Transcript Chapter 1. Introduction to Data Communications

Chapter 10. The Internet
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Chapter 10. Learning Objectives
• Understand the overall design of the Internet
• Be familiar with DSL, cable modem and
Wireless Application Protocol
• Be familiar with Internet 2
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Chapter 10. Outline
• Introduction
• How the Internet Works
– Basic Architecture, Connecting to an ISP, The
Internet Today
• Internet Access Technologies
– Digital Subscriber Line, Cable Modems, Fixed
Wireless, Mobile Wireless, Future Technologies
• Internet Governance
• Internet 2
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Introduction
• The Internet is not one network but a network of
networks made up of thousands of networks of
national and state government agencies, non-profit
organizations and for-profit companies.
• It exists only to the extent that these networks
agree to use Internet protocols and to exchange
data packets among one another.
• All networks on the Internet must conform to the
_____________ for the transport and network
layers, without which data communications over
the Internet would not be possible.
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How The Internet Works
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Basic Architecture: NAPs and national ISPs
• The Internet has a hierarchical structure.
• At the highest level are large national
___________________________ that
interconnect through Network Access Points
(NAPs).
• The Chicago NAP
• There are about a dozen NAPs in the U.S., run by
common carriers such as Sprint and Ameritech
(Figure 10-1), and many more around the world.
• Regional ISPs interconnect with national ISPs and
provide services to their customers and sell access
to local ISPs who, in turn, sell access to
individuals.
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Basic Architecture: MAEs and local ISPs
• As the number of ISPs has grown, a new type of
network access point, called a metropolitan area
exchange (MAE) has arisen.
• There are about 50 such MAE around the U.S.
today.
• Sometimes large regional and local ISPs also have
access directly to NAPs.
• Indiana University, for example, which provides
services to about 40,000 individuals, connects
directly to the Chicago NAP.
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Figure 10-1 Basic Internet Architecture
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Internet Packet Exchange Charges
• ISPs at the same level usually do not charge
each other for exchanging messages.
• This is called _____________.
• Higher level ISPs, however, charge lower
level ones (national ISPs charge regional
ISPs which in turn charge local ISPs) for
carrying Internet traffic.
• Local ISPs, of course, charge individuals
and corporate users for access.
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Connecting to an ISP
• ISPs provide access to the Internet through a
__________________________________.
• Individual users access the POP through a dial-up line
using the PPP protocol.
• The call connects the user to the ISP’s modem pool, after
which a remote access server (RAS) checks the userid
and password.
• Once logged in, the user can send TCP/IP/[PPP] packets
over the telephone line which are then sent out over the
Internet through the ISP’s POP.
• Corporate users might access the POP using a T-1, T-3 or
ATM OC-3 connections provided by a common carrier.
• Figure 10-2 shows an example of a POP using a collapsed
backbone with a layer 2 switch.
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Individual
Dial-up Customers
ISP POP
ISP Point-of Presence
Modem Pool
ISP POP
Corporate
T1 Customer
T1 CSU/DSU
Layer-2
Switch
Corporate
T3 Customer
ATM
Switch
ISP POP
T3 CSU/DSU
Remote
Access
Server
Corporate
OC-3 Customer
ATM Switch
Figure 10-2 Inside an ISP Point of Presence
NAP/MAE
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From the ISP to the NAP/MAE
• Each ISP acts as an autonomous system, with is own
interior and exterior routing protocols.
• Messages destined for locations within the same ISP are
routed through the ISP’s own network.
• Since most messages are destined for other networks, they
are sent to the nearest MAE or NAP where they get routed
to the appropriate “next hop” network.
• Figure 10-3 shows the connection from the local ISP to the
NAP. From there packets are routed to the next higher
level of ISP.
• Actual connections can be complex and packets
sometimes travel long distances. Each local ISP might
connect a different regional ISP, causing packets to flow
between cities, even though their destination is to another
local ISP within the same city.
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ISP A
ISP D
Router
Router
ATM
Switch
ISP B
ISP E
Router
ISP C
Router
ATM Switch
Route
Server
ISP F
ATM Switch
Figure 10-3 Inside an Internet Network Access Point 13 of 32
Figure 10-4 Three national ISPs in North America
http://www.caida.org/tools/visualization/mapnet/
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Internet Access Technologies
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Internet Access Technologies
?
• Most people today are still using 56K dialup lines to access the Internet, but a number
of new access technologies are now being
offered.
• The main new access technologies are:
–
–
–
–
Digital Subscriber Line
Cable Modems
Fixed Wireless (including satellite access)
Mobile Wireless (WAP)
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Digital Subscriber Line
• Digital Subscriber Line (DSL) is one of the most
promising technologies now being implemented to
significantly increase the data rates over
traditional ____________ lines.
• Historically, voice telephone circuits have had
only a limited capacity for data communications
because they were constrained by the 4 kHz
bandwidth voice channel.
• Most local loop telephone lines actually have a
much higher bandwidth and can therefore carry
data at much higher rates.
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Digital Subscriber Line
• DSL services are quite new and not all common
carriers offer them.
• Two general categories of DSL services have
emerged in the marketplace.
– Symmetric DSL (SDSL) provides the same
transmission rates (up to 128 Kbps) in both directions
on the circuits.
– Asymmetric DSL (ADSL) provides different data rates
to (up to 640 Kbps) and from (up to 6.144 Mbps) the
carrier’s end office. It also includes an analog channel
for voice transmissions.
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Digital Subscriber Line
Download channel
Upload channel
Voice channel
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Customer Premises
DSL Modem
Local Carrier End Office
Main
Distribution
Frame
Line Splitter
Voice
Telephone
Network
Local Loop
Hub
Telephone
ATM Switch
Computer
Computer
Customer
Premises
ISP POP
DSL Access
Multiplexer
ISP POP
ISP POP
ISP POP
Customer
Premises
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Figure 10-5 DSL Architecture
Type
Maximum Length
of Local Loop
Maximum
Downstream
Rate
Maximum
Upstream Rate
T1
18,000 feet
1.5 Mbps
384 Kbps
E1*
16,000 feet
2.0 Mbps
384 Kbps
T2
12,000 feet
6.1 Mbps
384 Kbps
E2*
9,000 feet
8.4 Mbps
640 Kbps
* E1 and E2 are the European standard services similar to
T1 and T2 services in North America
Figure 10-6 ADSL data rates
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Cable Modems
• One potential competitor to DSL is the “cable
modem” a digital service offered by cable
television companies which offers an upstream
rate of 1.5-10 Mbps and a downstream rate of 2-30
Mbps.
• A few cable companies offer downstream services
only, with upstream communications using regular
telephone lines.
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Cable Company
Fiber Node
Customer Premises
Cable Modem
Cable Company Distribution Hub
TV Video
Network
Cable Splitter
Downstream
Optical/Electrical
Converter
Combiner
Upstream
Hub
TV
Router
Computer
Computer
Shared
Coax
Cable
System
Cable
Company
Fiber Node
Cable Modem
Termination
System
Customer
Premises
ISP POP
Customer
Premises
Figure 10-8 Cable Modem Architecture
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Fixed Wireless
• Fixed Wireless is another “dish-based” microwave
transmission technology.
• It requires “_______________” access between
transmitters.
• Both point-to-point and point-multipoint forms are
available.
• Multipoint forms allow access by a limited
number of stations.
• Data access speeds range from 1.5 to 11 Mbps
depending on the vendor.
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Fixed Wireless (Figure 10-9)
• Fig. 10-9 is an example of fixed wireless technology.
• Transmissions travel between transceivers at the customer
premises and ISP’s wireless access office.
• Incoming signals at the customer site are first demultiplexed
and then sent to the MDF where the signal is combined with
voice transmissions.
• This combined signal is then distributed to individual
customer premises where a line splitter separates out the
voice communications.
• The data transmission is then sent to a DSL modem which is
connected to a hub on the customer’s LAN.
• The transceiver at the wireless access office is connected to
a router which then sends outgoing packets over the
Internet.
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Customer Premises
Individual Premise
DSL Modem
Main
Distribution
Frame
Line Splitter
Voice
Telephone
Network
Hub
Telephone
Individual
Premise
Wireless
Transceiver
Individual
Premise
DSL Access
Multiplexer
Computer Computer
Wireless Access Office
Customer
Premises
Wireless
Transceiver
Customer
Premises
Fig. 10-9 Fixed
Wireless Architecture
Router
ISP POP
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Future Access Technologies
• Two potentially important technologies for
Internet access in the near future are:
• Passive Optical Networking (PON)
– PON, also called Fiber to the Home will unleash the
potential of optical fiber communications to end users.
– With WDM hundreds or thousand of channels are
possible. Passive optical doesn’t require electricity,
lowering cost, but limiting its maximum distance.
• Ethernet to the Home
– Gives home users 10BaseT or 100BaseT connections.
– Yipes.com is now doing this in several large US cities.
– The common carrier installs TCP/IP routers connected
to an Ethernet MAN.
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Internet 2
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Internet 2 (Figure 10-11)
• New networks are being developed to develop future Internet
technologies including:
– The very high performance Backbone Network Service
(vBNS) run by Worldcom. 34 universities participate.
– The Abilene network (also called Internet 2) is being
developed by the University Corporation for Advanced
Internet Development (UCAID).
– CA*Net3 is the Canadian government initiative.
• Access is through Gigapops, similar to NAPs, but which
operate at very high speeds (622 Mbps to 2.4 Gbps) using
SONET, ATM and IPv6 protocols.
• Protocol development focuses on issues like Quality of
Service and multicasting.
• New applications include tele-immersion and
videoconferencing.
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Abilene
vBNS
CA*Net 3
Figure 10-11 Gigapops and high speed backbones
of Internet 2/Abilene, vBNS, and CA*Net 3 30 of 32
___________________
•
Putting the Promise of Experimental Network Infrastructure into the Hands
of Our Nation's Scientists and Researchers.
•
This is a major initiative of U.S. research universities and private sector
technology companies to provide a national scale infrastructure for research
and experimentation in networking technologies and applications.
•
NLR aims to catalyze innovative research and development into next
generation network technologies, protocols, services and applications.
•
NLR puts the control, the power and the promise of experimental network
infrastructure in the hands of our nation’s scientists and researchers.
•
http://www.nlr.net/
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