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 N- the level in the hierarchy. The levels in the North American digital network included in this standard are: DS1 (1.544 Mbit/s), DS1C (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 DS1A (2.048 Mbit/s) level of the 2048 kbits/s hierarchy which is sometimes used for interconnection with networks using the North American hierarcy.

Cross-connects

Any digital equipment, e.g., a multiplex or transmission facility, may be terminated on both ends at equipment capable of supporting a standard level interface. This (cross-connect) equipment provides a convenient central facility for circuit rearrangements, patching, and testing purposes. The implementation of the interface is not constrained to follow a particular technological approach but as an aid in transmission loss budgeting, annex B describes details of hard-wired, manual cross-connect equipment widely used in the North American network for providing the cross-connect and interface functions.

Interface specification

A DSN or STS-N level interconnection specification describes the electrical and physical characteristics for signals appearing at the appropriate level digital interface. IT does not explicitly specify parameters either for transmitting or receiving equipment or for the cabling that connects such equipment to the interface¹⁾. Annex C describes the cabling characteristics widely in use in the North American network.

Equipment characteristics are described here only to the extent necessary to assure proper operation of transmission facilities and higher order multiplex equipment. End-to-end compatibility of two digital terminals is not assured by adherence to these interconnection specifications alone.

¹⁾ It is the responsibility of the manufacturer to specify to specify the conditions under which their equipment meets the specifications in this standard.