I cut my teeth in this industry working with and for telephone companies. But telephone service is now considered by most in the industry to be a commodity barely worth any consideration – it’s just something that’s easy and works. Except when it doesn’t. Cellular carriers have run into problems maintaining voice calls when customers roam between the new 5G frequency bands and the older 4G frequencies.
Each of the cellular carriers has launched new frequency bands in the last few years and has labeled them as 5G. The new frequency bands are not really yet 5G because the carriers haven’t implemented any 5G features yet. But the carriers have implemented the new frequencies to be ready for full 5G when it finally arrives. The new frequencies are operated as separate networks and are not fully integrated into the traditional cellular network – in effect, cellular companies are now operating two side-by-side networks. They will eventually launch true 5G on the new frequencies and over time will integrate the 4G networks with the new 5G networks. It’s a smart migration plan.
The cellular carriers are seeing dropped voice calls when a customer roams and a voice connection is handed off between the two networks. Traditionally, roaming happened when a customer moved from one cellular site to a neighboring one. Roaming has gotten more complicated because customers can now be handed between networks while still using the same cell site. The coverage areas of the old and new frequencies are not the same, and customers roam when moving out of range of a given frequency or when hitting a dead spot. The most acute difference in coverage is between 4G coverage and the area covered by millimeter-wave spectrum being used in some center cities.
It turns out that a lot of telephone calls are dropped during the transition between the two networks. There has always been some small percentage of calls that get dropped while roaming, and we’ve each experienced times when we unexpectedly lost a voice call – but the issue is far more pronounced when roaming between the 5G and 4G networks.
The solution that has been created to fix the voice problems is labeled as Voice over New Radio (VoNR). The technology is bringing an old concept to the 5G networks. ISPs like cable companies and WISPs process IP voice calls through an IP Multimedia Core Network Subsystem (IMS). The IMS core used standard protocols like SIP (Session Initiation Protocol) to standardize the handoff of IP calls so that calls can be exchanged between disparate kinds of networks.
VoNR packetizes the media layer along with the voice signal. This embedded system means that a call that is transferred to 4G can quickly establish a connection with voice over LTE before the call gets dropped. This sounds like a simple concept, but on a pure IP network, it’s not easy to distinguish voice call packets from other data packets. That alone causes some of the problems on 5G because a voice call doesn’t get priority over other data packets. If a 5G signal weakens for any reason, a voice call suffers and can drop like any other broadband function. We barely notice when there is a hiccup when web browsing or watching a video, but even a quick temporary hiccup can end a voice call.
The new technology brings a promise of some interesting new functions to 5G. For example, it should be possible in the future to prioritize calls made to 911 so that they can’t be dropped. The new technology also will allow for improved voice quality and new features. For example, with 5G, there is enough bandwidth to create a conference call between multiple parties without losing call quality. This should also allow for establishing guaranteed voice and music connections while gaming or doing other data-intensive functions.
As an old telco guy, it’s a little nostalgic to see engineers working to improve the quality of voice. Over the last decades, we’ve learned to tolerate low-quality cellular voice connections, and we’ve mostly forgotten how good the connections used to be on our old black Bell rotary-dial phones. This isn’t one of the touted benefits of 5G, but perhaps Voice over New Radio can bring that back again.