Vodacom data billing changes: how you’re affected

Vodacom has increased the data billing increment on its network to 10 kilobytes (KB), a spokesperson for the network has confirmed.

Previously the data sessions on Vodacom were billed in increments of 1KB on most contract packages. Some exceptions, and pre-paid and top-up tariff plans, had unitisation of between 5KB and 10KB.

The change was made a few weeks ago, towards the middle of October 2014.

Though at first glance it may appear that this would have significant ramifications for users who mostly transmit small amounts of data at a time, Vodacom has explained that for the typical consumer nothing will change.

“Older telemetry modems that establish and then intentionally tear down the packet data protocol (PDP) context might be affected,” a spokesperson for Vodacom said.

Vodacom spoke to its telemetry customers (such as vehicle tracking companies) to ensure they would not be affected, the operator said.

It went on to provide detailed answers to technical questions pertaining to the billing increment increase, but in brief the reason for the change was to decrease the load on its billing system.

The full technical explanation from Vodacom will be provided in the second half of the article.

Asked when the change was made and why customers weren’t informed, Vodacom said that the alterations to its unitisation parameters were made in the last few weeks.

“As explained previously, normal subscribers are not affected and Vodacom engaged with its telemetry customers to ensure they are not affected,” the operator said.

Other subscribers who might be affected are those being billed more than R1/MB, such as pre-paid subscribers being billed ad-hoc or out-of-bundle rates.

The maximum rounding error introduced by the change for these users is 1c per PDP session.

Vodacom explained that a PDP session must not be confused with a TCP or UDP session, as it may span multiple connections to multiple Internet services.

Queried about rumours that Vodacom upped its billing increment to negatively impact “over the top” services like WhatsApp, which send small amount of data at a time, the network said that OTT services had nothing to do with it.

“It was done to ease constraints on the rating and billing systems in such a way that subscribers are not affected,” the spokesperson said.

“While an OTT message might be less than 10KB, it must be remembered that it is part of all the data that flows across the PDP session.”

A single PDP session would be much larger than 10KB, Vodacom said (“likely tens or hundreds of Megabytes”), and thus every WhatsApp message will not be rated as a separate unit of usage.

Which brings us to the technical details Vodacom provided in response to questions about the change.

Can you even maths, bro?

Of unitisation and PDP contexts

Unitisation is the smallest amount that is rated and billed on the network. It is typically calculated as a function of the smallest chargeable financial value, which in our case is 1c (one South African cent).

For most contract price plans, usage is billed in increments of 1KB, with out-of-bundle usage rounded up to 1c where applicable.

However, there are some exceptions, such as the Vodacom MyMeg 0 package. Data is billed at R2/MB, which means that 1 cent of usage translates to 5KB units.

Similarly, if you are a pre-paid or top-up customer with an out-of-bundle (OOB) rate of R1/MB, then you are already unitised in 10KB increments (1c worth of usage at R1/MB equals 10KB).

In other words, if you used 1MB out-of-bundle at R1 per Megabyte (MB), the charge would be R1. If you use 1MB + 2KB, the charge would be rounded up to R1.01.

OK… but what was wrong with the unitisation as it was?

Vodacom said that it had resisted making changes to its billing increments for some time, but due to the increased load experienced by its back-end rating and billing systems it had no choice.

The rating and billing systems are taking strain for a number of reasons, Vodacom said:

  1. Increase in active data users — Vodacom now provides data services to more than 18 million unique users every month.
  2. Increase in data usage — there is much richer content available, and modern devices are also able to consume large amounts of high-capacity services.
  3. Increase in network speed — average throughput has gone up more than 50-fold from less than 100Kbps, when the billing system was put in place, to over 5Mbps.

To illustrate the point, Vodacom showed a quick calculation of an increase from 1 million users at an average speed of 500kbps to 15 million users at an average speed of 5Mbps.

Its billing system would need to be able to deal with a 150-fold increase in the potential peak billing record rate, from 62.5 million records per second to 9.375 billion records per second.

“From the above it is clear if we kept the unitisation at 1KB the systems would not cope, especially with the big drive to deploy LTE across the country,” Vodacom said.

“After careful consideration, the decision was thus made to increase to unitisation to 10KB, resulting in a system load increase factor of between 10 and 20,” Vodacom said. “While this is still substantial, it was felt it was practical and manageable.”

It added that another benefit of changing to 10KB unitisation across the board was that there would be consistency across plans.

“A single allocation and calculation method allows simpler and more reliable billing and rating systems to be implemented as well as better reporting, and capacity planning,” Vodacom said.

Am I being screwed?

Vodacom assured that careful consideration was given to how this would impact subscribers, and it found that for average consumer usage there was no impact.

It found that the following factors could influence subscribers:

  1. Number of PDP sessions created by a device on the network — a data connection to the Vodacom network that should not be confused with TCP or UDP sessions. Vodacom said it looked at how often a typical data device creates a session on the network and what factors influence this process.
  2. The duration of a session — this is almost unlimited nowadays, and is thus not a factor.
  3. The amount of data transferred in a session — the bigger the volume of data in one session, the less the impact of rounding up to 10KB will be.

Vodacom said that modern devices establish a PDP session when the phone boots up and will not typically tear it down in normal operation.

With the higher average data consumption seen today, the “rounding up” also constitutes a very small percentage increase, Vodacom argued.

For example, if a session had a volume of 1.0035MB (1MB + 3.5KB), the rounding up changed from 1.004MB to 1.010MB. This is an increase 0.5% in usage, but at a rate of 20c/MB, for example, the charge in both cases is 21c.

Where this might impact subscribers is on ad-hoc usage or out-of-bundle usage which is billed at R2/MB. Instead of being billed R2.01 for the above usage, for example, those users will be billed R2.02.

This means that the increase in unitisation to 10KB will not increase your bill at all so long as your data tariff is R1/MB or below.

Those on R2/MB data rates may be billed more, but the maximum they could be charged extra for any session of sufficient size is 1c.

Similarly, so long as your PDP sessions are sufficiently large, the impact on data bundles will also be minimal, Vodacom said.

Making and breaking PDP sessions

The following actions will cause a PDP session to be torn down or re-established:

  • Switching off the device
  • Turning off mobile data on the device
  • Idle timer expiring, which is currently set to 5 days on the Vodacom network
  • Admin disconnect — if Vodacom needs to clear a subscriber based on some fault or upgrade on the network
  • Admin lock/barring on the Home Location Register or Home Subscriber Server — when a SIM is locked, such as when it is reported stolen
  • Instruction from the Online Charging System or Customer Charging System to the Gateway GPRS Support Node — such as if your account is suspended
  • Unsuccessful handover from one radio access technology type to the next — such as when switching from 2G to 3G, and the handover breaks
  • Abnormal disconnect — if something major goes wrong on the mobile data network itself, such as the GPRS core network failing

Making and receiving calls, dropped calls, and normal handovers will not cause the PDP session to be torn down in modern devices, Vodacom said.

There are some legacy devices on its network which manually set up and tear down the PDP context, especially among telemetry providers, but Vodacom said it engaged with these customers to ensure they aren’t adversely affected.

Vodacom acknowledged that there are marginal use cases and legacy systems using its data network which may not have been taken into account.

It asks those users to contact them with their specific case to see if a solution can be found.

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Vodacom data billing changes: how you’re affected