SIP ALG, or Session Initiation Protocol Application Layer Gateway, is a tool that some networks use to speed along SIP requests to initiate connections. This tool involves rewriting the packet headers of SIP requests that pass through the router out to the internet. For some services, this tool may be useful. Still, for many VoIP providers, the rewritten SIP packet header strips out information that is necessary to securely authorize the device making the connection. More importantly, it responds directly to the device that is requesting the connection. This feature can lead to some of the most common issues that customers have with VoIP — phones losing connection, dropped calls, and one-way audio.