(Greek: near; resembling that which is named by the combining root)
Almost synchronous refers to a transmission where the sending and receiving devices are synchronized, but set to different clocks. Although the bits may not arrive in the same time slot as they were sent, as long as they arrive within a certain, defined range, the transmission is said to be plesiochronous (ples" ee AH kroh nuhs).
The term is used in the Plesiochronous Digital Hierarchy (PDH), the widely-used system in which the transmissions from one continent (such as, North America) are internetworked with transmissions in other continents (such as, Europe) by making small adjustments in the differing data rates between the systems. The European and American versions of the PDH system differ slightly in the details of their functions, but the principles are the same.
A plesiochronous situation can arise when two systems have slightly different clock readings over time. In such circumstances, one of the components, or a third system, would need to notice the mismatch and make some compensating adjustments; such as, repeating or deleting a data packet or frame.
2. Close to or nearly the same shape.
2. Characterized by a form which is similar or like another one.
An evolutionary trait that is homologous within a particular group of organisms but is not unique to members of that group and therefore cannot be used as a diagnostic or defining character for the group.
For example, vertebrae are found in zebras, cheetahs, and orangutans; but the common ancestor in which this trait first evolved is so distant that the trait is shared by many other animals. As a result, possession of vertebrae sheds no light on the phylogenetic relations of these three species.