ISSUES IN MULTIMEDIA ISSUES IN MULTIMEDIA SYSTEM DESIGNSYSTEM DESIGN

Jayabalan SathiasulanJayabalan Sathiasulan WET020051WET020051

Kumaran KrishnanKumaran KrishnanWET020054WET020054

Nik Nor Aini Nik MahmoodNik Nor Aini Nik MahmoodWET020107WET020107

Rajendran VignaswaranRajendran Vignaswaran WET020145WET020145

Santhrakala MathuvaySanthrakala Mathuvay WET020154WET020154

==> Presented by:

Table of ContentsTable of Contents1.1. IntroductionIntroduction

Presented by: Rajendran VignaswaranPresented by: Rajendran Vignaswaran

2.2. Congestion ControlCongestion ControlPresented by: Jayabalan SathiasulanPresented by: Jayabalan Sathiasulan

3.3. Admission ControlAdmission Control4.4. Traffic PolicingTraffic Policing

Presented by: Kumaran KrishnanPresented by: Kumaran Krishnan

5.5. Traffic Analysis and PredictionTraffic Analysis and PredictionPresented by: Nik Nor Aini Nik MahmoodPresented by: Nik Nor Aini Nik Mahmood

6.6. Buffer ManagementBuffer Management7.7. SchedulingScheduling

Presented by: Santhrakala MathuvayPresented by: Santhrakala Mathuvay

IntroductionIntroduction

►Multimedia system design refers to the Multimedia system design refers to the design of the network subsystem.design of the network subsystem.

►Therefore, all issues that are covered Therefore, all issues that are covered will relate to the design for networks will relate to the design for networks that are sensitive to the multimedia that are sensitive to the multimedia traffic.traffic.

► In general, communication can be classified as follows:-In general, communication can be classified as follows:-

1.1. Point-to-PointPoint-to-Point

2.2. Point-to-MultipointPoint-to-Multipoint

3.3. Multipoint-to-MultipointMultipoint-to-Multipoint► These classifications are based on the fact that there are These classifications are based on the fact that there are

one or multiple sources and/or destinations.one or multiple sources and/or destinations.► The functional requirements for any of these The functional requirements for any of these

communications are:-communications are:-

1.1. Identify the destinationsIdentify the destinations

2.2. Find the route to the destinationsFind the route to the destinations

3.3. Transfer dataTransfer data

►Connection establishmentConnection establishment refers to refers to the process of finding a route to the the process of finding a route to the destination(s). destination(s).

►A connection has to be established A connection has to be established prior to the start of data prior to the start of data transmission.transmission.

► It is referred to as It is referred to as unicastunicast if it is if it is Point-to-Point and Point-to-Point and multicastmulticast if it is if it is Point-to-Multipoint.Point-to-Multipoint.

► In multimedia applications, during route In multimedia applications, during route finding, the QoS (Quality of Service) is finding, the QoS (Quality of Service) is considered while selecting the network considered while selecting the network service provider(s) from the source to the service provider(s) from the source to the destination.destination.

►By selecting a route and reserving By selecting a route and reserving resources along the route, a multimedia resources along the route, a multimedia call is said to be admitted into the network.call is said to be admitted into the network.

►This is referred to as This is referred to as call admission call admission controlcontrol..

► In a network, many applications will be trying In a network, many applications will be trying to establish connections at the same time.to establish connections at the same time.

► All the applications that have calls admitted All the applications that have calls admitted will essentially start sharing the resources.will essentially start sharing the resources.

► When units of information start flowing When units of information start flowing through the network, it may so happen that through the network, it may so happen that at one or more intermediate switches at one or more intermediate switches queuing delays will start increasing.queuing delays will start increasing.

► Such an occurrence is an indication of a Such an occurrence is an indication of a temporary overload condition referred to as temporary overload condition referred to as congestioncongestion..

► It is essential to monitor and control the It is essential to monitor and control the connection after call admission, that is, connection after call admission, that is, during the data transfer.during the data transfer.

► Traffic characteristics from the source can Traffic characteristics from the source can be continuously monitored, and any be continuously monitored, and any violation can be regulated by regulating or violation can be regulated by regulating or shaping the traffic at the source. shaping the traffic at the source.

► This process of forcing the traffic to abide by This process of forcing the traffic to abide by the demanded QoS values is known as the demanded QoS values is known as traffic policingtraffic policing..

► In many designs, it is combined with In many designs, it is combined with traffic traffic shapingshaping, which is a preventive measure. , which is a preventive measure.

► Well-behaved streams do not mean that all the QoS Well-behaved streams do not mean that all the QoS parameters will be satisfied through the network.parameters will be satisfied through the network.

► This is because the end-to-end behavior This is because the end-to-end behavior experienced by an application largely depends on experienced by an application largely depends on the delays incurred at the intermediate switches.the delays incurred at the intermediate switches.

► In order to guarantee the end-to-end QoS In order to guarantee the end-to-end QoS parameter, it is essential that the media streams parameter, it is essential that the media streams are are scheduledscheduled using a certain service discipline at using a certain service discipline at all the intermediate switches during the lifetime of all the intermediate switches during the lifetime of the connection.the connection.

► The issues and their interactions are shown in the The issues and their interactions are shown in the figure below.figure below.

Figure1: Interaction Among Different Network Figure1: Interaction Among Different Network FunctionsFunctions

Congestion ControlCongestion Control

► The unpredictable statistical of traffic The unpredictable statistical of traffic flows is the main cause for flows is the main cause for congestion in high-speed networks.congestion in high-speed networks.

► There are 2 types of congestion There are 2 types of congestion control mechanisms which are control mechanisms which are attempted in design. They are:-attempted in design. They are:-

1.1. Reactive congestion controlReactive congestion control

2.2. Preventive congestion controlPreventive congestion control

►Reactive congestion control refers to Reactive congestion control refers to the regulation of traffic flow at the the regulation of traffic flow at the access points, when congestion occurs access points, when congestion occurs in the network. in the network.

►For achieving this, a feedback For achieving this, a feedback mechanism with adequate lead time to mechanism with adequate lead time to react is required.react is required.

►Hence, this method may not be Hence, this method may not be considered desirable for broadband considered desirable for broadband multimedia applications. multimedia applications.

► The preventive congestion control The preventive congestion control mechanism tries to prevent the network mechanism tries to prevent the network from reaching an unacceptable level of from reaching an unacceptable level of congestion.congestion.

► This approach is best suited for connection-This approach is best suited for connection-oriented networks such as ATM networks.oriented networks such as ATM networks.

► This is because the decision to admit a new This is because the decision to admit a new connection can be made based on the connection can be made based on the knowledge of the state of the proposed knowledge of the state of the proposed route of the new connection.route of the new connection.

► Congestion control for high-speed networks can be viewed Congestion control for high-speed networks can be viewed as a collection of 3 independent functions. They are:-as a collection of 3 independent functions. They are:-

1.1. Admission control and resource reservationAdmission control and resource reservation

2.2. Traffic enforcement (policing and shaping)Traffic enforcement (policing and shaping)

3.3. SchedulingScheduling► Admission control determines whether to accept or reject a Admission control determines whether to accept or reject a

new connection at the time of call setup.new connection at the time of call setup.► This decision is based on the traffic characterictics of the This decision is based on the traffic characterictics of the

new connection and the current network load.new connection and the current network load.► A new connection is admitted if and only if the required A new connection is admitted if and only if the required

resources are available and it is ensured that such an resources are available and it is ensured that such an addition will not cause overuse of network resources.addition will not cause overuse of network resources.

Admission ControlAdmission Control

► There are several admission control policies.There are several admission control policies.► Based on the performance metrics, they can Based on the performance metrics, they can

be classified as algorithms that use link-level be classified as algorithms that use link-level performance measures and algorithms that performance measures and algorithms that use connection-level performance measures. use connection-level performance measures.

► The link-level performance measures are The link-level performance measures are based on the statistical behavior of cells on a based on the statistical behavior of cells on a link.link.

► Since cells on a link over high-speed Since cells on a link over high-speed networks are statistically multiplexed from networks are statistically multiplexed from many connections, it’s difficult to distinguish many connections, it’s difficult to distinguish from which sources cells are generated.from which sources cells are generated.

► Even though global performance objectives can Even though global performance objectives can be achieved using link-level performance be achieved using link-level performance measures, individual connections may measures, individual connections may experience a higher loss rate and queuing experience a higher loss rate and queuing delay than desired.delay than desired.

► As satisfactory link-level performance does not As satisfactory link-level performance does not guarantee satisfactory user-level performance, guarantee satisfactory user-level performance, it may not be possible to satisfy user-level QoS it may not be possible to satisfy user-level QoS using link-level performance measures.using link-level performance measures.

► Connection-level performance measures give Connection-level performance measures give the performance for individual connections and the performance for individual connections and are better suited to manage QoS.are better suited to manage QoS.

Traffic PolicingTraffic Policing

► Multimedia information covers traffic Multimedia information covers traffic characteristics ranging from low bit-rates to characteristics ranging from low bit-rates to broadband bit-rates.broadband bit-rates.

► These heterogeneous traffic sources also differ These heterogeneous traffic sources also differ widely in the degree of burstiness, correlations widely in the degree of burstiness, correlations and expected QoS from the network.and expected QoS from the network.

► Access control algorithms is required to Access control algorithms is required to enforce and maintain a specific QoS for each enforce and maintain a specific QoS for each traffic.traffic.

► Access control algorithms enforce specific QoS Access control algorithms enforce specific QoS by either by either bit or cellbit or cell dropping mechanisms or dropping mechanisms or feedback preventive controlfeedback preventive control mechanisms. mechanisms.

► In the bit dropping method, the cells or In the bit dropping method, the cells or packets that violate the negotiated packets that violate the negotiated traffic call admission parameters are traffic call admission parameters are dropped. dropped.

►The feedback preventive control uses a The feedback preventive control uses a control signal that is a function of the control signal that is a function of the buffer occupancy level to control the buffer occupancy level to control the source coder sampling rate.source coder sampling rate.

►Frequent decisions to drop increase the Frequent decisions to drop increase the cell or packet loss probability.cell or packet loss probability.

► In networks where packets or cells are In networks where packets or cells are transferred without flow control between the transferred without flow control between the user and network, a need to control the user and network, a need to control the individual cell or packet streams arises individual cell or packet streams arises automatically.automatically.

► The control must be enforced during the The control must be enforced during the entire duration of the call in order to ensure entire duration of the call in order to ensure an acceptable QoS for all outgoing calls that an acceptable QoS for all outgoing calls that are sharing the network resources.are sharing the network resources.

► Such a control is exercised by introducing Such a control is exercised by introducing policingpolicing and (or) and (or) shapingshaping..

Traffic Analysis and Traffic Analysis and PredictionPrediction

► Ideally, performance evaluation should be Ideally, performance evaluation should be based on measurements taken directly from an based on measurements taken directly from an actual, fully operating multimedia network. actual, fully operating multimedia network.

► Since such a network does not exist yet, two Since such a network does not exist yet, two other approaches to performance evaluation other approaches to performance evaluation have been used by network analysts. have been used by network analysts.

► The first and most common approach is based The first and most common approach is based on a presumed traffic model that encapsulates on a presumed traffic model that encapsulates some of the stochastic characteristics of the some of the stochastic characteristics of the actual input stream(s).actual input stream(s).

► Such a model can be used in subsequent Such a model can be used in subsequent queuing analysis or simulations of buffers at queuing analysis or simulations of buffers at nodes.nodes.

► The second approach is based on traces of actual The second approach is based on traces of actual traffic streams. traffic streams.

► These traces can be used as traffic inputs to These traces can be used as traffic inputs to simulationssimulations. .

► Indeed, this latter approach relies heavily on the Indeed, this latter approach relies heavily on the availability of such traces. availability of such traces.

► Whatever assumptions are used to characterize the Whatever assumptions are used to characterize the arrival process of the traffic will have a significant arrival process of the traffic will have a significant impact on the predicted performance. impact on the predicted performance.

► Therefore, it is necessary when studying the Therefore, it is necessary when studying the performance to use traffic models that capture the performance to use traffic models that capture the most important characteristics of the actual traffic. most important characteristics of the actual traffic.

► Another strategy is to build models at a functional level, and Another strategy is to build models at a functional level, and use them to predict the traffic by appropriately combining use them to predict the traffic by appropriately combining the models with values measured from actual networks. the models with values measured from actual networks.

► For instance, the functional behavior of an orchestrated For instance, the functional behavior of an orchestrated multimedia presentation describes the events that happen multimedia presentation describes the events that happen in time domain. in time domain.

► These events specify the objects to be part of the These events specify the objects to be part of the presentation in different media streams that make up the presentation in different media streams that make up the presentation. presentation.

► This functional behavior of an orchestrated presentation, This functional behavior of an orchestrated presentation, represented by its synchronization characteristics, can be represented by its synchronization characteristics, can be effectively used for understanding the performance effectively used for understanding the performance behavior of the application. behavior of the application.

► For characterizing the performance behavior, we need to For characterizing the performance behavior, we need to describe the multimedia application in terms of tangible describe the multimedia application in terms of tangible system-related parameters such as the QoS discussed system-related parameters such as the QoS discussed earlier. earlier.

Buffer ManagementBuffer Management

► A traffic model of an application, which is A traffic model of an application, which is based on the functional behavior, is based on the functional behavior, is represented as a sequence of objects to be represented as a sequence of objects to be presented at different time instants with an presented at different time instants with an associated duration of presentation. associated duration of presentation.

► Such a sequence gives an implicit Such a sequence gives an implicit description of the traffic associated with the description of the traffic associated with the orchestrated presentation. orchestrated presentation.

► But the actual traffic generated by an But the actual traffic generated by an application also depends on the object application also depends on the object retrieval schedule adopted by the client.retrieval schedule adopted by the client.

► The retrieval schedule basically determines the time instant(s) at which the client wants to receive the object(s).

► This schedule depends on the buffering that can be done at the client side.

► In a similar manner, the QoS requirements of a client carrying out the application depends on the size of different media objects to be presented, the duration available for retrieving them, and the buffering strategies adopted by the client.

SchedulingScheduling

► The heart of a QoS architecture is the multiplexing The heart of a QoS architecture is the multiplexing policy used at the switching nodes. policy used at the switching nodes.

► Multiplexing is the allocation of link capacity to Multiplexing is the allocation of link capacity to competing connections. competing connections.

► The manner in which multiplexing is performed has The manner in which multiplexing is performed has a profound effect on the end-to-end performance of a profound effect on the end-to-end performance of the system. the system.

► Since each connection might have different traffic Since each connection might have different traffic characteristics and service requirements, characteristics and service requirements,

► it is important that the multiplexing discipline treats it is important that the multiplexing discipline treats them differently, in accordance with their them differently, in accordance with their negotiated QoS. negotiated QoS.

► However, this flexibility should not However, this flexibility should not compromise the integrity of the scheme, that compromise the integrity of the scheme, that is, a few connections should not be able to is, a few connections should not be able to degrade service to other connections to the degrade service to other connections to the extent that the performance guarantees are extent that the performance guarantees are violated. violated.

► Also, the scheme should lend itself to analysis Also, the scheme should lend itself to analysis since performance guarantees are to be given. since performance guarantees are to be given.

► Finally, it should be simple enough for Finally, it should be simple enough for implementation in high-speed switches. implementation in high-speed switches.