Chapter 1: Introduction
roadmap
1.1 What is the Internet?
1.2 Network edge
 end systems, access networks, links
1.3 Network core
 circuit switching, packet switching, network structure
1.5 Protocol layers, service models
1.6 Networks under attack: security
Introduction
1-1
What’s the Internet: “nuts and bolts” view
PC
 millions of connected
computing devices:
hosts = end systems
wireless
laptop
 running network
smartphone
apps
 communication links
 fiber, copper,
wireless
links
radio, satellite
wired
links
 transmission
rate = bandwidth
 routers: forward
router
packets (chunks of
data)
Mobile network
Global ISP
server
Home network
Regional ISP
Institutional network
Introduction
1-2
“Cool” internet appliances
(Internet of Things, IOT)
Internet gaming, chatting
Tweet-a-watt:
monitor energy use
Computer in refrigerator
Radio
Frequency
Identification
(RFID)
Internet phones
Nest Thermostat
Introduction
1-3
What’s the Internet: “nuts and bolts” view
 protocols control sending,
Mobile network
receiving of msgs

e.g., TCP, IP, HTTP, Skype,
Ethernet
 Internet: “network of
networks”


loosely hierarchical
public Internet versus
private intranet
Global ISP
Home network
Regional ISP
Institutional network
 Internet standards
 RFC: Request for comments
 IETF: Internet Engineering
Task Force
Introduction
1-4
What’s a protocol?
human protocols:
 “what’s the time?”
 “I have a question”
 introductions
… specific msgs sent
… specific actions taken
when msgs received,
or other events
network protocols:
 machines rather than
humans
 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
Introduction
1-5
What’s a protocol?
a human protocol and a computer network protocol:
Hi
TCP connection
request
Hi
TCP connection
response
Got the
time?
Get http://www.awl.com/kurose-ross
2:00
<file>
time
Introduction
1-6
Chapter 1: roadmap
1.1 What is the Internet?
1.2 Network edge
 end systems, access networks, links
1.3 Network core
 circuit switching, packet switching, network structure
1.4 Delay, loss and throughput in packet-switched
networks
1.5 Protocol layers, service models
1.6 Networks under attack: security
1.7 History
Introduction
1-7
A closer look at network structure:
 network edge:
applications and
hosts
 access networks,
physical media:
wired, wireless
communication links
 network core:
 interconnected
routers
 network of
networks
Introduction
1-8
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
1-9
Residential access: point to point access
 Dialup via modem
up to 56Kbps direct access to
router (often less)
 Can’t surf and phone at same
time: can’t be “always on”

 DSL: digital subscriber line
< 2.5 Mbps upstream transmission rate (typically < 1 Mbps)
 < 24 Mbps downstream transmission rate (typically < 10
Mbps)
 Why asymmetric ? Why not 0 bps for upstream?

Introduction
1-10
Access net: digital subscriber line (DSL)
central office
DSL splitter
modem
voice, data transmitted
at different frequencies over
dedicated line to central office


telephone
network
DSLAM
ISP
DSL access
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
Different ages of phone lines may have different capacities
 Your house may not have the new lines that support the top speed in ads
Introduction
1-11
Access net: cable network
cable headend
…
cable splitter
modem
V
I
D
E
O
V
I
D
E
O
V
I
D
E
O
V
I
D
E
O
V
I
D
E
O
V
I
D
E
O
D
A
T
A
D
A
T
A
C
O
N
T
R
O
L
1
2
3
4
5
6
7
8
9
Channels
frequency division multiplexing: different channels transmitted
in different frequency bands
Introduction
1-12
Access net: home network
wireless
devices
to/from headend or
central office
often combined
in single box
cable or DSL modem
wireless access
point (54 Mbps)
router, firewall, NAT
wired Ethernet (100 Mbps)
Introduction
1-13
Physical Media
 Bit: propagates between
transmitter/rcvr pairs
 physical link: what lies
between transmitter &
receiver
 guided media:

Twisted Pair (TP)
 two insulated copper
wires



Category 5: 100 Mbps, 1
Gpbs Ethernet
Category 6: 10Gbps
Why twisted?
signals propagate in solid
media: copper, fiber, coax
 unguided media:
 signals propagate freely,
e.g., radio
Introduction
1-14
Physical Media: coax, fiber
Coaxial cable:
Fiber optic cable:
conductors
 bidirectional
 baseband:
pulses, each pulse a bit
 high-speed operation:
 two concentric copper


single channel on cable
legacy Ethernet
 broadband:
 multiple channels on
cable
 HFC
 glass fiber carrying light

10’s-100’s Gps
 low error rate: immune to
electromagnetic noise
 Why lights not go out?
Introduction
1-15
From Google Image: Optical Fiber Cable
Introduction
1-16
Physical media: radio
 signal carried in
electromagnetic
spectrum
 no physical “wire”
 bidirectional
 propagation
environment effects:



reflection
obstruction by objects
interference
Radio link types:
 terrestrial microwave
 e.g. up to 45 Mbps channels
 LAN (e.g., Wifi)
 11Mbps, 54 Mbps
 wide-area (e.g., cellular)
 3G cellular: ~ 1 Mbps
 4G (LTE): ~ 1 Gbps (??)
 satellite
 Kbps to 45Mbps channel (or
multiple smaller channels)
 280 msec end-end delay
 geosynchronous versus low
altitude
Introduction
1-17
From Google Image: Cellular
Tower
Microwave dishes
Cell tower
Introduction
1-18
Wireless Sensor Network
Sensor nodes monitor nearby environment and send
back sensed information
Battlefield sensor network
Sensor Mote
Wild life sensor
http://www.cotsjournalonline.com/article
s/view/102158
http://www.eecs.berkeley.edu/IPRO/Summar
y/Old.summaries/03abstracts/polastre.1.html
Introduction
1-19
Wireless Ad Hoc Network
 Decentralized network
No fixed network infrastructure, routers
 Mostly nodes are mobile

Emergency ad
hoc network
Unmanned mini helicopter
with wireless relay node
Introduction
1-20
Harvard School’s Project:
Kilobot (mimic a swarm of fish)
http://www.eecs.harvard.edu/ssr/projects/progSA/kilobot.html
Introduction
1-21
Chapter 1: roadmap
1.1 What is the Internet?
1.2 Network edge
 end systems, access networks, links
1.3 Network core
 circuit switching, packet switching, network structure
1.4 Delay, loss and throughput in packet-switched
networks
1.5 Protocol layers, service models
1.6 Networks under attack: security
1.7 History
Introduction
1-22
The Network Core
 mesh of interconnected
routers
 the fundamental
question: how is data
transferred through net?
 circuit switching:
dedicated circuit per
call: telephone net
 packet-switching: data
sent thru net in
discrete “chunks”
Introduction
1-23
Network Core: Circuit Switching
network resources
(e.g., bandwidth)
divided into “pieces”
 pieces allocated to calls
 resource piece idle if
 dividing link bandwidth
into “pieces”
 frequency division
 time division
not used by owning call
(no sharing)
Introduction
1-24
Circuit Switching: FDM and TDM
Example:
FDM
4 users
frequency
TDM (GSM uses this)
time
frequency
time
TDMA: Time Division Multiplexing Access
Introduction
1-25
Network Core: Packet Switching
each end-end data stream
divided into packets
 user A, B packets share
network resources
 each packet uses full link
bandwidth
 resources used as needed
Bandwidth division into “pieces”
Dedicated allocation
Resource reservation
C
A
B
D
Introduction
1-26
Network Core: Packet Switching
resource contention:
 aggregate resource demand can exceed amount
available
 congestion: packets queue, wait for link use
 store and forward: packets move one hop at a time

Node receives complete packet before forwarding
C
A
B
D
Introduction
1-27
Two key network-core functions
routing: determines source-
destination route taken by packets
 routing algorithms
forwarding: move packets from
router’s input to appropriate
router output
routing algorithm
local forwarding table
header value
0100
0101
0111
1001
output link
1
3
2
2
1
3 2
dest address in arriving
packet’s header
Network Layer
4-28
Packet switching versus circuit switching
packet switching allows more users to use network!
example:
 1 Mb/s link
 each user:
•
•

100 kb/s when “active”
active 10% of time
1 Mbps link
circuit-switching:


N
users
10 users
packet switching:

with 35 users, probability >
10 active at same time is
less than .0004 *
Q: how did we get value 0.0004?
Q: what happens if > 35 users ?
* Check out the online interactive exercises for more examples
Introduction
1-29
Packet switching versus circuit switching
Is packet switching a “slam dunk winner?”
 Great for bursty data
resource sharing
 simpler, no call setup
 Excessive congestion: 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
 QoS – Quality of Service
 still an unsolved problem (chapter 7)

Introduction
1-30
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
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
Internet structure: network of networks
Option: connect each access ISP to every other access ISP?
access
net
access
net
access
net
access
net
access
net
access
net
access
net
connecting each access ISP to
each other directly doesn’t scale:
O(N2) connections.
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
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
net
access
net
access
net
access
net
global
ISP
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
net
access
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
net
access
net
access
net
access
net
ISP A
access
net
access
net
access
net
ISP B
ISP C
access
net
access
net
access
net
access
net
access
net
access
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
net
access
net
access
net
access
net
access
net
IXP
access
net
ISP A
IXP
access
net
access
net
access
net
access
net
ISP B
ISP C
access
net
peering link
access
net
access
net
access
net
access
net
access
net
Internet structure: network of networks
… and regional networks may arise to connect access nets to ISPs
access
net
access
net
access
net
access
net
access
net
IXP
access
net
ISP A
IXP
access
net
access
net
access
net
access
net
ISP B
ISP C
access
net
access
net
regional net
access
net
access
net
access
net
access
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
net
access
net
IXP
access
net
ISP A
access
net
Content provider network
IXP
access
net
access
net
access
net
ISP B
ISP B
access
net
access
net
regional net
access
net
access
net
access
net
access
net
Internet structure: network of networks
Tier 1 ISP
Tier 1 ISP
IXP
IXP
Regional ISP
access
ISP

access
ISP
Google
access
ISP
access
ISP
IXP
Regional ISP
access
ISP
access
ISP
access
ISP
access
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
its data centers to Internet, often bypassing tier-1, regional ISPs
Introduction
1-39
Tier-1 ISP: e.g., Sprint
POP: point-of-presence
to/from backbone
peering
…
…
…
…
…
to/from customers
Introduction
1-40
“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 probes
3 probes
3 probes
Introduction
1-41
“Real” Internet delays and routes
traceroute: gaia.cs.umass.edu to www.eurecom.fr
Three 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-oceanic
8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms
link
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 * * *
* means no response (probe lost, router not replying)
18 * * *
19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms
Under Windows is “tracert”
Introduction
1-42
Traceroute from My Home Computer (last year)
Introduction
1-43
Traceroute from My Home
Computer (another time)
Introduction
1-44
Introduction
1-45
Online Traceroute Tools
 Because UCF campus network blocks all
ICMP packets, you need an outside machine
to try it.
Try on http://tools.pingdom.com/ping/
 Try from different countries from
www.traceroute.org
 Check traceroute virtual path at:

• http://traceroute.monitis.com/
and
• http://www.yougetsignal.com/tools/visual-tracert/
Introduction
1-46
Chapter 1: roadmap
1.1 What is the Internet?
1.2 Network edge
 end systems, access networks, links
1.3 Network core
 circuit switching, packet switching, network structure
1.4 Delay, loss and throughput in packet-switched
networks
1.5 Protocol layers, service models
1.6 Networks under attack: security
1.7 History
Introduction
1-47
Protocol “Layers”
Networks are complex!
 many “pieces”:
 hosts
 routers
 links of various
media
 applications
 protocols
 hardware,
software
Question:
Is there any hope of
organizing structure of
network?
Or at least our discussion
of networks?
Introduction
1-48
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?
 Duplicate functions
Introduction
1-49
Internet protocol stack
 application: supporting network
applications

FTP, SMTP, STTP
application
 transport: host-host data transfer
 TCP, UDP
transport
 network: routing of datagrams from
network
source to destination

IP, routing protocols
 link: data transfer between
neighboring network elements

link
physical
PPP, Ethernet
 physical: bits “on the wire”
Introduction
1-50
ISO/OSI reference model
 presentation: allow applications to
interpret meaning of data, e.g.,
encryption, compression, machinespecific conventions
 session: synchronization,
checkpointing, recovery of data
exchange
 Internet stack “missing” these
layers!
 these services, if needed, must
be implemented in application
 needed?
application
presentation
session
transport
network
link
physical
Introduction
1-51
source
message
segment Ht
datagram Hn Ht
frame
Hl Hn Ht
M
M
M
M
Encapsulation
application
transport
network
link
physical
Hl Hn Ht
M
link
physical
Hl Hn Ht
M
switch
destination
M
Ht
M
Hn Ht
Hl Hn Ht
M
M
application
transport
network
link
physical
Hn Ht
Hl Hn Ht
M
M
network
link
physical
Hn Ht
Hl Hn Ht
M
M
router
Introduction
1-52
Chapter 1: roadmap
1.1 What is the Internet?
1.2 Network edge
 end systems, access networks, links
1.3 Network core
 circuit switching, packet switching, network structure
1.4 Delay, loss and throughput in packet-switched
networks
1.5 Protocol layers, service models
1.6 Networks under attack: security
1.7 History
Introduction
1-53
Network Security
 attacks on Internet infrastructure:
 infecting/attacking hosts: malware, spyware,
worms, unauthorized access (data stealing, user
accounts)
 denial of service: deny access to resources
(servers, link bandwidth)
 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
1-54
What can bad guys do: malware?
 Spyware:
 Worm:
 infection by downloading
 infection by passively
web page with spyware
receiving object that gets
itself executed
 records keystrokes, web
sites visited, upload info
 self- replicating: propagates
to collection site
to other hosts, users
 Virus
 infection by receiving
object (e.g., e-mail
attachment), actively
executing
 self-replicating:
propagate itself to
other hosts, users
Sapphire Worm: aggregate scans/sec
in first 5 minutes of outbreak (CAIDA, UWisc data)
Introduction
1-55
Denial of service attacks
 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 malware)
3. send packets toward
target from
compromised hosts
target
Introduction
1-56
Sniff, modify, delete your packets
Packet sniffing:
broadcast media (shared Ethernet, wireless)
 promiscuous network interface reads/records all
packets (e.g., including passwords!) passing by

C
A
src:B dest:A
payload
B
Ethereal software used for end-of-chapter labs
is a (free) packet-sniffer
 more on modification, deletion later
Introduction

1-57
Masquerade as you
 IP spoofing: send packet with false source address
C
A
src:B dest:A
payload
B
Introduction
1-58
Masquerade as you
 IP spoofing: send packet with false source address
 record-and-playback: sniff sensitive info (e.g.,
password), and use later
 password holder is that user from system point of
view
A
C
src:B dest:A
user: B; password: foo
B
Introduction
1-59
Masquerade as you
 IP spoofing: send packet with false source address
 record-and-playback: sniff sensitive info (e.g.,
password), and use later
 password holder is that user from system point of
view
later …..
C
A
src:B dest:A
user: B; password: foo
B
Introduction
1-60
Network Security
 more throughout this course
 chapter 8: focus on security
 cryptographic techniques
Introduction
1-61
Chapter 1: roadmap
1.1 What is the Internet?
1.2 Network edge
 end systems, access networks, links
1.3 Network core
 circuit switching, packet switching, network structure
1.4 Delay, loss and throughput in packet-switched
networks
1.5 Protocol layers, service models
1.6 Networks under attack: security
1.7 History
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
 circuit switching, packet switching, network structure
1.4 Delay, loss and throughput in packet-switched
networks
1.5 Protocol layers, service models
Added: cellular and mobile technologies
1.6 Networks under attack: security
1.7 History
Introduction
1-63
Cellular and mobile technologies
Overview of smart phone technologies
 Overview of IOS and Andriod operating
systems
 Mobile protocols
 Mobile logical channel descriptions, registration
procedures, encryptions standards
 Mobile identifiers, and Location-based Services

Introduction
1-64
Introduction: Summary
Covered a lot of material!
 Internet overview
 what’s a protocol?
 network edge, core, access
network
 packet-switching versus
circuit-switching
 Internet structure
 performance: loss, delay,
throughput
 layering, service models
 security
 history
You now have:
 context, overview,
“feel” of networking
 more depth, detail to
follow!
Introduction
1-65