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Akamai and the tale of the download servers

Akamai and the tale of the download servers

Akamai and the tale of the download servers

In order to manage the traffic on our network we use different rules for different types of traffic. Within certain types of traffic we make a differentiation between different sources and whether the traffic is "interactive" or "non-interactive". An example being Usenet traffic. Text Usenet traffic is very low bandwidth and interactive so gets a high priority, binary Usenet can be very bandwidth intensive, non-interactive and gets a low priority, when the network is busy it may be rate limited to a lower speed. With HTTP we have a similar classification. We split the traffic into three groupings, the first is a set of high volume download sites like Rapidshare and Megaupload, the second are certain "mirror sites" and servers run by Akamai, again high volume sites and the third is everything else. This distinction is done to separate out these high volume sites so that downloads from them don't impact on interactive traffic like browsing. They are treated at the same priority on the network as browsing but will have a rate limit applied when the network is busy. The Akamai download sites can generate considerable amounts of traffic. Microsoft’s Windows Update traffic is counted in this group, as Microsoft now have an approach of releasing patches on the second Tuesday of every month, we will see a big spike in HTTP download traffic on the Tuesday evening and the Wednesday morning and evening as the patches are downloaded by our customers. The more patches there are and the bigger the files the higher the amount of traffic. A recent example is this month's patch Tuesday. On Tuesday evening we saw a large increase in HTTP download traffic as expected but the rate limit spread the traffic out and helped to prevent the volume of traffic from having any knock on effects. This was also noted by other ISPs as per this article on The Register and also reported as causing problems (albeit in a different way) for Skype users. Wednesday morning was slightly different, likely as business begin work, we saw the expected increase in HTTP download traffic but without the rate limit the spike of traffic was a lot higher than the previous evening (in the region of 550Mbps in the morning compared to around 375Mbps Tuesday evening and a "normal high" of about 250Mbps). This higher than normal amount of extra gold traffic would have had a knock on effect to lower priority traffic like P2P and usenet, slowing it down, and may have had an effect on browsing. The graphs were showing that the total amount of gold traffic was at or near to the maximum amount allowed and pushing the lower priority non-interactive traffic towards the minimum amounts and thus the gold HTTP download traffic may have been contending against other gold traffic like browsing. In situations like that we would see an increase in gold latency and customers may see a decrease in speeds as well as the possibility of gold packet drops. Gaming and VoIP traffic in the titanium queue would be unaffected and would continue to see low ping times. We may also consider switching to our Plan B - high demand network configuration to give more bandwidth to gold or to lower the rate limits on other non-interactive traffic. Many, if not most, of the files from Akamai will be non-interactive traffic like the Windows Update files, game, driver and other file downloads. Akamai are also delivering some streaming and dynamic web content, with the rate limit set at the lowest 1Mbps under normal operation this should not have a significant detrimental on this type of traffic. We are of course pro-actively monitoring the performance of traffic delivered via Akamai and would welcome customer feedback on this, particularly regarding the performance of any interactive traffic such as streaming as we are more than happy to review the rate limits. As an experiment we removed the rate limit on Akamai traffic on Sunday between 6pm and midnight, with it being a nice bank holiday weekend a lot of people would be out or away and so the network was quieter than a normal Sunday. Immediately at 6pm there was an increase in traffic by around 50% but levelled off towards about 8pm. It is therefore sensible to manage this traffic with a rate limit so that it doesn't impact on the experience of everything else. Whilst the large patch Tuesday are irregular there is always the potential for large amounts of non-interactive traffic to have knock on effects to interactive traffic like browsing. As always we welcome feedback and in this case particularly would like to hear from customers that use Akamai sites and anyone that's noticed any problems when the rate limits have been in place. Dave Tomlinson

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