Updated A moment of inattention has allowed the ITU’s proposed deep packet inspection (DPI) standard to escape.

The slip-up happened when an Australian CryptoParty activist Asher Wolf put out a public call on Twitter asking for a copy of the text. The ITU duly sent it by e-mail – only later realising its mistake and asking her to treat it as for her eyes only.

By which time, Vulture South and other journalists had seen the document…

So what is the ITU proposing?

The document – all 95 pages of it – is exactly what it purports to be: a proposed technical interoperability standard for deep packet inspection systems (its very existence comes as something of a surprise to this vulture: in the context of network performance, I asked several vendors when this would be standardised, and the unanimous response was “never”).

The standard describes itself as applicable to “application identification, flow identification, inspected traffic types” – which The Register would highlight as the most sensitive functions – along with how DPI systems manage signatures, report to network management systems, and interact with their policy engines.

A block diagram is going to be needed.

A thumbnail outline of the ITU's concept of DPI

What’s odd about the ITU’s decision to standardise DPI is this: the point of standardisation is interoperability – and interoperability matters most where systems interact with the outside world.

Looking at this block diagram, the biggest question that occurs to The Register has been the same question throughout the life of DPI: if the interfaces behave themselves, passing packets in and out as they should, what’s the point of standardising the internals?

Yet that is what the ITU is attempting – whether or not this can be taken as an endorsement of DPI is another matter.

At the high level, there’s nothing remarkable. Packet identification – unidirectional or bi-directional – is specified as a necessary component of DPI because it is. The ITU spec says that the flow identification should comply with IETF RFCs 5101 and 5102.

The next piece defines the existence and operation of the signature library, the specification for which requires “only” that the signature library exist and what signatures it contains. It also demands that the library be secured. And – naturally enough – that signatures can be added, removed, modified and so on.

There’s a lot more, but the first thing to understand is this: much of the standard does nothing more than describe the functional components of DPI systems that already exist.

What about the impact on the network?

Here, at least, the ITU seems aware that DPI can carry risks, so it insists that deployments don’t impact emergency telecommunications (for example, by introducing excessive, unwanted latency or packet loss).

The devil's in the appendices

If you’ve stayed with me this long, congratulations. It’s in the appendices that we reach the part of the spec that has people worried. Specifically, Appendix I: application scenarios.

This section looks at various use-cases: service differentiation (which, of course, raises the debate about network neutrality); traffic monitoring for resource allocation based on subscriber policy (ie, “premium” versus “best effort” services – neutrality again); malicious traffic identification (which isn’t a bad idea); service-based billing (which could, again, tie back to the neutrality question)…

...and so on, ad infinitum.

Having read the document – twice now - this Register author is starting to form the opinion that for a 95-page epic, the ITU proposed DPI standard is less than the sum of its parts.

As has been pointed out to me privately, and will no doubt give rise to extensive public condemnation, the proposed standards use-case examples include VoIP blocking, BitTorrent detection, SIP blocking and so on.

I don’t suspect for a moment that the ITU conceived such ideas on its own. They read as if they were drawn from vendor configuration manuals. In other words the examples were provided - because they already existed.

And if the standard were adopted, what then?

The argument that the standard will act as an enabler to repressive regimes seems to ignore the long history of DPI deployment that already exists, across both democratic and non-democratic countries. It’s already there.

Also, the argument against the WCIT’s proposed International Telecommunications Regulations runs that the ITU’s involvement will stifle innovation and hamper the Internet. Why would the same body’s involvement become an enhancer and enabler to DPI?

It seems to me that DPI could do with the kind of stifling that the ITU is accused of threatening to the online world.

Unless, of course, the outcry over the DPI standard is intended as another rallying cry against the virtual black helicopters of the ITU… ®

Updated to add

The ITU has now announced that the DPI standard has been approved. Its announcement spins the standard in the direction of performance management, managing not to dwell on unwelcome issues such as BitTorrent or VoIP blocking.

It states that the standard will soon be available for download. ®