™ Common carrier Services & Hierarchies
o Telephone companies began by providing
their subscribers with ANALOG services
using
ANALOG networks
o Later digital services were introduced
o Nowadays carriers are even thinking about
changing their service lines digital too
o Soon the entire n/w will be digital
o For now both types of services are
available and both FDM and TDM are in use
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™ Analog Services
o Of the many analog services available to
telephone subscribers, two are really
important:
-Switched
Analog Services
-Leased Analog
Services
o Familiar dial up service most often
encountered when using a home telephone
o Uses twisted pair cable to connect subscriber's
phone to the network via exchange
o This connection is called LOCAL LOOP
o The n/w it joins is called PSTN
o Signal on a local loop is Analog and BW
is usually b/w 0 and 4000 Hz
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