1. Interconnection Issues
John Horrocks (DTI)
John Horrocks (DTI)
8-9 June 1999
ETSI Seminar on transmission quality for VoIP

2. ETSI Seminar on transmission quality for VoIP
Current Approach
Circuit switched networks with digital cores
Focus is on delay and use of echo cancellers
Still loosely based on apportionment and need to avoid echo cancellers for most European calls
8-9 June 1999
ETSI Seminar on transmission quality for VoIP

3. Problems with apportionment
Needs a reference model but no single model possible
Cannot handle growing range of connection topologies and dynamic routing
Normally based on worst case, so over pessimistic
Needs a reference model but no single model possible
Cannot handle growing range of connection topologies and dynamic routing
Normally based on worst case, so over pessimistic
8-9 June 1999
ETSI Seminar on transmission quality for VoIP

4. What is really happening today?
No problems with loss
Few low rate codecs except in radio and indirect access networks
Echo control is good enough given low delays in fixed networks
Planning and apportionment still attempted for majority of cases
8-9 June 1999
ETSI Seminar on transmission quality for VoIP

5. What is happening today - 2
Some operators require interconnected operators to follow plan, but…
Planning allows for 10% to exceed limits and no one knows exactly what happens
Quality meets users’ expectations
Responsibility not very clear - end-end or only your own network?
8-9 June 1999
ETSI Seminar on transmission quality for VoIP

6. What is happening today - 3
Circuit switching moves statistical effects of network loading into call blocking
Quality is “excessive” on most calls so networks less efficient (excessive means provide more than user would be prepared to accept)
Quality is not guaranteed but pretend it is!
8-9 June 1999
ETSI Seminar on transmission quality for VoIP

7. ETSI Seminar on transmission quality for VoIP
Responsibility
EG assigns responsibility to network that charges
Responsibility limited to what is charged
Issue is meeting the responsibility when dependent on interconnected networks
8-9 June 1999
ETSI Seminar on transmission quality for VoIP

8. ETSI Seminar on transmission quality for VoIP
New factors from VoIP
Greater delays and greater variation make echo control necessary (almost) everywhere - no great problem!
Delays likely to affect interactivity, previously only an issue for satellites
Wider range of qualities - some better but higher proportion of calls with greater distortion (Ie)
Main new factor is cell loss resulting from buffer overflow - statistics now affect quality rather than blocking
Effects of cell loss depend on codec so include in Ie, which becomes time varying!
8-9 June 1999
ETSI Seminar on transmission quality for VoIP

9. Factors for responsibility
There is no alternative to the terminating network
There will normally be alternatives for transit networks
Quality will change during call unless simulate circuit switched networks
Any innovation requiring co-operation between networks will face a very long migration period before there is widespread implementation
8-9 June 1999
ETSI Seminar on transmission quality for VoIP

10. ETSI Seminar on transmission quality for VoIP
What is guarantee?
Nothing can be delivered with 100% certainty
Refund if quality below specified limit but what about variation during call and how measure the quality
8-9 June 1999
ETSI Seminar on transmission quality for VoIP

11. Choices towards the user
Specified level and refund if below limit
Specified level and refund if user complains
Unspecified level (best efforts) but sample user satisfaction and modify network accordingly, maybe support with own network measurements
Alter charge depending on observed quality of call (unrealistic)
Do you deliver a call known to be poor?
8-9 June 1999
ETSI Seminar on transmission quality for VoIP

12. ETSI Seminar on transmission quality for VoIP
Delivering quality
Involves information on current state (stored information or measurements)
Requires controls to change performance of critical parameter
8-9 June 1999
ETSI Seminar on transmission quality for VoIP

13. Choices towards other networks
Information - call by call
1-way delay
Use of voice activity detection
Codec type
Instantaneous Ie including effect of cell loss, needs measurement
Use of echo control
Information - average
?????????? (the missing key?)
8-9 June 1999
ETSI Seminar on transmission quality for VoIP

14. Choices towards other networks
Control (call-by-call or average?)
How to formulate the request
How to deliver what is requested (call-by-call or on average)
8-9 June 1999
ETSI Seminar on transmission quality for VoIP

15. Personal views (jump to conclusions!)
Migration for signalling developments will take far too long - need to focus now on shorter term
Call-by-call control would need control of router where cells are being lost to produce improvement - not practicable from top level but could do local re-routing
Best achievable is degrees of effort
8-9 June 1999
ETSI Seminar on transmission quality for VoIP

16. ETSI Seminar on transmission quality for VoIP
Personal views - 2
Not convinced of offering different quality levels at different prices, but at most 2 levels
Solve echo by universal echo cancelling except for fax/data
Tandem free operation worth promoting
Aim for cell loss levels sufficiently low that codecs will not be affected significantly
Develop measures for cell loss on whole networks to give some quality rating
8-9 June 1999
ETSI Seminar on transmission quality for VoIP

17. ETSI Seminar on transmission quality for VoIP
Conclusions
Telecoms community needs to specify some performance targets and measures for individual IP networks
IP community needs to work on meeting these targets with dimensioning and inter-router protocols
8-9 June 1999
ETSI Seminar on transmission quality for VoIP