Cell Relay Archive

[hrood@xs4all.nl (Hendrik Rood)]

marcr@adc.com (Marc Randolph) enlightened me about:

>In article <ays-1408971748050001@pm3-ppp3.well.com>,
>Alan Y. Schaevitz <ays@hooked.net> wrote:
>[...]
>>
>>SONET's version of TDM).  One VT could carry ATM traffic while another
>>could carry, say, voice or video.  However, since ATM can carry voice and
>>video, what would be the point of segregating the SONET capacity?  TDM is
>>not really an efficient utilization of capacity.  That's why virtual
>>circuits are so popular.
>
>   The point of segregating the SONET capacity is legacy traffic.
>People are wanting to go to ATM, but for whatever reason, can't
>or won't give up their TDM (especially the LEC's and such).  ATM
>over SONET allows them to ease into ATM without losing their 
>existing TDM customers or equipment investments.

As a former telco systems engineer who was involved in puirchasing
both SDH and ATM I can give you my own view (widely shared in a lot of
companies)
1. Transmission equipment (SONET/SDH) is mostly hardware and
relatively light on embedded processors/management software.
Innovation speed in hardware is much higher.
2. There are a series of services which can be done by ATM, but are
easier to solve in simpler transmission solutions. Main service:
SDH/SONET drop and continue of digital broadcasting signals to
headends
3. Transmission departments have been culturally divided from
switching departments since a century. Transmission engineers and
designers have their roots in Cabling and Microwave/Radio. Wide area
datanetworking people in Telegraphy both do not have much knowledge of
Telephony and switching in particular.
I have personally observed that these differences continue to survive
all telco reorganisations. Administrative systems can be traced back
to either of these three roots. Telegraphy has evolved in most telco's
to leased line & wide area datanetworking departments. 
Transmission & Cablingpeople are nowadays busy in satellite, microwave
and optical equipment and all the twisted pair and coax techniques.
Telephony people nowadays are working more on software and system
management on public switches.
4. The organisational split is also seen in the suppliers chains. THey
are also organized in the same split.
5. Transmission departments are nowadays moving over to all optical
networks (optical cross-connects, wavelength division multiplexing,
fibre amplifiers etc.). In their purchasing for the year 2000
SONET/SDH is allready moving to the edges of the optical backbone
networks.

6. (A non argument). Telco's could buy Lucent Technologies 5ESS public
switch allready from the start with their own fibre optic cables
between the Host unit and the remote Switching modules. There has
hardly been any operator who did that. 

I have tought some SDH basics to a very senior switch engineer (An EE
MSc who erects local exchanges in third world countries during his
holidays) for his next international aid-job. He was extremely
surprised why the switch manufacturers had not yet integrated SONET
TDM interfaces on their public switches, because it was a much cheaper
and efficient solution. Well, I gave him the answer above. It has more
to do with culture than with technical efficiency. 

Somehow I feel the same bad mood when I here technicians deeply
involved in IP talking about ATM and vice-versa. They might both need
a "foe" to get a feeling of "competition".

So your question is not stupid, but it might be better to discuss this
with a professor in psychology (groupdynamics). 

Hendrik Rood