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.

Symbiosis in Sync?

There’s currently lots of focus in the synchronisation industry on the concept of "on-path support" - making network elements timing aware and treating timing protocols (e.g. PTP packets) differently to other services. This typically means implementing a "Boundary Clock" or a "Transparent Clock", in which efforts are made to mitigate or eliminate the variable delays that timing packets experience when being switched through a network element. These types of techniques are seen as necessary to achieve the sort of phase-sync performance levels that the ITU-T and 3GPP are working on to support some of the LTE-A technologies talked about elsewhere on this blog. Increasingly there is a realisation that on-path support can also extend to "frequency assistance" from the physical layer. This implies a PRC-traceable frequency is somehow available to the element, either through classical SDH/SONET or Synchronous Ethernet sync trails, or possibly even a co-located or integrated GNSS timing receiver - integrating the SETS function from the physical layer with the time/phase functions from the packet-layer clocks. 

When "Next Generation Networks" were first mooted in the mid-00s, it seemed like there was a need for a new implementation of a single synchronisation technology to solve all the problems, as if either one of SyncE OR PTP would win the day. What is becoming more and more apparent is that both SyncE AND PTP AND now even GNSS technologies are part of the overall sync solution; techniques available for deployment in the toolbox of the network planners & designers. Some of the more elegant & sophisticated sync services I’ve seen recently are provided by integrating 2 or more of whatever sync technologies are available.

“Symbiosis” in a term usually applied to biological species that somehow live together for mutual benefit, but I’ve often seen it applied in a technological sense - and seems to fit right here - e.g SyncE and PTP can and do work together to increase the performance of the phase & time services that are being delivered.

SyncE is used as a source of long-term PRC-level stability that can drive a timebase with which packet timestamps are measured and hence network delays are estimated. Consider the usual implementation of a PTP Slave - its timebase is its local oscillator and the budget for this component will dictate the stability available to the algorithms that are time-stamping the PTP packets, estimating network delays and hence synthesising or steering that local timebase. Generally, the locking process of a PTP Slave is a two stage process: first, frequency lock is achieved with the master, and then phase lock is achieved. If physical layer frequency stability is available, then one immediate benefit is it speeds up the initial locking stage, as frequency-lock can generally be achieved much quicker with the physical layer signals than the packet layer. Once frequency and phase time lock is reached, having a stable frequency can holdover the phase/time lock through brief periods of packet loss, or through large step-changes in measured network delay (e.g. caused by network topology change/packet re-routes) hence vastly increasing the available performance available to network operators without having to deploy (relatively more expensive) atomic clocks.

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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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LTE-B: Terrible TLA but coming to a device near you soon

One of the key upcoming technologies in the 3GPP world for some years now has been MBMS "Multimedia Broadcast Multicast Service" and latterly eMBMS "Evolved Multimedia Broadcast Multicast Service". This allows adjacent sites to transmit the same broadcast data, allowing devices an effectively higher data rate for streaming content. Promised but as yet undelievered, eMBMS requires microsecond (1us to 32us dependent on implementation) phase synchronisation between sites.

Three stories have appeared in short order to show this technology is becoming a reality. Last week Samsung announced they are working with Korea Telecom to deliver eMBMS services to their LTE subscribers. This was quickly followed by Verizon trialing "LTE Multicast" tied to the Super Bowl, and Telstra conducting the first stadium trial of "LTE Broadcast" at a T20 Cricket match at the MCG (well they call T20 Cricket but that's a subject I'm not going to touch here!).

I feel the marketeers won't be able to resist using LTE-B for this. Its even better than LTE-A!!

 

 

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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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Phase Performance Requirements

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Beyond G.811? Standards Supporting Phase Requirements

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Preparing for Phase Delivery - Ensuring GPS is fit for Phase

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Beyond G.811? GPS and Phase

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Beyond G.811? Phase Error v Frequency Error

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Beyond G.811? Time Accuracy Requirements

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Small Cells World Summit Report - David Chambers

Good overview of the Summit from Think Small Cells's David Chambers HERE. Particular interest for me in the embedded video of interviews David conducted is Todd Mersch of Radisys talking about the two key areas that will be exploited from LTE-A. Todd can of course speak for himself but the two areas he identified - Carrier Aggregation (CA) and SON / Interference Mitigation - will have stringent phase sync requirements!

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First Small Cells Backhaul Summit a success

Just back from the Small Cells World Summit and decided to sit in on the whole of the inaugural Backhaul Summit track. Had to sit on my hands at times to not ask the "what about phase sync?" question, but I was pleasantly surprised that there was some awareness at least of the challenges coming our way.

Some very interesting battles to come in the sub 6GHz non line of sight area if the debates at this summit were anything to go by!

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Sync MasterClass - updated sections on phase & time

With the explosion of HetNets and Small Cells as solutions to the problem of ever-increasing demand for mobile services, the Synchronisation MasterClass now includes updated sections covering phase and time synchronisation - valuable tools in Network Operators' strategies to manage and integrate these new nodes into their existing networks, enabling rapid deployment of 4G-and-beyond services. 

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Preparing for Phase

Chronos is preparing to attend Alcatel-Lucent’s SReXperts event being held 3-6 June in Prague. Chronos will share with Alcatel’s invited guests its experiences in helping operators, manufacturers and system integrators prepare networks to support Phase. 

As delegates heard at our recent Phase Ready event held in London, Phase is not only required for TDD technology but also for small cell deployment and other applications riding over FDD technology.  Chronos is already supporting operators as they execute active internal projects to make their networks “Phase Ready”.

Chronos has assisted many fixed and mobile operators prepare for supporting frequency synchronisation over Ethernet/IP networks using PTP and now that very same PTP deployment is expected to support the delivery of Phase to the network edge.   Our customers need to determine what is the most efficient, technical and cost-effective way to characterise their current PTP deployment so they can determine what changes, if any, are required to support Phase in their network.

Chronos will demonstrate the engineering and operational tools available to help the vendor selection process, system deployment and the on-going operational support of PTP within networks whether it is to deliver frequency or Phase.

If you are attending the SReXperts event and wish to meet Chronos staff please contact your Alcatel-Lucent account team direct or Chronos.

 

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Presentations available: Is your Network Phase Ready?

Presentations available: Is your Network Phase Ready?

Presentations from the Chronos 'Is your Network Phase Ready?' event held at Kings Place, London on 8 May 2013 are now available to download.  Authors include Simon Saunders - Real Wireless; Martin Kingston - EE; Chris Farrow and Chris Roberts - Chronos Technology.

www.phaseready.com

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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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Tim Frost, Principal Technologist with Symmetricom to deliver Network Time Distribution for Small Cells

Small cells pose a particular challenge for synchronization.  Not only are they small, inexpensive devices, they are often indoors, and connected over low grade, low cost access technology.  However, depending on their location, the synchronization requirements of a small cell are similar to those of a macrocell.

This paper looks at the different deployment scenarios for small cell, and the time and frequency accuracy requirements in each case. It addresses the various ways in which time and frequency can be distributed to small cells, including packet-based timing (e.g. PTP), physical layer timing (e.g. SyncE) and satellite timing (e.g. GPS).

Finally, it looks at ways in which each of these can be combined to produce a solution that will work in each of the varied deployment situations that may exist.  Each of these technologies can be used symbiotically to complement the weaknesses of each other, and in some cases to improve the overall performance of the system.   It will also consider the potential architecture for synchronization distribution to allow such complementary operation. The result is a time distribution system of high accuracy and high reliability that can be trusted to support the many revenue-earning and critical applications dependent on accurate time.

Join us at our free event at Kings Place, London on 8 May - Is Your Network Phase Ready?

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