I'm no EE, but it's my understanding that most IEEE 802.3af midspans inject power on unused pairs because it's not easy/cheap to inject it on data-carrying pairs. It's no problem for Ethernet switches, because they are generating both.
Kind regards, Frank -----Original Message----- From: Enfield, Chuck [mailto:[EMAIL PROTECTED] Sent: Thursday, June 28, 2007 12:09 PM To: [email protected] Subject: Re: [WIRELESS-LAN] The strategic importance of 5GHz I doubt it has anything to do with power over signaling conductors. If that can work on endspan, it should work just fine on midspan. If the transmission performance of the midspan is good enough, there's no reason a midspan couldn't use the detection methods specified for endspan to provide power with GigE. If otherwise 3af compatible, such a device would simply exceed the requirements of the standard. Apparently the PowerDsine 6000G and 3001G do that. Maybe others will too. I don't know the reason that midspan power for GigE was excluded from the standard, but I'm happy to venture a guess. I assume the required data transmission performance made it too difficult for some manufacturers to do it. From a transmission perspective, the minimum requirements for 3af devices seem to be aimed at maintaining cat-5 performance. Since a continuous 90m cat-5 link is barely up to the task of 1000BASE-T, the requirement that a midspan device would support GigE on that same cat-5 link was probably a dealbreaker. At the risk of looking foolish by prognosticating, I see 802.3at including midspans for 1000BASE-T, but only on cat-5e or higher cable. Chuck -----Original Message----- From: Frank Bulk - iNAME [mailto:[EMAIL PROTECTED] Sent: Wednesday, June 27, 2007 8:43 PM To: [email protected] Subject: Re: [WIRELESS-LAN] The strategic importance of 5GHz Chuck: If I understand what you're saying, midspan can only inject power on unused powers, and since GigE uses all four pairs, PoE for GigE needs to be driven from endspans using what Wikipedia calls 'phantom power' (http://en.wikipedia.org/wiki/Power_over_Ethernet). Is that right? Frank -----Original Message----- From: Enfield, Chuck [mailto:[EMAIL PROTECTED] Sent: Wednesday, June 27, 2007 2:41 PM To: [email protected] Subject: Re: [WIRELESS-LAN] The strategic importance of 5GHz Sorry, I've been using midspan power so long I sometimes forget there are other options. I don't have time to look it up, but I'm reasonably sure that 802.3af doesn't include midspan power for 1000BASE-T. Much has been made of the fact that 802.3at will. That's not to say there are no midspan devices out there that comply with 3af AND do power for GigE. If they can get adequate transmission performance through the interconnect, there's no reason it shouldn't work. I'll have to look into the PowerDsine PSE. Chuck -----Original Message----- From: Philippe Hanset [mailto:[EMAIL PROTECTED] Sent: Wednesday, June 27, 2007 11:16 AM To: [email protected] Subject: Re: [WIRELESS-LAN] The strategic importance of 5GHz If you look for instance at a PowerDsine 6000 serie Midspan power injector, it is 802.3af compliant, and supports GigE. That's what we buy today in preparation for 802.11n. (and crossing our fingers ;-) I have a secret hope that 802.11b/g will be for coverage, (the Iphone will decide!) 802.11n at 5 Ghz for performance and who knowns what will happened to 802.11a (cheap point-to-point?) Hopefully the 15 watts of 802.3af will suffice for b/g and n at 5Ghz on one AP! Philippe Hanset University of Tennessee On Wed, 27 Jun 2007, Enfield, Chuck wrote: > Since we can't do 3af power with GigE, that one connection would have > to be 100Mb. If we're going to use two cables for power let's hope > we'll be given the chance to use two data channels as well. > > Chuck > > -----Original Message----- > From: Tomo [mailto:[EMAIL PROTECTED] > Sent: Wednesday, June 27, 2007 4:14 AM > To: [email protected] > Subject: Re: [WIRELESS-LAN] The strategic importance of 5GHz > > The Airwave webinar (for which a link was sent round last week) > mentioned that some vendors are looking at providing two Ethernet > sockets on MIMO / 802.11n Access Points, so they could draw 2 x > 802.3af power connections and one live Ethernet connection. > > _________________________________ > > Tomo | Senior Network & Telecommunications Infrastructure Engineer > Direct > line: +44 (0)20 7000 7777 | Email: [EMAIL PROTECTED] > > www.london.edu > > > > -----Original Message----- > > From: Frank Bulk - iNAME [mailto:[EMAIL PROTECTED] > > Sent: 27 June 2007 02:32 > > To: [email protected] > > Subject: Re: [WIRELESS-LAN] The strategic importance of 5GHz > > > > Dale: > > > > I've heard from at least one vendor that a b/g radio with and > > 802.11n radio may operate within 802.3af power limits. But I've > > heard nothing absolutely definite so far and I anticipate that we'll > > know more by the end of > the > > summer as these products move from short-run samples to production. > > > > The whole 802.11n PoE and GigE port thing really puts most > organizations > > into a pickle...they can cheat with using 100BaseT at the edge but > > if > you > > really want to do full 802.11n on two radios it's going to > > necessitate > a > > midspan, PoE injectors, or a new switch (and that will be at least a > year > > away). If vendors can make an AP with an 802.11b/g radio and an > 802.11n > > radio operate within 802.3af power limits that should give > organizations > > the > > breathing room they need to upgrade their edge switching > infrastructure > > over > > the next 3-5 years. > > > > Frank > > > > -----Original Message----- > > From: Dale W. Carder [mailto:[EMAIL PROTECTED] > > Sent: Tuesday, June 26, 2007 3:55 PM > > To: [email protected] > > Subject: Re: [WIRELESS-LAN] The strategic importance of 5GHz > > > > On Jun 25, 2007, at 11:57 AM, Enfield, Chuck wrote: > > > We currently only have one UTP cable to an AP location. > > > > > > The alternative is one GigE drop with either local power or > > > proprietary UTP based power (including possible pre-standard > > > 802.3at). > > > > One thing we did for the last 3 years is to pull siamese cable to > > each AP location, setting up the infrastructure in advance for a > > technology change. > > > > What will probably screw us as you mention is not enough PoE via > 802.3af. > > Having an AP with bg on 2.4 and MIMO on 5 will probably require > 802.3at. > > So in addition to replacing your AP's, you are now also forklifting > your > > PoE switches... > > > > Dale > > > > ********** > > Participation and subscription information for this EDUCAUSE > Constituent > > Group discussion list can be found at http://www.educause.edu/groups/. > > > > ********** > > Participation and subscription information for this EDUCAUSE > Constituent > > Group discussion list can be found at http://www.educause.edu/groups/. > > > > ____________________________________________________________________ > > __ > > > > This email has been scanned by the MessageLabs Email Security System > > on behalf of the London Business School community. > > For more information please visit http://www.messagelabs.com/email > > ____________________________________________________________________ > > __ > > ______________________________________________________________________ > > This email has been scanned by the MessageLabs Email Security System > on behalf of the London Business School community. > For more information please visit http://www.messagelabs.com/email > ______________________________________________________________________ > > ********** > Participation and subscription information for this EDUCAUSE > Constituent Group discussion list can be found at http://www.educause.edu/groups/. > > ********** > Participation and subscription information for this EDUCAUSE > Constituent Group discussion list can be found at http://www.educause.edu/groups/. > ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/. ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/. ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/. ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/. ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/.
