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Least-cost routing

Least-cost routing is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Least-cost routing rather than just read about it. In short: In voice telecommunications, least-cost routing (LCR) is the process of selecting the path of outbound communications traffic based on cost. Within a telecoms carrier, an LCR team might periodically (monthly, weekly or even daily) choose between routes from several or even hundreds of carriers.

Key takeaways

  • Least-cost routing belongs to science; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Least-cost routing to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Least-cost routing from memory before moving on to harder problems.

Reference excerpt

In voice telecommunications, least-cost routing (LCR) is the process of selecting the path of outbound communications traffic based on cost. Within a telecoms carrier, an LCR team might periodically (monthly, weekly or even daily) choose between routes from several or even hundreds of carriers. This function might also be automated by a device or software program known as a least-cost router.

Telecoms carriers as suppliers and customers Telecoms carriers often buy and sell call termination services with other carriers. A carrier such as Telewest or France Telecom will be interconnected with other telecoms carriers and might have a number of routing options of different price, quality and capacity to a given country. In the de-regulated EU, these will be licensed alternative operators (e.g. Cable and Wireless / Colt in the UK or Jazztel in Spain) or the postal, telegraph and telephone services of other countries, such as T-Systems (Germany), Telefónica (Spain), NTT (Japan) or Telstra (Australia), who establish offices or a point of presence (POP) in a major telecommunications hub city such as London, New York, Hong Kong or Amsterdam. The major US carriers, Sprint, Verizon, AT&T and Level 3 in the US International telecommunications routes also have POPs in these hub cities. There are also niche carriers which specialise in providing termination to a small number of destinations, sometimes through the use of grey routes.

Margin management cycles The LCR team in a carrier might follow a cycle:

The buyers negotiate with their suppliers and get a new price schedule. The prices are loaded into software to calculate and compare termination costs. A route is chosen, fixing a cost-for-pricing, and new prices are issued based on the costs-for-pricing. The new routes are implemented on the switch and finally the traffic volumes and margins are monitored through reports from the billing system. Loss-making traffic and odd routing are investigated, and either the billing system has its data corrected or routing and pricing action is taken. Carriers sign interconnect agreements with each other specifying the terms under which they will do business. Such agreements define terms of payment, methods and procedures of dispute resolution, and the means by which the carriers will notify each other of pricing changes. The industry standard is currently seven days for price increases while price decreases often take effect on the day of notification. Because the margins in the carrier-carrier market are extremely slim, re-routes or price increases must be made quickly to a destination where the current route is going to increase in price.

Impact of mobile-number portability in VoIP and LCR environments Mobile number portability impacts the internet telephony, VoIP (Voice over IP) and Least Cost Routing (LCR) businesses. Mobile number portability (MNP) is a service that makes it possible for subscribers to keep their existing mobile phone number when changing the service provider (or mobile operator). With number portability now in place in many countries, LCR providers can no longer rely on using only a portion of the dialed telephone number to route a call. Instead, they now need to discover the actual current network of every number before routing the call. Thus, LCR solutions also need to handle MNP when routing a voice call. In countries without a central database like UK it might be necessary to query the GSM network about the home network a mobile phone number belongs to. MNP checks are important to assure that this quality of service is met; by handling MNP lookups before routing a call and assuring that the voice call will actually work, VoIP companies give businesses the necessary reliability they look for in an internet telephony provider. In countries such as Singapore, the most recent MNP solution is expected to open the doors to new business opportunities for non-traditional telecommunication service providers like wireless broadband providers and VoIP providers. In November 2008 the United States' FCC (Federal Communications Commission) released an order extending number portability obligations to interconnected VoIP providers and carriers that support VoIP providers.

Number plan management and analysis Whereas markets in commodities such as pork bellies or oil have agreed definitions and arbitrating bodies for the commodities they trade, the carrier-carrier market has no agreed definitions of its destinations. Every carrier uses the International Telecommunication Union E.164 standard for country codes, but each carrier uses different codes for destinations within a country, usually because it is using different suppliers within that country. Number plan management monitors changes in suppliers' dial codes and adds or removes codes from the company's own code tables to improve costs. Implementing the changes across the company's switches, billing systems, calling card and other IN platforms is a significant task for the engineering and billing departments.

Cherry-picking One aim of LCR teams is to cherry-pick. This happens when Carrier A's team finds that Carrier B defines a code range as being fixed-line and therefore cheap, while Carrier A defines it as mobile and therefore more expensive. Carrier A will send that range to Carrier B, pay a low fixed-line rate, and charge at a high mobile rate to maximize profit. Carrier B will sustain losses if it does not notice that its supplier, C, also defines that range as belonging to a mobile operator and charges a higher rate. Caught in the middle, B can sustain five- or even six- figure losses in a very short time.

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with Least-cost routing

Start with the simplest possible case. Write down what Least-cost routing claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Least-cost routing before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Least-cost routing ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Least-cost routing

In research
Least-cost routing appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Least-cost routing in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Least-cost routing is common in secondary-school and first-year university syllabi. It links to neighbouring topics Telecommunications economics, Teletraffic, so understanding it makes those chapters shorter.
In everyday life
Look for Least-cost routing outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Least-cost routing in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Least-cost routing means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Least-cost routing out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Least-cost routing in simple terms?

In voice telecommunications, least-cost routing (LCR) is the process of selecting the path of outbound communications traffic based on cost. Within a telecoms carrier, an LCR team might periodically (monthly, weekly or even daily) choose between routes from several or even hundreds of carriers.

Why does Least-cost routing matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Least-cost routing?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Least-cost routing.

Tags

  • Telecommunications economics
  • Teletraffic

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