VoIP Impairment, Failure, and Restrictions

Coverage Type: research
Broadband Internet Technical Advisory Group (BITAG), 1550 Larimer Street, Denver, CO, 80202, United States

A substantial portion of global voice communications are now carried over Internet Protocol (IP) and the Internet has become a fundamental medium supporting voice services.

Voice over IP (VoIP) services allow users to make calls between IP-based endpoints, and to interconnect with the traditional public switched telephone network. Impairment, failure, or restriction of VoIP services can create significant problems for users of those services, and can create problems for the operators of VoIP services, who may be required to troubleshoot or work around issues (where possible) to restore their users’ connectivity.

As VoIP services become more common around the world, incidences of VoIP impairment, failure, or restriction also have the potential to be construed as anti-competitive, discriminatory, or motivated by non-technical factors. With this report BITAG clarifies how VoIP may be impaired, fail, or be restricted in residential, mobile, application provider, and consumer networks and devices; the methods for mitigating VoIP impairments, failures, or restrictions; and recommendations concerning such. Among other things, the report recommends that:

  • Network operators should avoid impairing or restricting VoIP applications unless no reasonable alternatives are available to resolve technical issues.
  • VoIP-related Application Layer Gateways (ALGs) in operator-supplied home routers should minimize their impact on traffic other than the operator’s VoIP service where possible.
  • Manufacturers of home routers should disable VoIP-related ALGs by default.
  • Port blocking rules in consumer equipment should be user-configurable.
  • If network operators intentionally use network policies or practices that impair or restrict VoIP, they should provide disclosures about those policies and practices and provide communications channels for feedback.
  • Application developers should design VoIP applications to be port-agile where possible.


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