Ch1 internet Networks
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This document provides an introduction to computer networking and the Internet. It begins with an overview of what the Internet is, including its key components like end systems, communication links, and packet switches. It then discusses the network edge, including access networks and physical media. The core network and packet switching are introduced. Sources of delay, loss, and throughput in networks are covered. Finally, the chapter roadmap is provided, outlining topics like protocol layers, network security, and history that will be discussed.
![Introduction
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
Web
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
1990, 2000’s: commercialization, the Web, new
apps
Internet history
1-63](https://image.slidesharecdn.com/1-internet-200414170948/85/Ch1-internet-Networks-62-320.jpg)
Ch1 internet Networks
- 1. Introduction 1-1 Chapter 1 Introduction Computer Networking: A Top Down Approach 6th edition Jim Kurose, Keith Ross Addison-Wesley March 2012
- 2. Introduction Chapter 1: 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 delay, loss, throughput in networks 1.5 protocol layers, service models 1.6 networks under attack: security 1.7 history 1-2
- 3. Introduction What’s the Internet: “nuts and bolts” view millions of connected computing devices: hosts = end systems running network apps communication links fiber, copper, radio, satellite transmission rate: bandwidth Packet switches: forward packets (chunks of data) routers and switches wired links wireless links router mobile network global ISP regional ISP home network institutional network smartphone PC server wireless laptop 1-3
- 4. Introduction Internet: “network of networks” Interconnected ISPs protocols control sending, receiving of msgs e.g., TCP, IP, HTTP, Skype, 802.11 Internet standards RFC: Request for comments IETF: Internet Engineering Task Force What’s the Internet: “nuts and bolts” view mobile network global ISP regional ISP home network institutional network 1-4
- 5. What’s the Internet: a service view Infrastructure that provides services to applications: Web, VoIP, email, games, e-commerce, social nets, … provides programming interface to apps hooks that allow sending and receiving app programs to “connect” to Internet provides service options, analogous to postal mobile network global ISP regional ISP home network institutional network Introduction 1-5
- 6. Introduction 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 msg transmission, receipt 1-6
- 7. Introduction a human protocol and a computer network protocol: Q: other human protocols? Hi Hi Got the time? 2:00 TCP connection response Get http://www.awl.com/kurose-ross <file> time TCP connection request What’s a protocol? 1-7
- 8. Introduction Chapter 1: 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 delay, loss, throughput in networks 1.5 protocol layers, service models 1.6 networks under attack: security 1.7 history 1-8
- 9. Introduction A closer look at network structure: network edge: hosts: clients and servers servers often in data centers access networks, physical media: wired, wireless communication links network core: interconnected routers network of networks mobile network global ISP regional ISP home network institutional network 1-9
- 10. Introduction 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? 1-10
- 11. Introduction Access net: digital subscriber line (DSL) central office ISP telephone network DSLAM voice, data transmitted at different frequencies over dedicated line to central office 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 < 10 Mbps) DSL modem splitter DSL access multiplexer 1-11
- 12. Digital Subscriber Lines Operation of ADSL
- 13. Introduction Enterprise access networks (Ethernet) typically used in companies, universities, etc 10 Mbps, 100Mbps, 1Gbps, 10Gbps transmission rates today, end systems typically connect into Ethernet switch Ethernet switch institutional mail, web servers institutional router institutional link to ISP (Internet) 1-13
- 14. Introduction 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 (WiFi): 11, 54 Mbps transmission rate wide-area wireless access provided by telco (cellular) operator, 10’s km between 1 and 10 Mbps 3G, 4G: LTE to Internet to Internet 1-14
- 15. Introduction 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 twisted pair (TP) two insulated copper wires Category 5: 100 Mbps, 1 Gpbs Ethernet Category 6: 10Gbps 1-15
- 16. Introduction Physical media: coax, fiber coaxial cable: two concentric copper conductors fiber optic cable: glass fiber carrying light pulses, each pulse a bit high-speed operation: high-speed point-to-point transmission (e.g., 10’s- 100’s Gpbs transmission rate) low error rate: repeaters spaced far apart immune to electromagnetic noise 1-16
- 17. Introduction Physical media: radio signal carried in electromagnetic spectrum no physical “wire” bidirectional propagation environment effects: reflection obstruction by objects interference radio link types: terrestrial microwave e.g. up to 45 Mbps channels LAN (e.g., WiFi) 11Mbps, 54 Mbps wide-area (e.g., cellular) 3G cellular: ~ few Mbps satellite Kbps to 45Mbps channels 1-17
- 18. Introduction Chapter 1: 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 delay, loss, throughput in networks 1.5 protocol layers, service models 1.6 networks under attack: security 1.7 history 1-18
- 19. Introduction 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 The network core 1-19
- 20. Host: sends packets of data host sending function: takes application message breaks into smaller chunks, known as packets, of length L bits transmits packet into access network at transmission rate R link transmission rate, aka link capacity, aka link bandwidth R: link transmission rate host 12 two packets, L bits each packet transmission delay time needed to transmit L-bit packet into link L (bits) R (bits/sec) = = 1-20
- 21. Introduction Packet-switching: store-and- forward takes L/R seconds to transmit (push out) L-bit packet into link at R bps store and forward: entire packet must arrive at router before it can be transmitted on next link one-hop numerical example: L = 7.5 Mbits R = 1.5 Mbps one-hop transmission delay = 5 sec more on delay shortly … 1-21 source R bps destination 123 L bits per packet R bps end-end delay = 2L/R (assuming zero propagation delay)
- 22. Introduction Packet Switching: queueing delay, loss A B CR = 100 Mb/s R = 1.5 Mb/s D Equeue of packets waiting for output link 1-22 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
- 23. Introduction 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 1-23
- 24. Introduction Circuit switching: FDM versus TDM FDM frequency time TDM frequency time 4 users Example: 1-24
- 25. Introduction Chapter 1: roadmap 1.1 what is the Internet? 1.2 network edge end systems, access networks, links 1.3 network core packet switching, circuit switching 1.4 delay, loss, throughput in networks 1.5 protocol layers, service models , network structure 1.6 networks under attack: security 1.7 history 1-25
- 26. Introduction How do loss and delay occur? packets queue in router buffers packet arrival rate to link (temporarily) exceeds output link capacity packets queue, wait for turn A B packet being transmitted (delay) packets queueing (delay) free (available) buffers: arriving packets dropped (loss) if no free buffers 1-26
- 27. Introduction Four sources of packet delay dproc: nodal processing check bit errors determine output link typically < msec A B propagation transmission nodal processing queueing dqueue: queueing delay time waiting at output link for transmission depends on congestion level of router dnodal = dproc + dqueue + dtrans + dprop 1-27
- 28. Introduction dtrans: transmission delay: L: packet length (bits) R: link bandwidth (bps) dtrans = L/R dprop: propagation delay: d: length of physical link s: propagation speed in medium (~2x108 m/sec) dprop = d/sdtrans and dprop very different Four sources of packet delay propagation nodal processing queueing dnodal = dproc + dqueue + dtrans + dprop 1-28 A B transmission * Check out the Java applet for an interactive animation on trans vs. prop delay
- 29. Introduction R: link bandwidth (bps) L: packet length (bits) a: average packet arrival rate 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! averagequeueing delay La/R ~ 0 Queueing delay (revisited) La/R -> 1 1-29 * Check out the Java applet for an interactive animation on queuing and loss
- 30. Introduction “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 1-30
- 31. Introduction “Real” Internet delays, 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: gaia.cs.umass.edu to www.eurecom.fr 3 delay measurements from gaia.cs.umass.edu to cs-gw.cs.umass.edu * means no response (probe lost, router not replying) trans-oceanic link 1-31 * Do some traceroutes from exotic countries at www.traceroute.org
- 32. Introduction Packet loss queue (aka buffer) preceding link in buffer has finite capacity packet arriving to full queue dropped (aka lost) lost packet may be retransmitted by previous node, by source end system, or not at all A B packet being transmitted packet arriving to full buffer is lost buffer (waiting area) 1-32* Check out the Java applet for an interactive animation on queuing and loss
- 33. Introduction 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 file of F bits to send to client link capacity Rs bits/sec link capacity Rc bits/sec server sends bits (fluid) into pipe pipe that can carry fluid at rate Rs bits/sec) pipe that can carry fluid at rate Rc bits/sec) 1-33
- 34. Introduction Throughput (more) Rs < Rc What is average end-end throughput? Rs bits/sec Rc bits/sec Rs > Rc What is average end-end throughput? link on end-end path that constrains end-end throughput bottleneck link Rs bits/sec Rc bits/sec 1-34
- 35. Introduction Throughput: Internet scenario 10 connections (fairly) share backbone bottleneck link R bits/sec Rs Rs Rs Rc Rc Rc R per-connection end-end throughput: min(Rc,Rs,R/10) in practice: Rc or Rs is often bottleneck 1-35
- 36. Introduction Chapter 1: 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 delay, loss, throughput in networks 1.5 protocol layers, service models 1.6 networks under attack: security 1.7 history 1-36
- 37. Introduction 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? 1-37
- 38. Introduction ticket (purchase) baggage (check) gates (load) runway (takeoff) airplane routing departure airport arrival airport intermediate air-traffic control centers airplane routing airplane routing ticket (complain) baggage (claim gates (unload) runway (land) airplane routing ticket baggage gate takeoff/landing airplane routing Layering of airline functionality layers: each layer implements a service via its own internal-layer actions relying on services provided by layer below 1-38
- 39. Introduction 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? 1-39
- 40. Introduction 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 physical: bits “on the wire” application transport network link physical 1-40
- 41. Introduction 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 1-41
- 42. Introduction source application transport network link physical HtHn M segment Ht datagram destination application transport network link physical HtHnHl M HtHn M Ht M M network link physical link physical HtHnHl M HtHn M HtHn M HtHnHl M router switch Encapsulationmessage M Ht M Hn frame 1-42
- 43. 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
- 44. 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 netaccess net access net
- 45. 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 access net access net access net access net access net access net access netaccess net access net connecting each access ISP to each other directly doesn’t scale: O(N2) connections.
- 46. Internet structure: network of networks 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 netaccess net access net Option: connect each access ISP to a global transit ISP? Customer and provider ISPs have economic agreement. global ISP
- 47. Internet structure: network of networks 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 netaccess net access net But if one global ISP is viable business, there will be competitors …. ISP B ISP A ISP C
- 48. Internet structure: network of networks 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 netaccess net access net But if one global ISP is viable business, there will be competitors …. which must be interconnected ISP B ISP A ISP C IXP IXP peering link Internet exchange point
- 49. Internet structure: network of networks 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 netaccess net access net … and regional networks may arise to connect access nets to ISPS ISP B ISP A ISP C IXP IXP regional net
- 50. Internet structure: network of networks 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 netaccess net access net … and content provider networks (e.g., Google, Microsoft, Akamai ) may run their own network, to bring services, content close to end users ISP B ISP A ISP B IXP IXP regional net Content provider network
- 51. Introduction Internet structure: network of networks 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 tier-1, regional 1-51 access ISP access ISP access ISP access ISP access ISP access ISP access ISP access ISP Regional ISP Regional ISP IX P IX P Tier 1 ISP Tier 1 ISP Google IX P
- 52. Introduction Chapter 1: 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 delay, loss, throughput in networks 1.5 protocol layers, service models 1.6 networks under attack: security 1.7 history 1-53
- 53. Introduction 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 “catch-up” security considerations in all layers! 1-54
- 54. Introduction 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 1-55
- 55. Introduction target 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 Bad guys: attack server, network infrastructure 1-56
- 56. Introduction 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 A B C src:B dest:A payload wireshark software used for end-of-chapter labs is a (free) packet-sniffer 1-57
- 57. Introduction Bad guys can use fake addresses IP spoofing: send packet with false source address A B C src:B dest:A payload 1-58 … lots more on security (throughout, Chapter 8)
- 58. Introduction Chapter 1: 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 delay, loss, throughput in networks 1.5 protocol layers, service models 1.6 networks under attack: security 1.7 history 1-59
- 59. Introduction Internet history 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 1961-1972: Early packet-switching principles 1-60
- 60. Introduction 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 1972-1980: Internetworking, new and proprietary nets Internet history 1-61
- 61. Introduction 1983: deployment of 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 new national networks: Csnet, BITnet, NSFnet, Minitel 100,000 hosts connected to confederation of networks 1980-1990: new protocols, a proliferation of networks Internet history 1-62
- 62. Introduction 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 Web 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 1990, 2000’s: commercialization, the Web, new apps Internet history 1-63
- 63. Introduction 2005-present ~750 million hosts Smartphones and tablets Aggressive deployment of broadband access Increasing ubiquity of high-speed wireless access Emergence of online social networks: Facebook: soon one billion users Service providers (Google, Microsoft) create their own networks Bypass Internet, providing “instantaneous” access to search, emai, etc. E-commerce, universities, enterprises running their services in “cloud” (eg, Amazon EC2) Internet history 1-64
- 64. Introduction Introduction: summary covered a “ton” of material! Internet overview what’s a protocol? network edge, core, access network packet-switching versus circuit-switching Internet structure performance: loss, delay, throughput layering, service models security history you now have: context, overview, “feel” of networking more depth, detail to follow! 1-65