scope:

General

The North American digital network is made up of sources of digital signals, including channel banks, digital switches, and multiplex equipment, interconnected by transmission facilities. These operate at several different bit rates. At any one level in the digital hierarchy there may be several signal sources with unique bit stream formats, but these need to have certain common characteristics to permit interconnection with transmission facilities at that level and with multiplex equipment connecting to a higher level.

The designation DSN or STS-N refers to those common features of the digital signal at the Nth level in the hierarchy. The levels in the North American digital network included in this standard are: DSl (1.544 Mbit/s), DSlC (3.152 Mbit/s), DS2 (6.312 Mbit/s), DS3 (44.736 Mbit/s), STS-1 (51.840 Mbit/s), DS4NA (139.264 Mbit/s), and STS-3 (155.520 Mbit/s). This standard also includes the DSlA (2.048 Mbit/s) level of the 2048 kbits/s hierarchy which is sometimes used for interconnection with networks using the North American hierarchy.