-
Introduction1-*Chapter 1 IntroductionComputer Networking: A Top
Down Approach , 5th edition. Jim Kurose, Keith Ross Addison-Wesley,
April 2009. A note on the use of these ppt slides:Were making these
slides freely available to all (faculty, students, readers). Theyre
in PowerPoint form so you 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) in substantially unaltered form, that you mention their
source (after all, wed like people to use our book!) 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
All material copyright 1996-2009J.F Kurose and K.W. Ross, All
Rights Reserved
Introduction
-
Introduction1-*Chapter 1: IntroductionOur goal: get feel and
terminologymore depth, detail later in courseapproach:use Internet
as example
Overview:whats the Internet?whats a protocol?network edge;
hosts, access net, physical medianetwork core: packet/circuit
switching, Internet structureperformance: loss, delay,
throughputsecurityprotocol layers, service modelshistory
Introduction
-
Introduction1-*Chapter 1: roadmap1.1 What is the Internet?1.2
Network edge end systems, access networks, links1.3 Network core
circuit switching, packet switching, network structure1.4 Delay,
loss and throughput in packet-switched networks1.5 Protocol layers,
service models1.6 Networks under attack: security1.7 History
Introduction
-
Introduction1-*Whats the Internet: nuts and bolts viewmillions
of connected computing devices: hosts = end systems running network
appscommunication linksfiber, copper, radio, satellitetransmission
rate = bandwidthrouters: forward packets (chunks of data)
Introduction
-
Introduction1-*Cool internet appliancesWorlds smallest web
serverhttp://www-ccs.cs.umass.edu/~shri/iPic.htmlIP picture
framehttp://www.ceiva.com/Web-enabled toaster +weather
forecasterInternet phones
Introduction
-
Introduction1-*Whats the Internet: nuts and bolts viewprotocols
control sending, receiving of msgse.g., TCP, IP, HTTP, Skype,
EthernetInternet: network of networksloosely hierarchicalpublic
Internet versus private intranetInternet standardsRFC: Request for
commentsIETF: Internet Engineering Task Force
Introduction
-
Introduction1-*Whats the Internet: a service viewcommunication
infrastructure enables distributed applications:Web, VoIP, email,
games, e-commerce, file sharingcommunication services provided to
apps:reliable data delivery from source to destinationbest effort
(unreliable) data delivery
Introduction
-
Introduction1-*Whats a protocol?human protocols:whats the time?I
have a questionintroductions
specific msgs sent specific actions taken when msgs received, or
other eventsnetwork protocols:machines rather than humansall
communication activity in Internet governed by protocolsprotocols
define format, order of msgs sent and received among network
entities, and actions taken on msg transmission, receipt
Introduction
-
Introduction1-*Whats a protocol?a human protocol and a computer
network protocol:
Q: Other human protocols? HiHiTCP connection request
Introduction
-
Introduction1-*Chapter 1: roadmap1.1 What is the Internet?1.2
Network edge end systems, access networks, links1.3 Network core
circuit switching, packet switching, network structure1.4 Delay,
loss and throughput in packet-switched networks1.5 Protocol layers,
service models1.6 Networks under attack: security1.7 History
Introduction
-
Introduction1-*A closer look at network structure:network edge:
applications and hostsaccess networks, physical media: wired,
wireless communication links network core: interconnected
routersnetwork of networks
Introduction
-
Introduction1-*The network edge:end systems (hosts):run
application programse.g. Web, emailat edge of networkclient/server
modelclient host requests, receives service from always-on
servere.g. Web browser/server; email client/serverpeer-peer model:
minimal (or no) use of dedicated serverse.g. Skype, BitTorrent
Introduction
-
Introduction1-*Access networks and physical mediaQ: How to
connect end systems to edge router?residential access
netsinstitutional access networks (school, company)mobile access
networksKeep in mind: bandwidth (bits per second) of access
network?shared or dedicated?
Introduction
-
Uses existing telephony infrastructureHome is connected to
central officeup to 56Kbps direct access to router (often less)Cant
surf and phone at same time: not always onDial-up Modem
Introduction
-
Digital Subscriber Line (DSL)
Also uses existing telephone infrastrutureup to 1 Mbps upstream
(today typically < 256 kbps)up to 8 Mbps downstream (today
typically < 1 Mbps)dedicated physical line to telephone central
office
Introduction
-
Introduction1-*Residential access: cable modemsDoes not use
telephone infrastructureInstead uses cable TV infrastructureHFC:
hybrid fiber coaxasymmetric: up to 30Mbps downstream, 2 Mbps
upstreamnetwork of cable and fiber attaches homes to ISP
routerhomes share access to router unlike DSL, which has dedicated
access
Introduction
-
Introduction1-*Residential access: cable modemsDiagram:
http://www.cabledatacomnews.com/cmic/diagram.html
Introduction
-
Introduction1-*Cable Network Architecture: Overviewhomecable
headendcable distributionnetwork (simplified)Typically 500 to 5,000
homes
Introduction
-
Introduction1-*Cable Network Architecture: Overviewhomecable
headendcable distributionnetwork
Introduction
-
Introduction1-*Cable Network Architecture: Overviewhomecable
headendcable distributionnetwork (simplified)
Introduction
-
Introduction1-*Cable Network Architecture: Overviewhomecable
headendcable distributionnetworkFDM (more shortly):
Introduction
-
Fiber to the HomeOptical links from central office to the
homeTwo competing optical technologies: Passive Optical network
(PON) Active Optical Network (AON)Much higher Internet rates; fiber
also carries television and phone services
Introduction
-
Ethernet Internet accessTypically used in companies,
universities, etc10 Mbs, 100Mbps, 1Gbps, 10Gbps EthernetToday, end
systems typically connect into Ethernet switch
Introduction
-
Introduction1-*Wireless access networksshared wireless access
network connects end system to routervia base station aka access
pointwireless LANs:802.11b/g (WiFi): 11 or 54 Mbpswider-area
wireless accessprovided by telco operator~1Mbps over cellular
system (EVDO, HSDPA)next up (?): WiMAX (10s Mbps) over wide
areabasestationmobilehostsrouter
Introduction
-
Introduction1-*Home networksTypical home network components: DSL
or cable modemrouter/firewall/NATEthernetwireless access
pointwirelessaccess
pointwirelesslaptopsrouter/firewallcablemodemto/fromcableheadendEthernet
Introduction
-
Introduction1-*Physical MediaBit: propagates between
transmitter/rcvr pairsphysical link: what lies between transmitter
& receiverguided media: signals propagate in solid media:
copper, fiber, coaxunguided media: signals propagate freely, e.g.,
radioa. Twisted Pair (TP)two insulated copper wiresCategory 3:
traditional phone wires, 10 Mbps EthernetCategory 5: 100Mbps
Ethernet
Introduction
-
Introduction1-*Physical Media: coax, fiberb. Coaxial cable:two
concentric copper conductorsbidirectionalbaseband:single channel on
cablelegacy Ethernetbroadband: multiple channels on cable HFCc.
Fiber optic cable:glass fiber carrying light pulses, each pulse a
bithigh-speed operation:high-speed point-to-point transmission
(e.g., 10s-100s Gps)low error rate: repeaters spaced far apart ;
immune to electromagnetic noise
Introduction
-
The internet undersea world Introduction1-*
Introduction
-
Introduction1-*Physical media: radiosignal carried in
electromagnetic spectrumno physical wirebidirectionalpropagation
environment effects:reflection obstruction by
objectsinterferenceRadio link types:terrestrial microwavee.g. up to
45 Mbps channelsWLAN (e.g., Wifi)11Mbps, 54 Mbpswide-area (e.g.,
cellular)3G cellular: ~ 1 MbpssatelliteKbps to 45Mbps channel (or
multiple smaller channels)270 msec end-end delaygeosynchronous
versus low altitude
Introduction
-
Introduction1-*Chapter 1: roadmap1.1 What is the Internet?1.2
Network edge end systems, access networks, links1.3 Network core
circuit switching, packet switching, network structure1.4 Delay,
loss and throughput in packet-switched networks1.5 Protocol layers,
service models1.6 Networks under attack: security1.7 History
Introduction
-
Introduction1-*The Network Coremesh of interconnected routersthe
fundamental question: how is data transferred through net?circuit
switching: dedicated circuit per call: telephone
netpacket-switching: data sent thru net in discrete chunks
Introduction
-
Introduction1-*Network Core: Circuit SwitchingEnd-end resources
reserved for calllink bandwidth, switch capacitydedicated
resources: no sharingcircuit-like (guaranteed) performancecall
setup required
Introduction
-
Introduction1-*Network Core: Circuit Switchingnetwork resources
(e.g., bandwidth) divided into piecespieces allocated to
callsresource piece idle if not used by owning call (no
sharing)dividing link bandwidth into piecesfrequency divisiontime
division
Introduction
-
Introduction1-*Circuit Switching: FDM and TDM
Introduction
-
Introduction1-*Numerical exampleHow long does it take to send a
file of 640,000 bits from host A to host B over a circuit-switched
network?All links are 1.536 MbpsEach link uses TDM with 24
slots/sec500 msec to establish end-to-end circuit
Lets work it out!
Introduction
-
Introduction1-*Network Core: Packet Switchingeach end-end data
stream divided into packetsuser A, B packets share network
resources each packet uses full link bandwidth resources used as
needed
resource contention: aggregate resource demand can exceed amount
availablecongestion: packets queue, wait for link usestore and
forward: packets move one hop at a timeNode receives complete
packet before forwarding
Introduction
-
Introduction1-*Packet Switching: Statistical
MultiplexingSequence of A & B packets does not have fixed
pattern, bandwidth shared on demand statistical multiplexing.TDM:
each host gets same slot in revolving TDM frame.
ABC100 Mb/sEthernet1.5 Mb/sstatistical multiplexingqueue of
packetswaiting for outputlink
Introduction
-
Introduction1-*Packet-switching: store-and-forwardtakes L/R
seconds to transmit (push out) packet of L bits on to link at R
bpsstore and forward: entire packet must arrive at router before it
can be transmitted on next linkdelay = 3L/R (assuming zero
propagation delay)Example:L = 7.5 MbitsR = 1.5 Mbpstransmission
delay = 15 secRRRLmore on delay shortly
Introduction
-
Introduction1-*Packet switching versus circuit switching1 Mb/s
linkeach user: 100 kb/s when activeactive 10% of time
circuit-switching: 10 userspacket switching: with 35 users,
probability > 10 active at same time is less than .0004
Packet switching allows more users to use network!N users1 Mbps
link
Introduction
-
Introduction1-*Packet switching versus circuit switchinggreat
for bursty dataresource sharingsimpler, no call setupexcessive
congestion: packet delay and lossprotocols needed for reliable data
transfer, congestion controlQ: How to provide circuit-like
behavior?bandwidth guarantees needed for audio/video appsstill an
unsolved problem (chapter 7)Is packet switching a slam dunk
winner?Q: human analogies of reserved resources (circuit switching)
versus on-demand allocation (packet-switching)?
Introduction
-
Introduction1-*Internet structure: network of networksroughly
hierarchicalat center: tier-1 ISPs (e.g., Verizon, Sprint,
AT&T, Cable and Wireless), national/international coveragetreat
each other as equalsTier 1 ISPTier 1 ISPTier 1 ISP
Introduction
-
Introduction1-*Tier-1 ISP: e.g., Sprint
Introduction
-
Introduction1-*Internet structure: network of networksTier-2
ISPs: smaller (often regional) ISPsConnect to one or more tier-1
ISPs, possibly other tier-2 ISPs
Tier 1 ISPTier 1 ISPTier 1 ISP
Introduction
-
Introduction1-*Internet structure: network of networksTier-3
ISPs and local ISPs last hop (access) network (closest to end
systems)
Tier 1 ISPTier 1 ISPTier 1 ISP
Introduction
-
Introduction1-*Internet structure: network of networksa packet
passes through many networks!
Tier 1 ISPTier 1 ISPTier 1 ISP
Introduction
-
Introduction1-*Chapter 1: roadmap1.1 What is the Internet?1.2
Network edge end systems, access networks, links1.3 Network core
circuit switching, packet switching, network structure1.4 Delay,
loss and throughput in packet-switched networks1.5 Protocol layers,
service models1.6 Networks under attack: security1.7 History
Introduction
-
Introduction1-*How do loss and delay occur?packets queue in
router buffers packet arrival rate to link exceeds output link
capacitypackets queue, wait for turnAB
Introduction
-
Introduction1-*Four sources of packet delay1. nodal processing:
check bit errorsdetermine output link2. queueingtime waiting at
output link for transmission depends on congestion level of
router
Introduction
-
Introduction1-*Delay in packet-switched networks3. Transmission
delay:R=link bandwidth (bps)L=packet length (bits)time to send bits
into link = L/R4. Propagation delay:d = length of physical links =
propagation speed in medium (~2x108 m/sec)propagation delay =
d/sNote: s and R are very different quantities!
Introduction
-
Introduction1-*Caravan analogycars propagate at 100 km/hrtoll
booth takes 12 sec to service car (transmission time)car~bit;
caravan ~ packetQ: How long until caravan is lined up before 2nd
toll booth?
Time to push entire caravan through toll booth onto highway =
12*10 = 120 secTime for last car to propagate from 1st to 2nd toll
both: 100km/(100km/hr)= 1 hrA: 62 minutes
Introduction
-
Introduction1-*Caravan analogy (more)Cars now propagate at 1000
km/hrToll booth now takes 1 min to service a carQ: Will cars arrive
to 2nd booth before all cars serviced at 1st booth?
Yes! After 7 min, 1st car at 2nd booth and 3 cars still at 1st
booth.1st bit of packet can arrive at 2nd router before packet is
fully transmitted at 1st router!See Ethernet applet at AWL Web
site
Introduction
-
Introduction1-*Nodal delaydproc = processing delaytypically a
few microsecs or lessdqueue = queuing delaydepends on
congestiondtrans = transmission delay= L/R, significant for
low-speed linksdprop = propagation delaya few microsecs to hundreds
of msecs
Introduction
-
Introduction1-*Queueing delay (revisited)R=link bandwidth
(bps)L=packet length (bits)a=average packet arrival ratetraffic
intensity = La/RLa/R ~ 0: average queueing delay smallLa/R -> 1:
delays become largeLa/R > 1: more work arriving than can be
serviced, average delay infinite!
Introduction
-
Introduction1-*Real Internet delays and routesWhat 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 destinationrouter i will return packets to
sendersender times interval between transmission and reply.
3 probes3 probes3 probes
Introduction
-
Introduction1-*Real Internet delays and routes1 cs-gw
(128.119.240.254) 1 ms 1 ms 2 ms2 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 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 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
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 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136
mstraceroute: gaia.cs.umass.edu to www.eurecom.frThree delay
measurements from gaia.cs.umass.edu to cs-gw.cs.umass.edu * means
no response (probe lost, router not replying)trans-oceaniclink
Introduction
-
Introduction1-*Packet lossqueue (aka buffer) preceding link in
buffer has finite capacitypacket arriving to full queue dropped
(aka lost)lost packet may be retransmitted by previous node, by
source end system, or not at allABpacket being transmittedpacket
arriving tofull buffer is lostbuffer (waiting area)
Introduction
-
Introduction1-*Throughputthroughput: rate (bits/time unit) at
which bits transferred between sender/receiverinstantaneous: rate
at given point in timeaverage: rate over longer period of
timeserver, withfile of F bits to send to clientlink capacity Rs
bits/seclink capacity Rc bits/secserver sends bits (fluid) into
pipe
Introduction
-
Introduction1-*Throughput (more)Rs < Rc What is average
end-end throughput? Rs bits/sec
Introduction
-
Introduction1-*Throughput: Internet scenario10 connections
(fairly) share backbone bottleneck link R
bits/secRsRsRsRcRcRcRper-connection end-end throughput:
min(Rc,Rs,R/10)in practice: Rc or Rs is often bottleneck
Introduction
-
Introduction1-*Chapter 1: roadmap1.1 What is the Internet?1.2
Network edge end systems, access networks, links1.3 Network core
circuit switching, packet switching, network structure1.4 Delay,
loss and throughput in packet-switched networks1.5 Protocol layers,
service models1.6 Networks under attack: security1.7 History
Introduction
-
Introduction1-*Protocol LayersNetworks are complex! many
pieces:hostsrouterslinks of various
mediaapplicationsprotocolshardware, softwareQuestion: Is there any
hope of organizing structure of network?
Or at least our discussion of networks?
Introduction
-
Introduction1-*Organization of air travela series of steps
Introduction
-
Introduction1-*Layering of airline functionalityLayers: each
layer implements a servicevia its own internal-layer actionsrelying
on services provided by layer below
Introduction
-
Introduction1-*Why layering?Dealing with complex
systems:explicit structure allows identification, relationship of
complex systems pieceslayered reference model for
discussionmodularization eases maintenance, updating of
systemchange of implementation of layers service transparent to
rest of systeme.g., change in gate procedure doesnt affect rest of
systemlayering considered harmful?
Introduction
-
Introduction1-*Internet Protocol (TCP/IP) stackapplication:
supporting network applicationsFTP, SMTP, HTTPtransport:
process-to-process process data transferTCP, UDPNetwork/internet:
routing of datagrams from source to destination
(network-to-network)IP, routing proto colslink: data transfer
between neighboring network elements (host-to-host)PPP,
Ethernetphysical: bits on the wire
Introduction
-
Introduction1-*ISO/OSI reference modelpresentation: allow
applications to interpret meaning of data, e.g., encryption,
compression, machine-specific conventionssession: synchronization,
checkpointing, recovery of data exchangeInternet stack missing
these layers!these services, if needed, must be implemented in
applicationneeded?
Introduction
-
Introduction1-*sourceapplicationtransportnetworklinkphysicalsegmentdatagramdestinationapplicationtransportnetworklinkphysicalrouterswitchEncapsulationmessageframe
Introduction
-
Introduction1-*Chapter 1: roadmap1.1 What is the Internet?1.2
Network edge end systems, access networks, links1.3 Network core
circuit switching, packet switching, network structure1.4 Delay,
loss and throughput in packet-switched networks1.5 Protocol layers,
service models1.6 Networks under attack: security1.7 History
Introduction
-
Introduction1-*Network SecurityThe field of network security is
about:how bad guys can attack computer networkshow we can defend
networks against attackshow to design architectures that are immune
to attacksInternet not originally designed with (much) security in
mindoriginal vision: a group of mutually trusting users attached to
a transparent network Internet protocol designers playing
catch-upSecurity considerations in all layers!
Introduction
-
Introduction1-*Bad guys can put malware into hosts via
InternetMalware can get in host from a virus, worm, or trojan
horse. Spyware malware can record keystrokes, web sites visited,
upload info to collection site. Infected host can be enrolled in a
botnet, used for spam and DDoS attacks. Malware is often
self-replicating: from an infected host, seeks entry into other
hosts
Introduction
-
Introduction1-*Bad guys can put malware into hosts via
InternetTrojan horseHidden part of some otherwise useful
softwareToday often on a Web page (Active-X, plugin)Virusinfection
by receiving object (e.g., e-mail attachment), actively
executingself-replicating: propagate itself to other hosts,
usersWorm:infection by passively receiving object that gets itself
executedself- replicating: propagates to other hosts, usersSapphire
Worm: aggregate scans/sec in first 5 minutes of outbreak (CAIDA,
UWisc data)
Introduction
-
Introduction1-*Bad guys can attack servers and network
infrastructureDenial of service (DoS): attackers make resources
(server, bandwidth) unavailable to legitimate traffic by
overwhelming resource with bogus trafficselect targetbreak into
hosts around the network (see botnet)
send packets toward target from compromised hosts
Introduction
-
Introduction1-*The bad guys can sniff packetsPacket sniffing:
broadcast media (shared Ethernet, wireless)promiscuous network
interface reads/records all packets (e.g., including passwords!)
passing byABCWireshark software used for end-of-chapter labs is a
(free) packet-sniffer
Introduction
-
Introduction1-*The bad guys can use false source addressesIP
spoofing: send packet with false source addressABC
Introduction
-
Introduction1-*The bad guys can record and
playbackrecord-and-playback: sniff sensitive info (e.g., password),
and use laterpassword holder is that user from system point of
viewABCsrc:B dest:A user: B; password: foo
Introduction
-
Introduction1-*Network Securitymore throughout this
coursechapter 8: focus on securitycrypographic techniques: obvious
uses and not so obvious uses
Introduction
-
Introduction1-*Chapter 1: roadmap1.1 What is the Internet?1.2
Network edge end systems, access networks, links1.3 Network core
circuit switching, packet switching, network structure1.4 Delay,
loss and throughput in packet-switched networks1.5 Protocol layers,
service models1.6 Networks under attack: security1.7 History
Introduction
-
Introduction1-*Internet History1961: Kleinrock - queueing theory
shows effectiveness of packet-switching1964: Baran -
packet-switching in military nets1967: ARPAnet conceived by
Advanced Research Projects Agency1969: first ARPAnet node
operational
1972: ARPAnet public demonstrationNCP (Network Control Protocol)
first host-host protocol first e-mail programARPAnet has 15
nodes1961-1972: Early packet-switching principles
Introduction
-
Introduction1-*Internet History1970: ALOHAnet satellite network
in Hawaii1974: Cerf and Kahn - architecture for interconnecting
networks1976: Ethernet at Xerox PARCate70s: proprietary
architectures: DECnet, SNA, XNAlate 70s: switching fixed length
packets (ATM precursor)1979: ARPAnet has 200 nodesCerf and Kahns
internetworking principles:minimalism, autonomy - no internal
changes required to interconnect networksbest effort service
modelstateless routersdecentralized controldefine todays Internet
architecture1972-1980: Internetworking, new and proprietary
nets
Introduction
-
Introduction1-*Internet History1983: deployment of TCP/IP1982:
smtp e-mail protocol defined 1983: DNS defined for
name-to-IP-address translation1985: ftp protocol defined1988: TCP
congestion controlnew national networks: Csnet, BITnet, NSFnet,
Minitel100,000 hosts connected to confederation of networks
1980-1990: new protocols, a proliferation of networks
Introduction
-
Introduction1-*Internet HistoryEarly 1990s: ARPAnet
decommissioned1991: NSF lifts restrictions on commercial use of
NSFnet (decommissioned, 1995)early 1990s: Webhypertext [Bush 1945,
Nelson 1960s]HTML, HTTP: Berners-Lee1994: Mosaic, later
Netscapelate 1990s: commercialization of the Web
Late 1990s 2000s:more killer apps: instant messaging, P2P file
sharingnetwork security to forefrontest. 50 million host, 100
million+ usersbackbone links running at Gbps
1990, 2000s: commercialization, the Web, new apps
Introduction
-
Introduction1-*Internet History2007:~500 million hostsVoice,
Video over IPP2P applications: BitTorrent (file sharing) Skype
(VoIP), PPLive (video)more applications: YouTube, gamingwireless,
mobility
Introduction
-
Introduction1-*Introduction: SummaryCovered a ton of
material!Internet overviewwhats a protocol?network edge, core,
access networkpacket-switching versus circuit-switchingInternet
structureperformance: loss, delay, throughputlayering, service
modelssecurityhistoryYou now have: context, overview, feel of
networkingmore depth, detail to follow!
Introduction
*****************************Two simple multiple access control
techniques.
Each mobiles share of the bandwidth is divided into portions for
the uplink and the downlink. Also, possibly, out of band
signaling.
As we will see, used in AMPS, GSM, IS-54/136*The link is 1,536
Mbps, but is time divisioned multiplexed. One circuit uses one
timeslot, which means it gets 1/24th of the link bandwidth. So, one
circuit has a bandwidth of 64 Kbps (=1.536/24).So the actual
transfer time to move 640.000 bits (=640 Kb) over that circuit is
10 seconds (=640/64).Add the connection setup time of 500 msec and
you get a total of 10.500 msec or 10,5 seconds.
*************************************