Protocols supported

DUAL Softswitch supports both H.323 and SIP for inbound and outbound calls. It automatically converts between those protocols where necessary. So, for example, if your customers make calls using SIP devices such as PAP2s from dynamic IP addresses and your carriers require you to send calls using the H.323 protocol, DUAL Softswitch will make the necessary changes and allow the calls to be switched.

Calls using the G.723.1, G.729 and G.711 codecs can be handled, although DUAL Softswitch does not support transcoding. This means that your callers' devices and your carriers' gateways must support a common codec. Media transmission is usually negotiated such that audio is streamed directly between your callers' devices and your carriers' gateways. The switch supports an RTP proxy service whereby the audio is relayed in both directions through our servers. This can sometimes be necessary if your callers' endpoints are behind NAT devices and your carriers' do not offer NAT Penetration. There is an extra charge for this service.

DTMF (touchtone) can transmitted in band using audio tones or the RFC 2833 specification. Alternatively, DUAL Softswitch will relay out of band DTMF transmission in both directions using SIP INFO messages and tunnelled H.323 UserInputIndication messages.

Faxes can be relayed through DUAL Softswitch using the T.38 protocol, which is supported for both H.323 and SIP. Both the calling and called party must support T.38 for this method to work.