4-Port SIP VoIP Gateway (4 FXS) VGW-420FS Datasheet Manual Firmware FeaturesSIP ApplicationsIETF SIP RFC3261 based on UDP/TCP/TLS4-line FXS connects to analog phone set or PABXFax over T.38 and Pass-throughITU-T G.711 A-law, G.711 μ-law, G.723.1 and G.729 voice codingIn-band / out of band DTMF (RFC4733, RFC2833 / SIP INFO)Echo cancellation exceeding ITU-T G.168, up to 128ms tail lengthSupports SIP Trunk and Caller ID: DTMF/FSK CLI PresentationInternet FeaturesSupports SNMP v1/v2/v3 Supports VLAN 802.1P and 802.1QSupports Layer3 QoS and DiffServSupports STUN (RFC 3489) and Outbound ProxySupports TR069 and Auto Provisioning Supports TLS/SRTP Security Call FeaturesCall waiting / transfer (Blind transfer, Attend transfer)Call hold / Quick pickCall Forwarding UnconditionalCall Forwarding on No ReplyHotline / Speed Dial / Direct IP CallDo Not Disturb (DND) / Three-way conference