Home > Articles > Networking

This chapter is from the book

The Development of SONET

Some people view SONET as a new technology, and it is only in the last decade that SONET has been deployed extensively. However, SONET did not just appear suddenly on the scene. Extensive research has been underway for well over a decade on many of the features that are found in SONET. One notable achievement began in 1984. It focused on the efforts of several standards groups and vendors to develop optical transmission standards for what is known as the mid-span meet (also known as transverse compatibility). The goal was to publish a specification that would allow different vendors' equipment to interoperate with each other at the fiber level.

In addition, due to the breakup of the Bell System in 1984, there were no standards developed beyond T3 technology. Prior to the divestiture, all equipment was built by AT&T's manufacturing arm, Western Electric (WECO), which ensured that there would be no compatibility problems in any network components.

After the breakup, there was little incentive for the other carriers (such as MCI and Sprint) to purchase AT&T-based equipment. Indeed, there was no incentive to purchase AT&T equipment, since AT&T, MCI, and Sprint had begun competing with each other for long distance services. This situation led to the rapid growth of alternate equipment vendors (such as Nortel Networks), who were developing advanced digital switching technologies.

The 1984 divestiture paved the way for alternate long distance carriers through the equal access ruling. The alternate carriers were given equal access to the local exchange carrier (LEC) infrastructure and connections to AT&T for end-to-end long distance service. The LEC could connect to MCI, Sprint, and others through their switching facilities at an interface in the LEC or long distance carrier offices called the point of presence (POP).

During this time, higher capacity schemes beyond T3 became proprietary, creating serious compatibility problems for network operators who purchased equipment from different manufacturers. In addition, the early 1980s witnessed the proliferation of incompatible and competing optical fiber specifications.

Precursors to SONET

We interrupt the discussion on divestiture to explain some of the technology that was being developed during the early 1980s. A landmark project that contributed to SONET was Metrobus, an optical communications system developed at AT&T's Bell Labs in the early 1980s. Its name was derived from its purpose: It was situated in a metropolitan area to serve as a high-speed optical transport network.

Metrobus demonstrated the feasibility of several new techniques that found their way into SONET. (They are explained in this chap- ter and subsequent chapters.) Among the more notable features were (a) single-step multiplexing, (b) synchronous timing, (c) extensive overhead for network management, (d) accessing low level signals directly, (e) point-to-multipoint multiplexing, and (f) the employment of multimegabit media for achieving high bandwidth network transmission capacity (of approximately 150 Mbit/s).

This latter decision along with the ensuing research and testing was important, because a 150 Mbit/s signal rate can accommodate voice, video, and data signals, as well as compressed high definition television (HDTV). Moreover, these techniques permitted the use of relatively inexpensive graded-index multimode fibers instead of the more expensive single mode fibers, although single mode fiber is now the preferred media for SONET.

The various standards groups began the work on SONET after MCI send a request to them to establish standards for the mid-span meet. The SONET specifications were developed in the early 1980s, and Bellcore submitted its proposals to the American National Standards Institute (ANSI) T1X1 Committee in early 1985,1 based on a 50.688 Mbit/s transfer rate. The initial SONET work did not arouse much interest until the Metrobus activity became recognized.

Later, using the innovative features of Metrobus, the SONET designers made modifications to the original SONET proposal, principally in the size of the frame and the manner in which T1 signals were mapped into the SONET frame.

From 1984 to 1986, various alternatives were considered by the ANSI T1 Committee, who settled on what became known as the synchronous transport signal number one (STS-1) rate as a base standard. Finally, in 1987, the ANSI T1X1 committee published a draft document on SONET.

Participation by ITU-T

During this time, the international standards body now known as the International Telecommunication Union-Telecommunication Standardization Sector (ITU-T) had rejected the STS-1 rate as a base rate in favor of a base rate of 155.520 Mbit/s. For a while, it appeared that the North American and European approaches might not converge, but the SONET frame syntax and structure were altered one more time to a rate of 51.84 Mbit/s which permitted this rate to be multiplexed (concatenated) by an integer of three to the European preference of 155.52 Mbit/s. This work has resulted in almost complete compatibility between the North American and ITU-T approaches. The ITU-T Recommendations are now considered the "official" standards and are collectively called the Synchronous Digital Hierarchy (SDH).

Once the major aspects of the standards were in place, vendors and manufacturers began to develop SONET and SDH equipment and software. These efforts came to fruition in the early 1990s and, as of this writing, SONET and SDH have been deployed throughout the United States and other parts of the world.

Key ITU-T Documents

Listed below are some of the most commonly cited SDH standards available from the ITU-T.2

  • ITU-T G.707: Network Node Interface for the Synchronous Digital Hierarchy (SDH)

  • ITU-T G.781: Structure of Recommendations on Equipment for the Synchronous Digital Hierarchy (SDH)

  • ITU-T G.782: Types and Characteristics of Synchronous Digital Hierarchy (SDH) Equipment

  • ITU-T G.783: Characteristics of Synchronous Digital Hierarchy (SDH) Equipment Functional Blocks

  • ITU-T G.803: Architecture of Transport Networks Based on the Synchronous Digital Hierarchy (SDH)

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.

Overview


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.

Surveys

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.

Newsletters

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.

Security


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

Children


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

Marketing


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.

Choice/Opt-out


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.

Links


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