One of the important reasons for opting for an IP PBX is the options it gives for long distance calling through VOIP. Though these features could be implemented using mixed type of PBX (TDM based PBX enabling VOIP Communications), their functionalities are limited. So, let us take a look at how VOIP enables reduce long distance charges for enterprise companies. Please note that even though VOIP can enable these features, it may be illegal to use them or not available, in certain countries.
IP Trunking between multiple PBX:
If you have multiple branches in multiple countries/states, you would notice that the calling charges between your employees in these branches are quite high as they keep calling themselves very frequently (For example, branch to HO) and it happens every month (repetitive charges). So, one good idea would be to have VOIP enabled between your IP PBX in all the branches. Most of the companies would have taken a certain bandwidth for data. Some of it can be allocated for voice communications between your branches. The IP PBX in all your branches need to be trunked over IP or SIP (Note that some PBX vendors have their proprietary protocols for interconnecting (trunking) their PBX’s over IP or they can do it over the open standard protocol – SIP). So, when these two are enabled, all the local calls (to your own branches) could be programmed to take the VOIP way and hence would not be charged extra (as you are already paying for the data bandwidth). But this is only for calls within your company branches where the bandwidth is available and the PBX can be trunked with each other.
SIP Trunks from a Service Provider:
Certain service providers provide SIP Trunks – They are like your PRI Lines but the difference being, the calls are taken over an IP Network instead of the PSTN Network. So, if you have high calling volumes to different customers in a particular country, instead of dialling there through the ISD (which is generally very high), you could take advantage of SIP Trunks which work over VOIP. They are quite cheap when compared to the ISD charges per minute.
Least Cost Routing(LCR) in PBX:
Generally, large companies have multiple service providers to provide SIP trunks for voice. Each provider may have a different price for each country. So, when your callers are calling a number in a particular country, the PBX can determine which service provider can offer the least cost for that country and route the call through that provider (This may include maintaining a database of call charges offered by all the service providers or the call can be routed based on the country code).
Some PBX allow least cost routing using the infrastructure available there. For example, if you want to call some one in a certain country, and dial that number. Your PBX recognizes that there is a branch for your company in that country and that PBX is trunked with this one. So, it routes the call over IP to that PBX (for which there no additional charges) and from there, it can go over the local PSTN and only the PSTN charges apply for that call. Not all PBX support this model and it is illegal in certain countries.
Least Cost Routing can also be applicable by interconnecting IP PBX with cellular networks with Fixed Cellular Terminal (FCT).
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