Electronic Design

Gigabit Ethernet PoE Midspans Manage Four Data Pairs

The proportion of Ethernet switches shipping with Gigabit ports should reach 25% this year and pass 50% in 2007, according to industry analysts IDC. Seizing the opportunity, PowerDsine offers the industry's first Power over Gigabit Ethernet midspan, the 24-port 6024G. It's the initial device in a line of midspan power products for Gigabit Ethernet.

PowerDsine believes a desire to merge workers' PCs with feature-loaded Internet Protocol phones is driving new 1000BaseT installations. A full-featured PC, even a laptop, is too much of a power hog to be able to use Power over Ethernet (PoE). Yet PoE is still attractive for powering phones through their data connection.

Other popular PoE applications like wireless hotspots and security equipment don't need Gigabit speeds. Still, remote power must be applied consistently with the IEEE 802.3af standard if they're to be connected to jacks fed by 1000BaseT switches.

Gigabit Ethernet uses all four data pairs in the Ethernet cable. Regular 10/100BaseT midspans, which parallel and then power the two "spare pairs" in the cable, won't work as a result. A 10/100/1000BaseT midspan must maintain continuity through all four data pairs while energizing the pairs connected to pins 4/5 and 7/8 through a transformer centertap (see the figure).

PowerDsine demonstrated the 6024G at the Networld+Interop show in May. Field trials are under way, and general availability is expected next month. The 24-port midspan costs $1140.


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