... firmware by local or internet7,Field proven compatible with Asterisk-based softswitches ModelSinoV-S504GSinoV-S508GNumber of Channels4GSM8GSMFrequency850/900/1800/1900MHzCall Control ... , UDP, PPPoE, DHCP, DNS, NAT, Telnet, HTTP, FTP, TFTPConfiguration andMaintenance·Web-based GUI·Console, Telnet command line·Centralized network managementFirmware UpdateLocal file ...