COMP2602 Chapter 1 Computer Networks and the Internet 8th_2024_2025 use postedc stu .pdf

Tutorials start with Chap 1 questions (tutor). Chapter 1 Students to use text book, slides and research to Introduction...

Tutorials start with Chap 1 questions (tutor). Chapter 1 Students to use text book, slides and research to Introduction answer questions A note on the use of these PowerPoint slides: We’re making these slides freely available to all (faculty, students, readers). They’re in PowerPoint form so you see the animations; and can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent a lot of work on our part. In return for use, we only ask the following: ▪ If you use these slides (e.g., in a class) that you mention their source (after all, we’d like people to use our book!) ▪ If you post any slides on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material. Computer Networking: A For a revision history, see the slide note for this page. Top-Down Approach Thanks and enjoy! JFK/KWR 8th edition All material copyright 1996-2020 Jim Kurose, Keith Ross J.F Kurose and K.W. Ross, All Rights Reserved Pearson, 2020 Chapter 1: introduction Chapter goal: Overview/roadmap: What is the Internet? Get “feel,” “big picture,” What is a protocol? introduction to Network edge: hosts, access network, physical media terminology Network core: packet/circuit switching, more depth, detail later in course internet structure Approach: Performance: loss, delay, throughput Security use Internet as example Protocol layers, service models History Introduction: 1-2  “Fun” Internet-connected devices Pacemaker & Monitor Tweet-a-watt: monitor energy use Amazon Echo IP picture frame Web-enabled toaster + weather forecaster Internet refrigerator Slingbox: remote control cable TV Security Camera Internet phones Fitbit (activity trackers)  mobile network 4G Internet: “network of national or global ISP networks” Streaming Interconnected ISPs IP Skype video ▪ protocols are everywhere local or regional control sending, receiving of ISP messages home network content provider e.g., HTTP (Web), streaming video, HTTP network datacenter Skype, TCP, IP, WiFi, 4G, Ethernet Ethernet network ▪ Internet standards TCP RFC: Request for Comments enterprise network IETF: Internet Engineering Task Force. The IETF is a large open international community WiFi of network designers, operators, vendors, and researchers concerned with the evolution of the Internet architecture and the smooth operation of the Internet. The Internet: a “nuts and bolts” view Billions of connected mobile network computing devices: national or global ISP ▪ hosts = end systems ▪ running network apps at Internet’s “edge” Packet switches: forward local or packets (chunks of data) Internet regional ISP ▪ routers, switches home network content Communication links provider network ▪ fiber, copper, radio, datacenter network satellite ▪ transmission rate: bandwidth Networks enterprise ▪ collection of devices, routers, links: network managed by an organization Introduction: 1-5 The Internet: a “service” view Infrastructure that mobile network national or global ISP provides services to applications: Skype Streaming video Web, streaming video, multimedia local or teleconferencing, email, games, e- regional ISP commerce, social media, inter- home network connected appliances, … content provider HTTP network ▪ provides programming interface datacenter network to distributed applications: “hooks” allowing enterprise sending/receiving apps to network “connect” to, use Internet transport service Hooks allow a programmer to provides service options, insert customized code. Eg analogous to postal service implement chat program but TCP/IP code present What’s a protocol? Human protocols: Network protocols: ▪ “what’s the time?” ▪ computers (devices) rather than humans ▪ “I have a question” ▪ all communication activity in Internet ▪ introductions governed by protocols Protocols define the format, order of … specific messages sent messages sent and received … specific actions taken among network entities, and when message received, or other events actions taken on msg transmission, receipt 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://gaia.cs.umass.edu/kurose_ross 2:00 time Q: other human protocols? Chapter 1: roadmap What is the Internet? What is a protocol? Network edge: hosts, access network, physical media Network core: packet/circuit switching, internet structure Performance: loss, delay, throughput Security Protocol layers, service models History Introduction: 1-9  A closer look at Internet structure mobile network Network edge: national or global ISP hosts: clients and servers servers often in data centers local or regional ISP home network content provider network datacenter network enterprise network Data centre-a large group of networked computer servers typically used by organizations for the remote storage, processing, or distribution of large amounts of data. Introduction: 1-10  A closer look at Internet structure mobile network Network edge: national or global ISP hosts: clients and servers servers often in data centers local or regional Access networks, physical media: ISP home network content wired, wireless provider network datacenter communication links network enterprise network Introduction: 1-11  A closer look at Internet structure mobile network Network edge: national or global ISP hosts: clients and servers servers often in data centers Access networks, physical media: local or regional wired, wireless communication home network ISP content links provider network datacenter network Network core: ▪ interconnected routers enterprise ▪ network of networks network Introduction: 1-12 Access networks and physical media Q: How to connect end systems mobile network to edge router? national or global ISP residential access nets institutional access networks (school, company) mobile access networks (WiFi, 4G/5G) local or regional ISP What to look for: home network content provider ▪ transmission rate (bits per second) of access network datacenter network? network ▪ shared or dedicated access among users? enterprise network Introduction: 1-13 Access networks: cable-based access cable headend … cable splitter modem C O V V V V V V N I I I I I I D D T D D D D D D A A R E E E E E E T T O O O O O O O A A L 1 2 3 4 5 6 7 8 9 Channels frequency division multiplexing (FDM): different channels transmitted in different frequency bands Introduction: 1-14 Access networks: cable-based access cable headend … cable splitter cable modem modem CMTS termination system data, TV transmitted at different frequencies over shared cable ISP distribution network ▪ HFC: hybrid fiber coax asymmetric: up to 40 Mbps – 1.2 Gbs downstream transmission rate, 30-100 Mbps upstream transmission rate ▪ network of cable, fiber attaches homes to ISP router homes share access network to cable headend Introduction: 1-15 Access networks: digital subscriber line (DSL) central office telephone network DSL splitter modem DSLAM voice, data transmitted ISP at different frequencies over DSL access dedicated line to central office 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 ▪ 24-52 Mbps dedicated downstream transmission rate ▪ 3.5-16 Mbps dedicated upstream transmission rate DSLAM connects multiple DSL subscribers to one Internet backbone. Introduction: 1-16 Access networks: home networks wireless devices to/from headend or central office often combined in single box cable or DSL modem WiFi wireless access router, firewall, NAT point (54, 450 Mbps) wired Ethernet (1 Gbps) Introduction: 1-17 Wireless access networks Shared wireless access network connects end system to router ▪ via base station aka “access point” Wireless local area networks Wide-area cellular access networks (WLANs) ▪ provided by mobile, cellular network ▪ typically within or around operator (10’s km) building (~100 ft) ▪ 10’s Mbps ▪ 802.11b/g/n (WiFi): 11, 54, 450 ▪ 4G cellular networks (5G coming) Mbps transmission rate to Internet to Internet Introduction: 1-18 Access networks: enterprise networks Enterprise link to ISP (Internet) institutional router Ethernet institutional mail, switch web servers ▪ companies, universities, etc. ▪ mix of wired, wireless link technologies, connecting a mix of switches and routers (we’ll cover differences shortly) ▪ Ethernet: wired access at 100Mbps, 1Gbps, 10Gbps ▪ WiFi: wireless access points at 11, 54, 450 Mbps Introduction: 1-19 Host: sends packets of data host sending function: ▪ takes application message two packets, ▪ breaks into smaller chunks, L bits each known as packets, of length L bits ▪ transmits packet into access 2 1 network at transmission rate R link transmission rate, aka link host capacity, aka link bandwidth R: link transmission rate packet time needed to L (bits) transmission = transmit L-bit = delay packet into link R (bits/sec) Introduction: 1-20 Links: physical media ▪ bit: propagates between Twisted pair (TP) transmitter/receiver pairs ▪ two insulated copper wires ▪ physical link: what lies Category 5: 100 Mbps, 1 Gbps Ethernet between transmitter & Category 6: 10Gbps Ethernet receiver ▪ guided media: signals propagate in solid media: copper, fiber, coax ▪ unguided media: signals propagate freely, e.g., radio Introduction: 1-21 Links: physical media Coaxial cable: Fiber optic cable: ▪ two concentric copper conductors ▪ glass fiber carrying light pulses, each pulse a bit ▪ bidirectional ▪ high-speed operation: ▪ broadband: high-speed point-to-point multiple frequency channels on cable transmission (10’s-100’s Gbps) 100’s Mbps per channel ▪ low error rate: repeaters spaced far apart immune to electromagnetic noise Introduction: 1-22 Links: physical media Wireless radio Radio link types: ▪ signal carried in ▪ terrestrial microwave electromagnetic spectrum up to 45 Mbps channels ▪ no physical “wire” ▪ Wireless LAN (WiFi) Up to 100’s Mbps ▪ broadcast and “half-duplex” (sender to receiver) ▪ wide-area (e.g., cellular) ▪ propagation environment 4G cellular: ~ 10’s Mbps effects: ▪ satellite reflection up to 45 Mbps per channel obstruction by objects 270 msec end-end delay interference geosynchronous versus low- earth-orbit Introduction: 1-23  L1:slide 1-24 L2: slide 25 Chapter 1: roadmap What is the Internet? What is a protocol? Network edge: hosts, access network, physical media Network core: packet/circuit switching, internet structure Performance: loss, delay, throughput Security Protocol layers, service models 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-and-forward L bits per packet 32 1 source destination R bps R bps ❖ takes L/R seconds to one-hop numerical example: transmit (push out) L-bit packet into link at R bps ▪ L = 7.5 Mbits ❖ store and forward: entire ▪ R = 1.5 Mbps packet must arrive at router ▪ one-hop transmission before it can be transmitted delay = 5 sec on next link ❖ end-end delay = 2L/R (assuming zero propagation delay) more on delay shortly … Introduction 1-26 Packet Switching: queueing delay, loss R = 100 Mb/s C A D R = 1.5 Mb/s B queue of packets E waiting for output link 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 source- forwarding: move packets from destination route taken by router’s input to appropriate packets router output ▪ routing algorithms routing algorithm local forwarding table header value output link 0100 3 1 0101 2 0111 2 3 2 1001 1 dest address in arriving packet’s header Network Layer 4-27 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 (Full bandwidth for a certain time) frequency time Introduction 1-30 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 Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet-switching)? Introduction 1-31 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 Tier 1 ISP Tier 1 ISP Google IXP IXP IXP Regional ISP Regional ISP access access access access access access access access ISP ISP ISP ISP ISP ISP ISP 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 D. Hollinger it data centers to Internet, often bypassing tier-1, regional ISPs Introduction 1-32 Chapter 1: roadmap 1. what is the Internet? 2. network edge ▪ end systems, access networks, links 3. network core ▪ packet switching, circuit switching, network structure 4. delay, loss, throughput in networks 5. protocol layers, service models 6. networks under attack: security 7. history Introduction 1-34 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 packet being transmitted (delay) A B packets queueing (delay) free (available) buffers: arriving packets dropped (loss) if no free buffers Introduction 1-35 Four sources of packet delay transmission A propagation B nodal processing queueing dnodal = dproc + dqueue + dtrans + dprop dproc: nodal processing dqueue:queueing delay ▪ check bit errors ▪ time waiting at output link ▪ determine output link for transmission ▪ typically < msec ▪ depends on congestion level of router Introduction 1-36 Four sources of packet delay transmission A propagation B nodal processing queueing dnodal = dproc + dqueue + dtrans + dprop dtrans:transmission delay: dprop:propagation delay: ▪ L:packet length (bits) ▪ d:length of physical link ▪ R:link bandwidth (bps) ▪ s:propagation speed in medium ▪ dtrans = L/R (~2x108 m/sec) dtrans and dprop ▪ dprop = d/s very different * Check out the Java applet for an interactive animation on trans vs. prop delay Introduction 1-36  Packet delay Transmission delay The transmission delay is L/R. This is the amount of time required to push (that is, transmit) all of the packet’s bits into the link. Propagation Delay Once a bit is pushed into the link, it needs to propagate to router B. The time required to propagate from the beginning of the link to router B is the propagation delay. The bit propagates at the propagation speed of the link. The propagation speed depends on the physical medium of the link (that is, fiber optics, twisted- pair, copper wire, and so on) The propagation delay is the distance between two routers divided by the propagation speed. That is, the propagation delay is d/s, where d is the distance between router A and router B and s is the propagation speed of the link.  Queueing delay (revisited) average queueing ❖ R: link bandwidth (bps) delay ❖ L: packet length (bits) ❖ a: average packet arrival rate traffic intensity = La/R average rate at which bits arrive at the queue is La bits/sec La/R ~ 0 R is the ability to service load La ❖ La/R ~ 0:avg.queueing delay small -La much smaller than R ❖ La/R -> 1:avg.queueing delay large-La meeting R capacity ❖ La/R > 1:more “work” arriving than can be serviced,average delay infinite!–packets lost La/R -> 1 * Check out the Java applet for an interactive animation on queuing and loss Introduction 1-39 “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 Introduction 1-40 “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 7nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms 8 trans-oceanic 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 link 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 * * * * means no response (probe lost, router not replying) 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 1-41 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 buffer (waiting area) packet being transmitted A B packet arriving to full buffer is lost * Check out the Java applet for an interactive animation on queuing and loss Introduction 1-40 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 server ,withbits sends linkpipe that can carry linkpipe capacity that can carry file ofinto (fluid) F bits pipe capacity fluid at rate Rc bits/sec fluid at rate to send to client Rs bits/sec Rs bits/sec) Rc bits/sec) Introduction 1-43 Chapter 1: roadmap 1. what is the Internet? 2. network edge ▪ end systems, access networks, links 3. network core ▪ packet switching, circuit switching, network structure 4. delay, loss, throughput in networks 5. protocol layers, service models 6. networks under attack: security 7. history Introduction 1-44 Protocol “layers” Networks are complex, with many “pieces”: ▪ hosts Question: ▪ routers is there any hope of ▪ links of various organizing structure of media network? ▪ applications ▪ protocols …. or at least our ▪ hardware discussion of networks? , software Introduction 1-45 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 1-46 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 airplane routing airplane routing departure intermediate air-traffic arrival airport control centers airport layers: each layer implements a service ▪ via its own internal-layer actions ▪ relying on services provided by layer below Introduction 1-47 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 Introduction 1-48 Internet protocol stack ❖ application: supporting network applications ▪ FTP, SMTP, HTTP application ❖ transport: process-process data transfer transport ▪ TCP, UDP network ❖ network: routing of datagrams from source to destination link ▪ IP, routing protocols ❖ link: data transfer between physical neighboring network elements ▪ Ethernet, 802.11 (WiFi), PPP ❖ physical: bits “on the wire” Introduction 1-49 ISO/OSI reference model ❖ presentation: allow applications to interpret meaning of data, application e.g., encryption, compression, presentation machine-specific conventions ❖ session: synchronization, session checkpointing, recovery of data transport exchange network ❖ Internet stack “missing” these layers! link ▪ these services, if needed, must be physical implemented in application ▪ needed? Introduction 1-50  source message M application Encapsulation segment Ht M transport datagram Hn Ht M network frame Hl Hn Ht M link physical link physical switch destination Hn Ht M network M application Hl Hn Ht M link Hn Ht M Ht M transport physical Hn Ht M network Hl Hn Ht M link router physical Introduction: 1-51 Chapter 1: roadmap 1. what is the Internet? 2. network edge ▪ end systems, access networks, links 3. network core ▪ packet switching, circuit switching, network structure 4. delay, loss, throughput in networks 5. protocol layers, service models 6. networks under attack: security 7. history Introduction 1-52 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! Introduction 1-53 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 itselfexecuted ❖ 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 1-54 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 1-55 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 C src:B dest:A payload B ❖ wireshark software used for end-of-chapter labs is a (free) packet-sniffer Introduction 1-56 Bad guys can use fake addresses IP spoofing: send packet with false source address A C src:C dest:A payload B … lots more on security (throughout,Chapter 8) Introduction 1-57 Introduction:summary covereda “ton” of material! you nowhave: ❖ Internet overview ❖ context, overview, “feel” ❖ what’s a protocol? of networking ❖ network edge, core, access ❖ more depth, detail to network follow! ▪ packet-switching versus circuit-switching ▪ Internet structure ❖ performance:loss,delay, throughput ❖ layering,service models ❖ security ❖ history Introduction 1-58