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CENG415 – Communication Networks

CENG415 – Communication Networks. Lectures 2 Internet structure. Chapter 1. What is the Internet? Network edge Network core Network access and physical media Internet structure and ISPs Delay & loss in packet-switched networks Protocol layers, service models

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CENG415 – Communication Networks

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  1. CENG415 – Communication Networks Lectures 2 Internet structure

  2. Chapter 1 • What is the Internet? • Network edge • Network core • Network access and physical media • Internet structure and ISPs • Delay & loss in packet-switched networks • Protocol layers, service models • Networks under attack: security (covered in CENG410) • History

  3. NAP Tier-1 providers also interconnect at public network access points (NAPs) Tier-1 providers interconnect (peer) privately Internet structure – network of networks • roughly hierarchical • at center: “tier-1” ISPs • Examples are Sprint, AT&T… • Offer national/international coverage Tier 1 ISP Tier 1 ISP Tier 1 ISP

  4. Internet structure – network of networks • Tire 1 ISPs are the top of the hierarchy • Tire 1 ISPs offer services to each others • physically join their individual network backbones to create the global Internet backbone. • This includes the undersea cables that connect the continents • Tire 1 ISPs offer services to tire 2 ISPs

  5. NAP Tier-2 ISPs also peer privately with each other, interconnect at NAP* • Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet • tier-2 ISP is customer of tier-1 provider Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Internet structure – network of networks • “Tier-2” ISPs: smaller (often regional) ISPs • Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs Tier 1 ISP Tier 1 ISP Tier 1 ISP

  6. Internet structure – network of networks • Tier 2 ISPs are the next tier in terms of backbone access • Tier 2 ISPs pay Tier 1 ISPs to provide their customers with global Internet access

  7. Tier 3 ISP local ISP local ISP local ISP local ISP local ISP local ISP local ISP local ISP NAP Local and tier- 3 ISPs are customers of higher tier ISPs connecting them to rest of Internet Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Internet structure – network of networks • “Tier-3” ISPs and local ISPs • last hop (“access”) network (closest to end systems) Tier 1 ISP Tier 1 ISP Tier 1 ISP

  8. Tier 3 ISP local ISP local ISP local ISP local ISP local ISP local ISP local ISP local ISP NAP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Internet structure – network of networks • a packet passes through many networks! Tier 1 ISP Tier 1 ISP Tier 1 ISP

  9. Chapter 1 • What is the Internet? • Network edge • Network core • Network access and physical media • Internet structure and ISPs • Delay & loss in packet-switched networks • Protocol layers, service models • Networks under attack: security (covered in CENG410) • History

  10. packet being transmitted (delay) packets queueing (delay) free (available) buffers: arriving packets dropped (loss) if no free buffers How do loss and delay occur? packets queue in router buffers • packet arrival rate to link exceeds output link capacity • packets queue, wait for turn A B

  11. Four sources of packet delay? • nodal processing (router open packet for validation) • check bit errors • determine output link • queuing (node "i") = Qi/Rout • time waiting at output link for transmission • depends on congestion level of router • Transmission delay: • R=link bandwidth (bps) • L=packet length (bits) • time to send bits into link = L/R • Propagation delay = d/s • d = length of physical link • s = propagation speed in medium (~2x108 m/sec) A transmission propagation B nodal processing queuing

  12. packet delay computation? • dproc = processing delay (negligible) typically a few microsecs (actually,nanosec.s) or less • dqueue = queuing delay depends on congestion • dtrans = transmission delay = L/R, significant for low-speed links • dprop = propagation delay a few microsecs to hundreds of msecs sum over nodes (Qi/Ri) sum over links (Ri) Xtotal / s Multiple links:

  13. In reality? • tracert (trace route) is a windows utility to trace a packet from sender to destination. • How tracert works set max number of routers to 1 repeat send 3 packets wait for reply from routers compute time between sending and receiving increase by 1 the max number of routers until destination reached 3 probes 3 probes 3 probes

  14. Chapter 1 • What is the Internet? • Network edge • Network core • Network access and physical media • Internet structure and ISPs • Delay & loss in packet-switched networks • Protocol layers, service models • Networks under attack: security (covered in CENG410) • History

  15. 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 Layers by example Layers: each layer implements a service • via its own internal-layer actions • relying on services provided by layer below

  16. application transport network link physical Layers • application: supporting network applications • FTP, SMTP, HTTP • transport: process-process data transfer • TCP, UDP • network: routing of datagrams from source to destination • IP, routing protocols • link: data transfer between neighboring network elements • PPP, Ethernet • physical: bits “on the wire” (Ethernet or WiFi adapter)

  17. network link physical link physical M M M Ht M Hn Hn Hn Hn Ht Ht Ht Ht M M M M Ht Hn Ht Hl Hl Hl Hn Hn Hn Ht Ht Ht M M M Encapsulation source message application transport network link physical segment datagram frame Ethernet switch destination application transport network link physical router

  18. Chapter 1 • What is the Internet? • Network edge • Network core • Network access and physical media • Internet structure and ISPs • Delay & loss in packet-switched networks • Protocol layers, service models • Networks under attack: security (covered in CENG410) • History

  19. History • 1961: L. Kleinrock - queuing theory shows effectiveness of packet-switching • 1964: P. Baran - packet-switching in military nets • 1967: ARPAnet conceived by Advanced Research Projects Agency • 1969: first ARPAnet node operational • 1972: ARPAnet public demonstration (15 nodes) • NCP (Network Control Protocol) first host-host protocol • first e-mail program • 1979: ARPAnet has 200 nodes • 1982:smtp e-mail protocol defined • 1988: TCP congestion control • Early 1990’s: ARPAnet decommissioned. new national networks: Csnet, BITnet, NSFnet, Minitel • Since then: html, http, netscape, instant messaging • 1961-1972: Early packet-switching principles

  20. Today 2007: ~500 million hosts Voice, Video over IP P2P applications:BitTorrent (file sharing) Skype (VoIP) PPLive (video)‏ more applications: YouTube wireless, mobility 2009: a quarter of Earth's population uses the services of the Internet. Visualization of the various routes through a portion of the Internet. img_src: wikipedia

  21. LAB: Packet tracer • Is a CISCO utility to simulate and test a network. • Double click on the file CENG415-network.pkt

  22. LAB: Packet tracer • We will use this network all over this semester. • Components are: • PC • Switches (connect PCs together to build a network) • Routers (connect different networks) • Servers (offer a services) Click on PC0, go to Desktop and click on Command prompt • ipconfig /all • ping www.ceng415.com (where did PC0 find the address of www.ceng415.com)>

  23. LAB: Packet tracer • Find the IP of PC0 • Find the IP of the DNS server • Find the IP of the Web server • How many routers do we have? • How many switches? • How many networks do we have? • Why cables between routers are dashed? • Open a command prompt window on PC0 and trace the path to www.ceng415.com • Open a browser on PC0 and enter the URL www.ceng415.com • To modify the page, go to the server / config / http and change the HTML code.

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