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On November 6th, 2012, we broadcast a webinar via  This was well attended and generated a large number of questions.  While I responded to the questions on the webinar site, I thought it would be useful to pull these questions and answers together in this blog entry.

For readers that may not follow exactly what in the world I’m talking about, Sybase 365 (an SAP company) now offers an LTE Roaming  service as one of our IPX services.  LTE Roaming requires the usage of the Diameter protocol.  Earlier in 2012, I published a blog entry outlining the “plumbing” that goes into enabling subscribers to roam on LTE networks, as a bit of background.

So, without further ado, here are the actual questions and my answers about Diameter hubbing and LTE Roaming./wp-content/uploads/2012/12/lte_logo_163510.jpg

Question:  Could a Diameter Edge Agent be used in a CSFB configuration which would act as a SS7 / Diameter protocol translator without having to buy a IMS based equipment.

Answer:  Yes, it could… it could be offered on the Diameter hubbing service (e.g. DRA) — not necessarily the Edge Agent. Diameter hub providers offer or will be offering such interworking (MAP / Diameter).

Question:  Can any IPX provider be a diameter gateway? Or does it need other measures like the case of roaming hub?

Answer: Certainly, having an IPX network is a primary prerequisite. But to make the business model work, you should also be a reasonably sized GRX provider AND you must make the investment in Diameter hubbing technology.

Question: Understanding that mobile roaming is both an IPX and handset/tablet requirement, when do you expect LTE mobile roaming to replace the end user from just switching SIM cards?

Answer:  LTE Roaming will certainly grow in the coming years; however, in the short term, due to frequency fragmentation, sometimes the only way would be to switch SIM cards. There will be some operators, especially in the early years that will be virtually unreachable from a roaming standpoint, due to their chosen frequency bands (or spectrum limitations of their country).

Question: How do you address the diameter security from IPX perspective? Also there have been some debates about whether the IPSEC should be optional or mandatory between the operator’s diameter edge agent and IPX. What is your view?

Answer: The security of the IPX does not make it necessary for traffic to be encrypted between the DEA and the operator — in fact, it reduces the overall QoS. But, if an operator or pair of operators requests it, it could certainly be configured. But we do not recommend it.

Question: How does a mobile operator compare and differentiate between existing GRX providers who claim to be an IPX provider and someone such as yourselves who say you are a complete IPX provider? Why would I not stay with my current GRX/IPX provider where community/ecosystem already exists?

Answer: That’s a good question.

I will say that not all GRX providers can provide a strong IPX capability. “True” IPX takes some investment in a high QoS backbone and commitment to growing that as more IP services come online. For example, a smaller GRX player may not find the necessary business case to grow and evolve their underlying network to IPX standards. And bandwidth and quality requirements will only grow. Consequently, it is our opinion that your safest bet is working with one or more of the larger IPX players.

Question: Is LTE roaming in EVDO Rev A or B possible?

Answer:  No, these are two different standards; HOWEVER, and let’s look at a large CDMA (EVDO Rev A) operator like Verizon Wireless, whose 3G is EVDO Rev A, but also supports LTE. An LTE subscriber roaming to another network might “fall-back” to EVDO in the visited network, if the visited network does not have compatible LTE frequencies or does not have LTE at all. Most EVDO devices that support LTE support both standards, depending on what network they can connect to.

Question:  Since the routing is done through the home network, does this not diminish the importance of the TAP file from the home operator’s perspective?

Answer: No, it does not do away with the necessity of TAP files. Regardless of whether the subscriber is home-routed or local-break-out on the visited network, the Diameter information is not enough to complete a full TAP record.

Question:  My question is related to steering of roaming (SoR) for LTE roaming. What would be the impact and how it should be done effectively?

Answer:  Steering of Roaming should “translate” to LTE roaming as well and it should be done though the Diameter hubbing provider. In fact, we are engaging with the appropriate partners who would work through our Diameter hub, based on the policies of the home network, to provide roaming steering to preferred networks. Of course, the concept is not different from what happens today in 3G; however, this would involve accessing the appropriate Diameter traffic to insure that the subscriber connects where the home networks desires them to.

Bottom line, we think SoR would definitely have its place in LTE roaming scenarios.

Question:  How realistic is it to expect devices to be able to support frequencies available in North America, Asia and Europe?

Answer:  Initially, as discussed, there will be devices that will try and support some frequencies more targeted for specific regions. For example, look at the iPhone 5 / new iPads. Two of the devices support the 1800 band which should support roaming in a lot of different networks as well as supporting the US bands (e.g. 700 MHz band). Overall, many networks will support at least one of the more “common” bands such as 800/1800/2600 in addition to AWS and some of the more off frequencies such as the 700 MHz bands. It’s early yet. But, I think you will see devices with 5, maybe even 6 band support.  More, I don’t know. Of course, there will always be some country or operator that deploys on some very odd frequency bands.

I expect that over time, we’ll see a strong roaming market— at least for the top 100 operators worldwide, but we are not quite there yet.

Question: How do you see the challenges posed by Voice over LTE networks when roaming?

Answer:  The roaming LTE subscriber that will be launching a VoLTE call will trigger some additional Diameter exchanges between the visited and home networks, EACH time a call is initiated — as well as the SIP call setup.

This certainly plays into the necessity for a very good network – e.g. an IPX — connecting the two networks — if not just for the additional Diameter traffic, but also the user data (e.g. the call itself).

Question: I would be interested especially on your view especially on the call handling in case of VoLTE roaming  – especially in the context that in current Telco environment, the routing and charging is done primarily on E.164 numbers while in case of VoLTE roaming, the routing between the S- and P-CSCF is done based on domain names contained in SIP headers given in the registration procedure to the UE.

Can you comment whether the current IPX framework provides this functionality yet?

Answer: I am not aware that IPX framework – any IPX framework — provides this functionality – yet; however, once we start supporting VoLTE functionality (roaming or interworking), we will address the conversion between E.164 numbers, identifying the subscriber UE, and the domain names (or specifically the SIP URI). The SIP URI of the User Equipment should be unique and I’m sure we can find a way, if necessary to map that to the E.164 number.

Question: Do you see the need for IPsec over IPX/GRX?

Answer: Possibly; however, I would be concerned about quality of service with an IPSec. Besides, if you already have an IPX connection, then you can certainly leverage that, without needing an IPsec connection. Some operators are asking for different VREs to differentiate the type of traffic – for example, lower bandwidth for the Diameter traffic and either re-use their GRX channels for the “user data” for home routing.

Question: In exchanging Charging Control info’ is that practical when dealing with real-time balance management for pre-paid subs?

Answer: Yes, I think it would be. This exchange of information really happens when the subscriber firsts registers with the visited network — which, as you know, sometimes takes several minutes, even in 3G. It should only take a second or two to authenticate the subscriber. In some of our tests with live operators, that has been the case.

Question:  How are testing LTE connections and what are the challenges between operators?

Answer:  Testing is typically done in a two-stage process: Testing between the DRA and the DEA (of the operator) and then end-to-end testing. We must accurately define the desired outcomes for both phases. We have found that some operators do not necessarily follow the standards, which becomes quite evident during the testing process; however, through our function a Diameter hubbing provider, we can provide some interworking and/or mediation to resolve these capabilities.

A Diameter hubbing provider should also be able to simulate Diameter traffic before end-to-end testing with another or multiple operators begins. By that point, the DRA (Diameter hubbing provider) should expose a standard interface to all other operators.

Question: What is the last progress in Ir25 documents for LTE testing?   Also what about the agreements between operators? Do we [operators] need to sign new agreements?

Answer: I can’t really answer the IR 25 part yet. We do not play a role in that group.

In terms of agreements  – that is up to the operators — there is no specific requirement. Many will amend existing agreements to cover LTE roaming.

NOTE TO ALL READERS: My blog entries are the process of being moved from the Sybase blog site to the SAP Community Network (SCN) – Mobile blog.  You will be able to find all my consolidated blog entries on my SCN Content page.  This entry will be posted both at the Sybase blog site and the SCN Mobile site as well. 

Please follow me on Twitter: wdudley2009.

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