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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.

8 of 32Figure 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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ISP Point-of Presence

Modem Pool

Individual Dial-up Customers

Corporate T1 Customer

T1 CSU/DSU

Corporate T3 Customer

T3 CSU/DSU

Corporate OC-3 Customer

ATM Switch

Layer-2 Switch

ISP POP

ISP POP

ISP POP

NAP/MAE

Figure 10-2 Inside an ISP Point of Presence

RemoteAccess Server

ATM Switch

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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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ATM Switch

RouteServer

Router

ISP A

Router

ISP B

Router

ISP C

Router

ISP D

ISP E

ATM Switch

ISP F

ATM Switch

Figure 10-3 Inside an Internet Network Access Point

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Figure 10-4 Three national ISPs in North Americahttp://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 dial-

up 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

20 of 32Figure 10-5 DSL Architecture

Local Carrier End Office

Line Splitter

Customer Premises

Telephone

DSL Modem

Hub

Computer Computer

Local Loop

MainDistribution

Frame

CustomerPremises

CustomerPremises

VoiceTelephoneNetwork

DSL AccessMultiplexer

ATM Switch

ISP POP

ISP POP

ISP POP

ISP POP

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  Type Maximum Lengthof Local Loop

MaximumDownstream

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.

23 of 32Figure 10-8 Cable Modem Architecture

Cable Company Distribution Hub

Cable Splitter

Customer Premises

TV

Cable Modem

Hub

Computer Computer

SharedCoaxCable

System

Combiner

CustomerPremises

CustomerPremises

TV VideoNetwork

Cable ModemTermination

System

ISP POP

Cable CompanyFiber Node

Optical/ElectricalConverter

Downstream

Upstream

Router

Cable Company

Fiber Node

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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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Fig. 10-9 Fixed Wireless Architecture

Wireless Access Office

WirelessTransceiver

Customer Premises

Telephone

DSL Modem

Hub

Computer Computer

CustomerPremises

CustomerPremises

MainDistribution

Frame

VoiceTelephoneNetwork

DSL AccessMultiplexer

WirelessTransceiver

Router

Line Splitter

Individual Premise

IndividualPremise

IndividualPremise

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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Figure 10-11 Gigapops and high speed backbones of Internet 2/Abilene, vBNS, and CA*Net 3

Abilene vBNS CA*Net 3

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___________________

• 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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