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Chapter 1: Introduction

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  1. Chapter 1: Introduction • What is a Network? What is Internet? Compared with postal service & telephone system • Services provided • “Nuts and Bolts” description • Packet Switching vs. Circuit Switching • Fundamental Issues in Computer Networking • Protocol and Layered Architecture • Internet Protocols, Architecture & History Readings: Chapter 1, Lecture Notes CSci4211: Introduction

  2. Goal and Motivating Questions Our goal: get “feel” and terminology more depth, detail later in course approach: use Internet as example Motivating Questions: What is internet? What’s so special about it? What’s a protocol? How do I build a network? How do I deal with the complexity? What does real Internet look like now? Why I download slowly? CSci4211: Introduction 2

  3. Internet is the network! • It’s big! • It’s diverse! • It’s complex! • It’s everywhere (almost)! • … and it keeps growing and changing! CSci4211: Introduction 3

  4. Inter-networking • A network can be defined recursively as... • two or more networks connected by two or more nodes • two or more nodes connected by a link, or • Internet: networks of networks • started as ARPAnet with only 4 nodes 4 CSci4211: Introduction

  5. Map of Internet

  6. csci4211 Introduction 6

  7. csci4211 Introduction 7

  8. Low-tier High-tier Local Area Wide Area Low Mobility High Mobility More gadgets are plugged in … • smart mobile phones, iPads, e-readers, … • servers, desktops, laptops, … • now TVs, thermostats, smart meters, etc., soon toasters, fridges, … • Wireless technologies revolutionizing Internet! • WiFi, bluetooth, 3/4G cellular networks, … mobile computing location services 8 CSci4211: Introduction

  9. Internet:a huge transformative & disruptive force! What has become of the Internet: Information Service and E-Commerce Platform deliver all kinds of information, news, music, video, shopping web, spotify, iTune, youtube, Netflix, Hulu, … Global Information Repository store and search for all kinds of information google, flickr, dropbox, icloud, … Cyberspace and Virtual Communities keep in touch with friends and strangers email, facebook, twitter, … Enormous Super-Computer mobile, cloud computing and services We’re increasingly depending on it ! 9 CSci4211: Introduction

  10. So what’s so special about the Internet? But first, what is a Network? CSci4211: Introduction

  11. What is a Network? • There are many types of networks! • Key Features of Networks • Providing certain services • transport goods, mail, information or data • Shared resources • used by many users, often concurrently • Basic building blocks • nodes (active entities): process and transfer goods/data • links (passive medium): passive “carrier” of goods/data • Typically distributed & “multi-hop”: • two “end points” cannot directly reach each other • need other nodes/entities to relay CSci4211: Introduction

  12. What is a Network … Compare Internet with Postal Service and Telephone System • Services Provided • Various Key Pieces and Their Functions • How the pieces work together to provide services CSci4211: Introduction

  13. Nuts and Bolts Description Network is fundamentally distributed in nature: a collection of distinct entities: “nodes” and “links” • Postal: • Mailboxes • Local/Branch Postal Offices, Regional, Central Postal Offices • Mail Sorting Machines • Postmen, Delivery Trucks/Trains/Planes, Roads, … • Telephone: • Phones • Local Switching Office, Central Switching Offices, … • Telephone Switches • Wires • Internet ? CSci4211: Introduction

  14. Internet: Building Blocks • Nodes: PCs, special-purpose hardware, … • Hosts (or end systems): servers, PCs, laptops, mobile devices, smart meters, …… • Switches: routers, switches, … • Links: coax cable, optical fiber, wireless, … • point-to-point • multiple access CSci4211: Introduction

  15. Inter-networking • A network can be defined recursively as... • two or more nodes connected by a link, or • two or more networks connected by two or more nodes • Internet: networks of networks CSci4211: Introduction

  16. Service Perspective Basic Services Provided • Postal: deliver mail/package from people to people • First class, express mail, bulk rate, certified, registered, … • Telephone: connect people for talking • You may get a busy dial tone • Once connected, consistently good quality, unless using cell phones • Internet: transfer information between people/machines • Reliable connection-oriented or unreliably connectionless services! • You never get a busy dial tone, but things can be very slow! • You can’t ask for express delivery (not at the moment at least!) CSci4211: Introduction

  17. Fundamental Issues in Networking Network is a shared resource • Provide services for many people at same time • Carry bits/information for many people at same time • Switching and Multiplexing • How to share resources among multiple users, and transfer data from one node to another node • Naming and Addressing • How to find name/address of the party (or parties) you would like to communicate with • Address: byte-string that identifies a node • unicast, multicast and broadcast addresses • Routing and (end-to-end) Forwarding: • Routing: process of determining how to send packets towards the destination based on its address • find out neighbors, build “maps” (routing tables), … • transfer data from source to destination “hop-by-hop” CSci4211: Introduction

  18. What’s so special about the Internet? • Internet is based on the notion of “packet switching” • enables statistical multiplexing • better utilization of network resources for transfer of “bursty” data traffic CSci4211: Introduction

  19. Switching & Multiplexing • Network is a shared resource • Provide services for many people at same time • Carry bits/information for many people at same time • How do we do it? • Switching: how to deliver information from point A to point B? • Multiplexing: how to share resources among many users Think about postal service and telephone system! Switching and multiplexing are closely related! CSci4211: Introduction

  20. Switching Strategies • Circuit switching • set up a dedicated route (“circuit”) first • carry all bits of a “conversation” on one circuit • original telephone network • Analogy: railroads and trains/subways • Packet switching • divide information into small chunks (“packets”) • each packet delivered independently • “store-and-forward” packets • Internet (also Postal Service, but they don’t tear your mail into pieces first!) • Analogy: highways and cars • Pros and Cons? - think taking subways vs. driving cars, during off-peak vs. rush hours! CSci4211: Introduction

  21. Analogy: railroad and train 21 CSci4211: Introduction

  22. Analogy: Highway and cars CSci4211: Introduction

  23. Circuit Switching network resources (e.g., bandwidth) divided into “pieces” pieces allocated to calls resource piece idle if not used by owning call (no sharing) • dividing link bandwidth into “pieces” • frequency division • time division • code division • Trivia Q: • You must have heard of the term “CDMA” (think the company Qualcom, for which it is most associated with), what does “CD” in CDMA stands for? CSci4211: Introduction

  24. Circuit Switching: FDM and TDM Example: 4 users FDM frequency time TDM frequency time CSci4211: Introduction

  25. Numerical example How long does it take to send a file of 640,000 bits from host A to host B over a circuit-switched network? All links are 1.536 Mbps Each link uses TDM with 24 slots/sec 500 msec to establish end-to-end circuit Let’s work it out! 10.5 seconds CSci4211: Introduction

  26. Networks with Circuit Switchinge.g., conventional (fixed-line) telephone networks End-end resources reserved for “call” link bandwidth, switch capacity dedicated resources: no sharing circuit-like (guaranteed) performance call setup required CSci4211: Introduction

  27. Circuit Switched Networks • All resources (e.g. communication links) needed by a call dedicated to that call for its duration • Example: telephone network • Call blocking when all resources are used CSci4211: Introduction

  28. Packet Switching Each end-end “data stream” divided into packets users A, B packets share network resources each packet uses full link bandwidth resources used as needed Bandwidth division into “pieces” Dedicated allocation Resource reservation resource contention: • aggregate resource demand can exceed amount available • congestion: packets queue, wait for link use • store and forward: packets move one hop at a time • Node receives complete packet before forwarding • Packets may suffer delay or losses! CSci4211: Introduction

  29. Statistical Multiplexing • Time division, but on demand rather than fixed • Reschedule link on a per-packet basis • Packets from different sources interleaved on the link • Buffer packets that are contending for the link • Buffer buildup is called congestion • This ispacket switching, used in computer networks CSci4211: Introduction

  30. Packet Switching: Statistical Multiplexing Sequence of A & B packets does not have fixed pattern, shared on demand  statistical multiplexing. TDM: each host gets same slot in revolving TDM frame. D E 100 Mb/s Ethernet C A statistical multiplexing 1.5 Mb/s B queue of packets waiting for output link CSci4211: Introduction

  31. Packet-switching: store-and-forward Takes L/R seconds to transmit (push out) packet of L bits on to link or R bps Entire packet must arrive at router before it can be transmitted on next link: store and forward delay = 3L/R (assuming zero propagation delay) Example: L = 7.5 Mbits R = 1.5 Mbps delay = ? L R R R 15 sec more on delay later … CSci4211: Introduction

  32. Packet switching versus circuit switching 1 Mb/s link each user: 100 kb/s when “active” active 10% of time circuit-switching: 10 users packet switching: with 35 users, probability > 10 active less than .0004 Packet switching allows more users to use network! N users 1 Mbps link Q: how did we get value 0.0004? CSci4211: Introduction

  33. Circuit Switching vs Packet Switching CSci4211: Introduction

  34. Packet switching vs. circuit switching Great for bursty data resource sharing simpler, no call setup Excessive congestion: packet delay and loss protocols needed for reliable data transfer, congestion control Q: How to provide circuit-like behavior? bandwidth guarantees needed for audio/video apps still an unsolved problem (chapter 7) Is packet switching a “slam dunk winner?” Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet-switching)? CSci4211: Introduction

  35. What’s so special about the Internet? • Internet is based on the notion of “packet switching” • enables statistical multiplexing • better utilization of network resources for transfer of “bursty” data traffic • Internet’s key organizational/architectural principle: “smart” end systems + “dumb” networks • architecture: functional division & function placement • hourglass Internet architecture: enables diverse applications and accommodates evolving technologies • “dumb” network (core): simple packet-switched, store-forward, connectionless “datagram” service, with core functions: global addressing, routing & forwarding • “smart” end systems/edges: servers, PCs, mobile devices, …; diverse and ever-emerging new applications! CSci4211: Introduction

  36. Internet Hourglass Architecture • enabling diverse applications • & new types of end devices p2p file sharing, skype, YouTube, Netflix, Cloud Computing bitTorrent, DHT, SIP, DASH, …. • accommodating evolving • & new technologies network edge/end hosts WiFi, Bluetooth, Docsis, gMPLS, DWDM/fiber, …, 3G/4G cellular, …. network core CSci4211: Introduction

  37. “Dumb” Networks & “Smart” End Systems • Five Layer Architecture: • Lower three layers are implemented everywhere • Top two layers are implemented only at hosts Host A Host B Application Application Transport Transport Router Network Network Network Datalink Datalink Datalink Physical Physical Physical Physical medium CSci4211: Introduction

  38. An Overview of Network Structure:a “horizontal view” network edge: applications and hosts network core: routers network of networks access networks, physical media: communication links CSci4211: Introduction

  39. What’s the Internet: “nuts and bolts” view millions of connected computing devices: hosts = end systems running network apps communication links fiber, copper, radio, satellite transmission rate = bandwidth routers: forward packets (chunks of data) router workstation server mobile local ISP regional ISP company network CSci4211: Introduction

  40. The network edge: end systems (hosts): run application programs e.g. Web, email at “edge of network” client/server model client host requests, receives service from always-on server e.g. Web browser/server; email client/server peer-peer model: minimal (or no) use of dedicated servers e.g. Skype, BitTorrent, KaZaA CSci4211: Introduction

  41. The network edge: end systems (hosts): run application programs e.g. Web, email at “edge of network” client/server model client host requests, receives service from always-on server e.g. Web browser/server; email client/server Cloud & Mobile Computing peer-peer model: minimal (or no) use of dedicated servers e.g. Skype, BitTorrent, KaZaA cloud computing CSci4211: Introduction

  42. Network edge: connection-oriented service Goal: data transfer between end systems handshaking: setup (prepare for) data transfer ahead of time Hello, hello back human protocol set up “state” in two communicating hosts TCP - Transmission Control Protocol Internet’s connection-oriented service TCP service[RFC 793] reliable, in-order byte-stream data transfer loss: acknowledgements and retransmissions flow control: sender won’t overwhelm receiver congestion control: senders “slow down sending rate” when network congested CSci4211: Introduction

  43. Network edge: connectionless service Goal: data transfer between end systems same as before! UDP - User Datagram Protocol [RFC 768]: connectionless unreliable data transfer no flow control no congestion control App’s using TCP: HTTP (Web), FTP (file transfer), Telnet (remote login), SMTP (email), Flash videos, DASH stream videos App’s using UDP: streaming media, teleconferencing, DNS, Internet telephony CSci4211: Introduction

  44. The Network Core mesh of interconnected routers shared by many users the fundamental questions: how network is shared how to find the other party (person, website, …) you want how is data transferred through net? CSci4211: Introduction

  45. On the Internet Edge … • Large # of (mobile & stationary) users • Large # of “dumb” or smart devices & appliances • Some “always-on,” high-speed connection • Others intermittent connectivity with varying bandwidth • Diverse applications and services • Heterogeneous technologies social networks music streaming games web video streaming & IPTV others Internet smart pads & e-readers home users sensors & smart home surveillance & security VoIP banking & e-commerce dumb & smart phones POTS CSci4211: Introduction

  46. Within the Internet “Cloud” • Network Core: • big ISPs (& cellular providers) with large geographical span • As well as medium & smaller ISPs • And the “other end/edge”: • big content providers with huge data centers • High bandwidth, dense and rich topology • Enormous computing & storage capacities to support cloud, mobile computing/services CSci4211: Introduction

  47. Well, Internet is too complex for me to learn. How can they even build it?And what’s a protocol & why do we need protocols? Motivating Questions 3-5 CSci4211: Introduction

  48. Network Architecture(or organizational principles) Networks are complex! many “pieces”: hosts routers links of various media hardware, software applications protocols ….. Question: Is there any hope of organizing structure or principle of network? Or at least our discussion of networks? Network architecture: “blue prints” (or principles) regarding functional division and function placement CSci4211: Introduction

  49. Organization of air travel a series of steps ticket (complain) baggage (claim) gates (unload) runway landing airplane routing ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing airplane routing CSci4211: Introduction

  50. Layering of airline functionality Layers: each layer implements a service via its own internal-layer actions relying on services provided by layer below ticket ticket (purchase) baggage (check) gates (load) runway (takeoff) airplane routing ticket (complain) baggage (claim gates (unload) runway (land) airplane routing baggage gate airplane routing airplane routing takeoff/landing airplane routing departure airport intermediate air-traffic control centers arrival airport CSci4211: Introduction