Nameserver demand estimation
Global Traffic Management's function is to return answers for DNS queries based on who is asking. Queries are sent by client nameservers, which are usually operated by the end user's ISP or public recursive providers such as Google Public DNS or OpenDNS. As a DNS-based system, GTM has no way of knowing the IP addresses of the actual end users; it only knows them by the client nameservers they use.
When GTM sends or maps a client nameserver to a data center, it is implicitly directing all end users who use that nameserver to that data center. Client nameservers are usually shared by many users. Some client nameservers might have only a few users, while others might be used by all the customers in a metropolitan area of a large cable TV company for example. Thus, some nameservers represent more Internet traffic than others.
To balance load effectively, GTM needs to know whether a nameserver has a lot of traffic demand behind it or a little. To learn this, Akamai continually analyzes the logs of GTM's authoritative nameservers and keeps track of how often a client nameserver sends a query for a particular name. Consider client nameserver A, which repeatedly refreshes a name as soon as its TTL expires. It probably has more load than client nameserver B, which only refreshes the name once an hour. B probably has more load than client name server C, which only refreshes the name once a day. By analyzing the logs, GTM can learn the IP addresses of nearly all the nameservers on the Internet and develop an estimate of how much demand is behind each one.
Internet traffic measured across large populations shows characteristic variations. As an example, most nameservers show more load in the middle of the day than in the middle of the night (local time), and the daily peaks tend to be lower on weekends. For this reason, nameserver demand estimates are aggregated and averaged over five to seven days.
Nameserver demand estimates are used by some of GTM's load balancing modes. See the Load Balancing section for more information.