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CSE524: Lecture 3

CSE524: Lecture 3. Internet history (Part 2), Internet challenges, Physical layer. Administrative. Homework #1 due Wednesday, Oct. 3 rd CSE524 e-mail list created E-mail TA if you have not received the introductory message. Last episode. Started on brief run-down of Internet history

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CSE524: Lecture 3

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  1. CSE524: Lecture 3 Internet history (Part 2), Internet challenges, Physical layer

  2. Administrative • Homework #1 due Wednesday, Oct. 3rd • CSE524 e-mail list created • E-mail TA if you have not received the introductory message

  3. Last episode • Started on brief run-down of Internet history • TCP/IP deployment

  4. LAN • Metcalfe • Invents Ethernet (Xerox PARC) 1973 • Proteon, IBM • Token Ring 1970s • Proliferation of LANs leads to redefining IP space • Split space into 3 classes A, B, and C • C=LANs (large number of networks with small number of hosts • B=Regional scale networks • A=Large scale national networks

  5. Application protocols • SMTP • Simple Mail Tranfer Protocol (Aug. 1982) Postel • http://www.rfc-editor.org/rfc/rfc821.txt • DNS • Hostnames server, SRI (Mar. 1982) Harrenstien • http://www.rfc-editor.org/rfc/rfc811.txt • Current hierarchical architecture (Aug. 1982) Su, Postel • http://www.rfc-editor.org/rfc/rfc819.txt • Domain Name System standard (Nov. 1983) Mockapetris • http://www.rfc-editor.org/rfc/rfc882.txt • http://www.rfc-editor.org/rfc/rfc882.txt

  6. Application protocols • Telnet • Telnet protocol (May 1983) Postel, Reynolds • http://www.rfc-editor.org/rfc/rfc854.txt • FTP • File transfer protocol (Oct. 1985) Postel, Reynolds • http://www.rfc-editor.org/rfc/rfc959.txt

  7. Meanwhile, in a parallel universe • Competing mostly inoperable networks from jealous government agencies and companies • DOE: MFENet (Magnetic Fusion Energy scientists) • DOE: HEPNet (High Energy Physicists) • NASA: SPAN (Space physicists) • NSF: CSNET (CS community) • NSF: NSFNet (Academic community) 1985 • AT&T: USENET with Unix, UUCP protocols • Academic networks: BITNET (Mainframe connectivity) • Xerox: XNS (Xerox Network System) • IBM: SNA (System Network Architecture) • Digital: DECNet • UK: JANET (Academic community in UK) 1984

  8. NSFNet • NSF program led by Jennings, Wolff (1986-1995) • Network for academic/research community • Selects TCP/IP as mandatory for NSFNet • Structures with DARPA “Requirements for Internet Gateways” to ensure interoperability • http://www.rfc-editor.org/rfc/rfc985.txt • Builds out wide area networking infrastructure • Develops strategy for developing and handing it over eventually to commercial interests • Historical note: Al Gore helps win funding for NSFNet program

  9. NSFNet • Structure • 6 nodes with 56kbs links • Jointly managed exchange points • Statistical, non-metered peering agreements • CSNET (Farber) • Kahn (ARPANET) • Cost-sharing of infrastructure • Seek out commercial, non-academic customers • Help pay for and expand regional academic facilities • Economies of scale • Prohibit commercial use of NSFNet to encourage commercial backbones • Leads to PSINet, UUNET, ANS, CO+RE backbone development

  10. TCP/IP software • Berkeley • Unix TCP/IP available at no cost (DoD) • Incorporates BBN TCP/IP implementation • Later re-implements • Large dispersal to community • Critical mass (like the fax machine) • PCs • Low cost PC access (Wintel) • Economies of scale

  11. Privatization • Commercial interconnection • US Federal Networking Council (1988-1989) • MCI Mail allowed • ARPANET decommissioned (1990) • NSFNet decommissioned (1995) • 21 nodes with multiple T3 (45Mbs) links • Regional academic networks forced to buy national connectivity from private long haul networks • TCP/IP supplants and marginalizes all others to become THE bearer service for the Internet • Total cost of NSF program? $200 million from 1986-1995

  12. Growing pains • Explosion of networks • Routing initially flat, each node runs the same distributed routing algorithm • Moved to hierarchical model • IGP (interior gateway protocol) within a region • EGP (exterior gateway protocol) to tie regions together • Individual regions use their own IGP • Saves on cost (CPU+bandwidth) • Allows rapid reconfiguration, robustness, scalability • Distributes control (a bit) • Evolves into AS=Autonomous System • IGP ->Intra-AS routing (RIP/OSPF) • EGP -> Inter-AS routing (BGP)

  13. Growing pains • Each backbone router keeps global table of exponentially increasing network routes • CIDR • Classless Inter-Domain Routing • Aggregate numerically adjacent routes going to the same AS • Variable-length subnetting • Saves space, but makes lookups harder • Longest prefix match lookup

  14. IETF • Origins • DARPA • Cerf forms coordination bodies (late 1970s) • ICB (International Cooperation Board) • ICCB (Internet Configuration Control Board) • Leiner takes over Internet research program (1983) • ICCB disbanded • Forms structure of task forces • Forms umbrella IAB (Internet Activities Board) to manage TFs • IETF (Internet Engineering) is one task force • Internet research program discontinued (1985) • IAB becomes default leadership organization for the Internet • IESG created (Internet Engineering Steering Group) • IRTF created (Internet Research Task Force)

  15. IETF • CNRI (Corporation for National Research Initiatives) • Headed by Kahn (1991) • Creates Internet Society to make process open and fair across research and commercial interests • IAB reorganized to Internet Architecture Board under Internet society • IAB, IESG, and IETF in place as they are now • Process for arbitration and operation established

  16. WWW • CERN (European Organization for Nuclear Research) • Berners-Lee, Caillau work on WWW (1989) • First WWW client (browser-editor running under NeXTStep) • Defines URLs, HTTP, and HTML • Berners-Lee goes to MIT and LCS to start W3C • Responsible for evolving protocols and standards for the web • http://www.w3.org/People

  17. WWW • NCSA (National Center for Supercomputing Applications) • Federally funded research center at University of Illinois at Urbana-Champaign • Andreessen: Mosaic and eventually Netscape (1994) • http://www.dnai.com/~thomst/marca.html

  18. Internet challenges • Not a complete list • Address depletion (IPv4, IPv6) • NAT and the loss of transparency • Routing infrastructure • Quality of service • Security • DNS scaling • Dealing with privatization • Interplanetary Internet

  19. Address depletion • IPv4: 32-bit address (4.3 billion identifiers) • 25% in use 960 million addresses (advertised in BGP tables) • http://www.caida.org/outreach/resources/learn/ipv4space/ • Inactive IP addresses advertised as well • Estimated 86 million active (July 2000) • http://www.netsizer.com/ • Do we need more addresses? • IPv6: 128-bit address

  20. Current IP address allocation

  21. NAT • Network address translation • Source and destination IP addresses and (sometimes) ports rewritten by device • Rewritten without knowledge of end-hosts • Translation typically performed only on IP address portion of packet not on addresses within data • Envelope analogy • Return address on outside changed • Return address on inside unchanged • Application data must be rewritten to maintain consistency

  22. NAT • What’s bad about NAT? • Breaks transparency of IP • Breaks hourglass and end-to-end principles (network must be changed for new applications to be deployed) • FTP, servers, P2P services and NAT • SIP, conferencing applications • Breaks IPsec • Man-in-the-middle attacks • What’s good about NAT? • Renumbering easy

  23. NAT • Application writing before NAT • New applications require no changes to be deployed on the Internet • New applications require no changes in the Internet to be deployed • Application writing after NAT • All new applications must be written with explicit knowledge of intermediate devices which rewrite network and application information

  24. Routing infrastructure • http://www.telstra.net/ops/bgptable.html • Backbone routers must keep table of all routes (75000 entries) • Growth of table size • Alleviated with CIDR aggregation and NAT • Potentially exacerbated if portable addressing used • Routing instability • Frequency of updates increases with size • Update damping occuring already • Potential for breakdown in connectivity

  25. Routing infrastructure

  26. Routing infrastructure • Reducing state in the network • Global state at every backbone router • Other non-global approaches? • Ambulance routing • Airplane routing • Landmark routing • Chess games • Limited-distance look-ahead • Better scaling properties

  27. Routing infrastructure • Non-adaptive routing on backbone • Opt-out early routing • Tier 1 ISPs route traffic solely on whether destination is within network • Limited alternative paths • Limited robustness and poor performance

  28. Routing Infrastructure • Increasing routing performance • Lambda switching, MPLS • DWDM requires extremely fast forwarding • At edges, map traffic based on IP address to wavelength or other non-IP label • Wavelength or label switch across multiple hops to other edge • Eliminate intermediate IP route lookups • Faster IP lookups • Data structures and algorithms for fast lookups

  29. Routing Infrastructure • Other challenges • Policy-based routing, packet classification • Non-destination-based routing • Route-pinning for QoS

  30. Quality of service • Predictable performance • “Weak-link” phenomenon • Requires • ISP agreements • Global support for QoS • Applications • OS • All devices in the network (routing failures, updates, queuing) • Packet sizes and unpredictable media

  31. Security • Anonymity of IP • Sender fills in its address • Connectivity over security • Spoofing and DDoS • IP traceback • http://www.acm.org/sigs/sigcomm/sigcomm2001/p1.html • Ingress filtering • http://www.ietf.org/rfc/rfc2827.txt

  32. Security • DNS centralized • 13 root name servers • Limited due to packet size constraints • Routing decentralized • Rogue source sending updates • Convergence problems • L0pht • May 1998: 30min to shut down Internet

  33. DNS scaling • Relatively flat structure • 13 centralized TLD name servers • .com servers overloaded • DNS used as a directory service • Internet directory service? • RealNames • AOL Keywords

  34. Dealing with Privatization • Improving routing instability, traffic characterization, security, etc. difficult • Finding sources of disruption (software, hardware, users) difficult • Problems are hidden not shared • Open standards in the face of commercial interests • Patents on protocols • Closed protocols • ICQ, AIM, Hotmail • Potential for closed networks • Cable network consolidation, ISP consolidation

  35. Interplanetary Internet • Extremely long round-trip times • Protocols designed with terrestrial timeout parameters

  36. The rest of the course • From birds-eye view, we will now focus on specific components • Review Lectures 1, 2, and 3 for perspective when looking at the parts • Mostly classical material with some references to newer technologies

  37. Physical Layer • Plethora of physical media • Fiber, copper, air • Specifies the characteristics of transmission media • Too many to cover in detail, not the focus of the course • Many data-link layer protocols (i.e. Ethernet, Token-Ring, FDDI. ATM run across multiple physical layers) • Physical characteristics dictate suitability of data-link layer protocol and bandwidth limits

  38. PL: Good URLs • Get ‘em while they last…. • ftp://rtfm.mit.edu/pub/usenet-by-hierarchy/comp/answers/LANs/cabling-faq • http://fcit.coedu.usf.edu/network/

  39. PL: Common Cabling • Copper • Twisted Pair • Unshielded (UTP) • CAT-1, CAT-2, CAT-3, CAT-4, CAT-5, CAT-5e • Shielded (STP) • Coaxial Cable • Fiber • Single-mode • Multi-mode

  40. PL: Twisted Pair • Most common LAN interconnection • Multiple pairs of twisted wires • Twisting to eliminate interference More twisting = Higher bandwidth, cost • Standards specify twisting, resistance, and maximum cable length for use with particular data-link layer

  41. PL: Twisted pair • 5 categories • Category 1 • Voice only (telephone wire) • Category 2 • Data to 4Mbs (LocalTalk) • Category 3 • Data to 10Mbs (Ethernet) • Category 4 • Data to 20Mbs (16Mbs Token Ring) • Category 5 (100 MHz) • Data to 100Mbs (Fast Ethernet) • Category 5e (350 MHz) • Data to 1000Mbs (Gigabit Ethernet)

  42. PL: Twisted Pair • Common connectors for Twisted Pair • RJ11 (6 pairs) • RJ45 (8 pairs) • Allows both data and phone connections • (1,2) and (3,6) for data, (4,5) for voice • Crossover cables for NIC-NIC, Hub-Hub connection (Data pairs swapped)

  43. PL: UTP • Unshielded Twisted Pair • Limited amount of protection from interference • Commonly used for voice and ethernet • Voice: multipair 100-ohm UTP

  44. PL: STP • Shielded Twisted Pair • Not as common at UTP • UTP susceptible to radio and electrical interference • Extra shielding material added • Cables heavier, bulkier, and more costly • Often used in token ring topologies • 150 ohm STP two pair (IEEE 802.5 Token Ring)

  45. PL: Coaxial cable • Single copper conductor at center • Plastic insulation layer • Highly resistant to interference • Braided metal shield • Support longer connectivity distances over UTP

  46. PL: Coaxial cable • Thick (10Base5) • Large diameter 50-ohm cable • N connectors • Thin (10Base2) cables • Small diameter 50-ohm cable • BNC, RJ-58 connector • Video cable • 75-ohm cable • BNC, RJ-59 connector • Not compatible with RJ-58

  47. PL: Fiber • Center core made of glass or plastic fiber • Transmit light versus electronic signals • Protects from electronic interference, moisture • Plastic coating to cushion core • Kevlar fiber for strength • Teflon or PVC outer insulating jacket

  48. PL: Fiber • Single-mode fiber • Smaller diameter (12.5 microns) • One mode only • Preserves signal better over longer distances • Typically used for SONET or SDH • Lasers used to signal • More expensive • Multi-mode fiber • Larger diameter (62.5 microns) • Multiple modes • LEDs used to signal • WDM and DWDM • Photodiodes at receivers

  49. PL: Fiber connectors • ESCON • Duplex SC • ST • MT-RJ (multimode) • Duplex LC

  50. PL: Wireless • Entire spectrum of transmission frequency ranges • Radio • Infrared • Lasers • Cellular telephone • Microwave • Satellite • Acoustic (see ESE sensors) • Ultra-wide band • http://www.ntia.doc.gov/osmhome/allochrt.html

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