VoLTE Roaming Architectures S8HR and LBO

In an earlier blog, I was going over some of the questions that came up during a webinar that I recently did with Hot Telecom analysts Isabelle Paradis and Steve Heap on IPX Services and the Pathways to Innovation. In the first blog (which can read by clicking here), we answered the question on the current state of VoLTE roaming where we described the two architectural approaches being deployed by service providers. One approach is known as S8HR or Home Routing where a roamer’s voice call is tunneled back to the home network’s IMS core over the S8 interface that connects the visited network’s and home network’s respective Evolved Packet Cores (EPCs). A question that came up from a very astute listener was whether that architecture was going to affect how calls are ultimately charged.

Why would Home Routing impact the way calls are charged by the operators and in what manner? In S8HR, both the SIP signaling traffic and RTP-based media is tunneled between the visited network and the home network using GTP protocol. The IMS infrastructure of the roamer’s home network is used to process the call. Home routing is very comparable to mobile data roaming scenarios and it’s advantageous from the standpoint that roamers can use VoLTE even if the visited network has not implemented an IMS.

From the visited network operator’s perspective, with a VoLTE call, the subscriber is using mobile data and at a level of quality better than “best effort” used by OTT applications riding over mobile data. The operator knows that the payload is IMS traffic because of the Access Point Name or APN selected and the way the dedicated bearers for the voice (QCI=1) and the video (QCI=2) sessions were established.

S8HR Method routes calls vial LTE back to Home Network's IMS for processing

Figure 1 - S8HR - A Home Routing approach leveraging the EPC of the home network is becoming popular due to its simplicity to deploy.

Regardless, when a roaming subscriber makes a VoLTE call in a visited network that connects to the home network using S8HR, the subscriber is using mobile data. The data stream that carries the voice and video traffic is a guaranteed bit rate – better than what is used for OTT services. The home network has the responsibility of processing and terminating the call to the appropriate destination network; the cost of which would be on top of any data roaming component charged by the visited operator. We already know that operators are not going to be able to charge more for VoLTE calls, but what about this ability for operators to differentiate the bearer type and provide very granular charging based on the associated quality supported? Will this enable them to charge differently for providing a higher level of guaranteed bit rate for a given service?

What you may start to see is a move from per minute charges for voice calls to QoS-based megabyte charging. Although, I think these QoS charging scenarios will leave subscribers scratching their collective heads, and if voice is charged by the megabyte, will subscribers know how much bandwidth a VoLTE call will take up, let alone what a real-time video session would consume. My back-of-the-envelope calculation for the bandwidth usage for a 2 minute voice conversation comes to about 2 megabytes notwithstanding any overhead due to the bearer protocol. Right now, I’m getting charged $0.25 per minute by my operator Verizon for a circuit switched roaming call when I go beyond my roaming bundle. Oddly enough, I’m getting charged $0.25 per megabyte of data!

Most users, however, probably don’t want to bother with trying to figure out the impact of voice on their giga/megabyte-based mobile data plan. They will look to other ways to communicate such as OTT applications and will further economize on their mobile broadband usage through Wi-Fi networks. This will especially be the case if operators don’t make roaming available or continue to make mobile data roaming so expensive that subscribers go silent when traveling abroad.

So why not make the service smart? Is there an opportunity to give subscribers free “on-net” VoLTE calls with charges occurring only when the call “breaks out” like OTT players do today? Why not add prompts or messages that alerts subscribers of the charges incurred using an OTT app on their mobile data versus VoLTE. Alternatively with the capability to do granular billing by QCI and service, why not implement sponsored roaming opportunities to provide VoLTE roaming to targeted subscribers for free and allow those sponsors to indicate this to the roamer in the dialer.

So what do you think operators should start doing? Is the time now to start changing the way voice services are billed? Is this an opportunity for operators to take a disruptive approach in how they charge for multimedia services? Let us know what you think by tweeting us at @Dialogic #VoLTERoaming. You can also watch the entire archived IPX webinar by clicking here.