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Course book:Computer NetworkingTop Down approach 3rd edition
y m urose an e ross
Computer Networks 3rd edition
Introduction 1-1
y n rew . anen aum
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Cha ter 1Computer Networks
Computer Networking:A Top Down ApproachFeaturing the Internet,
.Jim Kurose, Keith Ross
Introduction 1-2
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:Our goal: Overview:
get feel andterminology
whats the Internet whats a protocol?
,laterin course
approach:
ne wor e ge
network core
use Internet as
example
,
Internet/ISP structure
rotocol la ers, service models
network modeling
Introduction 1-3
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C a ter 1: road a
1.2 Network edge.
1.4 Network access and physical media
.
1.6 Protocol layers, service models
.
Introduction 1-4
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Whats the Internet: nuts and bolts view millions of connected
com utin devices: hostsrouter workstation
= end systems running network apps local ISP
servermobile
communication links
fiber, copper, radio,satellite re ional I P transmission rate =
bandwidth
(chunks of data)
company
Introduction 1-5
network
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Whats the Internet: nuts and bolts viewprotocolscontrol sending, router workstation
e.g., TCP, IP, HTTP, FTP, PPP
Internet: network of local ISP
servermobile
networks
loosely hierarchical re ional I Pprivate intranet
Internet standards
RFC: Request for comments IETF: Internet Engineering
Task Force company
Introduction 1-6
network
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Whats the Internet: a service view communication
infrastructure enables
distributed applications: Web, email, games, e-
,
communication services
provided to apps: Connectionless unreliable
connection-orientedreliable
Introduction 1-7
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ats a rotocolhuman protocols:
network protocols:
w a s e me
I have a question
mac nes ra er anhumans
specific msgs sent
activity in Internet
governed by protocols specific actions taken
when msgs received,protocols define format,
order of msgs sent and
entities, and actionstaken on msg
Introduction 1-8
transmission, receipt
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ats a rotocola human protocol and a computer network protocol:
Hi TCP connection
Hi
req
TCP connectiontime?
2:00Get http://www.awl.com/kurose-ross
time
Introduction 1-9
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C a ter 1: road a
1.2 Network edge.
1.4 Network access and physical media
.
1.6 Protocol layers, service models
.
Introduction 1-10
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A closer look at network structure:
applications andhosts
network core: routers network of
networks
access ne wor s,physical media:
Introduction 1-11
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T e networ ed e: end systems (hosts):
e.g. Web, email at edge of network
c en server mo e client host requests, receives
service from always-on server e.g. We rowser server; emai
client/server
peer-peer model: minimal (or no) use of dedicated
servers
e.g. Gnutella, KaZaA,bit torrent
Introduction 1-12
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Network ed e: connectionless service
:
between end systems same as before!
HTTP (Web), FTP (filetransfer), Telnet
UDP - User DatagramProtocol [RFC 768]:
remote ogin , SMTP(email)
unreliable datatransfer
Apps using UDP:
no flow control no congestion control
,teleconferencing, DNS,Internet telephony
Introduction 1-14
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C a ter 1: road a
1.2 Network edge.
1.4 Network access and physical media
.
1.6 Protocol layers, service models
.
Introduction 1-15
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T e Networ Core mesh of interconnected
routers thefundamental
ques on: ow s a atransferred through net?
circuit switchin :dedicated circuit percall: telephone net
pac e -sw c ng: a asent thru net indiscrete chunks
Introduction 1-16
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Network Core: Circuit Switchin
-
reserved for call link bandwidth, switch
capacity
dedicated resources:
circuit-like( uaranteed)
performance call setup required
Introduction 1-17
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Network Core: Circuit Switchinnetwork resources dividing link bandwidth
e.g., an wdivided into pieces
into pieces
frequency division
resource piece idleif
not used b ownin call(no sharing)
Introduction 1-18
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Circuit witc in : and TFDM
Example:
time
TDM
frequency
Introduction 1-19time
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Nu erical exa le
640,000 bits from host A to host B over acircuit-switched network? All links are 1.536 Mbps
Each link uses TDM with 24 slots 500 msec to establish end-to-end circuit
or ou
Introduction 1-20
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Network Core: Packet Switchineach end-end data stream resource contention:
user A, B packets share
network resources
aggrega e resource
demand can exceedamount available
each packet uses full link
bandwidth
congestion: packets
queue, wait for link use resources use as nee e store an orwar :
packets move one hopat a time Node receives complete
packet before forwardingBandwidth division into pieces
Dedicated allocation
Introduction 1-21
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Packet switchin versus circuit switchinPacket switching allows more users to use network!
1 Mb/s link each user:
100 kb/s when active
active 10% of time
circuit-switching:
10 users
1 Mbps link
pac e sw c ng: with 35 users,
probability > 10 active
Introduction 1-23
less than .0004
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Packet switchin versus circuit switchinIs packet switching a slam dunk winner?
Great for bursty data resource sharing
simpler, no call setup
Excessive congestion: packet delay and lossro oco s nee e or re a e a a rans er,congestion control
: How to rovide circuit-like behavior?
bandwidth guarantees needed for audio/videoapps
Introduction 1-24
still an unsolved problem (chapter 6)
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Packet-switchin : store-and- orwardL
Takes L/R seconds to Example:
packet of L bits on to
link or R bps
= . s
R = 1.5 Mbps
= Entire packet must
arrive at router before
on next link: store andforward
Introduction 1-25
e ay =
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Packet-switched networks: forwardin Goal:move packets through routers from source to
well study several path selection (i.e. routing) algorithms(chapter 4)
datagram network: destination address in packet determines next hop
routes ma chan e durin session
analogy: driving, asking directions
virtual circuit network:
eac packet carries tag virtua circuit ID , tagdetermines next hop
fixed path determined at call setup time, remains fixed
Introduction 1-26
t ru ca
routers maintain per-call state
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Network Taxonomy
Telecommunicationnetworks
Circuit-switched Packet-switchednetworks networks
FDM TDM Networkswith VCs
DatagramNetworks
Datagram network is noteither connection-orientedor connectionless. -
Introduction 1-27
connectionless services (UDP) to apps.
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C a ter 1: road a
1.2 Network edge.
1.4 Network access and physical media
.
1.6 Protocol layers, service models
.
Introduction 1-28
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Access networks and h sical mediaQ: How to connect end
residential access nets
networks (school,
company) mo e access networ s
Keep in mind:
an w t ts persecond) of accessnetwork?
Introduction 1-29
shared or dedicated?
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Residential access: oint to oint access
Dialu via modem
up to 56Kbps direct access torouter (often less)
Cant surf and phone at sametime: cant be always on
ADSL: asymmetric digital subscriber line
up to 1 Mbps upstream (today typically < 256 kbps)
FDM: 50 kHz - 1 MHz for downstream
4 kHz - 50 kHz for u stream
Introduction 1-30
0 kHz - 4 kHz for ordinary telephone
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Residential access: cable modems
Introduction 1-32Diagram: http://www.cabledatacomnews.com/cmic/diagram.html
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Cable Network Architecture: Overview
Typically 500 to 5,000 homes
home
cable headend
Introduction 1-33
network (simplified)
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Cable Network Architecture: Overview
home
cable headend
Introduction 1-34
network (simplified)
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Cable Network Architecture: Overview
server(s)
home
cable headend
Introduction 1-35
network
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Cable Network Architecture: Overview
FDM:
VI
D
E
VI
D
E
VI
D
E
VI
D
E
VI
D
E
VI
D
E
D
A
T
D
A
T
C
O
NT
R
O
Channels
1 2 3 4 5 6 7 8 9
home
cable headend
Introduction 1-36
network
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Com an access: local area networks company/univ local area
end system to edge router Ethernet:
shared or dedicated link
connects end system
10 Mbs, 100Mbps,Gi abit Ethernet
LANs: chapter 5
Introduction 1-37
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Wireless access networks shared wirelessaccess
to router via base station aka access
router
po n
wireless LANs: 802.11b (WiFi): 11 Mb s
basestation
wider-area wireless access provided by telco operator
~ ps
Will it happen??
WAP/GPRS in Europe
mobilehosts
Introduction 1-38
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Home networks
Typical home network components:
router/firewall/NAT Ethernet
wireless access
pointwirelesslaptops
router/cableto/from
wirelessaccess
irewamo emheadend
Introduction 1-39
po n
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Ph sical Media Bit: ro a ates between
Twisted Pair (TP)
transmitter/rcvr pairs
physical link: what lies wires Category 3: traditionale ween ransm er
receiver
uided media:
p one w res, psEthernet
Category 5: signals propagate in solid
media: copper, fiber, coax
ps erne
signals propagate freely,
e.g., radio
Introduction 1-40
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Ph sical Media: coax fiberCoaxial cable: Fiber optic cable:
two concentric copper
conductors
pulses, each pulse a bit high-speed operation:
baseband:
single channel on cable
high-speed point-to-pointtransmission (e.g., 5 Gps)
: legacy Ethernet
broadband:
spaced far apart ; immuneto electromagnetic noise
HFC
Introduction 1-41
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Ph sical media: radio signal carried in Radio link types:
spectrum no h sical wire
e.g. up to 45 Mbps channels LAN (e. ., Wifi)
bidirectional
propagation
2Mbps, 11Mbps
wide-area (e.g., cellular)env ronment e ects:
reflection
obstruction b ob ects
e.g. : un re s o ps
satellite u to 50Mb s channel or
interference multiple smaller channels) 270 msec end-end delay
Introduction 1-42
altitude
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C a ter 1: road a
1.2 Network edge.
1.4 Network access and physical media
.1.6 Protocol layers, service models
.
Introduction 1-43
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Internet structure: network of networks roughly hierarchical
at center: tier-1 ISPs (e.g., UUNet, BBN/Genuity,
Sprint, AT&T), national/international coverage
Tier-1 providers
also interconnectTier 1 ISPer-
providersinterconnect
eer
NAP
at public networkaccess points(NAPs)
Tier 1 ISP Tier 1 ISPprivately
Introduction 1-44
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Tier-1 I P: e rintSprint US backbone network
Introduction 1-45
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Internet structure: network of networks
Tier-2 ISPs: smaller (often regional) ISPs onnect to one or more tier- S s, possi y ot er tier- S s
Tier-2 ISPTier-2 ISPTier-2 ISP pays-
Tier-2 ISPsalso peer
privately withTier 1 ISP
NAP
connectivity torest of Internet tier-2 ISP is
each other,interconnectat NAP
Tier 1 ISP Tier 1 ISP
- -
Tier-2 ISP
cus omerotier-1 provider
Introduction 1-46
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Internet structure: network of networks
Tier-3 ISPs and local ISPs ast op access networ c osest to en systems
local
Tier-2 ISPTier-2 ISP
ISPlocalISP
ocaISP
ISP
Local and tier-
3 ISPs areTier 1 ISP
NAPcustomersofhigher tierISPs
Tier 1 ISP Tier 1 ISP
- -
Tier-2 ISP
local
them to restof Internet
Introduction 1-47
localISP
local
ISP
local
ISP
ISP
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Internet structure: network of networks
a packet passes through many networks!
local
Tier-2 ISPTier-2 ISP
ISPlocalISP
ocaISP
ISP
Tier 1 ISPNAP
Tier 1 ISP Tier 1 ISP
- -
Tier-2 ISP
local
Introduction 1-48
localISP
local
ISP
local
ISP
ISP
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C a ter 1: road a
1.2 Network edge.
1.4 Network access and physical media
. 1.6 Protocol layers, service models
.
Introduction 1-49
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Protocol a ersNetworks are complex!
many p eces :
hosts Question:
links of various
media
s ere any ope oorganizingstructure of
network? applications
protocols Or at least our discussion
hardware,software
o ne wor s
Introduction 1-50
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Or anization o air travelticket (purchase) ticket (complain)
baggage (check)
baggage (claim)
gates oa
runway takeoff
ga es un oa
runway landing
airplane routing airplane routing
airplane routing
a series o ste s
Introduction 1-51
Layering of airline functionality
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Layering of airline functionality
ticket (purchase)
baggage (check)gates (load)
ticket (complain)
baggage (claimgates (unload)
ticket
baggage
gate
runway (takeoff)
airplane routing
departure arrivalintermediate air-traffic
airplane routing airplane routing
runway (land)
airplane routing
takeoff/landing
airplane routing
airport airportcontrol centers
Layers: each layer implements a service
via its own internal-layer actions relying on services provided by layer below
Introduction 1-52
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la erinDealing with complex systems:
exp icit structure a ows i enti ication,
relationship of complex systems pieces
modularization eases maintenance, updating of
system change of implementation of layers service
transparent to rest of system
. .,rest of system
la erin considered harmful?
Introduction 1-53
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Internet rotocol stac application: supporting network
app ca ons
FTP, SMTP, STTP trans ort: host-host data transfer
application
TCP, UDP
network: routing of datagrams fromnetwork
source o es na on IP, routing protocols
in : data trans er between
link
neighboring network elements PPP, Ethernet
physical
Introduction 1-54
p ys ca : s on e w re
source Encapsulation
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messa e a licationMEncapsulation
segmentdatagram
frame
transportnetwork
linkHtHnHl MHtHn M
Ht M
physical
linkh sical
HtHnHl M HtHnHl M
switch
destination
a licationM
networklinkHtHnHl M
HtHn M
HtHnHl M
HtHn M
transportnetworklinkHtHnHl M
HtHn M
Ht M
physical
router
Introduction 1-55
physical
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C a ter 1: road a
1.2 Network edge.
1.4 Network access and physical media
. 1.6 Protocol layers, service models
.
Introduction 1-56
Internet History
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Internet History
1961-1972: Early packet-switching principles
-theory showseffectiveness of packet-
:
ARPAnet demonstratedpublicly
1964: Baran - packet-
switching in military nets
NCP Network ControProtocol) first host-host protocol
by Advanced ResearchProjects Agency
irst e-mai program
ARPAnet has 15 nodes
operational
Introduction 1-57
Internet History
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Internet History
:
1972-1980: Internetworking, new and proprietary nets
network in Hawaii
1973: Metcalfes PhD thesis
er an a n sinternetworking principles:
minimalism, autonomy -
1974: Cerf and Kahn -architecture for
no n erna c angesrequired tointerconnect networks
late70s: proprietary
architectures: DECnet, SNA,XNA
model
stateless routers
late 70s: switching fixed
length packets (ATMrecursor
ecentra ze contro
define todays Internetarchitecture
Introduction 1-58
1979: ARPAnet has 200 nodes
Internet History
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Internet History
1990, 2000s: commercialization, the Web, new apps
decommissioned
1991: NSF lifts restrictions on
a e s s:
more killer apps: instantmessaging, P2P file sharing
(decommissioned, 1995)
early 1990s: Web
network security toforefront
est. 50 million host, 100 ypertext us , e son1960s]
HTML, HTTP: Berners-Lee
million+ users
backbone links running atGbps
1994: Mosaic, later Netscape
late 1990s:commercialization of the Web
Introduction 1-59
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Introduction: u arCovered a ton of material! You now have: Internet overview whats a protocol?
context, overview,
feel of networking, ,
network
packet-switching versus
,follow!
circuit-switc ing Internet/ISP structure
,
layering and servicemodels
Introduction 1-60
s ory