BITAG Urges Fixes to Avoid VoIP Service Impairments

Network operators should avoid impairing or restricting VoIP applications “unless no reasonable alternatives are available to resolve technical issues,” said the Broadband Internet Technical Advisory Group’s (BITAG) Technical Working Group Thursday in a report. Some network management actions, such as port blocking or traffic limitations meant to impede hacking of vulnerable VoIP services, may limit or restrict VoIP traffic “as a method of ensuring network integrity,” BITAG said. VoIP impairments, failures and restrictions could potentially be construed as “anticompetitive, discriminatory or motivated by non-technical factors,” the group said. Network operators should ensure they take such actions in a way that will “minimize the impact of the approach on legitimate VoIP use,” BITAG said (http://bit.ly/SVotYb). BITAG, a non-profit formed to develop industry consensus on Internet rules, previously released a report in October on best practices to reduce network congestion (CD Oct 23 p10).

Network operators should disclose any policies that intentionally impair or restrict VoIP and allow users to communicate with them about those policies, BITAG said. It noted instances when a network operator intentionally used port blocking -- blocking Internet traffic based on its port number and transport protocol -- against ports the VoIP applications commonly use. Operators could make those disclosures publicly available through the operator’s public website or as part of a page on its network management policies, BITAG said. The operator should list specific VoIP applications or services involved in the restriction, the group said.

BITAG recommended that consumer equipment should include an option for users to configure port blocking rules. Some of the port blocking involving VoIP is unintentional, stemming from either misconfiguration of network or end-user equipment or misconfigured policies between networks, BITAG said. VoIP restrictions caused by port blocking may also stem from firewalls within an end-user’s router that may disable the VoIP service, the group said. Technically savvy users may be able to reconfigure their routers in a way that removes the port blocking, BITAG said. Equipment manufacturers should include a listing of default ports the router blocks and instructions on how to modify the rules, the group said.

VoIP application developers should design VoIP applications to be port-agile, BITAG said. Port-agile applications that can tolerate random source ports or allow user-configurable port selection are better able to avoid VoIP impairments, the group said. Port agility may depend on whether redesigned versions of an application can be made compatible with existing versions, BITAG said.

Router manufacturers should disable VoIP-related Application-Level Gateways (ALGs) by default in routers supplied by network operators, BITAG said. There have been instances when VoIP failed because of default ALGs included in operator-provided equipment, BITAG said. VoIP-related ALGs in operator-supplied routers should be configured in a way that minimizes their impact on other traffic where possible, the group said. It said network operators should let users disable such ALGs when they don’t subscribe to the operator’s VoIP service or to minimize those ALGs’ impact on independent VoIP services or other traffic. (jphillips@warren-news.com)