Lecture 1.pptx

Computer Networks Basics Lecturer Dr. Ayman E. Taha TAs: Eng. Verina Saber Eng. Mohamed Nour  Assessment Assessment method Weight (%) Quizzes / Assignment, Lab Assessment Before MT 20 % Mid-Term Examination 15...

Computer Networks Basics Lecturer Dr. Ayman E. Taha TAs: Eng. Verina Saber Eng. Mohamed Nour  Assessment Assessment method Weight (%) Quizzes / Assignment, Lab Assessment Before MT 20 % Mid-Term Examination 15 % Project 20 % Quizzes / Assignment, Lab Assessment Before MT 20 % Final Exam 25 % Course Resources Text Books: ○ Jim Kurose, Keith Ross, “ Computer Networking: A Top Down Approach”, 8th edition, Addison-Wesley, 2020 IDE: ○ Python ○ Wireshark Online Resources  Course Contents Introduction to Computer Networks Application Layer The Transport Layer The Network Layer Network Basics Chapter 1: Introduction © Spring 2024 - Dr. Ayman Taha Chapter 1: introduction Chapter goal: Overview/roadmap: What is the Internet? Get “feel,” “big picture,” What is a protocol? introduction to terminology Network edge: hosts, access network, ○ more depth, detail later in physical media course Network core: packet/circuit switching, Approach: internet structure ○use Internet as Performance: loss, delay, throughput example Security Protocol layers, service models History Introduction: 1-6 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 packets (chunks of data) local or Internet regional  routers, switches ISP home network content Communication links provider  fiber, copper, radio, satellite network datacenter network  transmission rate: bandwidth Networks enterprise  collection of devices, routers, network links: managed by an organization Introduction: 1-7  “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 The Internet: a “nuts and bolts” view mobile network 4G national or global ISP Internet: “network of networks” ○ Interconnected ISPs  protocols are everywhere Skype IP Streaming video control sending, receiving of messages local or regional e.g., HTTP (Web), streaming video, ISP Skype, TCP, IP, WiFi, 4G, Ethernet home network content provider  Internet standards HTTP network datacenter network RFC: Request for Comments Ethernet IETF: Internet Engineering Task TCP Force enterprise network WiFi Introduction: 1-9 The Internet: a “service” view mobile network Infrastructure that provides national or global ISP services to applications: ○ Web, streaming video, multimedia teleconferencing, Streaming Skype video email, games, e-commerce, social media, inter-connected local or regional  provides programming appliances, … interface ISP 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, enterprise network analogous to postal service Introduction: 1-10 What’s a protocol? Human protocols: Network protocols:  “what’s the time?”  computers (devices) rather than  “I have a question” humans  introductions  all communication activity in Internet governed by protocols … specific messages sent Protocols define the format, order … specific actions taken of messages sent and received when message among network entities, and received, or other events actions taken on msg transmission, receipt Introduction: 1-11 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: 1-12 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: 1-13 A closer look at Internet structure mobile network national or global ISP Network edge: hosts: clients and servers servers often in data centers local or regional ISP home network content provider network datacenter network enterprise network Introduction: 1-14 A closer look at Internet structure mobile network national or global ISP Network edge: hosts: clients and servers servers often in data centers local or regional Access networks, physical ISP home network content media: provider network datacenter wired, wireless communication network links enterprise network Introduction: 1-15 A closer look at Internet structure mobile network national or global ISP Network edge: hosts: clients and servers servers often in data centers local or Access networks, physical regional ISP media: home network content provider wired, wireless communication links network datacenter network Network core:  interconnected routers enterprise  network of networks network Introduction: 1-16 Access networks and physical media mobile network Q: How to connect end systems to national or global ISP edge router? 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  transmission rate (bits per second) of access network datacenter network network?  shared or dedicated access among users? enterprise network Introduction: 1-17 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: 1-18 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: 1-19 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: 1-20 Access networks: home networks wireless devices to/from headend or central office often combined in single box cable or DSL modem WiFi wireless router, firewall, NAT access point (54, 450 wired Ethernet (1 Mbps) Gbps) Introduction: 1-21 Wireless access networks Shared wireless access network connects end system to router  via base station aka “access point” Wireless local area Wide-area cellular access networks (WLANs) networks  typically within or around  provided by mobile, cellular building (~100 ft) network operator (10’s km)  802.11b/g/n (WiFi): 11, 54,  10’s Mbps 450 Mbps transmission rate  4G cellular networks (5G coming) to Internet to Internet Introduction: 1-22 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: 1-23 Host: sends packets of data host sending function:  takes application message  breaks into smaller chunks, two packets, L bits each known as packets, of length L bits 2 1  transmits packet into access network at transmission rate R host link transmission rate, aka R: link transmission rate link capacity, aka link bandwidth packet time needed to L (bits) transmission = transmit L-bit = delay packet into link R (bits/sec) Introduction: 1-24 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 between transmitter & Ethernet receiver Category 6: 10Gbps Ethernet  guided media: signals propagate in solid media: copper, fiber, coax  unguided media: signals propagate freely, e.g., radio Introduction: 1-25 Links: physical media Coaxial cable: Fiber optic cable:  two concentric copper  glass fiber carrying light pulses, conductors each pulse a bit  high-speed operation:  bidirectional high-speed point-to-point  broadband: transmission (10’s-100’s Gbps) multiple frequency channels on  low error rate: cable repeaters spaced far apart 100’s Mbps per channel immune to electromagnetic noise Introduction: 1-26 Links: physical media Wireless radio Radio link types:  signal carried in  terrestrial microwave up to 45 Mbps channels electromagnetic spectrum  Wireless LAN (WiFi)  no physical “wire” 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 reflection channel obstruction by objects 270 msec end-end delay interference geosynchronous versus low-earth-orbit Introduction: 1-27  Mobile Data Speed Comparison Typical Real World Network Speeds Theoretical Maximum Network Speeds Download Upload Speed Download Network Type Network Type Upload Speed Speed (Mbps) (Mbps) Speed 3G 3 0.4 3G 7.2Mbps 2Mbps 3G HSPA+ 6 3 3G HSPA+ 42Mbps 22Mbps 4G LTE 20 5 4G LTE 150Mbps 50Mbps 4G LTE- 4G LTE- 42 10 300Mbps 150Mbps Advanced Advanced 10Gbps+ 1Gbps 5G 200 12-20 5G Introduction: 1-28 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: 1-29 The network core mobile network mesh of interconnected national or global ISP routers packet-switching: hosts break application-layer messages into packets local or regional ○ forward packets from one ISP router to the next, across home network content links on path from source to provider network datacenter destination network ○ each packet transmitted at full link capacity enterprise network Introduction: 1-30  Packet-switching: store-and-forward L bits per packet 321 source destination R bps R bps Transmission delay: takes L/R seconds to transmit (push out) L-bit packet into link at R bps One-hop numerical example: Store and forward: entire packet must  L = 10 Kbits arrive at router before it can be  R = 100 Mbps transmitted on next link  one-hop transmission End-end delay: 2L/R (above), assuming delay = 0.1 msec zero propagation delay (more on delay Introduction: 1-31 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 routerIntroduction: 1-32  Two key network-core functions routing Routing: algorithm localforwarding local forwarding table table  global action: Forwarding: local action: header value output link determine source- move arriving 0100 0101 3 2 destination paths taken by packets 0111 2 packets from 1001 1 router’s input link to  routing algorithms appropriate 1 router output link 3 2 11 01 destination address in arriving packet’s header Introduction: 1-33 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: 1-34  Circuit switching: FDM and TDM Frequency Division 4 users Multiplexing(FDM) frequency optical, electromagnetic frequencies divided into (narrow) frequency bands each call allocated its own band, can transmit at max rate of that narrow band time Time Division Multiplexing (TDM) frequency  time divided into slots  each call allocated periodic slot(s), can transmit at maximum rate of (wider) frequency band, but only during its time slot(s) time Introduction: 1-35 Packet switching versus circuit switching packet switching allows more users to use network! Example:  1 Gb/s link  each user: N ….. 100 Mb/s when “active” users 1 Gbps link active 10% of time  circuit-switching: 10 users Q: how did we get value 0.0004?  packet switching: with 35 users, probability > 10 active at Q: what happens if > 35 users ? same time is less than.0004 * * Check out the online interactive exercises for more examples: h ttp://gaia.cs.umass.edu/kurose_ross/interactive Introduction: 1-36 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? bandwidth guarantees traditionally used for audio/video applications Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet switching)? Introduction: 1-37 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: 1-38 Internet structure: a “network of networks” Question: given millions of access ISPs, how to connect them together? … access net access 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: 1-39 Internet structure: a “network of networks” Question: given millions of access ISPs, how to connect them together? … access net access net … access 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 … … … net access access net access net net Introduction: 1-40 Internet structure: a “network of networks” Option: connect each access ISP to one global transit ISP? Customer and provider ISPs have economic agreement. … access net access 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: 1-41 Internet structure: a “network of networks” But if one global ISP is viable business, there will be competitors …. … access net access net … access net access access net net access access ISP A net net … … access net ISP B access net access net ISP C access net access net access … … net access access net access net net Introduction: 1-42 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 ISP A net net … … access net IXP ISP B access net access net ISP C access net access net peering link access … … net access access net access net net Introduction: 1-43 Internet structure: a “network of networks” … and regional networks may arise to connect access nets to ISPs … … access net access net access net access access net net IXP access access ISP A net net … … access net IXP ISP B access net access net ISP C access net access net regional ISP access … … net access access net access net net Introduction: 1-44 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 net access net access net access access net net IXP access access ISP A net net … … Content provider network access net IXP ISP B access net access net ISP C access net access net regional ISP access … … net access access net access net net Introduction: 1-45  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: 1-46 Tier-1 ISP Network map: Sprint (2019) POP: point-of-presence to/from other Sprint PoPS links to peering networks … … … … … links to/from Sprint customer networks 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 History Introduction: 1-48 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 dela A B packets in buffers (queueing delay) free (available) buffers: arriving packets dropped (loss) if no free buffers Introduction: 1-49 Packet delay: four sources transmission A propagation B nodal processing queueing dnodal = dproc + dqueue + dtrans + dprop dproc: nodal dqueue: queueing delay processing  time waiting at output link for  check bit errors transmission  determine output link  depends on congestion level of router  typically < msec Introduction: 1-50 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  s: propagation speed (~2x108 (bps) m/sec)  dtrans = L/R dtrans and dprop  dprop = d/s * Check out the online interactive exercises: very different http://gaia.cs.umass.edu/kurose_ross Introduction: 1-51  Caravan analogy 100 km 100 km ten-car caravan toll booth toll booth (aka 10-bit (aka router) packet)  cars “propagate” at 100 km/hr  time to “push” entire caravan  toll booth takes 12 sec to service through toll booth onto car (bit transmission time) highway = 12*10 = 120 sec  car ~ bit; caravan ~ packet  time for last car to propagate from 1st to 2nd toll both:  Q: How long until caravan is lined 100km/(100km/hr) = 1 hr up before 2nd toll booth?  A: 62 minutes Introduction: 1-52 Caravan analogy 100 km 100 km ten-car caravan toll booth toll booth (aka 10-bit (aka router) packet)  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: 1-53 Packet queueing delay (revisited) average queueing  R: link bandwidth (bps) delay  L: packet length (bits)  a: average packet arrival rate  La/R ~ 0: avg. queueing delay traffic intensity = La/R 1 small  La/R -> 1: avg. queueing delay La/R ~ 0 large  La/R > 1: more “work” arriving is more than can be serviced - average delay infinite! La/R -> 1 Introduction: 1-54 “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: 1-55 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 11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms looks like delays 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: 1-56 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: 1-57  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 linkpipe capacity that can linkthat pipe capacity can carry carry fluid at rate server server, with Rsfluid sends bits/sec at rate R c bits/sec filebits of F bits (Rc bits/sec) (fluid) to sendinto pipe to client (Rs bits/sec) Introduction: 1-58 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: 1-59 Throughput: network scenario  per-connection end- Rs end throughput: Rs Rs min(Rc,Rs,R/10)  in practice: Rc or Rs R is 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: 1-60 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: 1-61 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: 1-62 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: 1-63 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: 1-64 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: 1-65 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: 1-66 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: 1-67 Protocol “layers” Networks are complex, with many “pieces”:  hosts  routers Question: is there any hope of organizing  links of various structure of network? media  applications …. or at least our discussion of networks?  protocols  hardware, software 1-68 Introduction 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 1-69 Introduction 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 1-70 Introduction Why layering? dealing with complex systems: explicit structure allows identification, relationship of complex system’s pieces ○ layered reference model for discussion modularization eases maintenance, updating of system ○ change of implementation of layer’s service transparent to rest of system ○ e.g., change in gate procedure doesn’t affect rest of system layering considered harmful? 1-71 Introduction  Internet protocol stack application: supporting network applications ○ FTP, SMTP, HTTP application transport: process-process data transfer transport ○ TCP, UDP network: routing of datagrams from source to destination network ○ IP, routing protocols link: data transfer between neighboring network elements link ○ Ethernet, 802.111 (WiFi), PPP physical: bits “on the wire” physical 1-72 Introduction  ISO/OSI reference model presentation: allow applications to interpret meaning of data, e.g., encryption, application compression, machine-specific conventions presentation session session: synchronization, checkpointing, transport recovery of data exchange network Internet stack “missing” these layers! link ○ these services, if needed, must be implemented in physical application ○ needed? 1-73 Introduction Reference Models The OSI reference model. Reference Models (2) The TCP/IP reference model. Hybrid Model The hybrid reference model to be used in this course.  source Encapsulation message M application 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 1-77 Introduction 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 Internet history 1961-1972: Early packet-switching principles  1961: Kleinrock - queueing  1972: theory shows effectiveness of ARPAnet public demo packet-switching NCP (Network Control  1964: Baran - packet- Protocol) first host-host switching in military nets protocol  1967: ARPAnet conceived by first e-mail program Advanced Research Projects ARPAnet has 15 nodes Agency  1969: first ARPAnet node operational Introduction: 1-79 Internet history 1972-1980: Internetworking, new and proprietary nets  1970: ALOHAnet satellite network in Hawaii Cerf and Kahn’s internetworking  1974: Cerf and Kahn - principles: architecture for interconnecting  minimalism, autonomy - no networks internal changes required to  1976: Ethernet at Xerox PARC interconnect networks  best-effort service model  late70’s: proprietary architectures: DECnet, SNA, XNA  stateless routing  late 70’s: switching fixed length  decentralized control packets (ATM precursor) define today’s Internet  1979: ARPAnet has 200 nodes architecture Introduction: 1-80 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 confederation of networks name-to-IP-address translation  1985: ftp protocol defined  1988: TCP congestion control Introduction: 1-81 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  early 1990s: Web million+ users hypertext [Bush 1945, Nelson 1960’s] HTML, HTTP: Berners-Lee  backbone links running at 1994: Mosaic, later Netscape Gbps late 1990s: commercialization of the Web Introduction: 1-82 Internet history 2005-present: more new applications, Internet is “everywhere”  ~18B devices attached to Internet (2017) rise of smartphones (iPhone: 2007)  aggressive deployment of broadband access  increasing ubiquity of high-speed wireless access: 4G/5G, WiFi  emergence of online social networks: Facebook: ~ 2.5 billion users  service providers (Google, FB, Microsoft) create their own networks bypass commercial Internet to connect “close” to end user, providing “instantaneous” access to search, video content, …  enterprises run their services in “cloud” (e.g., Amazon Web Services, Microsoft Azure) Introduction: 1-83  Internet Future 1-84 Introduction Chapter 1: summary We’ve covered a “ton” of material!  Internet overview  what’s a protocol? You now have:  network edge, access network,  context, core overview, packet-switching versus circuit- vocabulary, switching “feel” of Internet structure networking  performance: loss, delay,  more depth, throughput detail, and fun to  layering, service models follow!  security  history Introduction: 1-85