  Content delivery networks are a key infrastructure component used by Video on
Demand (VoD) services to deliver content over the Internet. We study a content
delivery system consisting of a central server and multiple co-located caches,
each with limited storage and service capabilities. This work evaluates the
performance of such a system as a function of the storage capacity of the
caches, the content replication strategy, and the service policy. This analysis
can be used for a system-level optimization of these design choices.
  The focus of this work is on understanding the benefits of allowing caches to
pool their resources to serve user requests. We show that the benefits of
resource pooling depend on the popularity profile of the contents offered by
the VoD service. More specifically, if the popularity does not vary drastically
across contents, resource pooling can lead to significant improvements in the
system performance. In contrast, if the content popularity is uneven, the
benefits of resource pooling are negligible.
