Okokuqala, imishini ye-PCM nemishini ye-PDH ingamadivayisi ahluke ngokuphelele.I-PCM iyimishini yokufinyelela yesevisi edidiyelwe, kanti okokusebenza kwe-PDH kuyimishini yokudlulisa amehlo.

Isignali yedijithali ikhiqizwa ngesampula, ukulinganisa kanye nokufakwa kwekhodi isignali ye-analog eqhubekayo, ebizwa ngokuthi i-PCM (i-pulse code modulation), okungukuthi, i-pulse code modulation.Lolu hlobo lwesignali yedijithali kagesi ibizwa ngokuthi i-digital baseband signal, eyenziwa ngetheminali kagesi ye-PCM.Izinhlelo zamanje zokudlulisa idijithali zonke zisebenzisa i-pulse-code modulation (Pulse-code modulation) uhlelo.I-PCM yayingasetshenziselwa ukudlulisa idatha yekhompyutha, kodwa ukuba nomugqa we-trunk phakathi kwamaswishi esikhundleni sokudlulisa isignali yocingo kuphela.

Imishini yokudlulisa amehlo ye-PDH, ohlelweni lokuxhumana lwedijithali, amasignali adluliswayo wonke ama-pulse ahlelwe ngokwedijithali.Uma le mifudlana yesignali yedijithali idluliswa phakathi kwemishini yokushintsha yedijithali, amanani azo kufanele ahambisane ngokuphelele ukuze kuqinisekiswe ukunemba kokudluliswa kolwazi.Lokhu kubizwa ngokuthi “ukuvumelanisa.”Ohlelweni lokudluliswa kwedijithali, kukhona uchungechunge olubili lokudlulisela kwedijithali, olulodwa lubizwa ngokuthi “Plesiochronous Digital Hierarchy” (Plesiochronous Digital Hierarchy), esifushanisiwe njenge-PDH;enye ibizwa ngokuthi “I-Synchronous Digital Hierarchy” (I-Synchronous Digital Hierarchy), efushanisiwe njenge-SDH.

Ngokuthuthuka okusheshayo kokuxhumana kwedijithali, kukhona ukuthunyelwa okuqondile okumbalwa nokumbalwa, futhi ukuthunyelwa okuningi kwedijithali kufanele kushintshwe.Ngakho-ke, uchungechunge lwe-PDH alukwazi ukuhlangabezana nezidingo zokuthuthukiswa kwebhizinisi lezokuxhumana zesimanje kanye nezidingo zokuphathwa kwenethiwekhi yezokuxhumana yesimanje..I-SDH iwuhlelo lokudlulisa oluvelile ukuhlangabezana nalesi sidingo esisha.