SoftswitchAlso known as Software switch, VoIP switch

What a softswitch does

The original softswitch architecture split a telephone exchange into a media gateway controller (the call-control “brain”) and separate media gateways that handle the audio. In practice the term now covers any server-based call-routing platform.

• Routing: chooses a destination route by dialled prefix, cost, quality or priority, with failover.
• Authentication and authorisation of customers and peers by IP or credentials.
• Capacity control: limits concurrent calls and calls per second per customer or route.
• Number manipulation: adds or strips prefixes and normalises to E.164.
• Accounting: writes CDRs for billing and reports metrics such as ASR and ACD.

Class 4 vs Class 5 softswitches

Softswitches are classified after the old North American switching hierarchy. A Class 4 softswitch is a transit or tandem switch that moves large volumes of calls between carriers. A Class 5 softswitch serves end subscribers with features such as voicemail, call forwarding and hosted PBX. Many products combine both. See Class 4 vs Class 5 softswitch.

Softswitches and gateways

Modern softswitches scale horizontally, with several call-control nodes behind load balancers and a shared database, so capacity can grow without replacing hardware.

A softswitch rarely touches the physical network itself; it hands calls to SIP trunks, SBCs and gateways. A mobile GSM gateway appears to the softswitch as one more route. GSMCalls connects to softswitches as a standard SIP trunk and reports per-route CDRs, ASR and ACD; see the platform.