[Gllug] Data pots and optics

[John Hearns]

On Sat, 2005-07-02 at 12:41 +0100, t.clarke wrote:

> (or something along those lines!).  My limited understanding of current
> telephony is that the digitised analogue voice signals are carried in quite
> small 'packets' over some sort of time-multiplexed system such that once the
> route is established a dedicated amount of bandwidth is allocated to the call
> so that the digitised voice arrives at the other end nicely in sync with no
> 'jitter' or loss and relatively low latency.  This would not seem to be the
> case if IP is used to transport the data (bigger packets? - greater latency? -
> packet loss and jitter??).  Or am I missing something.  Some enlightenment
> from those with greater knowledge would be appreciated.
Not much greater knowledge here!
64K circuits for voice (hence ISDN lines being, conicidentally, 64K)

The 64K circuits are multiplexed together, as you say, into a series of
larger and larger trunks.
The overall term for this is SONET - Synchronous Optical Network.
So any large data pipe would be a multiple of 64K.
I believe the US and the rest of the world used different multiples, but
I may be wrong.

My knowledge is out of date, as AFAIK BT is switching over to a fully IP
based network.  Marconi, the British company who used to provide a large
part of the SONET kit failed to gain the contract and so is in big
trouble.

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