Southern Linc official discusses MCPTT migration, interoperability with new partner Catalyst

Southern Linc—the wireless-communications carrier that is subsidiary of the Southern Company electric utility—is nearing completion of its internal migration to LTE-only mission-critical-push-to-talk (MCPTT) and is preparing to implement the LMR-LTE interoperability solution of new partner Catalyst Communications throughout its network.

Ritesh Desai, product engineering manager for Southern Linc, said that Southern Company workers use the Ericsson-powered MCPTT service on Southern Linc almost all push-to-talk (PTT) communications and internally will cease using LMR technology entirely in the near future.

“Southern Company has one—and only one—geographic location that has LMR—and that is going to be gone fairly quickly,” Desai said during an interview with IWCE’s Urgent Communications. “Once Catalyst comes around and we fully deploy it there, that piece of the pie will disappear from Southern Company, and we will have zero LMR and zero non-LTE communications means out there. So, Southern will be fully LTE-based at that point.”

When this occurs, it will mark a key milestone in a lengthy communications journey for Southern Linc, which serves the southeastern U.S. as a carrier and provide communications support to the Southern Company utility. Southern Linc was among the first entities to commit to building a mission-critical LTE network in 2013, pursued MCPTT with Motorola Solutions, and eventually opted for mission-critical technology from Ericsson.

Desai applauded the audio quality of MCPTT-to-MCPTT calls using the Ericsson technology.

“From a quality standpoint, it’s probably the best audio people have ever heard—even above and beyond the previous Motorola system,” Desai said. “It’s an upgrade, from a vocoder perspective, so the quality is on the top end of the spectrum.”

Southern Linc’s MCPTT supports all of the features and functionality that PTT users want, and the reliability has improved noticeably in recent months, according to Desai.

“We’ve had a couple of issues here and there over the past six months, and they’ve been addressed,” he said. “For the past four months—since February—it’s been quite stable, and it looks to be that way moving forward.”

LMR may not be part of the future internal communications at the Southern Company and Southern Linc, but narrowband technologies are expected to play a key role in the communications for many Southern Linc customers, including governments and public-safety agencies.

Southern Linc customers utilize a wide variety of LMR technologies, and it is important that each customer’s LMR users can communicate with its LTE users. After years of using donor-radio-based solutions, Southern Linc plans to deploy the more scalable and more reliable Catalyst LMR-LTE interoperability solution—an offering showcased during the PSCR 2022 Broadband Stakeholders Meeting earlier this month—throughout its network during the next two years, Desai said.

“We’re trying to upgrade that from donor-based solution to a wireline solution, which Catalyst is able to provide,” Desai said. “We understand that there’s IWF [3GPP’s Interworking Function] from a standards perspective, but the Catalyst solution is a ‘now’ thing that’s readily available, which is what we’re looking for.

“And they hit all of the buttons for what we needed. It’s a fairly small system, from a deployment standpoint—it’s not like it’s several servers or something like that. It’s a small-scale deployment, and there are multiple ways … to do it; there’s not just a one-size-fits-all type of thing. We’re able to buy components of that system to fit each of our individual customer’s needs.”

Catalyst’s current solution supports interoperability as a gateway—powered by Softil’s MCPTT stack—that leverages 3GPP standards from Release 12, not the IWF standard that was completed in March as part of Release 17.

Southern Linc is monitoring the development of IWF, but very few vendors have made the new technology available yet, Desai said.

“Scale is an issue, and it all boils down to cost,” Desai said. “If I needed to bridge a P25 system, and I had a choice between IWF and a system that requires CSSI or even an LMR donor, I would go with the IWF. It’s a pure wireline solution end-to-end in both cases, and it’s standard-based.

“Catalyst, I think, will get there. They’re just not there yet, I think.”

Desai said the existing Catalyst solution is being tested at Southern Linc customer locations, and the initial feedback has been encouraging. Initial operational deployments are expected to begin with a large Alabama customer seeking statewide coverage late this year and continue throughout the Southern Linc footprint during the next couple of years, assuming funding is available.

“I think that, over the next 24 months, a good chunk of our users that have a need to bridge calls between LMR and LTE will be using this [Catalyst] solution,” Desai said.

In addition to deploying Catalyst’s interoperability solution throughout its network, Southern Linc last week announced a partnership under which Southern Linc will promote and sell Catalyst’s LMR LTE Interworking solution in the southeast U.S.

Catalyst President Robin Grier expressed optimism about the partnership.

“It is my pleasure to announce that Catalyst technology will be available to Southern Linc customers through this Agreement.” Grier said in a prepared statement. “We are proud to be associated with Southern Linc and their excellent reputation for stellar customer service and problem-solving solutions for their customers.”

Southern Linc COO Carmine Reppucci echoed this sentiment.

“Catalyst has best-in-class technology and has been serving the public safety community with innovative communications solutions for 25 years.” Reppucci said in a prepared statement. “We look forward to helping Southern Linc customers move forward with this innovative new technology.”

One potential challenge for some Southern Linc customers is the fee assessed by some LMR vendors—most notably, Motorola Solutions—to enable interoperability, Desai said.

“Ultimately, [paying this fee to the LMR vendor is] going to fall back to that [customer] organization—it’s not going to fall back to the Southern Lincs, AT&Ts and Verizons,” Desai said. “Somebody’s going to have to front that money, and it’s likely going to be from the organization that needs it, unfortunately.

“And as bad as it may sound … Aside from the fact that it lets you scale, it’s going to be cost-prohibitive to smaller deployments. That’s just the fact of the matter, if something doesn’t change in that [LMR fee]. Because of the licensing, ISSI is just so expensive. It’s a seven-figure number oftentimes.”

This and other factors need to be considered by users when making interoperability plans, Desai said. As with so many aspects of the wireless industry, scale can have a significant impact on the best interoperability solution for a given entity, he said.

“If you’re extra small—like a sheriff’s department with only 10 people with a [network] site or two—then go with your old legacy donor solution,” Desai said. “Anything above that, go with the Catalyst solution. And if you’re a carrier like us, and you want to bridge carrier to carrier, go with IWF.”