When you purchase such a SIP Trunk, it provides the ability to place one call at a time through the service provider's network.
当你购买这样一个SIP中继，它提供了能够在一个地方通过一次电话服务供应商的网络。
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SIP Trunk is a logical connection between an IP PBX and a Service Provider's application servers that allows voice over IP traffic to be exchanged between the two.