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Chapter 1 Introductio n 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...

Chapter 1 Introductio n 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 Jim Kurose, Keith Ross All material copyright 1996-2020 J.F Kurose and K.W. Ross, All Rights Reserved Pearson, 2020 Introduction: 1-1 Chapter 1: introduction Chapter goal: Overview/roadmap:  Get “feel,” “big picture,”  What is the Internet? introduction to terminology  What is a protocol? more depth, detail later in  Network edge: hosts, access network, course physical media  Approach:  Network core: packet/circuit switching, use Internet as example internet structure  Performance: loss, delay, throughput  Security  Protocol layers, service models  History Introduction: 1-2 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: 1-3  “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 AR devices sensorized, bed Internet phones mattress Others? Fitbit Introduction: 1-4 The Internet: a “nuts and bolts” view mobile network 4G  Internet: “network of networks” national or global ISP Interconnected ISPs Streaming  protocols are everywhere Skype IP video control sending, receiving of messages local or e.g., HTTP (Web), streaming video, regional ISP Skype, TCP, IP, WiFi, 4G, Ethernet home network content provider  Internet standards HTTP network datacenter network Ethernet RFC: Request for Comments IETF: Internet Engineering Task TCP Force enterprise network WiFi Introduction: 1-5 The Internet: a “service” 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: 1-6 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 … specific messages sent Protocols define the format, order of … specific actions taken when message received, messages sent and received among or other events network entities, and actions taken on msg transmission, receipt Introduction: 1-7 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: 1-8 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 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 Access networks, physical media: regional ISP  wired, wireless communication links home network content provider network datacenter 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 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: 1-12 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) local or  mobile access networks (WiFi, 4G/5G) regional ISP What to look for: home network content provider network  transmission rate (bits per second) of access network? datacenter 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 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  breaks into smaller chunks, known two packets, as packets, of length L bits L bits each  transmits packet into access network at transmission rate R 2 1 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”  wide-area (e.g., cellular) (sender to receiver) 4G cellular: ~ 10’s Mbps  propagation environment  satellite effects: up to 45 Mbps per channel reflection 270 msec end-end delay obstruction by objects geosynchronous versus low- interference earth-orbit Introduction: 1-23 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 mobile network national or global ISP routers  packet-switching: hosts break application-layer messages into packets local or regional ISP forward packets from one router home network content to the next, across links on path provider network datacenter from source to destination network each packet transmitted at full link capacity enterprise network Introduction: 1-25  Packet-switching: store-and- forward L bits per packet 3 2 1 source destination R bps R bps  Transmission delay: takes L/R seconds to transmit (push out) L-bit packet into link at R One-hop numerical example: 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  End-end delay: 2L/R (above), assuming zero = 0.1 msec propagation delay (more on delay shortly) Introduction: 1-26 Packet-switching: queueing delay, loss R = 100 Mb/s A C D B R = 1.5 Mb/s E queue of packets waiting for output link Packet queuing and loss: if arrival rate (in bps) to link exceeds transmission rate (bps) of link for a 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: 1-27  Two key network-core functions routing algorithm Routing:  global action: Forwarding: local forwarding table  local action: move header value output link determine source- 0100 3 destination paths arriving packets 0101 2 from router’s 0111 1001 2 1 taken by packets input link to  routing algorithms appropriate router 1 output link 3 2 11 01 destination address in arriving packet’s header Introduction: 1-28 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 Introduction: 1-29 Internet structure: a “network of networks”  Hosts connect to Internet via access Internet Service Providers (ISPs) residential, enterprise (company, university, commercial) 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 Introduction: 1-30 Internet structure: a “network of networks” Question: given millions of access ISPs, how to connect them together? access … access net access net … net access access net net access access net net … … access access net net access net access net access net access … net access net access net … access net Introduction: 1-31 Internet structure: a “network of networks” Question: given millions of access ISPs, how to connect them together? access … access net access net … net access access net … … net access access net net connecting each access ISP to … … each other directly doesn’t scale: … O(N2) connections. access access … net net access net access net access net access … access … … net access net access net net Introduction: 1-32 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 access net … net access access net net access access net net … … global access net ISP access net access net access net access net access … net access net access net … access net Introduction: 1-33 Internet structure: a “network of networks” But if one global ISP is viable business, there will be competitors …. access … access net access net … net access access net net access access net net ISP A … … access net ISP B access net access net ISP C access net access net access … net access net access net … access net Introduction: 1-34 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 access net … net access access net net IXP access access net net ISP A … … access net IXP ISP B access net access net ISP C access net access net peering link access … net access net access net … access net Introduction: 1-35 Internet structure: a “network of networks” … and regional networks may arise to connect access nets to ISPs access … access net access net … net access access net net IXP access access net net ISP A … … access net IXP ISP B access net access net ISP C access net access net regional ISP access … net access net access net … access net Introduction: 1-36 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 access net net access access net net IXP access access net net ISP A … … Content provider network access net IXP ISP B access net access net ISP C access net access net regional ISP access … net access net access net … access net Introduction: 1-37  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: 1-38  Tier-1 ISP Network map: Sprint (2019) POP: point-of-presence to/from other Sprint PoPS links to peering https://www.s networks ubmarinecable … … map.com … … … links to/from Sprint customer networks Introduction: 1-39 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: 1-40 How do packet loss and delay occur? packets queue in router buffers  packets queue, wait for turn  arrival rate to link (temporarily) exceeds output link capacity: packet loss packet being transmitted (transmission delay) A B packets in buffers (queueing delay) free (available) buffers: arriving packets dropped (loss) if no free buffers Introduction: 1-41 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 transmission  determine output link  depends on congestion level of router  typically < msec Introduction: 1-42 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 * Check out the online interactive exercises: http://gaia.cs.umass.edu/kurose_ross very different Introduction: 1-43 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: 1-44  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 pipecapacity that can carry linkthat pipe capacity can carry serverserver, sends with bits Rsfluid at rate bits/sec Rfluid c at rate bits/sec (fluid) fileinto of Fpipe bits (Rs bits/sec) (Rc bits/sec) to send to client Introduction: 1-45 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: 1-46 Throughput: network scenario  per-connection end-end Rs 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: 1-47 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 Introduction: 1-48 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: 1-49 Bad guys: malware  malware can get in host from: virus: self-replicating infection by receiving/executing object (e.g., e-mail attachment) worm: self-replicating infection by passively receiving object that gets itself executed  spyware malware can record keystrokes, web sites visited, upload info to collection site  infected host can be enrolled in botnet, used for spam or distributed denial of service (DDoS) attacks Introduction: 1-50 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) target 3. send packets to target from compromised hosts Introduction: 1-51 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: 1-52 Bad guys: fake identity IP spoofing: send packet with false source address A C src:B dest:A payload B … lots more on security (throughout, Chapter 8) Introduction: 1-53 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 Introduction: 1-54 Protocol “layers” and reference models Networks are complex, with many “pieces”: Question:  hosts is there any hope of  routers organizing structure of  links of various media network?  applications  protocols  hardware, software …. or at least our discussion of networks? Introduction: 1-55 Example: 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 airline travel: a series of steps, involving many services Introduction: 1-56 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 Q: describe in words  via its own internal-layer actions the service provided  relying on services provided by layer below in each layer above Introduction: 1-57 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 in layer's service implementation: transparent to rest of system e.g., change in gate procedure doesn’t affect rest of system  layering considered harmful?  layering in other complex systems? Introduction: 1-58 Internet protocol stack  application: supporting network applications IMAP, SMTP, HTTP application  transport: process-process data transfer TCP, UDP transport  network: routing of datagrams from source to destination network IP, routing protocols link  link: data transfer between neighboring network elements physical Ethernet, 802.11 (WiFi), PPP  physical: bits “on the wire” Introduction: 1-59  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: 1-60 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! Introduction: 1-61