Editing E-carrier (section)

==Hierarchy levels==
The [[Plesiochronous Digital Hierarchy|PDH]] based on the E0 signal rate is designed so that each higher level can [[Multiplexing|multiplex]] a set of lower level signals. Framed E1 is designed to carry 30 or 31 E0 data channels plus 1 or 2 special channels, all other levels are designed to carry 4 signals from the level below. Because of the necessity for overhead bits, and justification bits to account for rate differences between sections of the network, each subsequent level has a capacity greater than would be expected from simply multiplying the lower level signal rate (so for example E2 is 8.448&nbsp;Mbit/s and not 8.192&nbsp;Mbit/s as one might expect when multiplying the E1 rate by 4).

Note, because bit interleaving is used, it is very difficult to demultiplex low level tributaries directly, requiring equipment to individually demultiplex every single level down to the one that is required.

{{see also|Comparison of T-carrier and E-carrier systems}}