Chapter 7

1

Chapter 7The

Internet

Networking

in the

Internet Age

by Alan Dennis

Copyright © 2002 John Wiley & Sons, Inc.

2

Copyright John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that named in Section 117 of the United States Copyright Act without the express written consent of the copyright owner is unlawful. Requests for further information should be addressed to the Permissions Department, John Wiley & Sons, Inc. Adopters of the textbook are granted permission to make back-up copies for their own use only, to make copies for distribution to students of the course the textbook is used in, and to modify this material to best suit their instructional needs. Under no circumstances can copies be made for resale. The Publisher assumes no responsibility for errors, omissions, or damages, caused by the use of these programs or from the use of the information contained herein.

3

Chapter 7. Learning Objectives

• Understand the overall design of the Internet

• Understand DSL and cable modem

• Be familiar with wireless services

• Be familiar with Internet 2

4

Chapter 7. 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• The Best Practice Internet Access Design

5

Introduction

6

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.

7

How The Internet Works

8

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 7-1), 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.

9

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.

10Figure 7-1 Basic Internet architecture

11

Internet Packet Exchange Charges

• ISPs 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.

12

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 7-2 shows an example of a POP using a collapsed backbone with a Layer-2 switch.

13Figure 7-2 Inside an ISP point of presence

14

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 7-3 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 to a different regional ISP, causing packets to flow between cities, even though their destination is to another local ISP within the same city.

15Figure 7-3 Inside an Internet network access point

16

The Internet in 2002

• Figure 7-4 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.

17Figure 7-4 Three national ISPs in North America

18

Internet Backbones in 2002

• Today, 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 2002.

• 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) in 2001. It is expected to reach 35 Tbps by 2005.

19

Internet Access Technologies

20

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)

21

Digital Subscriber Line

• Digital Subscriber Line (DSL) is now being implemented on a widespread basis because it can 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 intrinsic bandwidth capability and can therefore carry data at much higher rates.

22

DSL Topology (see Figure 7-5)

• DSL provides both a voice circuit and a point-to-point full –duplex data circuit.

• DSL installations commonly use line splitters to separate the voice and data channels.

• Data from the splitter goes to the DSL modem, which sends Ethernet frames for the customer’s LAN.

• In the local end office, the data stream from the local loop goes to the main distribution facility (MDF) which splits off the voice to the PSTN

• The data stream first goes to a DSL Multiplexer (DSLAM) which combines it with other DSL signals before sending it on the ISP.

23Figure 7-5 DSL architecture

24

DSL Multiplexing

• One thing all DSL services have in common is that they use Frequency Division Multiplexing to divide available bandwidth into three channels.

• The channels are separated by guardbands which are dead spaces that separate the channels so they don’t interfere with each other (see Figure 7-6).

• The three channels are:– A relatively small voice channel (0-4 kHz)– An upstream channel with a 300 to 700 kHz

bandwidth– A downstream channel with a 1000 to 10000

KHz bandwidth

25Figure 7-6 DSL multiplexing

26

Types of DSL

• DSL services are quite new and not all common carriers offer them.

• Two general categories of DSL services have so far emerged ADSL and VDSL.

• Asymmetric DSL (ADSL) provides different data rates to (up to 640 Kbps) and from (up to 8.4 Mbps)

• Maximum data rates also depend on the distance from the customer premises to the carrier’s end office. (see Figure 7-7).

27

Type Maximum Length

of 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

 Note: E1 and E2 are the European standard services similar to T1 and T2 services in North America

Figure 7-7 ADSL data rates

28

Very-High-Data-Rate DSL (VDSL)

• VDSL is a high-speed member of the DSL family designed for local loops of 4500 feet or less, but the protocol is not yet standardized.

• The upstream and downstream data rates for VDSL’s channels depend on the distance of the end user from the nearest telephone exchange and are listed in Figure 7-8.

29

Type Maximum Length

of Local Loop

MaximumDownstream

Rate

Maximum Upstream

Rate

1/4 OC-1

4,500 feet 13 Mbps 1.6 Mbps

1/2 OC-1

3,000 feet 26 Mbps 2.3 Mbps

OC-1 1,000 feet 52 Mbps 2.3 Mbps

Figure 7-8 Anticipated VDSL data rates

30

Cable Modems

• The most important high speed alternative to DSL today is “cable modem”, a digital service offered by cable television companies.

• Although not a formal standard, the Data Over Cable System Interface Specification (DOCSIS) is now a widely accepted industry standard for cable modem communications and has led to the production of standardized equipment.

• Most cable companies provide their services using hybrid fiber coax (HFC) networks that combine optical fiber backbones with coax cable access lines.

31

Cable Modem Topology (Figure 7-9)

• Cable modems use shared multipoint circuits. Data is split off by the cable splitter, then the cable modem translates the data into 10BaseT frames.

• The coax cable leaving the customer premises connects to a fiber node, which converts the converts the coaxial cable’s electrical signal into a light signal using an opto-electrical converter.

• Two circuits connect to the fiber node: – The upstream circuit connects to the cable modem

termination system (CMTS), which is then connects to the ISP

– The downstream circuit connects to a combiner where it is combined with the incoming cable signal.

32Figure 7-9 Cable modem architecture

Cable Splitter

Cable Modem

XXXXXXXXXXXXXXXX

33

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 connect a multiplexed group of users from a single location to the wireless service provider’s network (e.g., an apartment building).

• Data access speeds range from 1.5 to 11 Mbps depending on the vendor.

34

Fixed Wireless (Figure 7-10)

• Fig. 7-10 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 de-

multiplexed 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.

35Figure 7-10 Fixed wireless architecture

36

Satellite Internet Access• For Internet access via satellite, a small satellite

dish is installed outside the home or office.• Satellite Internet services usually provide

downstream data rates of about 500 kbps and 128 kbps upstream.

• One problem with the service is propagation delay, due to distance the signal must travel, resulting in relatively slow response times.

• For example, a to get a response from a Web server, a signal must travel from the user’s site to the satellite, then down to the ISP and back, or about 90,000 miles, ½ second at the speed of light.

37

Mobile Wireless • 1G cell phones of the 1980s were analog (1G). • Digital 2G cell phones followed in the mid-1990s but

they are only capable of low speed data communications (ca. 14.4 kbps). – The Global System for Mobile communications (GSM) is

the most popular 2G mobile phone standard.

• 3G wireless, officially known as UMTS, is intended to be higher speed, but is not yet standardized.– Enhanced Data GSM Environment (EDGE) is a possible

3G standard, with a proposed data rate of 384 kbps. – Other proposals are for 2Mbps 3G services.

• Discussions on 4G at even higher data rates have already begun.

38

Mobile Wireless Protocols

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

• WAP uses WAE and Wireless Markup Language (WML) instead of HTTP and HTML,

• These protocols streamline access to the web since the low speed and small screen mobile networking environment is order to make Web access practical.

39

Basic WAP Architecture (Figure 7-11)

• 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.

40Fig 7-11 Mobile wireless architecture for WAP applications

41

Future Access Technologies• Two key future Internet access technologies are:• Passive Optical Networking (PON)

– PON, part of fiber-to-the-home will unleash the potential of fiber optics to home users.

– Passive optical splitters don’t require electricity, lowering cost, but limiting its maximum distance to about 10 miles.

– WDM is also used so hundreds or thousands of channels are possible at very high speeds.

• 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.

42

Internet Governance

43

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, copyright laws, 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.

44

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.

45

Internet 2

46

Internet 2 (Figure 7-12)• 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 (see Figure 7-13).

• Protocol development focuses on issues like Quality of Service and multicasting.

• New applications include tele-immersion and videoconferencing.

47

Figure 7-12 Gigapops and high speed backbones of Internet 2/Abilene, vBNS, and CA*Net 3

48Fig. 7-13 Inside the Pacific Northwest gigapop

49

The Best Practice Internet Access Design

50

Recommendations

• If mobility is important, then WAP is really the only viable alternative at present.

• Choosing between cable modem, DSL and satellite is difficult because each technology has shared elements that can impact performance and vary from location to location.

• The main factors to investigate are:– number of users on shared segments– Capacity from the ISPs POP to the Internet

51

End of Chapter 7