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

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

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

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

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

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

ETSI Seminar on transmission quality for VoIP Responsibility EG 202 086 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

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

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

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

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

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

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

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

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

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

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