Chapter 1

Introduction

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Introduction 1-1
Chapter 1: introduction
our goal: overview:
❖ get “feel” and ❖ what’s the Internet?
terminology ❖ what’s a protocol?
❖ network edge; hosts, access net,
❖ more depth, detail
physical media
later in course ❖ network core: packet/circuit
❖ approach: switching, Internet structure
▪ use Internet as ❖ performance: loss, delay, throughput
example ❖ security
❖ protocol layers, service models
❖ history

Introduction 1-2
Chapter 1: roadmap
1.1 what is the Internet?
1.2 network edge
▪ end systems, access networks, links
1.3 network core
▪ packet switching, circuit switching, network structure
1.4 delay, loss, throughput in networks
1.5 protocol layers, service models
1.6 networks under attack: security
1.7 history

Introduction 1-3
What’s the Internet: “nuts and bolts” view
PC
❖ millions of connected mobile
network
serve
r
computing devices:
wireles ▪ hosts = end systems global
s ISP
laptop
smartphone ▪ running network apps
home
❖ communication links networ
k regional
wireles ▪ fiber, copper, radio, ISP
s
links
satellite
wire
d ▪ transmission rate:
links
bandwidth

❖ Packet switches: forward

route
r
packets (chunks of data) institutional

▪ routers and switches network

Introduction 1-4
“Fun” internet appliances

Web-enabled toaster
+
weather forecaster
IP picture frame
http://www.ceiva.com/

Tweet-a-watt:
monitor energy use

Slingbox: watch,
control cable TV
Internet remotely
refrigerato Internet
r phones
Introduction 1-5
What’s the Internet: “nuts and bolts” view
mobile
❖ Internet: “network of networks” network
▪ Interconnected ISPs
global
❖ protocols control sending, ISP
receiving of msgs
▪ e.g., TCP, IP, HTTP, Skype, 802.11 home
networ
❖ Internet standards k regional
▪ RFC: Request for comments ISP
▪ IETF: Internet Engineering Task
Force

institutional
network

Introduction 1-6
What’s the Internet: a service view
mobile
❖ Infrastructure that network

provides services to global

applications: ISP

▪ Web, VoIP, email, games, e- home

commerce, social nets, … networ
k regional
❖ provides programming ISP
interface to apps
▪ hooks that allow sending
and receiving app
programs to “connect” to
Internet
▪ provides service options, institutional
analogous to postal service network

Introduction 1-7
What’s a protocol?
human protocols: network protocols:
❖ “what’s the time?” ❖ machines rather than
❖ “I have a question” humans
❖ introductions ❖ all communication
activity in Internet
… specific msgs sent governed by protocols
… specific actions taken
when msgs received, or protocols define format,
other events
order of msgs sent and
received among network
entities, and actions
taken on msg
transmission, receipt
Introduction 1-8
What’s a protocol?
a human protocol and a computer network protocol:

H TCP
i connection
H request
TCP
i connection
Got response
the Get http://www.awl.com/kurose-ross
time?
2:0
<file
0
tim >
e

Q: other human protocols?

Introduction 1-9
Chapter 1: roadmap
1.1 what is the Internet?
1.2 network edge
▪ end systems, access networks, links
1.3 network core
▪ packet switching, circuit switching, network structure
1.4 delay, loss, throughput in networks
1.5 protocol layers, service models
1.6 networks under attack: security
1.7 history

Introduction 1-10
 A closer look at network structure:
❖ network edge: mobile
network
▪ hosts: clients and servers
global
▪ servers often in data ISP
centers
home
❖ access networks, networ
k regional
physical media: wired, ISP
wireless
communication links
❖ network core:
▪ interconnected routers
▪ network of networks institutional
network

Introduction 1-11
Access networks and physical media

Q: How to connect end

systems to edge router?
❖ residential access nets
❖ institutional access
networks (school,
company)
❖ mobile access networks
keep in mind:
❖ bandwidth (bits per
second) of access network?
❖ shared or dedicated?

Introduction 1-12
Access net: digital subscriber line (DSL)
central office telephon
e
network

DSL splitte
mode r DSLAM
m

IS
voice, data transmitted
at different frequencies over DSL P
dedicated line to central access
office multiplexer

❖ use existing telephone line to central office DSLAM

▪ data over DSL phone line goes to Internet
▪ voice over DSL phone line goes to telephone net
❖ < 2.5 Mbps upstream transmission rate (typically < 1 Mbps)
❖ < 24 Mbps downstream transmission rate (typically < 10 Mbps)
Introduction 1-13
Access net: cable network
cable headend

cable splitte
mode r
m

C
O
V V V V V V N
I I I I I I D D T
D D D D D D A A R
E E E E E E T T O
O O O O O O A A L

1 2 3 4 5 6 7 8 9
Channel
s
frequency division multiplexing: different channels
transmitted
in different frequency bands
Introduction 1-14
Access net: cable network
cable headend

cable splitte cable modem

mode r CMTS termination system
m
data, TV transmitted at different
frequencies over shared cable IS
distribution network P

❖ HFC: hybrid fiber coax

▪ asymmetric: up to 30Mbps downstream transmission rate,
2 Mbps upstream transmission rate
❖ network of cable, fiber attaches homes to ISP router
▪ homes share access network to cable headend
▪ unlike DSL, which has dedicated access to central office
Introduction 1-15
Access net: home network
wireles
s
devices

to/from headend or
central office
often
combined
in single box

cable or DSL modem

wireless access router, firewall, NAT

point (54 Mbps)
wired Ethernet (100 Mbps)

Introduction 1-16
Enterprise access networks (Ethernet)

institutional link
to
ISP (Internet)
institutional
router
Ethernet institutional
mail,
switch web servers

❖ typically used in companies, universities, etc

❖ 10 Mbps, 100Mbps, 1Gbps, 10Gbps transmission rates
❖ today, end systems typically connect into Ethernet switch

Introduction 1-17
Wireless access networks
❖ shared wireless access network connects end system to router
▪ via base station aka “access point”

wireless LANs: wide-area wireless access

▪ within building (100 ft) ▪ provided by telco (cellular)
▪ 802.11b/g (WiFi): 11, 54 operator, 10’s km
Mbps transmission rate ▪ between 1 and 10 Mbps
▪ 3G, 4G: LTE

to
Internet
to
Internet
Introduction 1-18
 Host: sends packets of data
host sending function:
❖ takes application message
❖ breaks into smaller chunks, two packets,
known as packets, of length L bits each
L bits
❖ transmits packet into access
network at transmission 2 1
rate R R: link transmission rate
▪ link transmission rate, hos
aka link capacity, aka t
link bandwidth

packet time needed to L (bits)

transmission = transmit L-bit =
R (bits/sec)
delay packet into link
1-19
Physical media
❖ bit: propagates between
transmitter/receiver pairs
❖ physical link: what lies twisted pair (TP)
between transmitter & ❖ two insulated copper
receiver wires
❖ guided media: ▪ Category 5: 100 Mbps, 1
Gpbs Ethernet
▪ signals propagate in solid ▪ Category 6: 10Gbps
media: copper, fiber, coax
❖ unguided media:
▪ signals propagate freely, e.
g., radio

Introduction 1-20
Physical media: coax, fiber
coaxial cable: fiber optic cable:
❖ two concentric copper ❖ glass fiber carrying light
conductors pulses, each pulse a bit
❖ bidirectional ❖ high-speed operation:
❖ broadband: ▪ high-speed point-to-point
▪ multiple channels on cable transmission (e.g., 10’s-100’s
Gpbs transmission rate)
▪ HFC
❖ low error rate:
▪ repeaters spaced far apart
▪ immune to electromagnetic
noise

Introduction 1-21
Physical media: radio
❖ signal carried in radio link types:
electromagnetic spectrum ❖ terrestrial microwave
❖ no physical “wire” ▪ e.g. up to 45 Mbps channels
❖ bidirectional ❖ LAN (e.g., WiFi)
❖ propagation environment ▪ 11Mbps, 54 Mbps
effects: ❖ wide-area (e.g., cellular)
▪ reflection ▪ 3G cellular: ~ few Mbps
▪ obstruction by objects ❖ satellite
▪ Kbps to 45Mbps channel (or
▪ interference multiple smaller channels)
▪ 270 msec end-end delay
▪ geosynchronous versus low
altitude

Introduction 1-22
Chapter 1: roadmap
1.1 what is the Internet?
1.2 network edge
▪ end systems, access networks, links
1.3 network core
▪ packet switching, circuit switching, network structure
1.4 delay, loss, throughput in networks
1.5 protocol layers, service models
1.6 networks under attack: security
1.7 history

Introduction 1-23
The network core
❖ mesh of interconnected
routers
❖ packet-switching: hosts
break application-layer
messages into packets
▪ forward packets from one
router to the next, across
links on path from source
to destination
▪ each packet transmitted
at full link capacity

Introduction 1-24
Packet-switching: store-and-forward

L bits
per packet
3 2 1
sour destinati
ce R R
on
bps bps
❖ takes L/R seconds to one-hop numerical
transmit (push out) L-bit
example:
packet into link at R bps
▪ L = 7.5 Mbits
❖ store and forward: entire
packet must arrive at ▪ R = 1.5 Mbps
router before it can be ▪ one-hop transmission
transmitted on next link delay = 5 sec
❖ end-end delay = 2 L/R (assuming
zero propagation delay) more on delay shortly …
Introduction 1-25
Packet Switching: queueing delay, loss

R = 100 Mb/s C
A
D
R = 1.5 Mb/s
B
queue of packets E
waiting for output link

queuing and loss:

❖ If arrival rate (in bits) to link exceeds transmission rate of
link for a period of time:
▪ packets will queue, wait to be transmitted on link
▪ packets can be dropped (lost) if memory (buffer) fills up

Introduction 1-26
 Two key network-core functions
routing: determines source- forwarding: move packets
destination route taken by from router’s input to
packets appropriate router output
▪ routing algorithms

routing algorithm

local forwarding
table value output link
header
010 3 1
0 2
010 2 3 2
1 1
0111 11
01
100
1

dest address in arriving

packet’s header
Network Layer 4-27
Alternative core: circuit switching
end-end resources allocated
to, reserved for “call”
between source & dest:
❖ In diagram, each link has four
circuits.
▪ call gets 2 circuit in top
nd

link and 1st circuit in right

link.
❖ dedicated resources: no sharing
▪ circuit-like (guaranteed)
performance
❖ circuit segment idle if not used
by call (no sharing)
❖ Commonly used in traditional
telephone networks
Introduction 1-28
Circuit switching: FDM versus TDM
Example
FD : users
4
M

frequenc
y
tim
TD
e
M

frequenc
y
tim
e Introduction 1-29
Packet switching versus circuit switching
packet switching allows more users to use network!

example:
▪ 1 Mb/s link
▪ each user: N

….
.
● 100 kb/s when “active” user
s 1 Mbps
● active 10% of time
link
❖ circuit-switching:
▪ 10 users
❖ packet switching: Q: how did we get value
▪ with 35 users, probability >
0.0004?
10 active at same time is less Q: what happens if > 35 users
than .0004 *
?

* Check out the online interactive exercises for more examples Introduction 1-30
Packet switching versus circuit switching
is packet switching a “slam dunk winner?”
❖ great for bursty data
▪ resource sharing
▪ simpler, no call setup
❖ excessive congestion possible: packet delay and loss
▪ protocols needed for reliable data transfer, congestion
control
❖ Q: How to provide circuit-like behavior?
▪ bandwidth guarantees needed for audio/video apps
▪ still an unsolved problem (chapter 7)

Q: human analogies of reserved resources (circuit switching)

versus on-demand allocation (packet-switching)?
Introduction 1-31
Internet structure: network of networks
❖ End systems connect to Internet via access ISPs (Internet
Service Providers)
▪ Residential, company and university ISPs
❖ Access ISPs in turn must be interconnected.
❖ So that any two hosts can send packets to each other
❖ Resulting network of networks is very complex
❖ Evolution was driven by economics and national policies
❖ Let’s take a stepwise approach to describe current Internet
structure
Internet structure: network of networks
Question: given millions of access ISPs, how to connect them
together?
… access
net
access
net
…
access
net
access
access net
net
access
access net
net
…

…
access access
net net

access
net
access
net
access
net
access
… … net
access access
net access net
net
Internet structure: network of networks
Option: connect each access ISP to every other access ISP?

… access
net
access
net
…
access
net
access
access
net … … net

access
access net
net

connecting each access ISP

…

…
to each other directly doesn’t

…
access access
…

net scale: O(N2) connections. net

access
net
access
net
access
net
access
…

… … net
access access
net access net
net
Internet structure: network of networks
Option: connect each access ISP to a global transit ISP?
Customer and provider ISPs have economic agreement.
… access
net
access
net
…
access
net
access
access net
net
access
access net
net
…

…
global
access
net
ISP access
net

access
net
access
net
access
net
access
… … net
access access
net access net
net
Internet structure: network of networks
But if one global ISP is viable business, there will be competitors
….
… access
net
access
net
…
access
net
access
access net
net
access
access net
net ISP A
…

…
access access
net ISP B net

access
ISP
net C access
net
access
net
access
… … net
access access
net access net
net
Internet structure: network of networks
But if one global ISP is viable business, there will be competitors
…. which must be interconnected
Internet exchange point
…
access access
net net
…
access
net
access
access net
net
IX access
access net
net ISP A P
…

…
access
IX access
net P ISP B net

access
ISP
net C access
net
access peering link
net
access
… … net
access access
net access net
net
Internet structure: network of networks
… and regional networks may arise to connect access nets to
ISPS
… access
net
access
net
…
access
net
access
access net
net
IX access
access net
net ISP A P
…

…
access
IX access
net P ISP B net

access
ISP
net C access
net
access
net
regional net
access
… … net
access access
net access net
net
Internet structure: network of networks
… and content provider networks (e.g., Google, Microsoft,
Akamai ) may run their own network, to bring services, content
close to end users
… access
net
access
net
…
access
net
access
access net
net
IX access
access net
net ISP A P
…

…
Content provider network
access
IX access
net P ISP B net

access
ISP B
net
access
net
access
net
regional net
access
… … net
access access
net access net
net
 Internet structure: network of networks

Tier 1 Tier 1
Google
ISP ISP

IXP IXP IXP

Regional Regional
ISP ISP

acc acc acc acc acc acc acc acc

ess ess ess ess ess ess ess ess
ISP ISP ISP ISP ISP ISP ISP ISP

❖ at center: small # of well-connected large networks

▪ “tier-1” commercial ISPs (e.g., Level 3, Sprint, AT&T, NTT), national &
international coverage
▪ content provider network (e.g, Google): private network that connects
it data centers to Internet, often bypassing tier-1, regional ISPs Introduction 1-40
Tier-1 ISP: e.g., Sprint
POP: point-of-
presence
to/from
backbone
peerin
… … g …
…

to/from customers

Introduction 1-41
Chapter 1: roadmap
1.1 what is the Internet?
1.2 network edge
▪ end systems, access networks, links
1.3 network core
▪ packet switching, circuit switching, network structure
1.4 delay, loss, throughput in networks
1.5 protocol layers, service models
1.6 networks under attack: security
1.7 history

Introduction 1-42
How do loss and delay occur?
packets queue in router buffers
❖ packet arrival rate to link (temporarily) exceeds output link
capacity
❖ packets queue, wait for turn
packet being transmitted
(delay)

B
packets queueing
(delay)
free (available) buffers: arriving
packets
dropped (loss) if no free buffers
Introduction 1-43
Four sources of packet delay
transmissio
A n
propagatio
n

B
nodal
processin queuein
g g
dnodal = dproc + dqueue + dtrans + dprop

dproc: nodal processing dqueue: queueing delay

▪ check bit errors ▪ time waiting at output
▪ determine output link link for transmission
▪ typically < msec ▪ depends on congestion
level of router
Introduction 1-44
Four sources of packet delay
transmissio
A n
propagatio
n

B
nodal
processin queuein
g g
dnodal = dproc + dqueue + dtrans + dprop

dtrans: transmission delay: dprop: propagation delay:

▪ L: packet length (bits) ▪ d: length of physical link
▪ R: link bandwidth (bps) ▪ s: propagation speed in medium
▪ dtrans = L/R (~2x108 m/sec)
d trans and d prop ▪ dprop = d/s
very different
* Check out the Java applet for an interactive animation on trans vs. prop delay Introduction 1-45
Caravan analogy
100 km 100 km
ten-car toll toll
carava boot boot
n h h
❖ cars “propagate” at ▪ time to “push” entire
100 km/hr caravan through toll
❖ toll booth takes 12 sec to booth onto highway =
service car (bit transmission 12*10 = 120 sec
time) ▪ time for last car to
❖ car~bit; caravan ~ packet propagate from 1st to
❖ Q: How long until caravan is 2nd toll both: 100km/
lined up before 2nd toll (100km/hr)= 1 hr
booth? ▪ A: 62 minutes

Introduction 1-46
Caravan analogy (more)
100 km 100 km
ten-car toll toll
carava boot boot
n h h
❖ suppose cars now “propagate” at 1000 km/hr
❖ and suppose toll booth now takes one min to service a car
❖ Q: Will cars arrive to 2nd booth before all cars serviced at
first booth?
▪ A: Yes! after 7 min, 1st car arrives at second booth; three
cars still at 1st booth.

Introduction 1-47
Queueing delay (revisited)

average queueing
❖ R: link bandwidth (bps)

delay
❖ L: packet length (bits)
❖ a: average packet arrival
rate
traffic intensity
= La/R
❖ La/R ~ 0: avg. queueing delay small La/R ~
0
❖ La/R -> 1: avg. queueing delay large
❖ La/R > 1: more “work” arriving
than can be serviced, average delay infinite!

* Check out the Java applet for an interactive animation on queuing and loss La/R ->
1 1-48
Introduction
“Real” Internet delays and routes
❖ what do “real” Internet delay & loss look like?
❖ traceroute program: provides delay
measurement from source to router along end-
end Internet path towards destination. For all i:
▪ sends three packets that will reach router i on path
towards destination
▪ router i will return packets to sender
▪ sender times interval between transmission and reply.

3 3
probes probes
3
probes

Introduction 1-49
“Real” Internet delays, routes
traceroute: gaia.cs.umass.edu to www.eurecom.fr
3 delay measurements from
gaia.cs.umass.edu to cs-gw.cs.umass.edu
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 trans-
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 oceanic
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 link
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 * * * * means no response (probe lost, router not replying)
19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms

* Do some traceroutes from exotic countries at www.traceroute.org

Introduction 1-50
Packet loss
❖ queue (aka buffer) preceding link in buffer has finite
capacity
❖ packet arriving to full queue dropped (aka lost)
❖ lost packet may be retransmitted by previous node,
by source end system, or not at all

buffer
(waiting packet being
A transmitted
area)

B
packet arriving
to
full buffer is lost
* Check out the Java applet for an interactive animation on queuing and loss Introduction 1-51
Throughput
❖ throughput: rate (bits/time unit) at which bits
transferred between sender/receiver
▪ instantaneous: rate at given point in time
▪ average: rate over longer period of time

server,sends
server withbits link that can carry
pipe link that can carry
pipe
file of into
(fluid) F bits
pipe capacity
fluid at rate capacity
fluid at rate
to send to Rs bits/sec Rc bits/sec
client Rs bits/sec) Rc bits/sec)

Introduction 1-52
Throughput (more)
❖ 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

bottleneck
link
link on end-end path that constrains end-end throughput
Introduction 1-53
Throughput: Internet scenario

❖ per-connection end-
end throughput: Rs
min(Rc,Rs,R/10) Rs Rs
❖ in practice: Rc or Rs
is often bottleneck
R

Rc Rc

Rc

10 connections (fairly) share

backbone bottleneck link R bits/sec
Introduction 1-54
Chapter 1: roadmap
1.1 what is the Internet?
1.2 network edge
▪ end systems, access networks, links
1.3 network core
▪ packet switching, circuit switching, network structure
1.4 delay, loss, throughput in networks
1.5 protocol layers, service models
1.6 networks under attack: security
1.7 history

Introduction 1-55
Protocol “layers”
Networks are
complex,
with many “pieces”:
▪ hosts Question:
▪ routers is there any hope of
organizing structure of
▪ links of various network?
media
▪ applications
…. or at least our
▪ protocols discussion of networks?
▪ hardware,
software

Introduction 1-56
Organization of air travel
ticket (purchase) ticket
(complain)
baggage
(check) baggage (claim)

gates (load) gates (unload)

runway takeoff runway landing

airplane routing airplane routing

airplane
routing

❖ a series of steps

Introduction 1-57
Layering of airline functionality

ticket (purchase) ticket (complain) ticke

t
baggage (check) baggage (claim baggag
e
gates (load) gates (unload) gat
e
runway (takeoff) runway (land) takeoff/
landing
airplane routing airplane routing airplane routing airplane routing airplane
routing
departur intermediate air- arrival
e traffic airpor
airport control centers t

layers: each layer implements a service

▪ via its own internal-layer actions
▪ relying on services provided by layer below

Introduction 1-58
Why layering?
dealing with complex systems:
❖ explicit structure allows identification,
relationship of complex system’s pieces
▪ layered reference model for discussion
❖ modularization eases maintenance, updating of
system
▪ change of implementation of layer’s service
transparent to rest of system
▪ e.g., change in gate procedure doesn’t affect rest of
system
❖ layering considered harmful?

Introduction 1-59
Internet protocol stack
❖ application: supporting network
applications
▪ FTP, SMTP, HTTP application
❖ transport: process-process data
transfer transport
▪ TCP, UDP
network
❖ network: routing of datagrams
from source to destination
▪ IP, routing protocols link
❖ link: data transfer between
physical
neighboring network elements
▪ Ethernet, 802.111 (WiFi), PPP
❖ physical: bits “on the wire”
Introduction 1-60
ISO/OSI reference model
❖ presentation: allow applications
to interpret meaning of data, e. application
g., encryption, compression,
machine-specific conventions presentation
❖ session: synchronization, session
checkpointing, recovery of transport
data exchange
network
❖ Internet stack “missing” these
layers! link
▪ these services, if needed, must physical
be implemented in application
▪ needed?

Introduction 1-61
 messag M
sourc
e
application
Encapsulation
e H
segmen M transport
t H Ht
datagra M network
m H H
n H
t
fram M link
l n t
e physical
link
physical

switc
h

H H
destination M network
H H
n H
t
H H
M application M link M
l n t
H physical n t
M transport
H H
t
M network
H H
n H
t
route
M link
l n t r
physical

Introduction 1-62
Chapter 1: roadmap
1.1 what is the Internet?
1.2 network edge
▪ end systems, access networks, links
1.3 network core
▪ packet switching, circuit switching, network structure
1.4 delay, loss, throughput in networks
1.5 protocol layers, service models
1.6 networks under attack: security
1.7 history

Introduction 1-63
Network security
❖ field of network security:
▪ how bad guys can attack computer networks
▪ how we can defend networks against attacks
▪ how to design architectures that are immune to
attacks
❖ Internet not originally designed with (much)
security in mind
▪ original vision: “a group of mutually trusting users
attached to a transparent network” ☺
▪ Internet protocol designers playing “catch-up”
▪ security considerations in all layers!

Introduction 1-64
Bad guys: put malware into hosts via Internet
❖ malware can get in host from:
▪ virus: self-replicating infection by receiving/executing
object (e.g., e-mail attachment)
▪ worm: self-replicating infection by passively receiving
object that gets itself executed
❖ spyware malware can record keystrokes, web
sites visited, upload info to collection site
❖ infected host can be enrolled in botnet, used for
spam. DDoS attacks

Introduction 1-65
Bad guys: attack server, network infrastructure
Denial of Service (DoS): attackers make resources
(server, bandwidth) unavailable to legitimate traffic
by overwhelming resource with bogus traffic

1. select target
2. break into hosts around
the network (see botnet)
3. send packets to target from
compromised hosts
targe
t

Introduction 1-66
Bad guys can sniff packets
packet “sniffing”:
▪ broadcast media (shared ethernet, wireless)
▪ promiscuous network interface reads/records all packets
(e.g., including passwords!) passing by

A C

src:B dest:A payload

B

❖ wireshark software used for end-of-chapter labs is a

(free) packet-sniffer
Introduction 1-67
Bad guys can use fake addresses
IP spoofing: send packet with false source address
A C

src:B dest:A payload

… lots more on security (throughout,

Chapter 8)
Introduction 1-68
Chapter 1: roadmap
1.1 what is the Internet?
1.2 network edge
▪ end systems, access networks, links
1.3 network core
▪ packet switching, circuit switching, network structure
1.4 delay, loss, throughput in networks
1.5 protocol layers, service models
1.6 networks under attack: security
1.7 history

Introduction 1-69
Internet history
1961-1972: Early packet-switching principles
❖ 1961: Kleinrock - ❖ 1972:
queueing theory shows ▪ ARPAnet public demo
effectiveness of packet- ▪ NCP (Network Control
switching Protocol) first host-host
❖ 1964: Baran - packet- protocol
switching in military nets ▪ first e-mail program
❖ 1967: ARPAnet ▪ ARPAnet has 15 nodes
conceived by Advanced
Research Projects
Agency
❖ 1969: first ARPAnet
node operational

Introduction 1-70
Internet history
1972-1980: Internetworking, new and proprietary nets
❖ 1970: ALOHAnet satellite
network in Hawaii Cerf and Kahn’s
❖ 1974: Cerf and Kahn - internetworking principles:
architecture for ▪ minimalism, autonomy - no
interconnecting networks internal changes required to
❖ 1976: Ethernet at Xerox PARC interconnect networks
▪ best effort service model
❖ late70’s: proprietary
architectures: DECnet, SNA, ▪ stateless routers
XNA ▪ decentralized control
❖ late 70’s: switching fixed length define today’s Internet
packets (ATM precursor) architecture
❖ 1979: ARPAnet has 200 nodes

Introduction 1-71
Internet history
1980-1990: new protocols, a proliferation of networks
❖ 1983: deployment of TCP/ ❖ new national networks:
IP Csnet, BITnet, NSFnet,
❖ 1982: smtp e-mail Minitel
protocol defined ❖ 100,000 hosts connected
❖ 1983: DNS defined for to confederation of
name-to-IP-address networks
translation
❖ 1985: ftp protocol defined
❖ 1988: TCP congestion
control

Introduction 1-72
Internet history
1990, 2000’s: commercialization, the Web, new apps
❖ early 1990’s: ARPAnet late 1990’s – 2000’s:
decommissioned ❖ more killer apps: instant
❖ 1991: NSF lifts restrictions on messaging, P2P file sharing
commercial use of NSFnet ❖ network security to
(decommissioned, 1995) forefront
❖ early 1990s: Web ❖ est. 50 million host, 100
▪ hypertext [Bush 1945, million+ users
Nelson 1960’s] ❖ backbone links running at
▪ HTML, HTTP: Berners-Lee Gbps
▪ 1994: Mosaic, later Netscape
▪ late 1990’s:
commercialization of the Web

Introduction 1-73
Internet history
2005-present
❖ ~750 million hosts
▪ Smartphones and tablets
❖ Aggressive deployment of broadband access
❖ Increasing ubiquity of high-speed wireless access
❖ Emergence of online social networks:
▪ Facebook: soon one billion users
❖ Service providers (Google, Microsoft) create their own
networks
▪ Bypass Internet, providing “instantaneous” access
to search, emai, etc.
❖ E-commerce, universities, enterprises running their
services in “cloud” (eg, Amazon EC2)

Introduction 1-74
Introduction: summary
covered a “ton” of material! you now have:
❖ Internet overview ❖ context, overview, “feel”
❖ what’s a protocol? of networking
❖ network edge, core, access ❖ more depth, detail to
network follow!
▪ packet-switching versus
circuit-switching
▪ Internet structure
❖ performance: loss, delay,
throughput
❖ layering, service models
❖ security
❖ history

Introduction 1-75