Home > Articles > Software Development & Management

Understanding WAN Bandwidth Delivery

Beginning with the invention of Morse code and then the telephone, mankind has been seeking new ways to transmit information effectively and efficiently. In this article, Kyle Cassidy explains the popular types of WAN bandwidth delivery used in relaying data from one end to the other.
This article is excerpted from The Concise Guide to Enterprise Internetworking and Security.

"We are in great haste to construct a magnetic telegraph from Maine to Texas; but Maine and Texas, it might be, have nothing important to communicate…as if the main object were to talk fast and not to talk sensibly."

—Henry David Thoreau, Walden

Introduction to Bandwidth Delivery: How the Computer Crashed into the Telephone

There has been an electronic bandwidth infrastructure in this country since the 1800s, when Samuel Morse's invention allowed messages to be sent long distances over copper wire nearly instantaneously. Since that time, there has been significant change in the way data is encoded and transmitted. These changes, and the inherent differences between voice and data, have created technology that is often at odds with one or the other. Because voice transmission has long been the goal of the telephone company (or telco), it is the transmission of data that usually suffers.

From the beginning, this communications infrastructure was torn between digital and analog. The initial form of communication over wire, Morse code, was digital in theory. Binary information was designated by short or long pulses (a dot being 0, a dash being 1); however, the transmission media was analog. The pulses were sent as voltage changes along copper line.

Later it was discovered that information could be sent significantly faster in a wholly analog form, and voice transmission over wire took over. After all, who wants to tap out Morse code when you can talk instead? Very fast Morse code operators can send about 30 words a minute—how fast can you talk?

After many people began using voice over wire, the phone company became concerned that it would eventually run out of copper, or places to hang it. A town with 20 telephone owners could well afford 20 copper wires running from individual houses to the telco, but a city of 50,000 or half a million certainly could not.

The goal of transmitting multiple analog signals over a single piece of copper wire became absolutely necessary for telephone expansion to continue. Eventually, some clever person discovered frequency-division multiplexing, which allowed several conversations to be transmitted over a single pair of wires.

How does that work? Well, like many technological miracles, it uses methods that have existed since the beginning of history. In the same way that you can tune in to one voice at a cocktail party and carry on a conversation with that one person while dozens of other people are talking, frequency division multiplexing allows computers to distinguish among multiple conversations going on at once by listening only for signals of a higher or lower frequency than the others.

To a certain extent, that's also the way it's done in frequency-division–multiplexed data signals. Now, you certainly don't want to be in a telephone conversation where you can hear a half dozen other people talking in the background, so the signals have to be separated at the telco before they get to you. But how? It would be extremely difficult for any equipment belonging to the phone company to figure out what voice belongs with which conversation, so the signal is modified before it's bound to other signals. This is done by "painting" the signal to change its characteristics.

For example, you have the following four streams of numbers you want to send along the same wire:

















If you just toss them on the wire, it will be impossible to sort them out because the numbers are all very similar. However, if you add 100 to each number in column 2, add 200 to every number in column 3, and add 300 to every number in column 4, you get numbers that are easy to separate at the receiving end:

















So, by adding a known quantity to the frequency of the signal, they're made unique. They're decoded at the telco, and the proper conversation is sent to your house along your dedicated phone circuit. Figure 1 shows how it might look as sound waves.

Figure 1 Frequency-division multiplexing allows multiple signals to travel over a single wire.

Packet-Switched Versus Circuit-Switched Networks

Data transmission can be either packet-switched or circuit-switched. There are advantages to each.


Large blocks of data are broken down into smaller parts, called packets. Each of these packets contains all the addressing information to get it from point A to point B. The packets take whatever route is available; there is no fixed path.


A path from point A to point B is negotiated at the beginning of the transmission and kept open until the end of the transmission. During that time, nothing else can use that pipe.

The best example of circuit-switched networking is a telephone call. You dial your best friend, and a circuit is opened between your phone and hers. As long as you have the phones off the hook, that data pipe belongs to you. No one else can use it. If someone calls your house, he'll get a busy signal. A circuit-switched network connection is the fastest and most reliable, but it suffers because no one else can use the line. If you were to take a one-hour phone conversation and remove all the fraction of seconds where there is silence on the line, you'll be left with a lot of silence. Every time you're transmitting silence, you're wasting bandwidth. Unlike people, computers talk only when they have something to say, so their conversations are much more direct—hence, packet-switched.

The Telco Engineers Versus the Network Engineers

When computers crashed into the phone company, there was some carnage. From the outset, telco engineers and computer network engineers were at design odds with one another. After all, they have entirely different goals. The primary goal of the telco is to deliver real-time voice transmission. This can be done at the expense of cost and accuracy. Cost is passed on down the line to the consumer, and accuracy…well, the assumption is that if there's a distracting noise in the background, people will retransmit themselves, usually in the manner of, "Huh? What did you say Bob? There was a bus passing by just then." Network engineers are more concerned that data will be accurate and less concerned that it will be real-time. If faulty wiring causes a handful of static to be thrown into a telephone conversation, most people won't notice, but that same static could alter critical data in the transmission of a computer file, resulting in errors.

What we are left with is a telephone infrastructure designed for analog voice through which digital computer data must be sent. There is a push today for an entirely digital telco that can serve both voice and data. To an extent, this is already happening. Much of the innards of the U.S. telephone system is digital; what remains is known as the "last copper mile," or the local loop of wiring between a consumer's house and the telco building. The investment in that wiring and telephones compatible with it is extensive and expensive, and its replacement will be hard-fought.

For this reason, we have an amalgamation of technologies providing service in sometimes rather strange and kludgy ways.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020