Chapter 1: Introduction
Our goal:
Overview:
 get “feel” and
 what’s the Internet
terminology
 more depth, detail
later in course
 approach:
 use Internet as
example
 what’s a protocol?
 network edge
 network core
 access net, physical media
 Internet/ISP structure
 performance: loss, delay
 protocol layers, service models
 network modeling
Introduction
1-1
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
1-2
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
1-3
“Cool” internet appliances
Tweet-a-watt:
monitor energy use
Internet gaming, chatting
Computer in refrigerator
Radio
Frequency
Identification
(RFID)
IP picture frame
http://www.ceiva.com/
Internet phones
Google map on smartphone
Introduction
1-4
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
1-5
What’s the Internet: a service view
 communication infrastructure
enables distributed
applications:
 Web, VoIP, email, games, ecommerce, file sharing
 communication services
provided to apps:
 reliable data delivery from
source to destination
 “best effort” (unreliable)
data delivery
 Provide a comment playground
for everyone
Introduction
1-6
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
1-7
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
1-8
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
1-9
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
1-10
The network edge:
 end systems (hosts):



run application programs
e.g. Web, email
at “edge of network”
peer-peer
 client/server model


client host requests, receives
service from always-on server
client/server
e.g. Web browser/server;
email client/server
 peer-peer model:


minimal (or no) use of
dedicated servers
e.g. Skype, BitTorrent, Joost
Introduction
1-11
Network edge:
connection-oriented service (TCP)
Goal: data transfer
between end systems
 handshaking: setup
(prepare for) data
transfer ahead of time


Hello, hello back human
protocol
set up “state” in two
communicating hosts
 TCP - Transmission
Control Protocol

Internet’s connectionoriented service
TCP service [RFC 793]
 reliable, in-order byte-
stream data transfer

loss: acknowledgements
and retransmissions
 flow control:
 sender won’t overwhelm
receiver
 congestion control:
 senders “slow down sending
rate” when network
congested
Introduction
1-12
Network edge:
connectionless service (UDP)
Goal: data transfer
between end systems

same as before!
 UDP - User Datagram
Protocol [RFC 768]:
 connectionless
 unreliable data
transfer
 no flow control
 no congestion control
 No need to setup
App’s using TCP:
 HTTP (Web), FTP (file
transfer), Telnet/ssh
(remote login), SMTP
(email)
App’s using UDP:
 streaming media,
teleconferencing, DNS,
Internet telephony
Introduction
1-13
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
1-14
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
1-15
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
1-16
Access net: cable network
cable headend
…
cable splitter
modem
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Channels
frequency division multiplexing: different channels transmitted
in different frequency bands
Introduction
1-17
Access net: cable network
cable headend
…
cable splitter
modem
data, TV transmitted at different
frequencies over shared cable
distribution network


CMTS
cable modem
termination system
ISP
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
1-18
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
1-19
Enterprise access networks (Ethernet)
institutional link to
ISP (Internet)
institutional router
Ethernet
switch
institutional mail,
web servers
 typically used in companies, universities, etc


10 Mbps, 100Mbps, 1Gbps, 10Gbps transmission
rates
today, end systems typically connect into Ethernet
Introduction
switch
1-20
Wireless access networks

shared wireless access network connects to router

via base station aka “access point”
wide-area wireless access
wireless LANs:
 within building (100 ft)
 802.11b/g (WiFi): 11, 54 Mbps
transmission rate
 provided by telco (cellular)
operator, 10’s km
 between 1 and 10 Mbps
 3G, 4G: LTE
• WiMAX (31mile, 70Mbps) over
wide area?
• 802.11 mesh network?
to Internet
to Internet
Introduction
1-21
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
1-22
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
1-23
From Google Image: Optical Fiber Cable
Introduction
1-24
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
1-25
From Google Image: Cellular
Tower
Microwave dishes
Cell tower
Introduction
1-26
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
1-27
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
1-28
Harvard School’s New Project:
Kilobot (mimic a swarm of fish)
http://www.eecs.harvard.edu/ssr/projects/progSA/kilobot.html
Introduction
1-29