[LEAPSECS] Mobile network time

[Warner Losh]

On Jul 23, 2013, at 10:20 AM, Ask Bjørn Hansen wrote:


> 

> On Jul 23, 2013, at 9:00, Warner Losh wrote:

> 

>> Cellular *NETWORKS* know what time it is down to the microsecond level, but that isn't want's displayed on the phone...

> 

> At the recent leap seconds the clocks known to sync time off the CDMA network were among the last to "jump" the second (days later).  (Which I guess for their purposes (have a synchronized clock) is fine.


CDMA networks must be synced to the sub-millisecond level for the phones to work. It has been 20 years since I was doing time stuff there, but the synchronization is to the GPS time with extra data provided to recover UTC from that time. But these timing functions are generally unavailable to the handset outside of the CDMA chipset.


> I might be wrong, but I didn't think GSM networks needed a synchronized clock.


GSM networks require stable frequency to interface properly to other networks. There's a number of different standards that need to be met by different timing elements in the GSM network. There may not be an absolute phase element like CDMA has. A quick google search was unfruitful on this point.

Warner