Xeta Group
(Primary Rate Interface)
Making the move from PSTN to SIP Trunk:
The trusted old Public Switched Telephone Network (PSTN), with its Analog lines, ISDN BRI, E1 or T1 lines, are gradually being replaced by IP telephony. An increasing number of businesses are using more modern and flexible SIP Trunks.

The major telecom providers are fast phasing out the old PSTN functionality, and are moving customers to IP. The majority of businesses these days are already using modern IP phone systems and SIP trunks, although some smaller business may still rely on outdated technology.

What Is PRI And How Does It Work?

What Is A PRI?
PRI is a Primary Rate Interface (PRI) phone service consisting of 23 voice or data channels (B channels) and one ISDN PRI line channel for signaling (D channel). ISDN PRI service is used by businesses to provide local and long distance voice service as well as other applications including video conferencing, fax, and dial-up. ISDN PRI T1 provides increased efficiency through a PBX phone system by setting up and breaking down the PRI phone calls faster than a regular voice T1 or phone lines. An ISDN T1 offers robust features like Caller ID and Direct Inward Dialing (DID) through the D channel signaling on the ISDN PRI line. PRI T1 lines are also known as T1 Phone Service, Digital T1, Voice T1, Local T1, Long Distance T1, or T1 Trunk.

How PRI Works.
A single Primary Rate Interface (PRI) circuit is extended from Telephone Exchange (Central Office), which contains 23 multiplexed channels. The IP phones, fax machines, analog phones and Wi-Fi phones can all use the PBX to connect with the PRI line and make up to 23 simultaneous calls to the external world. A PRI line is an end-to-end digital circuit. It is a voice-only T1 circuit, utilizing ISDN technology and can pass important call information, such as caller ID and Dialed Number Information Service (DNIS).
How PRI Works
What IS PRI And How PRI Works
Pros Of PRI
No Reliance On Bandwidth
Does not rely on data bandwidth to support voice calls
Dedicated Circuit
High quality via dedicated line structure
Failover Option
Can be made redundant via the addition of a second PRI circuit for failover
Cons Of PRI
PRI is expensive to implement and upgrade and requires costly monthly phone service
Long-term Contracts
May require long-term contracts with traditional telecom companies for local and long-distance calling
Dedicated Capacity
Requires dedicated capacity that can only be purchased in 23 line units
Flexibility & Scalability
Slow to scale, modifications to infrastructure may take weeks of waiting.
Best Use Cases Of PRI
Limited Bandwidth Access
Organizations with legacy PRI infrastructure and limited access to fiber-optic internet connectivity or sufficient bandwidth to support IP-based phones.
Hybrid PRI And SIP Trunking
Hybrid PRI and SIP trunking implementations, where organizations retain legacy PRI technology for local calls while using SIP for multimedia communications and saving costs on long-distance/international calling.
What Is SIP Trunking And How Does It Work?
What Is A SIP Trunk?
A SIP trunk
is the virtual version of an analog phone line. A SIP Trunk is the emerging standard for VoIP trunk service using Session Initiation Protocol (SIP) to set-up voice calls over public or private IP networks. SIP trunking service is used by businesses to provide local and long distance voice service as well as other applications. SIP trunk service provides increased efficiency through an IP PBX phone system by utilizing IP network access for SIP voice calls, without the need for regular phone lines.

SIP VoIP service is very flexible and can work with numerous protocols and scale quickly. SIP trunking providers also offer non-native variations of SIP VoIP service including SIP PRI and SIP T1 handoffs. SIP VoIP services are also known as SIP Trunk Services, SIP Trunking Services, SIP Lines, VoIP PRI, VoIP T1, Hosted VoIP PBX, and Hosted IP PBX.

How SIP Trunking Works.
A SIP trunk is the modern day equivalent of a T1 trunk. Where in the past you would buy a T1 trunk from a Telco provider and connect it to your legacy PBX, today you can buy a SIP trunk from an ITSP (Internet Telephony Service Provider) and connect it to your VoIP/IP PBX. SIP trunks use the SIP standard. The name 'trunk' comes from the telecom world and it means, more or less, a group of phone lines.

Using this standard protocol, telecom service (VoIP) providers connect one or more channels to your PBX, allowing you to make local, long distance, and international calls over the Internet. Phone numbers and DIDs are linked to the SIP trunk and in most cases numbers can be ported to the SIP Trunk. If you have an on-premises PBX in your office, a SIP trunk provider can connect to you and allow you to make outbound calls on your existing system, without restrictions on the number of concurrent calls.
How SIP Trunking Works
SIP Trunking For Dummies
SIP Trunking For Dummies
Learn To:
  • Understand The Basic Of SIP Trunking
  • Realize Huge Cost Savings With SIP Trunking
  • Appreciate The Importance Of An SBC In SIP Trunking
  • Choose A SIP Trunking Solution That Is Future Proof
Pros Of SIP Trunking
Our farewell to the PSTN brings many benefits. SIP Trunks deliver:
Lower Monthly Line & DID Rental
The monthly fee to have a number of lines installed at your office drops significantly with SIP Trunks and can be as much as 30-40% less than PRI. And DIDs cost a lot less.
Lower Call Charges
There are many SIP Trunk providers and competition has driven down call charges significantly. Some SIP Trunks even come with unlimited calling and you can save on international call charges, too.
Only Pay For Capacity Needed
Sold by vendors on a per-channel basis on-demand, so you only pay for the capacity needed.
Disaster Recovery
Offers failover to mobile phones in case of loss of office data connectivity
Flexibility And Scalability
Offers simple support for multiple sites and remote workers. It is easy to add channels to your SIP Trunk to cope with increased calls. A simple phone call will allow you to add channels, and often this can be done immediately. Some providers include easy-to-use administrative portals for easy management. Compare that to the delay in having additional lines installed and then having to upgrade your old PBX to handle more lines!
Move Offices And Keep The Same Number
SIP Trunks are not bound to a location, so it's easy to move offices without having to change your stationary or inform your customers. There is no longer any need to pay to forward phone calls to the new offices.
Eliminate VoIP Gateways
SIP Trunks will eliminate the need to buy and manage VoIP Gateways. All phone calls come in via IP. No extra conversion often means better quality too.
Leverage A Modern IP PBX
Modern IP PBX / Unified Communications solutions will give customers increased productivity, mobility and boost sales. Can be integrated with multimedia communications for collaboration and productivity. May include rich mobile features and mobile-first design. Connecting an IP PBX to SIP Trunks is much easier than via the PSTN. You can go on-premise or hosted, the choice is yours.
PRI Hand-off
If your PBX does accept native SIP then some providers offer a PRI hand-off to the PBX
Cons Of SIP Trunking vs PRI
Requires internet bandwidth, ideally business fiber internet, to support quality of service (QoS).
Network Security
Needs sufficient network information security, like firewalls, to prevent cybercrime risks.
Quality Of Service
The quality and extensibility of service offered by hosted VoIP vendors can significantly vary.
Best Use Cases Of PRI
Cost Savings
Saving money on business phone service, especially for organizations with long-distance and international outbound calling.
Contact Center Support
Cost-effective support for contact centers.
IT Administration
Reducing the burden of phone system management on internal IT personnel.
Future Proof
Moving towards hosted, multi-channel cloud communications or Unified Communications as a Service (UCaaS)
Flexibility And Scalability
Gaining the ability to quickly scale business communications by adding and removing lines and features on-demand.

How Much Does A PRI Cost?

A PRI circuit can cost around $500 each month, with some variation depending on region and other factors. Assuming a business is using the circuit for just 23 lines, that comes to an average of $21.74 per phone line, which can seem like a reasonably good deal. However, there are some other costs associated with PRI circuit investment, which aren't necessarily reflected in monthly pricing.

  • Many organizations need to purchase a T1 card to use a PRI with a legacy PBX system, which can cost between $500-1200.
  • Circuit installs and upgrades to physical infrastructure can be incredibly costly and may require a 30-45 day waiting period.
  • PRI circuits require physical servicing by expert technicians, which can cost $150 per "truck roll" or site visit.
  • Adding a single line of capacity requires the purchase of a PRI circuit and an increase in monthly costs by $500 each month.
  • Redundancy in case of disaster or equipment failure requires the purchase of additional PRI circuits for failover, which can add $500 each month for each failover PRI circuit purchased.
Taking all of these factors into consideration, the cost of a PRI circuit is definitely not $21.74 per phone line. With redundancy, it's $42.48, and the average costs per line only increase with site visits, capacity upgrades, or unused channels.

5 Ways To Reduce The Cost Of Your Business Phone Lines

1. Business Phone Line Elimination – Modem lines are a thing of the past. Fax lines are headed in the same direction. Alarm lines can be replaced with wireless connections that carry fewer fees and surcharges. Inventory your POTS lines and eliminate the lines that you no longer need.

2. Business Phone Line Repricing – If the majority of your POTS lines are with the same incumbent phone company, contact your account rep and inquire about volume pricing. If your carrier rep claims that bulk pricing doesn't exist, work through a telecom consultant who has an agency relationship with that carrier. Telecom consultants act as customer advocates and have to prove their value. If volume pricing is available, a telecom consultant will make you aware of it.

3. Business Phone Line Transformation – If you have a number of POTS lines at any given location, it might pay to convert them to PRI or SIP Trunks. PRI offers 23 channels, which can be shared by a number of employees. For example, 40 POTS lines could cost $2000 a month. 40 employees could share one PRI, which would cost about $500 a month. POTS lines could also be converted to SIP. SIP stands for Session Initiation Protocol. SIP trunks are voice paths over the internet and they're less expensive than POTS lines or PRI circuits and carry fewer taxes and surcharges.

4. Business Phone Line Aggregation or Managed SIP Trunking – If you are a large, multi location company and you have hundreds of POTS lines spread out across the country, supplied and billed by different carriers, POTS consolidation is something you should consider. POTS aggregators can provide one bill and one point of contact for your entire POTS inventory. This can greatly reduce the administrative costs related to the service. The other option is moving to Managed SIP Trunking since SIP Trunking is not location specific and you can get the exact number of channels needed and share across sites.

5. Move To A Modern Business Communications System – Most businesses have or are in the process of migrating from analog to IP telephony. A lot of this has to do with the fact that VoIP offers more cost savings compared to its traditional counterpart. Moving to VoIP can save businesses as much as 60% in telecommunications costs.

If you would like help inventorying, auditing, managing and lowering the cost of your Business Phone Line inventory, contact Xeta Group today.
Is PRI vs. SIP Trunking Best for My Business?
PRI and SIP Trunking are competing approaches to phone technology that carry distinct advantages and disadvantages.

For many organizations, SIP trunking to support VoIP telephony or UCaaS is the smarter choice and enables access to the benefits of significant cost savings, improved collaboration tools, and better reliability.

For other firms, a hybrid approach to using both PRI and SIP is the right decision. Educational institutions may decide to implement Unified Communications, but maintain a few PRI lines to support legacy intercom technology and some disaster recovery planning scenarios. For other businesses still, PRI may be the right choice.
Head to Head: PRI vs. SIP on 4 Key Business Considerations
1. Cost
For the vast majority of organizations, SIP is much cheaper than PRI. Cost is an important consideration for organizations, even though it's not the only factor to take into account when you're investing in a business phone system. Organizations that need to scale their system, add features, and perform long-distance calling are likely to achieve massive cost savings.

There are very rare instances where PRI may be less costly than SIP. These use cases are generally limited to small, brick-and-mortar businesses with no need for advanced phone features like eFax or integrated messaging. For organizations that are not going to grow or adopt different communication technologies, maintaining an existing PRI system could be the right choice.

Who wins? SIP Trunking most of the time.

2. Information Security
PRI is considered more secure, which isn't strictly correct. Copper cabling can be subject to a number of information security risks, including interference and interception. However, organizations that lack on-site information security expertise to achieve adequate network security and attempt to run consumer-class VoIP over public internet connectivity may be very vulnerable to security risks.

Who wins? SIP Trunking with adequate network security.

3. Flexibility
The biggest con to PRI is also among the greatest pros of SIP trunking; flexibility and scalability. With PRI, organizations are required to purchase additional user capacity in 24 lines. With SIP, organizations can add a line for a service month to accommodate a temporary or seasonal employee, and remove the line as soon as it's no longer needed. SIP can enable organizations to unlock truly usage-paid billing on-demand, while organizations using PRI may need to wait weeks to schedule a technician for very high-cost infrastructure upgrades.

Who wins? SIP Trunking.

4. Reliability
The reliability of copper-based phone cabling can be damaged through a number of risks, including inclement weather, vandalism, or simple degradation of an aging infrastructure. While PRI is considered a very reliable technology, and it generally is, organizations will lose access to phone service if a component of their infrastructure is damaged.

SIP is reliable, provided organizations partner with a reliable vendor and invest in fiber-optic internet connectivity which is very resistant to weather and other common types of damage. With mobile failover, organizations can continue using dedicated phone lines even if there is a loss of data connectivity on site.

Who Wins? It depends. Generally, SIP wins, but some organizations may prefer a hybrid approach.
Choosing Between PRI vs. SIP Trunking
Is PRI or SIP trunking the best choice for your business? Ultimately, that depends on your organization, your goals, and your desire to adopt next-generation communication and collaboration features. The majority of organizations today have adopted or plan to switch to VoIP phones and UCaaS as a tool for cost savings, better value, and business agility. While PRI is the right choice for some select organizations, many firms find that SIP beats out traditional PRI phones.
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