Int. J. Communications, Network and System Sciences, 2010, 3, 745-749
doi:10.4236/ijcns.2010.39099 Published Online September 2010 (http://www.SciRP.org/journal/ijcns)
Design and Implementation on the P2P VOD System Based
on the RF-IPS Algorithm
Zhiyi Qu, Lili Li, Jianxu Li
School of Information Science & Engineering, Lanzhou University; Information Management Department, Lanzhou
Jiaotong University bowen college, Lanzhou, China
Received July 15, 2010; revised August 17, 2010; accepted September 10, 2010
Abstract
This paper presents a P2P VOD system based on the RF-IPS algorithm, and this system consists of two parts,
server-side and clients. We put emphasis on the piece selection module of server-side, and in this part we
apply the RF-IPS algorithm proposed in the past. In the piece selection module, we also proposed a weight-
ing function except the RF-IPS algorithm. Using this function we will find the best server peers effectively
and quickly, it will enhance the performance of this system. We carry on experiments on RF-IPS algorithm,
and the results show this algorithm is efficient. Overall, we believe that the RF-IPS algorithm is feasible to
further improve system performance and provide a cost-effective P2P VOD service with acceptable user
experience.
Keywords: VOD, P2P, RF-IPS, Piece Selection
1. Introduction
Video-on-Demand (VOD) has becoming one of the most
important streaming service and catches many people’s
research interest. VOD connection is an active connection
between the client and the server or the client and the
client, and people can select the video resources as they
pleased at any time and can do some VCR operations,
such as FORWARD, BACKWARD and REWIND [1]. In
the traditional VOD system, users only download video
resource from the server, and the server becomes the
bottleneck of the system when the users reach a certain
numbers. Once the server failure, the whole system would
be paralyzed. But in the mode of P2P VOD technology,
video resource is uploaded or downloaded between the
clients, that are peer nodes, and it is effective to avoid the
bottleneck of the system. As the P2P network can provide
the basic network support for the large-scale VOD appli-
cations, many of the emerging P2P VOD distribution
strategies are able to provide the most basic way of data
transmission in the P2P network. Described in this paper
based on the RF-IPS algorithm of P2P VOD system also
has a server part, but it is not the traditional sense of the
server, just as a super-node has more service capabilities.
The client is the peer node in the P2P network, and it can
be the family PC, laptop computer and smart cell phones
and so on [2].
2. Related Work
VOD system is on-demand video system and a major
application of streaming technology. It is great to challenge
the traditional video services, where the users can only
receive the broadcast programs passively, and can not
afford the program content [3]. But somewhat differently,
the VOD service system equipped with a large video
library, and users can browse the video directory and
choose one of the programs on demand at any time,
while the system plays the corresponding broadcast
program based on the users’ requests. Traditional VOD
system consists of server system, network system and
client system.
2.1. Server System
Server system consists of three modules, service module
[4], application service module and management module.
The media service module is mainly used to provide
users with multimedia and service information. The
application service module is mainly used to accept
users’ requests and download a variety of user terminals,
achieve the data exchange with external network and

Z. Y. QU ET AL. 746
offer users access interface. The management module is
responsible for the running of the whole system and
record the relevant information. In addition [5], server
system also includes a Web-based management system,
where administrators can manage the system via any
terminals after certifications in any location.
2.2. Network System
Network system is responsible for the real-time trans-
mission of a stream of video information, and it is a very
critical part to affect the performance of continuous
media web services. Including some network transmis-
sion equipments, you can use the mode of LAN or WAN
[6]. Also include the QoS of the network and some
application layer protocols. If only reasonably choose the
available network protocols and make the network
bandwidth and latency time to maintain a certain level,
the video data can smoothly playback on the client node.
2.3. Client System
Client system mainly includes some user terminals,
achieved by personal computers and special set-top
boxes. High performance personal computer can be
achieved by loading software [7]. Lower performance
personal computers can be achieved by Decompression
Card to complete the decoding. We can watch TV by
using a special set-top box.
This system is based on the C/S mode [8], and the
server connects with each user by the way of unicast.
The P2P VOD technology is that the media server sends
only a few media flow to several users connected firstly.
Users connected later get data from the previous users
but not from the server directly. In the P2P VOD system,
the function of the server is no longer a traditional server
but a peer with better service abilities. It is just achieved
to guide the clients to download, maintain the informa-
tion of the users and the video.
3. Design and Implementation of the P2P
VOD System
3.1. Structure Design and Implementation
This system consists of two parts, server and client. The
server is not in the traditional sense, can be understood as
a super node in the P2P network, and is mainly responsible
for maintaining the users’ state, updating the resource list,
maintaining the hot video resource, piece selection and
guiding the client to download resource. The client is not
in the traditional sense either, and it is the peer in the P2P
network, and is responsible for uploading and down-
loading resource, maintaining the media buffer, and
searching and classifying some information. Figure 1
shows the structure of this system.
3.2. Client Modules
The client in the P2P network has dual roles, is both the
video provider and the video receiver. However, the
function of cache management should be considered
when we designed, and ensure to upload the existing
resource and download and play the needed resource.
The following is the proceeding and handling methods
for each module, and include buffer management module,
P2P network module and video playback module. The
relationship among these modules is complementary as
Figure 2. The P2P network module is achieved to the
message communication and data transmission between
server and client, or among the clients. The buffer manage-
ment module receives the data from P2P network module
and manages the data effectively.
3.3. Server Modules
The server can be divided into two parts, Index Server
(IS) and Entry Server (ES). The IS part consists of four
main function modules, including User Information
Maintain module, Resource List Maintain module, Video
and User Synchronize module and the Expired Resource
Deletion module. The ES part also consists of four main
function modules, including Hot Resource Maintain
module, Resource Transmission module, Buffer Man-
agement module and Piece Selection module. Figure
3 shows the processing modules between the two servers.
3.4. Piece Selection Modules
1) The function of piece selection module
The main function of piece selection module is to re-
ceive the ID information of requests peers, and calculate
Figure 1. The structure of the P2P VOD system.

Z. Y. QU ET AL. 747
Figure 2. The relationship among three modules.
Figure 3. The processing between the two servers.
the piece ID and its download address based on the
RF-IPS algorithm for this peer. In order to minimize the
users’ processing, these functions are both implemented
on the server. In this module, we adopt the RF-IPS algo-
rithm to choose the server peers. Figure 4 show the main
function of this module
There are a variety of peers with different performances
distributed in the P2P network. When many Peers owned
the video resource users needed at the same time, how to
choose the server peers becomes one of the functions of
this module. Specific methods are as follows:
a) Scan table Res_ID_Peers and table Res_ID_Pieces,
and get the list of user information owned the piece. Table
Res_ID_Peers is used to save the information of the users
owned the relevant resource and table Res_ID_Pieces is
used to save the information of the resource.
b) According to the weighting function, get the first
numbers of users owned the maximum weight.
The weighting function is as follows:
1234
fabcdkakbkckd
××××
（，，，）＝ ＋＋ －
In this function, a is relevant to user’s IP, b is relevant
to the user’s level, c is relevant to user whether to be
mobile, d is relevant to the user’s maximum weight, and
k1, k2, k3, k4 are weights.
c) Return the piece number and the list of download
address to the client.
Figure 4. The main function of this module.
2) The RF-IPS algorithm
In this algorithm, we use buffer to record the states of
every piece of a peer and partition it into three parts. We
call each part an interval. According to the degree of
urgently need for the pieces, put the pieces into intervals
accordingly, and the pieces in different intervals are
downloaded by using the sequential downloading strategy,
RF downloading strategy, and random downloading
strategy separately [9].
Figure 5 shows the partitioned buffer, where p and g
are two pointers which respectively point to the current
playback position and the position of data obtained. The
pieces have already downloaded are in t0 and those have
downloaded but not to be played are in t1. The pieces
need to be downloaded later are in t2, which will be
partitioned into three parts, —interval t3, interval t4, and
interval t5.
The current data in t3 will be played immediately, so it
is more urgently needed than the data in other intervals.
We adopt sequential downloading strategy and set higher
selection priority to the pieces in this interval at a time.
The pieces in t4 are not so urgently needed than those
in t3, but more urgently needed than those in t5. In order
to ensure the harmonious distribution of data in the P2P
network we adopt RF strategy in t4.
Interval t5 is the farthest away from the playback posi-
tion, so in this interval we adopt random selection
mechanism.
Figure 6 shows the processing procedure of the RF-
IPS algorithm.
4. Experiments
The experiments we describe below were performed on a

Z. Y. QU ET AL. 748
Figure 5. The buffer partitions in RF-IPS algorithm.
Figure 6. The processing of the RF-IPS algorithm.
50 peers of Inter(R) Pentium(R) D CPU 2.80GHz, 1GB
Memory, running Red Hat Linux 3.2.3-47 with kernel
2.4.21-27 using network bandwidth of 100Mb/s in the
lab of our university. One peer executed the index server
to guide client-side to download, whereas other peers
executed multiple instances of clients. The format of a
movie is “wmv”, the code rate is 756 Kb/s, the length is
120 minutes, and the piece size is 256 K.
In order to ensure the fair results for every algorithm,
we designed five systems to represent five algorithms
and tested them respectively at the same conditions. We
present performance results of our experiments in these
parts: the initial delay time and the delay time after 4
times fast-forward operations, including Played at 10 s,
fast forward to 120 s, Played at 10 min, fast forward to
20 min, Played at 30 min, fast forward to 70 min and
Played at 71 min, fast forward to 119 min. Table 1 pre-
sents all results of our experiments.
From Table 1, we obtain that the RF-IPS algorithm
and sequential downloading algorithm both have the
Table 1. Experiment results.
The delay time (s)
System
name Initial
0.17~2(
min) 10~20( min) 30~70 (min) 71~119 (min)
Sequential
Downloading
7 10 85 128 146
RF 10 8 48 108 120
Bittorrent 9 8 50 80 88
Data Block
scheduling 10 5 21 97 101
RF-IPS 7 3 4.5 6 7
shortest initial delay time. When played at 0.17 min,
fast-forward to 2 min, the delay time of five algorithms is
similar, only the RF-IPS algorithm has the shortest delay.
Yet, the delay time of the five algorithms have a great
difference when the time interval increased gradually,
the delay time of RF-IPS is steady, while the others
increase dramatically. So we come to the conclusion that
the performance of our proposed algorithm is optimal
and the algorithm can improve user experience.
5. Conclusions
It is a challenging job to provide VOD service on the
Internet. The rapid development of P2P technology
makes it become the powerful tool to build the
large-scale distributed system in the WAN. The P2P
VOD system becomes a hot topic in the recent distributed
system area as one of the most application of P2P tech-
nology. Although the applications of P2P at the aspect of
streaming have researched and implemented at some
degree, their performances and results are still not ideal
and mature. This paper examines the RF-IPS algorithm
in the P2P VOD system, and achieves the P2P VOD
system as a basis. Although this system solve the key
problem in the VOD transmission system, and achieve
the RF-IPS algorithm, there are many problem existed,
because of limited time. With the further improvement of
the network bandwidth and the enhancement of the
computer performance, we believe that more and better
VOD system will be broadly applied.
6. References
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[2] Media Stream Website. http://www.lmtw.com.
[3] X. Liao, H. Jin, Y. Liu, L. M. Ni and D. Deng, “Anysee:

Z. Y. QU ET AL. 749
Peer-to-Peer Live Streaming,” INFOCOM, 2006.
[4] B. Cohen “Bit Torrent Protocol Specification”. http://
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[5] PP Stream, http://www.ppstreaming.com.
[6] Y. Cai and J. Zhou, “An Overlay Subscription Network
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[7] PPlive, http://www.pptv.com.
[8] A. Habia and J. Chuang, “Incentive Mechanism for Peer-
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