Key Considerations When Migrating Away From ISDN to SIP Trunks

Key Considerations When Migrating Away From ISDN to SIP Trunks

What are the key ingredients businesses need to consider when migrating ISDN across to SIP Trunks and how does it stack up as a replacement for voice?

For almost 40 years, Integrated Services Digital Network (ISDN) has serviced the needs of Australia’s businesses, from small to multi-national enterprises. Telecom Australia, known as Telstra today, was one of the first carriers to provide the ISDN technology which meant that Australians were spoilt with high quality, reliable, voice-communications.

This article will explore the basic concepts of ISDN, the reason it’s being disconnected, and what a business or technician needs to consider when migrating their customers or employees to a SIP Trunk replacement technology.

ISDN: The end of an era

ISDN outperformed your standard telephone services because it allowed a business to have multiple channels and numbers delivered to their telephone system. For example, if you had a business that required 10 simultaneous calls, rather than purchasing 10 single telephone services, a business could purchase a single ISDN10 delivered to their premises along with additional number blocks. A key benefit over a standard telephone or PSTN service was that voice was delivered by a digital signal rather than analogue. The voice would then transmit through a digital channel with a guaranteed bandwidth of 64 kilobits per second (Kbps). It doesn’t seem like a lot of bandwidth today, especially when we speak of megabits per second (Mbps) or even with 5G being able to deliver gigabits per second (Gbps). However, when you are only delivering voice by a single channel, and it is fully dedicated the customer will receive a far greater call experience.

Now with copper-based PSTN and ISDN coming to an end since the Government’s 2009 approval to develop the National Broadband Network (NBN), businesses (from July 2019) are now required to move their ISDN services to a digital voice equivalent.

“So, what is the digital equivalent today? SIP Trunks, let me explain.”

When the Internet was initially developed, a common language was required to allow two devices on a network to communicate. An example of these protocols is the Hypertext Transfer Protocol (HTTP) and (HTTPS). HTTP is referred to the protocol used to deliver text via your web browsers and HTTPS (note the S) is simply HTTP traffic that is transmitting over a secure protocol via encryption meaning that text when in transit it can’t be read by a human.

Similarly, voice also requires a protocol so it could be transmitted, as Voice over IP or commonly known as VoIP. It utilises the Session Initiated Protocol or SIP for short.

With the ability now to convert voice into digital communication and send it by the Internet (SIP), there is no longer a requirement to have a dedicated line into a business, and like data traffic, voice can now pass over the Internet.  Therefore, the business justification to support the ISDN and PSTN networks to deliver voice is no longer viable. Goodbye to PSTN and ISDN, and hello NBN.

SIP Trunking: How does it measure up?

Extending the SIP communication into multiple channels is known as SIP Trunks. For example, a SIP Trunk with 10 Channels allows for 10 simultaneous calls mirroring that of an ISDN10.

“So, to quickly recap.”

“ISDN was a high quality, dedicated, digital-based, multi-channel technology connecting your telephone system to the world. Our government is switching it off forcing you to replace ISDN with a non-dedicated, over the top (OTT) service called a SIP Trunk and everything will roll smoothly right?”

“No, not really”

If you managed to get to this point you will have realised that the very thing that allowed ISDN to be of high quality was its dedicated link. SIP Trunks are provided as an OTT service and we start to get into several issues such as reliability, features, voice quality, capability, and connectivity because unlike ISDN we share the basic Internet connection with everyone.

There are hundreds of SIP Trunk providers in Australia all claiming to offer the best price with significant cost reductions by removing the ISDN and providing your voice service by an Internet connection. This is great in theory but, the SIP protocol (described above) sends data from point A to Point B in many small packets. The consistent delivery of these packets to either endpoint is extremely important to voice as it is being delivered in real-time.

Imagine, that you are negotiating a $1.1 million deal. If we said this out loud, we would say “One”, “Million”, “One”, “Hundred”, “Thousand”, “Dollars”. If each word is delivered by a SIP packet and each packet needs to be delivered in the correct order it requires some guarantee. Without the guarantee this message could be delivered as;

“0ne”, “Hundred”, “Dollars” and during transmission we lost the “One”, “Million”, “Thousand”.  So, we have negotiated a $100, NOT because we didn’t say it, but the person on the other end didn’t hear it, because the voice packets were never received.

Worse case, the voice quality was so bad both parties had to hang-up because the conversation went along the lines of “can you hear me? hello? wow, this line quality is really bad, hello?”.

If we hypothesised as to what created the above scenarios, we can conclude that during the time of conversation, someone was playing the latest version of Destiny 2 (free-to-play online-only multiplayer first-person shooter video game). Whilst another person was watching the latest Netflix series through your $79 100/40 Mbps with NBN (best efforts TC4) service.

It’s like trying to drain an Olympic swimming pool with a 4-inch pipe but expecting it to be done in 10 minutes. It’s never going to happen as the maximum flow rate can never be achieved. The data flow has the same issues.

“ISDN had a dedicated 64Kbps per channel, which is 0.064% of 100 Mbps that NBN claims to deliver. However, with ISDN, 64 Kpbs is dedicated only to your telephony call and nothing else.”

How about we deliver the Internet and voice over a business-grade (i.e. NBN TC2) link such as 10 Mbps with a 10 Mbps synchronous internet link?

This will remove some of the issues above, however, you need to ensure you scope your Internet requirements correctly. 10 Mbps is not a lot of bandwidth especially if you are a data-hungry business, so you will end up in the same position. Business-grade synchronous services are very expensive. To make matters worse, you have increased your Internet cost significantly. The better the quality, the higher the cost. 

How can we measure our call quality?

But I hear you say, “I have a 1 Gbps service into my office, surely I’m ok now?”

So, let us throw an additional curve ball into this conversation. Is your router capable of handling 1 Gbps without cooking your kilo of steak? Due to the heat its generating, probably not. Most business routers can handle 100 Mbps without starting to go into meltdown. 

With that example out of the way, let’s introduce the technical terms Jitter, latency and buffering* which are all required to meet certain levels to deliver a high quality and consistent voice in real-time traffic over a shared Internet connection. If we combined these variables accordingly, we can generate what is referred to as the Mean Opinion Score (MOS). The MOS score provides a user with an indication of what they could expect their voice service to be like.

As a guide, a MOS of 4.1 is required for good voice conversation. The table below references the scores you can expect from a MOS test. 

MOS Quality Impairment
5 Excellent Imperceptible
4 Good Perceptible but not annoying
3 Fair Slightly annoying
2 Poor Annoying
1 Bad Very annoying

If your MOS score is less than 4.1 there are many factors that come into play all relating to latency, jitter and buffering. Generally, your Internet provider may be contending the Internet traffic they receive from all their subscribers. What does this mean? Imagine for a moment you are cruising down a very busy 8 lane highway moving at a consistent pace, the wind is blowing in your hair, everything is great until… “Roadworks ahead” merge into two lanes… Everyone slows down and 8 lanes of traffic merge into 2 with no control of the situation, going from 100 kilometres per hour (km/h) to 10 km/h and you’re still 5 kilometres from the road works. 

Similarly, Internet traffic suffers from the same congestion, data packets are now being held up and the voice quality and real-time speech requirement are lost – all thanks to your Internet provider.

Roadworks don’t only happen in one spot; choke points exist across the entire network. This is important to know because we have mentioned the theoretical speed the Internet link is able to achieve. For example, a 100 Mbps NBN connection may never actually be able to reach 100 Mbps.

Why? Because your Internet provider is limiting the available bandwidth in their network. To design a network for fifty 100 Mbps NBN services, the cost to deliver 5000 Mbps (50 * 100) at a 1:1 contention ratio is too costly. So, an Internet provider may contend the service to 20:1, for every 20 Mbps purchased they allocate 1 Mbps in the network for use. For our example to service this customer we would require 250 Mbps.

If we have all 50 customers accessing the network at the same time the maximum bandwidth available to the customer is only 5 Mbps (250 Mbps divided by the 50 customers). So, the actual speed available becomes a function of the available bandwidth. For this reason, some businesses opt to get an NBN TC4 (best effort service) for data and a dedicated TC2 or business grade service only for voice. Why, because a TC2 service has a 1:1 contention ratio but that’s now increasing the cost.

To test your MOS score click here. This will test the connection from your business location to the Novum Networks voice infrastructure.

Now that we have discussed the delivery requirements, it is also important for a business to understand the features and capabilities that your SIP provider gives you. For example, not all SIP Trunk providers can provide HICAPs or EFTPOS facilities, so if your business needs them, ensure you ask the right questions.

Finally, can you just order a SIP Trunk and expect it to work with your PBX phone system?  No, your PBX must be IP compatible or you will require additional hardware to allow SIP Trunking to work. So, is SIP a comparable replacement for ISDN?  NO.  Is it able to replace ISDN when scoped and deployed properly? YES

Glossary of Terms
Latency The delay before a transfer of data begins following an instruction for its transfer.
Jitter Region of a physical memory storage used to temporarily store data while it is being moved from one place to another.
Buffering Slight irregular movement, variation, or unsteadiness, especially in an electrical signal or electronic device.

ISDN and SIP Trunking Comparisons

Let’s look at the differences between the two services.

  ISDN SIP Trunks
Reliability Limited failover redundancy options Automatic failover options available for example 4/5G
Future Approaching confirmed end of life Well mapped out and ready for voice/data convergence; scalable
Savings High rental costs for equipment Reduced line rentals and management costs
Disaster Recovery Faults can take hours to repair Business continuity enables and can reroute calls to backup sites in seconds
Flexibility Tied to a geographical area Make instant changes and not tied to a geographical location

My SIP Trunking options?

If your business needs to upgrade from ISDN, you don’t need to limit your service to a like-for-like voice replacement when there are superior SIP Trunking services on the market. 

For example, some providers can supply a SIP Trunking Plus solution that enables end-users to access Unified Communications and Mobility features on a SIP Trunk extension. So now a SIP Trunks is not only an ISDN replacement but can provide your business with extra functionality at a reasonable cost. Businesses can enjoy the following features with a SIP Trunking Plus solution.

Have calls to your office number ring your mobile and be notified that it is from your office when answered.

  Use a mobile app to receive calls from your office number as well as make calls from your mobile, presenting your office number. 

  Transfer answered calls to other office extensions using the app.

  Set up a hybrid SIP Trunking solution by using your on-premise PBX and additional Cloud PBX for remote office users and sites, as well as overlay      Call Centre Agent features such as call queueing, automatic call distribution (ACD) and many more. 

As much as speed, reliability, and functionality are necessary for your SIP Trunking service, it’s also important to consider a good through-put (via a data service) otherwise the voice quality will be diminished.  These are the key ingredients that must be considered when migrating your ISDN to a SIP Trunking solution.  It is also important to select a service provider that can deliver a superior SIP Trunking Plus solutions that will extend the life of your current phone system while future-proofing your business communication needs.

To download this blog, click here.

Nigel Keswick, Managing Director at Novum Networks

Nigel has over 35 years in telecommunications, and is technical specialist in voice, data and infrastructure networks. Nigel manages Novum’s technical team and has a wealth of experience in working with businesses and technology vendors to understand their needs and deliver turn-key and efficient solutions. Nigel’s core expertise is educating and communicating our wholesale and channel partners to empower them to succeed in today’s connected economy.

To find out more about SIP Trunking Plus for your business, contact us here or call us on 1300 725 127.

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