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What are "bridge" and "blind" transfer?

Answers to common Plum DEV questions

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What are "bridge" and "blind" transfer?

Post by support »

When the platform is directed to perform a "bridge" transfer, it first claims an unused channel and makes an outbound call to the number specified in the <transfer> tag. When the party being called picks up, the platform patches together the original inbound call and the newly established outbound call. A bridge transfer will thus take up two channels on the platform as long as both parties are on the call. As soon as either party hangs up, the bridge is torn down and the VoiceXML call session is concluded.

A "blind" transfer avoids the two channel penalty. When the platform is directed to perform a blind transfer, it signals back to the PBX over the channel that the original inbound call is on. The platform requests that the original inbound call be transferred and then it hangs up the call since it assumes the PBX will now handle patching the original call through to the proper destination. Thus, once a blind transfer request is completed, there are no channels on the platform being used to maintain the call.

Bridge transfer is possible with any telephone lines as long as outbound calls are permitted on those lines.

Blind transfer is only possible on PBX analog lines that support hook-flash transfer or PBX channelized T1 trunks that support the digital equivalent of analog hook-flash transfer.