Within the Tunnellink project we developed a simple, effective, adaptable and low cost building brick for all solutions that require a SIP auto responding voice entity
The following diagram outlines the typical functional blocks where Tunnellink building bricks should be introduced:



The Software stack is developed to be as light as possible solving the weakness in computational power available on embedded hardware.
The green portion of the diagram acts as a normal SIP network where the SIP SERVER is normally an Asterisk server (with all the functionalities richness and security that this kind of server can provide) and the PHONE entity acts as a normal SIP user agent. The sepia portion of the diagram implements a dedicated distributed algorithm that enables an external SUPERVISOR to administrate every single tunnellink entity setting.
Tunnellink test results revealed that in an ATMEL AT91SAM9260 based board, even with an ARM926EJ-S processor, with 8K bytes instruction cache, 8K bytes data cache memory and a 190 MHz clock, the utilization of the CPU power did not exceed the 10%. Additionally audio latency does not exceed 100 ms.
Tunnellink is a suitable solution for low cost embedded hardware having a great ratio between sound quality and deployment costs.
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