Mudhijitari yekufambiswa kwemagetsi, kune maviri edhijitari optical transceiver series, imwe inonzi "Plesiochronous Digital Hierarchy" (Plesiochronous Digital Hierarchy), inonzi PDH optical transceiver; imwe yacho inonzi "Synchronous Digital Hierarchy" (Synchronous Digital Hierarchy), inonzi SDH optical transceiver.

Iyo sisitimu inoshandisa plesiochronous digital series (PDH) ndeyekuseta yakakwirira-chaiyo wachi pane imwe neimwe yedhijitari network network, masaini ewachi aya ese ane yunifomu chiyero. Kunyange zvazvo kururama kwewachi imwe neimwe kwakakwirira zvikuru, panogara paine misiyano miduku. Kuti uve nechokwadi chehutano hwekutaurirana, mutsauko uripo pakati pewachi idzi haufanire kudarika huwandu hwakatarwa. Naizvozvo, iyi nzira yekuyananisa haisi yechokwadi kuwiriranisa, saka inonzi "quasi-synchronous."

Munguva yakapfuura nharembozha dzenhare, mazhinji ePDH optical transceiver midziyo yakashandiswa, iyi nhevedzano ine yakanaka kuchinjika kune echinyakare point-to-point kutaurirana.Nekukurumidza kukurumidza kwekukurukurirana kwedhijitari, kune mashoma uye mashoma anonongedzera-kusvika-kunongedza zvakananga. , uye madhijitari mazhinji anofanirwa kuendeswa, saka, iyo PDH yakatevedzana haigone kusangana nezvinodiwa zvemazuva ano ekufambiswa kwesevhisi yekufambiswa kwenhare uye yemazuva ano telecommunication network manejimendi. SDH inzira yekufambisa iyo yakabuda kuti isangane nechido chitsva ichi.