Green Clouds: the network connection - by Peter Judge

Views and Opinions on Green IT (Feb 7 2011)

1. 

   So is the cloud green or not? If you’re here, reading this, you may be sick of the question. But it did push me towards the issue of green networks, when I spoke at Cloud Expo in London.

   We talked a lot about making data centres more efficient, about virtualisation, about boosting utilisation and closing down unused capacity. But I also tried to go into the network question.

   Whatever else it does, it's obvious that putting stuff out on the cloud increases the distance that data travels. I'll often forward a message by Google Mail to a colleague on the next desk. That means the data goes to a central server - maybe to a different country - to travel a metre.

   It takes energy to send data across a network takes energy, so does the cloud’s increase in network traffic offset - or even cancel out - the energy saved through virtualisation and efficiency?

   First off, this question is like “how long is a piece of string?” How much energy your app uses in the network will depend on what your specific app does, what traffic it produces, and how your particular users treat it. It will have a lot more to do with decisions made in the user interface design than almost anything else.

   So, there’s no single answer.

   But there is a basic truth that data travelling uses very little energy. And the energy it uses is in no way proportional to the distance it travels.

   Energy use could be cut by 1000

   The GreenTouch Consortium, founded a year ago by Alcatel Lucent and others, came out of observations from Bell Labs that networks could really be a lot more efficient than they are. According to Shannon’s Law (or the Shannon-Hartley Theorem, as it is more properly known) the amount of information that can be passed depends on the signal power, so there is a theoretical limit to how much you can reduce the energy used by a network.

   As with data centres, however, we are well above that limit. Bell Labs’ people worked out the world’s communications networks currently use about 10,000 times the minimum energy - and GreenTouch set itself the goal of cutting that by a factor of 1000, to only ten times the minimum energy used.

   Last week, GreenTouch demonstrated technology that could get us part of the way there.

   Much of what it suggests is straightforward stuff like shutting down kit that is not tranmitting or receiving data (your home router uses 20W continuously, even when you are asleep, for instance).

   Other ideas introduce better technology, such as Massive MIMO, now rebranded as large scale antenna systems, which came out of Bell Labs and is being productised by a group including Alcatel Lucent of course, Huawei and others.

   Normal cell tower antennas broadcast signals over a wide sector. Turning on more antennas can reduce this because superposing their signals can create a beam, focused on the receiving phone. Sixteen antennas, according to the demo I saw, uses about one-sixteenth the energy of a single antenna.

   That is a good thing - and especially good in places like the third world, where getting energy to cell towers in the first place is a major issue, and often relies on dirty and expensive solutions such as diesel.

   Access uses more energy than the core

   But this is at the access part of the network. Now, that is the right part for GreenTouch to be looking at, because access uses about eighty percent of the energy in the world’s communications networks, and only 20 percent is used in the core.

   This may be counter to expectations. Access (the last mile) is probably about one percent of the distance travelled by bits - though with caching this may not be quite true.

   When we talk about the cloud moving data further, we are talking about two things. One is the increase in mobile, wireless and basically anywhere-you-are access to data. That factor is going to boost energy use a lot, as it’s in the access part of the network.

   It’s also not fair to pin the blame for that energy use on the cloud, since that demand is hitting us whether our applications are in-house or on Amazon. People want access anywhere, because they have Androids, iPhones, iPads and neat laptops, along with data roaming contracts and Wi-Fi.

   The other impact the cloud has on the way data travels is in moving data centres. That’s mainly increases traffic on the core network and - in terms of energy - we really shouldn’t worry about that.

   Once data has been turned into light and put on a fibre, there is no friction. Light can travel 100km along an optical and come out the other end with half its energy gone. Data on fibres can go halfway round the world for a negligible energy cost.

   Put data centers where you want, but...

   So this means two things. Firstly, we really can put energy centers where we want. Indeed, since the other thing data centers need - power - really does lose in transmission, they should all be right alongside good power sources.

   But secondly, network traffic is often just wasted bits of back-and-forth chatter caused by poor user interface design. And when data reaches the data center, the processing on it is often duplicated, pointless or inefficient.

   Once the underlying tech is optimised, there will still be more to do. 

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