Ngokuthuthuka kokuxhumana, ulwazi oludingekayo ukuze ludluliselwe akulona izwi kuphela, kodwa futhi umbhalo, idatha, izithombe, nevidiyo. Kuhlanganiswe nokuthuthukiswa kokuxhumana kwedijithali nobuchwepheshe bekhompyutha, ngeminyaka yawo-1970 nawo-1980, amasistimu enkampani yenethiwekhi ye-T1 (DS1)/E1 (1.544/2.048Mbps), i-X.25 frame relay, ISDN (Integrated Services Digital Network) kanye ne-FDDI ( Optical fibre i-interface yedatha esabalalisiwe) nobunye ubuchwepheshe benethiwekhi. Ngokufika komphakathi wolwazi, abantu banethemba lokuthi amanethiwekhi okudlulisa ulwazi esimanje angahlinzeka ngamasekethe namasevisi ahlukahlukene ngokushesha, ngokwezomnotho, nangempumelelo. Kodwa-ke, ngenxa ye-monotonicity yezinsizakalo zabo, inkimbinkimbi yokunwetshwa, kanye nomkhawulo womkhawulokudonsa, ubuchwepheshe benethiwekhi obalulwe ngenhla bukhona kuphela Ukuguqulwa kokuqala noma ukuthuthukiswa ngaphakathi kohlaka akusasizi.I-SDHyathuthukiswa ngaphansi kwalesi sizinda. Phakathi kobuchwepheshe obuhlukahlukene benethiwekhi ye-broadband optical fiber access, uhlelo lwenethiwekhi yokufinyelela olusebenzisa ubuchwepheshe be-SDH yilona olusetshenziswa kakhulu.Ukuzalwa kwe-SDH kuxazulula inkinga yokungakwazi ukuhambisana nokuthuthukiswa kwenethiwekhi yomgogodla kanye nezidingo zesevisi yomsebenzisi ngenxa yomkhawulo womkhawulokudonsa wemidiya engenayo, kanye nenkinga yokufinyelela "ibhodlela" phakathi komsebenzisi nenethiwekhi eyinhloko. , futhi ngesikhathi esifanayo, ikhulise inani elikhulu lomkhawulokudonsa kunethiwekhi yokudlulisela. Izinga lokusetshenziswa. Kusukela kwethulwa ubuchwepheshe be-SDH ngeminyaka yawo-1990, kube ubuchwepheshe obuvuthiwe nobujwayelekile. Isetshenziswa kakhulu kumanethiwekhi omgogodla futhi intengo iyancipha futhi yehla. Ukusetshenziswa kobuchwepheshe be-SDH kunethiwekhi yokufinyelela kunganciphisa umkhawulokudonsa omkhulu kunethiwekhi eyinhloko. Izinzuzo kanye nezinzuzo zezobuchwepheshe zilethwa emkhakheni wokufinyelela amanethiwekhi, ukusetshenziswa ngokugcwele kwe-SDH synchronous multiplexing, ukuxhumana optical standardized, amandla okuphatha inethiwekhi enamandla, flexible network topology amakhono kanye nokuthembeka okuphezulu ukuletha izinzuzo, kanye nezinzuzo zesikhathi eside ekwakheni kanye ukuthuthukiswa kwamanethiwekhi okufinyelela .