SIP ALG can cause problems with VoIP traffic because it can re-write headers and cause communication problems between the VoIP phone and the VoIP server. SIP ALG can cause problems with VoIP traffic Only 1 phone in a hunt group with multiple phones is ringing.1.

Only 1 phone in a hunt group not ringing.

Inbound faxes to a fax machine failing at the start of a fax.Unable to retrieve a call off of hold or park.Unable to put a call on hold or park on phones.Dead air/dropped calls when first picking up a phone call.One-way audio when first picking up a phone call.This makes the router unable to keep track of which phone or fax device first sent the VoIP packet. Your router does not know which phone/fax device to send the data back to because SIP ALG removed the private IP address of the phone from the voice/fax packets. The problem with SIP ALG occurs when our servers send voice and fax data back to your network. This is done to protect you from hackers hijacking your phone equipment and making fraudulent long distance and international calls that run up your bill. Modern VoIP systems like Intermedia Cloud Voice are designed to work with phones and fax adapters that are behind firewalls. The setting was first designed for old VoIP phone systems that could not work behind a firewall (NAT). SIP ALG modifies voice and fax packets to make them appear as if they have a public IP address and are not behind a firewall. Why will SIP ALG affect my phones and faxes? Therefore if you are experiencing problems we recommend that you check your router settings and turn SIP ALG off if it is enabled. This can give you unexpected behavior, such as phones not registering and incoming calls failing.

SIP ALG modifies SIP packets in unexpected ways, corrupting them and making them unreadable. This setting modifies SIP packets, which controls voice calls and faxes.Įven though SIP ALG is intended to assist users who have phones on private IP addresses, in many cases it is implemented poorly and actually causes more problems than it solves. It is enabled by default on many commercial routers and internet gateways (modems). SIP ALG stands for Session Initiation Protocol Application Layer Gateway.

Alg application layer gateway service