VoIP GSM gateway with 8 channels, bridging between GSM network and IP-based systems. Designed to slash the cost of telephone calls, it can find the cheapest route and use the most economical SIM card Number of GSM channels (Max): 8 Network type: 850/900/1800/1900MHz Protocol: SIP (RFC3261),IAX2 Transport Protocol: UDP,TCP,TLS,SRTP DTMF: RFC2833, SIP INFO, In-band Codec: G.711A/U law, G.722, G.723.1, G.726, G.729a. Echo Cancellation: ITU-T G.168 LEC LAN: 1 (10/100Mbps) Network: Static IP, DHCP Client, Firewall, VLAN, DDNS, QoS, OpenVPN NAT Traversal: Static NAT, STUN