Cov cuab yeej no muab 1-4 * E1 interface, Standard 2 xov xov tooj raws li engineering xaj-hlau (yeem).Nws hloov tau yooj yim heev.Nws muaj lub tswb ua haujlwm.Kev ua haujlwm yog txhim khu kev qha, ruaj khov, thiab kev siv hluav taws xob tsawg, kev sib koom ua ke siab, me me.