This is the basic service and was the first to be standardized. For transporting PDH over SDH, there are units called containers (C-n) that divide the data into packets. This is due to the fact that the tributaries are from plesiochronous networks, which makes it necessary to carry out a justification process. This process adapts the plesiochronous bit rate to the pre-established nominal bit rate in order to introduce each tributary in the SDH network. All the rates defined in the PDH hierarchies have specific containers associated to them. This was an initial requirement to ensure the compatability of European and American hierarchies and migration from the PDH base already installed.

Many voice and data networks use this service. For instance, a GSM network where only the interface between the mobile and the base station is wireless and the rest are 2 Mbit/s PDH circuits. Other networks like the PSTN, ISDN, Frame Relay and leased lines also use PDH circuits to interconnect their respective switching exchanges.