plesio-, plesi-

Derived from the Greek plesio, "near, close", and chronos, "time", and refers to the fact that plesiochronous systems run in a situation when different parts of the system are almost, but not quite perfectly, synchronized.

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.

Similar in form.

Nearly alike in form.

An ancestral or primitive character.

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.

A symptom exhibited by tissues not yet dead but in the process of dying; wilting for example.

A “near” (“approximate to the Saurians”) from Early Jurassic Europe (England and Germany). It was not a dinosaur. Named by De la Beche and William Daniel Conybeare in 1821.

Nearly simultaneous; (broadly) happening at the same time.