References Model and Specification - Module 10 MULTIMEDIA SYNCHRONIZATION Lesson 34 Notes

: References Model and Specification - Module 10 MULTIMEDIA SYNCHRONIZATION Lesson 34 Notes

 Page 1


 
 
 
 
 
 
 
Module  
10 
 MULTIMEDIA 
SYNCHRONIZATION 
Version 2 ECE IIT, Kharagpur 
 
Page 2


 
 
 
 
 
 
 
Module  
10 
 MULTIMEDIA 
SYNCHRONIZATION 
Version 2 ECE IIT, Kharagpur 
 
 
 
 
 
 
 
 
Lesson 
34 
References Model 
and Specification 
 
 
Version 2 ECE IIT, Kharagpur 
 
Page 3


 
 
 
 
 
 
 
Module  
10 
 MULTIMEDIA 
SYNCHRONIZATION 
Version 2 ECE IIT, Kharagpur 
 
 
 
 
 
 
 
 
Lesson 
34 
References Model 
and Specification 
 
 
Version 2 ECE IIT, Kharagpur 
 
Instructional objectives 
At the end of this lesson, the students should be able to :  
 
1. State why a reference model is needed.  
2. Give some examples of multi-layer reference model 
3. Define the roles of media layer, stream layer, object layer and 
specification layer.  
4. State why synchronization is more complex in distributed environment  
5. State the mechanisms for achieving distributed environment 
synchronization  
34.0 Introduction  
In lesson-33, we had studied the basic synchronization requirements for 
multimedia communication. Although we explained the basic issues, run-time 
mechanisms to support execution of synchronization can only be explained with 
respect to a reference model. This will be our focus for this lesson. In addition, 
we shall also cover the synchronization aspects in distributed environment. We 
shall also study which specifications are needed to specify synchronization.  
 
34.1 Multi layer reference model  
The reference model that is used to execute synchronization is organized in 
multiple layers. At the highest layer of abstraction, we have the application layer 
and at the lowest layer, we have the physical, or the media layer. The reference 
model is used to classify the multiple synchronization systems and the existing 
classification methods are :  
 
• Little and Ghafoor [1] identified a physical level, system level and a human 
level for synchronization but gave no description of synchronization. 
 
• Gibbs et al [2] map a synchronized multimedia object to an uninterrupted 
byte stream. 
 
• Ehley et al [3] classify intermedia synchronization techniques that are 
used to control jitter between media streams according to the type and 
location of the synchronization control.  
 
Version 2 ECE IIT, Kharagpur 
 
Page 4


 
 
 
 
 
 
 
Module  
10 
 MULTIMEDIA 
SYNCHRONIZATION 
Version 2 ECE IIT, Kharagpur 
 
 
 
 
 
 
 
 
Lesson 
34 
References Model 
and Specification 
 
 
Version 2 ECE IIT, Kharagpur 
 
Instructional objectives 
At the end of this lesson, the students should be able to :  
 
1. State why a reference model is needed.  
2. Give some examples of multi-layer reference model 
3. Define the roles of media layer, stream layer, object layer and 
specification layer.  
4. State why synchronization is more complex in distributed environment  
5. State the mechanisms for achieving distributed environment 
synchronization  
34.0 Introduction  
In lesson-33, we had studied the basic synchronization requirements for 
multimedia communication. Although we explained the basic issues, run-time 
mechanisms to support execution of synchronization can only be explained with 
respect to a reference model. This will be our focus for this lesson. In addition, 
we shall also cover the synchronization aspects in distributed environment. We 
shall also study which specifications are needed to specify synchronization.  
 
34.1 Multi layer reference model  
The reference model that is used to execute synchronization is organized in 
multiple layers. At the highest layer of abstraction, we have the application layer 
and at the lowest layer, we have the physical, or the media layer. The reference 
model is used to classify the multiple synchronization systems and the existing 
classification methods are :  
 
• Little and Ghafoor [1] identified a physical level, system level and a human 
level for synchronization but gave no description of synchronization. 
 
• Gibbs et al [2] map a synchronized multimedia object to an uninterrupted 
byte stream. 
 
• Ehley et al [3] classify intermedia synchronization techniques that are 
used to control jitter between media streams according to the type and 
location of the synchronization control.  
 
Version 2 ECE IIT, Kharagpur 
 
• Meyer et al [4] proposed a three layer classification scheme. It consists of 
a media layer for intra-stream synchronization, a stream layer for inter-
stream synchronization and an object layer for the presentation. 
 
• Blackowski-Steinmetz [5] proposed a four layer reference model to be 
used for the synchronization classification. This will be presented in the 
next section.  
 
 
34.2 Blackowski –Steinmetz four layer reference model  
 
The four layer reference model is illustrated in fig 34.1  
 
Specification Layer 
Object Layer
Stream Layer
Multimedia application  
 
  Level of 
abstraction  
      High 
 
 
 
 
 
 
 
      Low Media Layer 
 
 
Fig 34.1 Blackowski –Steinmetz four layer reference model. 
 
As shown, the lower layers may be called by the upper layers or by the 
multimedia application itself. The roles of these individual layers are discussed as 
follows.  
 
34.2.1 Media Layer:  
At the media layer, an application operates on a single continuous media stream, 
which is treated as a sequence of LDUs. A continuous media stream can be set 
up by the application executing a process for each stream. Using the media 
layer, the application itself is responsible for intra-media synchronization.  
 
34.2.2 Stream Layer :  
The stream layer operates on continuous media streams, as well as on groups of 
media streams. In a group, all streams are presented in parallel by using 
mechanisms for inter-stream synchronization.  
 
The streams are executed in a real time environment (RTE), where all 
processing is constrained by well-defined time specifications. The applications 
requiring stream layer services are executed in non real time environment 
(NRTE). Typical operations invoked by an application to manage stream are:  
Version 2 ECE IIT, Kharagpur 
 
Page 5


 
 
 
 
 
 
 
Module  
10 
 MULTIMEDIA 
SYNCHRONIZATION 
Version 2 ECE IIT, Kharagpur 
 
 
 
 
 
 
 
 
Lesson 
34 
References Model 
and Specification 
 
 
Version 2 ECE IIT, Kharagpur 
 
Instructional objectives 
At the end of this lesson, the students should be able to :  
 
1. State why a reference model is needed.  
2. Give some examples of multi-layer reference model 
3. Define the roles of media layer, stream layer, object layer and 
specification layer.  
4. State why synchronization is more complex in distributed environment  
5. State the mechanisms for achieving distributed environment 
synchronization  
34.0 Introduction  
In lesson-33, we had studied the basic synchronization requirements for 
multimedia communication. Although we explained the basic issues, run-time 
mechanisms to support execution of synchronization can only be explained with 
respect to a reference model. This will be our focus for this lesson. In addition, 
we shall also cover the synchronization aspects in distributed environment. We 
shall also study which specifications are needed to specify synchronization.  
 
34.1 Multi layer reference model  
The reference model that is used to execute synchronization is organized in 
multiple layers. At the highest layer of abstraction, we have the application layer 
and at the lowest layer, we have the physical, or the media layer. The reference 
model is used to classify the multiple synchronization systems and the existing 
classification methods are :  
 
• Little and Ghafoor [1] identified a physical level, system level and a human 
level for synchronization but gave no description of synchronization. 
 
• Gibbs et al [2] map a synchronized multimedia object to an uninterrupted 
byte stream. 
 
• Ehley et al [3] classify intermedia synchronization techniques that are 
used to control jitter between media streams according to the type and 
location of the synchronization control.  
 
Version 2 ECE IIT, Kharagpur 
 
• Meyer et al [4] proposed a three layer classification scheme. It consists of 
a media layer for intra-stream synchronization, a stream layer for inter-
stream synchronization and an object layer for the presentation. 
 
• Blackowski-Steinmetz [5] proposed a four layer reference model to be 
used for the synchronization classification. This will be presented in the 
next section.  
 
 
34.2 Blackowski –Steinmetz four layer reference model  
 
The four layer reference model is illustrated in fig 34.1  
 
Specification Layer 
Object Layer
Stream Layer
Multimedia application  
 
  Level of 
abstraction  
      High 
 
 
 
 
 
 
 
      Low Media Layer 
 
 
Fig 34.1 Blackowski –Steinmetz four layer reference model. 
 
As shown, the lower layers may be called by the upper layers or by the 
multimedia application itself. The roles of these individual layers are discussed as 
follows.  
 
34.2.1 Media Layer:  
At the media layer, an application operates on a single continuous media stream, 
which is treated as a sequence of LDUs. A continuous media stream can be set 
up by the application executing a process for each stream. Using the media 
layer, the application itself is responsible for intra-media synchronization.  
 
34.2.2 Stream Layer :  
The stream layer operates on continuous media streams, as well as on groups of 
media streams. In a group, all streams are presented in parallel by using 
mechanisms for inter-stream synchronization.  
 
The streams are executed in a real time environment (RTE), where all 
processing is constrained by well-defined time specifications. The applications 
requiring stream layer services are executed in non real time environment 
(NRTE). Typical operations invoked by an application to manage stream are:  
Version 2 ECE IIT, Kharagpur 
 
 
• Start stream  
• Stop stream 
• Create group (list of streams) 
• Start group  
• Stop group  
 
The interaction with time-independent media objects and user interactions is 
performed by attachment of events to the continuous media streams.  
 
34.2.3 Object Layer:  
The object layer has one level of abstraction higher than the stream layer. To the 
application, it offers a complete, synchronized media. The object layer operates 
on all types of media and hides the differences between time independent and 
time-dependent media.  
 
This layer takes a synchronization specification as input and is responsible for 
the correct schedule of the overall presentation. The object layer does not handle 
the inter-stream and intra-stream synchronization. For this purposes, it uses the 
services of the stream layer. 
 
34.2.4 Specification layer : 
This layer offers the highest level of abstraction in the four-layer reference model. 
This layer contains applications and tools that allow one to create 
synchronization specification. Examples of such tools are synchronization 
editors, multimedia document editors and authoring systems.  
 
The specifications layer is also responsible for mapping QoS requirements of the 
user level to the qualities actually offered at the object layer.  
 
Synchronization specification methods can be classified into the following main 
categories:  
 
• Interval based specification – temporal relationships between the time 
intervals of the presentation of the media objects.  
 
• Axes-based specification – relates presentation events to axes that are 
shared by the objects of presentation. 
 
• Control flow based specification – at given synchronization points, the 
flow of the presentation is synchronized.  
 
Version 2 ECE IIT, Kharagpur 
 
Read More
Use Code STAYHOME200 and get INR 200 additional OFF
Use Coupon Code

Download free EduRev App

Track your progress, build streaks, highlight & save important lessons and more!