There is no physical limitation for number of SIP trunks that be configured from BE3K. However, the number of SIP session supported on a trunk will be limited by following:
Number of sessions, that the peer gateway that the SIP trunk connects to, supports. CUBE-Lite is the officially supported SBC with BE3K. It supports max of 15 sessions. So what we have tested is 10 trunks, which represents one trunk from central site to each of remote sites. Looking at memory and CPU usage from that test, more than 10 trunks can easily be supported.
Amount of available bandwidth. Top-tier service providers exert CAC in their networks, and how much protection this offers enterprise network depends on who your service provider is and how well the controls are implemented. So it is strongly recommended that you protect your own network with your own CAC at your Border element.
We should use the sizing tool to provide some guidance in data sheet for SIP trunk also.
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