Wednesday, July 21, 2010

Shaping / policing in 3G networks

This is my first blog entry on the world of traffic shaping. We have all been hearing about the need for shaping in 3G mobile networks. The subject’s popularity exploded with the publicity of network overload problems that some operators were experiencing with the introduction of the iPhone. Most of that turned out to be due to signaling overload. However, almost everyone is convinced that if flat-rate plans remain then true data congestion will become acute at some point, and some sort of bandwidth shaping and policing will then be needed.

The question is where to apply the shaping. Most of the many solutions that I have seen are positioned relatively high up in the network, at the Gn (between SGSN and GGSN) or Gi (between GGSN and Internet) interfaces. And it’s easy to see why. Lower down (at the Iu or Iub RAN interfaces) there are scalability concerns and the protocols are much more complex.

The problem is that the same data overload concerns are forcing mobile operators to cache and/or offload traffic as close to the end-user as possible. This traffic doesn’t traverse shaping / policing functions positioned higher up, and thus leads them to believe that all is well. Hence the RAN becomes even more overloaded.

Two fixes come to mind. The more complex one is to signal the true situation upwards. This one may be preferred by operators, as it could potentially allow non-flat-rate billing even for traffic that doesn’t traverse their core. The cleaner solution is to perform the shaping lower down (e.g., at the Iub), before the caching/offloading. This solution entails classifying user traffic that is usually encrypted and even if in the clear is hidden by a plethora of complex protocols. The actual shaping is also complicated because of multiplexing.

I would appreciate hearing as to preference or other alternatives.