Fiber Cable Failure Impacts, Survivability Principles, and Measures of Survivability

This chapter is from the book

3.8 Measures of Outage and Survivability Performance

Let us now introduce various quantitative measures of failure impact, given a failure occurs, and of intrinsic survivability performance in terms of the ability to resist failures in the first place. Given the impact of failures, there is growing regulatory interest in attempts to quantify the magnitude of the impact of various failures that occur. The notion is that hurricanes, tornadoes and earthquakes each have a system for classification of their severity, so why not network failures too? Network operators are also interested in such standardized measures for quality improvement and competitive processes. A second sense of "measuring survivability" is to ask about those intrinsic properties of a network that by design make it less likely to sustain an outage in the face of failures within itself. These are the basic notions of reliability and availability and what we define as the restorability. Let us touch on these in sequence.

3.8.1 McDonald's ULE

McDonald [McDo94] was perhaps the first to advocate development of quantifiable measure of network outages. McDonald's argument was that any drive toward a standard method for quantification for network failures would focus attention on the issue and inevitably lead to improvements in avoiding outage. His proposed measure is the "User-Lost Erlangs" (ULE) defined as:

Equation 3.3

where E = average historical traffic intensity (in Erlangs) through the outage period and H = outage duration in hours. The measure is logarithmic, like the Richter scale. 10 Erlangs blocked for one hour is 1 ULE. 10 ULE is equivalent to an hour-long outage affecting 100 Erlangs of normally offered traffic, or 6 minutes of outage on 1000 Erlangs, etc. The logarithmic nature is a key idea for its utility. McDonald argues a logarithmic measure discriminates well between events of major and minor consequences. And it reflects a plausible belief that the overall societal impact somehow scales with the exponent of the total outage. We would add that it is also appropriate to avoid false precision: the data going into a ULE calculation will at best be estimates, so what is important is indeed the order of magnitude, not linear differences.

3.8.2 The (U,D,E) Framework for Quantifying Service Outages

The ULE notion was developed further with an eventual aim toward standardization in [T1A193]. In this framework the impact of a failure is assessed in terms of: Unservability (U), Duration (D) and Extent (E), called a (U, D, E) triple. The three parameters of the (U, D, E) framework are:

Unservability (U)

is defined in terms of a basic capability and unit of usage appropriate to the application. For example, in a circuit switched network, this would be the ability to establish connections with acceptable blocking and transmission performance. The unit of usage is a call attempt and the unservability is the percentage of call attempts that fail. In a packet network, the unit of usage is a packet and the unservability is the percentage of packets that were not delivered within a stipulated delay. In a leased line network, unservability is defined as the percentage of DS-0, DS-1 or DS-3 leased signals that are not available.

Duration (D)

is the elapsed time interval during which performance falls below the threshold for defining unservability.

Extent (E)

reflects the geographic area, population affected, traffic volumes, and customer traffic patterns, in which the unservability exceeds a given threshold.

The idea is not to operate on U, D, E values further boiling them down to a single measure but to preserve them as a three-dimensional characterization of any outage event. A (U, D, E) triple can thus be plotted in the corresponding 3-space for classification of the event as catastrophic, major, or minor, depending on which predefined "volume shell" the (U, D, E) vector enters. Figure 3-15 illustrates. It seems reasonable that some vector weighting scheme might also be agreed upon for definition of the qualifying regions. Or, conversely, a general (U, D, E) classification model would not necessarily have simple spherical shells for defining classifications unless the intent is to give strictly equal weight among U, D, E.

Figure 3-15. (U, D, E) concept for classification of network outages (source: [T1A193]).

(U, D, E) shells can be used both to categorize events as well as to lay down prescriptive policy for what might constitute an event requiring a company review of an incident or methods. For example, a Local Switch failure may be defined to have occurred whenever 500 subscriber lines (the extent E) are totally isolated (the definition of unservable, U) for 2 minutes or more (the duration, D), i.e., (U, D, E) = (100,2,500).

Outage Index

Later work in the T1A1.2 committee that produced [T1A193] considers an approach leading to a single Outage Index. It is conceptually equivalent to formation of a vector weighted magnitude of the (U, D, E) triple but involves predefined nonlinear weighting curves for D, E and discrete multipliers for time of day, type of trunk affected (inter- or intra-LATA, 911 etc.) Such weightings are ultimately arbitrary but nonetheless can be fully detailed in a standardized method and then be of valuable service when applied industry-wide.

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