in the General/Verizon phone system we only converted from SXS equipment
in the late 80s
this was in southern Pa where I worked. We had computer controlled
systems but just to
set up connections the talk path was still relay. With the digital
conversion initially each branch
exchange locked off central. York Main was tied in to a master via a
dedicated T1! which in addition
to being the master also carried traffic. With the change over to Signal
System 7 which used a data
circuit that checked the status of each call and did or didnt set up a
talk path to the end switch
This was determined by this SS7 system. at around this time we started to
put Sat Receivers on each
exchange for locking each office. I believe the switches were good for
several weeks before
the LO went off ,, in the event of losing the Sat.
I retired in 99 so not sure where things are I hear the next big thing
will be VOIP which no longer
required near as many people to maintain and will replace the telephone
but will need fiber to the curb side ,, with the price of copper this
should happen pretty fast
to recover the salvage in all the cables
On Thu, 19 Jun 2008 18:28:56 +0100 "Andy Talbot"
<[email protected]> writes:
> Good - I'm glad to know the telecomms opeators have thought about
> vulnerabilities inherent with putting all their eggs into the GPS
> timing basket. I had been told - clearly from a not too informed
> source - that GPS timing units were used at each base station.
> Does the same apply to 3G (or GSM for that matter) mobile networks
> as well?
> Andy G4JNT
> 2008/6/19 Stewart Bryant <[email protected]>:
> > Andy Talbot wrote:
> >> The article has a very good point to make about GPS jamming
> though. I
> >> think its probably the first time I've seen it talked about in
> >> open-press. Our telecomms infrastructure now is so critically
> >> dependent on accurate timing that a few well deployed low power
> >> jammers could cause serious disruption.
> > Although modern communications systems are dependent on sync,
> > the current systems in the UK need frequency not time.
> > Although the UK SDH networks use GPS for local time sources,
> > to drive reference oscillators, all the systems I know
> > use multiple Cesiums as a backup. Most other networks
> > (for example the mobile phone networks) connect to
> > an SDH network by some means or other and take their sync
> > from that source.
> > The big R&D problem in this space is how we manage the
> > migration to packet networks with Ethernet delivery, and
> > great lengths are being taken to avoid the need to rely
> > on GPS for critical sync functions. Indeed GPS-only sync
> > would be regarded as a show-stopper by all of the sync
> > network designers I have spoken to.
> > A lot of newer sync technology (the media access systems)
> > needs relatively course (1us class) time as well as frequency
> > to function, but there is work in hand to deliver that
> > over packet networks (IEEE1588, IETF TICTOC etc)
> > So I would not worry about GPS jamming disrupting comms.
> > Navigation is a different matter, and as Alan says Loran
> > is vulnerable, perhaps not quite as vulnerable as civilian
> > GPS, but certainly more vulnerable than seems to be claimed.
> > Stewart/G3YSX
> Andy G4JNT
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