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<TH align=middle colSpan=3>3.2. Scenario 1: Long-distance least cost
routing</TH></TR>
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<H2 class=title style="CLEAR: both"><A id=LCR>3.2. Scenario 1:
Long-distance least cost routing</H2></DIV></DIV>
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<P>This scenario is likely to be adopted by enterprises with high-cost call
volumes. Traditionally, separate links have been used for transferring voice and
data between two sites (see <A
title="Figure 3.1. Traditional separation of data and telephony between locations"
href="http://www.informatik.uni-bremen.de/~prelle/terena/cookbook/main/ch03s02.html#scen_longdist_legacy">Figure 3.1</A>),
thus making it simple to achieve a reduction in costs by establishing accounts
with a lower-cost long-distance carrier. Voice over IP offers an alternative
solution for this kind of problem: existing enterprise data networks (using IP
protocol) may be used to carry long-distance voice traffic to certain
destinations, thus lowering the total costs (see <A
title="Figure 3.2. Integration of data and telephony between locations"
href="http://www.informatik.uni-bremen.de/~prelle/terena/cookbook/main/ch03s02.html#scen_longdist_combined">Figure 3.2</A>).
A combination of lower-cost, long-distance carrier and Voice over IP voice-data
integration is seen as the most cost-effective solution in this area. This
requires the routing of calls to the lowest-cost network, depending on time of
day and destination and it is referred to as Least-Cost Routing (LCR). In order
to achieve greater savings, it routes calls to destinations by re-dialing them
through the lowest cost alternative carrier / terminator available. A basic
scenario's architecture (depicted in <A
title="Figure 3.3. Least cost routing architecture"
href="http://www.informatik.uni-bremen.de/~prelle/terena/cookbook/main/ch03s02.html#least-cost-routing-architecture">Figure 3.3</A>)
shall be able to handle all calls originating from the enterprise network.
Elements needed to deploy this scenario are: terminals (both IP and PSTN) and
the necessary Gateways to route the call from the IP network to the
ISDN/PSTN/GSM and vice versa; other elements like MCUs or servers may be
optionally present, but are not required. </P>
<DIV class=figure><A id=scen_longdist_legacy>
<P class=title><B>Figure 3.1. Traditional separation of data and
telephony between locations</B></P>
<DIV class=mediaobject align=center><IMG
alt="Traditional separation of data and telephony between locations"
src="ch03s02.files/scen_longdist_legacy.png" align=middle></DIV></DIV>
<DIV class=figure><A id=scen_longdist_combined>
<P class=title><B>Figure 3.2. Integration of data and telephony
between locations</B></P>
<DIV class=mediaobject align=center><IMG
alt="Integration of data and telephony between locations"
src="ch03s02.files/scen_longdist_combined.png" align=middle></DIV></DIV>
<P>The hybrid solution, including both traditional processing of calls over
PSTN/ISDN and an additional IP Telephony part, results in this detailed
architecture:</P>
<DIV class=figure><A id=least-cost-routing-architecture>
<P class=title><B>Figure 3.3. Least cost routing architecture</B></P>
<DIV class=mediaobject align=center><IMG alt="Least cost routing architecture"
src="ch03s02.files/least-cost-routing-architecture.png"
align=middle></DIV></DIV>
<P>The features such an architecture may provide can be basically summarized
in:</P>
<DIV class=itemizedlist>
<UL type=disc>
<LI>Call routing by time of day and day of the week, allowing selection of the
best rates for specific time periods.
<LI>Call routing by destination, allowing selection of the best rates
depending on the destination of the call.
<LI>Number modification, allowing dial-string manipulation of the original
number dialed, to facilitate prefix-based routing.
<LI>Class of Service management, allowing management of individual extensions
with differentiated class of service, to give that higher level of service to
users who need it.</LI></UL></DIV>
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<H3 class=title><A id=d0e2168>3.2.1. Least Cost Routing - An implementation
example</H3></DIV></DIV>
<DIV></DIV>
<P>A company with head-quarter offices and multiple branch-office sites in
Europe makes daily long distance calls to contact customers located all over the
world. Since many telephone carriers provide cheap telephone rates depending on
geographic areas, the competitive telephone market may be used to reduce
communication costs. A first solution would require the maintenance of an
up-to-date table, based on the savings depending on the time of day and
destination. The problems arising from this solution in the maintenance and
distribution of this table to the employees are evident. Moreover, it is certain
that not every employee will remember to dial the extra digits for each
appropriate prefix, both because it is time-consuming and as a result of
negligence. Therefore, an engineering process is needed to mantain the costs
low. Least-Cost Routing is the solution to this kind of problems, as it allows
the telephone system to automatically route the long distance call to the most
economical telephony carrier / network, saving money on the long distance bill
and reduceing the employee's effort in making calls.</P>
<P>In order to put such solution in place, the company needs to deploy a set of
Gateways in the locations where branch offices are located, to take advantage of
the integration of data and telephony links between locations as depicted in <A
title="Figure 3.2. Integration of data and telephony between locations"
href="http://www.informatik.uni-bremen.de/~prelle/terena/cookbook/main/ch03s02.html#scen_longdist_combined">Figure 3.2</A>.
This can result in savings from both calls located in the area of the branch
offices, as well as office-to-office calls, taking advantage of the data network
connecting the company's sites. Note that in this case, a distributed routing
table has to be implemented, in order to facilitate control by the system
administrator, who may wish to update it anytime changes in long-distance rates
occur.</P></DIV></DIV>
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