Analysis of Tandem PIT and CS with Non-Zero Download Delay

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Analysis of Tandem PIT and CS with Non-Zero Download Delay
by Huichen Dai, Bin Liu, Haowei Yuan, Patrick Crowley, and Jianyuan Lu.

Collapsed forwarding has long been used in cache
systems to reduce the load on servers by aggregating requests
for the same content. Named Data Networking (NDN) as a
future Internet architecture incorporates this technique through
a data structure called Pending Interest Table (PIT). The request
aggregation feature suggests that PIT can be viewed as a nonreset
time-to-live (TTL) based cache. The Content Store (CS) is a
content cache placed in front of the PIT on the NDN forwarding
path, so they make up a tandem cache network. To investigate
the metrics of interest in this network, like the hit probability for
the PIT and the CS, the expected PIT size, non-zero download
delay (non-ZDD) should be taken into consideration.
Caching policies usually assume zero download delay (ZDD),
i.e., request and object arrive simultaneously, and numerous
analytical methods have been proposed to study the ZDD caching
policies. In this paper, after dissecting the LRU policy, we for
the first time propose two LRU variants considering non-ZDD by
defining separate operations for the request and object arrivals.
When CS adopts the proposed LRU variants, the analysis of
the CS-PIT network can still take advantage of the existing
models, so the metrics of interest can be computed. Especially,
the distribution for the “inter-miss” time of this network can be
derived, which has not been achieved by prior works. Finally,
the analytical results are verified through simulations.