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PoE 802.3af connection speed
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| davey_fl |
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Posts: 16
Joined: 11 May 2008
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Posted: Mon Jun 30, 2008 3:49 pm
Post subject: PoE 802.3af connection speed
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I'm trying to determine whether using PoE 802.3af to power a ptz IP camera reduces the connection speed of the camera down to 10mb from 100mb? In other words, does using one of the twisted pairs for DC reduce the number of twisted pairs avail for data since 100mb needs all 4 pairs? Or does the standard simply piggyback DC and data down one of the twisted pairs?
Thanks
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| ak357 |
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Posts: 317
Joined: 16 Nov 2005
Location: Canada
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Posted: Mon Jun 30, 2008 7:46 pm
Post subject: Re: PoE 802.3af connection speed
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| davey_fl wrote: |
I'm trying to determine whether using PoE 802.3af to power a ptz IP camera reduces the connection speed of the camera down to 10mb from 100mb? In other words, does using one of the twisted pairs for DC reduce the number of twisted pairs avail for data since 100mb needs all 4 pairs? Or does the standard simply piggyback DC and data down one of the twisted pairs?
Thanks |
The IEEE 802.3af standard uses the same "data" pairs as ethernet, leaving the "spare" pairs free. This PoE adds DC power to the data pairs using signal transformers, and pickes off power at the far end the same way. A comprehensive set of technical standards for Power Sourcing Equipment (PSE) and Powered Devices (PD) create an "idiot proof" system protected from shorted wiring, polarity reversal, or accidentally plugging in non-PoE equipment. IEEE 802.3af is technically complex and best implemented with power management chips specially designed for the purpose, supplied by Dallas, Maxim, Linear Technology, Texas Instruments, and others, that are intended to be embedded into the PoE devices themselves.
The new IEEE 802.3af standard alternatively allows the "spare" wire pairs to be energized, to be compatible with both types of wiring. You may mix 802.3af with older or homebrew PoE devices, but the result may not be "idiot proof". If your mixed network has only PoE sources that are IEEE 802.3af compliant, your mixed network is pretty safe from damage, but older devices may or may not operate correctly. This mixed PoE allows brands to migrate to the common standard.
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| zmxtech |
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Posts: 285
Joined: 09 May 2007
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Posted: Tue Jul 01, 2008 3:39 am
Post subject: ip
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FYI
10mb and 100mb use 2 pairs each [4] there are 4 spare for power or 1000mb if you use it
z
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| davey_fl |
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Posts: 16
Joined: 11 May 2008
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Posted: Tue Jul 01, 2008 6:54 am
Post subject:
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of course! I was thinking of gigabit! thx.
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| kalpesh_nikumbh |
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Posts: 145
Joined: 24 Jun 2008
Location: Mumbai , India
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Posted: Sat Jul 26, 2008 2:51 am
Post subject:
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thanks ak357!!
for additing the info...
Power added over ethernet dosen't make any diffrence in terms of speed!!
right??
Kalpesh niumbh
india
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| Thomas |
Moderator
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Posts: 2102
Joined: 17 May 2004
Location: Houston, TX
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Posted: Sat Jul 26, 2008 4:51 am
Post subject:
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| kalpesh_nikumbh wrote: |
thanks ak357!!
for additing the info...
Power added over ethernet dosen't make any diffrence in terms of speed!!
right??
Kalpesh niumbh
india |
Yes and no. The short answer is no. The slightly longer answer is that as long as your equipment is putting out fairly clean power you won't introduce cross talk which would slow the speed of the connection down.
_________________
Thomas
Sales Support
Video Insight
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| kalpesh_nikumbh |
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Posts: 145
Joined: 24 Jun 2008
Location: Mumbai , India
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Posted: Sat Jul 26, 2008 5:22 am
Post subject:
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Ok. Thomas my brother!!
Kalpesh Nikumbh
India
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| riggstech |
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Posts: 6
Joined: 25 Jul 2008
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Posted: Mon Nov 17, 2008 10:59 pm
Post subject: PoE Variant A and Variant B
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In responce to AK357,
IEEE-802.3af states that the Power Sourcing Equipment PSE can choose either Variant A, which places power on lines 1,2,3 ,6 or Variant B lines 4,5,7,8.
A Powered Device (PD) that is IEEE-802.3af compliant must be able to accept power from both sources. Also within the IEEE-802.3 standard the PD device must accept positive or negative on either lines.
From our research we found that most Injectors and Mid spans use Variant B with Positive power on Pins 4.5 and Negative power on 7,6.
Network Switches with PoE seem to use Variant A.
Cisco also uses Variant B but with Positive power on 7,8 and Negative power 4,5.
But all this has nothing to do with the bandwidth of Ethernet per say. Yes unclean power can foster cross talk which can effect things.
james.
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| bobby1471 |
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Posts: 9
Joined: 18 Aug 2008
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Posted: Tue Nov 25, 2008 5:01 pm
Post subject: Re: PoE Variant A and Variant B
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| riggstech wrote: |
In responce to AK357,
IEEE-802.3af states that the Power Sourcing Equipment PSE can choose either Variant A, which places power on lines 1,2,3 ,6 or Variant B lines 4,5,7,8.
A Powered Device (PD) that is IEEE-802.3af compliant must be able to accept power from both sources. Also within the IEEE-802.3 standard the PD device must accept positive or negative on either lines.
From our research we found that most Injectors and Mid spans use Variant B with Positive power on Pins 4.5 and Negative power on 7,6.
Network Switches with PoE seem to use Variant A.
Cisco also uses Variant B but with Positive power on 7,8 and Negative power 4,5.
But all this has nothing to do with the bandwidth of Ethernet per say. Yes unclean power can foster cross talk which can effect things.
james. |
reviving old posts? But Your right, POE does nothing to the speed on 99% of your installs.
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