Cs 457 Computer Networks Introduction 1 The Internet

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Cs 457 Computer Networks Introduction 1

Cs 457 Computer Networks Introduction 1

The Internet q A global network of q q computers who runs it? who

The Internet q A global network of q q computers who runs it? who pays for it? who invented the internet? How do the computer’s communicate? v There are many levels of abstraction, just like speech router server workstation mobile local ISP regional ISP UVa network Introduction 2

What’s a protocol? Hi TCP connection request Hi TCP connection response Got the time?

What’s a protocol? Hi TCP connection request Hi TCP connection response Got the time? Get http: //www. awl. com/kurose-ross 2: 00 <file> time Introduction 3

What’s a protocol? protocols define format, order of msgs sent and received among network

What’s a protocol? protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt Introduction 4

A closer look at network structure: q network edge: applications and hosts q network

A closer look at network structure: q network edge: applications and hosts q network core: routers v network of networks v q access networks, physical media: communication links Introduction 5

Distributed Applications q end systems (hosts): v v v run application programs e. g.

Distributed Applications q end systems (hosts): v v v run application programs e. g. Web, email at “edge of network” q client/server model v v client host requests, receives service from always-on server e. g. Web browser/server; email client/server q peer-peer model: v v minimal (or no) use of dedicated servers e. g. Skype, Bit. Torrent, Ka. Za. A Introduction 6

Connection-oriented Vs Connectionless Services q TCP: supports connection oriented services q UDP: supports connectionless

Connection-oriented Vs Connectionless Services q TCP: supports connection oriented services q UDP: supports connectionless services q what's the difference? v Reliability q What’s needed to make this difference? v flow control: slows down when receiver is slow v congestion control: slows down when network is slow q Trade-off? v UDP is faster Introduction 7

Connnection vs Connectionless services App’s using TCP: q HTTP (Web), FTP (file transfer), Telnet

Connnection vs Connectionless services App’s using TCP: q HTTP (Web), FTP (file transfer), Telnet (remote login), SMTP (email) App’s using UDP: q streaming media, teleconferencing, DNS, Internet telephony Introduction 8

The Network Core q mesh of interconnected links Introduction 9

The Network Core q mesh of interconnected links Introduction 9

Switching q How to transfer data between these four nodes? q Reserved bandwidth q

Switching q How to transfer data between these four nodes? q Reserved bandwidth q On-demand bandwidth Introduction 10

Circuit Switching End-end resources reserved for “call” q dedicated resources: no sharing q circuit-like

Circuit Switching End-end resources reserved for “call” q dedicated resources: no sharing q circuit-like (guaranteed) performance q call setup required Introduction 11

Circuit Switching: FDM and TDM network resources (e. g. , bandwidth) divided into “pieces”

Circuit Switching: FDM and TDM network resources (e. g. , bandwidth) divided into “pieces” FDM 4 users frequency time TDM frequency time Introduction 12

Numerical example q How long does it take to send a file of 640,

Numerical example q How long does it take to send a file of 640, 000 bits from host A to host B over a circuit-switched network? All links are 1. 536 Mbps v Each link uses TDM with 24 slots/sec v 500 msec to establish end-to-end circuit v 1, 536, 000/24 = 64000 640, 000/64, 000=10 seconds 10 +. 5 = 1 -. 5 seconds Introduction 13

Packet Switching each end-end data stream divided into packets q user A, B packets

Packet Switching each end-end data stream divided into packets q user A, B packets share network resources q each packet uses full link bandwidth q resources used as needed disadvantages: q aggregate resource demand can exceed amount available q store and forward delay: packets move one hop at a time v Bandwidth division into “pieces” Dedicated allocation Resource reservation Node receives complete packet before forwarding q Queue delay: must wait for link use Introduction 14

Packet Switching vs TDM 100 Mb/s Ethernet A B statistical multiplexing C 1. 5

Packet Switching vs TDM 100 Mb/s Ethernet A B statistical multiplexing C 1. 5 Mb/s queue of packets waiting for output link D E Sequence of A & B packets does not have fixed pattern, shared on demand statistical multiplexing. TDM: each host gets same slot in revolving TDM frame. Introduction 15

Propagation delay L R q Do we need to receive R entire packet before

Propagation delay L R q Do we need to receive R entire packet before forwarding? q Takes L/R seconds to transmit (push out) packet of L bits on to link or R bps q Entire packet must arrive at router before it can be transmitted on next link: store and forward q delay = 3 L/R (assuming zero propagation delay) R Example: q L = 640, 000 bits q R = 1. 5 Mbps q delay = 3*640, 000/1. 5=1. 28 s Introduction 16

Propagation delay L R R R q 1. 28 is much faster than 10.

Propagation delay L R R R q 1. 28 is much faster than 10. 5 seconds for circuit switched routing q What if there were other users? ? q --revisit this question later Introduction 17

Packet switching versus circuit switching Is packet switching a “slam dunk winner? ” q

Packet switching versus circuit switching Is packet switching a “slam dunk winner? ” q Great for bursty data resource sharing v simpler, no call setup q Excessive congestion: packet delay and loss v protocols needed for reliable data transfer, congestion control q Q: How to provide circuit-like behavior? v bandwidth guarantees needed for audio/video apps v still an unsolved problem (chapter 7) v Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet-switching)? Introduction 18

Chapter 1: roadmap 1. 1 What is the Internet? 1. 2 Distributed applications 1.

Chapter 1: roadmap 1. 1 What is the Internet? 1. 2 Distributed applications 1. 3 Routing 1. 4 Physical media 1. 5 Internet structure 1. 6 Delay & loss 1. 7 Protocol layers 1. 8 History Introduction 19

Access networks and physical media Q: How to connect end systems together? Introduction 20

Access networks and physical media Q: How to connect end systems together? Introduction 20

Home networks Typical home network components: q ADSL or cable modem q router/firewall/NAT q

Home networks Typical home network components: q ADSL or cable modem q router/firewall/NAT q Ethernet q wireless access point to/from cable headend cable modem router/ firewall Ethernet wireless laptops wireless access point Introduction 21

Physical Media q Bit: propagates between transmitter/rcvr pairs q physical link: what lies between

Physical Media q Bit: propagates between transmitter/rcvr pairs q physical link: what lies between transmitter & receiver q guided media: v signals propagate in solid media: copper, fiber, coax Twisted Pair (TP) q two insulated copper wires v v Category 3: traditional phone wires, 10 Mbps Ethernet Category 5: 100 Mbps Ethernet q unguided media: v signals propagate freely, e. g. , radio Introduction 22

Sharing the Medium packet Ethernet protocol: 1. Listen 2. If channel is clear, send

Sharing the Medium packet Ethernet protocol: 1. Listen 2. If channel is clear, send 3. If collision, back off 1 234567 cable headend cable distribution network (simplified) home Introduction 23

Getting more data on the wire FDM: V I D E O V I

Getting more data on the wire FDM: V I D E O V I D E O D A T A C O N T R O L 1 2 3 4 5 6 7 8 9 Channels cable headend cable distribution network home Introduction 24

Chapter 1: roadmap 1. 1 What is the Internet? 1. 2 Distributed Applications 1.

Chapter 1: roadmap 1. 1 What is the Internet? 1. 2 Distributed Applications 1. 3 Routing 1. 4 Physical media 1. 5 Internet structure 1. 6 Delay & loss 1. 7 Protocol layers 1. 8 History Introduction 25

Internet structure: network of networks q roughly hierarchical q at center: “tier-1” ISPs (e.

Internet structure: network of networks q roughly hierarchical q at center: “tier-1” ISPs (e. g. , MCI, Sprint, AT&T, Cable and Wireless), national/international coverage v treat each other as equals Tier-1 providers interconnect (peer) privately Tier 1 ISP NAP Tier-1 providers also interconnect at public network access points (NAPs) Tier 1 ISP Introduction 26

Tier-1 ISP: e. g. , Sprint US backbone network Seattle Tacoma DS 3 (45

Tier-1 ISP: e. g. , Sprint US backbone network Seattle Tacoma DS 3 (45 Mbps) OC 3 (155 Mbps) OC 12 (622 Mbps) OC 48 (2. 4 Gbps) POP: point-of-presence to/from backbone Stockton … … Kansas City. … Anaheim peering … … San Jose Cheyenne New York Pennsauken Relay Wash. DC Chicago Roachdale Atlanta to/from customers Fort Worth Orlando Introduction 27

Internet structure: network of networks q “Tier-2” ISPs: smaller (often regional) ISPs v Connect

Internet structure: network of networks q “Tier-2” ISPs: smaller (often regional) ISPs v Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet q tier-2 ISP is customer of tier-1 provider Tier-2 ISP Tier 1 ISP Tier-2 ISP NAP Tier 1 ISP Tier-2 ISPs also peer privately with each other, interconnect at NAP Tier-2 ISP Introduction 28

Internet structure: network of networks q “Tier-3” ISPs and local ISPs v last hop

Internet structure: network of networks q “Tier-3” ISPs and local ISPs v last hop (“access”) network (closest to end systems) local ISP Local and tier 3 ISPs are customers of higher tier ISPs connecting them to rest of Internet Tier 3 ISP Tier-2 ISP local ISP Tier-2 ISP Tier 1 ISP Tier-2 ISP local ISP NAP Tier 1 ISP Tier-2 ISP local ISP Introduction 29

Internet structure: network of networks q a packet passes through many networks! local ISP

Internet structure: network of networks q a packet passes through many networks! local ISP Tier 3 ISP Tier-2 ISP local ISP Tier-2 ISP Tier 1 ISP Tier-2 ISP local ISP NAP Tier 1 ISP Tier-2 ISP local ISP Introduction 30

Review q Transport Layer v Connection-oriented v Connectionless q The Internet q Network Layer

Review q Transport Layer v Connection-oriented v Connectionless q The Internet q Network Layer v Circuit switching v Packet switching q Link Layer v Ethernet v FDM Introduction 31

Transport Layer Review q Connection-oriented (TCP) v Acknowledgements (can have retries) v Flow control

Transport Layer Review q Connection-oriented (TCP) v Acknowledgements (can have retries) v Flow control v Congestion control v Better for most protocols q Connectionless (UDP) v No acknowledgements v Send as fast as needed v Some packets will get lost v Better for video, telephony, etc q Human speech? Introduction 32

Network Layer Review q Circuit-switching v Divide resources into “slots” v Reserve all end-to-end

Network Layer Review q Circuit-switching v Divide resources into “slots” v Reserve all end-to-end resources (a “circuit”) v Provides known latency v Better for phones networks, etc q Packet switching v Divide resources into “packets” v Send a packet whenever needed v Maximizes throughput v Better for random traffic, eg. internet, etc Introduction 33

Packet Switching q Virtual Circuit Networks v Initialize: tell each router it is on

Packet Switching q Virtual Circuit Networks v Initialize: tell each router it is on the circuit v Send each packet with the Virtual Circuit ID q Datagram Networks v No initialization v Send each packet with the destination address q Trade offs? v VC networks minimize routing tables v Datagram networks minimize setup time Introduction 34

Network Layer Taxonomy Introduction 35

Network Layer Taxonomy Introduction 35

Link Layer q Physical media v Ethernet v Fiber optics v DSL v Cable

Link Layer q Physical media v Ethernet v Fiber optics v DSL v Cable q Sharing techniques v FDM v TDM v Ethernet protocol v Etc. q Human sharing protocols? Introduction 36

Transport Layer TCP UDP Connectionoriented Connectionless Network Layer IP Link Layer Ethernet Cable FDMA

Transport Layer TCP UDP Connectionoriented Connectionless Network Layer IP Link Layer Ethernet Cable FDMA Wireless TDMA CSMA DSL Fiber CDMA Introduction 37

Chapter 1: roadmap 1. 1 What is the Internet? 1. 2 Network edge 1.

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 Introduction 38

Four sources of packet delay q 1. nodal processing: v check bit errors v

Four sources of packet delay q 1. nodal processing: v check bit errors v determine output link q 2. queueing v time waiting at output link for transmission v depends on congestion level of router A B nodal processing queueing Introduction 39

Delay in packet-switched networks 3. Transmission delay: q R=link bandwidth (bps) q L=packet length

Delay in packet-switched networks 3. Transmission delay: q R=link bandwidth (bps) q L=packet length (bits) q time to send bits into link = L/R transmission A 4. Propagation delay: q d = length of physical link q s = propagation speed in medium (~2 x 108 m/sec) q propagation delay = d/s Note: s and R are very different quantities! propagation B nodal processing queueing Introduction 40

Caravan analogy 100 km ten-car caravan toll booth q Cars “propagate” at 100 km/hr

Caravan analogy 100 km ten-car caravan toll booth q Cars “propagate” at 100 km/hr q Toll booth takes 12 sec to service a car (transmission time) q car~bit; caravan ~ packet q Q: How long until caravan is lined up before 2 nd toll booth? 100 km toll booth q Time to “push” entire caravan through toll booth onto highway = 12*10 = 120 sec q Time for last car to propagate from 1 st to 2 nd toll both: 100 km/(100 km/hr)= 1 hr q A: 62 minutes Introduction 41

Caravan analogy (more) 100 km ten-car caravan toll booth q Cars now “propagate” at

Caravan analogy (more) 100 km ten-car caravan toll booth q Cars now “propagate” at 1000 km/hr q Toll booth now takes 1 min to service a car q Total transmit time is: 10*1+. 1 = 10. 1 minutes q Which scenario is more like internet routers? 100 km toll booth 1 st bit of packet can arrive at 2 nd router before packet is fully transmitted at 1 st router! Introduction 42

Nodal delay q dproc = processing delay v typically a few microsecs or less

Nodal delay q dproc = processing delay v typically a few microsecs or less q dqueue = queuing delay v depends on congestion q dtrans = transmission delay v = L/R, significant for low-speed links q dprop = propagation delay v a few microsecs to hundreds of msecs Introduction 43

Queueing delay (revisited) q R=link bandwidth (bps) q L=packet length (bits) q a=average packet

Queueing delay (revisited) q R=link bandwidth (bps) q L=packet length (bits) q a=average packet arrival rate traffic intensity = La/R Output Rate q La/R ~ 0: average queueing delay small q La/R -> 1: delays become large q La/R > 1: more “work” arriving than can be serviced, average delay infinite! Introduction 44

How does loss occur? q packet arrival rate to link exceeds output link capacity

How does loss occur? q packet arrival rate to link exceeds output link capacity q Queue grows q When no more space in queue, packets are lost q lost packet may be retransmitted by previous node, by source end system, or not retransmitted at all A B packets queueing (delay) free (available) buffers: arriving packets dropped (loss) if no free buffers Introduction 45

“Real” Internet delays and routes q What do “real” Internet delay & loss look

“Real” Internet delays and routes q What do “real” Internet delay & loss look like? q Traceroute program: provides delay measurement from source to router along end-end Internet path towards destination. For all i: v v v sends three packets that will reach router i on path towards destination router i will return packets to sender times interval between transmission and reply. 3 probes Introduction 46

“Real” Internet delays and routes traceroute: gaia. cs. umass. edu to www. eurecom. fr

“Real” Internet delays and routes traceroute: gaia. cs. umass. edu to www. eurecom. fr Three delay measurements from gaia. cs. umass. edu to cs-gw. cs. umass. edu 1 cs-gw (128. 119. 240. 254) 1 ms 2 border 1 -rt-fa 5 -1 -0. gw. umass. edu (128. 119. 3. 145) 1 ms 2 ms 3 cht-vbns. gw. umass. edu (128. 119. 3. 130) 6 ms 5 ms 4 jn 1 -at 1 -0 -0 -19. wor. vbns. net (204. 147. 132. 129) 16 ms 11 ms 13 ms 5 jn 1 -so 7 -0 -0 -0. wae. vbns. net (204. 147. 136) 21 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 trans-oceanic 8 62. 40. 103. 253 (62. 40. 103. 253) 104 ms 109 ms 106 ms link 9 de 2 -1. de. geant. net (62. 40. 96. 129) 109 ms 102 ms 104 ms 10 de. fr 1. fr. geant. net (62. 40. 96. 50) 113 ms 121 ms 114 ms 11 renater-gw. fr 1. fr. geant. net (62. 40. 103. 54) 112 ms 114 ms 112 ms 12 nio-n 2. 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 r 3 t 2 -nice. cssi. renater. fr (195. 220. 98. 110) 126 ms 124 ms 15 eurecom-valbonne. r 3 t 2. ft. net (193. 48. 50. 54) 135 ms 128 ms 133 ms 16 194. 211. 25 (194. 211. 25) 126 ms 128 ms 126 ms 17 * * means no response (probe lost, router not replying) 18 * * * 19 fantasia. eurecom. fr (193. 55. 113. 142) 132 ms 128 ms 136 ms Introduction 47

Chapter 1: roadmap 1. 1 What is the Internet? 1. 2 Network edge 1.

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 Introduction 48

Protocol “Layers” Networks are complex! q many “pieces”: v hosts v routers v links

Protocol “Layers” Networks are complex! q many “pieces”: v hosts v routers v links of various media v applications v protocols v hardware, software Question: How do they all fit together? Introduction 49

Organization of air travel ticket (purchase) ticket (complain) baggage (check) baggage (claim) gates (load)

Organization of air travel ticket (purchase) ticket (complain) baggage (check) baggage (claim) gates (load) gates (unload) runway takeoff runway landing airplane routing Introduction 50

Layering of airline functionality ticket (purchase) ticket (complain) ticket baggage (check) baggage (claim baggage

Layering of airline functionality ticket (purchase) ticket (complain) ticket baggage (check) baggage (claim baggage gates (load) gates (unload) gate runway (takeoff) runway (land) takeoff/landing airplane routing departure airport airplane routing intermediate air-traffic control centers arrival airport Layers: each layer implements a service v Providing an interface to higher layers v And relying on services provided by layer below Introduction 51

Why layering? Dealing with complex systems: q modularization eases maintenance, updating of system v

Why layering? Dealing with complex systems: q modularization eases maintenance, updating of system v change of implementation of layer’s service transparent to rest of system v e. g. , change in gate procedure doesn’t affect rest of system q layering considered harmful? Introduction 52

Internet protocol stack q application: supporting network applications v FTP, SMTP, HTTP q transport:

Internet protocol stack q application: supporting network applications v FTP, SMTP, HTTP q transport: process-process data transfer v TCP, UDP q network: routing of datagrams from source to destination v IP, routing protocols q link: data transfer between application transport network link physical neighboring network elements v PPP, Ethernet q physical: bits “on the wire” Introduction 53

Encapsulation source message segment Ht M datagram Hn Ht M frame Hl Hn Ht

Encapsulation source message segment Ht M datagram Hn Ht M frame Hl Hn Ht M M application transport network link physical switch destination M Ht M Hn Ht Hl Hn Ht M M application transport network link physical Hn Ht Hl Hn Ht M M network link physical Hn Ht M router Introduction 54

Chapter 1: roadmap 1. 1 What is the Internet? 1. 2 Network edge 1.

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 Introduction 55

Internet History 1961 -1972: Early packet-switching principles q 1961: Kleinrock - queueing theory shows

Internet History 1961 -1972: Early packet-switching principles q 1961: Kleinrock - queueing theory shows effectiveness of packetswitching q 1964: Baran - packetswitching in military nets q 1967: ARPAnet conceived by Advanced Research Projects Agency q 1969: first ARPAnet node operational q 1972: v v ARPAnet public demonstration NCP (Network Control Protocol) first host-host protocol first e-mail program ARPAnet has 15 nodes Introduction 56

Internet History 1972 -1980: Internetworking, new and proprietary nets q 1970: ALOHAnet satellite q

Internet History 1972 -1980: Internetworking, new and proprietary nets q 1970: ALOHAnet satellite q q q network in Hawaii 1974: Cerf and Kahn architecture for interconnecting networks 1976: Ethernet at Xerox PARC ate 70’s: proprietary architectures: DECnet, SNA, XNA late 70’s: switching fixed length packets (ATM precursor) 1979: ARPAnet has 200 nodes Cerf and Kahn’s internetworking principles: v minimalism, autonomy - no internal changes required to interconnect networks v best effort service model v stateless routers v decentralized control define today’s Internet architecture Introduction 57

Internet History 1980 -1990: new protocols, a proliferation of networks q 1983: deployment of

Internet History 1980 -1990: new protocols, a proliferation of networks q 1983: deployment of q q TCP/IP 1982: smtp e-mail protocol defined 1983: DNS defined for name-to-IP-address translation 1985: ftp protocol defined 1988: TCP congestion control q new national networks: Csnet, BITnet, NSFnet, Minitel q 100, 000 hosts connected to confederation of networks Introduction 58

Internet History 1990, 2000’s: commercialization, the Web, new apps q Early 1990’s: ARPAnet decommissioned

Internet History 1990, 2000’s: commercialization, the Web, new apps q Early 1990’s: ARPAnet decommissioned q 1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995) q early 1990 s: Web v hypertext [Bush 1945, Nelson 1960’s] v HTML, HTTP: Berners-Lee v 1994: Mosaic, later Netscape v late 1990’s: commercialization Late 1990’s – 2000’s: q more killer apps: instant messaging, P 2 P file sharing q network security to forefront q est. 50 million host, 100 million+ users q backbone links running at Gbps of the Web Introduction 59

Introduction: Summary Course in a nutshell q Internet overview q what’s a protocol? q

Introduction: Summary Course in a nutshell q Internet overview q what’s a protocol? q network edge, core, access network v packet-switching versus circuit-switching q Internet/ISP structure q performance: loss, delay q layering and service models q history Rest of course: q Ch 2: applications q Ch 3: transport q Ch 4: network q Ch 5: link q Ch 6: wireless q Ch 8: security Introduction 60