7 Reasons to Adopt SIP Trunking in Your Contact Center

August 25, 2021
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If you haven’t already moved your contact center from PRI trunks to SIP trunks, it may be time to give it another look. That’s because several recent cloud-driven technology trends have made the case for SIP trunking even stronger. Putting SIP trunks in place could not only save money and increase agility, but also enable you to dramatically improve customer experiences.

There are three major trends at work:

  1. Cloud-based natural language processing engines are enabling contact centers to deploy voicebots (aka virtual agents) that are less costly and offer better experiences than live agents. These services connect to the PSTN via SIP trunks.
  2. Cloud-based contact center as a service (CCaaS) is displacing on-premises infrastructure by offering more flexibility and better economics. Like voicebots, these services connect to the PSTN via SIP trunks.
  3. A new category of cloud-based SIP trunking services provide more flexibility and better geographic coverage than traditional telco-based SIP trunks.

When you combine these trends with the many inherent advantages of SIP trunking over PRIs, it makes for a pretty compelling case. Even if you don’t have immediate plans to adopt any of these cloud technologies, moving to SIP trunking provides many benefits and puts you in a better position to leverage them when you’re ready. In this blog, I’ll sum up all the reasons you should consider ditching your PRIs for SIP trunks.

What is SIP Trunking?

SIP trunks replace the dedicated physical connections between your contact center and the telephone network with virtual connections that are transported over an IP network.

Legacy public switched telephone network (PSTN) connections are based on time division multiplexing (TDM) technology and are called primary rate interfaces (PRI). They have been in use since the 1980s. A PRI requires specialized on-premises equipment and a dedicated line from a telecommunications company, making them expensive to operate and less reliable than modern IP-based technology.

In contrast, SIP trunks enable you to establish PSTN connections over any IP-based network. The Session Initiation Protocol (SIP) formats phone calls into IP packets that can be carried over MPLS and public internet services. This allows you to consolidate telephony services onto the same broadband IP connection used for all your digital applications, saving money and increasing flexibility.

Today, market analysts estimate over half of PRI connections in the world have been converted to SIP trunks. In addition, many telecommunications service providers have announced plans to retire their PRI services. Clearly, it’s only a matter of time before the entire telephone network is converted to SIP trunking.

What is the Difference Between Cloud and Telco-based SIP Trunking?

Over the past six years, two categories of SIP trunking services have emerged: those offered by traditional telecommunications companies (e.g. Lumen, Verizon, Orange, BT) and those offered by communications platform as a service companies (e.g. Twilio, Plivo, Bandwidth, Vonage).

Telcos developed the first generation of SIP trunks to deliver service within their operating region. These services inherited certain characteristics of their PRI predecessors, including:

  • Services and pricing are set under rigid multi-year contracts;
  • Access to the service and availability of local telephone numbers is limited to the areas served by the telco, which correspond with its national operating region;
  • The number of concurrent calls that can be established at any time is fixed and bursting to accommodate unexpected traffic spikes is limited.

Communications platform as a service (CPaaS) companies offer the newest generation of SIP trunking service, with far greater flexibility and geographic coverage. These SIP trunking services inherit the characteristics of most cloud-based applications:

  • Pay-as-you-go pricing with the ability to instantly configure service online using a credit card;
  • Services accessible across multiple regions with local phone numbers available;
  • Unlimited capacity for concurrent calls with no penalties
  • Self-service configuration and real time control

There is lots more to discuss on this topic. See Comparing Cloud vs Telco SIP Trunks: Which is Better? for more information.

Why SIP Trunking in the Contact Center?

Now, let’s get to the heart of the matter. Why should you switch your PRIs to SIP trunks? Here are seven very strong reasons.

1 - Flexible Routing and Access to Advanced Services

Because SIP trunks run over an IP network, they are easily routed to specific contact center locations or services, and the routing can be quickly reconfigured to take advantage of new resources. For example, you can connect trunks to on-premises infrastructure today, and move them to a cloud-based voicebot service, tomorrow.

Cloud-based natural language processing services support real time call hand-off via SIP interfaces. IBM Watson is the first major service to accept calls via a contact center’s SIP trunk service, plus the ability to transfer calls from its bot service back to a human contact center agent in case the bot is unable to satisfy a customer request. It allows you to add a voicebot service to your omnichannel contact center that wouldn’t be possible with PRI trunks.

Google Dialogflow, Amazon Lex and Microsoft Azure, the other major NLP services, connect to the PSTN via their own SIP trunk interfaces and can’t yet accept or transfer calls through a contact center’s SIP trunk.

Another example: SIP trunking is the only way to connect your inbound callers to the contact center as a service (CCaaS) offerings from Twilio, Genesys, Talkdesk, Five9 and other major providers. Most major providers offer two ways to make the SIP connection: You can bring your own carrier (BYOC) or the CCaaS can manage everything for you. By moving to SIP trunking, you position your organization to leverage CCaaS when it’s ready. BYOC Secrets: There is More to SIP Trunking Than You Think explains further.

2 - Increased Reliability

A fiber cut or an equipment failure on a PRI access line can idle all the agents in a contact center and negatively affect customer experiences.

SIP trunks are more resilient than PRIs. They can instantly reroute calls over an alternative link to keep agents connected when a network or equipment failure occurs. In addition, multi-location contact centers can increase agent utilization because calls can be more easily routed between locations and agents.

3 - Instant Scalability

With SIP trunking, you don’t have to worry whether your PSTN connection has enough capacity to handle the next promotional campaign or the annual Christmas holiday sales surge. SIP trunks scale effortlessly to any number of concurrent calls. Unlike PRIs, you don’t buy capacity in 23/30 channel increments. SIP trunking offers elastic capacity.

In outbound contact centers, SIP trunks connect easily to automated dialers. This enables you to simultaneously initiate high volumes of calls. Auto dialers are key to keeping agents busy and they make it possible to rapidly issue recorded voice notifications to a large audience (e.g. reverse 911 services).

There is a caveat with telco-based SIP trunks, however. Unlike cloud-based SIP trunking, which is elastic, telco-based SIP trunking must be configured with a fixed concurrent call capacity for each destination IP address. Many telcos support “bursting” which enables you to exceed the configured capacity. But, there are limits with bursting, too.

4 - Global PSTN Connectivity

If you operate a multinational business, you’re keenly aware of the hassles of provisioning PRIs in each country where you have a contact center. A different telco vendor is required in each case, adding complexity. In addition, you may need more vendors to provision toll-free or local phone numbers in each country where you have customers, instructing them to route calls to the proper contact center.

With a cloud-based SIP trunking service, you can enjoy the simplicity that comes from being able to connect to the PSTN in scores of countries around the world through a single vendor that can also provision toll-free and local phone numbers. You can dynamically route calls from each number to any contact center or agent to optimize utilization and customer experience.

Another caveat: Most telco-based SIP trunking services don’t offer multinational services. If you need service in multiple countries, a cloud-based SIP trunking provider may be a better choice.

5 - Better Voice Quality

SIP trunking services support a range of HD codecs that can reduce agent fatigue. Most PRI services are limited to narrowband G.711 and compressing codecs that produce poor quality sound.

In contrast, SIP trunking enables your contact center to connect with callers using the highest quality codec supported by both endpoints. Major mobile carriers support AMR wideband and internet telephony services often support Opus, another wideband codec. SIP trunking enables you to use both of these HD codecs, producing noticeably richer sound quality than G.711 and better customer experiences.

6 - Advanced Features

When was the last time a new feature was added to your PRI service? The answer is probably not in this century. In the case of SIP trunking, major providers add new features all the time. For example, at Twilio, we added 19 features to our Elastic SIP Trunking service over 12 months from 2020-2021 (see Twilio Elastic SIP Trunking Increases Momentum).

Here is a short list of features offered by most major SIP trunking providers that are relevant to contact centers:

  • Encryption - SIP trunking supports strong TLS/SRTP encryption to protect calls from eavesdropping as they travel between the agent and the PSTN.
  • Cloud-based recording - Major SIP trunking service providers offer cloud-based recording with support for two channel separation. This makes it easy for contact centers to record, transcribe and analyze calls.
  • Call transfer API - Contact center applications can transfer calls between trunks using a SIP REFER, providing more ways to move calls between contact center locations and agents.
  • CallerID attestation - Outbound contact centers can improve their call connection rates because CallerID will receive an “A” attestation from their service provider when they use SIP trunking. Inbound contact centers can be assured calls are not fraudulent because the SIP trunking provider verifies the CallerID. In contrast, calls traversing PRIs may not participate in attestation under STIR/SHAKEN implementation exceptions allowed by the FCC.

7 - Cost Reduction

If you’re having trouble accomplishing your goals because of budget limitations, SIP trunking is a good way to free up some cash. Organizations that replace their PRIs with SIP trunks can reduce telecom costs up to 50%, according to Eastern Management Group (2020-2027 SIP Global Market 7-Year Forecast and Analysis). These savings are driven by reductions in their telecommunications bills and lower operating costs.

With PRIs, you pay a monthly PSTN access fee to a telecommunications company for each increment of 23 channels (30 channels in Europe and Asia) in each location. This fee is separate from the per-minute usage fees for terminating toll-free and outbound calling services. You can eliminate access fees with SIP trunks and pay only usage fees (NB: Telco-based SIP trunking services add a concurrent call capacity fee; however, this is still lower than monthly PRI access fees).

Operating costs are reduced by dramatic consolidation. Banks of channel service unit (CSU) hardware that are installed at each contact center location are replaced by a single session border controller (SBC) that can be virtualized and installed in any data center, including in the cloud. This slashes maintenance costs and simplifies administration.

Cloud-based Services Make the SIP Trunking Case

A range of new cloud-based technologies are making a compelling case for contact centers to switch their PRIs to SIP trunking services. Natural language processing services that power voicebots and cloud contact center services that provide omnichannel customer experiences are only accessible via SIP trunking services.

What’s more, communication platform as a service (CPaaS) providers are offering a new generation of SIP trunking services that are more flexible and provide better geographic coverage than the telco-based services that came before them.

Combine these arguments with the low cost, increased reliability and better scalability that are inherent advantages for SIP trunking and you’ve got a convincing proposition. If you haven’t already pulled the trigger, it could be time to plan your SIP trunking migration.