Testing voice-over-IP interoperability at ComNet 2001

MIs there a difference between what vendors say they can do in terms of voice-over-IP interoperability and what they can actually do on that front? Network World Global Test Alliance partner Miercom, an industry leader in voice-over-IP research and testing, has tracked the state of voice-over-IP standards and interoperability for more than two years. Based on data Miercom collected from voice-over-IP vendors late last year, the industry is getting closer to achieving interoperability on a larger scale. More than 70% of the 79 vendors we queried are convinced that more than half of the voice-over-IP products would interoperate with some other vendors' voice-over-IP products via a variety of standards including H.323 (Versions 2, 3 and 4), Session Initiation Protocol, H.248/Megaco and to a lesser extent, Media Gateway Control Protocol.

With that said, Miercom and Network World are offering ComNet 2001 attendees the opportunity to observe the state of H.323 interoperability among many leading voice-over-IP products. This hands-on voice-over-IP lab will be conducted in Conference Rooms 1 and 2 from Jan. 30 to Feb. 1 at the Washington, D.C., Convention Center.

Miercom's role in establishing this interoperability workshop is to provide basic testing methodologies on which the vendors' ability to interoperate could be assessed in a practical and realistic environment. To test for interoperability, Miercom built a state-of-the-art voice-over-IP test lab that includes a network backbone comprised of Extreme Networks Summit 48 and Black Diamond Layer 4 switches, several diagnostic tools, including Network Associates' Sniffer and Agilent' s Internet Advisors, and load/voice quality test equipment including Hammer IT, and H.323 Call Generation Tools from Empirix (formerly Hammer Technologies). Miercom uses this gear to decode and diagnose the dialog between voice-over-IP endpoints (or gateways) and to verify interoperability between vendors' equipment.

For the purposes of this interoperability demonstration, Miercom defines basic interoperability as the establishment of a bidirectional voice path between two endpoints, which can be IP phones, IP PBXs, wireless IP phones or PC software.

Miercom verifies voice-path connectivity by establishing a phone call between two systems in one of two scenarios. In the first, communication gets established between an endpoint or voice-over-IP gateway and an endpoint or gateway in a static configuration (that is, with no gatekeeper).

Version 2 of the H.323 specification, on which most of the testing is based because that is the most widely implemented version of the standard, defines a basic call setup as one in which neither endpoint is registered to a gatekeeper. The two endpoints communicate directly.

In Miercom's second scenario, a bi-directional communications path gets established between an endpoint or gateway to another endpoint or gateway through a gatekeeper. In the H.323 specification, the optional gatekeeper provides call-control services to the H.323 endpoints.

Endpoints used in the second scenario of tests included IP phones and similar devices.

In either scenario, once a call gets established, Miercom' s engineers ensured that the voice path was established in both directions, regardless of which product initiated the call. Miercom also verified that calls closed gracefully, so that network resources were freed up quickly and available to subsequent callers, regardless of which side terminated the call.

This story, "Testing voice-over-IP interoperability at ComNet 2001" was originally published by Network World.

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