Standards for phones give manufacturers incentive to mass-produce products that support those standards. That drives down the price and ups the feature set. In our survey, vendors indicated that the most common standards their phones support are H.323, MEGACO (Media Gateway Controller) and SIP (Session Initiation Protocol). H.323 has been around the longest, while SIP is the newcomer. One of the vendors listed in our Buyer's Guide charts, Zultys Technologies, supports only SIP. But the company supports five phone vendors, more than any other survey participant.
Alcatel supports SIP, MEGACO and H.323, and three phone vendors. It's important to clarify which features are supported on each corresponding protocol, regardless of the vendor. Siemens and Shoreline support only their own VoIP phones, though Shoreline pointed out that it supports analog phones from other vendors.
If you've ever gone to Wal-Mart to buy a phone for your home, you took it for granted that an analog phone will work with any vendor's phone system. Unfortunately that's not true with VoIP. SIP has emerged as the standard that will make cross-vendor support possible in the future (for more information about the SIP protocol, see "It's Time To Take a Look At SIP").
Before purchasing a VoIP phone system, you have to verify that your data network is up to the task. At minimum you will want to have switching on your LAN. If you're not moving around large amounts of data, 10 Mbps to the desktop may be sufficient, but 100 Mbps will give you a little more headroom. Most VoIP phones have a built-in, two-port switch that lets you share your Ethernet connection with your PC. Most also support QoS (quality of service), which will ensure that your voice packets get priority if you blast a lot of data from your PC.
You'll also want to have both bandwidth and QoS on your backbone connections, which is a concern when bandwidth gets expensive, as with WAN connections. Consider putting your switches and your PBX on UPSs, so you won't lose your phones during a quick (or prolonged) power outage. This works especially well if you can power the phones from the switches. The IEEE 802.3af (Power over Ethernet) standard is about to receive final ratification, and many vendors are releasing switches and phones with support for this standard.
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