Verizon Blocks SIP Traffic Using ALG [telecom]

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In Depth: Verizon Blocks SIP Traffic Using ALG

By Eric Phipps

As one of the largest mobile broadband carriers in the country, the Verizon 4G LTE network is used by a sizable portion of the VoIP population. Unfortunately, it appears that Verizon is intentionally blocking SIP traffic on their 4G LTE network. Verizon is currently operating a network level SIP ALG which blocks 3rd party SIP Registrations at worst, and hinders functionality at best. Our NOC Technicians Eric Phipps and Dave Jodhan sat down to document the ALG in action.