Ch 1 Chapter 1 Introduction Introduction Computer Networking: A T D A h A note on the use of these ppt slides: We’re making these slides freely available to all (faculty, students, readers). They’re in PowerPoint form so you can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously A Top Down Approach , 4 th edition. Jim Kurose, Keith Ross Addis W sl Jl 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) in substantially unaltered form, that you mention their source (after all, we’d like people to use our book!) If you post any slides in substantially unaltered form on a www site that Addison-Wesley, July 2007. If you post any slides in substantially unaltered form 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. Thanks and enjoy! JFK/KWR Introduction 1-1 All material copyright 1996-2007 J.F Kurose and K.W. Ross, All Rights Reserved Chapter 1: Introduction Chapter 1: Introduction Our goal: Overview: get “feel” and terminology Overview: what’s the Internet? what’s a protocol? more depth, detail later in course pp h: what s a protocol? network edge; hosts, access net physical media approach: use Internet as example net, physical media network core: packet/circuit switching, Internet structure example performance: loss, delay, throughput protocol layers, service models Introduction 1-2 Chapter 1: roadmap Chapter 1: roadmap 1 1 Wh i h I 1.1 What is the Internet? 1.2 Network edge d k li k end systems, access networks, links 1.3 Network core circuit switchin packet switchin network structure circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks networks 1.5 Protocol layers, service models Introduction 1-3 What’s the Internet: “nuts and bolts” view millions of connected Mobile network PC computing devices: hosts = end systems k Global ISP server wireless laptop running network apps Home network Regional ISP laptop cellular handheld i ti li k I tit ti l t k Regional ISP access points communication links fiber, copper, radio satellite Institutional network wired links radio, satellite transmission rate = bandwidth router rate = bandwidth routers: forward packets (chunks of Introduction 1-4 packets (chunks of data)
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Ch 1Chapter 1IntroductionIntroduction
Computer Networking: A T D A h
A note on the use of these ppt slides:We’re making these slides freely available to all (faculty, students, readers). They’re in PowerPoint form so you can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously
A Top Down Approach ,4th edition. Jim Kurose, Keith RossAddis W sl J l
( g ) y y yrepresent 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) in substantially unaltered form, that you mention their source (after all, we’d like people to use our book!)
If you post any slides in substantially unaltered form on a www site that Addison-Wesley, July 2007.
If you post any slides in substantially unaltered form 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.
Thanks and enjoy! JFK/KWR
Introduction 1-1
All material copyright 1996-2007J.F Kurose and K.W. Ross, All Rights Reserved
1 1 Wh i h I1.1 What is the Internet?1.2 Network edge
d k li kend systems, access networks, links1.3 Network core
circuit switchin packet switchin network structurecircuit switching, packet switching, network structure1.4 Delay, loss and throughput in packet-switched
networksnetworks1.5 Protocol layers, service models
Introduction 1-10
A closer look at network structure:A closer look at network structure:network edge:network edge:applications and hostshostsaccess networks, physical media:physical media:wired, wireless communication linkscommunication linksnetwork core:
i t t d interconnected routersnetwork of
Introduction 1-11
network of networks
The network edge:The network edge:end systems (hosts):end systems (hosts):
run application programse.g. Web, emailgat “edge of network” peer-peer
client/server model
client/server
client host requests, receives service from always-on servere g Web browser/server; e.g. Web browser/server; email client/server
peer-peer model:p pminimal (or no) use of dedicated serverse g Skype BitTorrenth
Introduction 1-12
e.g. Skype, BitTorrenth
Network edge: reliable data transfer service
G l P Goal: data transfer between end systemsh d h k
TCP service [RFC 793]reliable, in-order byte-
d fhandshaking: setup (prepare for) data transfer ahead of time
stream data transferloss: acknowledgements and retransmissionstransfer ahead of time
Hello, hello back human protocol
and retransmissionsflow control:
sender won’t overwhelm pset up “state” in two communicating hosts
TCP T s issi
sender won t overwhelm receiver
congestion control:TCP - Transmission Control Protocol
Internet’s reliable data
senders “slow down sending rate” when network congested
Introduction 1-13
Internet s reliable data transfer service
congested
Network edge: best effort (unreliable) data transfer service
G l ’ PGoal: data transfer between end systems
b f !
App’s using TCP:HTTP (Web), FTP (file
f ) l same as before!UDP - User Datagram Protocol [RFC 768]:
App’s usin UDP:unreliable data transferno flow control
App s using UDP:streaming media, teleconferencing DNS no flow control
no congestion controlteleconferencing, DNS, Internet telephony
Introduction 1-14
Access networks and physical mediaAccess networks and physical media
Q: How to connect end Q How to conn ct n systems to edge router?residential access netsinstitutional access networks (school, company)mobile access networks
Keep in mind: bandwidth (bits per ( psecond) of access network?
Introduction 1-15
shared or dedicated?
Residential access: point to point accessResidential access: point to point access
l dDialup via modemup to 56Kbps direct access to
t ( ft l )router (often less)Can’t surf and phone at same time: can’t be “always on”time: can t be always on
DSL: digital subscriber linedeployment: telephone company (typically)up to 1 Mbps upstream (today typically < 256 kbps)up to 8 Mbps downstream (today typically < 1 Mbps)dedicated physical line to telephone central office
La/R ~ 0: average queueing delay smallLa/R -> 1: delays become largeLa/R -> 1: delays become largeLa/R > 1: more “work” arriving than can be serviced average delay infinite!
Introduction 1-52
serviced, average delay infinite!
“Real” Internet delays and routesReal Internet delays and routes
Wh d “ l” I d l & l l k lik What do “real” Internet delay & loss look like? Traceroute program: provides delay
s t f s t t l d d 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 sends three packets that will reach router i on path towards destinationrouter i will return packets to sendersender times interval between transmission and reply.
3 b 3 b3 probes
3 probes
3 probes
Introduction 1-53
“Real” Internet delays and routesReal Internet delays and routestraceroute: gaia.cs.umass.edu to www.eurecom.fr
1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms
gThree delay measurements from gaia.cs.umass.edu to cs-gw.cs.umass.edu
g ( )2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms4 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 ms6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms
trans-oceaniclink
10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms15 lb 3t2 ft t (193 48 50 54) 135 128 13315 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms17 * * *18 * * *19 f t i f (193 55 113 142) 132 128 136
* means no response (probe lost, router not replying)
Introduction 1-54
19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms
Packet lossPacket loss
( k b ff ) di li k i b ff h queue (aka buffer) preceding link in buffer has finite capacitypacket arriving to full queue dropped (aka lost)lost packet may be retransmitted by previous p y y pnode, by source end system, or not at all
buffer
Apacket being transmitted
buffer (waiting area)
Bpacket arriving to
Introduction 1-55
full buffer is lost
ThroughputThroughputthroughput: rate (bits/time unit) at which throughput: rate (bits/time unit) at which bits transferred between sender/receiver
instantaneous: rate at given point in timeinstantaneous: rate at given point in timeaverage: rate over long(er) period of time
h link capacity link capacityi h server, withfile of F bits
to send to client
link capacityRs bits/sec
link capacityRc bits/sec
pipe that can carryfluid at rateRs bits/sec)
pipe that can carryfluid at rateRc bits/sec)
server sends bits (fluid) into pipe
Introduction 1-56
s c )
Throughput (more)Throughput (more)R < R What is average end end 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
link on end-end path that constrains end-end throughputbottleneck link
Introduction 1-57
link on end end path that constrains end end throughput
Throughput: Internet scenarioThroughput: Internet scenario
RRsper-connection Rs Rs
pend-end throughput:
R R
Rg p
min(Rc,Rs,R/10)in practice: R or Rc
Rc
Rcin practice: Rc or Rs is often bottleneck
10 connections (fairly) share
bottleneck
Introduction 1-58
( y)backbone bottleneck link R bits/sec
Chapter 1: roadmapChapter 1: roadmap
1 1 Wh i h I1.1 What is the Internet?1.2 Network edge
d k li kend systems, access networks, links1.3 Network core
circuit switchin packet switchin network structurecircuit switching, packet switching, network structure1.4 Delay, loss and throughput in packet-switched
networksnetworks1.5 Protocol layers, service models
Introduction 1-59
Protocol “Layers”Protocol LayersNetworks are complex! N twor s ar comp !
many “pieces”:hosts Question:hostsrouterslinks of various
Question:Is there any hope of organizing structure of links of various
mediaapplications
organizing structure of network?
ppprotocolshardware,
Or at least our discussion of networks?hardware,
software
Introduction 1-60
Organization of air travelOrganization of air travel
physicallink: data transfer between neighboring network elements
PPP, Ethernet
physical
Introduction 1-64
PPP, Ethernetphysical: bits “on the wire”
ISO/OSI reference modelISO/OSI reference modelpresentation: allow applications to presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine-
applicationpresentationyp p
specific conventionssession: synchronization, h k f d
presentationsession
checkpointing, recovery of data exchangeI t t t k “ i i ” th
transportnetwork
Internet stack “missing” these layers!
these services if needed must link
physicalthese services, if needed, must be implemented in applicationneeded?
physical
Introduction 1-65
needed?
sourceapplication
Encapsulationmessage M application
transportnetwork
li kHtHn M
segment Ht
datagram
pmessage M
Ht M
Hnlink
physicallink
HtHnHl Mframe
linkphysical
switch
d ti tidestinationapplicationtransportHt M
M
networklink
physicalHtHnHl M
HtHn M
HtHn M
transportnetwork
linkphysical
HtHnHl MHtHn M
t
router
Introduction 1-66
physical
Introduction: SummaryIntroduction: SummaryCovered a “ton” of material! Y h :f m
Internet overviewwhat’s a protocol?
You now have:context, overview, “feel” of networkingp
network edge, core, access network
k t it hi
feel of networkingmore depth, detail to follow!
packet-switching versus circuit-switchingInternet structureInternet structure
performance: loss, delay, throughputg playering, service modelssecurity