Information about the PDH hierarchies

E1 and T1 lines are the lowest level carriers in the plesiochronous digital hierarchies (PDHs). An E1 line multiplexes 32 individual telephone conversations on to a single line. A T1 line is similar but multiplexes 24 conversations on to the line.

The E- series is used in Europe and is based on the ITU standard G732, while the T- series is used in North America and is based on an AT & T standard.
An E1 line has a data rate of 2.048Mbps, while a T1 line has a data rate of 1.544Mbps. 4 E/T1 lines can be multiplexed together to form an E/T2 line and so on. This is where the "hierachies" come in. These lines are multiplexed together in a hierarchial structure.

Note: The PDH hierarchies are now being replaced by a new ITU standard called Synchronous Digial Hierarchies (SDH). More information about SDH can be found at WebDesk.


Link Overview of PDH and SDH
Link DataPro report on trends on multiplexing hierarchies
Link Information about SDH/SONET at WebDesk
Link SDH/SONET at TechFest

Previous pageReturn to previous page]

Introduction - Modems - ISDN - DSL - cable modems - Mobile comms - Conclusion - Glossary