Transcript Internet - CUNY.edu

Internet Overview: roadmap
1.1 What is the Internet?
1.2 Network edge
 end systems, access networks, links
1.3 Protocol layers, service models
1.4 Network core
 network structure, circuit switching, packet switching
1.5 Delay, loss and throughput in Internet
Lecture 1
1-1
Image courtesy: http://www.seopher.com/images/internet.jpg
What is the Internet?
Internetworked networks – Internet !
Lecture 1
1-2
What is the Internet?
 A vast universe of computer networks growing continuously
 Not just computers but also other mobile devices like our smart
phones, PDAs etc. are also becoming part of it
 Difficult to manage without a proper structure…
 Designed as a hierarchical structure
 A simple example:



Computers combine to form a Local Area Network (LAN) (e.g., our lab)
LANs combine to form an Autonomous System (AS) (e.g., our college or CUNY)
Autonomous Systems combine to form the Internet!
Lecture 1
1-3
What’s the Internet: the “hardware” view
PC
1.
server
wireless
laptop
cellular
handheld
Millions of connected
computing devices:
hosts = end systems

Global ISP
running network apps
Home network
2. Communication links
 Wired (example: fiber,
access
points
copper cables)
wired
 Wireless (example:
links
radio, satellite)
router
Mobile network
Regional ISP
Institutional network
3. Routers
 forward packets
(chunks of data)
Lecture 1
1-4
What’s the Internet: “operational” view
Mobile network
 Internet: “network of
networks”

Global ISP
Requires sending, receiving
of messages
Home network
Regional ISP
 Requires mechanisms
(protocols) to control
sending, receiving of
messages
Institutional network
 Design of protocols is the
key for Internet
Lecture 1
1-5
What’s a protocol?
A protocol is defined as a code of correct conduct.
human protocols:
Hi
Hi
… specific questions asked
… specific actions taken when
questions asked…
… constant learning of protocols
Got the
time?
2:00
human protocol
time
Lecture 1
1-6
What’s a protocol in the Internet?
Internet:
 computers rather than
humans
 But the concept of
protocol remains same

Code of correct conduct
 set of rules which is
used by computers to
communicate with each
other across a network
 As the Internet grows
rapidly so does the
necessity of these
rules (protocols)…
Lecture 1
1-7
A web browsing protocol example
a human protocol and a computer network protocol:
Time request
Slides request
Hi
Connection req.
Hi
Connection reply
Auhtentication req.
Got the
time?
Username, password
Get http://jjcweb.jjay.cuny.edu/ssengupta/slide.ppt
2:00
human protocol
<file>
time
Internet protocol example
Lecture 1
1-8
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
1-9
That is a high-level overview of the
Internet!
Now, A closer look at the
Internet structure!
Lecture 1
1-10
We already know the components of Internet:
 Hosts (end-users)
 e.g. computers
 Access networks,
physical media:
wired, wireless
communication links
 Interconnected
routers
Let’s look at little more detail of each of these components!
Lecture 1
1-11
The network edge: two communication models
 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
1-13
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
1-14
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
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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

WiMAX (10’s Mbps) over
wide area
Lecture 1
mobile
hosts
1-17
Protocol “Layers”
 Millions of operations and
Networks are complex!
conflicts among them:
1.
 Millions of components:
2.
hosts
 routers
 Access networks

3.
4.
5.
6.
7.
Question:
How to organize such complex
structure?
8.

What if multiple computers transmit
at the same time?
What if packets get lost?
How to retransmit packets?
Retransmission: How many times?
What about the other packets?
How to find routes in the Internet?
What if I am browsing web or I am
watching live broadcasting?
How to distinguish among computers
(addressing)?
Just a few mentioned here…
Lecture 1
1-18
An analogy: Organization of airline functionality
ticket (purchase)
ticket (complain)
ticket
baggage (check)
baggage (claim
baggage
gates (load)
gates (unload)
gate
runway (takeoff)
runway (land)
takeoff/landing
airplane routing
airplane routing
airplane routing
departure
airport
airplane routing
airplane routing
intermediate air-traffic
control centers
arrival
airport
 a series of steps
 Layers: each layer implements a service
via its own internal-layer actions
 relying on services provided by layer above/below

 Another example: Postal Service!
Lecture 1
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What are the adv. of layering?
 Reduce the design complexity
 Ease of updating the system
change of implementation of layer’s service
transparent to rest of system
 e.g., Postal service (overnight flight or overnight
ground)

 Network is a huge complex system
 Why not take help of layering architecture?
Lecture 1
1-20
Internet protocol stack
 application


support host/network applications
Email, FTP, HTTP (HTML)
 transport


application
process-process data transfer
transport
TCP, UDP
 network


network
routing of datagrams from
src. to destn.
IP address, routing protocols
 link


data transfer between neighboring network
elements
physical
Ethernet, PPP
 physical

link
bits “on the wire”
(Compare with the Postal System!)
Lecture 1
1-21
ISO/OSI reference model
(Open Systems Interconnection model)
 presentation: allow applications to
interpret meaning of data, e.g.,
encryption, compression, machinespecific conventions
 session: synchronization,
checkpointing, recovery of data
exchange
 The 5-layer protocol stack is more
application
presentation
session
transport
network
link
physical
famous
Lecture 1
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