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Administrative Things

Administrative Things. Textbook in the bookstore ? Lecture notes on the web ?? Any questions and suggestions so far ??? … . Chapter 1: roadmap. 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs

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Administrative Things

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  1. Administrative Things • Textbook in the bookstore ? • Lecture notes on the web ?? • Any questions and suggestions so far ??? • … Lecture-3

  2. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History Lecture-3

  3. network edge: applications and hosts connection-oriented and connectionless services Internet protocols: ??? and ??? network core: routers, network of networks data switching: circuit switching and packet switching comparison of the two switching approaches virtual circuit networks and datagram networks access networks, physical media Dail-up, DSL, Cable modem, LAN, wireless LAN, 3G, Satellite Twisted pair copper, Coaxial cable, fiber optics, ratio A Review of Last Lecture Lecture-3

  4. roughly hierarchical at center: “tier-1” ISPs e.g., UUNet, BBN/Genuity, Sprint, AT&T national/international coverage NAP Tier-1 providers also interconnect at public network access points (NAPs) Tier-1 providers interconnect (peer) privately Internet structure: network of networks Tier 1 ISP Tier 1 ISP Tier 1 ISP Lecture-3

  5. “Tier-2” ISPs: smaller (often regional) ISPs Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs 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 1 ISP Tier 1 ISP Tier 1 ISP Lecture-3

  6. “Tier-3” ISPs and local ISPs last hop (“access”) network (closest to end systems) 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 1 ISP Tier 1 ISP Tier 1 ISP Lecture-3

  7. 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 A packet passes through many networks Tier 1 ISP Tier 1 ISP Tier 1 ISP Lecture-3

  8. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History Lecture-3

  9. packets queue in router buffers, wait for turn packet being transmitted (delay) packets queueing (delay) free (available) buffers: arriving packets dropped (loss) if no free buffers How do loss and delay occur? A B Lecture-3

  10. 1. nodal processing: check bit errors determine output link transmission A propagation B nodal processing queueing Four sources of packet delay • 2. queueing • time waiting at output link for transmission • depends on congestion level of router Lecture-3

  11. 3. Transmission delay: R=link bandwidth (bps) L=packet length (bits) time to send bits into link = L/R 4. Propagation delay: d = length of physical link s = propagation speed in medium (~2x108 m/sec) propagation delay = d/s transmission A propagation B nodal processing queueing Delay in packet-switched networks Note: s and R are very different quantities! Lecture-3

  12. Cars “propagate” at 100 km/hr Toll booth takes 12 sec to service a car (transmission time) car~bit; caravan ~ packet Q: How long until caravan is lined up before 2nd toll booth? Time to “push” entire caravan through toll booth onto highway = 12*10 = 120 sec Time for last car to propagate from 1st to 2nd toll both: 100km/(100km/hr)= 1 hr A: 62 minutes toll booth toll booth Caravan analogy 100 km 100 km ten-car caravan Lecture-3

  13. Cars now “propagate” at 1000 km/hr Toll booth now takes 1 min to service a car Q:Will cars arrive to 2nd booth before all cars serviced at 1st booth? Yes! After 7 min, 1st car at 2nd booth and 3 cars still at 1st booth. 1st bit of packet can arrive at 2nd router before packet is fully transmitted at 1st router! toll booth toll booth Caravan analogy (more) 100 km 100 km ten-car caravan Lecture-3

  14. Nodal delay • dproc = processing delay • typically a few microsecs 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 Lecture-3

  15. R=link bandwidth (bps) L=packet length (bits) a=average packet arrival rate Queueing delay (revisited) traffic intensity = La/R • La/R ~ 0: average queueing delay small • La/R -> 1: delays become large • La/R > 1: more “work” arriving than can be serviced, average delay infinite! Lecture-3

  16. “Real” Internet delays and routes • What do “real” Internet delay & loss look like? • Traceroute program: provides delay measurement from source to router along end-end Internet path towards destination. For all i: • sends three packets that will reach router i on path towards destination • router i will return packets to sender • sender times interval between transmission and reply. 3 probes 3 probes 3 probes Lecture-3

  17. “Real” Internet delays and routes traceroute: fester.engr.uconn.edu to www.sun.com Three delay measurements from Fester.engr.uconn.edu to www.sun.com traceroute to www.sun.com (64.124.140.199), 30 hops max, 40 byte packets 1 137.99.15.129 (137.99.15.129) 5.902 ms 1.946 ms 4.148 ms 2 10.12.250.1 (10.12.250.1) 0.682 ms 0.618 ms 0.578 ms 3 137.99.24.193 (137.99.24.193) 0.891 ms 0.871 ms 0.852 ms 4 uconn-edge.net.uconn.edu (137.99.22.41) 1.478 ms 1.866 ms 2.736 ms 5 159.247.232.129 (159.247.232.129) 2.162 ms 1.983 ms 2.068 ms 6 65.115.97.193 (65.115.97.193) 6.237 ms 6.785 ms 6.199 ms 7 205.171.28.29 (205.171.28.29) 6.399 ms 8.517 ms 6.036 ms 8 205.171.8.19 (205.171.8.19) 11.142 ms 10.784 ms 11.431 ms 9 205.171.30.14 (205.171.30.14) 11.137 ms 11.752 ms 10.963 ms 10 pos4-1.pr1.lga1.us.mfnx.net (208.185.156.25) 13.200 ms 11.095 ms 11.963 ms 11 so-3-0-0.cr1.lga1.us.mfnx.net (208.185.0.237) 11.542 ms 12.008 ms 12.055 ms 12 so-1-0-0.cr1.iad1.us.mfnx.net (208.184.233.61) 15.587 ms 16.120 ms 16.459 ms 13 so-1-0-0.cr1.dca2.us.mfnx.net (208.184.233.125) 17.613 ms 17.086 ms 16.744 ms 14 so-3-0-0.mpr3.sjc2.us.mfnx.net (208.184.233.133) 80.789 ms 82.137 ms 82.055 ms 15 so-0-0-0.cr1.sjc3.us.mfnx.net (208.185.175.153) 82.030 ms 82.679 ms 82.160 ms 16 pos0-0.er2a.sjc3.us.mfnx.net (208.185.175.190) 81.658 ms 81.977 ms 80.668 ms 17 alt1-1.java.sun.com (64.124.128.212) 83.412 ms 82.077 ms 87.823 ms Lecture-3

  18. Packet loss • queue (aka buffer) preceding link in buffer has finite capacity • when packet arrives to full queue, packet is dropped (aka lost) • lost packet may be retransmitted by previous node, by source end system, or not retransmitted at all Lecture-3

  19. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History Lecture-3

  20. Networks are complex! many “pieces”: hosts routers links of various media applications protocols hardware, software Question: Is there any hope of organizing structure of network? Or at least our discussion of networks? Protocol “Layers” Lecture-3

  21. ticket (complain) baggage (claim) gates (unload) runway landing airplane routing ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing airplane routing Organization of air travel • a series of steps Lecture-3

  22. ticket (complain) baggage (claim) gates (unload) runway landing airplane routing ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing airplane routing Organization of air travel: a different view Layers: each layer implements a service • via its own internal-layer actions • relying on services provided by layer below Lecture-3

  23. Layered air travel: services 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 Lecture-3

  24. 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 Lecture-3

  25. Why layering? Dealing with complex systems: • explicit structure allows identification, relationship of complex system’s pieces • layered reference model for discussion • modularization eases maintenance, 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 • layering considered harmful? Lecture-3

  26. application: supporting network applications FTP, SMTP, STTP transport: host-host 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” application transport network link physical Internet protocol stack Lecture-3

  27. 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 Lecture-3

  28. E.g.: transport take data from app add addressing, reliability check info to form “datagram” send datagram to peer wait for peer to ack receipt analogy: post office network link physical application transport network link physical application transport network link physical application transport network link physical application transport network link physical data data data ack Layering: logical communication transport transport Lecture-3

  29. network link physical application transport network link physical application transport network link physical application transport network link physical application transport network link physical data data Layering: physical communication Lecture-3

  30. M M H H H H H H H H H H H H t t t n l n l t n t n t M M M M application transport network link physical application transport network link physical M M Protocol layering and data Each layer takes data from above • adds header information to create new data unit • passes new data unit to layer below source destination message segment datagram frame Lecture-3

  31. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 ISPs and Internet backbones 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History Lecture-3

  32. Homeworks • Reading assignments • Chapter 1: a good overview of computer networks • Written assignments • Part of 1st written assignment • Chapter 1: Problem #5, 10, 16 (a, b, c) • More (& due date) will be posted on the web • Try traceroute program again and do some delay analysis • choose whatever destination you like Lecture-3

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