Is your network PhaseReady?

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Phase Ready?

As you think about the evolution of your network, don't limit your thoughts to the frequency stability you need now. We want to help ensure that network roll-outs today will still be relevant come the explosion of HetNets and Small Cells.

Kings Place - another successful day

Thanks to everyone who attended our Kings Place (@Kingsplaceevent) event yesterday. I think it was a great success and as well as provoking thought about how best to deliver phase to the edge of the network in an operationally supportable way, we also had time to debate the future of engineering!

Use of TDD spectrum also had a good airing; interesting developments in Japan at 3.5GHz could mean phase is essential not only to ensure you use your own spectrum efficiently, but that you don't compromise your competition!

Special thanks to our independent Keynote speakers Zahid Ghadialy (@zahidtg) from TechUK and Hans Sjöstrand from Transmode.


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Donut or Doughnut - the wrong question?

Back in March I blogged asking whether you (well your phase delivery network actually) were a donut or doughnut person. The donut would be a ring of PRTCs (Primary Reference Time Clocks) at the edge of your network access layer delivering phase to Gateway devices and eNodeBs.The doughnut would have resilient (perhaps Caesium supported) PRTCs in your network core. The terms of this question were really about a battle of technologies as well as network architecture. I've since realised that this question is really not valid for a reliable supportable phase delivery network for TDD and LTE-A services that you are now on the verge of rolling out.

For me most of the technology issues are resolved (microwave links delivering phase being the most challenging), although implementations will vary wildly and standards have yet to catch up with real world network issues.

I think the key requirement for a phase delivery network is not the timing technology that underlines it but what happens when things fail! For example GPS directly connected at the eNodeB or Cell Site Gateway should easily deliver 1.5us at the air interface, but for how long will it continue to meet this requirement if some kind soul cuts through the GPS cable? Will it be long enough for your field force to get to site and effect a repair before the timing requirement is breached at an economic cost?

With this in mind I believe that the ideal phase implementation may well be a donut supported by a doughnut! I also believe this will be best delivered by an phase system independent of the network equipment. With PRTCs at the donut layer supported by PRTCs in the doughnut; especially if supported by Caesium in the core and Automatic Path Asymmetry Compensation (as implemented in the TimeProvider 2700) at the donut layer; next day mobilisation of field force could still allow fixes before the network edge breaks the 1.5us barrier.

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GPS Timing - coming to the edge of a Network near you?

This may seem a strange title for many readers - if you have a CDMA network you've been working with GPS at cell sites for many years. Here in Europe however we have tended in the past to use the E1 used for backhaul to deliver the sync quality we need to deliver 15ppb at the air interface. We've also more recently delivered this frequency performance from the core of Carrier Ethernet networks using PTP and SyncE.
Should your GPS have a problem, the holdover oscillator (lets say an OCXO) kicks in and gives you time to get out to site and make a fix. Likewise the PTP client devices usually use OCXO for holdover, and although the time to fix is usually shorter than is the case for GPS there is still adequate time to mobilise for a fix.

So why consider GPS at the edge now? Well we're probably a year or so away from having to roll out TD-LTE, or LTE-A features, that require adjacent cells (Macro or Small Cells) to be within +/-1.5us of each other. Packet based timing from the core is still being tested and standardised; microwave radio manufacturers have a real challenge to make this work well (and they're doing great work to get there);and you may not have end to end control of the backhaul network in any case. These issues may or may not be performance affecting enough to put a brake on considering PTP supported by SyncE for phase, but you'd be a fool not to consider the alternatives.

So we examine GPS at the edge; its been done successfully for years, right? Trouble is the game has changed - its got a lot harder. We're all OK with your GPS timing solution locked and running as it should, but what about failure? As in frequency networks the holdover technology kicks in - but OCXO will only hold the +/-1.5us for probably four HOURS, not four DAYS! Have you got the budget, or indeed available power in the cabinet, to use OCXO? TCXO performance continues to improve in leaps and bounds so perhaps using the latest TCXO could give you three hours to mobilise. How is Ops going to handle this? Will you need vehicles parked at strategic motorway junctions waiting for equipment to fail?
On a practical level where can you put the antenna? Have you mast space and the personnel required to roll this out at thousands of locations? Can you hide the antenna in the cabinet? Will it see enough of the sky to work there? Could you roll out Assisted GPS (A-GPS) to help here? If you deploy antennas at low level how long before they're vandalised? Does your network design allow for other cells to provide backup sync? If your timing is embedded in the eNodeB do you have to swap out a whole box to solve a GPS or sync issue?

These issues are real and need addressing, but none of them are necessarily show stoppers to delivering a robust network with adequate phase performance. The trick is to know what the issues are and to address them head on. Don't hope things won't go wrong because they will. Examine the cases of Edge GPS and Phase from the Core from a position that with the right planning and testing they will work.

Make sure you and your network are Phase Ready!
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Small Cells Summit Roundup

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Small Cells World Summit - sync is creeping on to the agenda!

Had the pleasure of contributing to a panel discussion at the Small Cells Backhaul Summit at the ExCeL last week. We had half an hour on the topic "Time and timing distribution for small cells". My co-panellists were Martin Kingston, Principal Designer at EE and Richard Strike, Business Development Manager, Ethernet Access at ADVA Optical Networking; and it was ably moderated by Rami Yaron. The discussion really centred on getting phase to the edge of mobile networks, and how the business case stacks up to achieve this.

Now half an hour doesn't seem like much, and in fact the discussion could have gone on for a LOT longer, but it is half an hour more than last year's event! There were a lot of presentations in the Backhaul Summit that mentioned to various degrees how difficult getting phase to the network edge is going to be, but no real expansion on that at all.

I was pleased that my view of the world chimed pretty well with Martin's; I've known him for many years now and respect his judgement and so if we are in accord I know I'm doing something right! Interestingly the area where we parted company was an unexpected one for me. I've thought that Small Cells would be more expendable than Macro Cells, and that operators could probably stand availability levels less than the five-nines we're used to in the Core. Martin was quite clear that if it is on his network it needs to be available! This will have quite an impact on timing and backhaul technologies; and pose some interesting questions for Small Cell holdover capability.

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Donut or Doughnut? Where will your Phase come from?

I've spent a lot of time since the beginning of the year talking to carriers and equipment vendors about the problems using PTP to get phase sync to the edge of networks. This includes talking to both the carrier and vendor about a network that is being installed this year and will need edge phase sync down the line. I've also spoken to two mobile carriers with very different philosophies of likely network rollout to achieve adequate phase sync, and another operator planning a network for rollout in a couple of years still to make such choices.

The fundamental choice seems to boil down to this - are you a donut or doughnut person? In much of the world a donut has a ring shape - hollow in the centre (center if we're following the spelling of donut!). Many believe they can deliver phase sync from "the edge of the core" or access layer. This would involve a layer of GPS PRTC / Boundary Clocks a minimal number of hops from the network edge - a phase sync "donut".

Here in the UK a doughnut is a disc shaped confection with no hole but a large amount of jam (jelly?) in the middle. In this case a smaller number of larger capacity and more resilient GPS PRTC devices would be deployed in the network core; disseminating phase sync through a network path that would probably demand full PTP awareness and on-path support.

Of course many factors in your network design could tip you from the donut to the doughnut - will you be deploying in largely legacy sites or is this a "green field" project; is it planned to have some or all of your traffic carried through a third party Managed Service; will you be using third party "dumb pipes" to transport your PTP packets for at least part of their journey to the edge?

Even if your LTE-A plans are a year or two away, you need to be thinking whether you are a donut or doughnut network. We at Chronos are developing "Phase Ready" tools to help carriers make these decisions, then implement and monitor them.

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An Independent Sceptic?

Very early in the development of PDH and SDH networks, carriers removed the timing functions from the network elements and implemented independent systems for time and timing dissemination and management. Interesting therefore that as timing requirements for edge applications are probably more stringent and difficult to achieve than ever, a large amount of timing dissemination and management is being taken back in to the network equipment!

What does that mean for you as a carrier? If you're a "bell head" traditional transmission person its a headache; if your a "net head" then perhaps not so much so. Fundamentally though to move microsecond phase coherence to the edge of your network you will need on-path support throughout (although don't jump to the conclusion that if you have on-path support that you will necessarily be successful in meeting all applications requirements).

But how well do these transparent and boundary clocks perform? What about the network in between them, especially if it is not in your control? Will the equipment vendor continue to support and improve their clock implementations for the long term? How do you manage failure scenarios? If you are using a managed service' phase implementation, how do you monitor its performance and hold them to account?

I think we at Chronos, and specialists like us, have a role to play in developing and maintaining your phase networks going forward. We can be that independent sceptic you need; one who understands the issues, can help with phase network design, verification, dimensioning and commissioning.

I will be developing these themes in the coming weeks and months. This is the biggest change in timing networks for at least twenty years and I believe we have the expertise and tools to help you make this process as pain free as possible!

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Is the "Phase Ready" message getting through - Part Two

We're engaged in some excellent work with several Wireless Backhaul manufacturers on PTP for phase and SyncE delivery at the moment. Fundamentally we have a simple message for those planning to roll out networks that require phase at the edge - if the radios have no On Path Support your network WILL NOT deliver microsecond phase coherence at the edge.

Interesting then that it looks like Phase is closer than some of us thought! We're currently assisting with the sync design of a Carrier Ethernet network that will require phase alignment at the edge, and frankly there is still a lot of engineering time and effort needed to find a solution that will deliver network requirements. Here's a good mantra to take with you in to any design exercise - "Don't think that On Path Support at every node ALONE will deliver adequate edge phase performance!"

We're also helping a Carrier with early planning of a Phase Ready network with lots of wireless backhaul that is probably three or four years away. Problem is their radio manufacturer currently does not have any product with On Path Support, but without this they can't engineer a network that will deliver! They're trying to be Phase ready but the market hasn't got there yet.

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Is the "Phase Ready" message getting through?

A couple of contrasting situations in big European Mobile Carriers demonstrates that the message is starting to get through - but there's still a lot of work to be done!

One major carrier who work closely with us at Chronos on sync and timing are busily engineering their edge network to be as symmetrical as possible to make sure their PTP for phase performance is a good as it can be. They currently have NO projects that require phase, although they use both SyncE and PTP for edge frequency.

I also heard this week of a carrier that committed only last year to a large rollout of Ethernet Microwave radios for backhaul, but selected a platform that cannot support PTP on path support. This is a supported product and so no criticism on selecting this for the project they had at the time, but they are now considering a trial of LTE-A requiring phase at the edge via a backhaul pipe that will impair phase performance with no upgrade path to help!

It really does make sense to think of the phase supporting future when considering frequency only projects today. This future is not as far away as you may think, and is likely to be in the lifetime of equipment you are currently considering for use.

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If the clock delivers, who cares about packets?

The most direct, and often least complicated, way to give visibility of whether packet timing technologies are delivering the expected synchronisation performance is to measure the produced or synthesised signals at the slave clock. Whether sync is delivered across a Carrier Ethernet, Microwave, or IP/MPLS network using IEEE 1588v2 (PTPv2) the ‘business end’ and proof of slave clock performance can be ascertained via the frequency, pulse, or time-code produced by it.

Connecting to a frequency, 1PPS or time-code output of a slave clock is often much quicker to perform and the, subsequent results simpler to analyse, than the more complicated procedures required to measure the performance or Packet Delay Variation (PDV) of an Ethernet or IP timing flow.

If the measured output performance is within specification for that part of the network, it doesn’t matter that PTPv2 packets may be occasionally dropped in the network or that the PDV sometimes strays outside the nominal quality levels because as long as the application is getting the quality of clock it requires then packet performance is of secondary importance.

Packet Delay Variation of the PTPv2 flow worries some engineers and they can, and do, invest valuable time and resources trying to unnecessarily find and solve perceived issues. From experience and sync monitoring projects, Chronos experts know that well engineered networks and PTPv2 clients will produce in-specification clock in many types of network conditions and this can be verified by monitoring the frequency, pulse or time-code from a test point. Of course if the measured clock is not within specification then investigation into the incoming flow is required but it does not need to be the first step.

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And You Thought Phase Would Be Tough?

I must admit that over the last year or so I thought, as far as PTP is concerned, that "frequency is done". From the early development days of PTP for frequency we went from "you can't trust it over more than 3 hops" to moving frequency through long networks of switches and microwave links without batting an eyelid. In this context the crusade to ask "Is Your Network Phase Ready?" began.

Intriguing then that I know of a situation TODAY where a Gateway device from a very reputable manufacturer with embedded PTP client is incapable of delivering adequate FREQUENCY to Node Bs after only a few network hops with even moderate traffic levels. This leads me to reinforce a view I've spoken about before - just because something is PTP aware doesn't mean it works!

We're seeing the drive today for full on path support in sync networks delivering phase to the edge, and people wanting to play in the Small Cells space (like Microwave Backhaul providers)  realise that they will have to interact with these PTP packets and will all be implementing a variety of boundary and transparent clock type solutions to do so.

I am still very much of the opinion then that your sync network should be INDEPENDENT of your transport network, or at least independently monitored and qualified for time and timing performance.

If you can't move adequate phase performance to the edge of your network you WILL have a negative impact on your customers' experience. Can you trust this key performance element to the people who supplied and support your transport network?

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Distributing Phase using PTP

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Tested Against What?

There was an interesting question from the floor during our Phase Ready Seminar on Wednesday; basically questioning the need for independent benchmarking and monitoring of phase in a network when manufacturers are building in an array of synchronisation performance statistics into their PTP Aware Switches and Routers.

From our perspective the response is simple - what are these statistics actually measuring and what are they measuring against? Of course in day to day operations the data available from within the end to end network management platform will be a key to deciding what actions if any are required should a particular set of circumstances arise. However, we think that, at the very least, these performance metrics should be calibrated against a set of independently verified and traceable measurements to put them in greater context.

This is why we are working with several equipment vendors to integrate SyncWatch into their EMS and OSS systems.

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Beyond G.811

So what's beyond G.811? G.811 has been around since the 1980s - it was there when frequency distribution was eventually sorted for PDH, and still there in the 1990s when SDH came along and turned things upside down for a short while. Even in the late 2000s when PTP and packet sync threatened to fox us all, G.811 kept calm, carried on, and frequency distribution over PTP was eventually done & dusted.

So what about the 2010s? Well, the latest challenge sort of ignores G.811; it's the relentless drive for bandwidth, fuelled by smartphones, dongles & tablets that's causing the wireless operators to scratch their (egg)heads and dream up ways to cram more capacity in & around the macro network. Current thinking is to fill in the cracks with lots of small cells, adding capacity & taking some of the strain away from the macro layer. The term "HetNets" (Hetrogenous Networks) has been coined to describe wireless access over a variety of types of access node. Macro, micro, pico & femto cells - the term "Small Cells" covers the 3 smallest types. But if only were that easy. Adding more radio transmitters into the already crowded spectrum means there's more management to be done, to minimise radio interference between the (now more) numerous cell types. The clever technologies already described by Steve Newcombe go some way to limit this, but that's just the tip of the iceberg. The stringent phase synchronisation called for by these technologies is pushing sync delivery & the backhaul network to the limit in terms of what it can deliver. If efficient spectrum management calls for 100s of nS of phase sync right at the very edge of the network, this poses a interesting conundrum for networking equipment vendors to solve. Even with time & timing delivery using GPS, antenna delay calibration and system tolerances could take the error budget close to 100nS - sloppy installations are out, this is precision stuff!

Beefing up the network that supplies the sync is already underway. Initial discussions in the standards bodies have focussed on utilising already existing techniques in DSL & PON to get phase alignment carried across & out of the network nodes to the advantage of the small cell. Techniques like NTR in DSL and modem ranging in PON are already being silently used by the network to do its job, but these have never before been made available as phase-sync alignment tools to end applications… will they be standardised in time to help with small cells?

So G.811 might eventual have to step aside, and a new kid on the block might be revealed, the saviour of phase sync...


The "Is Your Network Phase Ready" seminar at Kings Place on May 8th has a session exploring what lies beyond G.811. We'll try to give an impartial view of the options currently available, and their possible impact on delivering microsecond phase. Places at the Seminar are FREE - sign up HERE today.



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Phase Ready - Why Now?

Why is it important to consider phase synchronisation at the network edge when, at least here in the UK, you're only just rolling out your LTE Macro layer?

A valid question, but you may well also be rolling out 3G Small Cells for indoor coverage in public spaces and enterprises,data offload, or Outdoor Event systems. Choices that make perfect technical and economic sense for these systems may well come back to haunt you if you don't take heed of the future (and not so far flung future) phase requirements your network will have.

Take backhaul technologies for example. You will of course find backhaul that's perfectly suited to your requirement now; perhaps getting SyncE right out to the Small Cells to give great frequency sync for the Air Interface. But is this backhaul phase ready? When you need to overlay this great frequency network with PTP packets to get microsecond sync to Small Cells, will this backhaul deliver the timing performance you need?

Decisions taken now for Small Cells need to take account of the requirement you WILL have for phase when you're delivering LTE-A services. Think smart and you won't need to rip out your two year old backhaul network because it wasn't future proof.

Our "Is Your Network Phase Ready" seminar at Kings Place on May 8th has a session "Small Cells Backhaul - the “Wild West” Explained". We'll try to give an impartial view of the options currently available, and their possible impact on delivering microsecond phase. Places at the Seminar are FREE - sign up HERE today.

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Its Not Just Small Cells!

A recent Light Reading piece - eMBMS Unleashes New Potential for MBB Business Growth - shows that it won't just be the deployment of Small Cells and LTE-A that drives the need for phase synchronisation at the network edge.

eMBMS (Evolved Multimedia Broadcast Multicast Service) is the LTE flavour of MBMS; described by 3GPP for many years but not as yet deployed in any network - until now! Plans from Verizon and others have been announced to roll eMBMS services out over the next year or so, primarily for streaming live video content and supplying video on demand.

As content becomes king, delivery platform is less and less a concern for users. If their Mobile Carrier gives them Cable TV like services - with Cable like performance of course - why have separate subscriptions? But beware the fickle user. The Light Reading piece also says "Studies have also shown that for every second a user has to wait before an online video begins playing, 5.8% of all users will leave before the video ever loads ."

eMBMS relies on the creation of a Single Frequency Network (SFN) to send data simultaneously to many users in a sector, or between sectors. This will require microsecond phase alignment of cells to deliver this content efficiently, and eMBMS is equally at home in LTE-FDD networks as it will be in LTE-TDD.

So if you think "my FDD network doesn't need phase" well think again!

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Why Phase Ready?

Many of us have been, and are still, involved in the migration from SDH to Carrier Ethernet in networks; moving from the “certainties” of SDH timing to PTP and Synchronous Ethernet. The crossing of the “Bellhead / Nethead” boundary has mostly got beyond “Ethernet doesn’t need sync” and, in a surprisingly short period of time, getting good frequency performance to the edge of networks over Carrier Ethernet is just about done.

Now we see the next timing challenge on the horizon – PHASE synchronisation at the network edge. And the key driver for this requirement is not that networks will be using Time Domain transport technologies like LTE-TDD, but the coming of LTE-A, Heterogeneous Networks (HetNets), Small Cells and Enhanced InterCell Interference Coordination (eICIC).
It’s a given now (or seems to be) that in next generation mobile networks the Macro layer will simply not have the coverage and spectrum to deliver data densities and rates customers now require. The latest Small Cells Market Data white paper from the Small Cells Forum looks at the scale of likely rollouts. For example “Mobile Experts published a new forecast claiming that 70 million small cells will be shipped by 2017, including Femtocells deployed by mobile operators and picocells used for high-capacity urban networks. LTE small cells are a major part of the forecast growth over the next five years, with more than two-thirds of small cells deployed in 2017 devoted to LTE-FDD or TD-LTE.”

A blog post from leading industry consultant Frank Rayal called “More and More Small Cells, But Where’s the Gain?” notes that “In the absence of advanced interference management solutions, most capacity benefit will be obtained from deploying small cells in a targeted way with intimate knowledge of the location of traffic hotspot and interference profile. In other words, forget about mass uniform deployments for now. Planning will remain essential.”

Effective eICIC requires stringent phase synchronisation between deployed Small Cells and the Macro cell(s) under which they operate. And effective eICIC will be the tool to enable “mass uniform deployments”. This requirement and the issues around it are why we’ve launched

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