Phones/clients register, but incoming calls are not signalled.Possible symptoms for a disturbing SIP ALG or SIP Helper can be Unfortunately, this is very error-prone and always leads to problems. This is achieved by having a SIP ALG or SIP helper latch into the communication and replace IP addresses and/or media ports in the SIP packets. Then the SIP-ALG ensures that not all SIP Devices contact the provider with source port 5060. This is to ensure that a SIP gateway in the public network is presented with a remote station that can be reached via the public address.Ī SIP-ALG is also necessary if not only one but several SIP Devices want to register with a provider without an additional telecommunications solution.
Many next-generation firewalls contain so-called SIP - Application Layer Gateway functions (SIP-ALG) or SIP helpers, which in a NAT-based environment ensure that the ports and IP addresses used match the NAT tables of the firewall.
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