Choyamba, zida za PCM ndi zida za PDH ndizosiyana kwambiri. PCM ndi zida zophatikizika zopezera ntchito, ndipo zida za PDH ndi zida zowunikira.

Chizindikiro cha digito chimapangidwa ndi sampuli, quantizing ndi encoding mosalekeza kusintha kwa analogi chizindikiro, chomwe chimatchedwa PCM (pulse code modulation), ndiko kuti, pulse code modulation. Mtundu uwu wa chizindikiro chamagetsi chamagetsi chimatchedwa chizindikiro cha digital baseband, chomwe chimapangidwa. ndi chotengera chamagetsi cha PCM. Makina otumizira ma digito apano onse amagwiritsa ntchito makina a pulse-code modulation (Pulse-code modulation). PCM sinagwiritsidwe ntchito potumiza deta yamakompyuta, koma kukhala ndi thunthu pakati pa masiwichi m'malo mongotumiza chizindikiro cha foni.

Zida zotumizira zamagetsi za PDH, mu njira ya digito yolumikizirana, ma siginoloji otumizidwa ndi ma digitized pulse sequences. Pamene mitsinje yamagetsi ya digito iyi imafalikira pakati pa zida zosinthira digito, mitengo yawo iyenera kukhala yogwirizana kwathunthu kuti zitsimikizire kulondola kwa kufalitsa chidziwitso. Izi zimatchedwa "synchronization." M'dongosolo lachidziwitso la digito, pali mitundu iwiri yotumizira digito, imodzi imatchedwa "Plesiochronous Digital Hierarchy" (Plesiochronous Digital Hierarchy), yofupikitsidwa ngati PDH; ina imatchedwa "Synchronous Digital Hierarchy" (Synchronous Digital Hierarchy), yofupikitsidwa monga SDH.

Ndi chitukuko chofulumira cha mauthenga a digito, pali mauthenga ocheperapo ndi ochepa, ndipo mauthenga ambiri a digito ayenera kusinthidwa. Chifukwa chake, mndandanda wa PDH sungathe kukwaniritsa zosowa zamabizinesi amakono olumikizana ndi ma telecommunication komanso zosowa za kasamalidwe ka ma network amakono. . SDH ndi njira yotumizira yomwe yatulukira kuti ikwaniritse zosowa zatsopanozi.