It is related to the fair-queuing principle which groups packets into classes and shares the service capacity between them.
All practical schedulers approximate GPS and use it as a reference to measure fairness.
"[2] Generalized processor sharing assumes that traffic is fluid (infinitesimal packet sizes), and can be arbitrarily split.
There are several service disciplines which track the performance of GPS quite closely such as weighted fair queuing (WFQ),[3] also known as packet-by-packet generalized processor sharing (PGPS).
In a network such as the internet, different application types require different levels of performance.
For example, email is a genuinely store and forward kind of application, but videoconferencing isn't since it requires low latency.
When packets are queued up on one end of a congested link, the node usually has some freedom in deciding the order in which it should send the queued packets.
One example ordering is simply first-come, first-served, which works fine if the sizes of the queues are small, but can result in problems if there are latency-sensitive packets being blocked by packets from bursty, higher bandwidth applications.
flows (also called "classes", or "sessions") is configured with one weight
is continuously backlogged on this interval (i.e. the queue is never empty), then, for any other flow
Generalized processor sharing assumes that the traffic is fluid, i.e., infinitely divisible so that whenever an application type has packets in the queue, it will receive exactly the fraction of the server given by the formula above.
However, traffic is not fluid and consists of packets, possibly of variable sizes.
Therefore, GPS is mostly a theoretical idea, and several scheduling algorithms have been developed to approximate this GPS ideal: PGPS, aka Weighted fair queuing, is the most known implementation of GPS, but it has some drawbacks, and several other implementations have been proposed, as Deficit round robin or WF2Q.
GPS is insensible to packet sizes, since it assumes a fluid model.