This scenario is likely to be adopted by enterprises with high-cost call volumes. Since traditionally there is a separation of transport of data and voice between two locations (see Figure 3.1), to reduce costs, accounts with a lower-cost long-distance carrier are established. Voice over IP offers a second solution for this kind of problems: existing enterprises' 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 foreseen as the most cost-effective solution in this area. This solution requires to route 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 the bigger savings, it routes calls to destinations by re-dialing them through the lowest cost alternative carrier / terminator of the moment. A basic scenario's architecture (depicted in Figure 3.3) shall be able to handle all calls originated from the enterprise network. Elements needed to deploy this scenario are: terminals (both IP and PSTN) and Gateways (necessary in order to route call from the IP network to the ISDN/PSTN and viceversa); other elements like MCU or servers may be optionally present but are not required to.
The hybrid situation including both traditional processing of calls over PSTN/ISDN and an added IP Telephony part results in this detailed architecture:
The features such an architecture may provide can be basically resumed in:
- Call routing by time of day and day of the week, allowing to select the best rates applying to certain hours in the day.
- Call routing by destination, allowing to select the best rates depending on the destination of the call.
- Number modification, allowing to add or subtract digits from the original number dialled to facilitate prefix-based routing.
- Class of Service management, allowing to manage individual extensions with differentiated class of service to give that higher level of service to users who need it.
A company with one head-quarter and more than one branch-office site 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 geographical areas, the competitive telephone market may be used to reduce communication costs. A first solution would require to keep an up-to-date table based on the savings depending on the time of the day and destination. The problem arising with this solution in the mantainance and distribution to the employees of this table are evident. Moreover, provided that not every employee remembers to dial the extra digits for the leading code both because of time-consuming reasons and because of negligence, an engineering process is needed to keep the cost low. Least Cost Routing is the solution to this kind of problems, 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 reduces the employee's effort in making the calls.
In order to put in place such solution the company needs to deploy a set of Gateways in the locations where a branch office is located, to take advantage of the integration of data and telephony between locations as depicted in Figure 3.2. This in order to save both on calls located in the area of one of the branch offices and on office-to-office calls using, when possible, the data network connecting the company's sites. Moreover a distributed routing table has to be implemented in order to facilitate the control by the system administrator which may update it anytime whenever changes in long distance rates occur.