1. Introduction Computer Networking: A Top Down Approach 6th

1. Introduction Computer Networking: A Top Down Approach 6th edition Jim Kurose, Keith Ross Addison-Wesley March 2012 All material copyright 1996-2012 J.F Kurose and K.W. Ross, All Rights Reserved Introduction 1-1

1. Introduction Goals: get “feel” and terminology defer depth and detail to later in course understand concepts using the Internet as example Introduction 1-2

1. Introduction: roadmap 1.1 what is the Internet? 1.2 network edge end systems, access networks, links 1.3 network core packet switching, circuit switching, network structure 1.4 1.5 1.6 1.7 delay, loss, throughput in networks protocol layers networks under attack: security history Introduction 1-3

What’s the Internet: “nuts and bolts” view PC hosts server wireless laptop or end-systems millions of connected computing devices running network apps mobile network global ISP smartphone communication wireless links wired links links fiber, copper, radio, satellite with different transmission rates or bandwidth regional ISP packet router switches forward packets or chunks of data home network institutional network Introduction 1-4

“Fun” internet appliances Web-enabled toaster weather forecaster IP picture frame Tweet-a-watt: monitor energy use Slingbox: watch, control cable TV remotely Internet refrigerator Internet Internetphones phones Introduction 1-5

What’s the Internet: “nuts and bolts” view Internet: “network of networks” mobile network global ISP Interconnected ISPs protocols control sending, receiving of msgs e.g., TCP, IP, HTTP, Skype, 802.11 home network regional ISP Internet standards RFC: Request for comments IETF: Internet Engineering Task Force institutional network Introductio 1-6 n

What’s the Internet: a service view Infrastructure that provides services to applications: Web, VoIP, email, games, ecommerce, social nets, provides programming interface to apps mobile network global ISP home network regional ISP hooks that allow sending and receiving app programs to “connect” to Internet provides service options, analogous to postal service institutional network Introductio 1-7 n

What’s a protocol? human protocols: “what’s the time?” “I have a question” introductions specific msgs sent specific actions taken when msgs received, or other events network protocols: machines rather than humans all communication activity in Internet governed by protocols protocols define format, order of msgs sent and received among network entities, and actions taken on Introduction 1-8

What’s a protocol? a human protocol and a computer network protocol: Hi TCP connection request Hi TCP connection response Got the time? Get http://www.awl.com/kurose-ross 2:00 file time Q: other human protocols? Introduction 1-9

1. Introduction: roadmap 1.1 what is the Internet? 1.2 network edge end systems, access networks, links 1.3 network core packet switching, circuit switching, network structure 1.4 1.5 1.6 1.7 delay, loss, throughput in networks protocol layers, service models networks under attack: security history Introduction 1-10

A closer look at network structure: network edge: mobile network hosts: clients and servers servers often in data centers access networks, physical media: wired, wireless communication links network core: global ISP home network regional ISP interconnected routers network of networks institutional network Introduction 1-11

Access networks and physical media Q: How to connect end systems to edge router? residential access nets institutional access networks (school, company) mobile access networks keep in mind: bandwidth (bits per second) of access network? shared or dedicated? Introduction 1-12

Access net: digital subscriber line (DSL) central office DSL splitter modem voice, data transmitted at different frequencies over dedicated line to central office telephone network DSLAM ISP DSL access multiplexer use existing telephone line to central office DSLAM data over DSL phone line goes to Internet voice over DSL phone line goes to telephone net 2.5 Mbps upstream transmission rate (typically 1 Mbps) 24 Mbps downstream transmission rate (typically Introduction 1-13

Access net: cable network cable headend cable splitter modem V I D E O V I D E O V I D E O V I D E O V I D E O V I D E O D A T A D A T A C O N T R O L 1 2 3 4 5 6 7 8 9 Channels equency division multiplexing: different channels transmitte different frequency bands Introduction 1-14

Access net: cable network cable headend cable splitter modem data, TV transmitted at different frequencies over shared cable distribution network CMTS cable modem termination system ISP HFC: hybrid fiber coax asymmetric: up to 30Mbps downstream transmission rate, 2 Mbps upstream transmission rate network of cable, fiber attaches homes to ISP router homes share access network to cable headend Introduction 1-15

Fiber to the home (FTTH) Fully optical fiber path all the way to the home e.g., Verizon FIOS, Google 30 Mbps to 1Gbps Active (like switched Ethernet) or passive optical networking as shown below Introduction 1-16

Access net: home network wireless devices to/from headend or central office often combined in single box cable or DSL modem wireless access point (54 Mbps) router, firewall, NAT wired Ethernet (100 Mbps) Introduction 1-17

Enterprise access networks (Ethernet) institutional link to ISP (Internet) institutional router Ethernet switch institutional mail, web servers typically used in companies, universities, etc 10 Mbps, 100Mbps, 1Gbps, 10Gbps transmission rates end systems typically connect into Ethernet switch possibly through a wireless access point Introduction 1-18

Wireless access networks shared wireless access network connects end system to router via base station aka “access point” wireless LANs: within building (100 ft) 802.11b/g/n (WiFi): 11, 54,256 Mbps transmission rate wide-area mobile access provided by telco (cellular) operator, 10’s km between 1 and 20 Mbps 3G, 4G/LTE to Internet to Internet Introduction 1-19

Host: sends packets of data sending host: breaks app message into smaller chunks, known as packets, of length L bits transmits packet into access network at transmission rate R aka link capacity or link bandwidth packet transmission delay two packets, L bits each 2 1 R: link transmission rate host time needed to transmit L-bit packet into link L (bits) R (bits/sec) 1-20

Physical media bit: propagates between transmitter/receiver pairs physical link: what lies between transmitter & receiver guided media: signals propagate in solid media: copper, fiber, coax unguided media: signals propagate freely, e.g., radio Introduction 1-21

Physical media: twisted pair, coax, fiber twisted pair (TP) two insulated copper wires Category 5: 100 Mbps, 1 Gpbs Ethernet Category 6: 10Gbps coaxial cable: two concentric copper conductors broadband: multiple channels on cable HFC fiber optic cable: glass fiber carrying light pulses, each pulse a bit high-speed operation: high-speed point-to-point transmission (e.g., 10’s100’s Gpbs transmission rate) low error rate: repeaters spaced far apart immune to electromagnetic noise Introduction 1-22

Physical media: radio signal carried in electromagnetic spectrum, i.e., no physical “wire” radio link types: e.g. up to 45 Mbps channels propagation environment effects: reflection obstruction by objects interference terrestrial microwave LAN (e.g., WiFi) 11Mbps, 54 Mbps wide-area (e.g., cellular) 3G cellular: few Mbps satellite Kbps to 45Mbps channel (or multiple smaller channels) 270 msec end-end delay geosynchronous versus low earth-orbitting (LEO) Introduction 1-23

1. Introduction: roadmap 1.1 what is the Internet? 1.2 network edge end systems, access networks, links 1.3 network core packet switching, circuit switching, network structure 1.4 1.5 1.6 1.7 delay, loss, throughput in networks protocol layers, service models networks under attack: security history Introduction 1-24

The network core mesh of interconnected routers packet-switching: hosts break application-layer messages into packets forward packets from one router to the next across links on path from source to destination each packet transmitted at full link capacity Introduction 1-25

Packet-switching: store-andforward end-end transmission delay 2L/R L bits per packet source 3 2 1 R bps takes L/R seconds to transmit (push out) Lbit packet into link at R bps store and forward: entire packet must arrive at router before it can be transmitted on next link R bps destination Example L 1500B R 1.5Mbps Transmission delay ? Introduction 1-26

Packet Switching: queueing delay, loss A B C R 100 Mb/s R 1.5 Mb/s queue of packets waiting for output link D E queuing and loss: If arrival rate (in bits) to link exceeds transmission rate of link for a period of time: packets will queue, wait to be transmitted on link packets can be dropped (lost) if memory (buffer) fills up Introduction 1-27

Two key network-core functions routing: determines forwarding: move source-destination route taken by packets routing algorithms packets from router’s input to appropriate router output routing algorithm local forwarding table header value output link 0100 0101 0111 1001 1 3 2 2 1 3 2 1 01 1 dest address in arriving packet’s header Network Layer 4-28

Alternative core: circuit switching end-end resources allocated to, reserved for “call” between source & dest: In diagram, each link has four circuits. call gets 2nd circuit in top link and 1st circuit in right link. dedicated resources: no sharing circuit-like (guaranteed) performance circuit segment idle if not used by call (no sharing) Commonly used in traditional telephone networks Introduction 1-29

Circuit switching: FDM versus TDM Example: FDM 4 users frequency time TDM frequency time Introduction 1-30

Packet switching versus circuit switching packet switching allows more users to use network! 100 kb/s when “active” active 10% of time N users . example: 1 Mb/s link each user: 1 Mbps link circuit-switching: 10 users packet switching: Q: how did we get value 0.0004 with 35 users, probability 10 active Q: what happens if 35 users ? at same time is less than .0004 * Introduction 1-31

Packet switching versus circuit switching is packet switching a “slam dunk winner?” great for bursty data resource sharing simpler, no call setup excessive congestion possible: packet delay and loss protocols needed for reliable data transfer, congestion control Q: How to provide circuit-like behavior? bandwidth guarantees needed for audio/video apps still an unsolved problem (chapter 7) Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packetswitching)? Introduction 1-32

Q: Circuit-switched capacity Consider a circuit-switched network with N 100 users where each user is active with probability p 0.2 and when active, sends data at a rate R 1Mbps. How much capacity must the network be provisioned with to guarantee service to all users? A. B. C. D. E. 100 Mbps 20 Mbps 200 Mbps 50 Mbps 500 Mbps Introduction 1-33

Q: Packet-switched utilization Consider a packet-switched network with N 100 users where each user is active with probability p 0.2 and when active, sends data at a rate R 1Mbps. What is the probability that the senders are collectively using C 50Mbps of bandwidth? A. B. C. D. E. Np pC/R C(N,C/R)pC/R(1-p)N-C/R pC/R(1-p)N-C/R p/N Introduction 1-34

Internet structure: network of networks End systems connect to Internet via access ISPs (Internet Service Providers) Residential, company and university ISPs Access ISPs in turn must be interconnected. So that any two hosts can send packets to each other Resulting network of networks is very complex Evolution was driven by economics and national policies Let’s take a stepwise approach to describe current Internet structure

Internet structure: network of networks Question: given millions of access ISPs, how to connect them together? access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net

Internet structure: network of networks Option: connect each access ISP to every other access ISP? access net access net access net access net access net access net access net connecting each access ISP to each other directly doesn’t scale: O(N2) connections. access net access net access net access net access net access net access net access net access net

Internet structure: network of networks Option: connect each access ISP to a global transit ISP? Customer and provider ISPs have economic agreement. access access net access net net access net access net access net access net global ISP access net access net access net access net access net access net access net access net access net

Internet structure: network of networks But if one global ISP is viable business, there will be competitors . access net access net access net access net access net access net access net ISP A access net ISP B ISP C access net access net access net access net access net access net access net access net

Internet structure: network of networks But if one global ISP is viable business, there will be competitors . which must be interconnected Internet exchange point access access access net net net access net access net IXP access net access net ISP A IXP access net ISP B ISP C access net peering link access net access net access net access net access net access net access net

Internet structure: network of networks and regional networks may arise to connect access nets to ISPS access net access net access net access net access net IXP access net access net ISP A IXP access net ISP B ISP C access net access net regional net access net access net access net access net access net access net

Internet structure: network of networks and content provider networks (e.g., Google, Microsoft, Akamai ) may run their own network, to bring services, content close to end users access net access net access net access net access net IXP access net access net Content provider network IXP access net access net ISP B ISP B access net access net regional net access net access net access net access net ISP A access net

Internet structure: network of networks Tier 1 ISP Tier 1 ISP IX P IX P Regional ISP access ISP access ISP Google access ISP access ISP IX P Regional ISP access ISP access ISP access ISP access ISP at center: small # of well-connected large networks “tier-1” commercial ISPs (e.g., Level 3, Sprint, AT&T, NTT), national & international coverage content provider network (e.g, Google): private network that connects it data centers to Internet, often bypassing Introduction 1-43

Tier-1 ISP: e.g., Sprint POP: point-of-presence to/from backbone peering to/from customers Introduction 1-44

1. Introduction: roadmap 1.1 what is the Internet? 1.2 network edge end systems, access networks, links 1.3 network core packet switching, circuit switching, network structure 1.4 1.5 1.6 1.7 delay, loss, throughput in networks protocol layers, service models networks under attack: security history Introduction 1-45

How do loss and delay occur? packets queue (wait for their turn) in router buffers when packet arrival rate to link exceeds output link capacity packet being transmitted (delay) A B packets queueing (delay) free (available) buffers: arriving packets dropped (loss) if no free buffers Introduction 1-46

Four sources of packet delay transmission A propagation B processing queueing dnodal dproc dqueue dtrans dprop dproc: processing delay check bit errors determine output link typically msec dqueue: queueing delay time waiting at output link for transmission depends on Introduction 1-47

Four sources of packet delay transmission A propagation B processing queueing dnodal dproc dqueue dtrans dprop dtrans: transmission delay: L: packet length (bits) R: link bandwidth (bps) dtrans and dprop dtrans L/R very different dprop: propagation delay: d: length of physical link s: propagation speed in medium ( 2x108 m/sec) dprop d/s Introduction 1-48

Caravan analogy 100 km ten-car caravan 100 km toll booth cars “propagate” at 100 km/hr toll booth takes 12 sec to service car (bit transmission time) car bit; caravan packet Q: How long until caravan is lined up before 2nd toll booth? 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 Introduction 1-49

Caravan analogy (more) 100 km ten-car caravan toll booth 100 km toll booth suppose cars now “propagate” at 1000 km/hr and suppose toll booth now takes one min to service a car Q: Will cars arrive to 2nd booth before all cars serviced at first booth? A: Yes! after 7 min, 1st car arrives at second booth; three cars still at 1st booth. Introduction 1-50

R: link bandwidth (bps) L: packet length (bits) a: average packet arrival rate average queueing delay Queueing delay (revisited) traffic intensity La/R La/R 0: avg. queueing delay small La/R - 1: avg. queueing delay large La/R 1: more “work” arriving than can be serviced, average delay infinite! La/R 0 La/R - 1 Introduction 1-51

“Real” Internet delays and routes what do “real” Internet delay & loss look like? traceroute program: provides delay measurement from source to router along endend 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 Introduction 1-52

“Real” Internet delays, routes traceroute: gaia.cs.umass.edu to www.eurecom.fr 3 delay measurements from gaia.cs.umass.edu to cs-gw.cs.umass.edu 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 trans-oceanic 8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms link 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 * * * * means no response (probe lost, router not replying) 18 * * * 19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms * Do some traceroutes from exotic countries at www.traceroute.org Introduction 1-53

Delays: Q1 Propagation delay depends on the size of the packet. True or false? A. True B. False Introduction 1-54

Delays: Q2 Which of the following delays is significantly affected by the load in the network? A. B. C. D. Processing delay Queuing delay Transmission delay Propagation delay Introduction 1-55

Delays: Q3 Consider a packet that has just arrived at a router. What is a correct order of the delays encountered by the packet until it reaches the next-hop router? A. Processing, queuing, transmission, propagation B. Transmission, processing, propagation, queuing C. Propagation, processing, transmission, queuing D. Queuing, processing, propagation, transmission Introduction 1-56

Delays: Q4 Consider two packets P1, P2 queued at a router R1 at time t0 as shown above. At what time t1 does P1 reach R2? Assume zero processing delay and speed of light is V m/sec. A. B. C. D. D1/V 2L/C1 D1/V L/C1 D1/V 2L/C1 Introduction 1-57

Delays: Q5 Consider two packets P1, P2 queued at a router R1 at time t0 as shown above. At what time t2 does P2 reach R2? Assume zero processing delay and speed of light is V m/sec. 2L/C1 D1/V 2L/C1 2D1/V L/C1 2D1/V 2D1/V Introduction 1-58

Delays: Q6 Consider two packets P1, P2 queued at a router R1 at time t0 as shown above. At what time t3 does P1 leave R2? Assume zero processing delay and speed of light is V m/sec. L/C1 D1/V L/C2 2L/C1 2(D1/V L/C2) 2L/C1 2D1/V L/C1 D1/V D2/V Introduction 1-59

Delays: Q7 Consider two packets P1, P2 queued at a router R1 at time t0 as shown above. Does P2 experience queuing delay at R2? Assume zero processing delay and speed of light is V m/sec. Introduction 1-60

Throughput throughput: rate (bits/time unit) at which bits transferred between sender/receiver instantaneous: rate at given point in time average: rate over longer period of time server, with server sends file ofbits F bits to(fluid) send into to client pipe link capacity capacity pipe that can carry link pipe that can carry fluid at rate fluid at rate Rs bits/sec Rc bits/sec Rs bits/sec) Rc bits/sec) Introduction 1-62

Throughput (more) Rs Rc What is average end-end throughput? Rs bits/sec Rc bits/sec Rs Rc What is average end-end throughput? Rs bits/sec Rc bits/sec bottleneck link onlink end-end path that constrains end-end throughput Introduction 1-63

Throughput: Internet scenario Per-connection end-end throughput: min(Rc,Rs,R/k) in practice: R or c Rs is often bottleneck Rs Rs Rs R Rc Rc Rc Client connections (fairly) share backbone bottleneck link R bits/sec Introduction 1-64

1. Introduction: roadmap 1.1 what is the Internet? 1.2 network edge end systems, access networks, links 1.3 network core packet switching, circuit switching, network structure 1.4 1.5 1.6 1.7 delay, loss, throughput in networks protocol layers, service models networks under attack: security history Introduction 1-65

Protocol “layers” Networks are complex, with 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? Introduction 1-66

Organization of air travel ticket (purchase) ticket (complain) baggage (check) baggage (claim) gates (load) gates (unload) runway takeoff runway landing airplane routing airplane routing airplane routing a series of steps Introduction 1-67

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 airplane routing airplane routing departure airport airplane routing airplane routing intermediate air-traffic control centers arrival airport layers: each layer implements a service via its own internal-layer actions relying on services provided by layer below Introduction 1-68

Why layering? dealing with complex systems: explicit structure allows identification, relationship of complex system’s pieces layered reference model for discussion reusable component design modularization eases maintenance 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? Introduction 1-69

Internet protocol stack 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 Ethernet, 802.111 (WiFi), PPP application transport network link physical physical: bits “on the wire” Introduction 1-70

ISO/OSI reference model presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine-specific conventions session: synchronization, checkpointing, recovery of data exchange Internet stack “missing” these layers! these services, if needed, must be implemented in application needed? application presentation session transport network link physical Introduction 1-71

Encapsulatio n source message segment Ht M datagram Hn Ht M frame M Hl Hn Ht M application transport network link physical link physical switch M Ht M Hn Ht M Hl Hn Ht M destination Hn Ht M application transport network link physical Hl Hn Ht M network link physical Hn Ht M router Introduction 1-72

1. Introduction: roadmap 1.1 what is the Internet? 1.2 network edge end systems, access networks, links 1.3 network core packet switching, circuit switching, network structure 1.4 1.5 1.6 1.7 delay, loss, throughput in networks protocol layers, service models networks under attack: security history Introduction 1-73

Network security field of network security: how bad guys can attack computer networks how we can defend networks against attacks how to design architectures that are immune to attacks Internet not originally designed with (much) security in mind original vision: “a group of mutually trusting users attached to a transparent network” Internet protocol designers playing “catchup” security considerations in all layers! Introduction 1-74

Bad guys: put malware into hosts via Internet malware can get in host from: virus: self-replicating infection by receiving/executing object (e.g., e-mail attachment) worm: self-replicating infection by passively receiving object that gets itself executed spyware malware can record keystrokes, web sites visited, upload info to collection site infected host can be enrolled in botnet, used for spam. DDoS attacks Introduction 1-75

Bad guys: attack server, network infrastructure Denial of Service (DoS): attackers make resources (server, bandwidth) unavailable to legitimate traffic by overwhelming resource with bogus traffic 1. select target 2. break into hosts around the network (see botnet) 3. send packets to target from compromised hosts target Introduction 1-76

Bad guys can sniff packets packet “sniffing”: broadcast media (shared ethernet, wireless) promiscuous network interface reads/records all packets (e.g., including passwords!) passing by C A src:B dest:A payload B wireshark software used for labs is a (free) packet-sniffer Introduction 1-77

Bad guys can use fake addresses IP spoofing: send packet with false source address C A src:B dest:A payload B lots more on security (throughout, Chapter 8) Introduction 1-78

1. Introduction: roadmap 1.1 what is the Internet? 1.2 network edge end systems, access networks, links 1.3 network core packet switching, circuit switching, network structure 1.4 1.5 1.6 1.7 delay, loss, throughput in networks protocol layers, service models networks under attack: security history Introduction 1-79

Internet history 1961-1972: Early packet-switching principles 1961: Kleinrock queueing theory shows effectiveness of packet-switching 1964: Baran packet-switching in military nets 1967: ARPAnet conceived by Advanced Research Projects Agency 1969: first ARPAnet node operational 1972: ARPAnet public demo NCP (Network Control Protocol) first host-host protocol first e-mail program ARPAnet has 15 nodes Introduction 1-80

Internet history 1972-1980: Internetworking, new and proprietary nets 1970: ALOHAnet satellite network in Hawaii 1974: Cerf and Kahn architecture for interconnecting networks 1976: Ethernet at Xerox PARC late70’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: minimalism, autonomy - no internal changes required to interconnect networks best effort service model stateless routers decentralized control define today’s Internet architecture Introduction 1-81

Internet history 1980-1990: new protocols, a proliferation of networks 1983: deployment of TCP/IP 1982: SMTP e-mail protocol 1983: DNS defined for name-to-IP-address translation 1985: FTP protocol defined 1988: TCP congestion control new national networks: Csnet, BITnet, NSFnet, Minitel 100,000 hosts connected to confederation of networks Introduction 1-82

Internet history 1990, 2000’s: commercialization, the Web, new apps early 1990’s: ARPAnet decommissioned 1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995) early 1990s: Web hypertext [Bush 1945, Nelson 1960’s] HTML, HTTP: Berners-Lee 1994: Mosaic, later Netscape late 1990’s: commercialization of the late 1990’s – 2000’s: more killer apps: instant messaging, P2P file sharing network security to forefront est. 50 million host, 100 million users backbone links running at Gbps Web Introduction 1-83

Internet history 2005-present 1 billion traditional hosts (desktops, laptops, tablets) 4-5 billion phones about a billion of which are data capable Aggressive deployment of broadband access Increasing ubiquity of high-speed wireless access Emergence of online social networks: Facebook: 1 billion users Service providers (Google, Microsoft) create their own networks Bypass Internet, providing “instantaneous” access to search, email, etc. E-commerce, universities, enterprises running their services in “cloud” (eg, Amazon EC2) Introduction 1-84

Introduction: summary covered a “ton” of material! Internet overview what’s a protocol? network edge, core, access network packet-switching versus circuitswitching Internet structure performance: loss, delay, throughput layering, service models security history you now have: context, overview, “feel” of networking more depth, detail to follow! Introduction 1-85