Session 1: Applications – Needs for Time and Timing – Requirements & Vulnerabilities
Chair: Martin Kingston
- Mobile radio access networking has been one of the most discussed applications for synchronisation for many years now and the Keynote from Everything Everywhere (the network operator supporting T-Mobile and Orange brands in the UK) showed how this will continue to be the case as the transport further evolves and new air interface technologies bring new requirements. This was further expanded upon in papers later in the session.
- Mobile communication is not the only area bringing new challenges, and this was well illustrated by the paper jointly presented by the University of Galway and ESB Networks (the operator of the power distribution infrastructure in Ireland) which described the challenging timing requirements of controlling and monitoring Smart Grid infrastructure. Broadcasting network infrastructure is also an area of application with growing importance, as highlighted in the conclusions of the B21C study.
- The “microsecond challenge” was the theme of the conference and much of the panel discussion at the conclusion of the session revolved around this. Certainly there are many applications heading towards a requirement around this order of magnitude (though figures as low as 100 nanoseconds were mentioned too). Is this some fundamentally significant figure that will mark the end of the quest? It seems only time will tell.
Session 2: Time & Timing Performance - Establishing the Challenge, Suitability of the Metrics & Profiles
Chair: Tommy Cook
- France Telecom’s keynote set the scene showing the efforts the major carriers of the world are applying to assess the performance and role 1588v2 can provide in their future networks, both for the delivery of time, phase and frequency.
- A number of papers were regarding metrics. We heard how this is a critical step to mass deployment as if it is not possible to measure the behaviour of the network, it is very difficult to define standards and procedures that will enable Service Providers to deploy with confidence.
- A number of metrics are being evaluated. The ITU-T is providing a forum where different metrics are presented and assess to determine the role they can play in the future definition of network limits for PDV.
- The session concluded with an overview of an initiative that is currently underway. The IEEE1588 Conformity Alliance consists of a team of recognised experts from across the industry that are working towards a certification programme to assess the functionality and performance of equipment implementing IEEE1588v2 to transfer frequency, phase and/or time across a telecom’s network.
Session 3: Time & Timing Testing, Procedures, Test Cases & Results
Chair: Chris Farrow
- Anurag Gupta - Senior Staff Engineer, Juniper Networks, delivered The Packet Delay Variation across Timing 'Unaware' Network Elements and its Impact on Recovered PEC, showing the relationship between mix of packet sizes and packet clock performance, showing that the packet size mix is one of the main causes of variation in PDV signatures.
- Some real world measurement data showing characterisation of microwave link proprietary ACR technology along with assessment of PTP over IP performance was presented by Billy Marshall, Sales Engineer, Chronos Technology
- Developing Network Topologies with 1588v2 Boundary Clocks & Transparent Clocks delivered by Tommy Cook - CEO, Calnex Solutions. An overview of the theory of BC & TC implementations and a detailed look at how BCs & TCs can contribute to PDV accumulation. Some suggested test architectures for testing BCs & TCs, looking at how to quantify their contribution to overall PDV.
- Painless Migration of Synchronization - TDM to IEEE1588 by Kenneth Hann - Principal Engineer, Tellabs. An overview of migration strategies, TDM, SyncE & 1588 for time/phase delivery over PSNs, including ensembling 1588 flows to increase resilience. Emphasis on the many proprietary mechanisms surrounding 1588 – e.g. ensembling, packet selection, oscillator type etc.
- Long Term View of Synchronisation in Mobile Backhaul delivered by Anthony Magee - Principal Engineer - CTO Technology Team, ADVA Optical Networking Ltd. An overview of sync testing requirements and how it could be included into day-to-day network operation & management procedures. Looking forward to innovations both in time delivery using SyncE and widespread monitoring as part of everyday operation. Proposed incorporating monitoring capability into network elements.
- Antti Pietilainen - Senior Specialist, NSN – delivered a paper entitled Analysis of ITU-T G.8261 Test Cases which gave a very thorough analysis of G.8261 test cases with some good recommendations for changing this very important section of the standard. To avoid complicated test-setups, use of impairment emulators was considered, and it was shown that each emulator produces PDV profiles in slightly different ways. Proposals were made for seven redundant test cases from 8261 to be removed, consideration or microwave radio and DSL links to be added and other test case to be made more stringent.
- Session 3 was concluded with a Testing Panel moderated by Chris Farrow - Technical Services Manager, Chronos. Some good discussion with questions around testing strategies for both packet and physical layer measurements. Operators’ concerns over correlation between packet metrics and real-world client performance were raised, as was the need for very thorough testing and modelling before deployment.
Session 5: Challenges & Solutions for Access Technologies - GPON, DSL, Microwave Links etc
Chair: Stefano Ruffini
- The "microsecond challenge" was one key point addressed in session 5, Challenges & Solutions Technologies. Indeed the distribution of accurate time and timing became particularly important for supporting timing sensitive services in the mobile backhaul scenarios. This has stressed the need to provide accurate time and timing in the access portion of the network. This has become a challenging task especially due to the noise characteristics of some of the technologies being deployed in the access. Particularly critical is the presence of asymmetry in some transport media such as VDSL and GPON that may impair the distribution of accurate time.
- The session was opened by a keynote delivered by Kåre Gustaffson from Ericsson on the architecture and transport technologies for mobile backhaul. Kåre mentioned that with the rollout of Long Term Evolution the capacity of the radio access network backhaul needs to be upgraded to 100–150 Mb/s. Next generation mobile networks, such as LTE Release 10, will increase the requirement for backhaul capacity to gigabits per second. The need for increased capacity and decreased cost per transported bit drives packet-based mobile backhaul capacity boosts over microwave, copper and fibre. Key messages of the talk were that backhaul link technologies will not be a bottleneck for Mobile Broadband Traffic and Microwave Ethernet and Fibre will dominate new backhaul installations.
- Hal Roberts from Calix presented various solutions to deliver accurate time synchronization over XPON. Various approaches are possible and discussed in the standards: "distributed boundary clock", distributed transparent clock", "discrete transparent clock", "PTP equalizer". Is there a winner?
- VDSL2 is another technology where the intrinsic asymmetric nature of the technology requires the definition of specific solution to enable the accurate timing transport. This was the scope of the presentation from Dong Wei (Huawei) who presented a solution currently discussed in the standards.
- One key question common to all solutions in VDSL and xPON is what noise budget that can be allocated to the access segment of the network?
- A deeper look at what is possible to achieve when timing is carried via PTP over various access technologies was the focus of Charles Barry’s (Brilliant) talk. Several tests results were presented, PTP over Fibre Optic, Microwave, and SHDSL. Results from these tests could provide important guidance for future network deployment in mobile backhaul when timing is to be carried via packet timing.
- The market interest on OTN transport technology is growing and OTN may become more common also in future mobile backhaul scenarios. The new features offered by the new G.709 were presented by Ghani Abbas from Ericsson. The transport of synchronization (both frequency and time) over OTN is a major requirement. The possibility to carry frequency synchronization via SyncE over OTN has already been standardized. What about time sync over OTN? The various options were presented by Ghani. The OTN protection mechanisms (and related asymmetries that can be generated) is one key aspect that will require careful studies. The discussion based on this presentation provided important inputs to future standardization discussions.
- The talk provided by Slobodan Miljevic from Zarlink also concerned sync aspects in the OTN deployment. In the end the heart of any synchronization solution is the PLL. The correct recovery of the timing of signals carried over OTN shall be based on a careful desynchronizer (PLL) design and Slobodan presented some of the critical aspects to be considered in this activity.
- The session was concluded by Dr Rudi Frezel (Lantiq) who reminded that ADSL and VDSL support frequency synchronization across the physical layer is already defined since early versions of the standards. The use of this feature might become more common in the future in order to support the mobile backhaul needs.
Session 6: Standards Review and Future Development
Chair: Mike Gilson
- This session provided an opportunity for a standards progress review over the year presenting some specific achievements. Unlike previous ITSF events where the standards session has been at the beginning of the event this time it was at the end to give the delegates time to review the previous day’s discussion, debate and presentations and hopefully allow review of ITSF in the standards context. Session 6 was led by Mike Gilson of BT who introduced the speakers and explained the objective of the session. This year ITSF has an agreed relationship with ITU and Session 6 was run in collaboration with ITU with formal ITU “Logo Authorisation”. The intent of the session was twofold, to provide a standards review and attempt through forum participation to calibrate the industry direction and capture some key themes from the many participants expert in many relevant fields.
- Greg Jones, ITU-T SG15 counselor provided a general presentation of ITU-T, its working structures and methods. He presented the Focus groups and JCA (joint coordination activities), the cooperation with other standard organizations, IEEE, ETSI and IETF and the new involvement of Academia to bring new ideas.
- Speaking of Question 13, he said “Network synchronization performance are essential for successful operation and integration of digital transmission networks and associated switching and signaling systems”. Jean-Loup Ferrant (Calnex), ITU-T Question 13 (Q13) Rapporteur presented an update of the status of synchronization standards in Q13 for use in packet networks. He presented a review of this year’s Q13 achievements on the transport of frequency over packet networks and the structure of future recommendations for the transport of time over packet networks currently under definition in Q13. Silvana Rodrigues (IDT) editor of several Q13 Recommendations presented the recently consented ITU 1588 End to end telecom profile for the transport of frequency. She explained a “profile” for IEEE1588 and the ITU-T telecom profile. She presented the options defined in the telecom profiles, the BMCA (Best Master Clock Algorithm) located in slave clocks to select a master clock as frequency reference and the Telecom Slave Clock that has been defined for slave clocks.
- An interactive discussion was then chaired by Mike Gilson supported by Silvana Rodrigues and Ghani Abbas (Ericsson) ITU-T Question 9 Rapporteur, with a panel consisting of Jean-Loup Ferrant, Greg Jones and Stefano Ruffini (Ericsson) Deputy Q13 Rapporteur. Although initially this started slowly the general consensus at the end of the session was that it had been useful with much input from the delegates. The discussion was wide ranging but inevitably mobile aspects and LTE issues featured. Some key themes were that existing 1 pulse per second interfaces can be difficult to measure; several Time of Day interfaces may be required but should be minimised. GPS only is not a solution to the 1us problem and 100ns may be the fundamental limit for GPS. LTE rollout is happening now and pressure will grow to solve some of the key problems in standards otherwise propriety solutions will result. Also there was a general discussion on engineering the network properly but also being able to measure and characterise it correctly with useful metrics. At the end of the session Charles Curry took over to complete the wrap up of ITSF2010.