tailieunhanh - IP for 3G - (P6)

Quality of Service What is QoS? The basic definition of QoS is given by the ITU-T in recommendation as ‘‘the collective effect of service’’ performance, which determines the degree of satisfaction of a user of a service. There are a large number of issues, which affect user satisfaction with any network service. These include: † How much does it cost? † Can a user run the application they want? † Can a user contact any other user they want? None of these is a straightforward technical question | IP for 3G Networking Technologies for Mobile Communications Authored by Dave Wisely Phil Eardley Louise Burness Copyright 2002 John Wiley Sons Ltd ISBNs 0-471-48697-3 Hardback 0-470-84779-4 Electronic 6 Quality of Service Introduction What is QoS The basic definition of QoS is given by the ITU-T in recommendation as the collective effect of service performance which determines the degree of satisfaction of a user of a service. There are a large number of issues which affect user satisfaction with any network service. These include How much does it cost Can a user run the application they want Can a user contact any other user they want None of these is a straightforward technical question. If a user want to run a video-phone application this requires that The application is compatible with that used by the phoned party. The cost is not prohibitive. There is a network path available to the other party. The user does not have too many other applications running on their computer already so that the computer has available resources. The network path can deliver all the required data packets in a timely fashion. The user knows the IP address of the terminal the other user is at. The end terminals can reassemble the data packets into a sensible order. The end terminals understand how to handle any errors in packets. There are doubtless many other requirements. In identifying these requirements a few assumptions have already been made. In particular the basic IP principles have been followed as identified previously and it has been assumed for example that much of QoS is a user end-terminal responsibility. 202 QUALITY OF SERVICE Answering each of these questions leads to different fields of study within the general subject of QoS. These include Traffic engineering - This includes how a network manager makes the most efficient use of their network to reduce the cost. Policy management - Static network QoS provision for example to give the boss the best .