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year2525
year2525
12/16/2013 | 2:40:03 PM
Re: Need for fallback
So is it, to your knowledge, being implemented in small cells yet?

Weiss seemed to believe that European carriers were spending more on alternatives to GPS than their US counterparts.
Vitesse Semiconductor
Vitesse Semiconductor
12/16/2013 | 2:37:14 PM
Re: Need for fallback
It is already commercially available
year2525
year2525
12/16/2013 | 1:22:50 PM
Re: Need for fallback
So would you say this silicon is widely commercially available yet? Or testing, sampling etc?
Vitesse Semiconductor
Vitesse Semiconductor
12/16/2013 | 1:16:16 PM
Re: Need for fallback
We agree, in part, with Dr. Weiss' assertion that PTP can only maintain timing over a couple of hops. However, this is an implementation issue, rather than a protocol-specific issue. If network operators implement a simple, low-cost transparent clock or boundary clock on intermediate nodes, they can maintain PTP timing over many, many hops. An ITU-T demonstration in 2012 showed that time stamping in the PHY chips can keep time errors around 25-50ns – even over 10 hops. For transparent clocks, these time errors can be filtered out so they typically will perform even better.  This level of accuracy is sufficient even for LTE-Advanced, which requires times errors of 500ns or less. For macro networks, therefore, PTP can be a perfect backup to GPS. Plus, operators can move grand master clocks further into the network to be housed in secure locations where GPS is harder to compromise.

For small cell networks though, GPS becomes far less reliable. Thanks to recent advances in silicon technology, PTP can maintain timing without interfering with network encryption. Any multi-hop network requires this combination of security and timing, but small cells are particularly vulnerable and will need to rely on PTP as the primary timing solution.

Sarah Reedy's article from late November, and the discussion that followed, highlighted small cells' dual challenge of security and timing:

http://www.lightreading.com/mobile/mobile-security/small-cells-exposed!-securing-the-mini-rans/d/d-id/706759
DanJones
DanJones
12/11/2013 | 11:34:34 AM
Re: Need for fallback
Yep, add more LTE cells in the form of small cells and the sync and phase problem gets worse too.
rameshchandra0
rameshchandra0
12/11/2013 | 1:22:46 AM
Re: Need for fallback
This is more prone to LTE because of phase requirement. I guess, development of boundary clock functionality in transport shall maintain phase & frequency to more number of hops in PTP. Having PTP does not rule out jamming of GPS used with Grandmaster impacting whole network.

There is need for develoment of periodic reactivation of GPS while Grandmaser is in holdover mode for couple of hours. 

Ramesh
DanJones
DanJones
12/10/2013 | 11:08:07 AM
Re: Need for fallback
Yes, Weiss suggested that European carriers are actually spending more on hardware assisted PTP, which he said works as a back-up/supplement to GPS.

He doesn't think US carriers are investing in assisted PTP so much because they haven't seen problems with GPS yet and so don't see the need to spend the money on it.
MordyK
MordyK
12/10/2013 | 10:41:00 AM
Need for fallback
This highlights the need for backups to the "newfangled" technologies.

The early cellphone and car navigation systems relied solely on GPS which caused problems in urban canyons and under overpasses, but adding in WiFi and Cell ID along with sensor fusion which brought the old dead reckoning into the mix improved it.

The same applies to all new technologies, where its important not to forget the old which can be used as a fallback as well as creating backups - even at considerable expense - to ensure that services we come to rely on simply don't collapse.

During the blackout a few years back this came to the fore when old plain phones had DC power and service but most peopledidnt have operating phones because the were using "smarter"phones - or VoIP - which required AC power, which was also why the internet went down.

This same issue arose with Sandy when cell towers relied on a single source of both power and backhaul, which when cut effectively disabled the network (even with a few hours of diesel). There are technologies such as microwave and some new power sources which while expensive can be used for alternative sources, which although not cost effective nor "entirely" capable of supoporting our new needs, can still provide interim reduced capabilities.


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