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VoIP softswitch guide

What is a Class 4 softswitch? Class 4 vs Class 5 explained

If you carry VoIP traffic between carriers, you need a Class 4 softswitch. If you serve end users with phone lines, you need a Class 5 one. The names come from the old telephone network, but the difference still decides which platform fits your business. This guide explains both, compares them side by side and lists what to look for in a Class 4 switch.

What is a softswitch?

A softswitch is software that connects VoIP calls. It receives a call (usually over SIP), decides where to send it, connects it to the next network and records what happened for billing. In the old telephone network these jobs were done by hardware exchanges, which were grouped into "classes". VoIP kept the names: Class 4 for transit between networks and Class 5 for local service to users.

What is a Class 4 softswitch?

A Class 4 softswitch is a transit or "tandem" switch. It does not serve individual users; it moves large volumes of calls between carriers. A wholesale VoIP business uses it to receive calls from customers (other carriers, resellers, call centres) and send them on to vendors that terminate them in each country.

Its main jobs are routing (choosing the vendor for each call, often by least cost), rating (pricing each call with buy and sell rates) and monitoring quality and margin across many trunks at once.

What is a Class 5 softswitch?

A Class 5 softswitch is a local exchange for end users. It registers phones and softphones, gives each user a number and provides calling features such as voicemail, call forwarding, IVR menus, conference calls and hosted PBX. Retail VoIP providers, ITSPs and UCaaS companies use Class 5 platforms.

Class 4 vs Class 5: side by side

	Class 4 softswitch	Class 5 softswitch
Role	Transit between carriers	Local service to end users
Customers	Carriers, resellers, call centres	Businesses and consumers
Connections	SIP trunks with IP authentication	Registered phones, softphones and PBXs
Key features	LCR routing, A-Z rate decks, CDR rating, margin reports	Voicemail, IVR, call forwarding, conferencing, PBX
Billing	Wholesale: per-minute buy and sell rates, invoices between carriers	Retail: plans, bundles, per-user subscriptions
What matters most	Capacity, routing, margin and route quality (ASR, ACD)	Features, user experience and reliability

Which one do you need?

Wholesale voice carrier or reseller: Class 4. You buy and sell minutes between networks and live on routing and margin.
Call centre sending large outbound volumes to several vendors: Class 4, to pick the best vendor per destination.
Retail VoIP or hosted PBX provider: Class 5 for your users, often connected to a Class 4 switch or a wholesale carrier for termination.
Both: many operators run a Class 5 platform for customers and a Class 4 switch behind it to route their outbound traffic to the cheapest good vendor.

Must-have features in a Class 4 softswitch

Routing

Least cost routing with priority overrides, allow and block lists per customer and vendor, and a route tester that shows which vendor a number will use.

Rate management

Bulk A-Z deck upload with validation, per-customer rate plans with effective dates and one master list of destinations.

CDR rating and margin

Every call rated against buy and sell rates, margin per call, re-rating when rates change and margin reports by customer, vendor and destination.

Live operations

Real-time calls monitor, ASR and ACD on the dashboard, test calls to check routes and a NOC ticket system linked to CDRs.

Billing

Automatic invoices from rated CDRs, credit and debit notes, payments and statements of account for customers and vendors.

Control and security

IP-authenticated trunks, role-based users, a full audit log, a self-service portal for customers and data you own.

Route-Setu Voice: a Class 4 softswitch from LCR ONE

Route-Setu Voice is a carrier-grade Class 4 softswitch with a web control panel: LCR and priority routing, A-Z deck upload with 4-decimal precision, automatic rating and per-call margin, six margin report types, a real-time calls monitor, call-loop test campaigns, NOC tickets, automatic invoices and a customer self-service portal. It runs self-hosted on your own servers, or fully managed by LCR ONE.

See Route-Setu Voice → Book a free demo

FAQ

What is the difference between a Class 4 and a Class 5 softswitch?

A Class 4 softswitch carries calls between carriers (transit and wholesale), while a Class 5 softswitch serves end users with phone lines and features such as voicemail, IVR and PBX.

Do I need a Class 4 softswitch for wholesale VoIP?

Yes. Wholesale VoIP is about routing calls between customers and vendors at a margin, which is exactly what a Class 4 softswitch does with LCR routing, rate decks and CDR rating.

Can one switch do both Class 4 and Class 5?

Some platforms combine both, but most operators keep them separate: a Class 5 platform for users and a Class 4 switch for routing outbound traffic to vendors.

What is a tandem switch?

Tandem is another name for a transit switch that connects other switches or networks rather than end users. A Class 4 softswitch is a tandem switch for VoIP.

Should a Class 4 softswitch be self-hosted or cloud?

Both work. Self-hosting keeps your CDRs and rates on your own servers; a managed setup means the vendor runs the servers for you. Route-Setu Voice supports both options.

Last updated: 26 October 2026 · LCR ONE