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Chapter 9. The Internet

Business Data Communications and Networking Fitzgerald and Dennis,

7th EditionCopyright © 2002 John Wiley & Sons, Inc.

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Chapter 9. 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 9. 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

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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 TCP/IP standards 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 Internet

Service Providers that interconnect through Network Access Points (NAPs).

• There are about a dozen NAPs in the U.S., run by common carriers such as Sprint and Ameritech (Figure 9-1), 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.

9Figure 9-1 Basic Internet Architecture

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Internet Packet Exchange Charges

• ISP at the same level usually do not charge each other for exchanging messages.

• This is called peering. • 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 Point of

Presence (POP).• 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 9-2 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 9-2 Inside an ISP Point of Presence

RemoteAccess Server

ATM Switch

13Figure 9-2 Inside an ISP Point of Presence

• (See page 270, Figure 9-2)

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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 9-3 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 9-3 Inside an Internet Network Access Point

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The Internet in 2001

• Figure 9-4 illustrates the backbone networks of three national ISPs: Compuserve and CAIS in the US and iSTAR in Canada.

• Compuserve mostly uses T-3 lines for its backbone, CAIS uses a mix of T-3 and ATM OC-12 lines, while iSTAR uses T-1 lines.

• Compuserve and CAIS meet and peer at the Chicago NAP, while CAIS and iSTAR peer at the NAP in London, Ontario.

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Figure 9-4 Three national ISPs in North America

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Internet Backbones in 2001

• As of mid-2001, most backbone circuits for national ISPs in the US are 622 Mbps ATM OC-12 lines.

• The largest national ISPs are planning to convert to OC-192 (10 Gbps) by the end of 2001.

• A few are now experimenting with OC-768 (40 Gbps) and some are planning to use OC-3072 (160 Gbps).

• Aggregate Internet traffic reached 2.5 Terabits per second (Tbps) by mid-2001. It is expected to reach 35 Tbps by 2005.

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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 telephone 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.

23Figure 9-5 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 9-6 ADSL data rates

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Very High Rate Digital Subscriber Line (VDSL)

• VDSL is a high-speed member of the DSL family, designed for local loops of 1000 feet or less. Its three FDM channels are:

– 4 KHz analog voice channel

– Upstream digital 1.6 Mbps channel

– Downstream digital 52 Mbps channel

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Type Maximum Lengthof Local Loop

MaximumDownstream

Rate

Maximum Upstream Rate

1/4 OC-1 4,500 feet 12.96 Mbps 1.6 Mbps

1/2 OC-1 3,000 feet 25.92 Mbps 2.3 Mbps

OC-1 1,000 feet 51.84 Mbps 2.3 Mbps

  Figure 9-7 Anticipated VDSL 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.

28Figure 9-8 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 “line of sight” 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 9-9)

• Fig. 9-9 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. 9-9 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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Mobile Wireless

• Mobile wireless is the next step in cell phone technology, allowing users to access the Internet from any location.

• Access speeds are currently slow compared to fixed wired access such as DSL or cable modem.

• Mobile wireless uses the wireless application protocol (WAP) used by the wireless application environment (WAE).

• WAP uses WAE and WML instead of HTTP and HTML, which essentially streamlines the latter for use in the very limited low speed and small screen wireless mobile networking environment.

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Basic WAP Architecture (Figure 9-10)

• WAP clients (e.g., cell phone or palm computer) run a WAP program called a WAE user agent that generates WAE requests and sends them to the WAP gateway.

• The WAP gateway transceiver next passes the requests to a wireless telephony application (WTA) server.

• The server sends WAE responses back to the WAP client.

• If the client has requested a Web page, the WAE request is sent to a WAP proxy which translates both outgoing requests from WAE to HTTP and incoming HTTP responses back into WAE

• The WAE responses are then sent back to the WTA server which, in turn, sends them back to the WAP client.

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Web Server

Web Site

WAP Proxy

WAP Gateway

Wireless Telephony Application Server

HTTP Requests

HTTP Responses(plus HTML, jpeg, etc.)

Figure 9-10 Mobile Wireless Architecture for WAP applications

WAEResponses

(plus WML, etc.)

WAERequests

WAP Client

WirelessTransceiver

WAEUser

AgentWAE

Requests

WAEResponses

(plus WML, etc.)

WAERequests

WAEResponses

(plus WML, etc.)

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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 Governance

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ISOC and Internet Governance

• The Internet Society (ISOC) is the closest thing to an “owning” organization that exists for the Internet.

• ISOC is an open society whose members include 175 organizational and 8,000 professional members worldwide.

• ISOC works in three areas:– In public policy by participating in national and

international debates on issues such as censorship, copyrights, privacy and universal access.

– In education, ISOC provides training and education programs aimed at improving Internet infrastructure in developing nations.

– In standards, ISOC works through four inter-related standards bodies: IETF, IESG, IAB and IRTF.

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4 ISOC-related Standards Bodies• Internet Engineering Taskforce (IETF) includes network

designers, vendors, and researchers who develop new Internet architecture. IETF sends out requests for comment (RFCs) which form the basis of new Internet standards.

• Internet Engineering Steering Group (IESG) is responsible for technical management of IETF activities and standards and is governed by rules ratified by ISOC trustees. Each IETF group is chaired by an IESG member.

• Internet Architecture Board (IAB) provides strategic direction by promoting which actions the IETF and IESG should take. The IAB also elects the IETF chair and all IESG members out of the IETF nominating committee’s list.

• Internet Research Taskforce (IRTF) works through small research groups focused on specific research topics. IETF generally works on short-term issues, IRTF works on long-term ones related to Internet protocols, applications, architecture, and technology.

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Internet 2

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Internet 2 (Figure 9-11)• 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 9-11 Gigapops and high speed backbones of Internet 2/Abilene, vBNS, and CA*Net 3

Abilene vBNS CA*Net 3

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Figure 9-12 Inside the Pacific/Northwest Gigapop

Router

High-speedRouter

Abilene

DREN

WSU

Boeing

U Idaho

High-speedRouter

Router

Router

Montana State U

U Montana

U Alaska

Portland POP

Microsoft

Router Router

Switch

U Wash

Router

Switch Switch

CA*Net 3Sprint UUNet Verio

Router

AT&T

Sprint

Router

OC-48OC-12T-3

HSCC

Switch

SCCD

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End of Chapter 9