What does SIP trunk mean?

Session initiation protocol (SIP) trunking is a technology used for voice over IP (VoIP) communication. SIP trunks let businesses operate a large number of VoIP numbers over a single connection.

Historically, our telephones relied on the public switched telephone network, which used analog lines or ISDN BRI or T1 lines to connect users. If you wanted to run a contact center, you'd invest in a private branch exchange (PBX) and rent a T1 trunk from your telecommunications provider, to use with primary rate interface (PRI) connections.

The trouble With PSTN

A PRI connection lets you have up to 100 phone numbers but supports only 23 voice channels. This means you can't have a call taking place on each of those phone numbers at the same time. You're limited to just 23 simultaneous calls.

If you want to handle more calls, you'll need to add more PRI connections. SIP trunks offer an interesting solution to this, making use of an existing ethernet or fiber connection to power VoIP connections. According to a recent Gartner report, SIP trunking can cut business telecom expenses by as much as 50%.

Defining SIP trunk

To provide a simple SIP trunk definition, this technology connects your existing PBX to a data network using the Session Initiation Protocol. The SIP trunk is a virtual connection that uses a packet-switched model to let you make calls using a data connection.

With SIP trunking, it's possible to add as many users as you wish, there's no hard limit based on the capacity of the line. Each user is given a virtual connection, and a new phone number or extension is generated for them.

The limiting factor for IP connections is the bandwidth of the line and the VoIP codec you're using. The most common codec is G.711, which uses 64Kbps, but there are other codecs that have better compression. SIP is a two-way protocol, and you'll need both upload and download bandwidth for stable calls.

Why use SIP trunking?

SIP trunks offer several potential benefits over PRIs and legacy PBX hardware:

  • Lower installation costs: There's no need for expensive equipment.
  • Improved scalability: Adding new virtual connections is a matter of a few mouse-clicks.
  • Lower call charges: For long-distance calls in particular, SIP offers huge potential for cost-savings.
  • Flexibility: SIP numbers are portable, so you can move them to other locations and even create local numbers for areas you serve without needing a physical address in that area.

Today, even domestic connections are fast enough to accommodate multiple VoIP users. Business-grade connections should be able to accommodate hundreds of users quite comfortably, offering substantial cost savings over a traditional PBX.

Call quality may degrade if the internet connection is under heavy load, perhaps due to other applications also consuming bandwidth. Using QoS to prioritize voice data could reduce the risk of this happening and help maintain stable call quality.

If you're interested in learning about SIP trunking, VoIP and how these services could help you grow and scale your business, call 8x8 today or contact us to request a quote for our business phone services. Our cloud PBX systems make it easy to manage your contact center, providing everything you need in one simple app.