EXFO FTB-8510B Guia Del Usuario página 1271

Glossary
SDH Numbering Convention
DSn/PDH Numbering Convention
The DS1 numbering in DS3 shall be numbered with respect to the DS2
muxing [DS2,DS1]. For example a DS3 has 7 DS2 and a DS2 has 4 DS1, so
an example would be for a DS1 number [3,2]. The DS3 shall have a single
number to represent its position. That is [1] all the time whether it is used
in an STS-1 or it is the DS3 electrical interface.
The PDH do not have special grouping of the E1, E2, E3 or E4. This means
that the PDH has a single number. For example E1 number 2 shall be
number [2].
The E1 in DS3 via G.747 numbering uses the naming [DS2,E1]. However in
the grid the label shall adapt itself to DS2 [x] or 6.3M [x] (where x = 1 to 7)
with respect to the interface standard used: European or International.
621
SONET/SDH Application