I recently read a blog post that got my ire up. Rather than commenting on the other blog, I decided to write a full post here to address a number of misconceptions about VoLGA.
The original post is here: http://lteworld.org/blog/what-next-volga.
Specifically, the LTE World blog had a slide which I assume was presented at the LTE World Summit last month in Amsterdam. The slide highlights the 'benefits' of CS Fallback. I've posted it here to give some context to my comments:
I think the bullets need greater explanation:
- "CSFB falls back from EPS to CS domain." Why would any user (or operator) want that? What benefit is there in dropping my cool LTE data session and 'falling' back to GSM? I'm struggling to understand how an operator could position this as a 'feature' in their retail shops. By the way, AT&T spent millions of dollars trashing Verizon this year for the same fallback 'feature' which is native in CDMA.
- "CSFB reuses CS domain." That's exactly what VoLGA does.
- "EPS redirects UE to CS domain for CS services." See bullet 1 again. Why would anyone want this? If it were a VoLGA bullet, it would read "UE stays in EPS domain to access CS services, which can be combined with IMS/data services for a richer calling experience".
- "User can decide, based on CLI, whether to accept CSFB request." What this really means is the user can decide to NOT ANSWER THE PHONE. But I'm confused… aren't voice revenues 80% of mobile revenues today? How could anyone, especially the 3GPP, promote 'not answering the phone' as a BENEFIT for operators or of CSFB? Stunning really.
The last bullet, mis-mash of things, brings up one other 'point' on roaming. Frankly, I think this issue is going to be put to bed very quickly. First, handsets aren't going to support the various LTE spectrum bands any time soon to make roaming an issue. Roaming, for the foreseeable future, will be 3G. It exists today, it works today, there's no need to 'fall back' to roam. Just start on 3G.
Has anyone noticed that there is no one actually promoting CSFB (other than, apparently 3GPP, source of the slide referenced in the original blog post)? If you have any doubts, check out Dean Bubley's analysis of CSFB at disruptive-wireless.com.
Next, there was a comment on the LTE World blog post that VoLGA is 'too expensive,' and I'm not how this was determined, or what it was compared to.
From the beginning, the VoLGA Forum structured the specifications to require no modifications to a 3GPP standard Rel. 9 network. As a solution, VoLGA is a single VoLGA Controller (VAN-C); a simplified GAN controller. It relies on SR-VCC, a capability in the MME, to handle mobility. The VAN-C is simply a signaling gateway. It relies on existing Iu-CS interfaces into a standard, deployed R4 MSC.
If there is confusion on the capital cost of a VoLGA solution, don't hesitate to contact Kineto. Budgetary pricing is available. Alternatively, contact the other vendor who demonstrated a solution for Deutsche Telekom in Dec2009. There's already competition in the marketplace.
Suffice to say, VoLGA is a very low cost solution. It's so low-cost that some telecom OEMs quickly realized they could make a LOT more money selling an IMS kit than a VoLGA kit.
But more than VoLGA being the low-cost solution, CSFB is very expensive. Far more expensive than I think anyone realizes.
First, to support CSFB, one needs to upgrade the brand new LTE network... eNBs need to handle the process of falling back to GSM along with the MMEs. And to manage the handover, the PGW and SGW need to be upgraded as well. So much for supporting a 3GPP standard Rel. 9 network.
The CS domain must be upgraded too. It's not used to having handsets do "blind handovers" (needed to reduce latency to *only* double the call setup latency of VoLGA). So an operator needs to modify their CS domain. Is that all GSM (BSCs) and 3G (RNCs) or just 3G? Well, it depends on what network an operator wants handsets falling back to.
And of course, an upgrade is required on the MSC itself, which is not used to finding a handset on LTE.
When we talk about cost, should we consider signaling load? CSFB puts an enourmous signaling burden on the entire network because every phone call (except for the ones that users reject) triggers a complete network handover. Signaling messages fly to/from the device over LTE, and then to/from the device over the CS domain. The impact is felt across the network and even up to the HLR. Kineto's projections on CSFB signaling load are truly frightening.
Finally, let's consider the most likely time for a call to drop. Does it happen when we're sitting in our homes or at our desks? Or, are we most likely to drop a call when moving between cells and/or networks? You guessed it…..switching between cells definitely increases the potential for dropped calls. Now in the middle of trying to connect a user to a call, we ask the network to whip up a blind-handover and expect (or hope, or pray) that there won't be substantial call drops.
To conclude, there is no doubt that the 'cost' of VoLGA is significantly lower than CSFB. The capital cost is significantly lower. The signaling cost is much, much lower. But the most important cost of all is customer satisfaction, and no one is going to spend more capital to get a poorer customer experience.
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