On Oct. 5, Syniverse hosted its fourth webinar on one of the most rapidly growing areas of LTE – Voice over LTE, or VoLTE. The session, titled “VoLTE Roaming Charging and Clearing Explained,” built on our previous webinars – “Making VoLTE Interconnect Work,” and “Lessons Learned: Implementing VoLTE Roaming” – and included me along with Mary Clark, Chief Marketing Officer of Syniverse, and our special guest, Keith Dyer, Founder and Editor of The Mobile Network.
We were delighted to draw a large number of attendees and receive a wide range of questions during the sessions. To give a sample of some of the webinar highlights, in this post I’ve selected some of the top questions that I think are of the most interest and answered them below. I hope you find these insightful, and I also encourage you to check out the slide deck we shared.
We also hope you find this continuing discussion on VoLTE roaming stimulating, and we look forward to building on it with more webinars this year. If you have any suggestions for VoLTE topics, I would love for you to let me know in the comments section below.
Questions from “VoLTE Roaming Charging and Clearing Explained”
Single Radio Voice Call Continuity (SRVCC) is needed to support circuit-switched (CS) calls for VoLTE handoff, and this is not available with S8 home routing (S8HR). Could you explain?
SRVCC is available with S8HR, but it is challenging. A change request has to be submitted to IR.65 to clarify SRVCC for S8HR. It requires that an IMS interconnection be in place between the roaming partners. If an IMS interconnection is not in place and ISUP interconnect is in place between roaming partners, then Codec renegotiation for network Release 10 and above is needed, if media are anchored in the ATGW and the ATCF enhancement is used. MSS/MGCF configuration based on the STN-SR information coming on the international ISUP NNI is required for network Release 10 and above, if media is not anchored in the ATGW.
What is the impact of local breakout (LBO) on charging?
From a wholesale billing perspective, the MSESS and MSG TAP records introduced in TAP3.12 will be used for wholesale billing of voice and SMS-supported via local LBO. IMS accounting records can be generated from both the visited P-CSCF and home S-CSCF. The VPMN may create call detail records (CDRs) from either the S-Gateway or the P-Gateway. These CDRs, however, do not contain all of the information that is needed to create a TAP3.12 call session record, so another CDR must also be sent to the offline charging system from the P-CSCF.
When you talk about LBO being more consistent and easier than existing charging, have you considered the complexity associated with IMS interconnect, which is a prerequisite for VoLTE roaming with LBO
Each model presents its own specific advantages and challenges from both a network-support and billing perspective, and, yes, IMS interconnect does introduce additional complexity.
In principle, SRVCC should be possible in S8HR, too, using CS or IMS NNI technology. Do you agree?
Yes, a change request has be submitted to IR.65 to clarify SRVCC for S8HR. It requires that an IMS interconnection be in place between the roaming partners. If an IMS interconnection is not in place and ISUP interconnect is in place between roaming partners, then Codec renegotiation for network Release 10 and above is needed, if media is anchored in the ATGW and the ATCF enhancement is used. MSS/MGCF configuration based on the STN-SR information coming on the international ISUP NNI is required for network Release 10 and above, if media are not anchored in the ATGW. If only ISUP interconnect is in place between roaming partners, advanced SRVCC features like conference, mid-call, alerting and pre-alerting phase technologies are not supported.
In S8HR, there would be no messaging events, right?
From a wholesale billing perspective, if the partners agree to a volume-based charging model, then different charges may be applied based on quality-of-service class identifier (QCI) values. In this model, the messaging events would be difficult to differentiate from the rest of the IMS signaling QCI value “5”. For this reason, BA.27 recommends charging for signaling to prevent misuse of free SMS, spam or fraud.
If the MSESS call type is used for wholesale charging for VoLTE , what happens to the data charges? Are they also billed?
This would, of course, be up to the terms of the agreement between the partners, but if the partners are using the MSESS call type for wholesale charging, the data volume associated with the voice payload QC =1 should, would presumably not also be billed. Again, this must all be bilaterally agreed upon by the partners.
What TAP fields may be used to differentiate charges related to the IMS bearer for VoLTE calls from other data in a GPRS session?
The Call Type Level 2 values might be used for this purpose. CTL2 Value = ”25” (LTE interactive, specialized for signaling) would map from IMS signaling (including voice, video or SMS) from a QCI value =“5“.
Will there be different price lists for payload and signaling?
There may be a different charge for the payload of a voice call and a potentially lower value for the signaling in the volume-based charging model. This would be decided by the partner and included in the terms of the roaming agreement.
Through S8HR, there would be no messaging event, right? Would everything be rated by volume?
Based upon the volume-based charging model, the traffic for the SMS would be embedded in the QCI “5”signaling bearer, as well as the signaling for the voice call, so there would be the payload for the voice call and also the signaling event. BA.27 recommends charging for signaling to prevent misuse of free SMS, spam or fraud.
Is there a generally accepted formula to convert KBs to minutes in the S8HR scenario?
No, there is no generally no accepted formula and this will vary depending on which codecs are being applied.
If I use the MSESS call type for wholesale charging for VoLTE, what happens to the data charges? Are they also billed?
It’s assumed that the data charges associated with the voice bearer would not be charged. When charging for the MSESS and charging per minute, there’s a charge made for the voice minutes and also for the bearer. Using the charging IDs, the traffic can be identified and removed from the bearer for billing purposes, and therefore it isn’t mediated in the GPRS record, but rather put it in the MSESS record. Of course, this must all be agreed upon between the partners in the terms of the agreement.
The QCI1 session will reflect the length of a call unless there are overlapping calls. With that caveat, can duration-based charging be applied in S8HR since everything is rated by volume?
Yes, this could be possibly done, but probably not easily done. Monitoring the QCI level across the IMS and removing the bearer channel data are possible, but general perception when using S8HR is that it will be volume-based charging.
What does Syniverse see as the specific drivers that would push operators to support both S8HR and LBO, given the assumed complexity and cost to support both?
Many operators are finding that the S8HR model is easier and faster to implement. Other operators have shown a preference for LBO and question the S8HR model’s ability to support SRVCC, emergency call capability and lawful seizure. As an enabler of both models, Syniverse can see the value in each. Our previous VoLTE roaming webinar discusses both models, plus their advantages and challenges. As the question points out, there are complexities and costs associated with both models, and to that point, many larger operators may implement and provision both models in order to support other operators that may have infrastructure constraints because of the cost of implementing the necessary components for, say, LBO, including an IMS core.
Correlation billing is only required if there is SRVCC, and that is only an issue with LBO. S8HR doesn’t require TAP, but would this still need to have a third-party validation for bulk billing reconciliation?
Yes, if a volume-based charging model is used, correlation may not be necessary, as the data is all tunneled home (as GPRS is today). The HPMN has all information needed to bill its customer. It is assumed that TAP will be used for wholesale settlement of this traffic, but this could possibly evolve as the industry discusses possible alternative settlement models, like bulk data reconciliation.
What is the VoLTE cost of minutes versus MBs? In other words, how much would one minute represent in MBs?
Unfortunately there is no standard method to correlate minutes of use to MBs, and it will depend on what codecs are being applied.
Does Syniverse see some percentage of operators with VOLTE planning on supporting VOLTE-CS handoffs for roaming?
Today, with VoLTE roaming in its infancy, the majority of GSM-enabled operators are following their LTE traffic and supporting fallback to GSM. We don’t have an exact percentage, but what we are currently seeing today is support for LTE with a circuit switch fallback option. That’s the predominant model. Once operators implement VoLTE in a roaming scenario, then they will have the decision about LBO or S8HR, but that issue arises when subscribers travel outside of the coverage area and the subscribers have to fall back. SRVCC introduces additional complexity regardless of which model is chosen.
What are the challenges, if any, in using QCI values for differentiated data volume wholesale charging in S8HR?
With a QCI volume-based model, the differences between QCIs have to be maintained in the billing or mediation platform to support differentiation of the interoperator tariff rates based on QCI value. This may also affect the method used today by data clearing house providers for interoperator tariff validation during TAP processing. The operator must agree with its partner on the new volume-based charging model and coordinate how each will assess the QCI values and apply charges. SMS may be challenging since it is difficult to differentiate the traffic in the signaling bearer QCI=5.