2. Research On Streaming Media Online Charging System

A. A brief introduction to streaming media
Streaming media refers to the continuous audio/video
stream being transmitted and broadcasted on data network
according to time sequence. With the progress of 3G networks
and the improvement of network condition, the streaming
media services develop rapidly and attract more and more
attention. There has been a streaming media subject- "highperformance
information broadband network 3TNet" subject
that belongs to China’s "863 project". Beginning with typical
broadband streaming media services such as Internet TV, VoD,
High Definition TV, Time-Shifted TV and so on, the subject
established a high-performance, WAN (MAN) broadband
demonstration network 3TNet which is applicable to real-time
transmission of Internet TV and other media streams, and it
was deployed in the Yangtze-River-Delta region. It is so far the
largest integrated application platform for IPv6 interactive
multimedia broadband network.
B. Architecture of Streaming Media Online Charging System
The function of Online Charging System (OCS) is to
response to charging requests in real time, finish rating
according to billing policies, give feedbacks after deducting
corresponding service fees and generate billing details.
Furthermore, OCS ought to monitor customers’ account
balance and control service consumption in real time. In the
specification of R5 & R6, 3GPP proposed OCS and defined the
reference framework of OCS for IMS network [6]. The OCS
proposed by 3GPP is aimed at charging requirements of
telecom services and it is complex to support CAMEL
protocol. However, streaming media services have their own
features as multimedia, personalized interaction,
humanization, and their supporting networks are almost IPbased
broadband networks. In order to make the SMOCS
support streaming media services more effective and the
system be more scalable and more compatible, we design a
Common Interface Function (CIF) module to unify the
interaction with external devices, add the Session Management
module to monitor charging request session information and
adopt DiameterCC protocol to interact with streaming media
service control servers. On the principle of the separation
between billing control and billing applications, according to
function requirements of OCS in streaming media applications,
taking advantage of 3GPP’s related research achievements
[14], we designed architecture of Streaming Media Online
Charging System and it consists of Common Interface module,
Charging module, Account Balance Management module,
Charging gateway module, Rating module and Session
Management module. The detailed architecture of SMOCS is
shown in Figure 1.
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Figure 1. Framework of the Streaming Media Online Charging System
Access Convergence Router (ACR) and Media Server (MS)
are service control network elements in streaming media
application systems. They interact with SMOCS by
DiameterCC Protocol and realize the online charging function
in coordination. ACR in the backbone of network controls the
multicast of Internet TV, High Definition TV, Broadband
access, etc. MS around the edge of Metropolitan Area Network
(MAN) provides streaming service of VoD, Time-Shifted TV,
Time-shift VoD and other stream services for terminals.
SMOCS specifies a CIF module to unify the interaction with
external network devices and enhance the system’s
compatibility. CIF module interacts with external network
devices through DiameterCC Protocol and IPDR [10] file for
real-time billing information and billing details respectively;
Charging function module is one of control modules and it
supports charging function based on session, beater and events;
Rating function module is the charge calculation module and it
supports charging calculation for a variety of services through
configuration of billing rules; Main function of Account
Balance Management Function (ABMF) is monitoring
customers’ account balance, including reserving/releasing
account balance, deducting service fees, inquiring real-time
balance, etc. When a customer’ balance is below a dynamically
calculated threshold based on the customer’s level and history
bill records, the module reminds the customer to recharge
through short messages or E-mails; Main function of Session
Management Function (SMF) is to establish/close sessions,
monitor status of sessions and maintain session information;
According to pre-determined strategy in SMOCS, charging
Gateway produces IPDR files for further dealings in
accounting system [8].
C. Research on the AAA protocol
The Remote Authentication Dial In User Service
(RADIUS) protocol is one of the most popular AAA protocols
and it is widely used for its simpleness, easy management and
nice expansibility. However, RADIUS protocol can’t be
adapted to current networks for its own defects, such as
transmission by the unreliable UDP protocol, simple package
drop mechanism, without rules about retransmission and the
concentrated billing service mechanism. So the Diameter
protocol [10] is proposed. The Diameter protocol provides a
safe, reliable and scalable framework for various authentication
authorization and accounting services, and it can be applied to
practical applications conveniently. Compared to RADIUS
protocol, Diameter protocol has a nice mechanism to handle
transmission failure, the ability to rapidly detect the receiving
peer, and a better package drop mechanism. In addition, it
supports end-to-end security and makes authenticates and
authorizes for each session to ensure security. Based on
Diameter, DiameterCC protocol defines a billing mechanism
for prepaid services, adopts credit control mechanism to realize
session based charging, bearer based charging and event based
charging. And it satisfies billing requirements for prepaid
services. Therefore, SMOCS designed in this paper interacts
with external network devices by this protocol to realize online
charging function.