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  1. Computer Networks (EENG 4810) Computer Networks- Course Objectives & Scope - 1

  2. Course Objectives & Scope Computer Networks- Course Objectives & Scope - 2

  3. In this class, you are expected to learn - • A brief History of Computer Networks • Categorization of Computer Networks • Network Services and Internet Perspective • Network Components- Nuts and Bolts View • General Concepts of Network Design • Protocols and Layered Communication Architecture • Network Programming Computer Networks- Course Objectives & Scope - 3

  4. This class, however, does not deal with - • Network Hardware Design • Comparative analyses of different protocol standards • Special purpose networks such as ad hoc sensor nets • Applications of Queuing Theory to Network traffic control Computer Networks- Course Objectives & Scope - 4

  5. Lesson 1:History of Computer Networks

  6. Preview of the Lesson 1 • In this lesson, we cover History of Computer Networks organized into approximately 5 decades. • In passing, we get a hang of what all a computer network can do History of Computer Networks - 1

  7. History of Computer Networks • Development of Packet Switching: 1961-72 • Proprietary Networks and Internetworking: 1972-80 • Proliferation of Networks: 1980-90 • Internet Explosion: 1990-2000 • Recent Developments: Bubble burst? History of Computer Networks- 2

  8. Development of Packet Switching: 1961-72 • Telephone network - World’s dominant communication network , uses circuit switching. (Early 1960s) • Three research groups around the world independently invented packet switching (1964 – 1967) • Leonard Kleinrock at MIT used queuing theory to demonstrate effectiveness of packet switching for bursty traffic • Paul Baran of Rand Institute investigated packet switching for secure voice communication over military networks • Donald Davies and Roger Scantlebury were developing ideas on packet switching at the National Physical Lab, England. Lesson 1: History of Computer Networks - 3

  9. Development of Packet Switching: 1961-72(continued) • J.C.R. Licklider and Laurence Roberts led the CS program at ARPA (Advanced Projects Research Agency) and published a plan for ARPAnet in 1967. • Arpanet was the ancestor of today’s Internet. • Early Packet switches were known as Interface Message Processors (IMPs). BBN got the contract. • First IMP was installed at UCLA on Labor Day 1969 under Kleinrock’s supervision. Later 3 more at SRI, UCSB and University of Utah. Lesson 1: History of Computer Networks - 4

  10. Leonard Kleinrock with IMP Lesson 1: History of Computer Networks - 5

  11. Development of Packet Switching: 1961-72(continued) • First use of the net of 4 nodes was remote login from UCLA to SRI; it resulted in system crash. • Robert Kahn demonstrated 15-node ARPAnet in 1972 ICCN. • First host to host protocol was Network Control Protocol (NCP). • Ray Tomlinson at BBN wrote the first e-mail program in 1972. Lesson 1: History of Computer Networks - 6

  12. Proprietary Networks and Internet 1972-80 • ALOHAnet- microwave satellite net linking universities on Hawaii islands (Norman Abramson 1970). • Telenet- a BBN commercial packet network and Cyclades- a French Packet Net by Louis Pouzin. • Time-sharing networks such as Tymnet and GE Information Services Net (late 60s and early 70s). • Metcalfe’s PhD thesis proposing Ethernet. History of Computer Networks - 7

  13. Proprietary Networks and Internet 1972-80(Continued) • Proprietary Networks such as • IBM’s (1969-74) System Network Architecture (SNA) paralleling the ARPAnet (Schwartz 1977). • DEC’s DECnet and Xerox corporation’s XNA. • Vincent Cerf and Robert Kahn (Cerf 1974)- Architecture for interconnecting Networks (They coined the word Internet for network of networks). • DARPA’s packet satellite and packet-radio networks (Kahn 1978). History of Computer Networks - 8

  14. Proprietary Networks and Internet 1972-80(Early Internet Features) • Cerf and Kahn’s TCP (quite different from now) • It combined reliable in-sequence delivery of data by end-system retransmission (as now) with forwarding (as IP now) • Realization of usefulness of separation of unreliable, non-flow controlled end-to end transport service for applications such as packetized voice led to separation of IP. • Three internet protocols TCP, IP and UDP - conceptually in place by the end of 1970’s. • Main features of their InterNet- Minimalism, autonomy (no internal changes required for interconnection), Best effort delivery, stateless routers and decentalized control. History of Computer Networks - 9

  15. Proprietary Networks and Internet 1972-80(Early Ethernet Features) • Abramson’s ALOHA protocol- a multiple-access protocol for communication among geographically distributed users by a single shared broadcast medium. • Metcalfe and Bogg’s EtherNet protocol for wire-based shared networks was originally motivated by the need to connect multiple PCprinters Lesson 1: History of Computer Networks - 10

  16. Proliferation of Networks 1980-90 • 100 nodes by late 70’s • New national networks (100,000 by the end of 80’s) • BITNET for email and FTP services among many North East Universities • CSNET (computer Science Network) for researchers with no access to APRPAnet. • NSF-net for access to NSF-sponsored super-computing centers • Starting with a backbone of 56 kbps, NSF net was running at 1.5 Mbps by the end of the decade. History of Computer Networks - 11

  17. Proliferation of Networks 1980-90 (Continued) • Simple Message Transfer Protocol (SMTP): E-Mail 1982 • Deployment of TCP /IP replacing NCP (Jan. 1, 1983) • FTP- The File Transfer Protocol defined (1983). • Host-based TCP Congestion Control (Jacobson 1988). • Domain Name System (DNS)- mapping between human readable Internet computer name and 32-bit IP address. Lesson 1: History of Computer Networks - 12

  18. Proliferation of Networks 1980-90(The Minitel Project) • French Minitel project paralleling ARPAnet • Ambitious projest sponsored by the French Government • X.25 protocol suite using virtual circuits • By mid-90’s, it offered more than 20, 000 services- from home banking to research database • Used by more than 20% of the population • Generated over $1 billion in revenue • Was in most French homes 10 years before Americans had ever heard of the Internet. Lesson 1: History of Computer Networks - 14

  19. Internet Explosion: The1990s • Early 90’s Arpanet decommissioned as Milnet and Defense Data Net grew enough to carry all defense-related traffic. • NSF lifted restrictions on commercial use of NSFnet (1991). NSFnet began to serve as a backbone and was later decommissioned it in 1995. • Web invented at CERN by Tim Berners-Lee (89-91) • Developed intial versions of HTML, HTTP, a web server and a web browser - Based on the original work on Hypertext in 1940s by Bush (1945) and in 1960s by Ted Nelson • Marc Andreesen developed Mosaic- Popular GUI browser. History of Computer Networks -15

  20. Internet Explosion: First half of1990s • Marc Andreesen and Jim Clark formed Mosaic Communications in 1994(it later became Netscape). • By 1995, University students were able surf web. • Big and small companies started transacting on the web and transact commerce over the web. History of Computer Networks -16

  21. Internet Explosion: Second half of1990s • Microsoft (MS) started making browsers (1996) and this started the war with NetScape which MS won later. • E-mail evolved with address books, attachments, hot links, multimedia support. • 4 Killer applications • Web accessible email • Web browsing & internet commerce • instant messaging with contact lists pioneered by ICQ • peer-to-peer file sharing of MP3s , pioneered by Napster . • By late 90’s, 50 million computers with 100+ million users on the web. 1 GBs Back bone link speeds achieved. History of Computer Networks -17

  22. Recent Developments • Financial turmoil, many start-ups collapsed. Still many companies like eBay, Yahoo, Amazon and Cisco emerged as winners despite setbacks in their stock prices. • Advances in content distribution, internet telephony, high speed LANs and fast routers • 3 Important developments • High Speed Access Internet Access (Cable/DSL/Wireless LANs) • Secure applications • P2P (Point-to-point Networking) History of Computer Networks -18

  23. Three Important Recent Developments I- High Speed Internet Access • Increased penetration of broadband residential Internet via Cable and DSL with applications such as high-quality Video on Demand and high quality Video Conferencing • Increased ubiquity of public Wi-Fi nets (with 11 Mbps and higher speeds) • Internet access via mobile phones of 3rd Generation & Beyond. History of Computer Networks -19

  24. Three Important Recent DevelopmentsII- Security • Intrusion detection methods for early warning of denial of service attacks through worms (e.g. Blaster worm) that infect systems and clod networks. • Use of Firewalls to filter unwanted traffic before it enters the network. • Use of IP-traceback to pinpoint the origin of attacks. History of Computer Networks -20

  25. Three Important Recent DevelopmentsIII- P2P Networking • P2P application exploits resources (memory, disk-space, content and CPU cycles) in user’s computers. • It gives significant autonomy from central servers. • KaZaA is the most popular p2P-file sharing system. • Currently, this network has 4 million connected systems and its traffic constitutes 20-50% of Internet traffic. History of Computer Networks -21

  26. Summary and Follow-up • In this lesson, we covered History of Computer Networks organized into approximately 5 decades. • In passing, we found what all a computer networks can do. This will help you to write the first chapter of your project report i.e. to prepare a table of requirements for your own network! • You got used to some terminology e.g. circuit switching, packet switching, firewalls, etc. If any of those concepts are not clear, you may search the web, discuss with me or wait on till we take them up in a greater detail later. • Explore the concepts- Circuit/Virtual Circuit/Packet switching on the web. History of Computer Networks - 22

  27. Lesson 2:Overview of Computer Networks

  28. Preview of the Lesson 2 • In this lesson, we try to answer the question- What is a Computer Network? • We try to view computer networks from different perspectives. In other words, we try to answer the question: what are all the different types computer networks? • We will have an overview of different components of a computer network (Internet). • We also study a little bit of how the interconnected computers communicate with one another, that is, we will have cursory glance at protocol stacks. Overview of Computer Networks - 1

  29. Computer Networks- Definition & Perspectives Reference: • What is a Computer Network? A system for communication among two or more computers. • What are all the different types computer networks? Different ways of categorization of Computer networks are: • Range or extent of the network • Inter-nodal functional relationship • Network Topology • Specialized functions of the nodes Overview of Computer Networks - 2

  30. Network Categorization based on the Range I- Personal Area Network (PAN) • With a reach of a few meters, connects home/small office devices/computers or higher level net/Internet (in the latter case called an uplink) • could be wired (using Universal Serial Bus, shortly USB, or Fire-wire) or wireless (using blue-tooth or IrDA, that is, Infrared Data Association) • Blue Tooth PAN is also called Piconet • IEEE 802.15.1 adapts Physical and MAC layers from Bluetooth 1.1 • Zigbeee is a proprietary technology for low power radios based on IEEE 802.15.4 Overview of Computer Networks - 3

  31. Network Categorization based on the RangeII - Local Area Network (LAN) • Range is less than 1000 m2 • Could be used in home, small office or university. • Earlier popular LAN was proprietary - DataPoint’s ArcNet • IEEE later produced two LAN standards- Ether Net (IEEE 802.3) and Token Ring (IEEE 802.5) • LAN speeds could be 10/100 Mbps (Ether Net) and 4/16/100 mbps/1 Gbps (Token Ring) • Wireless LANs- IEEE 802.11 (Wi-Fi)- speeds up to 56 Mbps Overview of Computer Networks - 4

  32. Network Categorization based on the RangeIII - Metropolitan Area Network (MAN) • Spans a city or a big campus with range up to 200 km (125 miles) • Earlier technologies used for MANs were: • Fiber Distributed Data Interface (FDDI) • Switched Megabit Data Service (as defined by IEEE 802.6 MAN standard) using either B-ISDN or Distributed Dual-Queue Dual Bus (DQDB) with speeds 1.5/45 Mbs. • Asynchronous Transfer Mode (ATM) • Above technologies are being displaced by 1GB Ether Net based Mans • MAN links between LANs and WANs are usually microwave/ infra-red/radio. Overview of Computer Networks - 5

  33. Network Categorization based on the RangeIV - Wide Area Network (WAN) • Covers wide geographical areas spanning multiple cities. • Works on leased lines and connects multiple LANs • Uses protocols such as TCP/IP, x.25, Frame Relay and ATM • Usually used to connect different sites of an organization or service provider. For this reason, it is being replaced by Virtual Private Networks (VPNs). • VPNs are of two types- i) Secure (they use leased lines and use protocols like IPSEC ii) Trusted (They rely on security of single provider’s network and use protocols such as Multi-protocol label switching (MPLS) and Layer 2 Tunneling Protocol (L2TP) Overview of Computer Networks - 6

  34. Network Categorization based on the Functional Relationship of the Nodes • Client- Server Network • Multi-tier architecture (GUI, business logic and DB could be in 3 separate tiers) • Peer-to-Peer Network (each node acts as both a client and server, e.g. in case of e-mail). Overview of Computer Networks - 7

  35. Network Categorization based on the Network Topology • Bus Network • Star Network • Ring Network • Grid Network • Toroidal Networks and Hypercubes • Tree and Hyper-tree Networks Overview of Computer Networks - 8

  36. Network Categorization based on Specialized Function • Storage Area Network (SAN)- used for connecting multiple storage devices such as disk controllers and tape libraries to a server. • Server Farms (Network of servers maintained by an enterprise) • Process Control Network- transmits data between measurement and control units. • Value Added Network (VAN)- a third party network put up to add value (e.g. maintenance & admin) to an enterprise network • SOHO (small office home office) Network- use ethernet/Wi-Fi • Wireless Community Networks- meant for hobbyists and use wireless LANs- outgrowths of amateur radio clubs. Overview of Computer Networks - 9

  37. Nuts and Bolts view of Computer Network with Internet- Network of Networks Overview of Computer Networks - 10

  38. Network Building Blocks • Switch - connects computing devices to host computers, allowing a large number of devices to share a limited number of ports • Router - a Protocol-dependent device that connects sub-networks together • Bridge - a device that interconnects local or remote networks • Gateway - a device that can interconnect networks with different, incompatible communications Overview of Computer Networks - 11

  39. Network Building Blocks (Continued) • Network hosts, workstations, etc. - they generally represent the source and sink (destination) of data traffic (packets) • Multiplexer - telecommunications device that funnels multiple signals onto a single channel • Transceiver - (short for transmitter-receiver), is a device that both transmits and receives analog or digital signals. • Firewall - a system or group of systems that enforces an access control policy between an organization's network and the Internet for purposes of security.  Overview of Computer Networks - 12

  40. It is a loosely hierarchical network of networks (some private intranets) with millions of connected computing devices: Hosts, end-systems (Network Edge) pc’s workstations, servers PDA (Personal Digital Assistant)’s phones, toasters running network apps : Communication links (Network Access) fiber, coaxial cable, copper, radio, satellite Switches, routers, bridges, gateways (Network Core) router workstation server mobile local ISP regional ISP company network “Nuts and bolts” view of the Internet Overview of Computer Networks - 13

  41. Human protocols: A way of communication between humans Dictated by local culture Greeting, response, action taken Examples: “Hey, got time?,” “I have a dumb question,” This is so and so..” Network protocols: Machines rather than humans involved, but all Internet communication activity is governed by protocols Dictated by standards Protocols define format, order of messages sent and received among network entities, and actions taken on message transmission and receipt Example: TCP/IP, ISO What’s a protocol? Overview of Computer Networks - 14

  42. TCP connection reply. Get Got the time? 2:00 <file> time Human and Network Protocol Examples Hi TCP connection req. Hi Overview of Computer Networks - 15

  43. Protocols • Building blocks of a network architecture • Each protocol object has two different interfaces • service interface: defines operations on this protocol • peer-to-peer interface: defines messages exchanged with peer • Term “protocol” is overloaded • specification of peer-to-peer interface • module that implements this interface Overview of Computer Networks - 16

  44. Networks are complex; they have many heterogeneous “pieces”: Hosts, routers, links of various media, Application entities, protocols, hardware, software … Question: How to achieve effective communication in this mess? Simple Answer: Divide & Conquer Why Protocol “Layers?” Overview of Computer Networks - 17

  45. Why layering? Divide & Conquer Policy to handle Complex systems: • Explicit structure allows identification of complex system’s pieces and their inter-relationships. • Following slides present an example of a layered real-life protocol. • Modularization eases maintenance and updating of system • change of implementation of layer’s service transparent to rest of system e.g., change in gate procedure doesn’t affect rest of system Cost: Layering may affect efficiency, but is inevitable. Overview of Computer Networks - 18

  46. ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing airplane routing Steps in Organization of air travel Overview of Computer Networks - 19

  47. Layered services in air travel Counter-to-counter delivery of person+bags baggage-claim-to-baggage-claim delivery people transfer: loading gate to arrival gate runway-to-runway delivery of plane airplane routing from source to destination Overview of Computer Networks - 20

  48. airplane routing airplane routing airplane routing Distributed implementation of layer functionality ticket (complain) baggage (claim) gates (unload) runway landing airplane routing ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing arriving airport Departing airport intermediate air traffic sites Layers: each layer implements a service via its own intra-layer actions relying on services provided by layer below Overview of Computer Networks - 21

  49. Application: supporting network applications (e.g. ftp, smtp, http) Transport: host-host data transfer, defines quality and nature of data delivery (e.g. tcp, udp) application transport network link physical Internet protocol stack • Network: addressing and routing of datagrams from source to destination (e,g. Ip & other routing protocols) • Link: logical organization of data bits transmitted • on a particular medium; framing, addressing, error correction/detection (check sum) e.g. ppp, ethernet • Physical: bits “on the wire” Defines physical • Properties of various media e.g. Ether-Net cable size • 7-layer OSI protocol (of ISO) has session (reply and response packet pairing) and presentation layers (data syntax, encryption) above transport and below application layer. Overview of Computer Networks - 22

  50. Each layer: distributed “entities” implement layer functions at each node entities perform actions, exchange messages with peers network link physical application transport network link physical application transport network link physical application transport network link physical application transport network link physical Layering: logical communication Overview of Computer Networks - 23