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Multimedia Communications
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Multimedia Networks(Technical Issues)
MM applications and systems require new system mechanisms to
handle large volumes of time dependent data in real time (media
streams).
The most important mechanism is QoS management, which
includes resource negotiation, admission control, resource
reservation and resource management.
Negotiation and admission control ensure that resources are not
over allocated,
resource management ensures that admitted tasks receive the
resources they were allocated.
Excessive loss in video transmission affect the performance of
video quality.
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The necessary traffic management components to support QoS are:
· Admission control: The admission control component takes into account
resource reservation requests and the available capacity to determine whether to
accept a new request with its QoS requirements.
Admission control delivers a contract to the application guaranteeing:
For each computer: CPU time available at specific intervals, memory etc.
Before admission it must assess resource requirement and reserve them for the
application.
Flow specs provide some information for admission control.
There is a optimization problem: clients don't use all the resource that they
requested.
Flow specs may permit a range of qualities
Admission controller must negotiate with applications to produce an acceptable
result.
· Resource management: QoS can be provided using over-provisioning of a network,
which increases the cost incurred by the provider.
Efficient resource management is a cost-effective solution for the provider and it ensures
that applications will get the specified QoS during the course of its execution.
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· Scheduling of resources: The scheduling component provides QoS by allocating
resources depending on the service requirements.
This requires mapping the user-defined QoS requirement to resource allocations
for providing the service.
Fair scheduling allows all processes some portion of the resources based on
fairness.
eg. round robin scheduling (equal turns), fair queuing (keep queue lengths equal)
Not appropriate for real time MM because there are deadlines for the delivery of
data.
Real time scheduling: traditionally used in special OS for system control
application.
Eg avionics must ensure that tasks are completed by a scheduled time.
Real time MM requires real time scheduling with very frequent deadlines.
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• Scaling and filtering
• Scaling reduces flow rate at source.
• Temporal: skip frame or audio samples
• Spatial: reduce frame size or audio sample quality
• Filtering reduces flow at intermediate points.
• e.g: RSVP is QoS negotiation protocol that negotiates the
rate at each intermediate node, working from targets to the
source.
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· Congestion control: Congestion control is required to avoid
anything bad from happening inside a network domain.
The Internet is a packet switched network that unlike circuit switched
networks takes advantage of the statistical multiplexing giving
better bandwidth utilisation.
Lack of any access control mechanisms in the core Internet concept
allows injecting unlimited amount of data into the network.
As speed of links and router capabilities are limited, packets
buffering in the intermediate routers was introduced, so as to
queue incoming packets which cannot be handled instantly.
Furthermore, as buffers also have limited space, packets are
dropped when the router buffer is filled above some threshold.
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• Providing satisfactory service for multiple flows, requires the
network end-points to adapt their rates to existing network
conditions
Figure: illustrates possible congestion scenario
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Some applications may not follow the standard protocol description and try to steal
resources, thereby deteriorating the QoS of other applications. Mechanisms are
needed to recover from congestion and control flows accordingly.
· Policing/Shaping: Users might send traffic at a rate higher than the agreement.
Policing is necessary to monitor these situations, and shaping makes the traffic
smooth and reduces its variations over time.
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Challenges in Multimedia Networking
We analyze the challenges encountered in realizing scalable
multimedia networks with quality of service guarantees.
(i) seamless connection management between the network and
the multimedia devices,
(ii) multimedia abstractions with QOS guarantees, and
(iii) the integration of service, traffic control and network
management architectures.
The fundamental requirement on multimedia networks
supporting applications like interactive multimedia, teleconferencing, video on demand etc., is to guarantee quality of
service (QOS).
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Challenges in multimedia networking based on a reference model for
broadband networks and Multimedia Networks.
The IRM incorporates monitoring, control, communication,
and abstraction primitives that are organized into the Traffic
Control Architecture, the Management Architecture, the
Information Transport Architecture and the Telebase
Architecture, respectively.
The sub-division of the IRM into the Management and the
Traffic Control Architectures on the one hand, and the
Information Transport Architecture on the other, is based on
the principle of separation between communications and
controls.
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Multimedia Network Reference Model
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The Integrated Reference Model is organized into five planes
The Management Architecture resides in the network
management or N- plane, and covers the functional areas of
network management, namely,
configuration,
performance, fault,
accounting
and security management.
Manager and agents, its basic functional components, interact
with each other according to the client-server paradigm.
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The Traffic Control Architecture consists of the resource control,
The M-plane comprises the entities and mechanisms
responsible for resource control,
call scheduling,
call admission,
and call routing;
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C-plane those for connection management and control, and is
based on a signalling network.
The Information Transport Architecture is located in the user
transport or U-plane, and models the protocols and entities
for the transport of user information.
The U-plane is horizontally layered, following the ISO
Reference Model for Open System Interconnection.
Finally, the Telebase Architecture resides within the Data
Abstraction and Management or D-plane, and implements
the principles of data sharing for network monitoring and
control primitives.
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The extension of this model to the multimedia networking
architecture is simple.
The functionality of the planes is extended to include Customer
Premises Equipment (CPE),
i.e., multimedia devices. This simple extension of the IRM is mainly
possible due to the fact that multimedia systems and broadband
networks consist of producers, consumers and processors of
media.
The foundations for the operability of these devices in both,
multimedia systems and broadband networks, is the same; the
only difference appears to be in the overall goal that a group of
devices is set to achieve in the network or the multimedia
workstation.
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Therefore, the N-plane will include system management
functionality,
and the M-plane will include scheduling, buffer management,
routing (when applicable), admission control
and flow control.
The D-plane will contain objects modeling multimedia devices
C-plane binding functionality, and the U-plane transport of user
information within the CPE.
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Multimedia Hardware/Software
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Audio/Video Hardware: Traditional photographic and video
equipments have digital counterparts to facilitate the process of
graphics and mm creation:
Digital Video (DV): eliminates the method converting analogue
video to digital by capturing video digitally.

Analogue to Digital devices: convert analogue video signal to
digital video

Built-in Hardware: we can create audio file from audio CDs,
microphones and other external audio sources.
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Digital Video Software
Digital Software
•
The native video format for windows computers is
audio/video interleaved files. (AVI)
•
Once video is obtained, it may need editing via software.
•
Codecs are sued to compress movie files so that the are
small enough to deliver over the internet.
•
Also for reducing of data transfer rate.
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Multimedia software
•
MM software combines various elements of audio,
graphics, video tools.
•
Flash, quicktime, realmedia.
•
Realvideo, RealAudio.
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Communication architecture for MM systems
•
The TCP/IP five layer Reference Model is a widely
accepted model for designing network protocols.
To single out the multimedia characteristics, we logically
partition the five layer reference model into a four layer
multimedia design model .
Application layer,
the Multimedia Integration Control and Synchronization
(MICS) layer,
the Inter-Process Communication and Synchronization layer
(IPCS) and
the Network layer.
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Comparison of Stacks
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IPCS Layer
The IPCS layer constitutes the foundation of the multimedia
communication environment,
The layer provides a flexible set of communication and
synchronization primitives.
The general function of IPCS is to create a set of mechanisms that
allow location-independent exchange of multimedia information
between two processes,
and provide the adequate tools to express different types of
synchronization.
In other words, the IPCS layer primitives allow the MICS layer
to express communication and synchronization requirements that
enforce the characteristics of the supported real-time applications.
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MICS Layer
• The MICS layer is responsible for integrating different types
of related communication media, preserving the timing
relationships among the elements of the integrated media,
and providing the control operations required by the
supported applications.
• They use essentially the quality of services specified by the
user to precisely tailor the behavior of the communication
subsystem to the requirements of the user application.
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Application layer
• The Application layer of the proposed model provides the set
of user interaction functionalities required to handle different
types of user defined objects.
•
The interaction of the user with the system comes
usually in the form of queries to distributed
multimedia database, various editing commands and
animation operations.
• This layer is characterized by a coarse level of
synchronization which has direct implications
process scheduling and object manipulation.
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on
Network layer
The network layer protocols are required to provide
effective support for high quality video and audio
streams.
It also is required to handle interactive broadband
services and multitasking.
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INTERNET
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The Internet is an enormous global network of computers.
Often called a network of networks
it integrates thousands of dissimilar computer networks worldwide
through the use of technical standards that enable all types of
systems to interoperate
• Exchange electronic mail, or e-mail, with any other user at any
location participate in offline .
• discussions via e-mail with large groups of individuals interested in
particular topics, using ``mailing lists" and ``News Groups"
•Participate in online (i.e., real-time, or current) discussions with
large groups of individuals using the ``Internet Relay Chat" function
•Log on to remote computer sites worldwide using the Telnet
function
•Download files from remote sites and users and upload files to
remote sites and users. E0262 - Multimedia Communications
Connection to Internet
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How does the Internet work?
The first thing your browser has to do is to establish a network
connection to the machine where the document lives.
To do that, it first has to find the network location of the host
www.iisc.ernet.in (host is short for host machine or network host';
www.iisc.ernet.in is a typical hostname).
The corresponding location is actually a number called an IP address
To do this, your browser queries a program called a name server.
The name server may live on your machine, but it's more likely to
run on a service machine .
When you sign up with an ISP (Internet Service Provider), part of
your setup procedure will almost certainly involve telling your
Internet software the IP address of a name server on the ISP's
network.
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The name servers on different machines talk to each other,
exchanging and keeping up to date all the information needed
to resolve hostnames (map them to IP addresses).
Your nameserver may query three or four different sites across
the network in the process of resolving www.iisc.ernet.in, but
this usually happens very quickly (as in less than a second).
The nameserver will tell your browser that www.iisc.ernet.in's
IP address is 15.19.25.81(say); knowing this, your machine
will be able to exchange bits with www.iisc.ernet.in directly.
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The Domain Name System
The whole network of programs and databases that cooperates to
translate hostnames to IP addresses is called DNS (Domain Name
System).
When you see references to a DNS server, that means what we just
called a nameserver.
Internet hostnames are composed of parts separated by dots. A
domain is a collection of machines that share a common name
suffix.
Domains can live inside other domains. For example, the machine
www.iisc.ernet.in lives in the .iisc.ernet.in subsubdomain in the
.ernet.in subdomain of the .in domain.
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Each domain is defined by an authoritative name server that
knows the IP addresses of the other machines in the domain.
The authoritative (or primary') name server may have backups
in case it goes down; if you see references to a secondary
name server or (secondary DNS') it's talking about one of
those.
These secondaries typically refresh their information from their
primaries every few hours, so a change made to the
hostname-to-IP mapping on the primary will automatically be
propagated.
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How to get connected to Internet
Gateway Access
Gateway Access is also known as Level-One connection. It is the
access to the Internet from a network, which is not on the Internet.
The gateway allows the two
different types of networks to ``talk" to each other. But the users of
the Gateway Internet have limited access to the Internet. They
might not be able to use all the tools available on Internet. The local
Internet Service Provider (ISP) normally defines this limitation.
Good example of network with Level One connectivity within
India is that of VSNL (Videsh Sanchar Nigam Limited). All access
to Internet from India are through VSNL gateway.
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Dial-up Connection
Dial-up' connection is also known as Level Two connection. This provides
connection to Internet through a dial-up terminal connection. The
computer, which provides Internet access is known as ``Host'' and the
computer that receives the access, is ``Client'' or ``Terminal''. The client
computer uses modem to access a ``host" and acts as if it is a terminal
directly connected to that host. So this type of connection is also known as
``Remote Modem Access'' connection. And the host to which the client gets
connected is actually connected to the Internet by a full time connection.
In dial-up connection to Internet, Host carries all the command that are
typed on a client machine and forward them to Internet. It also receives the
data or information from the Internet on behalf of the ``Client'' and passes it
to them. The client computer acts as a ``dumb'' terminal connected to
remote host.
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This type of connection can further be divided into two
categories.
Shell Connection
In this type of Internet Connection, the user will get only textual
matter of a Web Page.
This connection does not support Graphics display. However the
user will be able to surf the Internet, do FTP, receive mail. Shell
Accounts were the only type of Internet access available for many
years before the Internet entered in to the world of graphics and
became more users friendly.
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TCP/IP Connection
Today's graphical World Wide Web browsers provide easier
access with multimedia sound and pictures.
The major difference between Shell and TCP/IP account is that,
Shell account can only display text and does not support
graphics display, whereas TCP/IP can display both.
Hence it is more popular Internet connection. Shell accounts
are slowly phasing out from the Internet scenario.
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To access any of these dial-up accounts you need the followings;
Computer
Modem
Telephone Connection
Shell or TCP/IP account from the ISP
Internet client software such as Internet browser.
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Multimedia Communications
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High-Density File Transfers
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Graphics File Transfers
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Audio File Transfers
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Video File Transfers
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Audio Communication
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Computer-Based Telephony
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Computer-Based Audio Conferencing
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Streaming Audio
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Video Communication
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Video Conferencing
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Streaming Video
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T
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and is based on a signalling network.
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Therefore, the N-plane will include system management
functionality, and the M-plane will include scheduling, buffer
management, routing (when applicable), admission control
and flow control.
The D-plane will contain objects modeling multimedia devices,
the C-plane binding functionality, and the U-plane transport of
user information within the CPE.
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