A Class 4 softswitch routes calls between carriers in bulk (wholesale transit and termination), while a Class 5 softswitch serves end users with features such as extensions, voicemail, IVR and calling plans. Wholesale VoIP carriers run Class 4 switches; retail VoIP providers, hosted PBX and calling card businesses run Class 5, and many platforms combine both.
What is a softswitch in VoIP?
A softswitch is software that does the job of a traditional telephone switch: it receives calls (usually over SIP), decides where to send them, connects them to the next network and records each call for billing. The names Class 4 and Class 5 come from the old North American switching hierarchy, where Class 4 switches were toll and tandem switches between exchanges and Class 5 switches were local exchanges that connected subscribers' lines.
Class 4 vs Class 5 softswitch: the differences
| Class 4 softswitch | Class 5 softswitch | |
|---|---|---|
| Connects | Carrier to carrier (trunks) | End users to the network |
| Main job | Routing, LCR, transit and termination | Subscriber services and features |
| Customers | Carriers, resellers, call centers buying wholesale | Businesses and consumers |
| Key features | Least cost routing, rate decks, ASR/ACD-based routing, CDR billing, number manipulation, high CPS | Extensions, voicemail, IVR, call forwarding, conferencing, calling cards, DIDs |
| Billing | Per minute between carriers, by destination prefix | Per user, per plan or per minute |
| Scale measured in | Concurrent calls and calls per second | Number of subscribers and features |
In practice, a wholesale carrier's Class 4 switch picks the cheapest supplier that meets quality targets for each prefix, using its rate decks (see least cost routing in telecom and what is a VoIP rate deck). A Class 5 switch knows each user and what they are allowed to do.
Which softswitch do you need?
- Selling termination to carriers or call centers: Class 4. You need per-customer rate plans, LCR, failover, ASR and ACD reporting and CDR export for CDR reconciliation.
- Selling phone service to businesses or consumers: Class 5, or a hosted PBX platform.
- Both: a combined platform, or a Class 5 platform that hands outbound calls to a Class 4 switch for termination.
Plan capacity with channels and CPS in mind: dialer traffic can need far more calls per second than conversational traffic.
What softswitch products and open-source options exist?
A few names that come up often, described from public information:
- VOS3000 by Kunshi Network Technology: a softswitch and billing platform used in wholesale VoIP, supporting SIP and H.323.
- Kolmisoft MOR and M4: Kolmisoft positions MOR (built on Asterisk) as a Class 5 platform and M4 (built on Kamailio, SEMS and RTPEngine) as its Class 4 wholesale switch.
- Telinta: a hosted softswitch platform that Telinta describes as both Class 4 and Class 5.
- Open source: Kamailio and OpenSIPS are SIP proxies often used as the core of Class 4 routing; Asterisk and FreeSWITCH are often used for Class 5 features. They are building blocks, so billing, rating and management interfaces have to be added.
When choosing, compare routing logic, CDR and billing accuracy, CPS capacity, fraud controls, security updates and support. Whatever you use, apply the protections in toll fraud and PBX hacking.
Softswitch vs SBC: what is the difference?
A session border controller (SBC) protects and normalises the edge of the network: it hides topology, filters attacks, fixes SIP differences between vendors and handles media and NAT. The softswitch decides routing and billing. Wholesale operators usually put an SBC in front of the Class 4 switch, and some products combine both roles.
Routes for your switch
A softswitch needs supply on the other side. VoIPMatcher sources wholesale VoIP termination from its carriers and manages it; you connect over SIP as with any supplier (see SIP interconnect setup). Request a voice route with your destinations and traffic type.
Frequently asked questions
What is VOS3000?
VOS3000 is a VoIP softswitch and billing platform developed by Kunshi Network Technology. It is used mainly by wholesale VoIP operators for routing, rating and billing calls between carriers, and supports SIP and H.323. Check the vendor for current versions and licensing.
Is there an open-source Class 4 softswitch?
There is no complete open-source Class 4 product with billing in one package, but Kamailio and OpenSIPS are widely used open-source SIP proxies for carrier routing. Operators combine them with media relays, rating and billing systems, or buy a commercial platform built on top of them.
Is Asterisk a Class 5 softswitch?
Asterisk is an open-source communications framework that provides Class 5 style features such as extensions, voicemail, IVR and conferencing. It is often used as the core of PBX and retail VoIP platforms, but it is not designed for high-volume carrier transit.
Do I need a softswitch to buy VoIP termination?
Not always. A call center can send calls from its dialer or PBX directly to a carrier over SIP. A softswitch becomes necessary when you buy from several carriers, resell to customers, or need least cost routing, failover and per-customer billing.
Need a route?
Send the destination, route type and target rate. We reply with what we can deliver.