Distribution and Rendering of Real-Time Scene Based on the Virtual Reality System - Advances in Image and Graphics Technologies - page 194

network bandwidth, but it is not advanced enough to support the different equipment,
which is not widely used in the live streaming transmission. P2p transmission is a way
to share resources between client nodes which emphasize the equivalence of node,
and the advantages of low cost, high scalability, high service quality and high securi-
ty. However, it will increase the time delay for client and is difficult to support to
support different clients as well. End-to-end transmission is a method that allows each
client to build connection with the server and request data from the server. There's an
advantage of fast response and strong adaptability. But there is a big pressure on the
server. The layered content delivery network [5-7] based on the end-to-end transmis-
sion can effectively solve the problem of the pressure on the server and network limi-
tation. Edge delivery node deployed in the system as the server is directly requested
by client. Request delay and stress to backbone is reduced because there is a cache of
hot data in the edge server.

2.3

Replacement Policy

As cache size is finite for the edge content disputation server, a cache replacement
policy is needed to manage cache content. If the data flow from the media server
needs to be stored when the cache is full, the policy will determine which data is
evicted to make room for the new data. The Replacement policy is generally classi-
fied as time-based policy, frequency-based policy, size-based policy, function-based
policy and randomized policy [8]. Hit rate and complexity are the main factors to be
considered. Latest recently used (LRU) as time-based policy and least frequent used
(LFU) as frequency-based policy are often employed in the web cache replacement
policy. Size-based policy is used when large file is less popular. Larger file will be
removed to contain more files with small size if data needs to be replaced. Function-
based policy performs best but has the highest complexity. Greedy dual size policy
[9] is a function-based policy that the files with larger fetch costs will be stated in the
cache longer. Randomized policy works the worst so that it is not used in practice.

3 The Overall Architecture Design

Different from the structure of traditional content distribution network, the data is
mostly collected and distributed according to the region. The design of the system
should meet the following characteristics: one is easy to deploy and extend on the
existing server structure, no need to alter the architecture of the virtual reality system;
the second is able to quickly respond to the large-scale users' requests by increasing
the hardware; the third is to support multiple platforms of virtual reality, including the
current virtual reality client and mobile virtual reality client; the last one is to provide
a stable flow of live streaming video and reduce the delay. The system consists