Why SIP Trunking Is Essential for Call Centre Efficiency and Cost Savings

SIP Trunking Article Summary

1. SIP trunking connects an IPBX to the public telephone network over an IP connection, helping businesses modernise legacy phone links while keeping existing telephony infrastructure.
   
2. Choosing the right SIP trunk solution depends on simultaneous call capacity, IPBX interoperability, service continuity, security settings, essential call features, and total cost.
3. Ringover does not offer traditional SIP trunking, but its BYOC add-on lets companies connect their existing operator’s SIP trunk to Ringover while using Ringover as the main cloud telephony platform.

With BYOC, a company can keep its operator and SIP trunk while using Ringover’s cloud features.

Internet now plays a central role in business communications, from instant messaging to video conferencing and IP telephony, or Internet Protocol telephony.

When researching a telephony solution for your company, you may have come across the terms “SIP trunk,” or “SIP trunking” without always knowing what they cover or how they differ.

What is a SIP trunk? What is it used for, how does it work, and what benefits can it offer a business? This article gives you practical answers and presents the main criteria to consider when choosing a SIP trunking solution suited to your infrastructure and use cases.

What Is a SIP Trunk?

A SIP trunk, sometimes called a “SIP account,” is the junction, or link, that allows a company with an internal Internet-based telephony system, such as a VoIP PBX, to route its phone communications to the public network.

It takes the form of channels established between the company’s internal telephony system and the Internet network. It corresponds to the old T0/T2 copper channels used when communications passed through traditional telephone systems, such as a PABX.

The higher the number of channels, the more communications the SIP trunk can carry simultaneously.

How Does a SIP Trunk Work?

When you make a call, several components are involved[2]:

1. The phone or telephony software sends the request to the IPBX.
2. The IPBX applies the dialling and routing rules.
3. The SIP trunk transmits the signalling to the operator’s infrastructure.
4. The operator routes the call to the public network and the recipient.
5. Once the session is established, the audio stream circulates between the relevant equipment.

The session border control is responsible for securing and ensuring the quality of communications. To put it simply, it plays the same role for your phone system as a firewall does for your Internet access.

The call then reaches the proxy, which chooses the best routing path before sending it to a second SBC dedicated to the operator. This SBC then routes the call to the recipient. If the recipient is available, they send an acceptance back to your phone and the call can begin. With a diagram, it becomes even clearer:

Can Your Company Benefit From a SIP Trunk? Who Is It For?

A SIP trunk is mainly designed for companies that already have a compatible IPBX and want to keep control of their telephony environment. A SIP trunk may suit an organisation that wants to:

• keep an IPBX and its associated call scenarios;
• replace legacy telephone access;
• consolidate calls from several sites;
• choose its operator and phone system separately;
• size the number of simultaneous communications;
• connect an existing telephony infrastructure to the public network.

Take the example of an industrial company with an IPBX connected to desk phones, intercoms, and an on-call system. Immediately replacing all this infrastructure with a cloud platform could create a disproportionately large project. A SIP trunk makes it possible to modernise the operator link while keeping the IPBX, at least temporarily.

Why Do Companies Replace Their Old Telephone Links?

The move to IP-based telephony is closely linked to the retirement of the Public Switched Telephone Network, or PSTN. BT has said it plans to retire its PSTN by January 2027, and providers that use BT’s network are expected to follow a similar timeline. This does not mean every business must choose SIP trunking.

Some companies may replace legacy phone lines with a SIP trunk while keeping an existing PBX, while others may move to hosted VoIP, cloud telephony, or a fully digital business phone system. Businesses should also review any services that depend on analogue lines, such as alarms, payment terminals, lift phones, entry systems, or fax machines, before the migration. Ofcom notes that the decision to close the PSTN was made by industry, not by Ofcom or the UK Government, and that landline calls are moving to digital technology over broadband connections.

This deadline does not mean that every company must adopt a SIP trunk. Several paths are possible:

• replace a legacy link with a SIP trunk while keeping the IPBX;
• migrate to a hosted IPBX;
• adopt a fully cloud-based telephony platform;
• temporarily keep certain equipment behind a compatible gateway.

What Is the Difference Between SIP, VoIP, and a SIP Trunk?

These three concepts refer to different things.

It is therefore not relevant to oppose “SIP” and “VoIP.” SIP can help power a VoIP service, but VoIP does not necessarily rely on SIP in every architecture.

The Benefits of SIP Trunking for Your Company

Keeping an Existing IPBX

The main benefit is that it modernises telephone connectivity without necessarily replacing the phone system. This approach limits changes for users and makes it possible to keep sometimes complex business configurations. It remains dependent on IPBX compatibility. Older equipment may require an update, a license, an SBC, or an additional gateway.

Adapting the Number of Channels

Capacity can be adjusted according to the expected number of simultaneous calls. This flexibility is especially useful for companies facing seasonal peaks or gradual team growth. However, the contract terms should be checked: activation time, minimum unit, commitment, and pricing for additional channels.

Separating the Choice of Operator From the Choice of IPBX

You can compare several operators without immediately questioning your phone system. This separation makes competitive comparison easier, subject to technical compatibility and portability conditions.

Increased Performance and Productivity

Unified communications can improve productivity and efficiency by facilitating collaboration, particularly through computer telephony integration, or CTI, and mobility. They are therefore especially useful in a remote work context.

Flexibility and Progressive Migration

With a SIP trunk, you can freely and simply add or remove channels according to your company’s needs and objectives. The SIP trunk can serve as an intermediate step before a full migration to the cloud. A company can keep certain functions on its IPBX, gradually transfer its numbers, and test a new architecture before the final switch.

How to Choose a SIP Trunk Solution

Here are the key points to consider when choosing your SIP trunk:

1. Measure Simultaneous Calls

Analyse inbound and outbound call peaks over several weeks. Add a suitable margin for sales campaigns, peak periods, and external transfers, which can use several channels depending on the architecture.

2. Check Interoperability

Ask the operator whether your IPBX model and version have already been tested. A general statement of “SIP compatibility” does not replace an interoperability matrix or pilot phase.

3. Examine Service Continuity

The contract should specify:

• the availability rate;
• the recovery time;
• the escalation procedures;
• the routing planned in case of failure;
• geographic redundancy;
• the conditions for using a second Internet access.

4. Check the Security Settings

Verify the authentication mechanisms, IP address filtering, TLS support for signalling, SRTP support for media, and tools for detecting abnormal use.

The goal is, in particular, to limit the risks of unauthorised access and telephone fraud. The mere presence of the word “SIP” or an SBC in an offer is not enough to demonstrate the level of protection.

5. Test Essential Features

Transfers, call forwarding, special numbers, international calls, and overflow scenarios should be tested before migration. A feature available on the IPBX may depend on the trunk’s behaviour to work correctly.

6. Compare the Total Cost

For two offers with the same number of channels, compare installation fees, included communications, destinations, security options, support, backup options, and exit terms.

An offer that is cheaper per channel can become more expensive if it requires a specific SBC, an integration service, or high communication charges.

Does Ringover Offer SIP Trunking?

No, Ringover is not a traditional SIP trunk provider designed to supply an external IPBX. It is first and foremost a cloud telephony platform: users make and receive calls through its interface, its applications, or the business tools it integrates with. The platform notably brings together routing, numbers, IVR, statistics, and communication features. However, you can use it with a SIP trunk.

BYOC: Connecting Your Operator to Ringover

Ringover offers a BYOC approach, for Bring Your Own Carrier. In this architecture, you keep your operator and connect that operator’s SIP trunk to the Ringover platform. You will find all the information needed to create this connection in our BYOC documentation.

The table below nevertheless helps you better understand how to use it:

BYOC is intended for companies that want to keep their operator while using Ringover as the main application layer and is offered as an add-on.

Keep Your Operator While Moving to Cloud Telephony

A SIP trunk is a relevant option for keeping a compatible IPBX while replacing old telephone links. However, the success of the project depends on four factors: technical compatibility, channel sizing, network resilience, and total cost of ownership.

For companies that want to keep their telephone operator while benefiting from Ringover’s cloud features, the BYOC option offers a complementary approach. It makes it possible to connect the current operator to Ringover in order to centralise calls, routing, users, statistics, and business integrations within a single platform.

Would you like to keep your operator while modernising your telephony environment? Contact a Ringover expert to study the compatibility of your infrastructure and the possibilities offered by BYOC.

SIP Trunk FAQ

What Is a SIP Trunk Used For?

A SIP trunk is a way to connect an IP phone system to a telephony service provider over the Internet. Its purpose is to provide companies with a flexible, cost-effective, and scalable communication solution by making it much easier to manage several simultaneous calls and significantly reducing communication costs.

What Is SIP?

In telecommunications, SIP, or Session Initiation Protocol, is a signalling protocol used to establish, modify, and close multimedia communication sessions. These may include phone and video calls over IP networks. The SIP protocol facilitates data routing, session management, and media stream management during these communications.

It plays a key role in IP telephony services because it ensures communication between different devices and networks. It offers advanced features that are essential for businesses, such as transfers, call forwarding, and voicemail.

How Do You Set Up a SIP Trunk?

To set up a SIP trunk within your system, follow these steps:

1. Evaluate the need for channels based on the maximum number of simultaneous inbound and outbound calls.
2. Choose a SIP trunk provider based on coverage, pricing, availability commitments, support, and backup solutions.
3. Check technical compatibility between the selected service and your IPBX, especially codecs, authentication methods, and security settings.
4. Configure the IP phone system with the identifiers, numbers, and routing rules provided by the supplier.
5. Test the main call scenarios: inbound and outbound calls, transfers, number presentation, simultaneous calls, and failover to the backup link.
6. Monitor service quality after deployment, particularly latency, packet loss, interruptions, and channel occupancy.

For a complex or multisite infrastructure, it is preferable to entrust the configuration to the operator, telecom integrator, or team responsible for the IPBX.

Does a SIP Trunk Work Without an IPBX?

It must be connected to a system capable of handling SIP calls, such as an IPBX, SBC, or compatible platform. If the company does not want to administer this infrastructure, cloud telephony may be more suitable.

How Do You Size a SIP Trunk?

You need to measure the maximum number of simultaneous inbound and outbound calls. The number of employees is not enough: 100 users may only occupy 20 channels at peak activity, while a smaller contact centre may need more.

Does a SIP Trunk Guarantee Better Audio Quality?

Not necessarily. Quality depends on the connection, local network, codecs, configuration, and operator service. Our recommendation is that a pilot under real conditions remains essential.

Can You Keep Your Numbers?

Portability is generally possible, but it must be confirmed for each number category and geographic area. You should also plan the porting schedule and account for the risk of interruption during migration.

What Is the Difference Between a SIP Trunk and Cloud Telephony?

With a SIP trunk, the company generally keeps its IPBX and buys connectivity from an operator. With cloud telephony, the phone system, routing, and applications are hosted and administered by the platform provider.

Citations

• [1]https://www.rfc-editor.org/info/rfc3261/
• [2]https://www.rfc-editor.org/info/rfc3550/
• [3]https://www.arcep.fr/mes-demarches-et-services/collectivites/fiches-pratiques/la-fermeture-du-reseau-cuivre-quels-enjeux-pour-la-connectivite-de-mon-territoire.html

Published on May 26, 2023.