Data Line Speeds

North American Digital Signal Hierarchy

The hierarchy defines the levels of multiplexing i.e. the first level of the hierarchy multiplexes (combines) a number of DS0s into a single digital signal (with a DSx designator) which is then placed on a carrier (with a T-x designator). The DSx defines an abstract signal or speed and the T-x defines a physical 'pipe' or format. The DSx and T-x series specs and most other telecom related specifications are standardized by the ANSI accredited Committee T1 (T1E1) (now part of Alliance for Telecommunications Industry solutions - ATIS) which then represents (via the US State Department) the US at ITU standard sessions.

Remember: a DS0 is 64K or 64,000 bits per second.

Notes:
BITDROPPING
Now if you have not been sleeping you will have figured out that for a T1 if you multiply 24 x DS0 (64,000) you do NOT get 1.544 Mbit/s (that would be 24 * 64,000 = 1.536 Mbit/s). The extra bits are lost between 'frames' where a frame consists of one 8 bit sample for each of the 24 channels (remember the DS0 basics). So every 192 bits (24 x 8 = 192) we add a 'frame separator' bit to give 193 bits per frame. The final arithmetic is 193 bits x 8K samples = 1.544 Mbit/s. Easy really.

If you do the same arithmetic for DS1C, T2 etc. the above will not give the right answer. In short above T1 things get even messier with M-Frames and M-subframes. Its mind numbing stuff and if you really want to know you need ANSI T1.107-2002 and lots of coffee.

European Digital Signal Hierarchy

Notes:
While the table above shows the European carriers as E-1, E-3 etc. in similar format to the American T-1 etc. this is of relatively recent vintage. The original carrier names were CEPT-1, CEPT-3 etc.

Summary Table

Notes:
The rates above T-3, E-3 etc are normally now optical (see below)

Optical Carrier Rates