First Things First: What Is a Softswitch?

The term softswitch is a portmanteau of the words software and switchboard. In the early days of telephony, switchboards were used to route calls from one phone to another; in order to connect the party making the call with its intended recipient, operators would manually switch lines from one circuit to another. In contrast, a softswitch is a type of software that routes calls virtually and automatically according to the logic of its programming without the need for an operator. 


  • What Is a VoIPswitch?
    A voipswitch simply refers to a softswitch that routes calls using VoIP rather than traditional PTSN (public switched telephone network) calls.
    Can a VoIPswitch Route Calls from and to Traditional (PSTN) Phones and Networks?

    Yes. A VoIPswitch can receive calls made to phone numbers within its network from traditional PSTN networks. This is referred to as call origination: calls made to numbers/endpoints within the VoIP network supported by a particular VoIPswitch/service provider originate in the PSTN network.
    A VoIPswitch can also route calls that originate from within its VoIP network to endpoints (phones and their associated numbers) in traditional PSTN networks. This is referred to as call termination: calls made within the VoIP network supported by a Class 5 softswitch are terminated in a traditional PSTN network.


    What Is a Class 5 Softswitch?
    A Class 5 softswitch routes calls between end-users or consumers in relatively small areas such as a city, town or even small state or country. To connect calls between international endpoints, Class 5 softswitches pass their traffic off to a Class 4 switch (see below).
    In the case of VoIP, there are a few ways that a Class 5 softswitch can deliver service to end users. The most direct method is to use IP phones or phones using IP adapters that connect directly with the softswitch. End users can also access VoIP services from a mobile device such as a smartphone or tablet using a mobile dialer (or softphone). In effect, mobile dialer apps function as IP adapters for mobile devices, allowing these devices to interact with a Class 5 softswitch.

  • Class 5 Softswitches can also provide service to non-IP devices such as regular phones and cellphones. Examples of such service are PINless and Calling Card services. While IP phones connect directly to the softswitch and communicate with it through IP, the aforementioned solutions allow end users to dial into a local Class 5 softswitch, which can then provide them with VoIP services.
    In contrast to a Class 5 softswitch, a Class 4 softswitch routes calls over long distances, such as between Toronto and Miami. As such, Class 4 switches route large volumes of traffic over and between different exchanges and LATAs (local access and transport areas). In other words, Class 4 softswitches route traffic between various Class 5 areas. One way to think about it is this: a Class 5 softswitch is a retail solution while a Class 4 softswitch is a wholesale solution.


    An Example: International VoIP Calling
    A person using an IP phone in New York makes a call to a PSTN number in Mumbai: The first portion of their call will be handled by their local VoIP provider using a Class 5 softswitch. The international portion of the call will be transferred from the local retail VoIP provider–using the Class 5 softswitch–to a wholesale VoIP carrier–using a Class 4 softswitch–that provides routes from New York to Mumbai. The wholesale carrier will transit the call from the New York retail provider to a local Mumbai telecom provider. This local Mumbai telecom provider is a PSTN provider, not a VoIP provider. Nonetheless, the international leg of the call was made through the wholesale VoIP carrier. The only portion of the call that was made through the PSTN was the last leg in Mumbai. The benefit: The international VoIP call (from New York to Mumbai), in effect, becomes a local Mumbai PSTN call (because the only PSTN section of the call was in a Mumbai PSTN exhange); the caller in New York, therefore, avoids the excessive fees they would otherwise incur were they to use a traditional PSTN carrier for the entire length of the call.