The optical carrier CSI

The DS carrier service infrastructure gave us two important building blocks that were used to further extend the  capacity for supporting VoIP networks. First and  foremost, the  DS network established that analog signals could be regenerated in digital  format. Second, the  DS network established that digital  signals could be aggregated with other digitally regenerated signals in the  form of DS0 channels. Thus,  the  capability to channelize digital  bandwidth evolved. Dedicated channels have  proven that they  can support VoIP with
the  same if not  better quality of service that we have  come to expect with
POTS over  the  PSTN.

The DS CSI

In 1964, the  carriers began channelizing and  aggregating analog inbound tele- phone calls onto digital,  high-bandwidth transports. The digital service (DS) carrier service infrastructure was born. The type  of wiring used for DS trans- ports was copper, like the  PSTN transport lines  in the PSTN. The DS transport lines,  however, were of a thicker gauge  and  were capable of sustaining higher bandwidth capacities. The carrier often referred to DS type  transport lines  as “high-cap” T1 lines  to distinguish them from other types of copper transport lines  in the  PSTN. Today most T1 transport lines  are provided using  fiber- optic lines.

The PSTN CSI

The public switched telephone network (PSTN) is the  oldest CSI, actually beginning with the work of Alexander Graham  Bell in the late 1800s.

Over the years, carriers have been installing, expanding, improving, and inter- connecting various parts of the  PSTN. Compared to all other carrier service infrastructures, the  PSTN is the  largest.