Hack66.Power Cisco Phones with Standard Inline Power

Hack 66. Power Cisco Phones with Standard Inline Power

To avoid lock-in with Cisco-only phones and switches, learn how to power Cisco phones from non-Cisco switches.

IP phones can be powered through their Ethernet connections. The standard for this inline power is called 802.3af, and many equipment manufacturers support itexcept for Cisco, which uses its own proprietary inline power method. Because of this, you can match Cisco IP phones only with Cisco-powered switches (unless you use Cisco's only phone model to support 802.3afthe 7970). This is an unfortunate form of vendor lock-in, but all is not lost. You can do a couple of things to get Cisco IP phones to draw power from non-Cisco switches.

If your budget permits, the obvious (though proprietary) solution to this problem is to use Cisco PoE switches to power the phones. Some other switch makers, like Foundry Networks, also support Cisco's proprietary PoE standard. If you can't afford to forklift your switches, you might instead want to power your Cisco phones by way of a power injector, which is a patch panel that adds inline power to a CAT5/CAT6 cable connection. Consider Cisco PoE-compatible injectors like those made by PowerDsine (http://www.powerdsine.com/).

But, if you can't do that either, do the next best thing: hack.

Hacking inline power will almost certainly void your IP phone's warranty, and probably your switch's or power injector's, too. A short circuit could fry your switch and phone if you're not careful. Proceed with caution!

By changing some wires on a standard UTP Ethernet patch cable, you can make a compatibility cable that lets you plug Cisco IP phones into any 802. 3af source, as shown in Figure 5-3. Essentially, you are flipping wires 4 and 7, and 5 and 8. Be advised, this technique could void the warranty of your phone and your switch.

Figure 5-3. The wiring diagram for a hacked PoE cable

Make sure your switch lets you program, port by port, which ports get power and which ones don't, because in a native Cisco PoE solution, Cisco IP phone power requirements are "auto-detected," so power can turn itself on and off as necessary on each port. There's no such provision when using a hacked cable to supply 802.3af power to a Cisco PoE-using phone. If this is a problem, and 802.3af won't work with the hacked cable, try using a device that does the two-pair flip but also works with auto-detection, such as 3Com's 48-volt IntelliJack switch converter, part number 3CNJVOIPCPOD.

The Cisco 7970 IP phone does support 802.3af power sources, unlike the more popular (and less expensive) 7960 and 7940 phones.

VoIP Hacks
VoIP Hacks: Tips & Tools for Internet Telephony
ISBN: 0596101333
EAN: 2147483647
Year: 2005
Pages: 156

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