Chapter1.pdf

Why Networks are Important ▪ Data, data, data! ▪ Modern organizations rely on the efficient transmission of data ▪ Enables distributed systems, real-time communication, electronic commerce, social media, and the Web Why Networks are Important ▪ By 2016, Cisco estimates that over 3,000 Petabytes of information will be transferred over the Internet DAILY! Can you find out how much is it in 2022? ▪ Netflix accounts for around 1/3 of primetime downstream traffic ▪ During the holiday 2013 season, Amazon sold an average of 426 items per SECOND! ▪ As of 2012, every DAY on Facebook there are: 2.7 Billion Likes 300 Million Photos uploaded >500 Terabytes of data transmitted Road Network Image Courtesy: https://www.mapsofworld.com Image Courtesy: Google Maps 3 Computer Network - Hardware 4 Computer Network - Software and Service  A computer network is an infrastructure providing service to applications - deliver bits of information from one program to another program. 5 How big is a Computer Network? What do you mean by "a network"? Computer Networks at Various Scales network coverage # of nodes distance (roughly) (rough numbers) (rough numbers) Personal Area Network (PAN) a person < 10 < 10 m Local Area Network (LAN) a house or a 10 ~ 1,000 ~ 1 km campus Metropolitan Area Network a city 1,000 ~ 1 million ~ 10 km (MAN) Wide Area Network (WAN) a country 1 million ~ 1 billion 100 ~ 1000 km The Internet (network of a planet ~ 10 billion ~ 10,000 km networks) 7 Personal Area Network (PAN)  Personal Area Network (PAN) connects devices over the range of a person.  e.g., bluetooth speaker, headset, smartwatch, smartphone, wireless keyboard 8 Local Area Network (LAN)  Local Area Network (LAN) connects devices in a home or several buildings.  e.g., enterprise network or campus network. 9 Metropolitan Area Network (MAN)  Metropolitan Area Network (MAN) connects devices over a metropolitan area.  e.g., Internet access over cable TV network or telephone network (DSL). 10 Wide Area Network (WAN)  Wide Area Network (WAN) connects devices over a country.  e.g., VPN or Internet core constructed by big ISP such as AT&T, Verizon. 11 The Internet  The Internet is the network of networks that connects devices and computers globally.  The Internet is built and own by multiple organizations worldwide. Image Courtesy: 5TJT, http://www.5tjt.com/the-internet-and-selling-chometz-a-halachic-analysis/ 12 Chapter 1 Introduction 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 1996-2023 Jim Kurose, Keith Ross J.F Kurose and K.W. Ross, All Rights Reserved Pearson, 2020 Modified by: Dr. Abdulhakim Sabur Introduction: 1-13 Chapter 1: introduction Chapter goal: Overview/roadmap: ▪ Get “feel,” “big picture,” ▪ What is the Internet? What is a introduction to terminology protocol? more depth, detail later in ▪ Network edge: hosts, access network, physical media course ▪ Network core: packet/circuit switching, internet structure ▪ Performance: loss, delay, throughput ▪ Protocol layers, service models ▪ Security ▪ History Introduction: 1-14 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 datacenter ▪ fiber, copper, radio, satellite network ▪ transmission rate: bandwidth Networks enterprise ▪ collection of devices, routers, network links: managed by an organization Introduction: 1-15 “Fun” Internet-connected devices Tweet-a-watt: monitor energy use bikes Pacemaker & Monitor Amazon Echo Web-enabled toaster + IP picture frame weather forecaster Internet refrigerator Slingbox: remote cars control cable TV Security Camera AR devices sensorized, scooters bed mattress Fitbit Gaming devices Others? Internet phones diapers Introduction: 1-16 The Internet: a “nuts and bolts” view mobile network 4G ▪ Internet: “network of networks” national or global ISP Interconnected ISPs ▪ protocols are everywhere Skype IP Streaming video control sending, receiving of messages local or regional ISP e.g., HTTP (Web), streaming video, Skype, TCP, IP, WiFi, 4/5G, Ethernet home network content provider HTTP network datacenter ▪ Internet standards network Ethernet RFC: Request for Comments IETF: Internet Engineering Task enterprise TCP Force network WiFi Introduction: 1-17 The Internet: a “services” view ▪ Infrastructure that provides mobile network services to applications: national or global ISP Web, streaming video, multimedia teleconferencing, email, games, e- Streaming commerce, social media, inter- Skype video connected appliances, … local or regional ISP ▪ provides programming interface to distributed applications: home network content provider “hooks” allowing sending/receiving HTTP network datacenter network apps to “connect” to, use Internet transport service provides service options, analogous enterprise to postal service network Introduction: 1-18 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 Rules for: Protocols define the format, order of … specific messages sent messages sent and received among … specific actions taken network entities, and actions taken when message received, or other events on message transmission, receipt Introduction: 1-19 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? Introduction: 1-20 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: 1-21 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 Introduction: 1-22 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 Access networks, physical media: regional ISP ▪wired, wireless communication links home network content provider network datacenter network enterprise network Introduction: 1-23 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 Access networks, physical media: regional ISP ▪wired, wireless communication links home network content provider network datacenter Network core: network ▪ interconnected routers ▪ network of networks enterprise network Introduction: 1-24 Access networks and physical media Q: How to connect end systems mobile network national or global ISP to edge router? ▪ residential access nets ▪ institutional access networks (school, company) local or ▪ mobile access networks (WiFi, 4G/5G) regional ISP home network content provider network datacenter network enterprise network Introduction: 1-25 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: 1-26 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 Gbps 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: 1-27 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 Introduction: 1-28 Access networks: home networks Wireless and wired 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: 1-29 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 ▪ 3G, 4G/5G cellular networks Mbps transmission rate to Internet to Internet Introduction: 1-30 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: 1-31 Access networks: data center networks mobile network ▪ high-bandwidth links (10s to 100s national or global ISP Gbps) connect hundreds to thousands of servers together, and to Internet local or regional ISP home network content provider network datacenter network Courtesy: Massachusetts Green High Performance Computing enterprise Center (mghpcc.org) network Introduction: 1-32 Host: sends packets of data host sending function: ▪ takes application message ▪ breaks into smaller chunks, two packets, known as packets, of length L bits L bits each ▪ 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) = (seconds) transmission transmit L-bit = delay packet into link R (bits/sec) Introduction: 1-33 *Links: physical media ▪ bit: propagates between Twisted pair (TP) transmitter/receiver pairs ▪ Two, Four or eight insulated copper wires ▪ physical link: what lies between transmitter & ▪ Ethernet (LAN) cables receiver 8 wires: (4 pairs each pair is twisted) ▪ Links= Media, Circuit, Channel Category 5 (Cat 5) : 100 Mbps, 1 Gbps Ethernet ▪ guided media: (Wired Media) Category 6 (Cat 6) : 10Gbps Ethernet signals propagate in solid media: Category 7 (Cat 7) e.g.: Twisted pair (TP), coax, fiber Unshielded TP (UTP), Shielded TP (STP) ▪ unguided media: (Wireless Media) signals propagate freely in air or space. e.g., radio, Satellite, WIFI, BT Introduction: 1-34 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: 1-35 *Links: physical media Wireless radio Radio link types: ▪ signal carried in various “bands” in ▪ Wireless LAN (WiFi) electromagnetic spectrum 10-100’s Mbps; 10’s of meters ▪ no physical “wire” ▪ wide-area (e.g., 4G cellular) ▪ Broadcast (Simplex), “half-duplex”, 10’s Mbps over ~10 Km or full-duplex ▪ propagation environment effects: ▪ Bluetooth: cable replacement reflection short distances, limited rates Refraction ▪ terrestrial microwave obstruction by objects point-to-point; 45 Mbps channels Buildings, Walls, Dust, smoke, fog, rain, … ▪ satellite Interference/noise up to 45 Mbps per channel Attenuation over distance 270 msec end-end delay Infra Red (IR) Introduction: 1-36 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: 1-37 The network core ▪ mesh of interconnected routers mobile network national or global ISP ▪ packet-switching: hosts break application-layer messages into packets network forwards packets from one local or regional ISP router to the next, across links on path from source to destination home network content provider network datacenter network enterprise network Introduction: 1-38 Two key network-core functions routing algorithm Routing: Forwarding: local local forwarding forwarding table table ▪ global action: header value output link determine source- ▪ aka “switching” 0100 3 destination paths ▪ local action: 0101 2 move arriving 0111 1001 2 1 taken by packets packets from ▪ routing algorithms router’s input link 1 to appropriate router output link 3 2 destination address in arriving packet’s header Introduction: 1-39 routing Introduction: 1-40 forwarding forwarding Introduction: 1-41 Packet-switching: store-and-forward L bits per packet 3 2 1 source destination R bps R bps ▪ packet transmission delay: takes L/R seconds to One-hop numerical example: transmit (push out) L-bit packet into link at R bps ▪ L = 10 Kbits ▪ store and forward: entire packet must arrive at ▪ R = 100 Mbps router before it can be transmitted on next link ▪ one-hop transmission delay = 0.1 msec Introduction: 1-42 Packet-switching: queueing R = 100 Mb/s A C D B R = 1.5 Mb/s E queue of packets waiting for transmission over output link Queueing occurs when work arrives faster than it can be serviced: Introduction: 1-43 Packet-switching: queueing R = 100 Mb/s A C D B R = 1.5 Mb/s E queue of packets waiting for transmission over output link Packet queuing and loss: if arrival rate (in bps) to link exceeds transmission rate (bps) of link for some period of time: ▪ packets will queue, waiting to be transmitted on output link ▪ packets can be dropped (lost) if memory (buffer) in router fills up Introduction: 1-44 Alternative to packet switching: circuit switching end-end resources allocated to, reserved for “call” between source and destination ▪ 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 * Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/interactive Introduction: 1-45 Circuit switching: FDM and TDM Frequency Division Multiplexing (FDM) 4 users frequency ▪ optical, electromagnetic frequencies divided into (narrow) frequency bands ▪ each call allocated its own band, can transmit at max rate of that narrow time band Time Division Multiplexing (TDM) frequency ▪ time divided into slots ▪ each call allocated periodic slot(s), can transmit at maximum rate of (wider) time frequency band (only) during its time slot(s) Introduction: 1-46 Packet switching versus circuit switching example: ▪ 1 Gb/s link N ▪ each user: users 1 Gbps link 100 Mb/s when “active” active 10% of time Q: how many users can use this network under circuit-switching and packet switching? ▪ circuit-switching: 10 users ▪ packet switching: with 35 users, Q: how did we get value 0.0004? probability > 10 active at same time is less than.0004 * A: HW problem (for those with course in probability only) * Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/interactive Introduction: 1-47 Packet switching versus circuit switching Is packet switching a “slam dunk winner”? ▪ great for “bursty” data – sometimes has data to send, but at other times not resource sharing simpler, no call setup ▪ excessive congestion possible: packet delay and loss due to buffer overflow protocols needed for reliable data transfer, congestion control ▪ Q: How to provide circuit-like behavior with packet-switching? “It’s complicated.” We’ll study various techniques that try to make packet switching as “circuit-like” as possible. Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet switching)? Introduction: 1-48 Internet structure: a “network of networks” mobile network ▪ hosts connect to Internet via access national or global ISP Internet Service Providers (ISPs) ▪ access ISPs in turn must be interconnected so that any two hosts (anywhere!) local or regional ISP can send packets to each other ▪ resulting network of networks is home network content provider very complex network datacenter network evolution driven by economics, enterprise national policies network Let’s take a stepwise approach to describe current Internet structure Internet structure: a “network of networks” Question: given millions of access ISPs, how to connect them together? access access net net access net access access net net access access net net access access net net access net access net access net access net access access net access net net Introduction: 1-50 Internet structure: a “network of networks” Question: given millions of access ISPs, how to connect them together? access access net net access net access access net net access access net net connecting each access ISP to each other directly doesn’t scale: access access net O(N2) connections. net access net access net access net access net access access net access net net Introduction: 1-51 Internet structure: a “network of networks” Option: connect each access ISP to one global transit ISP? Customer and provider ISPs have economic agreement. access access net net access net access access net net access access net net global access net ISP access net access net access net access net access net access access net access net net Introduction: 1-52 Internet structure: a “network of networks” But if one global ISP is viable business, there will be competitors …. access access net net access net access access net net access access net net ISP A access net ISP B access net access ISP C net access net access net access net access access net access net net Introduction: 1-53 Internet structure: a “network of networks” But if one global ISP is viable business, there will be competitors …. who will want to be connected Internet exchange point access access net net access net access access net net IXP access access net net ISP A access net IXP ISP B access net access ISP C net access net access net peering link access net access access net access net net Introduction: 1-54 Internet structure: a “network of networks” … and regional networks may arise to connect access nets to ISPs access access net net access net access access net net IXP access access net net ISP A access net IXP ISP B access net access ISP C net access net access net regional ISP access net access access net access net net Introduction: 1-55 Internet structure: a “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 access net net access net access access net net IXP access access net net ISP A Content provider network access net IXP ISP B access net access ISP C net access net access net regional ISP access net access access net access net net Introduction: 1-56 Internet structure: a “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 networks (e.g., Google, Facebook): private network that connects its data centers to Internet, often bypassing tier-1, regional ISPs Introduction: 1-57 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: 1-58 How do packet delay and loss occur? ▪ packets queue in router buffers, waiting for turn for transmission ▪ queue length grows when arrival rate to link (temporarily) exceeds output link capacity ▪ packet loss occurs when memory to hold queued packets fills up packet being transmitted (transmission delay) A B packets in buffers (queueing delay) free (available) buffers: arriving packets dropped (loss) if no free buffers Introduction: 1-59 Packet delay: four sources 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 for ▪ determine output link transmission ▪ typically < microsecs ▪ depends on congestion level of router Introduction: 1-60 Packet delay: four sources 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 transmission rate (bps) ▪ s: propagation speed (~2x108 m/sec) ▪ dtrans = L/R ▪ dprop = d/s dtrans and dprop very different Introduction: 1-61 Caravan analogy 100 km 100 km ten-car caravan toll booth toll booth toll booth (aka 10-bit packet) (aka link) ▪ car ~ bit; caravan ~ packet; toll ▪ time to “push” entire caravan service ~ link transmission through toll booth onto ▪ toll booth takes 12 sec to service highway = 12*10 = 120 sec car (bit transmission time) ▪ time for last car to propagate ▪ “propagate” at 100 km/hr from 1st to 2nd toll both: 100km/(100km/hr) = 1 hr ▪ Q: How long until caravan is lined up before 2nd toll booth? ▪ A: 62 minutes Introduction: 1-62 Caravan analogy 100 km 100 km ten-car caravan toll booth toll booth (aka 10-bit packet) (aka router) ▪ 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, first car arrives at second booth; three cars still at first booth Introduction: 1-63 Packet queueing delay (revisited) ▪ a: average packet arrival rate average queueing delay ▪ L: packet length (bits) ▪ R: link bandwidth (bit transmission rate) L.a arrival rate of bits “traffic : R service rate of bits intensity” traffic intensity = La/R 1 ▪ La/R ~ 0: avg. queueing delay small La/R ~ 0 ▪ La/R -> 1: avg. queueing delay large ▪ La/R > 1: more “work” arriving is more than can be serviced - average delay infinite! La/R -> 1 Introduction: 1-64 “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 (with time-to-live field value of i) router i will return packets to sender sender measures time interval between transmission and reply 3 probes 3 probes 3 probes Introduction: 1-65 Real Internet delays and 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 3 delay measurements 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 to border1-rt-fa5-1-0.gw.umass.edu 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 link 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 looks like delays 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 decrease! Why? 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: 1-66 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 publisher’s website) of queuing and loss Introduction: 1-67 Throughput ▪ throughput: rate (bits/time unit) at which bits are being sent from sender to receiver instantaneous: rate at given point in time average: rate over longer period of time link capacity pipe that can carry linkthat pipe capacity can carry Rsfluid bits/sec at rate Rfluid c bits/sec at rate serverserver, sends with bits (fluid) into pipe (Rs bits/sec) (Rc bits/sec) file of F bits to send to client Introduction: 1-68 Throughput 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 link on end-end path that constrains end-end throughput Introduction: 1-69 Throughput: network scenario ▪ per-connection end- Rs end throughput: Rs Rs min(Rc,Rs,R/10) ▪ in practice: Rc or Rs is R often bottleneck Rc Rc Rc * Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/ 10 connections (fairly) share backbone bottleneck link R bits/sec Introduction: 1-70 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: 1-71 Network security ▪ 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! ▪ We now need to think about: how bad guys can attack computer networks how we can defend networks against attacks how to design architectures that are immune to attacks Introduction: 1-72 Network security ▪ 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! ▪ We now need to think about: how bad guys can attack computer networks how we can defend networks against attacks how to design architectures that are immune to attacks Introduction: 1-73 Bad guys: packet interception 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 our end-of-chapter labs is a (free) packet-sniffer Introduction: 1-74 Bad guys: fake identity IP spoofing: injection of packet with false source address A C src:B dest:A payload B Introduction: 1-75 Bad guys: denial of service 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 target from compromised hosts Introduction: 1-76 Lines of defense: ▪ authentication: proving you are who you say you are cellular networks provides hardware identity via SIM card; no such hardware assist in traditional Internet ▪ confidentiality: via encryption ▪ integrity checks: digital signatures prevent/detect tampering ▪ access restrictions: password-protected VPNs ▪ firewalls: specialized “middleboxes” in access and core networks: ▪ off-by-default: filter incoming packets to restrict senders, receivers, applications ▪ detecting/reacting to DOS attacks … lots more on security (throughout, Chapter 8) Introduction: 1-77 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: 1-78 Protocol “layers” and reference models Networks are complex, Question: is there any with many “pieces”: hope of organizing ▪ hosts structure of network? ▪ routers ▪and/or our discussion ▪ links of various media of networks? ▪ applications ▪ protocols ▪ hardware, software Introduction: 1-79 Example: organization of air travel end-to-end transfer of person plus baggage ticket (purchase) ticket (complain) baggage (check) baggage (claim) gates (load) gates (unload) runway takeoff runway landing airplane routing airplane routing airplane routing How would you define/discuss the system of airline travel? ▪ a series of steps, involving many services Introduction: 1-80 Example: organization of air travel ticket (purchase) ticketing service ticket (complain) baggage (check) baggage service baggage (claim) gates (load) gate service gates (unload) runway takeoff runway service runway landing airplane routing routing service airplane routing airplane routing layers: each layer implements a service ▪ via its own internal-layer actions ▪ relying on services provided by layer below Introduction: 1-81 Why layering? Approach to designing/discussing complex systems: ▪ explicit structure allows identification, relationship of system’s pieces layered reference model for discussion ▪ modularization eases maintenance, updating of system change in layer's service implementation: transparent to rest of system e.g., change in gate procedure doesn’t affect rest of system Introduction: 1-82 *ISO/OSI reference model Two layers not found in Internet application 7 protocol stack! presentation 6 ▪ presentation: allow applications to interpret meaning of data, e.g., encryption, session 5 compression, machine-specific conventions transport 4 ▪ session: synchronization, checkpointing, network 3 recovery of data exchange link 2 ▪ Internet stack “missing” these layers! physical 1 these services, if needed, must be implemented in application The seven layer OSI/ISO reference model needed? Introduction: 1-83 *Internet (TCP/IP) reference model (Stack) ▪ application: supporting network applications HTTP, IMAP, SMTP, DNS ▪ transport: process-process data transfer TCP, UDP application application 5 ▪ network: routing of datagrams from source to destination transport transport 4 IP, routing protocols ▪ link: data transfer between neighboring network network 3 elements e.g.: Ethernet Wireless, 802.11 (WiFi), e.g.: Ethernet (Wired LAN), 802.3 link 2 … ▪ physical: bits “on the links” physical 1 ▪ Electrical pulses in copper cables ▪ Light Pulses in fiber optic cables ▪ Electromagnetic waves in wireless Introduction: 1-84 Services, Layering and Encapsulation M application Application exchanges messages to implement some application application service using services of transport layer Ht M transport Transport-layer protocol transfers M (e.g., reliably) from transport one process to another, using services of network layer network ▪ transport-layer protocol encapsulates network application-layer message, M, with link transport layer-layer header Ht to create a link transport-layer segment Ht used by transport layer protocol to physical implement its service physical source destination Introduction: 1-85 Services, Layering and Encapsulation M application application Ht M transport Transport-layer protocol transfers M (e.g., reliably) from transport one process to another, using services of network layer network Hn Ht M network Network-layer protocol transfers transport-layer segment [Ht | M] from one host to another, using link layer services link link ▪ network-layer protocol encapsulates transport-layer segment [Ht | M] with physical network layer-layer header Hn to create a physical network-layer datagram source Hn used by network layer protocol to destination implement its service Introduction: 1-86 Services, Layering and Encapsulation M application application Ht M transport transport network Hn Ht M network Network-layer protocol transfers transport-layer segment [Ht | M] from one host to another, using link layer services link Hl Hn Ht M link Link-layer protocol transfers datagram [Hn| [Ht |M] from host to neighboring host, using network-layer services physical physical ▪ link-layer protocol encapsulates network datagram [Hn| [Ht |M], with link-layer header source Hl to create a link-layer frame destination Introduction: 1-87 Encapsulation Matryoshka dolls (stacking dolls) message segment datagram frame Credit: https://dribbble.com/shots/7182188-Babushka-Boi Introduction: 1-88 Services, Layering and Encapsulation application message M M application transport segment Ht M Ht M transport network datagram Hn Ht M Hn Ht M network link frame Hl Hn Ht M Hl Hn Ht M link physical physical source destination Introduction: 1-89 message M source application Encapsulation: an segment datagram Hn Ht Ht M M transport network end-end view 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: 1-90 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: 1-91 Internet history 1961-1972: Early packet-switching principles ▪ 1961: Kleinrock - queueing ▪ 1972: theory shows effectiveness of ARPAnet public demo packet-switching NCP (Network Control Protocol) ▪ 1964: Baran - packet-switching first host-host protocol in military nets first e-mail program ▪ 1967: ARPAnet conceived by ARPAnet has 15 nodes Advanced Research Projects Agency ▪ 1969: first ARPAnet node operational Internet history 1972-1980: Internetworking, new and proprietary networks ▪ 1970: ALOHAnet satellite Cerf and Kahn’s internetworking network in Hawaii principles: ▪ 1974: Cerf and Kahn - ▪ minimalism, autonomy - no architecture for interconnecting internal changes required to networks interconnect networks ▪ best-effort service model ▪ 1976: Ethernet at Xerox PARC ▪ stateless routing ▪ late70’s: proprietary ▪ decentralized control architectures: DECnet, SNA, XNA define today’s Internet architecture ▪ 1979: ARPAnet has 200 nodes Introduction: 1-93 Internet history 1980-1990: new protocols, a proliferation of networks ▪ 1983: deployment of TCP/IP ▪ new national networks: CSnet, ▪ 1982: smtp e-mail protocol BITnet, NSFnet, Minitel defined ▪ 100,000 hosts connected to ▪ 1983: DNS defined for name- confederation of networks to-IP-address translation ▪ 1985: ftp protocol defined ▪ 1988: TCP congestion control Introduction: 1-94 Internet history 1990, 2000s: commercialization, the Web, new applications ▪ early 1990s: ARPAnet late 1990s – 2000s: decommissioned ▪ more killer apps: instant ▪ 1991: NSF lifts restrictions on messaging, P2P file sharing commercial use of NSFnet ▪ network security to forefront (decommissioned, 1995) ▪ est. 50 million host, 100 million+ ▪ early 1990s: Web users hypertext [Bush 1945, Nelson 1960’s] HTML, HTTP: Berners-Lee ▪ backbone links running at Gbps 1994: Mosaic, later Netscape late 1990s: commercialization of the Web Introduction: 1-95 Internet history 2005-present: scale, SDN, mobility, cloud ▪ aggressive deployment of broadband home access (10-100’s Mbps) ▪ 2008: software-defined networking (SDN) ▪ increasing ubiquity of high-speed wireless access: 4G/5G, WiFi ▪ service providers (Google, FB, Microsoft) create their own networks bypass commercial Internet to connect “close” to end user, providing “instantaneous” access to social media, search, video content, … ▪ enterprises run their services in “cloud” (e.g., Amazon Web Services, Microsoft Azure) ▪ rise of smartphones: more mobile than fixed devices on Internet (2017) ▪ ~15B devices attached to Internet (2023, statista.com) Introduction: 1-96 Chapter 1: summary We’ve covered a “ton” of material! ▪ Internet overview ▪ what’s a protocol? You now have: ▪ network edge, access network, core ▪ context, overview, packet-switching versus circuit- switching vocabulary, “feel” Internet structure of networking ▪ performance: loss, delay, throughput ▪ more depth, ▪ layering, service models detail, and fun to ▪ security follow! ▪ history Introduction: 1-97 Services, Layering and Encapsulation M application M application message Ht M transport Ht M transport segment network Hn Ht M Hn Ht M network datagram link Hl Hn Ht M Hl Hn Ht M link frame physical physical source destination Introduction: 1-98 Wireshark application (www browser, packet email client) analyzer application OS packet Transport (TCP/UDP) Network (IP) capture copy of all Ethernet frames Link (Ethernet) (pcap) sent/received Physical Introduction: 1-99

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