1,Introduction 1
Part I,Introduction
Our goal:
r get context,
overview,“feel” of
networking
r more depth,detail
later in course
r approach:
m descriptive
m use Internet as
example
Overview:
r what’s the Internet
r what’s a protocol?
r network edge
r network core
r access net,physical media
r performance,loss,delay
r protocol layers,service models
r backbones,NAPs,ISPs
r history
Assignment,read
chapter 1 in text
1,Introduction 2
What’s the Internet:,nuts and bolts” view
r millions of connected
computing devices,hosts,
end-systems
m pc’s workstations,servers
m PDA’s phones,toasters
running network apps
r communication links
m fiber,copper,radio,
satellite
r routers,forward packets
(chunks) of data thru
network
local ISP
company
network
regional ISP
router workstation
server mobile
1,Introduction 3
“Cool” internet appliances
World’s smallest web server
http://www-ccs.cs.umass.edu/~shri/iPic.html
IP picture frame
http://www.ceiva.com/
Web-enabled toaster+weather forecaster
http://dancing-man.com/robin/toasty/
1,Introduction 4
What’s the Internet:,nuts and bolts” view
r protocols,control sending,
receiving of msgs
m e.g.,TCP,IP,HTTP,FTP,PPP
r Internet:,network of
networks”
m loosely hierarchical
m public Internet versus
private intranet
r Internet standards
m RFC,Request for comments
m IETF,Internet Engineering
Task Force
local ISP
company
network
regional ISP
router workstation
server mobile
1,Introduction 5
What’s the Internet,a service view
r communication
infrastructure enables
distributed applications:
m WWW,email,games,e-
commerce,database.,
voting,file (MP3) sharing
r communication services
provided:
m connectionless
m connection-oriented
r cyberspace [Gibson]:
“a consensual hallucination experienced daily by
billions of operators,in every nation,...."
1,Introduction 6
What’s a protocol?
human protocols:
r,what’s the time?”
r,I have a question”
r introductions
… specific msgs sent
… specific actions taken
when msgs received,
or other events
network protocols:
r machines rather than
humans
r all communication
activity in Internet
governed by protocols
protocols define format,
order of msgs sent and
received among network
entities,and actions
taken on msg
transmission,receipt
1,Introduction 7
What’s a protocol?
a human protocol and a computer network protocol:
Q,Other human protocol?
Hi
Hi
Got the
time?
2:00
TCP connection
req.
TCP connection
reply.
Get http://gaia.cs.umass.edu/index.htm
<file>
time
1,Introduction 8
A closer look at network structure:
r network edge:
applications and
hosts
r network core:
m routers
m network of
networks
r access networks,
physical media:
communication links
1,Introduction 9
The network edge:
r end systems (hosts):
m run application programs
m e.g.,WWW,email
m at,edge of network”
r client/server model
m client host requests,receives
service from server
m e.g.,WWW client (browser)/
server; email client/server
r peer-peer model:
m host interaction symmetric
m e.g.,Gnutella,KaZaA
1,Introduction 10
Network edge,connection-oriented service
Goal,data transfer
between end sys.
r handshaking,setup
(prepare for) data
transfer ahead of time
m Hello,hello back human
protocol
m set up,state” in two
communicating hosts
r TCP - Transmission
Control Protocol
m Internet’s connection-
oriented service
TCP service [RFC 793]
r reliable,in-order byte-
stream data transfer
m loss,acknowledgements
and retransmissions
r flow control:
m sender won’t overwhelm
receiver
r congestion control:
m senders,slow down sending
rate” when network
congested
1,Introduction 11
Network edge,connectionless service
Goal,data transfer
between end systems
m same as before!
r UDP - User Datagram
Protocol [RFC 768],
Internet’s
connectionless service
m unreliable data
transfer
m no flow control
m no congestion control
App’s using TCP:
r HTTP (WWW),FTP
(file transfer),Telnet
(remote login),SMTP
(email)
App’s using UDP:
r streaming media,
teleconferencing,
Internet telephony
1,Introduction 12
The Network Core
r mesh of interconnected
routers
r the fundamental
question,how is data
transferred through net?
m circuit switching:
dedicated circuit per
call,telephone net
m packet-switching,data
sent thru net in
discrete,chunks”
1,Introduction 13
Network Core,Circuit Switching
End-end resources
reserved for,call”
r link bandwidth,switch
capacity
r dedicated resources,
no sharing
r circuit-like
(guaranteed)
performance
r call setup required
1,Introduction 14
Network Core,Circuit Switching
network resources
(e.g.,bandwidth)
divided into,pieces”
r pieces allocated to calls
r resource piece idle if
not used by owning call
(no sharing)
r dividing link bandwidth
into,pieces”
m frequency division
m time division
r dividing link bandwidth
into,pieces”
m frequency division
m time division
1,Introduction 15
Circuit Switching,TDMA and TDMA
FDMA
frequency
time
TDMA
frequency
time
4 users
Example:
1,Introduction 16
Network Core,Packet Switching
each end-end data stream
divided into packets
r user A,B packets share
network resources
r each packet uses full link
bandwidth
r resources used as needed,
resource contention:
r aggregate resource
demand can exceed
amount available
r congestion,packets
queue,wait for link use
r store and forward,
packets move one hop
at a time
m transmit over link
m wait turn at next
link
Bandwidth division into,pieces”
Dedicated allocation
Resource reservation
1,Introduction 17
Network Core,Packet Switching
Packet-switching versus circuit switching,human
restaurant analogy
r other human analogies?
A
B
C10 MbsEthernet
1.5 Mbs
45 Mbs
D E
statistical multiplexing
queue of packets
waiting for output
link
1,Introduction 18
Network Core,Packet Switching
Packet-switching,
store and forward behavior
r break message into
smaller chunks,
“packets”
r Store-and-forward,
switch waits until chunk
has completely arrived,
then forwards/routes
r Q,what if message was
sent as single unit?
1,Introduction 19
Packet switching versus circuit switching
r 1 Mbit link
r each user,
m 100Kbps when,active”
m active 10% of time
r circuit-switching,
m 10 users
r packet switching,
m with 35 users,
probability > 10 active
less than,0004
Packet switching allows more users to use network!
N users
1 Mbps link
1,Introduction 20
Packet switching versus circuit switching
r Great for bursty data
m resource sharing
m no call setup
r Excessive congestion,packet delay and loss
m protocols needed for reliable data transfer,
congestion control
r Q,How to provide circuit-like behavior?
m bandwidth guarantees needed for audio/video
apps
m still an unsolved problem (chapter 6)
Is packet switching a,slam dunk winner?”
1,Introduction 21
Packet-switched networks,routing
r Goal,move packets among routers from source to
destination
m we’ll study several path selection algorithms (chapter 4)
r datagram network:
m destination address determines next hop
m routes may change during session
m analogy,driving,asking directions
r virtual circuit network:
m each packet carries tag (virtual circuit ID),tag
determines next hop
m fixed path determined at call setup time,remains fixed
thru call
m routers maintain per-call state
1,Introduction 22
Access networks and physical media
Q,How to connection end
systems to edge router?
r residential access nets
r institutional access
networks (school,
company)
r mobile access networks
Keep in mind,
r bandwidth (bits per
second) of access
network?
r shared or dedicated?
1,Introduction 23
Residential access,point to point access
r Dialup via modem
m up to 56Kbps direct access to
router (conceptually)
r ISDN,integrated services
digital network,128Kbps all-
digital connect to router
r ADSL,asymmetric digital
subscriber line
m up to 1 Mbps home-to-router
m up to 8 Mbps router-to-home
m ADSL deployment,happening
1,Introduction 24
Residential access,cable modems
r HFC,hybrid fiber coax
m asymmetric,up to 10Mbps upstream,1 Mbps
downstream
r network of cable and fiber attaches homes to
ISP router
m shared access to router among home
m issues,congestion,dimensioning
r deployment,available via cable companies,e.g.,
MediaOne
1,Introduction 25
Residential access,cable modems
Diagram,http://www.cabledatacomnews.com/cmic/diagram.html
1,Introduction 26
Institutional access,local area networks
r company/univ local area
network (LAN) connects
end system to edge router
r Ethernet:
m shared or dedicated
cable connects end
system and router
m 10 Mbs,100Mbps,
Gigabit Ethernet
r deployment,institutions,
home LANs happening now
r LANs,chapter 5
1,Introduction 27
Wireless access networks
r shared wireless access
network connects end
system to router
r wireless LANs:
m radio spectrum replaces
wire
m e.g.,Lucent Wavelan 11
Mbps
r wider-area wireless
access
m CDPD,wireless access to
ISP router via cellular
network
base
station
mobile
hosts
router
1,Introduction 28
Home networks
Typical home network components,
r ADSL or cable modem
r router/firewall
r Ethernet
r wireless access
point
wireless
access
point
wireless
laptopsrouter/
firewall
cable
modem
to/from
cable
headend
Ethernet
(switched)
1,Introduction 29
Physical Media
r physical link:
transmitted data bit
propagates across link
r guided media:
m signals propagate in
solid media,copper,
fiber
r unguided media:
m signals propagate
freely,e.g.,radio
Twisted Pair (TP)
r two insulated copper
wires
m Category 3,traditional
phone wires,10 Mbps
Ethernet
m Category 5 TP,
100Mbps Ethernet
1,Introduction 30
Physical Media,coax,fiber
Coaxial cable:
r wire (signal carrier)
within a wire (shield)
m baseband,single channel
on cable
m broadband,multiple
channel on cable
r bidirectional
r common use in 10Mbs
Ethernet
Fiber optic cable:
r glass fiber carrying
light pulses
r high-speed operation:
m 100Mbps Ethernet
m high-speed point-to-point
transmission (e.g.,5 Gps)
r low error rate
1,Introduction 31
Physical media,radio
r signal carried in
electromagnetic
spectrum
r no physical,wire”
r bidirectional
r propagation
environment effects:
m reflection
m obstruction by objects
m interference
Radio link types:
r microwave
m e.g,up to 45 Mbps channels
r LAN (e.g.,WaveLAN)
m 2Mbps,11Mbps
r wide-area (e.g.,cellular)
m e.g,CDPD,10’s Kbps
r satellite
m up to 50Mbps channel (or
multiple smaller channels)
m 270 Msec end-end delay
m geosynchronous versus
LEOS
1,Introduction 32
Delay in packet-switched networks
packets experience delay
on end-to-end path
r four sources of delay
at each hop
r nodal processing,
m check bit errors
m determine output link
r queueing
m time waiting at output
link for transmission
m depends on congestion
level of router
A
B
propagation
transmission
nodal
processing queueing
1,Introduction 33
Delay in packet-switched networks
Transmission delay:
r R=link bandwidth (bps)
r L=packet length (bits)
r time to send bits into
link = L/R
Propagation delay:
r d = length of physical link
r s = propagation speed in
medium (~2x108 m/sec)
r propagation delay = d/s
A
B
propagation
transmission
nodal
processing queueing
Note,s and R are very
different quantities!
1,Introduction 34
Queueing delay (revisited)
r R=link bandwidth (bps)
r L=packet length (bits)
r a=average packet
arrival rate
traffic intensity = La/R
r La/R ~ 0,average queueing delay small
r La/R -> 1,delays become large
r La/R > 1,more,work” arriving than can be
serviced,average delay infinite!
1,Introduction 35
“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,routers,rt delays on source-dest path
also,pingplotter,various windows programs
1,Introduction 36
Protocol,Layers”
Networks are complex!
r many,pieces”:
m hosts
m routers
m links of various
media
m applications
m protocols
m hardware,
software
Question:
Is there any hope of
organizing structure of
network?
Or at least our discussion
of networks?
1,Introduction 37
Organization of air travel
r a series of steps
ticket (purchase)
baggage (check)
gates (load)
runway takeoff
airplane routing
ticket (complain)
baggage (claim)
gates (unload)
runway landing
airplane routing
airplane routing
1,Introduction 38
Organization of air travel,a different view
Layers,each layer implements a service
m via its own internal-layer actions
m relying on services provided by layer below
ticket (purchase)
baggage (check)
gates (load)
runway takeoff
airplane routing
ticket (complain)
baggage (claim)
gates (unload)
runway landing
airplane routing
airplane routing
1,Introduction 39
Layered air travel,services
Counter-to-counter delivery of person+bags
baggage-claim-to-baggage-claim delivery
people transfer,loading gate to arrival gate
runway-to-runway delivery of plane
airplane routing from source to destination
1,Introduction 40
Distributed implementation of layer functionality
ticket (purchase)
baggage (check)
gates (load)
runway takeoff
airplane routing
ticket (complain)
baggage (claim)
gates (unload)
runway landing
airplane routing
airplane routing
De
par
tin
g
air
po
rt
ar
rivi
ng
ai
rp
or
t
intermediate air traffic sites
airplane routing airplane routing
1,Introduction 41
Why layering?
Dealing with complex systems:
r explicit structure allows identification,
relationship of complex system’s pieces
m layered reference model for discussion
r modularization eases maintenance,updating of
system
m change of implementation of layer’s service
transparent to rest of system
m e.g.,change in gate procedure doesn’t affect
rest of system
r layering considered harmful?
1,Introduction 42
Internet protocol stack
r application,supporting network
applications
m ftp,smtp,http
r transport,host-host data transfer
m tcp,udp
r network,routing of datagrams from
source to destination
m ip,routing protocols
r link,data transfer between
neighboring network elements
m ppp,ethernet
r physical,bits,on the wire”
application
transport
network
link
physical
1,Introduction 43
Layering,logical communication
application
transport
network
link
physical
application
transport
network
link
physical application
transport
network
link
physical
application
transport
network
link
physical
network
link
physical
Each layer:
r distributed
r,entities”
implement
layer functions
at each node
r entities
perform
actions,
exchange
messages with
peers
1,Introduction 44
Layering,logical communication
application
transport
network
link
physical
application
transport
network
link
physical application
transport
network
link
physical
application
transport
network
link
physical
network
link
physical
data
data
E.g.,transport
r take data from app
r add addressing,
reliability check
info to form
“datagram”
r send datagram to
peer
r wait for peer to
ack receipt
r analogy,post
office
data
tra rt
tra ort
ack
1,Introduction 45
Layering,physical communication
application
transport
network
link
physical
application
transport
network
link
physical application
transport
network
link
physical
application
transport
network
link
physical
network
link
physical
data
data
1,Introduction 46
Protocol layering and data
Each layer takes data from above
r adds header information to create new data unit
r passes new data unit to layer below
application
transport
network
link
physical
application
transport
network
link
physical
source destination
M
M
M
M
Ht
HtHn
HtHnHl
M
M
M
M
Ht
HtHn
HtHnHl
message
segment
datagram
frame
1,Introduction 47
Internet structure,network of networks
r roughly hierarchical
r national/international
backbone providers (NBPs)
m e.g,BBN/GTE,Sprint,
AT&T,IBM,UUNet
m interconnect (peer) with
each other privately,or at
public Network Access Point
(NAPs)
r regional ISPs
m connect into NBPs
r local ISP,company
m connect into regional ISPs
NBP A
NBP B
NAP NAP
regional ISP
regional ISP
local
ISP
local
ISP
1,Introduction 48
National Backbone Provider
e.g,Sprint US backbone network
1,Introduction 49
Internet History
r 1961,Kleinrock - queueing
theory shows
effectiveness of packet-
switching
r 1964,Baran - packet-
switching in military nets
r 1967,ARPAnet conceived
by Advanced Research
Projects Agency
r 1969,first ARPAnet node
operational
r 1972:
m ARPAnet demonstrated
publicly
m NCP (Network Control
Protocol) first host-
host protocol
m first e-mail program
m ARPAnet has 15 nodes
1961-1972,Early packet-switching principles
1,Introduction 50
Internet History
r 1970,ALOHAnet satellite
network in Hawaii
r 1973,Metcalfe’s PhD thesis
proposes Ethernet
r 1974,Cerf and Kahn -
architecture for
interconnecting networks
r late70’s,proprietary
architectures,DECnet,SNA,
XNA
r late 70’s,switching fixed
length packets (ATM
precursor)
r 1979,ARPAnet has 200 nodes
Cerf and Kahn’s
internetworking principles:
m minimalism,autonomy -
no internal changes
required to
interconnect networks
m best effort service
model
m stateless routers
m decentralized control
define today’s Internet
architecture
1972-1980,Internetworking,new and proprietary nets
1,Introduction 51
Internet History
r 1983,deployment of
TCP/IP
r 1982,smtp e-mail
protocol defined
r 1983,DNS defined
for name-to-IP-
address translation
r 1985,ftp protocol
defined
r 1988,TCP congestion
control
r new national networks,
Csnet,BITnet,
NSFnet,Minitel
r 100,000 hosts
connected to
confederation of
networks
1980-1990,new protocols,a proliferation of networks
1,Introduction 52
Internet History
r Early 1990’s,ARPAnet
decommissioned
r 1991,NSF lifts restrictions
on commercial use of NSFnet
(decommissioned,1995)
r early 1990s,WWW
m hypertext [Bush 1945,
Nelson 1960’s]
m HTML,http,Berners-Lee
m 1994,Mosaic,later
Netscape
m late 1990’s,
commercialization of the
WWW
Late 1990’s:
r est,50 million
computers on
Internet
r est,100 million+
users
r backbone links
running at 1 Gbps
1990’s,commercialization,the WWW
1,Introduction 53
Introduction,Summary
Covered a,ton” of material!
r Internet overview
r what’s a protocol?
r network edge,core,access
network
m packet-switching versus
circuit-switching
r performance,loss,delay
r layering and service
models
r backbones,NAPs,ISPs
r history
You now have:
r context,overview,
“feel” of networking
r more depth,detail
later in course
Part I,Introduction
Our goal:
r get context,
overview,“feel” of
networking
r more depth,detail
later in course
r approach:
m descriptive
m use Internet as
example
Overview:
r what’s the Internet
r what’s a protocol?
r network edge
r network core
r access net,physical media
r performance,loss,delay
r protocol layers,service models
r backbones,NAPs,ISPs
r history
Assignment,read
chapter 1 in text
1,Introduction 2
What’s the Internet:,nuts and bolts” view
r millions of connected
computing devices,hosts,
end-systems
m pc’s workstations,servers
m PDA’s phones,toasters
running network apps
r communication links
m fiber,copper,radio,
satellite
r routers,forward packets
(chunks) of data thru
network
local ISP
company
network
regional ISP
router workstation
server mobile
1,Introduction 3
“Cool” internet appliances
World’s smallest web server
http://www-ccs.cs.umass.edu/~shri/iPic.html
IP picture frame
http://www.ceiva.com/
Web-enabled toaster+weather forecaster
http://dancing-man.com/robin/toasty/
1,Introduction 4
What’s the Internet:,nuts and bolts” view
r protocols,control sending,
receiving of msgs
m e.g.,TCP,IP,HTTP,FTP,PPP
r Internet:,network of
networks”
m loosely hierarchical
m public Internet versus
private intranet
r Internet standards
m RFC,Request for comments
m IETF,Internet Engineering
Task Force
local ISP
company
network
regional ISP
router workstation
server mobile
1,Introduction 5
What’s the Internet,a service view
r communication
infrastructure enables
distributed applications:
m WWW,email,games,e-
commerce,database.,
voting,file (MP3) sharing
r communication services
provided:
m connectionless
m connection-oriented
r cyberspace [Gibson]:
“a consensual hallucination experienced daily by
billions of operators,in every nation,...."
1,Introduction 6
What’s a protocol?
human protocols:
r,what’s the time?”
r,I have a question”
r introductions
… specific msgs sent
… specific actions taken
when msgs received,
or other events
network protocols:
r machines rather than
humans
r all communication
activity in Internet
governed by protocols
protocols define format,
order of msgs sent and
received among network
entities,and actions
taken on msg
transmission,receipt
1,Introduction 7
What’s a protocol?
a human protocol and a computer network protocol:
Q,Other human protocol?
Hi
Hi
Got the
time?
2:00
TCP connection
req.
TCP connection
reply.
Get http://gaia.cs.umass.edu/index.htm
<file>
time
1,Introduction 8
A closer look at network structure:
r network edge:
applications and
hosts
r network core:
m routers
m network of
networks
r access networks,
physical media:
communication links
1,Introduction 9
The network edge:
r end systems (hosts):
m run application programs
m e.g.,WWW,email
m at,edge of network”
r client/server model
m client host requests,receives
service from server
m e.g.,WWW client (browser)/
server; email client/server
r peer-peer model:
m host interaction symmetric
m e.g.,Gnutella,KaZaA
1,Introduction 10
Network edge,connection-oriented service
Goal,data transfer
between end sys.
r handshaking,setup
(prepare for) data
transfer ahead of time
m Hello,hello back human
protocol
m set up,state” in two
communicating hosts
r TCP - Transmission
Control Protocol
m Internet’s connection-
oriented service
TCP service [RFC 793]
r reliable,in-order byte-
stream data transfer
m loss,acknowledgements
and retransmissions
r flow control:
m sender won’t overwhelm
receiver
r congestion control:
m senders,slow down sending
rate” when network
congested
1,Introduction 11
Network edge,connectionless service
Goal,data transfer
between end systems
m same as before!
r UDP - User Datagram
Protocol [RFC 768],
Internet’s
connectionless service
m unreliable data
transfer
m no flow control
m no congestion control
App’s using TCP:
r HTTP (WWW),FTP
(file transfer),Telnet
(remote login),SMTP
(email)
App’s using UDP:
r streaming media,
teleconferencing,
Internet telephony
1,Introduction 12
The Network Core
r mesh of interconnected
routers
r the fundamental
question,how is data
transferred through net?
m circuit switching:
dedicated circuit per
call,telephone net
m packet-switching,data
sent thru net in
discrete,chunks”
1,Introduction 13
Network Core,Circuit Switching
End-end resources
reserved for,call”
r link bandwidth,switch
capacity
r dedicated resources,
no sharing
r circuit-like
(guaranteed)
performance
r call setup required
1,Introduction 14
Network Core,Circuit Switching
network resources
(e.g.,bandwidth)
divided into,pieces”
r pieces allocated to calls
r resource piece idle if
not used by owning call
(no sharing)
r dividing link bandwidth
into,pieces”
m frequency division
m time division
r dividing link bandwidth
into,pieces”
m frequency division
m time division
1,Introduction 15
Circuit Switching,TDMA and TDMA
FDMA
frequency
time
TDMA
frequency
time
4 users
Example:
1,Introduction 16
Network Core,Packet Switching
each end-end data stream
divided into packets
r user A,B packets share
network resources
r each packet uses full link
bandwidth
r resources used as needed,
resource contention:
r aggregate resource
demand can exceed
amount available
r congestion,packets
queue,wait for link use
r store and forward,
packets move one hop
at a time
m transmit over link
m wait turn at next
link
Bandwidth division into,pieces”
Dedicated allocation
Resource reservation
1,Introduction 17
Network Core,Packet Switching
Packet-switching versus circuit switching,human
restaurant analogy
r other human analogies?
A
B
C10 MbsEthernet
1.5 Mbs
45 Mbs
D E
statistical multiplexing
queue of packets
waiting for output
link
1,Introduction 18
Network Core,Packet Switching
Packet-switching,
store and forward behavior
r break message into
smaller chunks,
“packets”
r Store-and-forward,
switch waits until chunk
has completely arrived,
then forwards/routes
r Q,what if message was
sent as single unit?
1,Introduction 19
Packet switching versus circuit switching
r 1 Mbit link
r each user,
m 100Kbps when,active”
m active 10% of time
r circuit-switching,
m 10 users
r packet switching,
m with 35 users,
probability > 10 active
less than,0004
Packet switching allows more users to use network!
N users
1 Mbps link
1,Introduction 20
Packet switching versus circuit switching
r Great for bursty data
m resource sharing
m no call setup
r Excessive congestion,packet delay and loss
m protocols needed for reliable data transfer,
congestion control
r Q,How to provide circuit-like behavior?
m bandwidth guarantees needed for audio/video
apps
m still an unsolved problem (chapter 6)
Is packet switching a,slam dunk winner?”
1,Introduction 21
Packet-switched networks,routing
r Goal,move packets among routers from source to
destination
m we’ll study several path selection algorithms (chapter 4)
r datagram network:
m destination address determines next hop
m routes may change during session
m analogy,driving,asking directions
r virtual circuit network:
m each packet carries tag (virtual circuit ID),tag
determines next hop
m fixed path determined at call setup time,remains fixed
thru call
m routers maintain per-call state
1,Introduction 22
Access networks and physical media
Q,How to connection end
systems to edge router?
r residential access nets
r institutional access
networks (school,
company)
r mobile access networks
Keep in mind,
r bandwidth (bits per
second) of access
network?
r shared or dedicated?
1,Introduction 23
Residential access,point to point access
r Dialup via modem
m up to 56Kbps direct access to
router (conceptually)
r ISDN,integrated services
digital network,128Kbps all-
digital connect to router
r ADSL,asymmetric digital
subscriber line
m up to 1 Mbps home-to-router
m up to 8 Mbps router-to-home
m ADSL deployment,happening
1,Introduction 24
Residential access,cable modems
r HFC,hybrid fiber coax
m asymmetric,up to 10Mbps upstream,1 Mbps
downstream
r network of cable and fiber attaches homes to
ISP router
m shared access to router among home
m issues,congestion,dimensioning
r deployment,available via cable companies,e.g.,
MediaOne
1,Introduction 25
Residential access,cable modems
Diagram,http://www.cabledatacomnews.com/cmic/diagram.html
1,Introduction 26
Institutional access,local area networks
r company/univ local area
network (LAN) connects
end system to edge router
r Ethernet:
m shared or dedicated
cable connects end
system and router
m 10 Mbs,100Mbps,
Gigabit Ethernet
r deployment,institutions,
home LANs happening now
r LANs,chapter 5
1,Introduction 27
Wireless access networks
r shared wireless access
network connects end
system to router
r wireless LANs:
m radio spectrum replaces
wire
m e.g.,Lucent Wavelan 11
Mbps
r wider-area wireless
access
m CDPD,wireless access to
ISP router via cellular
network
base
station
mobile
hosts
router
1,Introduction 28
Home networks
Typical home network components,
r ADSL or cable modem
r router/firewall
r Ethernet
r wireless access
point
wireless
access
point
wireless
laptopsrouter/
firewall
cable
modem
to/from
cable
headend
Ethernet
(switched)
1,Introduction 29
Physical Media
r physical link:
transmitted data bit
propagates across link
r guided media:
m signals propagate in
solid media,copper,
fiber
r unguided media:
m signals propagate
freely,e.g.,radio
Twisted Pair (TP)
r two insulated copper
wires
m Category 3,traditional
phone wires,10 Mbps
Ethernet
m Category 5 TP,
100Mbps Ethernet
1,Introduction 30
Physical Media,coax,fiber
Coaxial cable:
r wire (signal carrier)
within a wire (shield)
m baseband,single channel
on cable
m broadband,multiple
channel on cable
r bidirectional
r common use in 10Mbs
Ethernet
Fiber optic cable:
r glass fiber carrying
light pulses
r high-speed operation:
m 100Mbps Ethernet
m high-speed point-to-point
transmission (e.g.,5 Gps)
r low error rate
1,Introduction 31
Physical media,radio
r signal carried in
electromagnetic
spectrum
r no physical,wire”
r bidirectional
r propagation
environment effects:
m reflection
m obstruction by objects
m interference
Radio link types:
r microwave
m e.g,up to 45 Mbps channels
r LAN (e.g.,WaveLAN)
m 2Mbps,11Mbps
r wide-area (e.g.,cellular)
m e.g,CDPD,10’s Kbps
r satellite
m up to 50Mbps channel (or
multiple smaller channels)
m 270 Msec end-end delay
m geosynchronous versus
LEOS
1,Introduction 32
Delay in packet-switched networks
packets experience delay
on end-to-end path
r four sources of delay
at each hop
r nodal processing,
m check bit errors
m determine output link
r queueing
m time waiting at output
link for transmission
m depends on congestion
level of router
A
B
propagation
transmission
nodal
processing queueing
1,Introduction 33
Delay in packet-switched networks
Transmission delay:
r R=link bandwidth (bps)
r L=packet length (bits)
r time to send bits into
link = L/R
Propagation delay:
r d = length of physical link
r s = propagation speed in
medium (~2x108 m/sec)
r propagation delay = d/s
A
B
propagation
transmission
nodal
processing queueing
Note,s and R are very
different quantities!
1,Introduction 34
Queueing delay (revisited)
r R=link bandwidth (bps)
r L=packet length (bits)
r a=average packet
arrival rate
traffic intensity = La/R
r La/R ~ 0,average queueing delay small
r La/R -> 1,delays become large
r La/R > 1,more,work” arriving than can be
serviced,average delay infinite!
1,Introduction 35
“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,routers,rt delays on source-dest path
also,pingplotter,various windows programs
1,Introduction 36
Protocol,Layers”
Networks are complex!
r many,pieces”:
m hosts
m routers
m links of various
media
m applications
m protocols
m hardware,
software
Question:
Is there any hope of
organizing structure of
network?
Or at least our discussion
of networks?
1,Introduction 37
Organization of air travel
r a series of steps
ticket (purchase)
baggage (check)
gates (load)
runway takeoff
airplane routing
ticket (complain)
baggage (claim)
gates (unload)
runway landing
airplane routing
airplane routing
1,Introduction 38
Organization of air travel,a different view
Layers,each layer implements a service
m via its own internal-layer actions
m relying on services provided by layer below
ticket (purchase)
baggage (check)
gates (load)
runway takeoff
airplane routing
ticket (complain)
baggage (claim)
gates (unload)
runway landing
airplane routing
airplane routing
1,Introduction 39
Layered air travel,services
Counter-to-counter delivery of person+bags
baggage-claim-to-baggage-claim delivery
people transfer,loading gate to arrival gate
runway-to-runway delivery of plane
airplane routing from source to destination
1,Introduction 40
Distributed implementation of layer functionality
ticket (purchase)
baggage (check)
gates (load)
runway takeoff
airplane routing
ticket (complain)
baggage (claim)
gates (unload)
runway landing
airplane routing
airplane routing
De
par
tin
g
air
po
rt
ar
rivi
ng
ai
rp
or
t
intermediate air traffic sites
airplane routing airplane routing
1,Introduction 41
Why layering?
Dealing with complex systems:
r explicit structure allows identification,
relationship of complex system’s pieces
m layered reference model for discussion
r modularization eases maintenance,updating of
system
m change of implementation of layer’s service
transparent to rest of system
m e.g.,change in gate procedure doesn’t affect
rest of system
r layering considered harmful?
1,Introduction 42
Internet protocol stack
r application,supporting network
applications
m ftp,smtp,http
r transport,host-host data transfer
m tcp,udp
r network,routing of datagrams from
source to destination
m ip,routing protocols
r link,data transfer between
neighboring network elements
m ppp,ethernet
r physical,bits,on the wire”
application
transport
network
link
physical
1,Introduction 43
Layering,logical communication
application
transport
network
link
physical
application
transport
network
link
physical application
transport
network
link
physical
application
transport
network
link
physical
network
link
physical
Each layer:
r distributed
r,entities”
implement
layer functions
at each node
r entities
perform
actions,
exchange
messages with
peers
1,Introduction 44
Layering,logical communication
application
transport
network
link
physical
application
transport
network
link
physical application
transport
network
link
physical
application
transport
network
link
physical
network
link
physical
data
data
E.g.,transport
r take data from app
r add addressing,
reliability check
info to form
“datagram”
r send datagram to
peer
r wait for peer to
ack receipt
r analogy,post
office
data
tra rt
tra ort
ack
1,Introduction 45
Layering,physical communication
application
transport
network
link
physical
application
transport
network
link
physical application
transport
network
link
physical
application
transport
network
link
physical
network
link
physical
data
data
1,Introduction 46
Protocol layering and data
Each layer takes data from above
r adds header information to create new data unit
r passes new data unit to layer below
application
transport
network
link
physical
application
transport
network
link
physical
source destination
M
M
M
M
Ht
HtHn
HtHnHl
M
M
M
M
Ht
HtHn
HtHnHl
message
segment
datagram
frame
1,Introduction 47
Internet structure,network of networks
r roughly hierarchical
r national/international
backbone providers (NBPs)
m e.g,BBN/GTE,Sprint,
AT&T,IBM,UUNet
m interconnect (peer) with
each other privately,or at
public Network Access Point
(NAPs)
r regional ISPs
m connect into NBPs
r local ISP,company
m connect into regional ISPs
NBP A
NBP B
NAP NAP
regional ISP
regional ISP
local
ISP
local
ISP
1,Introduction 48
National Backbone Provider
e.g,Sprint US backbone network
1,Introduction 49
Internet History
r 1961,Kleinrock - queueing
theory shows
effectiveness of packet-
switching
r 1964,Baran - packet-
switching in military nets
r 1967,ARPAnet conceived
by Advanced Research
Projects Agency
r 1969,first ARPAnet node
operational
r 1972:
m ARPAnet demonstrated
publicly
m NCP (Network Control
Protocol) first host-
host protocol
m first e-mail program
m ARPAnet has 15 nodes
1961-1972,Early packet-switching principles
1,Introduction 50
Internet History
r 1970,ALOHAnet satellite
network in Hawaii
r 1973,Metcalfe’s PhD thesis
proposes Ethernet
r 1974,Cerf and Kahn -
architecture for
interconnecting networks
r late70’s,proprietary
architectures,DECnet,SNA,
XNA
r late 70’s,switching fixed
length packets (ATM
precursor)
r 1979,ARPAnet has 200 nodes
Cerf and Kahn’s
internetworking principles:
m minimalism,autonomy -
no internal changes
required to
interconnect networks
m best effort service
model
m stateless routers
m decentralized control
define today’s Internet
architecture
1972-1980,Internetworking,new and proprietary nets
1,Introduction 51
Internet History
r 1983,deployment of
TCP/IP
r 1982,smtp e-mail
protocol defined
r 1983,DNS defined
for name-to-IP-
address translation
r 1985,ftp protocol
defined
r 1988,TCP congestion
control
r new national networks,
Csnet,BITnet,
NSFnet,Minitel
r 100,000 hosts
connected to
confederation of
networks
1980-1990,new protocols,a proliferation of networks
1,Introduction 52
Internet History
r Early 1990’s,ARPAnet
decommissioned
r 1991,NSF lifts restrictions
on commercial use of NSFnet
(decommissioned,1995)
r early 1990s,WWW
m hypertext [Bush 1945,
Nelson 1960’s]
m HTML,http,Berners-Lee
m 1994,Mosaic,later
Netscape
m late 1990’s,
commercialization of the
WWW
Late 1990’s:
r est,50 million
computers on
Internet
r est,100 million+
users
r backbone links
running at 1 Gbps
1990’s,commercialization,the WWW
1,Introduction 53
Introduction,Summary
Covered a,ton” of material!
r Internet overview
r what’s a protocol?
r network edge,core,access
network
m packet-switching versus
circuit-switching
r performance,loss,delay
r layering and service
models
r backbones,NAPs,ISPs
r history
You now have:
r context,overview,
“feel” of networking
r more depth,detail
later in course
