{"id":58542,"date":"2024-12-10T03:29:04","date_gmt":"2024-12-10T11:29:04","guid":{"rendered":"https:\/\/newrcblog.wpengine.com\/us\/en\/blog\/?p=58542"},"modified":"2025-06-10T02:08:53","modified_gmt":"2025-06-10T09:08:53","slug":"sip-trunking","status":"publish","type":"post","link":"\/us\/en\/blog\/sip-trunking\/","title":{"rendered":"What is SIP trunking, how does it work, and what other options does your business have?"},"content":{"rendered":"

With more and more businesses making the move to internet telephony, you don\u2019t want to get left behind. Especially as telecom providers worldwide are gradually switching from physical copper-based landlines to internet-based phone services.<\/span><\/p>\n

The thing is, if you have an on-premises PBX system with analog phone lines, you might not want to part with it just yet. That\u2019s where SIP trunking<\/span> comes in, helping you upgrade your comms without ditching all your legacy equipment.<\/span><\/p>\n

But what is SIP trunking, precisely? How does it benefit your business? And, most importantly, why might one of the alternative solutions work better for you?<\/span><\/p>\n

SIP trunking: What is a SIP trunk & what is it for?<\/strong><\/h2>\n

We\u2019ll get started with a<\/span> SIP trunk definition. SIP trunking is a technology that allows businesses to place digital phone calls using an existing on-premises PBX.<\/span><\/p>\n

A<\/span> Private Branch Exchange (PBX)<\/span><\/a>, if you didn\u2019t know, is a telephone network based and used within an organization. It connects plain old telephone service (POTS) lines to a public switched telephone network (PSTN).<\/span><\/p>\n

SIP stands for Session Initiation Protocol, which is a signaling protocol (a set of rules) for initiating, maintaining, and terminating communication sessions between two or more endpoints over an IP (Internet Protocol) network.<\/span><\/p>\n

A SIP trunk is a set of virtual phone lines or communications channels, consolidated into a single connection or \u201ctrunk.\u201d This may consist of 20 or more SIP lines or channels.\u00a0<\/span><\/p>\n

What are SIP trunks<\/span> used for? Well, they allow organizations to make and receive phone calls over the internet, instead of using traditional landlines.<\/span><\/p>\n

SIP trunking facilitates VoIP (Voice over Internet Protocol) connectivity between your on-premises phone system and the PSTN. This means you don\u2019t need physical trunk lines connecting the two, nor an ISDN (Integrated Services Digital Network) circuit at your office.<\/span><\/p>\n

In short, SIP trunking is a way of upgrading your PBX to a digital phone system, from which you can make both PSTN and VoIP-based calls. <\/span><\/p>\n

SIP trunking vs PRI<\/span><\/h3>\n

Before SIP came along, the connection between legacy PBXs and the PSTN took place over phone lines called primary rate interfaces (PRIs). PRI is a type of digital technology, but it uses the ISDN (Integrated Services Digital Network) protocol to provide connectivity.<\/span><\/p>\n

Each PRI consists of two pairs of copper wires, connecting the network to the end-user. Although it\u2019s actually a single line, it can transmit up to 23 calls simultaneously. Any more than that, and you\u2019d need multiple PRIs.<\/span><\/p>\n

PRI requires trained technicians for installation and maintenance, so it can be pricey\u2014and the hardware is fast becoming obsolete. It\u2019s inflexible, not very scalable, and vulnerable to local disruptions. The other downside of PRIs is that they can only carry voice traffic\u2014whereas SIP trunks support multiple forms of data traffic. <\/span><\/p>\n

How does SIP trunking work?<\/strong><\/h2>\n

Now that we understand the<\/span> SIP trunk meaning, let\u2019s take a closer look at how it all works.<\/span><\/p>\n

Your existing PBX provides internal communication between your various office locations. If you want to make or receive external calls, you have to be connected to the PSTN. SIP trunking is a more modern way of achieving that connection.\u00a0<\/span><\/p>\n

It acts as a middleman between your business phone system and the Internet Telephony Service Provider (ITSP) so that you can make and receive calls via your existing internet connection.\u00a0<\/span><\/p>\n

When someone calls your business, the SIP trunk directs the call through the internet to your phone system. When you dial an external number, the call is routed via the SIP trunk to traditional phone networks. In both cases, voice signals are converted into digital data \u201cpackets\u201d to travel over the internet network.<\/span><\/p>\n

There are two types of PBX systems: analog or legacy PBX (which only has phone lines for internal calling), and IP PBX (which already supports the use of SIP). If you have a legacy PBX, you\u2019ll need a gadget called a Session Border Controller (SBC) to connect the SIP trunk to the phone system, plus Analog Telephone Adapters (ATAs).<\/span><\/p>\n

\"An<\/p>\n

If you\u2019re setting up a SIP trunk, you\u2019ll need to make sure that you have enough internet bandwidth to accommodate VoIP calling. It\u2019s also recommended to configure your router and firewalls to allow SIP traffic, by implementing a dedicated voice VLAN or QoS rules to prioritize voice packets.<\/span><\/p>\n

Benefits of SIP trunking<\/strong><\/h2>\n

In comparison with traditional on-premises systems\u2014connected the old-fashioned way to the PSTN\u2014there are many advantages of SIP trunking.<\/span><\/p>\n

Cost-savings and protecting existing investment<\/span><\/h3>\n

Using SIP trunking helps you to reduce communication costs, especially if your business makes a lot of calls. That\u2019s partly because SIP trunking services<\/span> typically come with simplified pricing, charged per user or per minute.<\/span><\/p>\n

You can usually choose between metered and unmetered SIP trunk plans, with shorter contract durations than you\u2019d get with a traditional phone line. Landlines also charge higher prices for long-distance and international calls.<\/span><\/p>\n

Crucially, SIP trunking enables you to keep using your existing on-premises PBX. It\u2019s likely that you invested heavily in setting this up, not to mention what you\u2019ve spent on maintenance over the years. Instead of scrapping the equipment, you can use it as the basis of a new digital network.<\/span><\/p>\n

More communications options<\/span><\/h3>\n

A traditional on-premises PBX, connected to the PSTN via physical phone lines, doesn\u2019t give you many options for modern communication. SIP trunking can support instant messages and video conferencing alongside voice calls.<\/span><\/p>\n

And you\u2019ll have the ability to customize call management settings such as routing. For example, you might choose to have calls and messages forwarded to a team member or even routed to your smartphone when you\u2019re away from the office.<\/span><\/p>\n

With SIP trunking, call quality improves and you can encourage your customers to get in touch via virtual local and toll-free numbers. <\/span><\/p>\n

Greater scalability<\/span><\/h3>\n

Another key advantage of SIP trunking over legacy alternatives is that it can make your phone system much more scalable. Let\u2019s say you want to add new phone lines. With a traditional system, reliant on PRI, the copper wire lines would have to be installed physically\u2014but SIP lines are virtual.<\/span><\/p>\n

SIP trunk services are easier to manage than legacy phone systems. You can add or remove lines whenever you need to, catering for fluctuating call volumes. The ability to handle multiple calls simultaneously is also good for growing companies.<\/span><\/p>\n

Limitations and drawbacks of SIP trunking<\/strong><\/h2>\n

An on-premises PBX connected to the PSTN via SIP trunking isn\u2019t always the best solution. Here are some SIP trunk drawbacks that might sway you toward an alternative:<\/span><\/p>\n

Quality of Service (QoS) issues<\/span><\/h3>\n

If it seems like traditional landlines are getting a bad rap in this post, they do have their upsides. Call quality is one of these, since analog phones are extremely reliable and keep working even in a power outage.<\/span><\/p>\n

With SIP trunking, however, data travels over the public internet. If your internet connection isn\u2019t properly optimized, latency, <\/span>jitter<\/span><\/a>, and packet loss can affect call quality. This may also happen if the SIP trunk is split into too many channels.<\/span><\/p>\n

You can mitigate call quality problems by using the QoS settings on your router to prioritize SIP traffic for audio over less-demanding data traffic.\u00a0 <\/span><\/p>\n

Security concerns<\/span><\/h3>\n

Again, landline-based systems are reliable in terms of security\u2014it\u2019s very hard to hack into those systems, with the exception of wire-tapping. But any form of digital technology (such as SIP trunking) is potentially vulnerable to cyber-attacks.<\/span><\/p>\n

Because SIP communications are transmitted over the public internet as data packets, it\u2019s possible that they could be intercepted and hacked. To guard against things like Denial of Service (DoS) attacks, spoofing, eavesdropping, and fraud, you\u2019ll need to check that your SIP trunking provider<\/span> is hot on security.<\/span><\/p>\n

Hardware maintenance<\/span><\/h3>\n

Another of the drawbacks to SIP trunking is that although you have more flexibility and scalability, you still have your on-premises PBX to maintain. That\u2019s usually a task for IT professionals, which incurs a cost. And as the hardware gets older, the task becomes harder.<\/span><\/p>\n

You may need to update your PBX system in preparation for SIP trunking, and you\u2019ll have to configure the new service with your Internet Telephony Service Provider (ITSP).<\/span> Setup also involves checking the compatibility of things like firewalls and routers, and you may need gateways, or adapters to connect with other platforms and devices.\u00a0<\/span><\/p>\n

You could instead opt for a hosted PBX or full-fledged<\/span> cloud phone system<\/span><\/a> where there\u2019s no hardware to install or maintain.<\/span><\/p>\n

More limited feature set than cloud-based VoIP phone systems<\/span><\/h3>\n

As we\u2019ve discussed, SIP trunking gives you access to more functionality than a traditional landline-based system. But that still may not be enough for a growing business in the age of digital and omnichannel communications. A cloud-based <\/span>business phone system<\/span><\/a> will include more comprehensive features than those you can achieve with SIP trunking.<\/span><\/p>\n

\"RingCentral<\/p>\n

Cloud technology also makes it easy to add or remove features on demand, and connect to your organization\u2019s CRM, apps, and other software. It integrates multiple communication tools into a single, streamlined platform, instead of using separate apps.<\/span><\/p>\n

Implementing SIP trunking: Why do businesses turn to SIP trunk providers?<\/strong><\/h2>\n

If you want to modernize your business phone system, you may choose to go down the SIP trunking route. This is an option for growing companies experiencing increasing call volumes or needing to make international calls. You might simply want a more flexible and scalable solution.<\/span><\/p>\n

In this instance, you can turn to a SIP trunk provider<\/span> to help you digitize the connection between your on-premises PBX and the PSTN. SIP trunking providers<\/span> are the entities who supply the virtual phone lines and the phone numbers that go with them.<\/span><\/p>\n

As part of your purchased<\/span> SIP trunk service, most providers will assist with installation, onboarding, and porting existing numbers to the new service. This should minimize any interruption to your business.\u00a0<\/span><\/p>\n

Businesses also rely on SIP trunking providers to:<\/span><\/p>\n