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1: Introduction1 Introduction 3. 1: Introduction2 Delay in packet-switched networks packets experience delay on end-to-end path r four sources of delay.

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Presentation on theme: "1: Introduction1 Introduction 3. 1: Introduction2 Delay in packet-switched networks packets experience delay on end-to-end path r four sources of delay."— Presentation transcript:

1 1: Introduction1 Introduction 3

2 1: Introduction2 Delay in packet-switched networks packets experience delay on end-to-end path r four sources of delay at each hop r nodal processing: m check bit errors m determine output link r queueing m time waiting at output link for transmission m depends on congestion level of router A B propagation transmission nodal processing queueing

3 1: Introduction3 Delay in packet-switched networks Transmission delay: r R=link bandwidth (bps) r L=packet length (bits) r time to send bits into link = L/R Propagation delay: r d = length of physical link r s = propagation speed in medium (~2x10 8 m/sec) r propagation delay = d/s A B propagation transmission nodal processing queueing Note: s and R are very different quantities!

4 1: Introduction4 Queueing delay (revisited) r R=link bandwidth (bps) r L=packet length (bits) r a=average packet arrival rate traffic intensity = La/R r La/R ~ 0: average queueing delay small r La/R -> 1: delays become large r La/R > 1: more “work” arriving than can be serviced, average delay infinite!

5 1: Introduction5 “Real” Internet delays and routes 1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms 2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms 3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms 4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms 5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms 6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms 7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms 8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms 9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms 10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms 11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms 12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms 13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms 14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms 15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms 16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms 17 * * * 18 * * * 19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms traceroute (or tracert): routers, rt delays on source- dest path also: pingplotter, various windows programs

6 1: Introduction6 Protocol “Layers” Networks are complex! r many “pieces”: m hosts m routers m links of various media m applications m protocols m hardware, software Question: Is there any hope of organizing structure of network? Or at least our discussion of networks?

7 1: Introduction7 Internet protocol stack r application: supporting network applications m ftp, smtp, http r transport: host-host data transfer m tcp, udp r network: routing of datagrams from source to destination m ip, routing protocols r link: data transfer between neighboring network elements m ppp, ethernet r physical: bits “on the wire” application transport network link physical

8 1: Introduction8 Layering: logical communication application transport network link physical application transport network link physical application transport network link physical application transport network link physical network link physical Each layer: r distributed r “entities” implement layer functions at each node r entities perform actions, exchange messages with peers

9 1: Introduction9 Layering: logical communication application transport network link physical application transport network link physical application transport network link physical application transport network link physical network link physical data E.g.: transport r take data from app r add addressing, reliability check info to form “datagram” r send datagram to peer r wait for peer to ack receipt r analogy: post office data transport ack

10 1: Introduction10 Layering: physical communication application transport network link physical application transport network link physical application transport network link physical application transport network link physical network link physical data

11 1: Introduction11 Protocol layering and data Each layer takes data from above r adds header information to create new data unit r passes new data unit to layer below application transport network link physical application transport network link physical source destination M M M M H t H t H n H t H n H l M M M M H t H t H n H t H n H l message segment datagram frame

12 1: Introduction12 Internet structure: network of networks r roughly hierarchical r national/international backbone providers (NBPs) m e.g. BBN/GTE, Sprint, AT&T, IBM, UUNet m interconnect (peer) with each other privately, or at public Network Access Point (NAPs) r regional ISPs m connect into NBPs r local ISP, company m connect into regional ISPs NBP A NBP B NAP regional ISP local ISP local ISP

13 1: Introduction13 National Backbone Provider e.g. Sprint US backbone network

14 1: Introduction14 Internet History r 1961: Kleinrock - queueing theory shows effectiveness of packet- switching r 1964: Baran - packet- switching in military nets r 1967: ARPAnet conceived by Advanced Research Projects Agency r 1969: first ARPAnet node operational r 1972: m ARPAnet demonstrated publicly m NCP (Network Control Protocol) first host- host protocol m first e-mail program m ARPAnet has 15 nodes 1961-1972: Early packet-switching principles

15 1: Introduction15 Internet History r 1970: ALOHAnet satellite network in Hawaii r 1973: Metcalfe’s PhD thesis proposes Ethernet r 1974: Cerf and Kahn - architecture for interconnecting networks r late70’s: proprietary architectures: DECnet, SNA, XNA r late 70’s: switching fixed length packets (ATM precursor) r 1979: ARPAnet has 200 nodes Cerf and Kahn’s internetworking principles: m minimalism, autonomy - no internal changes required to interconnect networks m best effort service model m stateless routers m decentralized control define today’s Internet architecture 1972-1980: Internetworking, new and proprietary nets

16 1: Introduction16 Internet History r 1983: deployment of TCP/IP r 1982: smtp e-mail protocol defined r 1983: DNS defined for name-to-IP- address translation r 1985: ftp protocol defined r 1988: TCP congestion control r new national networks: Csnet, BITnet, NSFnet, Minitel r 100,000 hosts connected to confederation of networks 1980-1990: new protocols, a proliferation of networks

17 1: Introduction17 Internet History r Early 1990’s: ARPAnet decommissioned r 1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995) r early 1990s: WWW m hypertext [Bush 1945, Nelson 1960’s] m HTML, http: Berners-Lee m 1994: Mosaic, later Netscape m late 1990’s: commercialization of the WWW Late 1990’s: r est. 50 million computers on Internet r est. 100 million+ users r backbone links running at 1 Gbps 1990’s: commercialization, the WWW

18 1: Introduction18 Introduction: Summary Covered a “ton” of material! r Internet overview r what’s a protocol? r network edge, core, access network m packet-switching versus circuit-switching r performance: loss, delay r layering and service models r backbones, NAPs, ISPs r history You now have: r context, overview, “feel” of networking r more depth, detail later in course

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