Re: [ntp:questions] UK report on GPS vulnerabilities seems to overlook NTP
Harlan Stenn wrote: Uwe wrote: No GPS seems to kill any CDMA mobile networks. GSM isn't affected at all. How masochistic must one be to do telco infrastructure in such a haphazard way? That seems more sadistic than masochistic to me... H hehe. But it will fall back on you. That is the maso part, right ? G! uwe ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] UK report on GPS vulnerabilities seems to overlook NTP
"Chris Albertson" wrote in message news:aanlktimwu-ezzxv9pp-gbg9mft1ylhsf9edrdzlkj...@mail.gmail.com... > I can't defend the design of CDMA cell technology. But I'm sure a lot > of it was driven by trying to get as many calls as possible into a > limited bandwidth. Another requirement for precision timing comes > from the need to measure the signal's speed of light delay. They use > this to locate a phone by noting the differences in the delay to > several towers A uS is about 1000 feet so they need to do this far > better than to a uS. There are lots of other systems that will break as well that people didn't think of; Clustered microwave links Clustered WiMAX and point to multi point data access points TETRA P.25 (I think depending on the configuration) Motorola SmartZone & SmartNET (Depending on configuration) Digital Quazi/Simulcast radio networks (Mototurbo) Some of those platforms accept any valid clocking source but most depend in there default setup on GPS. So far as time of day goes - The people's systems I deal with have S0 GPS and MSF or DCF77 inputs to there S1 devices so that will be fine - Alas we don't have any proper caesium clock sources. ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] UK report on GPS vulnerabilities seems to overlook NTP
Uwe Klein wrote: > Chris Albertson wrote: >> NTP simply is not good enough for use in a tower so it is not used. >> And why would they use it when all towers by definition have a clear >> view of the sky > > IMHO the basic concept of your system is broken when you have > sync to such high requirements and need external infrastructure > to achieve this. > this then is an extremely fickle system that lacks robustness. > > uwe Then every system ever made that has the concept of a master timing clock, including TV and the computer you are working on, is "an extremely fickle system that lacks robustness". The concept hasn't changed over the years, just that we have progressed from R/C oscillators to crystal oscillators to GPS. Perhaps you think we would be better off if such systems had a master crystal osillator somewhere with coax to every remote system to keep them all in sync? -- Jim Pennino Remove .spam.sux to reply. ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] UK report on GPS vulnerabilities seems to overlook NTP
On Tue, Mar 8, 2011 at 1:14 PM, Uwe Klein wrote: > IMHO the basic concept of your system is broken when you have > sync to such high requirements and need external infrastructure > to achieve this. > this then is an extremely fickle system that lacks robustness. I can't defend the design of CDMA cell technology. But I'm sure a lot of it was driven by trying to get as many calls as possible into a limited bandwidth. Another requirement for precision timing comes from the need to measure the signal's speed of light delay. They use this to locate a phone by noting the differences in the delay to several towers A uS is about 1000 feet so they need to do this far better than to a uS. Does it lack robustness? Some phone companies publish their system availability statistics. I guess we could look it up. No need to speculate if such a system would work or not. Timing is actually simple and robust. The central part is a very stable local 10MHz oscillator. All the timing is derived from that local source. Then they have A GPS receiver that outputs one pulse per second. Every second they measure the time from the leading edge of the pulse to the next zero crossing of the oscillator and periodically adjust the oscillator frequency to keep that time a constant. It is robust in that if GPS goes away all that happens is the oscillator is no longer measured. But if it is well built, the oscillator will run correctly for a long time without adjustment. The system does not crash if GPS goes away. = Chris Albertson Redondo Beach, California ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] UK report on GPS vulnerabilities seems to overlook NTP
Chris Albertson wrote: NTP simply is not good enough for use in a tower so it is not used. And why would they use it when all towers by definition have a clear view of the sky IMHO the basic concept of your system is broken when you have sync to such high requirements and need external infrastructure to achieve this. this then is an extremely fickle system that lacks robustness. uwe ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] UK report on GPS vulnerabilities seems to overlook NTP
Uwe wrote: > No GPS seems to kill any CDMA mobile networks. > GSM isn't affected at all. > > How masochistic must one be to do telco infrastructure in such > a haphazard way? That seems more sadistic than masochistic to me... H ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] UK report on GPS vulnerabilities seems to overlook NTP
On Mar 8, 2011, at 11:28 AM, Chris Albertson wrote: >> And exactly what is that difference? While ntp is perhaps too slow to >> respond to local frequency changes, how do you see the difference >> between keeping a computer's idea of local time accurate from keeping a >> telecom's idea of local time accurate? > > The telecom equipment needs to know the time with less then one > microsecond error and to do that requires a clock that is at least 10X > better. NTP typicaly works at the microsecond level and has error > 1000X more than is required. It depends on which telecom equipment we're talking about; for example, the CDMA spec (IS-95, IS-2000 aka CDMA2000) requires the cell towers to be sync'ed to better than 10 microseconds. Without making any special efforts (ie, just using random NTP servers from the pool), NTPd does typically offer around a 1 millisecond accuracy. People who care a bit might configure nearby time sources and set up local peers, which will probably give accuracy around the +/- 100 microsecond level, and anyone who seriously cares about good timekeeping will find a way of using a PPS signal, in which case with kernel PPS_SYNC discipline, you can get accuracy better than microsecond level, depending on the quality of the PPS signal. For example, PHK measured +/- 120 nanosecond accuracy using relatively inexpensive Soekris hardware: http://phk.freebsd.dk/soekris/pps/ Regards, -- -Chuck ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] UK report on GPS vulnerabilities seems to overlook NTP
unruh wrote: > On 2011-03-08, j...@specsol.spam.sux.com wrote: >> JohnAllen wrote: >>> Maybe I read this too quickly, but the report published today by the >>> UK Royal Academy of Engineering (see >>> http://www.raeng.org.uk/news/publications/list/reports/RAoE_Global_Navigation_Systems_Report.pdf >>> and also the BBC coverage at >>> http://www.bbc.co.uk/news/science-environment-12668230) >>> seems to be saying that many organisations are vulnerable to GPS >>> failures because their IT systems rely on GPS for precise time. >>> >>> Can this be true? I would have thought that most systems are using >>> NTP, and synchronising with diverse enough time sources that >>> unavailable or incorrect GPS time would not cause short-term problems. >>> >>> The relevant part of the report is on pages 13-14, where it says: >>> >>> "GNSS timing is important for telecommunications applications. >>> Synchronous >>> technologies are much more efficient than asynchronous technologies >>> but require a >>> time source with appropriate accuracy, stability and reliability to >>> operate effectively >>> or at all, and GNSS can provide this. While ground-based clocks are >>> accurate enough >>> for this purpose (especially with the availability of chip scale >>> atomic clocks (CSAC)), >>> the synchronisation of many such clocks is problematic. GPS allows the >>> derivation of >>> synchronised UTC through resolving the signals from a number of >>> satellites at a >>> known position. Only a ???good guess??? of the current time is required >>> and quartz clocks >>> have therefore been adequate for this process making synchronous time >>> keeping >>> significantly more cost effective. >>> >>> The use of time can be split into three clear and separate aspects: >>> frequency >>> control, time of day and common epoch (usually UTC) time slot >>> alignment (also >>> known as ???Phase???). >>> Stability of radio communications transmission, constant digital traic >>> low, time >>> slot alignment and traditional services over next generation Ethernet >>> based >>> infrastructure are some of the features that good time and timing >>> bring to >>> communications networks. >>> Financial systems increasingly need precise time stamping to >>> prioritise trades and >>> to provide an audit trail." >>> >>> NTP is not mentioned anywhere in the report. >> >> Nor would I expect it to be. >> >> There is a big difference between keeping a computer's time of day clock >> set to the current time (NTP) and maintaining timing or frequency control >> in a telecom system. > > And exactly what is that difference? While ntp is perhaps too slow to > respond to local frequency changes, how do you see the difference > between keeping a computer's idea of local time accurate from keeping a > telecom's idea of local time accurate? Most telecom systems care very little that it is exactly 12:34:56 Tuesday and a lot that the leading edge of the XYZ sync pulse occurs every ABC milliseconds and is DEF milliseconds wide, for example. The difference is the difference between "time" and "timing". Some systems don't care what the time of day is at all but do care about timing. -- Jim Pennino Remove .spam.sux to reply. ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] UK report on GPS vulnerabilities seems to overlook NTP
Jan Ceuleers wrote: On 08/03/11 19:39, unruh wrote: And exactly what is that difference? While ntp is perhaps too slow to respond to local frequency changes, how do you see the difference between keeping a computer's idea of local time accurate from keeping a telecom's idea of local time accurate? GPS is used not only for navigation and time-of-day synchronisation, but also as a source of frequency signals for use by synchronous (e.g. SDH) or plesiosynchronous (e.g. PDH) networks. Jan I was really surprised when this came up recently. No GPS seems to kill any CDMA mobile networks. GSM isn't affected at all. How masochistic must one be to do telco infrastructure in such a haphazard way? uwe ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] UK report on GPS vulnerabilities seems to overlook NTP
On 08/03/11 19:39, unruh wrote: And exactly what is that difference? While ntp is perhaps too slow to respond to local frequency changes, how do you see the difference between keeping a computer's idea of local time accurate from keeping a telecom's idea of local time accurate? GPS is used not only for navigation and time-of-day synchronisation, but also as a source of frequency signals for use by synchronous (e.g. SDH) or plesiosynchronous (e.g. PDH) networks. Jan ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] UK report on GPS vulnerabilities seems to overlook NTP
>> There is a big difference between keeping a computer's time of day clock >> set to the current time (NTP) and maintaining timing or frequency control >> in a telecom system. > > And exactly what is that difference? While ntp is perhaps too slow to > respond to local frequency changes, how do you see the difference > between keeping a computer's idea of local time accurate from keeping a > telecom's idea of local time accurate? The telecom equipment needs to know the time with less then one microsecond error and to do that requires a clock that is at least 10X better. NTP typicaly works at the microsecond level and has error 1000X more than is required. It's for the same reason a cloth tape measure is perfectly good for a dress maker but useless to a machinist. NTP simply is not good enough for use in a tower so it is not used. And why would they use it when all towers by definition have a clear view of the sky = Chris Albertson Redondo Beach, California ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] UK report on GPS vulnerabilities seems to overlook NTP
On 2011-03-08, j...@specsol.spam.sux.com wrote: > JohnAllen wrote: >> Maybe I read this too quickly, but the report published today by the >> UK Royal Academy of Engineering (see >> http://www.raeng.org.uk/news/publications/list/reports/RAoE_Global_Navigation_Systems_Report.pdf >> and also the BBC coverage at >> http://www.bbc.co.uk/news/science-environment-12668230) >> seems to be saying that many organisations are vulnerable to GPS >> failures because their IT systems rely on GPS for precise time. >> >> Can this be true? I would have thought that most systems are using >> NTP, and synchronising with diverse enough time sources that >> unavailable or incorrect GPS time would not cause short-term problems. >> >> The relevant part of the report is on pages 13-14, where it says: >> >> "GNSS timing is important for telecommunications applications. >> Synchronous >> technologies are much more efficient than asynchronous technologies >> but require a >> time source with appropriate accuracy, stability and reliability to >> operate effectively >> or at all, and GNSS can provide this. While ground-based clocks are >> accurate enough >> for this purpose (especially with the availability of chip scale >> atomic clocks (CSAC)), >> the synchronisation of many such clocks is problematic. GPS allows the >> derivation of >> synchronised UTC through resolving the signals from a number of >> satellites at a >> known position. Only a ???good guess??? of the current time is required >> and quartz clocks >> have therefore been adequate for this process making synchronous time >> keeping >> significantly more cost effective. >> >> The use of time can be split into three clear and separate aspects: >> frequency >> control, time of day and common epoch (usually UTC) time slot >> alignment (also >> known as ???Phase???). >> Stability of radio communications transmission, constant digital traic >> low, time >> slot alignment and traditional services over next generation Ethernet >> based >> infrastructure are some of the features that good time and timing >> bring to >> communications networks. >> Financial systems increasingly need precise time stamping to >> prioritise trades and >> to provide an audit trail." >> >> NTP is not mentioned anywhere in the report. > > Nor would I expect it to be. > > There is a big difference between keeping a computer's time of day clock > set to the current time (NTP) and maintaining timing or frequency control > in a telecom system. And exactly what is that difference? While ntp is perhaps too slow to respond to local frequency changes, how do you see the difference between keeping a computer's idea of local time accurate from keeping a telecom's idea of local time accurate? > > > ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] UK report on GPS vulnerabilities seems to overlook NTP
JohnAllen wrote: > Maybe I read this too quickly, but the report published today by the > UK Royal Academy of Engineering (see > http://www.raeng.org.uk/news/publications/list/reports/RAoE_Global_Navigation_Systems_Report.pdf > and also the BBC coverage at > http://www.bbc.co.uk/news/science-environment-12668230) > seems to be saying that many organisations are vulnerable to GPS > failures because their IT systems rely on GPS for precise time. > > Can this be true? I would have thought that most systems are using > NTP, and synchronising with diverse enough time sources that > unavailable or incorrect GPS time would not cause short-term problems. > > The relevant part of the report is on pages 13-14, where it says: > > "GNSS timing is important for telecommunications applications. > Synchronous > technologies are much more efficient than asynchronous technologies > but require a > time source with appropriate accuracy, stability and reliability to > operate effectively > or at all, and GNSS can provide this. While ground-based clocks are > accurate enough > for this purpose (especially with the availability of chip scale > atomic clocks (CSAC)), > the synchronisation of many such clocks is problematic. GPS allows the > derivation of > synchronised UTC through resolving the signals from a number of > satellites at a > known position. Only a ‘good guess’ of the current time is required > and quartz clocks > have therefore been adequate for this process making synchronous time > keeping > significantly more cost effective. > > The use of time can be split into three clear and separate aspects: > frequency > control, time of day and common epoch (usually UTC) time slot > alignment (also > known as ‘Phase’). > Stability of radio communications transmission, constant digital traic > low, time > slot alignment and traditional services over next generation Ethernet > based > infrastructure are some of the features that good time and timing > bring to > communications networks. > Financial systems increasingly need precise time stamping to > prioritise trades and > to provide an audit trail." > > NTP is not mentioned anywhere in the report. Nor would I expect it to be. There is a big difference between keeping a computer's time of day clock set to the current time (NTP) and maintaining timing or frequency control in a telecom system. -- Jim Pennino Remove .spam.sux to reply. ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] UK report on GPS vulnerabilities seems to overlook NTP
JohnAllen wrote: Maybe I read this too quickly, but the report published today by the UK Royal Academy of Engineering (see http://www.raeng.org.uk/news/publications/list/reports/RAoE_Global_Navigation_Systems_Report.pdf and also the BBC coverage at http://www.bbc.co.uk/news/science-environment-12668230) seems to be saying that many organisations are vulnerable to GPS failures because their IT systems rely on GPS for precise time. Can this be true? I would have thought that most systems are using NTP, and synchronising with diverse enough time sources that unavailable or incorrect GPS time would not cause short-term problems. Most corporate ntp setups are probably using only network sources, and most of those lead to a gps as the S1 reference. There are however alternative clock sources, and many of the pool servers use multiple references. When GPS is temporarily unavailable, large parts of the ntp network will drop down one or two stratum levels, but we won't get too many orphaned islands. My corporate setup with 3 Oncore gps clocks use both pool servers and configured internet sources, I know that a couple of these use radio clocks, so my internal network will drop from S2 to S4 or so. Terje -- - "almost all programming can be viewed as an exercise in caching" ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
