SIP trunking explained: Moving from PSTN to SIP trunk
The trusted old Public Switched Telephone Network (PSTN), with its Analog lines, ISDN BRI, E1 or t1 lines, are gradually being replaced by IP telephony. An increasing number of businesses are using more modern and flexible SIP Trunks.
The major telecom providers are fast phasing out the old PSTN functionality and are moving customers to IP. Many European countries have already completely phased out ISDN with countless others to follow. The majority of businesses these days are already using modern IP phone systems and SIP trunks, although some smaller businesses may still rely on outdated technology.
Phone companies like Verizon have phased out ISDN in the U.S. and in the UK, ISDN lines have significantly decreased. In 2017 major telcos such as KPN, France Télécom, Deutsche Telekom, Telecom Italia, and British Telecom began to retire ISDN lines, with the UK announcing that their entire ISDN infrastructure would be retired by 2025.
As a result, Session Initiation Protocol (SIP) trunking has increased dramatically, with the market value expected to reach US$35.5 billion by 2030. Unlike a PSTN provider, the lines provided are not physical, but a service provided over your internet connection. Your provider supplies phone numbers and virtual lines, usually at better rates than the traditional carriers and with more flexibility and shorter contract durations.
This guide explains what SIP Trunks are, the difference from PSTN, their advantages, and how you can make the move.
What is a SIP trunk?
A SIP trunk is the modern-day equivalent of a T1 trunk. Where in the past you would buy a T1 trunk from a Telco provider and connect it to your legacy PBX, today you can make a purchase from an ITSP (Internet Telephony Service Provider) and connect it to your VoIP / IP PBX. SIP trunks use the SIP standard. The name ‘trunk’ comes from the telecom world and it means, more or less, a group of phone lines.
Using this standard protocol, telecom service (VoIP) providers connect one or more channels to the customer’s PBX. Phone numbers and DIDs are linked to the SIP trunk and in many cases, numbers can be ported to the new service.
What are the pros and cons of SIP trunking?
Pros
Cons
Selecting the right provider
The next step is to choose your provider. A few factors come into play when making this decision:
Upgrading internet connectivity
Once you have selected your provider, consider a dedicated internet line for the SIP Trunk. Most firewalls are able to handle multiple WAN connections, and, considering the low cost of an internet line in most places, a separate connection will be the most reliable way to ensure the quality of your VoIP calls.
Some providers bundle their offering with a dedicated internet line. This keeps your voice traffic separate from your data traffic. Much will depend on the cost and your network infrastructure. Check that your firewall is up-to-date and will be capable of handling VoIP traffic correctly.
How to upgrade the PBX to an IP PBX
Chances are that the old PSTN lines are connected into another old device, the hardware-based PBX system. This device is inflexible, difficult to manage and often expensive to maintain. Technically it is possible to buy a gateway that allows the old PBX to talk to the SIP Trunks. But why not upgrade to a modern IP PBX and leverage the flexibility and modern features IP telephony can bring to your business phone system. This allows you to take advantage of the cost savings, easy management, and productivity increases with full-scale Unified Communications that an IP PBX offers. 3CX can be easily deployed on-premise with Windows or Linux, virtualized with VMware, KVM or Hyper V. Alternatively you can opt for a hosted solution managed by 3CX or hosted in your private cloud account with Google, Amazon, Microsoft Azure and more.