Understanding SIP Trunk and SIP Lines

Understanding SIP Trunk and SIP Lines

Though there are many innovative ways to market to your customers via SMS and email, phone calls are still as important as ever to an organization’s communication strategy. It’s easy to stick to the traditional phone line status quo, but to do so is to ignore the opportunity to save money and take advantage of an affordable, scalable system on the cloud.

SIP trunk phone systems offer an opportunity to increase your efficiency while cutting the costs of a traditional, physical phone line system. Taking place entirely on the cloud, SIP systems enable an existing phone system to function online by routing calls via an on-premise private branch exchange (PBX) through a SIP line connected to an organization’s SIP trunk and then out to its intended recipient.

Whether you’re looking to make the switch to an entirely online SIP phone system or are just looking for some clarification of the important technical terms, we’ve got you covered. Let’s get into it!

Defining terms

Before we get into the nitty-gritty details, let’s review a couple of key terms and concepts about SIP trunk phone systems to make sure we’re all on the same page.

What is SIP trunking?

Session Initiation Protocol, or SIP, trunking is the process by which phone calls are placed online rather than on physical phone lines. SIP trunking relies on an existing PBX system connected to the cloud to place inbound and outbound calls.

By enabling your phone system to operate online rather than using physical phone lines, your business gains more flexibility in its ability to reach customers. Because you're routing calls online, you can contact any customer around the world, so long as they have an active phone number.

What is a SIP trunk?

A SIP trunk refers to the digital version of a traditional phone system. It can connect to many SIP lines, which provides individual phone numbers and lines across an organization.

What is a SIP line?

A SIP line or channel is the individual phone line connected to the greater SIP trunk. One SIP line can route one call at a time, but a SIP trunk can handle any number of SIP lines. Best practice dictates that companies should have one SIP line for every call the companies plan to place simultaneously.

SIP lines vs. SIP trunks

SIP trunks and SIP lines are two parts of the broader SIP trunking phone system and are, therefore, closely linked. Each SIP trunk must be equipped with SIP lines in order to place calls online, so let’s talk about capacity and cost.

Because capacities and costs vary by provider, we’ll use Twilio’s Elastic SIP Trunking as an example in the following sections.

SIP line vs. SIP trunk capacities

Elastic SIP Trunking from Twilio starts at 100 SIP trunks, allowing customers the flexibility needed to scale an SIP solution. Twilio’s SIP trunking solution allows one trunking termination call per second (CPS) and unlimited trunking origination calls per second. It also allows unlimited concurrent calls and origination phone numbers.

A few quick definitions:

• Trunking termination CPS refers to the number of new outbound SIP calls allowed in one second.
• Trunking origination refers to the number of inbound calls that can be received and, with Twilio’s Elastic SIP Trunking, this number is unlimited.
• Unlimited concurrent calls mean that you can place as many simultaneous calls as your servers allow in a given moment.

This allows you to build a completely customized SIP solution for your organization, no matter your telephony needs. As your organization grows and scales, Twilio can help you increase these numbers.

SIP line vs. SIP trunk costs

Twilio’s Elastic SIP Trunking operates on a pay-as-you-go system, allowing you to keep efficiency high and costs low. Outbound calls in the U.S.’s 48 contiguous states start at $0.0050 per minute, and inbound local calls start at $0.0034 per minute.

For more information about Twilio's Elastic SIP Trunking costs, check out our SIP trunking pricing page.

Requirements

In order to have a functioning SIP trunk phone system, you must have an existing PBX around which to build the SIP trunk. In a SIP system, calls are routed via PBX through the SIP trunk and then out to the call recipient. For this to work, the entire system must be connected to the cloud.

To configure your Twilio Elastic SIP Trunk, check out our step-by-step Elastic SIP Trunking documentation.

SIP system benefits

Because they live online, SIP systems provide organizations with much more flexibility than traditional physical phone lines. Each trunk can handle an infinite number of SIP lines, which allows you to place as many simultaneous calls as necessary. Additionally, SIP systems avoid the costly setup of traditional, physical systems, as setup and deployment can often be completed remotely. This makes maintenance and scaling easy once your system is live.

SIP systems also provide callers with analytics that traditional lines can't track, supplying you with all of the benefits of a call center. These analytics are invaluable in tracking your organization’s efficiency and understanding the customer experience.

Twitter’s global telephony infrastructure

Twitter uses Twilio Elastic SIP Trunking to support its telephony infrastructure around the world. Having experienced massive growth since its founding in 2006, its communications solutions needed to be able to scale with it internationally. Elastic SIP Trunking made the building and shipping process easy with solutions in each country that follow local regulations and match Twitter’s needs.

Read more about Twitter’s journey with Twilio here.

Elastic SIP Trunking at Twilio

Twilio’s Elastic SIP Trunking solution supplies you with everything you need to deploy a global VoIP infrastructure from the Twilio Console in minutes.

We provide the best possible support for your SIP system, redundantly routing your calls through our Super Network to increase global call reliability. At the same time, Voice Insights help you precisely track your analytics as you go.

Get started with Elastic SIP Trunking today or talk to an expert to learn more. We can’t wait to see what you build!