Jeff Davis wrote: > The IP 501 supports both Cisco and 802.11af with different cables. While > there are pin assignments differences, there are also electrical > differences in the discovery protocols. The special cable is an artifact > of this. > > I don't know of anyone who was able to make the phone work without the > cable, and the 501 is not designed to work without it. If it were just a > matter of pin assignments, then people would be selling cables on eBay. > > I notice that now that 802.11af is THE standard, Polycom is supporting > it on their new phones without any special cables.
The IEEE PoE standard -- for those who care -- is actually IEEE 802.3af, not 802.11af. The important one is the 802.3af-2003, because that introduced provisions for preventing ground loops between the PoE midspan and the switch. There's a white paper on the topic at Polycom's website which explains the need for non-standard cable (the newer version of which does in fact have some additional electronics in it): http://polycom.com/common/pw_item_show_doc/1,1276,2766,00.pdf I suspect that the 330, 430 and 550 phones have some sort of built-in ground loop detection and prevention. For anybody contemplating running the 501/301 phones with a straight Cat5 cable: in most cases, it won't work; in some cases, it will work, but you can bake your PoE injector, unless said injector has a ground loop prevention circuit built-in; all the newer ones are required to have this to be truly 802.3af compliant. Remember that a label indicating 802.3af compliance is no assurance, since the standard has been through numerous revisions in the last few years. The moral of the story -- it is probably safer to use the special cable if you have 301s or 501s. Thanks for the feedback! -Stephen- _______________________________________________ --Bandwidth and Colocation provided by Easynews.com -- asterisk-users mailing list To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-users
