John Horrocks +44 1483 797807 john@horrocks.co.uk Quality of Service John Horrocks +44 1483 797807 john@horrocks.co.uk

QoS and Interconnection? The Internet approach to interconnection is “open” The telco approach is “closed” - about control The reasons are: To enable usage-based charging To protect and support QoS Consequently service provision is complex

What is QoS to a user? Ease of set-up Ease of use Ability to make a call at any time Ability to continue the call undisturbed Freedom from unwanted calls Speech quality Everything apart from price

The Importance of QoS Why will people pay more for PSTN and other NGN services when they can use similar services on the Internet? The only answer is QoS! The benefits of QoS must exceed the extra costs of the complexity of the NGN compared to the Internet

The danger of QoS Users are not stupid Users may adopt a dynamic strategy of using the Internet as first choice and using NGN only when the Internet is too congested - The Internet can be good and there is a market mechanism to maintain it So NGN becomes the “Internet overflow network”

The Claims Guaranteed Quality Guaranteed minimum quality QoS enabled network Guaranteed connection and intelligibility for calls to emergency services

The Basics Finite resources and varying demand mean nothing can be absolutely guaranteed - demand peaks can be VERY high In circuit switched networks this results in call blocking, but call quality is constant In packet switched networks this results in variable packet delay and loss but effects on users may be constrained to some extent

QoS options - top level Allow varying quality - let users adapt as the users know their own needs best Access/usage denial = blocking (to protect established calls) - simulates circuit switching - denies user choice Prioritisation over non-delay-sensitive traffic Resource reservation

The technical realities Choice of codec dominates quality Codecs are outside operator control Main congestion problems are in user network and access systems - core is the least problem Prioritisation gives great improvement if there is high proportion of delay insensitive traffic Little knowledge of relationship between traffic, network design and jitter Call quality depends on both ends and each works independently

QoS is not signalling Standards work focussing on access control/denial Protocol designers are adding fields for QoS parameters, but…. How do you measure congestion? On which interfaces do you deny access? How do you deal with different traffic types? We are missing a system design

Summary QoS is very important for telcos But the telcos do not control the dominant factor - the terminal and user network and so cannot guarantee end-end quality But the telcos do not know how to design to achieve a specific level of QoS - it will be trial/error Prioritisation in a multi-service network can give good improvements A simple reservation or priority system in the access system is worthwhile

Key QoS questions What QoS features are needed for the core and for network interfaces? Will the core handle delay insensitive traffic, and so can a class-based prioritisation system be used? (Relation to Internet) Is any service/user related QoS mechanism needed? If not, the core can be simpler Will call control in transit networks reduce QoS by introducing processing bottlenecks? Can there be a simple system for cutting high demand peaks?