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SET TOP BOX
• What is set-top box ?
An interactive device which integrates the video
and audio decoding capabilities of television with
a multimedia application execution environment.
It provides a user friendly interface offering
personalized multimedia services and regular
cable TV service.
• How's STB different from multimedia computer ?
Multimedia computer
STB
Expensive and versatile
device
Inexpensive limited
functionality device
primarily targeted at
entertainment
Might be equipped with
floppy or a hard disk drive
Not likely to be so equipped
Can execute a wide
variety of application
programs
Limited scope of
applications that can be
executed
Digital video networks(DVN)
• Digital television advantage.
• Digital video delivery requirements
– High bandwidth.
– Fibre cable, satellite, broadcast and computer
networks can be used.
• Traditional cable networks analogue systems and their
drawbacks.
• Satellite and terrestrial networks.
• Internet suitability for interactive network and drawback.
DVN need to deliver a high bandwidth stream into
consumer homes and a low bandwidth
communication layer for interaction between the
STB user and the service provider.
• Cable operators approach for DVN.
– Need to extend unidirectional coaxial networking with
a communication path from subscriber home to cable
service gateways that can control the content being
sent to subscriber.
– Advantage of video compression technology.
– Constraints with cable networks.
• Telephone companies approach.
– Advantage with telephone companies.
• Already have set up for P2P and technology for
control and service gateways to manage wide area
switched star networks.
– Drawback.
• Low bandwidth between head end equipment and
consumer’s home.
•
Video dial tone network.
– Designed with fibre optic backbone with
coaxial cable or fibre optic cable to the
home.
– Figure.
– Has two types of networks
1. Unidirectional broadband network to distribute
video and audio as MPEG-2 transport packets
over ATM.
2. Bidirectional TCP/IP low speed signalling
network.
Set Top Box Hardware Architecture.
• Requirements based on functionality.
– Should have MPEG-2 sub-system to decode MPEG-2
video and audio.
– Should enable user to download custom applications
and execute them on the STB which requires a
general purpose microprocessor in the STB with an
architecture that supports control of the different
devices.
• Various hardware components.
– Figure.
STB software architecture
For personalized interactive services, a set top box
should be addressable in the video dial-tone
network, thus providing P2P communication
between a video and information provider and a
user. It should also have the ability to download
client applications and execute them locally.
The control software on the set top box ties
together all the hardware components into a
functioning unit.
• STB software has two parts.
– System software which provides the DAVID application
programming interface.
– Application software that provides cable TV functionality or some
other personalized multimedia service.
• DAVID system software includes.
– Operating system(os-9) kernel.
– Device drivers.
– File manager.
• Operating system(os-9) kernel is responsible for the
following:
• Scheduling different tasks for the microprocessor.
• Managing inter-process communication between different tasks and
processes in the STB.
• Memory management for the multi-tasking operating system.
• Maintaining the real time clock for the system.
•Device drivers
The various hardware components of STB have
programmable registers that can be used to control the
behaviour of the components. Each one of these devices
has a device driver task associated with it that allows the
main microprocessor to manage the device. The device
drivers also perform interrupt servicing for the components
and hide the details about device addresses and actual
register values.
•File manager
– File manager available for each device driver and provides a ‘file
like’ interface for the device.
– ‘file like’ interface provides a uniform layer of abstraction and is
generic to all the capabilities of STB.
– RTNFM, SPF, MPFM, AUXMAN.
• Application Software.
– interoperability of softwares.
– Navigator.
– Downloaded applications.
– Operating system upgrade.
– Other resident applications: config, display
Conclusion
For the hardware there will be strong trend towards very
flexible decoders in the form of signal processors and fast
CPU’s possibly even combined with even combined in one
large digital processing CPU. The arrangements for
sending information from terminal(STB) into the network
can be improved both in latency and in throughput. The
graphic subsystem is likely to grow towards 3D
applications.
STB software hides the machine and network specific
features of a set top box under a layer of abstraction and
provides a user friendly interface to access cable television
and video information services. The software components
are likely to increase with more integration and more
programmable components. This will increase the flexibility
of STB.