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I Was Given a Data Offload Solution for Christmas – But I Might Want to Trade Up

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Data offload is an over-abused term, and I get to read articles where it is taken as standard terminology, usually portrayed as providing a universal solution for many of Service Providers’ challenges, so it is worth taking a look in more detail at what it can really mean and what can be done with both current and upcoming technology options. This time I'll look at the current options.

One big challenge for cellular operators is the growth of mobile data driven by phenomena such as the rise of social media including the likes of Facebook, Twitter and YouTube; the related massive growth in smartphone use; and the growing phenomenon of internet tablets. Cisco’s Visual Networking Index from 2010 predicts a 26x growth between 2010 and 2015, so it’s a serious issue. However, there are a number of potential choke points in a cellular network – the radio spectrum, the backhaul from the cell site, and the core network routers are key ones.

The figure shows a simplified 3G network with a WiFi extension based on the 3GPP I-WLAN standard (although there are other mechanisms), and focusing on a home use scenario.

macro_femto_wifi.bmp

Click Image to Enlarge

In the figure the TOF is a Traffic Offload Function that separates external internet traffic from operator services data and routes it to the internet via a Packet Data Gateway (PDG), whilst the Tunnel Termination Gateway (TTG) handles access control, authentication and forwarding the user data to and from 3GPP format.

Consider the radio spectrum first. Today’s 3G and LTE networks make very efficient use of radio spectrum when they are transmitting and receiving, operating near the Shannon limit which is the theoretical maximum for a given level of interference. Consequently if you want to get more user data through part of a cellular network where the spectrum is heavily loaded then you only have a couple of options:  either reduce the interference level – typically by inserting more cells operating at lower power (e.g. femtocells), or get some more spectrum which could either mean obtaining more expensive licensed cellular spectrum, or making use of alternative technologies such as WiFi. One issue with WiFi is that there currently no deployed way to dynamically control whether a UE selects WiFi for a service rather than cellular or to handover from one to another – it can only be done as a general preference.

As far as backhaul is concerned. There are clear gains if you can make use of a user’s own backhaul (such as DSL line in the home) and there may be a better distribution of traffic load in an outdoor scenario if some is sent over WiFi rather than the macro network. The operator may be able to delay capital expenditure on upgrading the macro network backhaul links to, say, optical fibre.

Core network data routers (GGSNs) faced a massive load increase once the iPhone and subsequent smartphones were deployed as they made it much easier for people to consume and create data to and from the internet. This affects both the bandwidth needed to the processing centres where these were housed, and the amount of processing power needed in them. However, whichever way the user data is routed, it has to go through one of these routers in the operator’s (or a partner’s) core network. If the user is able to use WiFi directly from their home without going at least partially by the operator network then this will offload the core – but then the operator can’t bill for the data.

We can put together a table showing what currently deployed solutions impact:

Impact areaMacrocell UseFemtocell / Small CellWiFi
Radio SpectrumNoYesYes
BackhaulNoYes (if in home)Yes (if in the home)
Core NetworkNoNoOnly if free from operator control and charging
Service ImpactNoPotentially positive in the home if new services are introducedMobility control limited

The data offload solutions end up offloading the radio spectrum (in different ways) and potentially the backhaul, but not really the core network. As a small cell enthusiast this is good news for me – small cells were conceived to help meet the radio challenge - and it addresses a key immediate issue (radio spectrum) but it is not yet a total solution in itself - it is a good start but there are opportunities for future enhancement and convergence (Mark Grayson has a post on one approach here) some of which we have been working on in the standards bodies, and which we’ll look at in the future.

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