Introduction

As shown in Figure 6, Telephone A originates a call to Telephone B through a SIP server. If the link between the SIP server and Router B fails, the SIP server forwards the call back to Router A, which then forwards the call through its FXO interface.

In this case, the call from Telephone A eventually uses two DSP resources. This can be avoided by enabling the local call identification function, which helps to identify local calls. With this function enabled in this case, the voice interface corresponding to Telephone A can be directly connected with the FXO interface, thus saving the DSP resources.

	NOTE: Whether or not DSP resources can be saved depends on the voice card. This function can identify local calls originated by SIP, and cannot identify local calls originated by H.323.