introduction to multimedia1 multimedia network. zreference: guojun lu, “communication &...
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Introduction to Multimedia 1
Multimedia Network
Reference:Guojun Lu, “Communication & Computing for Distributing Multimedia Systems”Read Chapter page 124-150
Network Characteristics
1. The network bandwidth should be 1. The network bandwidth should be sufficiently high to support many sufficiently high to support many applications at the same time;applications at the same time;
2. Network resources should be shared 2. Network resources should be shared efficiently among applications so that as efficiently among applications so that as many applications as possible are many applications as possible are supported given certain resources;supported given certain resources;
3. The network should provide performance 3. The network should provide performance guarantees, if required, to applications;guarantees, if required, to applications;
4. The network should be scalable.4. The network should be scalable.
1. Network Speed vs Bandwidth
Sufficient BW for supporting multimedia communications.
Speed vs BW the time intervals representing each data bit “high-bandwidth network” instead of “high- speed network”
Network speed is determined by the physical transmission medium used, protocols, distance between intermediate nodes, and switching speed of intermediate nodes.
two different points of a network: user access pointuser access point
the bandwidth at this point is the bandwidth at this point is called user access bandwidth.called user access bandwidth.
network access point,network access point,
the same amount of bandwidth the same amount of bandwidth should be available for both should be available for both directions.directions.
2. Efficient Sharing of NW Resources
Each user requires a large amount of bandwidth, If each user reserves a bandwidth equal to its peak bit rate,
some bandwidth is wasted when the output bit rate is not at the highest solution: bandwidth on demand or statistical multiplexing discuss: Circuit switching technology?
Synchronous time division multiplexing (STDM)?Packet-switching network?Packet size?Retransmission of lost data?
A better approach to reduce the effect of lost packets on playback quality is to use traffic priorities the most likely source of data loss is buffer shortage in network exchanges. discard the lower priority data first
3. Performance Guarantee
the network should guarantee that a packet can access the network within a specified time
when the packet is on the network, it should be delivered within a fixed amount of time
when the performance is not guaranteed? transmission medium access control (MAC) transmission medium access control (MAC)
protocols?protocols? the network switches?the network switches?
Some techniques:1.Characteristics of different types of traffic should be
determined in terms of peak data rate, average data rate, bursty intervals, delay, and delay jitter requirements.
2. Network access time should be guaranteed.3. Network resources (bandwidth and buffer queues)
should be managed efficiently so that as many applications as possible are supported with performance guarantees.
4. Network Scalability
Three types of scalability: Distance ? Bandwidth ? The number of users ?
5. Multicasting Capability
There is a common need to distribute a stream to multiple destinations. For example, in a videoconference
It is slow and wasteful for the source to send a copy of the data to each destination one by one. Why?
Circuit switched or Packet switched ?
The suitable network for MM communication
The individual access bandwidth The individual access bandwidth should be at least a few Mbps. The should be at least a few Mbps. The aggregate bandwidth should at aggregate bandwidth should at least be in the order of 100 Mbps at least be in the order of 100 Mbps at the local area, and higher for the local area, and higher for WANs.WANs.
The network should be based on The network should be based on packet-switched statistical packet-switched statistical multiplexing instead of dedicated multiplexing instead of dedicated circuits for efficient sharing of circuits for efficient sharing of network resources.network resources.
The network should provide The network should provide throughput, error rate, delay, and throughput, error rate, delay, and delay jitter guarantee to delay jitter guarantee to applications.applications.
The network should be scalable in The network should be scalable in terms of bandwidth, the number of terms of bandwidth, the number of users, and distance covered.users, and distance covered.
The network should have The network should have multicasting capability. It is easier multicasting capability. It is easier to implement multicasting in to implement multicasting in packet-switched networks than in packet-switched networks than in circuit switched networks.circuit switched networks.
The suitable network for MM communication
End-to-End QoS for End-to-End QoS for Multimedia CommunicationMultimedia Communication
ICE BREAKER…..
“When communications networks are fast enough, multimedia communication can be achieved.”
Is this statement correct? Why?
IntroductionChallenges
Operational Issue Performance/Bandwidth Robustness/Stability Technology Integration
Business Issue Grow traffic and revenue Differentiate Services Respond quickly to customer application and
service requirements Efficiently capture and utilize key information for
flexible billing, planning, and monitoring
IntroductionServices Issues-1
Network Providers Increase utilization More money for some traffic Differentiation vs. Competition
Users Broad spectrum of choices Services enable applications
Industry New business area
IntroductionService Issue-2
What new differentiated services can be offered?
How to handle bandwidth hug multimedia applications and mission-critical application at the same time
How to handle congestion?How to provide scaleable performance for
new services?How to bill new servicesHow to support new services
Internet QoSNew Definition - Good Service
Better than “Best Effort Service” Service Classes
Enough for “Customer’s Needs” Bandwidth, Capacity, Usage Pattern
Support for “Various Applications” Multimedia Applications Mission-Critical Applications Secure Transactions ...
Internet QoSEffective Use of Networks
Exponential Growth Rate World-Wide 120 million subscribers today, 350 million in 3
years Ever increasing dial access numbers & speeds Increasing leased line access speeds Backbone bandwidth doubles every 6 months
Increasing bandwidth is only “passive solutions” Effective use of bandwidth is “active solutions”. Eliminate “overhead and useless usage”.
End-to-End Multimedia System
Introduction to Multimedia 22
Introduction
Why resource management?Resources in Multimedia SystemsRequirements of a multimedia systemQuality of Service
Layered Model QoS Parameters QoS Classes
Operations
Introduction to Multimedia 23
Why resource management?
Limited capacity in digital distributed systems despite data compression and utilization of new technologies.
End-to-end nature of multimedia applicationsProcessing of continuous data requires the
cooperation of every hardware and software component along the data path.
Competition for resources exists in an integrated multimedia system.
Resources required at different levels of a distributed multimedia system
Application, system, device, network...
Introduction to Multimedia 24
Window of insufficient resources
High-qualityaudio
Interactivevideo
Network fileaccess
1980 1990 2000
insufficient
insufficient Sufficient but scarce
abundant
Introduction to Multimedia 25
Resources in Multimedia Systems
Application Level
System Level (Operating System and Communication System)
Multimedia Device Level Network Level
Network host interface(bandwidth)
Multimedia devices(e.g. video/audio device)
CP
U
Mem
ory
Layered Partition of a Multimedia System wrt to required resources and processing/communication services
Introduction to Multimedia 26
Resources - Classification
Resourceis a system entity required by tasks for manipulating
information.
Types of resourcesActive vs. passive resources -
• e.g. CPU is an active resource, main memory is a passive resource
Shared vs. exclusive resources• CPU is a shared resource, video board is an exclusive
resourceSingle vs. multiple resources
• In a uniprocessor the CPU is a single resource whereas in a multiprocessor system the CPU is a multiple resource.
Introduction to Multimedia 27
Requirements
High level resource managementResource Reservation/Allocation/Adaptation
Process ManagementReal-time processing of continuous dataCommunication and Synchronization between
processes Memory Management
Guaranteed timing delay and efficient data manipulation functions
File System ManagementTransparent and guaranteed continuous retrieval of
audio/video. Device Management
Integration of audio/video devices
Introduction to Multimedia 28
Huge Real-time requirement
Real-time system• Correctness of a computation depends not only on
obtaining the right results, but also upon providing the result on time.
Real-time process• is a process which delivers the results of processing in a
given time-span.
Real-time applicationsTemperature control in a chemical plant
• Driven by interrupts from an external device that occur at regular and unpredictable intervals.
Control of a flight simulator• scheduling of commands that execute at periodic
intervals. This scheduling is performed by a timer service which the application requests from its OS.
Introduction to Multimedia 29
Deadlines
Deadlines represent the latest acceptable time for the presentation of a processing result.
Types of deadlinesSoft Deadline - In some cases the deadlines are
missed, but• not too many deadlines missed and• deadlines not missed by much.• E.g. flight arrival/departure
Hard Deadline • deadlines should never be violated since violations
imply system failure.• E.g. deadline failures in nuclear power plants, robotic
arm failures in process control systems
Introduction to Multimedia 30
Requirements for Real-time operating systems
Multi-tasking capabilities• Real time application is divided into multiple tasks.• Helps keep CPU busy and ensures that processing of one
event is not blocked because the application is waiting for a different event.
Short interrupt latencyInterrupt latency
• is the time interval between a hardware device generating an interrupt and execution of the first instruction of the software interrupt handler.
• Interrupt Latency = hardware delay to get interrupt signal to processor + time to complete current instruction + time executing system code in preparation for transferring execution to the device’s interrupt handler.
Introduction to Multimedia 31
Real-time operating system requirements
Fast context switchContext switch time (Dispatch latency)
• time between the OS recognizing that the awaited event has arrived and the beginning of execution of the waiting task.
Control of memory managementVirtual Memory vs. Real Memory
• A OS with VM support that aims to support real-time programming must provide a way for a task to lock its code and data into real memory so that it can guarantee predictable response to an interrupt.
Proper scheduling• OS must provide a facility to properly schedule time-
constrained tasks.
Introduction to Multimedia 32
Real-time Operating System requirements
Fine granularity timer servicesneed access to fine granularity interval timesMillisecond resolution is a bare minimum,
microsecond resolution is required in some cases.Accurate time-of-day services
Rich set of intertask communication mechanisms.
Message queues, shared memory, Synchronization - semaphoresevent flags
Introduction to Multimedia 33
Real-time and Multimedia
Audio and Videorepresent data streams of periodically changing
values.Semantics of multimedia information is dependant on
timely delivery.
Differences b/w real-time requirements for traditional real-time systems and multimedia systems
Fault tolerance and securitysoft deadline vs hard deadlineperiodic behavior vs. random behaviorbandwidth requirements
Introduction to Multimedia 34
Resource management in networked multimedia systems
Application
System
Network
Application
System
Network
Network ResourceManager
Res
ourc
e M
anag
emen
t
Res
ourc
e M
anag
emen
t
End-SystemEnd-System
Switch
Qos Definition-1
“Quality of service represents the set of those quantitative and qualitative characteristics
of a distributed multimedia system necessary to achieve the required
functionality of an application.”
QoS Definition-2
“QOS is a quantitative and qualitative specification of an application’s
requirement, which a multimedia system should satisfy in order to
achieve desired application quality.”
Conceptual Model
Sample QoS Parameters
Introduction to Multimedia 39
Quality of Service
Multimedia systems consist of a set of services These services may have different
requirements timeliness, delay, jitter, accuracy, performance etc.
These requirements are specified using QoS parameters.
Examples of QoS parametersAudio service
• sample rate of 8000 samples/sec, sample resolution of 8bits/sample
Network service• throughput of 100Mbps, connection setup time of 50ms
Introduction to Multimedia 40
QoS concept (continued
QoS originated in the networking service domainprovided a specification of how good the offered
network services are (ISO standard definition).
Layered model of QoSextended QoS concepts to include not only networking
services, but also OS services and services for the provision of end-to-end QoS to the human user.
Services may be performed on different objectsmedia sources, sinks, connections, tasksQoS specification characterizes the service objects.Various definitions of QoS parameters
• real-time channels, streams, sessions, media...
Introduction to Multimedia 41
Layered Model for QoS
User
NetworkMM devices
System
Application
(Network QoS)(Device QoS)
(System QoS)
(Application QoS)
(Perceptual QoS)
(Operating and Communication System)
Introduction to Multimedia 42
Application QoS parameter examples
Application Qos
Media Quality …... Media Relations
Intraframe
Media Characteristics
Interframe
Component Spec
Name
Size
Rate
Importance
Loss Rate
Transmission Characteristics
Sample Size
Sample Rate
Compression
End-to-end Delay
Sample Loss Rate
Importance
Cost
Synchronization Skew
Integration
Communication
Conversion
Introduction to Multimedia 43
System QoS parameter examples
System Qos
Application Subsystem Network Subsystem
Tasks per Connection Spec
Task Scheduler
Priority
Duration
Period
Task Ordering
Time Begin
Time Deadline
Space Requirements
Tasks per Medium Spec
Task Scheduler
Priority
Duration
Period
Task Ordering
Time Begin
Time Deadline
Space Requirements
Introduction to Multimedia 44
Network QoS parameter examples
Network Qos for a connection
Throughput Spec Performance Spec Connection ID
Traffic Spec
Packet Size
Throughput
Burstiness
Packet Loss Rate
Intermediate Delay
Packet End-to-end Delay
Ordering
Error Control
Fragment/Reassembly
Communication Type
Cost
Priority
Introduction to Multimedia 45
QoS Classes
QoS Service Classes determinereliability of offered QoSutilization of resources
Guaranteed Service ClassQoS guarantees are provided based on deterministic
and statistical QoS parameter values. Predictive Service Class
QoS parameter values are estimated and based on the past behavior of the service
Best-effort Service ClassNo guarantees or only partial guarantees providedNo QoS parameters are specified or some minimal
bounds are given.
Introduction to Multimedia 46
Resource Allocation Tradeoffs in QoS Classes
appl2
unused
unused
Needs of appl 1
Needs of appl 2
Needs of appl 1conflict
Reserved for appl 1
Reserved for appl 2
Reserved for appl 1
Reserved for appl 2
Introduction to Multimedia 47
Deterministic QoS parameter values
Single valueQoS1 - average value (QoS_ave), contractual value,
threshold value, target value.
Pair of values<QoS1,QoS2> -
• QoS1 - required value • QoS2 - desired value • <QoS_ave, QoS_peak>,<QoS_min,QoS_max> etc.
Triple of values<Qos1,Qos2,Qos3>
• QoS1 - best value, Qos2 = average value, QoS3 = worst value
• e.g. <BW_peak,BW_ave,BW_min>,similarly jitter….
Required value Desired value
Acceptable valueIncreasingquality
Introduction to Multimedia 48
Guaranteed QoS
Need to provide • 100% guarantees for QoS values (hard guarantees) or • very close to 100% guarantees (soft guarantees)
Current QoS calculations and resource allocations are based on
• hard upper bounds for imposed workloads• worst case assumptions about system behavior
Advantages• QoS guarantees are satisfied even in the worst possible
case, hence high reliabilityDisadvantages
• Over-reservation of resource capacities, hence needless rejection of reservation requests.
• Qos values may in reality require softer bounds and significantly less resources than calculated hard bounds.
Introduction to Multimedia 49
Predictive QoS parameters
AverageCan utilize QoS values in the past (QoS1,…QoSi) and
compute the average from 1 to i values. The desired QoS_bound at step K>I will be
• QoS_K = 1/i * QoS_j Maximum Value
Can utilize QoS values in the past (QoS1,…QoSi) and take maximum value as the desired QoS bound
• QoS_K = max QoS_i Minimum Value
Can utilize QoS values in the past (QoS1,…QoSi) and take minimum value as the desired QoS bound
• QoS_K = min QoS_i
j=1
i
i=1,..i
i=1,..i
i=1,..i
Introduction to Multimedia 50
Best Effort QoS
No Qos bounds or possible soft QoS bounds Possible calculation of performance one might
get is based on• average case with stochastic description of imposed
workload• average case with stochastic assumptions about the
system behavior.
Advantages• resource capacities can be statistically multiplexed,
hence more processing requests can be granted.
Disadvantages• QoS may be temporarily violated, hence the service
guarantees are not reliable.
Introduction to Multimedia 51
Relation between QoS and resources
Phase 1
Operations on QoSUser QoSrequirements
Resource reservation/allocation
QoS guarantees to user
Phase 2
QoS enforcement by resource control/adaptation
multimediaprocessing
Introduction to Multimedia 52
QoS Operations
QoS Translation must be bidirectional
human interface (user QoS) - application QoSapplication QoS - system QoSsystem QoS - network QoS
Media Scaling (reverse translation) Transparent Scaling Non-transparent Scaling
Introduction to Multimedia 53
Scaling - Examples
Audiotransparent scaling is difficult, non-transparent
scaling should be used.
VideoTemporal ScalingSpatial ScalingFrequency Scaling (reduction of DCT coefficients)Amplitude Scaling (reduction of color depth)Color Space Scaling (reduction of the number of
entries in the color space)
Introduction to Multimedia 54
QoS Negotiation
User (Caller)
Application (Caller)
System (Caller)
.
.
.
User (Callee)
Application (Callee)
System (Callee)
.
.
.
Caller to Callee
Peer to Peer
Service User to Service Provider
Layer to Layer
Overview of the QoS Negotiation Operation
Introduction to Multimedia 55
Bilateral Peer to Peer Negotiation
Caller Callee
Service Provider
Peer to Peer
Negotiation
Connect indication
Connect request
Connect response
Connect confirm
Requested QoS value
Changed QoS value
t_1 t_2 t_3t_4
Introduction to Multimedia 56
Triangular QoS Negotiation
Caller Callee
Service Provider
Peer to Peer
Negotiation
Connect indication
Connect request
Connect response
Connect confirm
Requested QoS value
Changed QoS value
t_1 t_2 t_3t_4
Changed QoS value
Introduction to Multimedia 57
Qos Negotiation in the Layered Model
Application-to-networkcommunication
Peer-to-Peercommunication
Tuning of Application QoS parameters
Negotiate/RenegotiateApplication QoS parameters
Negotiate/RenegotiateNetwork QoS parameters
QoS Translator(Bidirectional translation)
Accept/modify Reject
Introduction to Multimedia 58
Resource Management Operations
Resource Management consists of• resource managers• resource management protocols and services
Operations performed by resource managers to provide QoS
Establishment Phase• schedulable units utilizing shared resources must be
admitted and resources must be reserved and allocated.
Enforcement Phase• Reserved and allocated resources must be provided,
enforced and possibly adapted according to QoS requirements during the lifetime of the applications.
Introduction to Multimedia 59
QoS Establishment
The following operations must be performedQoS to resource mapping
• Need translation profilesResource admission
• Need admission tests to check availability of resourcesResource reservation
• must be done along the path from initiator to initiateeResource allocation
• done along the path from initiatee to initiator
Need a continuous media resource model• need to know how applications will use resources• model chain of resources during the traversal of
multimedia messages along the end-to-end path in a distributed multimedia system
Introduction to Multimedia 60
Admission Tests
Task schedulability tests for CPU Packet schedulability tests for sharing host
interfaces, switches• needed to provide delay and jitter reliability
guarantees.
Spatial Tests for Buffer Allocation• needed for delay and reliability guarantees
Link Bandwidth tests• throughput guarantees
Introduction to Multimedia 61
Resource reservation and allocation
2 types of reservationsPessimistic Approach
• worst case reservation of resourcesOptimistic Approach
• average case reservation of resources
For resource reservation, we need• Resource Table - information about managed resources• Reservation Table - current reserved resources• Reservation Function - maps QoS to resources and
operates on the reservation table.
Reservation Styles• Sender initiated• receiver initiated
Introduction to Multimedia 62
QoS Enforcement
Resource Schedulinge.g. rate monotonic scheduling
Rate Control - Traffic shapinge.g. leaky bucket
End-to-end Error Controle.g. forward error correction
Flow ControlOpen Loop Flow Control (no feedback)Closed Loop flow control (with feedback)
Flow synchronization
Introduction to Multimedia 63
QoS Management Issues
Resource and QoS Monitoringshould be flexible, variables should be optional and
monitoring can be turned on and off• User mode monitoring• Network mode monitoring
QoS Maintenance• compares monitored QoS with contract QoS
QoS Degradation• issues a QoS indication
QoS Signaling• specifies interval over which QoS should be monitored
and user informed about the delivered performance QoS Scalability
• includes QoS filtering and adaptation
Introduction to Multimedia 64
QoS Renegotiation
RenegotiationEntity
Network Management
Application Management ( User Interface) Application QoSparameters
Network QoSparameters
Signal “Change Application QoS”
Signal “Change Network QoS”
Introduction to Multimedia 65
QoS Resource Adaptation
As a result of a renegotiation request (request for change in quality)
adaptation in QoS and adaptation in resource allocation must occur.
Renegotiation request can come from• User• Host system• Network
Kinds of adaptationNetwork Adaptation (e.g dynamic rerouting
mechanism)Source Adaptation (e.g. temporal scaling with
feedback)
Introduction to Multimedia 66
Resource Deallocation
Free up resources used by requestTear down process:
Sender initiated closingReceiver initiated closing
Introduction to Multimedia 67
QoS Provisioning - Current State
IncompletenessInterfaces not QoS configurableOnly small sets of facilities to support MM flows exist
Lack of mechanisms to support QoS guarantees
Need research in distributed control, monitoring, adaptation, maintenance of QoS mechanisms
Lack of overall frameworksQoS frameworks for heterogeneous environments
Introduction to Multimedia 68
Design Principles for QoS
Integration • QoS should be configurable, predictable and
maintainable over all layers.
Separation • separation of transfer, control and management
Transparency • applications must be shielded from the complexity of
underlying QoS specification.
Asynchronous Resource Management• supports the functionality division between
architectural modules.
Performance• try to avoid multiplexing, layer processing, use
hardware...
QoS Mechanism
QOS can be guaranteed only when: sufficient resources are available and proper scheduling of processes is implemented
How to provide QoS guarantees??
Preventing overload requires admission control, and preventing applications using more resources than what is allocated requires policing mechanisms.
The four important subsystems of End-to-End Multimedia systems are networks, transport protocols, end-system architecture, and multimedia server.