Nidaamka gudbinta isgaarsiineed ee dhijitaalka ah, waxaa jira laba taxane ah oo transceiver indhaha dhijitaalka ah, mid waxaa loo yaqaan "Plesiochronous Digital Hierarchy" (Plesiochronous Digital Heerarchy), oo loo yaqaan transceiver indhaha PDH; Midda kale waxaa loo yaqaan "Synchronous Digital Hierarchy" (Isku-dhafka Dijital ah Heerarchy), oo loo yaqaan SDH indho-indhayn.

Nidaamka isticmaalaya taxanaha dhijitaalka ah ee plesiochronous (PDH) waa in la dejiyo saacad sax ah oo sare oo ku taal nood kasta oo ka mid ah shabakada isgaarsiinta dhijitaalka ah, calaamadaha saacadahaas oo dhan waxay leeyihiin heer isku mid ah. Inkasta oo saxnaanta saacad kasta ay aad u sarreyso, had iyo jeer waxaa jira kala duwanaansho yar. Si loo hubiyo tayada isgaarsiinta, farqiga u dhexeeya saacadahan waa inuusan dhaafin xadka la cayimay. Sidaa darteed, habkan isku-dubaridku maaha mid si adag oo run ah u wada shaqaynta, sidaa awgeed waxa loo yaqaan "quasi-synchronous."

Shabakado isgaarsiineed ee hore, inta badan qalabka PDH-ga ee transceiver-ka ayaa la isticmaalay, taxanahani waxa uu leeyahay laqabsi wanaagsan oo la xidhiidha isgaadhsiinta dhaqameed ee dhibic ilaa-dhibcood , iyo inta badan gudbinta dhijitaalka ah waa in la wareejiyaa, sidaa darteed, taxanaha PDH ma dabooli karo baahida horumarinta adeegga isgaarsiinta casriga ah iyo maamulka shabakada isgaarsiinta casriga ah. SDH waa nidaam gudbin oo u soo baxay si loo daboolo baahidan cusub.