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

2. 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

3. 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

4. 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

5. 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”

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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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?