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Net-centric Computing Nadeem Abdul Hamid Berry College Spring 2007 - CSC 450 Computer Networking: Net-centric Computing Nadeem Abdul Hamid Berry College Spring 2007 - CSC 450 Computer Networking: A Top Down Approach Featuring the Internet, 3 rd edition. Jim Kurose, Keith Ross Addison-Wesley, July 2004. Adapted from material copyright 1996 -2006 J. F Kurose and K. W. Ross, All Rights Reserved Introduction 1

This Course q Introduces the structure, implementation and theoretical underpinnings of computer networking and This Course q Introduces the structure, implementation and theoretical underpinnings of computer networking and the applications that have been enabled by that technology. Introduction 2

What You Will Learn q Terminology q Communication basics v Media and signals, bandwidth, What You Will Learn q Terminology q Communication basics v Media and signals, bandwidth, throughput, multiplexing q Networking and network technologies v Packet switching v Error detection, framing, parity v Network addressing v Connection and extension (hubs, switches, etc. ) v Topologies and wiring (star, ring, bus) v Forwarding and routing v Protocol layers v Wi. Fi Introduction 3

What You Will Learn q Internets and internetworking v Basic concepts v Internet Protocol What You Will Learn q Internets and internetworking v Basic concepts v Internet Protocol (IP), Internet routing v Address binding (ARP) v Internet control messages (ICMP) v Transport layer protocols (UDP/TCP) q Network applications v Client-server paradigm v Domain name system (DNS) v File transfer (FTP); mail (SMTP) v Web technologies (HTTP, …) v Network security Introduction 4

What We Will Not Cover q Commercial aspects v Products v Vendors v Prices What We Will Not Cover q Commercial aspects v Products v Vendors v Prices v Network operating systems q How to purchase/configure/operate q Network management* q Multimedia networking (e. g. streaming video, audio)* *Chapters in the textbook Introduction 5

Schedule of Topics q Introductory concepts and Python programming: ~2 weeks q Application layer: Schedule of Topics q Introductory concepts and Python programming: ~2 weeks q Application layer: ~3 weeks q Transport layer: ~2 weeks q Network layer: ~2 weeks q Link layer, LANs, hardware: ~2 weeks q Wireless networking: 1 week q Security: ~2 weeks Introduction 6

Programming q Primarily using Python as a tool for investigating and developing networking protocols Programming q Primarily using Python as a tool for investigating and developing networking protocols and applications q Maybe some C programming as well… Introduction 7

Coursework q Labs v Approx. half of each class sessions v Hands-on experience with Coursework q Labs v Approx. half of each class sessions v Hands-on experience with • Network programming and applications • Packet analysis • Network measurement q Written homeworks (weekly) q Programming assignments and project q Exams Introduction 8

Motivations and Practical Results q Information access q File transfer/access q Interaction among q Motivations and Practical Results q Information access q File transfer/access q Interaction among q E-mail cooperative application programs q Resource sharing q Web browsing q Remote login/execution q IP telephony q The Internet Introduction 9

Networks q Include: v Transmission hardware v Special-purpose devices • Interconnect transmission media • Networks q Include: v Transmission hardware v Special-purpose devices • Interconnect transmission media • Control transmission • Run protocol software v Protocol software • Encode/format data • Detect/correct problems q Provide communication that is: v v v Reliable Fair Efficient Secure From one application to another q Detect and correct: v Data corruption, loss, duplication, out-of-order delivery q Find optimal path from source to dest. Introduction 10

Chapter 1: Introduction Our goal: q get “feel” and terminology q more depth, detail Chapter 1: Introduction Our goal: q get “feel” and terminology q more depth, detail later in course q approach: v use Internet as example Overview: q what’s the Internet q what’s a protocol q network edge q network core q network access, physical media q Internet/ISP structure q performance: loss, delay q protocol layers, service models q network modeling Introduction 11

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. 8 History 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 Introduction 12

What’s the Internet: “nuts and bolts” view q millions of connected computing devices: hosts What’s the Internet: “nuts and bolts” view q millions of connected computing devices: hosts = end systems q running network apps q communication links v v router server workstation mobile local ISP fiber, copper, radio, satellite transmission rate = bandwidth regional ISP q routers: forward packets (chunks of data) company network Introduction 13

“Cool” internet appliances Web-enabled toaster + weather forecaster IP picture frame http: //www. ceiva. “Cool” internet appliances Web-enabled toaster + weather forecaster IP picture frame http: //www. ceiva. com/ World’s smallest web server http: //www-ccs. umass. edu/~shri/i. Pic. html Internet phones Introduction 14

What’s the Internet: “nuts and bolts” view q protocols control sending, receiving of msgs What’s the Internet: “nuts and bolts” view q protocols control sending, receiving of msgs v e. g. , TCP, IP, HTTP, FTP, PPP q Internet: “network of router server workstation mobile local ISP networks” v v loosely hierarchical public Internet versus private intranet q Internet standards v RFC: Request for comments v IETF: Internet Engineering Task Force regional ISP company network Introduction 15

What’s the Internet: a service view q communication infrastructure enables distributed applications: v Web, What’s the Internet: a service view q communication infrastructure enables distributed applications: v Web, email, games, ecommerce, file sharing q communication services provided to apps: v v Connectionless unreliable connection-oriented reliable Introduction 16

What’s a protocol? human protocols: q “what’s the time? ” q “I have a What’s a protocol? human protocols: q “what’s the time? ” q “I have a question” q introductions … specific msgs sent … specific actions taken when msgs received, or other events network protocols: q machines rather than humans q all communication activity in Internet governed by protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt Introduction 17

What’s a protocol? a human protocol and a computer network protocol: Hi TCP connection 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 time Q: Other human protocols? Introduction 18

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. 8 History 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 Introduction 19

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 20

The network edge: q end systems (hosts): v v v run application programs e. The network edge: 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 21

Network edge: connection-oriented service Goal: data transfer between end systems q handshaking: setup (prepare Network edge: connection-oriented service Goal: data transfer between end systems q handshaking: setup (prepare for) data transfer ahead of time v v Hello, hello back human protocol set up “state” in two communicating hosts q TCP - Transmission Control Protocol v Internet’s connectionoriented service TCP service [RFC 793] q reliable, in-order byte- stream data transfer v loss: acknowledgements and retransmissions q flow control: v sender won’t overwhelm receiver q congestion control: v senders “slow down sending rate” when network congested Introduction 22

Network edge: connectionless service Goal: data transfer between end systems v same as before! Network edge: connectionless service Goal: data transfer between end systems v same as before! q UDP - User Datagram Protocol [RFC 768]: v connectionless v unreliable data transfer v no flow control v no congestion control 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 23

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. 8 History 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 Introduction 24

The Network Core q mesh of interconnected routers q the fundamental question: how is The Network Core q mesh of interconnected routers q the fundamental question: how is data transferred through net? v circuit switching: dedicated circuit per call: telephone net v packet-switching: data sent thru net in discrete “chunks” Introduction 25

Network Core: Circuit Switching End-end resources reserved for “call” q link bandwidth, switch capacity Network Core: Circuit Switching End-end resources reserved for “call” q link bandwidth, switch capacity q dedicated resources: no sharing q circuit-like (guaranteed) performance q call setup required Introduction 26

Network Core: Circuit Switching network resources (e. g. , bandwidth) divided into “pieces” q Network Core: Circuit Switching network resources (e. g. , bandwidth) divided into “pieces” q pieces allocated to calls q dividing link bandwidth into “pieces” v frequency division v time division q resource piece idle if not used by owning call (no sharing) Introduction 27

Circuit Switching: FDM and TDM Example: FDM 4 users frequency time TDM frequency time Circuit Switching: FDM and TDM Example: FDM 4 users frequency time TDM frequency time Introduction 28

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 Let’s work it out! Introduction 29

Network Core: Packet Switching each end-end data stream divided into packets q user A, Network Core: 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 Bandwidth division into “pieces” Dedicated allocation Resource reservation resource contention: q aggregate resource demand can exceed amount available q congestion: packets queue, wait for link use q store and forward: packets move one hop at a time v Node receives complete packet before forwarding Introduction 30

Packet Switching: Statistical Multiplexing 100 Mb/s Ethernet A B statistical multiplexing C 1. 5 Packet Switching: Statistical Multiplexing 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 31

Packet-switching: store-and-forward L R q Takes L/R seconds to R transmit (push out) packet Packet-switching: store-and-forward L R q Takes L/R seconds to R transmit (push out) packet of L bits on to link of 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 = 7. 5 Mbits q R = 1. 5 Mbps q delay = 15 sec more on delay shortly … Introduction 32

Packet switching versus circuit switching Packet switching allows more users to use network! q Packet switching versus circuit switching Packet switching allows more users to use network! q 1 Mb/s link q each user: v 100 kb/s when “active” v active 10% of time q circuit-switching: v 10 users q packet switching: v with 35 users, probability > 10 active less than. 0004 N users 1 Mbps link Q: how did we get value 0. 0004? Introduction 33

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 34

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. 8 History 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 Introduction 35

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 packet-switching 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 36

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 37

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 38

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 of 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 the Web Introduction 39

Protocols and Standards q Protocol v Set of rules governing communication v What, how, Protocols and Standards q Protocol v Set of rules governing communication v What, how, and when… v Syntax v Semantics v Timing Forouzan, Ch. 1 q Standards v Agreed-upon rules v Create and maintain open, competitive market v Guarantee national and international interoperability v De facto: “by fact”, “by convention” v De jure: “by law” legislated by officially recognized body Introduction 40

Standards Organizations q ISO: International Standards Organization q ITU-T: International Telecommunications Union-Telecommunications Standards Sector Standards Organizations q ISO: International Standards Organization q ITU-T: International Telecommunications Union-Telecommunications Standards Sector (UN) q ANSI: American National Standards Inst. q IEEE: Institute of Electrical and Electronics Engineers q EIA: Electronic Industries Association Introduction 41

Internet Standards q Thoroughly tested specification adhered to by those working with the Internet Internet Standards q Thoroughly tested specification adhered to by those working with the Internet q Strict procedure Internet draft (working document): unofficial, six-month lifetime v Request for Comments (RFC): published recommendation, numbered and distributed v Introduction 42

RFC Maturity Levels Introduction 43 RFC Maturity Levels Introduction 43

RFC Requirement Levels Introduction 44 RFC Requirement Levels Introduction 44

Internet Administration Introduction 45 Internet Administration Introduction 45

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. 8 History 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 Introduction 46

Access networks and physical media Q: How to connect end systems to edge router? Access networks and physical media Q: How to connect end systems to edge router? q residential access nets q institutional access networks (school, company) q mobile access networks Keep in mind: q bandwidth (bits per second) of access network? q shared or dedicated? Introduction 47

Residential access: point to point access q Dialup via modem up to 56 Kbps Residential access: point to point access q Dialup via modem up to 56 Kbps direct access to router (often less) v Can’t surf and phone at same time: can’t be “always on” v q ADSL: asymmetric digital subscriber line up to 1 Mbps upstream (today typically < 256 kbps) v up to 8 Mbps downstream (today typically < 1 Mbps) v FDM: 50 k. Hz - 1 MHz for downstream v 4 k. Hz - 50 k. Hz for upstream 0 k. Hz - 4 k. Hz for ordinary telephone Introduction 48

Residential access: cable modems q HFC: hybrid fiber coax asymmetric: up to 30 Mbps Residential access: cable modems q HFC: hybrid fiber coax asymmetric: up to 30 Mbps downstream, 2 Mbps upstream q network of cable and fiber attaches homes to ISP router v homes share access to router q deployment: available via cable TV companies v Introduction 49

Residential access: cable modems Diagram: http: //www. cabledatacomnews. com/cmic/diagram. html Introduction 50 Residential access: cable modems Diagram: http: //www. cabledatacomnews. com/cmic/diagram. html Introduction 50

Cable Network Architecture: Overview Typically 500 to 5, 000 homes cable headend cable distribution Cable Network Architecture: Overview Typically 500 to 5, 000 homes cable headend cable distribution network (simplified) home Introduction 51

Cable Network Architecture: Overview server(s) cable headend cable distribution network home Introduction 52 Cable Network Architecture: Overview server(s) cable headend cable distribution network home Introduction 52

Cable Network Architecture: Overview cable headend cable distribution network (simplified) home Introduction 53 Cable Network Architecture: Overview cable headend cable distribution network (simplified) home Introduction 53

Cable Network Architecture: Overview FDM: V I D E O V I D E Cable Network Architecture: Overview 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 54

Company access: local area networks q company/univ local area network (LAN) connects end system Company access: local area networks q company/univ local area network (LAN) connects end system to edge router q Ethernet: v shared or dedicated link connects end system and router v 10 Mbs, 100 Mbps, Gigabit Ethernet q LANs: chapter 5 Introduction 55

Wireless access networks q shared wireless access network connects end system to router v Wireless access networks q shared wireless access network connects end system to router v via base station aka “access point” q wireless LANs: v 802. 11 b/g (Wi. Fi): 11 or 54 Mbps q wider-area wireless access v provided by telco operator v 3 G ~ 384 kbps • Will it happen? ? v GPRS in Europe/US router base station mobile hosts Introduction 56

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 57

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 58

Physical Media: coax, fiber Coaxial cable: Fiber optic cable: conductors q bidirectional q baseband: Physical Media: coax, fiber Coaxial cable: Fiber optic cable: conductors q bidirectional q baseband: pulses, each pulse a bit q high-speed operation: q two concentric copper v v single channel on cable legacy Ethernet q broadband: v multiple channels on cable v HFC q glass fiber carrying light v high-speed point-to-point transmission (e. g. , 10’s 100’s Gps) q low error rate: repeaters spaced far apart ; immune to electromagnetic noise Introduction 59

Physical media: radio q signal carried in electromagnetic spectrum q no physical “wire” q Physical media: radio q signal carried in electromagnetic spectrum q no physical “wire” q bidirectional q propagation environment effects: v v v reflection obstruction by objects interference Radio link types: q terrestrial microwave v e. g. up to 45 Mbps channels q LAN (e. g. , Wifi) v 11 Mbps, 54 Mbps q wide-area (e. g. , cellular) v e. g. 3 G: hundreds of kbps q satellite v Kbps to 45 Mbps channel (or multiple smaller channels) v 270 msec end-end delay v geosynchronous versus low altitude Introduction 60

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. 8 History 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 Introduction 61

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 62

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 63

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 64

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 65

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 66

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. 8 History 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 Introduction 67

How do loss and delay occur? packets queue in router buffers q packet arrival How do loss and delay occur? packets queue in router buffers q packet arrival rate to link exceeds output link capacity q packets queue, wait for turn packet being transmitted (delay) A B packets queueing (delay) free (available) buffers: arriving packets dropped (loss) if no free buffers Introduction 68

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 transmission A propagation B nodal processing queueing Introduction 69

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 70

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 71

Caravan analogy (more) 100 km ten-car caravan 100 km toll booth q Cars now Caravan analogy (more) 100 km ten-car caravan 100 km toll booth q Cars now “propagate” at 1000 km/hr q Toll booth now takes 1 min to service a car q Q: Will cars arrive to 2 nd booth before all cars serviced at 1 st booth? toll booth q Yes! After 7 min, 1 st car at 2 nd booth and 3 cars still at 1 st booth. q 1 st bit of packet can arrive at 2 nd router before packet is fully transmitted at 1 st router! v See Ethernet applet at AWL Web site Introduction 72

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 73

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 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 74

“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 75

“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 76

Packet loss q queue (aka buffer) preceding link in buffer has finite capacity q Packet loss q queue (aka buffer) preceding link in buffer has finite capacity q when packet arrives to full queue, packet is dropped (aka lost) q lost packet may be retransmitted by previous node, by source end system, or not retransmitted at all Introduction 77

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. 8 History 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 Introduction 78

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: Is there any hope of organizing structure of network? Or at least our discussion of networks? Introduction 79

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 q a series of steps Introduction 80

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 via its own internal-layer actions v relying on services provided by layer below Introduction 81

Why layering? Dealing with complex systems: q explicit structure allows identification, relationship of complex Why layering? Dealing with complex systems: q explicit structure allows identification, relationship of complex system’s pieces v layered reference model for discussion 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 82

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 83

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 84

Introduction: Summary Covered a “ton” of material! q Internet overview q what’s a protocol? Introduction: Summary Covered a “ton” of material! 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 You now have: q context, overview, “feel” of networking q more depth, detail to follow! Introduction 85