Distributed Systems reading notes (20)-----Distributed Multimedia system

Introduction

Today's distributed systems have become more and more to the application of distributed multimedia systems to go on the trend. The application of multimedia is essentially a consumption of continuous data flow. Audio and video are composed of audio sample and video frame. Sometimes because of the network conditions, he can allow partial delay, delay caused by the packet loss rate at a certain rate is also acceptable. In multimedia applications, it is very concerned about the quality of service quality requirements, so he needs the role of QoS manager here.

1, the application of distributed multimedia is often the demand is real-time, which requires the system for QoS control to do better.

2, in the application of multimedia often will have the following things happen, (1), multimedia applications are often highly distributed, the machine is located in different regions. (2), multimedia applications for resource requirements are dynamic changes. (3), the user to balance the cost of multimedia applications and other activities between the cost balance.

3, in order to solve some problems in the 2, there has been a QoS Management system service Quality management systems, his role is to ensure that the application can meet certain requirements at a certain time.

4, high-switching applications will have more requirements: (1), low-latency communication. (2), multimedia synchronization, people click on the pause, you should also show a suspended screen here. (3), additional synchronization, such as the update synchronization of shared files.

features of multimedia data

The feature of multimedia data is based on 2 words, which is continuous and time-base. Sustainability you can understand that the data currently playing will be replaced by subsequent data, whereas time-based features mean that each data has his or her own time to play, with the order of each data in front of it.

Service Quality Management

When multimedia applications run on the remote user's PC, they compete with the traditional application for resources on the user's computer. Conflicts occur when the network exceeds the load. The role of Qos manager lies in 2 areas:

Qos negotiation and admission control.

Qos Negotiation

The coordination of the quality of service relationship as long as the idea is based on the requested information and currently stored in the database system resource information comparison, to determine the ability to meet the request, and then respond, some parameters of the request information are: bandwidth, delay, packet loss rate. The process of coordination is to request each of the server node that has the QoS manager until a positive reply is reached.

Admission Control

Adminssion control means permission to enter controls. His role is to prevent the re-access of resources. Because these resources are resources that have already been reserved, that is, resources that have already been allocated.

Resource Management

The management of resources is also to improve QoS at a certain level.

Resources Scheduling

When it comes to the management of resources, we have to say the resource scheduling algorithm. A few multimedia scheduling algorithms are mentioned below.

Fair Scheduling

A queue-like FIFO scheduling rule that, when the data flow is competing for the same resource, can determine the order in which packets arrive in time.

Real-time scheduling

Real-time scheduling algorithms are generally used in more dynamic scenarios, such as variable CPU resources.

earliest deadline first scheduling

The EDF algorithm is scheduled according to the task deadline, which deadline is the earliest and most urgent, let the task run first.

Rate monotonic scheduling

The above in accordance with the deadline algorithm or slightly sloppy, personal feeling, and the RM algorithm is more than which task execution speed, let which run first, which can make the overall efficiency of the operation improved.

Flow Adaptation

When the above measures have been applied, perhaps we can not guarantee the guarantee of QoS, this time may find a way to do some of the data flow to adapt to the operation. When the network condition is not good, the data stream also transmits so much information certainly is not good, so this is you can choose to cut off part of the information, without affecting the whole situation, how to do change, continue to see.

1, in the video data transmission time, in the unit of time to reduce a certain number of frames.

2, in the video frame data in the picture to reduce a certain amount of pixels.

3, for the transmission of the picture to modify its compression algorithm, with a certain quality of loss in exchange for the increase in transmission speed.

4. Reduce the depth of color in each pixel of the image less.

These operations are best handled in the path from the source resource to the destination resource, rather than uniformly at the source resource send, the initial resource is unified, because the target environment is different and changes are made.

Learning Examples: tiger,bittorrent, End System multicast

A small title lists 3 examples of multimedia applications.

References: <<distributed sysytems Concepts and design>> original version fifth, Author:george Coulouris,jean Dollimore, Tim Kindberg,gordon Blair

Distributed Systems reading notes (20)-----Distributed Multimedia system