  With the advancement in telecommunications, packet traffic is rapidly
becoming the mainstream of data traffic. The use and deployment of Synchronous
Digital Hierarchy (SDH) networks for interconnection has gained traction
worldwide due to its flexibility and standard for interconnecting multiple
vendors, low operating cost and the high quality of service it provides.
Plesiochronous Digital Hierarchy (PDH) on the other hand has been used before
the introduction of the SDH standard and it also provides a means to transport
large quantity of data via digital equipment such as radio wave systems, optic
fibre and microwaves. In this paper, we shall discuss both PDH and SDH
technologies and identify some of the features of both and the issues in PDH
that brought about the introduction of the SDH technology.
