Performance and features
    SIP and IAX2
    Support Bridge and Router(NAT&NAPT) models.
    TCP/UDP/IP, ICMP, HTTP, DHCP Client (WAN Interface), DHCP Server(LAN Interface), DNS Client, DNS Relay, SNTP, PPPoE, FTP, TFTP.
    Voice Codecs: G.711(A-law/U-law),G.729A/B,ILBC
    NAT penetration: STUN client, AVS and Citron etc. Can modify SIP register port,
    HTTP server port, Telnet server port and RTP port. 
    Support standard voice features such as numeric Caller ID Display, Call Waiting, Hold, Transfer, Do-Not-disturb, Forward, in-band and out-of-band
    DTMF, Hotline (off hook autodial), ban outgoing.
    Support standard encryption and authentication (DIGEST using MD5, MD5- sess).
    Support Silence Suppression, VAD (Voice Activity Detection), CNG (Comfort Noise Generation), Line Echo Cancellation (G.168), and AGC (Automatic Gain Control).
    Provide easy configuration thru manual operation (Web interface and Telnet) or automated centralized configuration file via TFTP or HTTP.
    Support firmware upgrade via TFTP/FTP and HTTP.
    Support syslog, can send event of gateway to syslog server.
    It have 2-SIP account,one IAX2 account and one PSTN phone number,that means each ATA own 4 phone number,all can be used as callee at anytime.
    For the caller,these 4 account can be selected by dial different relevant prefix(including switch to PSTN as an ordinary PSTN phone),It can be used as PSTN phone when power off.