David Thorne HGI
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David Thorne HGI



FTTx Summit Europe 2012

FTTx Summit Europe 2012



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David Thorne HGI David Thorne HGI Presentation Transcript

  • NGA, QoS and the Customer Experience FTTx Summit Europe, April 2012 David Thorne, HGI Board Member“CONNECTING HOMES – ENABLING SERVICES”
  • Agenda Glossary What is QoS and who cares anyway ? QoS and NGA - FTTC, FTTP Service QoS requirements Basic QoS Techniques QoS Choices The business case for QoS QoS Assurance Home network QoS Summary and Conclusions 2
  • Glossary QoS is delivering a stream of associated packets with one or more of the following predefined attributes  Bit rate  Packet loss  Delay  Jitter QoE or Customer Experience is the user perception of a service, in particular not being annoyed by  Video - audio breaks, frame freezing, pixellation  Audio - delay, echo, audio breaks, speech quality SLA – Service Level Agreement  quantified ,demonstrable, contractual agreement with regard to 1 or more QoS parameters, plus availability and repair time NGA – Next Generation Access  Access technology with rates significantly greater than exchange (CO) based ADSL2+ 3
  • What is QoS For ? QoS is usually a means to an end, in particular to ensure the delivery of traffic so that a given service operates ‘as expected’ from the user perspective  especially true in the residential market Most residential users neither know or care about QoS in its own right QoS is not an ‘up to’ bit rate QoS can be part of a contractual SLA  especially for the business market  key parameters here are assured sustained bandwidth (site mirroring), and delay (financial market auto-trading) 4
  • Service QoS RequirementsService type Examples QoS RequirementsCasual Information Internet Browsing Peak bitrategatheringMass data up/down Facebook, work at home, Average bitrateload photo upload, backupInteractive, real-time Voice, video conferencing, Sustained bitrate,comms gaming delay, jitter, latencyNon interactive E-mail, Twitter NonecommsVideo streaming Sustained bitrate, peak bitrateM2M – mass market Automation, security None (autoconfig, security)M2M – mission Financial trading, smart grid Delay (availability,critical security) 5
  • Basic QoS Techniques1. Overdimension the network to the point where QoS control is unnecessary, even at peak times  still need monitoring to keep ahead of traffic growth2. Prioritise  may or may not involve policing  sometimes equated to diffserv3. Allocate sterilised bandwidth to different traffic types  can involve admission control and policing  sometimes equated to intserv1 is inflexible and can be expensive2 is simple, but is it enough ?3 can be complex, and has a lot of dependencies 6
  • QoS Choices Overdimension Prioritise AllocateWhat and where to Police or not Session based or trafficmonitor engineeredStatistical overload Per class or per stream Application layerprotection or not interactionTriggered overload Number of classes Police or rely onprotection or not admission control Session reservation and holding Point solutions or co- ordinated end to end Centralised or distributed in-home control 7
  • The Business Case for QoS QoS support requires network control and monitoring = network cost  in terms of both Capex and Opex Residential users are not prepared to pay for QoS in its own right = network cost  but can be used as a differentiator (market share, customer retention) QoS can be used to limit overdimensioning in a network = Capex saving Some business users are prepared to pay for QoS as a service enabler = revenue generation  normally associated with an SLA  it costs money to prove an SLADirect revenue opportunities from QoS are limited, so the costs of QoS have to be understood and controlled 8
  • What problem does QoS solve ? QoS is a way of managing temporary network congestion Network congestion occurs when the instantaneous offered load to a network egress point exceeds the physical, logical or contracted capacity QoS can handle sustained congestion to some degree  but only if the application of QoS leads to rate limiting by another layer (e.g. TCP back-off) Admission control can help to avoid congestion  but would only be a complete solution if all traffic and applications used admission control (they don’t) 9
  • QoS Assurance If QoS is being sold as in its own right (e.g. bandwidth, latency for the business market) then need to be able to demonstrate (in some way) that the contracted values, are, or can be delivered If QoS is a means to an end, a way of ensuring that the customer is getting an acceptable experience, then the network operator will have a variety of ways of monitoring, dimensioning and controlling network loading, but may not do proactive assurance to each end user, and cannot do assurance in the home network 10
  • The 3 QoS ManagementDomains Managed Services VOIP2 User End Wholesale Access VOIP1 management User Network provider management IPTV D SP HG S Backhaul BNG edge L A Network Internet M node Retail Service Provider Mgmt 11
  • Where do we need QoS ? Home Network Aggregate bandwidth can exceed the PHY capacity Time varying PHY capacity AN capacity can exceed Access Networkthe in-home LAN capacity Multiple video streams Issues may exceed the capacity Mix of WAN and LAN of the DS link traffic Multicast injectionMix of managed and OTT Upstream queuing Interconnect WAN traffic delays may introduce Interconnect bandwidth excessive delay and jitter contract limit Peering bandwidth costs 12
  • QoS and NGA - general One of the main drivers for NGA is concurrent application support, with a significant amount of video This is not just about QoS, but also packet error rate  this matters much more for multicast/UDP than unicast /TCP Video is not usually CBR Have to be able to cope with multiple video stream peaks, while still protecting the browsing experience, and constraining the latency on VOIP While overdimensioning alone is not sufficient, it is easier to manage a ‘generous’ resource than a very limited one Do care about the worst case bit rate 13
  • QoS and NGA Flavours FTTP and FTTC are different at the physical layer FTTC capacity varies with time  long term as a function of cable fill and hence crosstalk  this can be countered by vectoring VDSL has a higher packet error rate  this can be countered by PHY retransmission The cabinet (downstream, DS) is a potential congestion point for FTTC  need to match the DS rate to the VDSL PHY or product rate can be done higher up in the network (e.g. at a BRAS)  may need to prioritize certain traffic types (voice, video) PON is a shared medium, but has some mechanisms to support different traffic types, and control QoS between users PON can deliver higher peak ratesThe way in which QoS is managed may be a function of access technology typeThe customer will expect the same service experience for any kind of NGACan’t just wait for fibre to provide an enhanced customer experience 14
  • Home Network QoS The home network is a key element in the end to end service delivery chain Can be the most challenging from the QoS perspective Significant variations in the technologies used, largely beyond the control and visibility of the Broadband Service Provider The most popular in-home technologies are time variant Main technology problem is load exceeding capacity which can lead to a lot of dropped data The business problem is that little of the content is managed or revenue earning, but the ISP gets blamed for everything How can we deal with this ? The big choice is between centralised, admission controlled, and distributed, relative priority 15
  • Home Network Reality HG 100 Mbps Low-rate 100 upstream Mbps Access 100 High-rate to Ethernet 100 Mbps low-rate Switch Mbps bridge Wireless LAN MergingHigh-rate WAN-LAN and transit In-home networks have trafficdownstreamAccess proved to be fairly simple 100 Mbps Ethernet-PLT <10 Mbps (topology perspective) bridge – Wireless where it works • AP embedded in the HG – Ethernet patch cable to a main PC – Powerline-Ethernet bridges for Original HGI view of the in- some VAS video home network 16
  • Today’s home network 17
  • Home Network CongestionPoints WAP Multiple video streams > PLT PHY capacity 1 STB 2 3 Playback stream + Excessive ACK network streams > delay for TCP video Excessive ACK PLT PHY capacity delay for TCP video 18
  • The Initial HGI QoS Solution Identify services on a packet by packet basis by means of a service signature Send each packet to the appropriate queue  mix of Strict Priority and Weighted Round Robin queues QoS Management of all traffic that transits the HG - HN>WAN, HN>HN, WAN>HN Simple, static configuration by the SP (mainly) Relative, class-based QoS (as opposed to absolute and parameterised) No dependence on other network nodes Peaceful co-existence with other QoS schemes  In-home and network What is needed in the home (beyond the Gateway) to support QoS for NGA services ? 19
  • Quantifying the in-homeproblem Observation – users favour in-home technologies which require no new cabling – WiFi and PLT These are known to be time variant, but how extreme is the PHY variability ? BT has carried out extensive tests of these technologies in a (small number of) real homes, using representative traffic flows, concurrency and equipment locations Aim is to find a set of metrics that can be translated into application support This is being standardised as a set of KPIs and test methodology in the HGI 20
  • Real world PLT performance Variation between properties Time of day variation 21
  • Home Network Questions In-home PLT and wireless technologies show extreme time of day, intra, and inter-home variation The topology of Home Networks has turned out to be fairly simple Need to consider:  what additional in-home QoS mechanisms are necessary to support NGA service QoS  which are appropriate, given this variability In particular whether or not centralised control, and admission control make sense in the home 22
  • Home Network Admission ControlThis requires: An accurate knowledge of the available resource on the application path at the time the application wishes to start An accurate knowledge of the maximum bandwidth required during the session An assurance that that required resource remains available for the duration of the session All applications to have a signalling phase All applications to have awareness of their peak bandwidth requirements All applications to have an awareness of session duration A polite way of informing the user of denied access attempts A way of adding business logic into the admission control mechanism 23
  • Home Network CAC Commercial IssuesThere needs to be a way of monetising the investmentNetwork CAC is usually justified by under- dimensioning the network  this does not apply in the home Need to be sure that this does not result in more support calls than doing nothing  need to be aware of the implications of any implied liability 24
  • Home Network QoS Conclusions In-home CAC is very difficult given the (time variant) nature of the predominant in-home technologies Need to be sure that it could be done reliably, the application linkage can be done, and there is a way of monetising the investment Prioritisation method is much simpler, and can work well Can extend a simplified version of the HGI HG QoS model to HN infrastructure devices  Fewer queues  Simpler classifiers  Simple 2-port bridges 25
  • Summary and Conclusions - I One of the main drivers for NGA is to deliver a mix of services, some of which need QoS The residential user does not care about QoS as such, but about the service being delivered ‘properly’,  expects this as part of the service  this is usually a binary decision Cannot wait or depend on all-fibre networks to do this  have to be able to provide the same customer experience over all types of NGA  this may require different techniques, but the user doesn’t care  there will be capacity differences, these may or may not matter 26
  • Summary and Conclusions - II Both network and (some) in-home QoS are essential to the sustainable delivery of an overlay of managed services  this has to be very simple to scale, be manageable and affordable No need for tight, end to end co-ordination Class based, not flow based There will an increasing amount of intra-home traffic The Service Provider has limited influence and little control over the in-home network technology or usage This may therefore require better in-home, service specific monitoring and diagnostics In-home admission control is hard and unnecessary 27
  • The End Thank you Questions ? 28