Computer Networks & Internetswith Internet Applications, chapter 17, 18, 20 & 24 • Details of protocol layering will be covered in IEG3310 1: Introduction