SIP Phone Features (online only chart)
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We used BroadSoft's BroadWorks SIP services for our testing. This gave us the opportunity to partner with a leading SIP vendor for a reference platform for interoperability testing. BroadSoft employs a B2BUA (back-to-back user agent) for SIP signaling, meaning the proxy server stays available throughout the call and also for the termination of the call. Without B2BUA, the proxy server would drop out of the picture once the initial connection was completed. With B2BUA, we gained centralized tracking of the call for call-detail recording.
The most important thing we can say about these phones is that they worked as well as any quality business-class phone could be expected to work. We made phone calls easily and with confidence. In fact, the many hours of calls that we made during our tests--to vendors and co-workers alike and including several teleconferences--were made on SIP phones. It's also worth noting that our SIP server and gateway to the PSTN were located at BroadSoft's site, meaning that all call signaling and audio had to go across the Internet. Normally these services are delivered over a more private controlled network.
Interoperability among the phones was a key consideration during testing. What's the point of standards-based equipment if you can't mix and match? Although we were pleased that all the phones passed these interoperability tests with flying colors, we can't say we were surprised: Interoperability testing has been going on for more than four years. This testing has been closed to the public, but the 12 "SIPit" events held by the SIP Forum have given vendors the opportunity to test and re-test in a nonthreatening environment.
Although we told all the vendors that we would conduct interoperability testing, we didn't share any details. That obviously didn't deter the six that came to the party, and we can only speculate on whether it contributed to our high no-show rate. We did encounter a few glitches with some of our testing, but we simply captured the packets involved using Network Associates' Sniffer Voice analyzer software and sent them to the vendors. All came up with fixes in a couple of days. Fortunately, we didn't have to do much of this, and the result was that all the products earned perfect scores for interoperability.
We are also glad to report that another standard key to VoIP phone deployment, 802.3af PoE, was a cakewalk for all the phones. This is serendipitous timing for phone vendors because most network equipment vendors are rolling out 802.3af-compatible switches. Powering the phones in this manner means you need only one cable plugged into the phone. It also means that it's possible to provide UPS for the phones from centralized locations, such as wiring closets.