| 摘要 |
Automatic communication establishment between two telephone subscribers of different exchanges. The identities of the caller and the called are transferred to the called exchange in the event that the called line is busy, permitting disconnection of the two exchanges. The called's line is thereafter monitored until becoming free upon which the caller's identity is utilized by the called's exchange for calling back the caller. If the caller's line is now busy, the transfer of the called and the caller's identities take place again, this time back to the caller's exchange. The caller's line is similarly monitored until free, after which the method is repeated until communication is established.
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