TransNexus STI-CPS load test shows high scalability

STI-CPS Technology Is Highly Scalable, Suitable for the Largest Voice Service Providers

ATLANTA, GA - July 7, 2025 - TransNexus today announced the results of a load test performed on its Call Placement Service (STI-CPS), which is used for Out-of-Band SHAKEN. The load test showed that a reasonably designed STI-CPS can support a very high call volume even for the largest voice service providers.

This load test generated publish and retrieve requests to the TransNexus STI-CPS at a rate that is greater than the average call volume for all mobile phones in the U.S.

Load test design

We used the following assumptions to develop the load test:

• There were approximately 386 million mobile phone subscriptions in the U.S. in 2023, per Statista.
• The average person makes eight phone calls per day, according to SellCell.

386 million subscribers × 8 calls per day = 3.088 billion calls per day.

Rather than spread this call volume across 24 hours, we thought it would be more realistic to group it across eight hours.

3.088 billion calls / 8 hours = 386 million calls per hour = 107,222 calls per second. This is our target call rate.

Note that Out-of-Band SHAKEN does not require that the STI-CPS be used for every call. It’s used only by providers that use non-IP interconnections. We could get away with a much smaller load test and still get realistic results. However, we thought it would be better to remove any doubts about the assumptions. So, we made the test perhaps more difficult than needed.

We used an ST-OOBS (Out-of-Band Service) to generate and send 7.2 million publish requests and 7.2 million retrieve requests to our STI-CPS in 600 concurrent processes.

Here’s what happened.

Load test results

We measured the STI-CPS processing performance of these 14.4 million messages as follows:

Take note of the Message Rate and Observed Latency.

• The message rates are greater than would be experienced if we used the STI-CPS to send and receive PASSporTs for every mobile phone call in the U.S.
  • Out-of-Band is not required for every call, just those that cross non-IP segments in the call path.
• The latency is less than 5 milliseconds. This is extremely fast. It’s the same latency that we observe when we send small test batches to the STI-CPS.
  • The STI-CPS kept humming right along while processing an extremely high load of messages.

Findings and implications

The STI-CPS handled an extraordinary volume and rate of messages with no degradation in performance.

These results indicate that a reasonably designed STI-CPS is quite capable of handling call volume for even the largest voice service providers. All of them, in fact.

We did not design our STI-CPS with the intention that it must be able to handle call volume for the entire U.S. Instead, we designed it with scalability and redundancy to provide what we think is a reasonable measure of reliable and consistent performance.

As it turns out, however, this design provides a throughput capacity that can scale to handle out-of-band call processing for the entire U.S. This is partly a testament to the performance of the network resources but is mostly a demonstration that processing out-of-band PASSporT exchange is not a resource-intensive task for a well-designed STI-CPS.

We anticipate that other organizations will implement an STI-CPS, for example, STIR/SHAKEN solution providers as a service to their customers or voice service providers as an exclusive resource for use with their interconnection partners. The technology is readily available and highly scalable.

More information

• TransNexus STIR/SHAKEN Out-of-Band Call Placement Service
• Out-of-Band SHAKEN whitepaper
• STI-OOBS sample code. This code is provided under an MIT license. It’s free to use.

TransNexus solutions

TransNexus is a leader in developing innovative software to manage and protect telecommunications networks worldwide. The company has over 25 years of experience in providing telecom software solutions including toll fraud prevention, robocall mitigation and prevention, CDR and call analytics, advanced call routing, billing support, STIR/SHAKEN, and branded calling.