Glossary

PSTN (public switched telephone network)

The PSTN (public switched telephone network) is the public phone network: every landline and mobile number across all carriers. A contact center connects to it so customers can reach it from any phone and agents can call any number. This is usually a SIP trunk from a carrier, sometimes a T1/E1 line or a GSM gateway.

Why it mattersWithout a connection to it, nobody can reach your contact center from an ordinary phone, and you can't call anyone.

Also called: Public phone network, Public switched telephone network, Plain old telephone service (POTS)

How it works

The PSTN is made up of all phone carriers' networks, connected to each other. A customer on a mobile phone calls a landline number on another carrier's network, and the call goes through because carriers hand calls off to each other.

A contact center has its own phone system – a PBX or a platform. To be reachable from outside, it needs a way into the public network. A carrier provides it by assigning numbers and lines that carry the calls. The number of lines sets how many calls can run at the same time.

Options

Ways to connect

SIP trunkA line from a carrier over the internet or a dedicated link. The most common option: no hardware needed, and you add or remove lines by asking your carrier.

T1/E1 lineA dedicated digital line for 24 (T1, US) or 30 (E1, Europe) simultaneous calls. Found at large companies and on older PBXs; it connects to VoIP through a gateway.

GSM gatewayA device with mobile carrier SIM cards: as many simultaneous calls as SIM cards.

In CONTACT.WORK

How it works in CONTACT.WORK

The platform connects to the phone network through SIP trunks, T1/E1 lines, and GSM gateways from any carrier. You can keep your numbers and your carrier. You can also connect several carriers at once and split calls between them – for example, so calls fail over to one carrier when another has an outage.