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This document is an introduction to the concepts of computer networking, particularly focusing on the structure and functionality of the internet. It outlines key topics such as protocols, network edges and cores, performance metrics, and types of access networks. It also emphasizes the importance of understanding how interconnected networks operate and the different protocols governing data transmission.

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Introduction: 1-1 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. For a revision history, see the slide note for this page. Thanks and enjoy! JFK/KWR All material copyright 1996-2023 J.F Kurose and K.W. Ross, All Rights Reserved Computer Networking: A Top-Down Approach 8th edition Jim Kurose, Keith Ross Pearson, 2020
Chapter 1: introduction Chapter goal:  Get “feel,” “big picture,” introduction to terminology • more depth, detail later in course Overview/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  Protocol layers, service models  Security  History Introduction: 1-2
Internet The Internet: a “nuts and bolts” view mobile network home network enterprise network national or global ISP local or regional ISP datacenter network content provider network Packet switches: forward packets (chunks of data)  routers, switches Communication links  fiber, copper, radio, satellite  transmission rate: bandwidth Billions of connected computing devices:  hosts = end systems  running network apps at Internet’s “edge” Networks  collection of devices, routers, links: managed by an organization Introduction: 1-3
“Fun” Internet-connected devices Web-enabled toaster + weather forecaster Internet phones Slingbox: remote control cable TV Security Camera IP picture frame Internet refrigerator Tweet-a-watt: monitor energy use sensorized, bed mattress Amazon Echo Others? Gaming devices cars scooters bikes Introduction: 1-4 Pacemaker & Monitor AR devices Fitbit diapers
 Internet: “network of networks” • Interconnected ISPs The Internet: a “nuts and bolts” view mobile network home network enterprise network national or global ISP local or regional ISP datacenter network content provider network  protocols are everywhere • control sending, receiving of messages • e.g., HTTP (Web), streaming video, Skype, TCP, IP, WiFi, 4/5G, Ethernet Ethernet HTTP Skype IP WiFi 4G TCP Streaming video  Internet standards • RFC: Request for Comments • IETF: Internet Engineering Task Force Introduction: 1-5
 Infrastructure that provides services to applications: • Web, streaming video, multimedia teleconferencing, email, games, e- commerce, social media, inter- connected appliances, … The Internet: a “services” view mobile network home network enterprise network national or global ISP local or regional ISP datacenter network content provider network HTTP Skype Streaming video  provides programming interface to distributed applications: • “hooks” allowing sending/receiving apps to “connect” to, use Internet transport service • provides service options, analogous to postal service Introduction: 1-6
What’s a protocol? Human protocols:  “what’s the time?”  “I have a question”  introductions Network protocols:  computers (devices) rather than humans  all communication activity in Internet governed by protocols Protocols define the format, order of messages sent and received among network entities, and actions taken on message transmission, receipt Rules for: … specific messages sent … specific actions taken when message received, or other events Introduction: 1-7
What’s a protocol? A human protocol and a computer network protocol: Q: other human protocols? Hi Hi Got the time? 2:00 time TCP connection response <file> TCP connection request GET http://gaia.cs.umass.edu/kurose_ross Introduction: 1-8
Chapter 1: roadmap Introduction: 1-9  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
A closer look at Internet structure mobile network home network enterprise network national or global ISP local or regional ISP datacenter network content provider network Network edge:  hosts: clients and servers  servers often in data centers Introduction: 1-10
A closer look at Internet structure mobile network home network enterprise network national or global ISP local or regional ISP datacenter network content provider network Network edge:  hosts: clients and servers  servers often in data centers Access networks, physical media: wired, wireless communication links Introduction: 1-11
A closer look at Internet structure Network edge:  hosts: clients and servers  servers often in data centers Access networks, physical media: wired, wireless communication links Network core:  interconnected routers  network of networks mobile network home network enterprise network national or global ISP local or regional ISP datacenter network content provider network Introduction: 1-12
Access networks and physical media mobile network home network enterprise network national or global ISP local or regional ISP datacenter network content provider network Q: How to connect end systems to edge router?  residential access nets  institutional access networks (school, company)  mobile access networks (WiFi, 4G/5G) Introduction: 1-13
Access networks: cable-based access cable modem splitter … cable headend Channels V I D E O V I D E O V I D E O V I D E O V I D E O V I D E O D A T A D A T A C O N T R O L 1 2 3 4 5 6 7 8 9 frequency division multiplexing (FDM): different channels transmitted in different frequency bands Introduction: 1-14
Access networks: cable-based access cable modem splitter … cable headend data, TV transmitted at different frequencies over shared cable 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 cable modem termination system CMTS ISP Introduction: 1-15
ISP Access networks: digital subscriber line (DSL) central office telephone network DSLAM voice, data transmitted at different frequencies over dedicated line to central office  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 DSL modem splitter DSL access multiplexer Introduction: 1-16
Access networks: home networks to/from headend or central office cable or DSL modem router, firewall, NAT wired Ethernet (1 Gbps) WiFi wireless access point (54, 450 Mbps) Wireless and wired devices often combined in single box 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 (WLANs)  typically within or around building (~100 ft)  802.11b/g/n (WiFi): 11, 54, 450 Mbps transmission rate to Internet to Internet Wide-area cellular access networks  provided by mobile, cellular network operator (10’s km)  10’s Mbps  4G/5G cellular networks Introduction: 1-18
Access networks: enterprise networks  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 Ethernet switch institutional mail, web servers institutional router Enterprise link to ISP (Internet) Introduction: 1-19
Access networks: data center networks  high-bandwidth links (10s to 100s Gbps) connect hundreds to thousands of servers together, and to Internet mobile network home network enterprise network national or global ISP local or regional ISP datacenter network content provider network Courtesy: Massachusetts Green High Performance Computing Center (mghpcc.org) Introduction: 1-20
Host: sends packets of data host sending function:  takes application message  breaks into smaller chunks, known as packets, of length L bits  transmits packet into access network at transmission rate R • link transmission rate, aka link capacity, aka link bandwidth R: link transmission rate host 1 2 two packets, L bits each packet transmission delay time needed to transmit L-bit packet into link L (bits) R (bits/sec) = = Introduction: 1-21
Links: physical media  bit: propagates between transmitter/receiver pairs  physical link: what lies between transmitter & receiver  guided media: • signals propagate in solid media: copper, fiber, coax  unguided media: • signals propagate freely, e.g., radio Twisted pair (TP)  two insulated copper wires • Category 5: 100 Mbps, 1 Gbps Ethernet • Category 6: 10Gbps Ethernet Introduction: 1-22
Links: physical media Coaxial cable:  two concentric copper conductors  bidirectional  broadband: • multiple frequency channels on cable • 100’s Mbps per channel Fiber optic cable:  glass fiber carrying light pulses, each pulse a bit  high-speed operation: • high-speed point-to-point transmission (10’s-100’s Gbps)  low error rate: • repeaters spaced far apart • immune to electromagnetic noise Introduction: 1-23
Links: physical media Wireless radio  signal carried in various “bands” in electromagnetic spectrum  no physical “wire”  broadcast, “half-duplex” (sender to receiver)  propagation environment effects: • reflection • obstruction by objects • Interference/noise Radio link types:  Wireless LAN (WiFi) • 10-100’s Mbps; 10’s of meters  wide-area (e.g., 4G/5G cellular) • 10’s Mbps (4G) over ~10 Km  Bluetooth: cable replacement • short distances, limited rates  terrestrial microwave • point-to-point; 45 Mbps channels  satellite • up to < 100 Mbps (Starlink) downlink • 270 msec end-end delay (geostationary) Introduction: 1-24
Chapter 1: roadmap Introduction: 1-25  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
The network core  mesh of interconnected routers  packet-switching: hosts break application-layer messages into packets • network forwards packets from one router to the next, across links on path from source to destination mobile network home network enterprise network national or global ISP local or regional ISP datacenter network content provider network Introduction: 1-26
Two key network-core functions 1 2 3 0111 destination address in arriving packet’s header routing algorithm header value output link 0100 0101 0111 1001 3 2 2 1 local forwarding table Forwarding:  aka “switching”  local action: move arriving packets from router’s input link to appropriate router output link local forwarding table Routing:  global action: determine source- destination paths taken by packets  routing algorithms routing algorithm Introduction: 1-27
routing Introduction: 1-28
forwarding forwarding Introduction: 1-29
Packet-switching: store-and-forward  packet transmission delay: takes L/R seconds to transmit (push out) L-bit packet into link at R bps  store and forward: entire packet must arrive at router before it can be transmitted on next link source R bps destination 1 2 3 L bits per packet R bps One-hop numerical example:  L = 10 Kbits  R = 100 Mbps  one-hop transmission delay = 0.1 msec Introduction: 1-30
Packet-switching: queueing A B C R = 100 Mb/s R = 1.5 Mb/s D E queue of packets waiting for transmission over output link Queueing occurs when work arrives faster than it can be serviced: Introduction: 1-31
Packet-switching: queueing A B C R = 100 Mb/s R = 1.5 Mb/s D 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: 1-32
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) * Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/interactive  commonly used in traditional telephone networks Introduction: 1-33
Circuit switching: FDM and TDM frequency time frequency time 4 users Frequency Division Multiplexing (FDM)  optical, electromagnetic frequencies divided into (narrow) frequency bands Time Division Multiplexing (TDM)  time divided into slots  each call allocated its own band, can transmit at max rate of that narrow band  each call allocated periodic slot(s), can transmit at maximum rate of (wider) frequency band (only) during its time slot(s) Introduction: 1-34
Packet switching versus circuit switching example:  1 Gb/s link  each user: • 100 Mb/s when “active” • active 10% of time Q: how many users can use this network under circuit-switching and packet switching? * Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/interactive N users 1 Gbps link … ..  circuit-switching: 10 users Q: how did we get value 0.0004? A: HW problem (for those with course in probability only)  packet switching: with 35 users, probability > 10 active at same time is less than .0004 * Introduction: 1-35
Packet switching versus circuit switching  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. Is packet switching a “slam dunk winner”? Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet switching)? Introduction: 1-36
Internet structure: a “network of networks”  hosts connect to Internet via access Internet Service Providers (ISPs)  access ISPs in turn must be interconnected • so that any two hosts (anywhere!) can send packets to each other  resulting network of networks is very complex • evolution driven by economics, national policies Let’s take a stepwise approach to describe current Internet structure mobile network home network enterprise network national or global ISP local or regional ISP datacenter network content provider network
Internet structure: a “network of networks” Question: given millions of access ISPs, how to connect them together? access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net … … … … … … 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 net access net access net access net access net access net access net access net access net access net access net access net access net … … … … … … connecting each access ISP to each other directly doesn’t scale: O(N2 ) connections. Introduction: 1-39
Internet structure: a “network of networks” Option: connect each access ISP to one global transit ISP? Customer and provider ISPs have economic agreement. global ISP access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net … … … … … … Introduction: 1-40
ISP A ISP C ISP B Internet structure: a “network of networks” access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net … … … … … … But if one global ISP is viable business, there will be competitors …. Introduction: 1-41
ISP A ISP C ISP B Internet structure: a “network of networks” access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net … … … … … … But if one global ISP is viable business, there will be competitors …. who will want to be connected IXP peering link Internet exchange point IXP Introduction: 1-42
ISP A ISP C ISP B Internet structure: a “network of networks” access net access net access net access net access net access net access net access net access net access net access net … … … … … … … and regional networks may arise to connect access nets to ISPs IXP IXP access net access net regional ISP access net access net access net Introduction: 1-43
ISP A ISP C ISP B Internet structure: a “network of networks” access net access net access net access net access net access net access net access net access net access net access net … … … … … … … and content provider networks (e.g., Google, Microsoft, Akamai) may run their own network, to bring services, content close to end users IXP IXP access net access net access net access net access net Content provider network regional ISP Introduction: 1-44
Internet structure: a “network of networks” access ISP access ISP access ISP access ISP access ISP access ISP access ISP access 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 Regional ISP Regional ISP Tier 1 ISP Tier 1 ISP IXP Google IXP IXP Introduction: 1-45
Chapter 1: roadmap Introduction: 1-46  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
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 A B packet being transmitted (transmission delay) packets in buffers (queueing delay) free (available) buffers: arriving packets dropped (loss) if no free buffers Introduction: 1-47
Packet delay: four sources dproc: nodal processing  check bit errors  determine output link  typically < microsecs dqueue: queueing delay  time waiting at output link for transmission  depends on congestion level of router propagation nodal processing queueing dnodal = dproc + dqueue + dtrans + dprop A B transmission Introduction: 1-48
Packet delay: four sources propagation nodal processing queueing dnodal = dproc + dqueue + dtrans + dprop A B transmission dtrans: transmission delay:  L: packet length (bits)  R: link transmission rate (bps)  dtrans = L/R dprop: propagation delay:  d: length of physical link  s: propagation speed (~2x108 m/sec)  dprop = d/s dtrans and dprop very different Introduction: 1-49
Caravan analogy  car ~ bit; caravan ~ packet; toll service ~ link transmission  toll booth takes 12 sec to service car (bit transmission time)  “propagate” at 100 km/hr  Q: How long until caravan is lined up before 2nd toll booth?  time to “push” entire caravan through toll booth onto highway = 12*10 = 120 sec  time for last car to propagate from 1st to 2nd toll both: 100km/(100km/hr) = 1 hr  A: 62 minutes toll booth toll booth (aka link) ten-car caravan (aka 10-bit packet) 100 km 100 km toll booth toll booth (aka link) toll booth Introduction: 1-50
Caravan analogy toll booth toll booth (aka router) ten-car caravan (aka 10-bit packet) 100 km 100 km  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: 1-51
Packet queueing delay (revisited)  a: average packet arrival rate  L: packet length (bits)  R: link bandwidth (bit transmission rate)  La/R ~ 0: avg. queueing delay small  La/R -> 1: avg. queueing delay large  La/R > 1: more “work” arriving is more than can be serviced - average delay infinite! La/R ~ 0 La/R -> 1 traffic intensity = La/R average queueing delay 1 service rate of bits R arrival rate of bits L a . : “traffic intensity” Introduction: 1-52
“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: 3 probes 3 probes 3 probes • 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 Introduction: 1-53
Real Internet delays and routes 1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms 2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms 3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms 4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms 5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms 6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms 7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms 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 12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms 13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms 14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms 15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms 16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms 17 * * * 18 * * * 19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms traceroute: gaia.cs.umass.edu to www.eurecom.fr * Do some traceroutes from exotic countries at www.traceroute.org * means no response (probe lost, router not replying) 3 delay measurements from gaia.cs.umass.edu to cs-gw.cs.umass.edu 3 delay measurements to border1-rt-fa5-1-0.gw.umass.edu looks like delays decrease! Why? trans-oceanic link Introduction: 1-54
Packet loss  queue (aka buffer) preceding link in buffer has finite capacity A B packet being transmitted buffer (waiting area) * Check out the Java applet for an interactive animation (on publisher’s website) of queuing and loss packet arriving to full buffer is lost  packet arriving to full queue dropped (aka lost)  lost packet may be retransmitted by previous node, by source end system, or not at all Introduction: 1-55
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 server, with file of F bits to send to client link capacity Rs bits/sec link capacity Rc bits/sec server sends bits (fluid) into pipe pipe that can carry fluid at rate (Rs bits/sec) pipe that can carry fluid at rate (Rc bits/sec) Introduction: 1-56
Throughput Rs < Rc What is average end-end throughput? Rs bits/sec Rc bits/sec Rs > Rc What is average end-end throughput? link on end-end path that constrains end-end throughput bottleneck link Rs bits/sec Rc bits/sec Introduction: 1-57
Throughput: network scenario 10 connections (fairly) share backbone bottleneck link Rbits/sec Rs Rs Rs Rc Rc Rc R  per-connection end-end throughput: min(Rc,Rs,R/10)  in practice: Rc or Rs is often bottleneck * Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/ Introduction: 1-58
Chapter 1: roadmap Introduction: 1-59  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
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: 1-60
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: 1-61
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 B C src:B dest:A payload Wireshark software used for our end-of-chapter labs is a (free) packet-sniffer Introduction: 1-62
Bad guys: fake identity IP spoofing: injection of packet with false source address A B C src:B dest:A payload Introduction: 1-63
Bad guys: denial of service target Denial of Service (DoS): attackers make resources (server, bandwidth) unavailable to legitimate traffic by overwhelming resource with bogus traffic 1. select target 2. break into hosts around the network (see botnet) 3. send packets to target from compromised hosts Introduction: 1-64
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: 1-65
Chapter 1: roadmap Introduction: 1-66  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
Protocol “layers” and reference models Networks are complex, with many “pieces”: hosts routers links of various media applications protocols hardware, software Question: is there any hope of organizing structure of network? and/or our discussion of networks? Introduction: 1-67
Example: organization of air travel  a series of steps, involving many services ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing airplane routing How would you define/discuss the system of airline travel? end-to-end transfer of person plus baggage Introduction: 1-68
Example: organization of air travel ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing airplane routing ticketing service baggage service gate service runway service routing service layers: each layer implements a service  via its own internal-layer actions  relying on services provided by layer below Introduction: 1-69
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: 1-70
Layered Internet protocol stack  application: supporting network applications • HTTP, IMAP, SMTP, DNS  transport: process-process data transfer • TCP, UDP  network: routing of datagrams from source to destination • IP, routing protocols  link: data transfer between neighboring network elements • Ethernet, 802.11 (WiFi), PPP  physical: bits “on the wire” link application network transport physical application transport network link physical Introduction: 1-71
Services, Layering and Encapsulation source  transport-layer protocol encapsulates application-layer message, M, with transport layer-layer header Ht to create a transport-layer segment • Ht used by transport layer protocol to implement its service application transport network link physical destination application transport network link physical Transport-layer protocol transfers M (e.g., reliably) from one process to another, using services of network layer Ht M Application exchanges messages to implement some application service using services of transport layer M Introduction: 1-72
Services, Layering and Encapsulation source Transport-layer protocol transfers M (e.g., reliably) from one process to another, using services of network layer Ht M  network-layer protocol encapsulates transport-layer segment [Ht | M] with network layer-layer header Hn to create a network-layer datagram • Hn used by network layer protocol to implement its service application transport network link physical destination M application transport network link physical M Ht Hn Network-layer protocol transfers transport-layer segment [Ht | M] from one host to another, using link layer services Introduction: 1-73
Services, Layering and Encapsulation source Ht M  link-layer protocol encapsulates network datagram [Hn| [Ht |M], with link-layer header Hl to create a link-layer frame application transport network link physical destination M application transport network link physical M Ht Hn Link-layer protocol transfers datagram [Hn| [Ht |M] from host to neighboring host, using network-layer services M Ht Hn Hl Network-layer protocol transfers transport-layer segment [Ht | M] from one host to another, using link layer services Introduction: 1-74
Encapsulation Introduction: 1-75 message segment datagram frame Matryoshka dolls (stacking dolls) Credit: https://dribbble.com/shots/7182188-Babushka-Boi
Services, Layering and Encapsulation source application transport network link physical destination application transport network link physical M Ht Hn Hl M Ht Hn Ht M M M message Ht M segment M Ht Hn datagram frame M Ht Hn Hl Introduction: 1-76
network link physical application transport network link physical application transport network link physical Encapsulation: an end-end view source Ht Hn M segment Ht datagram destination Ht Hn Hl M Ht Hn M Ht M M Ht Hn Hl M Ht Hn M Ht Hn M Ht Hn Hl M router switch message M Ht M Hn frame link physical Introduction: 1-77
Chapter 1: roadmap Introduction: 1-78  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
Internet history  1961: Kleinrock - queueing theory shows effectiveness of packet-switching  1964: Baran - packet-switching in military nets  1967: ARPAnet conceived by Advanced Research Projects Agency  1969: first ARPAnet node operational  1972: • ARPAnet public demo • NCP (Network Control Protocol) first host-host protocol • first e-mail program • ARPAnet has 15 nodes 1961-1972: Early packet-switching principles
Internet history  1970: ALOHAnet satellite network in Hawaii  1974: Cerf and Kahn - architecture for interconnecting networks  1976: Ethernet at Xerox PARC  late70’s: proprietary architectures: DECnet, SNA, XNA  1979: ARPAnet has 200 nodes 1972-1980: Internetworking, new and proprietary networks Cerf and Kahn’s internetworking principles:  minimalism, autonomy - no internal changes required to interconnect networks  best-effort service model  stateless routing  decentralized control define today’s Internet architecture Introduction: 1-80
Internet history  1983: deployment of TCP/IP  1982: smtp e-mail protocol defined  1983: DNS defined for name- to-IP-address translation  1985: ftp protocol defined  1988: TCP congestion control  new national networks: CSnet, BITnet, NSFnet, Minitel  100,000 hosts connected to confederation of networks 1980-1990: new protocols, a proliferation of networks Introduction: 1-81
Internet history  early 1990s: ARPAnet decommissioned  1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995)  early 1990s: Web • hypertext [Bush 1945, Nelson 1960’s] • HTML, HTTP: Berners-Lee • 1994: Mosaic, later Netscape • late 1990s: commercialization of the Web late 1990s – 2000s:  more killer apps: instant messaging, P2P file sharing  network security to forefront  est. 50 million host, 100 million+ users  backbone links running at Gbps 1990, 2000s: commercialization, the Web, new applications Introduction: 1-82
Internet history  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) 2005-present: scale, SDN, mobility, cloud Introduction: 1-83
Chapter 1: summary Introduction: 1-84 We’ve covered a “ton” of material!  Internet overview  what’s a protocol?  network edge, access network, core • packet-switching versus circuit- switching • Internet structure  performance: loss, delay, throughput  layering, service models  security  history You now have:  context, overview, vocabulary, “feel” of networking  more depth, detail, and fun to follow!
Additional Chapter 1 slides Introduction: 1-85
ISO/OSI reference model Introduction: 1-86 Two layers not found in Internet protocol stack!  presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine-specific conventions  session: synchronization, checkpointing, recovery of data exchange  Internet stack “missing” these layers! • these services, if needed, must be implemented in application • needed? application presentation session transport network link physical The seven layer OSI/ISO reference model
Services, Layering and Encapsulation source application transport network link physical destination application transport network link physical Ht M M M Ht Hn M Ht Hn Hl M Ht Hn Ht M M message segment datagram frame M Ht Hn Hl Introduction: 1-87
Wireshark Introduction: 1-88 Transport (TCP/UDP) Network (IP) Link (Ethernet) Physical application (www browser, email client) application OS packet capture (pcap) packet analyzer copy of all Ethernet frames sent/received

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Chapter_1_v8.2.pptx Slides Fast Nuces Chap 1

  • 1. Introduction: 1-1 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. For a revision history, see the slide note for this page. Thanks and enjoy! JFK/KWR All material copyright 1996-2023 J.F Kurose and K.W. Ross, All Rights Reserved Computer Networking: A Top-Down Approach 8th edition Jim Kurose, Keith Ross Pearson, 2020
  • 2. Chapter 1: introduction Chapter goal:  Get “feel,” “big picture,” introduction to terminology • more depth, detail later in course Overview/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  Protocol layers, service models  Security  History Introduction: 1-2
  • 3. Internet The Internet: a “nuts and bolts” view mobile network home network enterprise network national or global ISP local or regional ISP datacenter network content provider network Packet switches: forward packets (chunks of data)  routers, switches Communication links  fiber, copper, radio, satellite  transmission rate: bandwidth Billions of connected computing devices:  hosts = end systems  running network apps at Internet’s “edge” Networks  collection of devices, routers, links: managed by an organization Introduction: 1-3
  • 4. “Fun” Internet-connected devices Web-enabled toaster + weather forecaster Internet phones Slingbox: remote control cable TV Security Camera IP picture frame Internet refrigerator Tweet-a-watt: monitor energy use sensorized, bed mattress Amazon Echo Others? Gaming devices cars scooters bikes Introduction: 1-4 Pacemaker & Monitor AR devices Fitbit diapers
  • 5.  Internet: “network of networks” • Interconnected ISPs The Internet: a “nuts and bolts” view mobile network home network enterprise network national or global ISP local or regional ISP datacenter network content provider network  protocols are everywhere • control sending, receiving of messages • e.g., HTTP (Web), streaming video, Skype, TCP, IP, WiFi, 4/5G, Ethernet Ethernet HTTP Skype IP WiFi 4G TCP Streaming video  Internet standards • RFC: Request for Comments • IETF: Internet Engineering Task Force Introduction: 1-5
  • 6.  Infrastructure that provides services to applications: • Web, streaming video, multimedia teleconferencing, email, games, e- commerce, social media, inter- connected appliances, … The Internet: a “services” view mobile network home network enterprise network national or global ISP local or regional ISP datacenter network content provider network HTTP Skype Streaming video  provides programming interface to distributed applications: • “hooks” allowing sending/receiving apps to “connect” to, use Internet transport service • provides service options, analogous to postal service Introduction: 1-6
  • 7. What’s a protocol? Human protocols:  “what’s the time?”  “I have a question”  introductions Network protocols:  computers (devices) rather than humans  all communication activity in Internet governed by protocols Protocols define the format, order of messages sent and received among network entities, and actions taken on message transmission, receipt Rules for: … specific messages sent … specific actions taken when message received, or other events Introduction: 1-7
  • 8. What’s a protocol? A human protocol and a computer network protocol: Q: other human protocols? Hi Hi Got the time? 2:00 time TCP connection response <file> TCP connection request GET http://gaia.cs.umass.edu/kurose_ross Introduction: 1-8
  • 9. Chapter 1: roadmap Introduction: 1-9  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
  • 10. A closer look at Internet structure mobile network home network enterprise network national or global ISP local or regional ISP datacenter network content provider network Network edge:  hosts: clients and servers  servers often in data centers Introduction: 1-10
  • 11. A closer look at Internet structure mobile network home network enterprise network national or global ISP local or regional ISP datacenter network content provider network Network edge:  hosts: clients and servers  servers often in data centers Access networks, physical media: wired, wireless communication links Introduction: 1-11
  • 12. A closer look at Internet structure Network edge:  hosts: clients and servers  servers often in data centers Access networks, physical media: wired, wireless communication links Network core:  interconnected routers  network of networks mobile network home network enterprise network national or global ISP local or regional ISP datacenter network content provider network Introduction: 1-12
  • 13. Access networks and physical media mobile network home network enterprise network national or global ISP local or regional ISP datacenter network content provider network Q: How to connect end systems to edge router?  residential access nets  institutional access networks (school, company)  mobile access networks (WiFi, 4G/5G) Introduction: 1-13
  • 14. Access networks: cable-based access cable modem splitter … cable headend Channels V I D E O V I D E O V I D E O V I D E O V I D E O V I D E O D A T A D A T A C O N T R O L 1 2 3 4 5 6 7 8 9 frequency division multiplexing (FDM): different channels transmitted in different frequency bands Introduction: 1-14
  • 15. Access networks: cable-based access cable modem splitter … cable headend data, TV transmitted at different frequencies over shared cable 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 cable modem termination system CMTS ISP Introduction: 1-15
  • 16. ISP Access networks: digital subscriber line (DSL) central office telephone network DSLAM voice, data transmitted at different frequencies over dedicated line to central office  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 DSL modem splitter DSL access multiplexer Introduction: 1-16
  • 17. Access networks: home networks to/from headend or central office cable or DSL modem router, firewall, NAT wired Ethernet (1 Gbps) WiFi wireless access point (54, 450 Mbps) Wireless and wired devices often combined in single box Introduction: 1-17
  • 18. Wireless access networks Shared wireless access network connects end system to router  via base station aka “access point” Wireless local area networks (WLANs)  typically within or around building (~100 ft)  802.11b/g/n (WiFi): 11, 54, 450 Mbps transmission rate to Internet to Internet Wide-area cellular access networks  provided by mobile, cellular network operator (10’s km)  10’s Mbps  4G/5G cellular networks Introduction: 1-18
  • 19. Access networks: enterprise networks  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 Ethernet switch institutional mail, web servers institutional router Enterprise link to ISP (Internet) Introduction: 1-19
  • 20. Access networks: data center networks  high-bandwidth links (10s to 100s Gbps) connect hundreds to thousands of servers together, and to Internet mobile network home network enterprise network national or global ISP local or regional ISP datacenter network content provider network Courtesy: Massachusetts Green High Performance Computing Center (mghpcc.org) Introduction: 1-20
  • 21. Host: sends packets of data host sending function:  takes application message  breaks into smaller chunks, known as packets, of length L bits  transmits packet into access network at transmission rate R • link transmission rate, aka link capacity, aka link bandwidth R: link transmission rate host 1 2 two packets, L bits each packet transmission delay time needed to transmit L-bit packet into link L (bits) R (bits/sec) = = Introduction: 1-21
  • 22. Links: physical media  bit: propagates between transmitter/receiver pairs  physical link: what lies between transmitter & receiver  guided media: • signals propagate in solid media: copper, fiber, coax  unguided media: • signals propagate freely, e.g., radio Twisted pair (TP)  two insulated copper wires • Category 5: 100 Mbps, 1 Gbps Ethernet • Category 6: 10Gbps Ethernet Introduction: 1-22
  • 23. Links: physical media Coaxial cable:  two concentric copper conductors  bidirectional  broadband: • multiple frequency channels on cable • 100’s Mbps per channel Fiber optic cable:  glass fiber carrying light pulses, each pulse a bit  high-speed operation: • high-speed point-to-point transmission (10’s-100’s Gbps)  low error rate: • repeaters spaced far apart • immune to electromagnetic noise Introduction: 1-23
  • 24. Links: physical media Wireless radio  signal carried in various “bands” in electromagnetic spectrum  no physical “wire”  broadcast, “half-duplex” (sender to receiver)  propagation environment effects: • reflection • obstruction by objects • Interference/noise Radio link types:  Wireless LAN (WiFi) • 10-100’s Mbps; 10’s of meters  wide-area (e.g., 4G/5G cellular) • 10’s Mbps (4G) over ~10 Km  Bluetooth: cable replacement • short distances, limited rates  terrestrial microwave • point-to-point; 45 Mbps channels  satellite • up to < 100 Mbps (Starlink) downlink • 270 msec end-end delay (geostationary) Introduction: 1-24
  • 25. Chapter 1: roadmap Introduction: 1-25  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
  • 26. The network core  mesh of interconnected routers  packet-switching: hosts break application-layer messages into packets • network forwards packets from one router to the next, across links on path from source to destination mobile network home network enterprise network national or global ISP local or regional ISP datacenter network content provider network Introduction: 1-26
  • 27. Two key network-core functions 1 2 3 0111 destination address in arriving packet’s header routing algorithm header value output link 0100 0101 0111 1001 3 2 2 1 local forwarding table Forwarding:  aka “switching”  local action: move arriving packets from router’s input link to appropriate router output link local forwarding table Routing:  global action: determine source- destination paths taken by packets  routing algorithms routing algorithm Introduction: 1-27
  • 30. Packet-switching: store-and-forward  packet transmission delay: takes L/R seconds to transmit (push out) L-bit packet into link at R bps  store and forward: entire packet must arrive at router before it can be transmitted on next link source R bps destination 1 2 3 L bits per packet R bps One-hop numerical example:  L = 10 Kbits  R = 100 Mbps  one-hop transmission delay = 0.1 msec Introduction: 1-30
  • 31. Packet-switching: queueing A B C R = 100 Mb/s R = 1.5 Mb/s D E queue of packets waiting for transmission over output link Queueing occurs when work arrives faster than it can be serviced: Introduction: 1-31
  • 32. Packet-switching: queueing A B C R = 100 Mb/s R = 1.5 Mb/s D 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: 1-32
  • 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) * Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/interactive  commonly used in traditional telephone networks Introduction: 1-33
  • 34. Circuit switching: FDM and TDM frequency time frequency time 4 users Frequency Division Multiplexing (FDM)  optical, electromagnetic frequencies divided into (narrow) frequency bands Time Division Multiplexing (TDM)  time divided into slots  each call allocated its own band, can transmit at max rate of that narrow band  each call allocated periodic slot(s), can transmit at maximum rate of (wider) frequency band (only) during its time slot(s) Introduction: 1-34
  • 35. Packet switching versus circuit switching example:  1 Gb/s link  each user: • 100 Mb/s when “active” • active 10% of time Q: how many users can use this network under circuit-switching and packet switching? * Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/interactive N users 1 Gbps link … ..  circuit-switching: 10 users Q: how did we get value 0.0004? A: HW problem (for those with course in probability only)  packet switching: with 35 users, probability > 10 active at same time is less than .0004 * Introduction: 1-35
  • 36. Packet switching versus circuit switching  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. Is packet switching a “slam dunk winner”? Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet switching)? Introduction: 1-36
  • 37. Internet structure: a “network of networks”  hosts connect to Internet via access Internet Service Providers (ISPs)  access ISPs in turn must be interconnected • so that any two hosts (anywhere!) can send packets to each other  resulting network of networks is very complex • evolution driven by economics, national policies Let’s take a stepwise approach to describe current Internet structure mobile network home network enterprise network national or global ISP local or regional ISP datacenter network content provider network
  • 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 net access net access net access net access net access net access net access net access net access net access net access net access net … … … … … … Introduction: 1-38
  • 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 net access net access net access net access net access net access net access net access net access net access net access net access net … … … … … … connecting each access ISP to each other directly doesn’t scale: O(N2 ) connections. Introduction: 1-39
  • 40. Internet structure: a “network of networks” Option: connect each access ISP to one global transit ISP? Customer and provider ISPs have economic agreement. global ISP access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net … … … … … … Introduction: 1-40
  • 41. ISP A ISP C ISP B Internet structure: a “network of networks” access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net … … … … … … But if one global ISP is viable business, there will be competitors …. Introduction: 1-41
  • 42. ISP A ISP C ISP B Internet structure: a “network of networks” access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net … … … … … … But if one global ISP is viable business, there will be competitors …. who will want to be connected IXP peering link Internet exchange point IXP Introduction: 1-42
  • 43. ISP A ISP C ISP B Internet structure: a “network of networks” access net access net access net access net access net access net access net access net access net access net access net … … … … … … … and regional networks may arise to connect access nets to ISPs IXP IXP access net access net regional ISP access net access net access net Introduction: 1-43
  • 44. ISP A ISP C ISP B Internet structure: a “network of networks” access net access net access net access net access net access net access net access net access net access net access net … … … … … … … and content provider networks (e.g., Google, Microsoft, Akamai) may run their own network, to bring services, content close to end users IXP IXP access net access net access net access net access net Content provider network regional ISP Introduction: 1-44
  • 45. Internet structure: a “network of networks” access ISP access ISP access ISP access ISP access ISP access ISP access ISP access 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 Regional ISP Regional ISP Tier 1 ISP Tier 1 ISP IXP Google IXP IXP Introduction: 1-45
  • 46. Chapter 1: roadmap Introduction: 1-46  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
  • 47. 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 A B packet being transmitted (transmission delay) packets in buffers (queueing delay) free (available) buffers: arriving packets dropped (loss) if no free buffers Introduction: 1-47
  • 48. Packet delay: four sources dproc: nodal processing  check bit errors  determine output link  typically < microsecs dqueue: queueing delay  time waiting at output link for transmission  depends on congestion level of router propagation nodal processing queueing dnodal = dproc + dqueue + dtrans + dprop A B transmission Introduction: 1-48
  • 49. Packet delay: four sources propagation nodal processing queueing dnodal = dproc + dqueue + dtrans + dprop A B transmission dtrans: transmission delay:  L: packet length (bits)  R: link transmission rate (bps)  dtrans = L/R dprop: propagation delay:  d: length of physical link  s: propagation speed (~2x108 m/sec)  dprop = d/s dtrans and dprop very different Introduction: 1-49
  • 50. Caravan analogy  car ~ bit; caravan ~ packet; toll service ~ link transmission  toll booth takes 12 sec to service car (bit transmission time)  “propagate” at 100 km/hr  Q: How long until caravan is lined up before 2nd toll booth?  time to “push” entire caravan through toll booth onto highway = 12*10 = 120 sec  time for last car to propagate from 1st to 2nd toll both: 100km/(100km/hr) = 1 hr  A: 62 minutes toll booth toll booth (aka link) ten-car caravan (aka 10-bit packet) 100 km 100 km toll booth toll booth (aka link) toll booth Introduction: 1-50
  • 51. Caravan analogy toll booth toll booth (aka router) ten-car caravan (aka 10-bit packet) 100 km 100 km  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: 1-51
  • 52. Packet queueing delay (revisited)  a: average packet arrival rate  L: packet length (bits)  R: link bandwidth (bit transmission rate)  La/R ~ 0: avg. queueing delay small  La/R -> 1: avg. queueing delay large  La/R > 1: more “work” arriving is more than can be serviced - average delay infinite! La/R ~ 0 La/R -> 1 traffic intensity = La/R average queueing delay 1 service rate of bits R arrival rate of bits L a . : “traffic intensity” Introduction: 1-52
  • 53. “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: 3 probes 3 probes 3 probes • 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 Introduction: 1-53
  • 54. Real Internet delays and routes 1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms 2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms 3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms 4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms 5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms 6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms 7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms 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 12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms 13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms 14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms 15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms 16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms 17 * * * 18 * * * 19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms traceroute: gaia.cs.umass.edu to www.eurecom.fr * Do some traceroutes from exotic countries at www.traceroute.org * means no response (probe lost, router not replying) 3 delay measurements from gaia.cs.umass.edu to cs-gw.cs.umass.edu 3 delay measurements to border1-rt-fa5-1-0.gw.umass.edu looks like delays decrease! Why? trans-oceanic link Introduction: 1-54
  • 55. Packet loss  queue (aka buffer) preceding link in buffer has finite capacity A B packet being transmitted buffer (waiting area) * Check out the Java applet for an interactive animation (on publisher’s website) of queuing and loss packet arriving to full buffer is lost  packet arriving to full queue dropped (aka lost)  lost packet may be retransmitted by previous node, by source end system, or not at all Introduction: 1-55
  • 56. 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 server, with file of F bits to send to client link capacity Rs bits/sec link capacity Rc bits/sec server sends bits (fluid) into pipe pipe that can carry fluid at rate (Rs bits/sec) pipe that can carry fluid at rate (Rc bits/sec) Introduction: 1-56
  • 57. Throughput Rs < Rc What is average end-end throughput? Rs bits/sec Rc bits/sec Rs > Rc What is average end-end throughput? link on end-end path that constrains end-end throughput bottleneck link Rs bits/sec Rc bits/sec Introduction: 1-57
  • 58. Throughput: network scenario 10 connections (fairly) share backbone bottleneck link Rbits/sec Rs Rs Rs Rc Rc Rc R  per-connection end-end throughput: min(Rc,Rs,R/10)  in practice: Rc or Rs is often bottleneck * Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/ Introduction: 1-58
  • 59. Chapter 1: roadmap Introduction: 1-59  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
  • 60. 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: 1-60
  • 61. 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: 1-61
  • 62. 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 B C src:B dest:A payload Wireshark software used for our end-of-chapter labs is a (free) packet-sniffer Introduction: 1-62
  • 63. Bad guys: fake identity IP spoofing: injection of packet with false source address A B C src:B dest:A payload Introduction: 1-63
  • 64. Bad guys: denial of service target Denial of Service (DoS): attackers make resources (server, bandwidth) unavailable to legitimate traffic by overwhelming resource with bogus traffic 1. select target 2. break into hosts around the network (see botnet) 3. send packets to target from compromised hosts Introduction: 1-64
  • 65. 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: 1-65
  • 66. Chapter 1: roadmap Introduction: 1-66  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
  • 67. Protocol “layers” and reference models Networks are complex, with many “pieces”: hosts routers links of various media applications protocols hardware, software Question: is there any hope of organizing structure of network? and/or our discussion of networks? Introduction: 1-67
  • 68. Example: organization of air travel  a series of steps, involving many services ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing airplane routing How would you define/discuss the system of airline travel? end-to-end transfer of person plus baggage Introduction: 1-68
  • 69. Example: organization of air travel ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing airplane routing ticketing service baggage service gate service runway service routing service layers: each layer implements a service  via its own internal-layer actions  relying on services provided by layer below Introduction: 1-69
  • 70. 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: 1-70
  • 71. Layered Internet protocol stack  application: supporting network applications • HTTP, IMAP, SMTP, DNS  transport: process-process data transfer • TCP, UDP  network: routing of datagrams from source to destination • IP, routing protocols  link: data transfer between neighboring network elements • Ethernet, 802.11 (WiFi), PPP  physical: bits “on the wire” link application network transport physical application transport network link physical Introduction: 1-71
  • 72. Services, Layering and Encapsulation source  transport-layer protocol encapsulates application-layer message, M, with transport layer-layer header Ht to create a transport-layer segment • Ht used by transport layer protocol to implement its service application transport network link physical destination application transport network link physical Transport-layer protocol transfers M (e.g., reliably) from one process to another, using services of network layer Ht M Application exchanges messages to implement some application service using services of transport layer M Introduction: 1-72
  • 73. Services, Layering and Encapsulation source Transport-layer protocol transfers M (e.g., reliably) from one process to another, using services of network layer Ht M  network-layer protocol encapsulates transport-layer segment [Ht | M] with network layer-layer header Hn to create a network-layer datagram • Hn used by network layer protocol to implement its service application transport network link physical destination M application transport network link physical M Ht Hn Network-layer protocol transfers transport-layer segment [Ht | M] from one host to another, using link layer services Introduction: 1-73
  • 74. Services, Layering and Encapsulation source Ht M  link-layer protocol encapsulates network datagram [Hn| [Ht |M], with link-layer header Hl to create a link-layer frame application transport network link physical destination M application transport network link physical M Ht Hn Link-layer protocol transfers datagram [Hn| [Ht |M] from host to neighboring host, using network-layer services M Ht Hn Hl Network-layer protocol transfers transport-layer segment [Ht | M] from one host to another, using link layer services Introduction: 1-74
  • 75. Encapsulation Introduction: 1-75 message segment datagram frame Matryoshka dolls (stacking dolls) Credit: https://dribbble.com/shots/7182188-Babushka-Boi
  • 76. Services, Layering and Encapsulation source application transport network link physical destination application transport network link physical M Ht Hn Hl M Ht Hn Ht M M M message Ht M segment M Ht Hn datagram frame M Ht Hn Hl Introduction: 1-76
  • 77. network link physical application transport network link physical application transport network link physical Encapsulation: an end-end view source Ht Hn M segment Ht datagram destination Ht Hn Hl M Ht Hn M Ht M M Ht Hn Hl M Ht Hn M Ht Hn M Ht Hn Hl M router switch message M Ht M Hn frame link physical Introduction: 1-77
  • 78. Chapter 1: roadmap Introduction: 1-78  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
  • 79. Internet history  1961: Kleinrock - queueing theory shows effectiveness of packet-switching  1964: Baran - packet-switching in military nets  1967: ARPAnet conceived by Advanced Research Projects Agency  1969: first ARPAnet node operational  1972: • ARPAnet public demo • NCP (Network Control Protocol) first host-host protocol • first e-mail program • ARPAnet has 15 nodes 1961-1972: Early packet-switching principles
  • 80. Internet history  1970: ALOHAnet satellite network in Hawaii  1974: Cerf and Kahn - architecture for interconnecting networks  1976: Ethernet at Xerox PARC  late70’s: proprietary architectures: DECnet, SNA, XNA  1979: ARPAnet has 200 nodes 1972-1980: Internetworking, new and proprietary networks Cerf and Kahn’s internetworking principles:  minimalism, autonomy - no internal changes required to interconnect networks  best-effort service model  stateless routing  decentralized control define today’s Internet architecture Introduction: 1-80
  • 81. Internet history  1983: deployment of TCP/IP  1982: smtp e-mail protocol defined  1983: DNS defined for name- to-IP-address translation  1985: ftp protocol defined  1988: TCP congestion control  new national networks: CSnet, BITnet, NSFnet, Minitel  100,000 hosts connected to confederation of networks 1980-1990: new protocols, a proliferation of networks Introduction: 1-81
  • 82. Internet history  early 1990s: ARPAnet decommissioned  1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995)  early 1990s: Web • hypertext [Bush 1945, Nelson 1960’s] • HTML, HTTP: Berners-Lee • 1994: Mosaic, later Netscape • late 1990s: commercialization of the Web late 1990s – 2000s:  more killer apps: instant messaging, P2P file sharing  network security to forefront  est. 50 million host, 100 million+ users  backbone links running at Gbps 1990, 2000s: commercialization, the Web, new applications Introduction: 1-82
  • 83. Internet history  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) 2005-present: scale, SDN, mobility, cloud Introduction: 1-83
  • 84. Chapter 1: summary Introduction: 1-84 We’ve covered a “ton” of material!  Internet overview  what’s a protocol?  network edge, access network, core • packet-switching versus circuit- switching • Internet structure  performance: loss, delay, throughput  layering, service models  security  history You now have:  context, overview, vocabulary, “feel” of networking  more depth, detail, and fun to follow!
  • 85. Additional Chapter 1 slides Introduction: 1-85
  • 86. ISO/OSI reference model Introduction: 1-86 Two layers not found in Internet protocol stack!  presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine-specific conventions  session: synchronization, checkpointing, recovery of data exchange  Internet stack “missing” these layers! • these services, if needed, must be implemented in application • needed? application presentation session transport network link physical The seven layer OSI/ISO reference model
  • 87. Services, Layering and Encapsulation source application transport network link physical destination application transport network link physical Ht M M M Ht Hn M Ht Hn Hl M Ht Hn Ht M M message segment datagram frame M Ht Hn Hl Introduction: 1-87
  • 88. Wireshark Introduction: 1-88 Transport (TCP/UDP) Network (IP) Link (Ethernet) Physical application (www browser, email client) application OS packet capture (pcap) packet analyzer copy of all Ethernet frames sent/received

Editor's Notes

  • #1: (8.2)Version History 7.2 (January 2020) All slides reformatted for 16:9 aspect ratio Use of Calibri font, rather that Gill Sans MT Updated slide content for 2020 link technologies and applications Add more animation throughout New Master slide Feb. 2020 (8.0) a few updates suggest by Catherine Rosenberg (thanks!) titles in a lighter font Sept 2020 (8.1) Added ~7 new slides, in particular: data center slide; routing versus forwarding; security line of defense; several on encapsulation and layers (this section is a lot better now). Other relative minor changes throughout Feb. 2023 (8.2) few minor updates (mostly speeds, technology details)
  • #3: the basic practical details.
  • #8: Explain important points distributed entities, exchanging messages (governed by protocols) Time going down go over definition of protocol (showing format, order of messages sent and received, and actions taken) We’ll see these kinds of diagrams a lot
  • #59: Segue: from performance to security
  • #75: Thanks to Nikko Bovornkeeratiroj, Phuthipong <[email protected]>, for the stacking dolls idea and slides