IP for 3G - (P6)

Quality of ServiceWhat is QoS? The basic definition of QoS is given by the ITU-T in recommendation E.800 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....
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IP for 3G - (P6) IP for 3G: Networking Technologies for Mobile Communications Authored by Dave Wisely, Phil Eardley, Louise Burness Copyright q 2002 John Wiley & Sons, Ltd ISBNs: 0-471-48697-3 (Hardback); 0-470-84779-4 (Electronic) 6 Quality of Service6.1 Introduction6.1.1 What is QoS? The basic definition of QoS is given by the ITU-T in recommendation E.800 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 require- ments 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 responsibil- ity.202 QUALITY OF SERVICE Answering each of these questions leads to different fields of study withinthe 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 network performance.† QoS middleware – This is how a software writer creates generic compo- nents for managing both network and local resources so as to enable an application to be able to adapt to different situations.† Control plane session management – As discussed in Chapter 4, how users contact each other and arrange the most suitable session character- istics.† Data plane session management – How end terminals make sense of the packets as they arrive.† Network QoS mechanisms – How to build networks that can forward packets according to application requirements (e.g. fast).† QoS signalling mechanisms – How networks and users communicate their QoS requirements. Consideration of these last three issues, loosely described as ‘User-drivenNetwork QoS’, is the focus of this chapter. The Internet today provides onlyone level of quality, best effort. It treats all users as equal. Introducing ‘Qual-ity of service’ almost by definition means that some users, for example thosenot able to pay more, will see a lower QoS. Those who are prepared to paymore will be able to buy, for example, faster Web browsing. However, moreimportantly, introducing QoS also means that a wider range of applicationswill be supported. These include:† Human – Human interactive applications like video-conferencing and voice.† Business critical applications, such as Virtual Private Networks, where a public network is provisioned in such a way as to behave like a private network, whilst still gaining some cost advantages from being a shared network. ‘User-driven Network QoS’ is essentially about allowing users to request‘QoS’ from the network. The type of QoS that may be requested couldinclude:† Guarantee that all packets for this session will be delivered within 200 ms, provided no more than 20 Mbit/s is sent.† Guarantee that only 1% of packets will be errored, when measured over 1 month. INTRODUCTION 2036.1.2 Why is QoS hard? QoS, especially in the Internet, is proving hard to provide. QoS was actually included in the first versions of IP – the TOS bits in the IP packet header were designed to allow a user to indicate to the network the required QoS. Yet, to date, there is very little QoS support in the Internet. One of the problems appears to be in defining what is QoS and what the network should do – questions that have been touched upon above. However, there are also a number of more pragmatic issues. Cost/Complexity/Strength of QoS Compromise Strong QoS can be obtained by giving each user much more capacity than they could ever use – perhaps by giving each user a 100-Mbit switched Ethernet link. Clearly, this would be a very costly approach to QoS. Within the standard telephone network, high levels of QoS are achieved by placing restrictions on the type of applications that can be supported – the telephone network only provides quality for a fixed data rate (typ ...