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 Figure 3.1), 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 Figure 3.2). 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 Figure 3.3) 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.
The hybrid solution, including both traditional processing of calls over PSTN/ISDN and an additional IP Telephony part, results in this detailed architecture:
The features such an architecture may provide can be basically summarized in:
- Call routing by time of day and day of the week, allowing selection of the best rates for specific time periods.
- Call routing by destination, allowing selection of the best rates depending on the destination of the call.
- Number modification, allowing dial-string manipulation of the original number dialed, to facilitate prefix-based routing.
- 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.
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.
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 Figure 3.2. 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.