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Internet Overview: roadmap
1.1 What is the Internet?
1.2 Network edge
 end systems, access networks, links
1.3 Network core
 network structure, circuit switching, packet switching
1.4 Delay, loss and throughput in Internet
1.5 Protocol layers, service models
1.6 Networks under attack: security
Lecture 1
1-1
How is the Internet Organized
 A hierarchical structure.
 hosts combine to form a Local Area
Network (LAN).
 LANs combine to form an Autonomous
System (AS)
 Autonomous Systems combine to form the
Internet.
Internetworked networks – Internet !
Lecture 1
1-2
What’s the Internet: “nuts and bolts” view
PC
 millions of connected
computing devices:
hosts = end systems
wireless
laptop
 running network
cellular
handheld
apps
 communication links
 fiber, copper,
access
points
radio, satellite
wired
links
 transmission
rate = bandwidth
 routers: forward
router
packets (chunks of
data)
Mobile network
server
Lecture 1
Global ISP
Home network
Regional ISP
Institutional network
1-3
What’s the Internet: “operational” view
Mobile network
 Internet: “network of
networks”

Global ISP
Requires sending, receiving
of messages
 protocols control sending,
Home network
Regional ISP
receiving of messages

e.g., TCP, IP, HTTP, Skype,
Ethernet etc.
Institutional network
 Design of protocols is the
key for Internet
Lecture 1
1-4
What’s the Internet: an operational view
a human protocol and a computer network protocol:
Hi
Hi
Got the
time?
2:00
human protocol
time
Lecture 1
1-5
What’s the Internet: an operational view
human protocols:
… 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
Lecture 1
1-6
What’s a protocol?
a human protocol and a computer network protocol:
Hi
Connection req.
Hi
connection
reply
Got the
time?
Get http://jjcweb.jjay.cuny.edu/ssengupta/slide.ppt
2:00
human protocol
<file>
time
Internet protocol example
Lecture 1
1-7
What’s the Internet: an operational view
Thus protocols define
• format, order of messages sent and
received among network entities,
• actions taken on message
transmission and receipt
• address conflicts among network
entities
Lecture 1
1-8
We have studied a high-level overview of
the Internet!
Now, A closer look at the
Internet structure!
Lecture 1
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Components of Internet:
 Hosts (end-users)
 e.g. computers
 access networks,
physical media:
wired, wireless
communication links
 network core:
 interconnected
routers
 network of
networks
Lecture 1
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The network edge:
 End-users (hosts):


run application programs
e.g. Web, email
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
Lecture 1
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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
Lecture 1
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Residential access: point to point access
 Dialup via modem

up to 56Kbps direct access to
router (conceptually)
 ADSL: asymmetric digital
subscriber line
 up to 1 Mbps home-to-router
 up to 8 Mbps router-to-home
 ADSL deployment: happening
Lecture 1
1-13
Residential access: cable modems
 HFC: hybrid fiber coax
asymmetric: up to 10Mbps upstream, 1 Mbps
downstream
 network of cable and fiber attaches homes to ISP
router
 shared access to router among home
 issues: congestion
 deployment: available via cable companies, e.g.,
MediaOne, CableVision

Lecture 1
1-14
Institutional access: local area networks
 company/univ local area
network (LAN) connects
end system to edge router
 Ethernet:
 shared or dedicated
cable connects end
system and router
 10 Mbps, 100Mbps,
Gigabit Ethernet
 deployment: institutions,
home LANs happening now
Lecture 1
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Wireless access networks
 shared wireless access
network connects end
system to router
 wireless LANs:


router
radio spectrum replaces
wire
e.g., 802.11b/g (WiFi): 11
or 54 Mbps
base
station
 wider-area wireless
access

next up (?): WiMAX (10’s
Mbps) over wide area
Lecture 1
mobile
hosts
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The Client/Server Model
 Client/server model is a basic design for Internet
applications


server - is the information provider
client - is the information consumer
 example
 web server and a client running web browser

a CNN web server simultaneously serves thousands of
clients.
 In this class, we will also learn how to construct
Web pages at the client end!
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Summary: What have we learnt?
 What is Internet?

Components…

Operational view…

System (structure) view…

Client-server and peer to peer model…
 Access Networks…
Lecture 1
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Next Up…
1.1 What is the Internet?
1.2 Network edge
 end systems, access networks, links
1.3 Network core
 network structure, circuit switching, packet switching
1.4 Delay, loss and throughput in Internet
1.5 Protocol layers, service models
1.6 Networks under attack: security
Lecture 1
1-19