1)With SIP protocol; 2)Provide E1, FXO, FXS interface;but also provide ... *Signaling support: SS7,ISDN-PRI, Q.SIG, V5.2,R2*SIP Protocol*Codes: G.711-pcma, G.711-pcmu, G.723 ... answer, Pre-set call transfer-Do not disturb function-Limit extension call out with account and password-Caller ID display*Add ...