Lantronix
SM24TBT2DPA Install Guide
33737 Rev. L
Page
29
of
38
PoE Modes and Compliance
PoE Deployment Environments A and B
IEEE802.3at-2009 defines two deployment environments in section 33.4.1:
Environment A
: when both PSE and PD are located indoors, inside the same building. In this environment, there
has to be electrical isolation between the PoE circuitry and the data circuitry inside a PSE. Multi-port PSE’s can all
share the same ground isolation. Environment A is therefore an
indoor PSE – indoor PD
environment (a.k.a.
indoor/indoor
).
Environment B
: when the PSE and PD are not located in the same building. In this environment there needs to be
electrical isolation between PoE and data, as well as between every port in a multi-port PSE. This isolation
between ports requirement de facto determines a completely separate power supply per port, which makes
multi-port PSE’s for outdoor PD deployment impractical. Environment B is therefore an
indoor PSE - outdoor PD
(a.k.a.
indoor/outdoor
) or outdoor PSE-outdoor PD (a.k.a. outdoor/outdoor) environment.
This means only single-port PSE’s should normally be used when PD’s are deployed outdoors. In summary, the
PD-PSE environment is one of these three combinations:
1. PoE Source is indoor, PD is indoor (Env. A)
2. PoE Source is indoor, PD is outdoor (Env. B)
3. PoE Source is outdoor, PD is outdoor (Env. B)
Option 3 is the most challenging environment since both the PD and PSE are installed outdoors.
Caution
: The
switch is an indoor device. If it is to be used with outdoor devices such as outdoor IP cameras or outdoor Wi-Fi
APs, then you are strongly suggested to install a surge protector or surge suppressor in order to protect the
switch. The switch is compliant with 802.3at in Environment A when using an isolated power supply. For 802.3at
Environment B applications, i.e. building to building, copper to copper endpoint connections: 1) use an Ethernet
network isolator module (PoE disabled), or 2) use mid-span injector(s) such as Lantronix’ MIL-L100i or L1000i-
at, between this switch’s PSE port and link partner PD port.
Mode A vs. Mode B
Alternative A, also known as Mode A, uses the data pairs of an Ethernet link to deliver power. Data Pairs include
pins 1,2 and 3,6. PSEs using Mode A supply a positive voltage to pins 1 and 2. Alternative B, also known as Mode
B, uses the spare pairs to deliver power. Spare Pairs include pins 4,5 and 7,8.
802.3af/at Standard “compliant” vs "compatible" PDs
Knowing the difference between PoE "compliant" devices and "compatible" devices can help avoid
interoperability and connectivity issues. Compliant and compatible PoE devices are not held to the same
802.3af/at standard:
•
802.3af/at “compliant” PDs fulfill the IEEE strict requirement to support both Mode A and Mode B power
modes.
•
802.3af/at "compatible" PDs typically can provide power using only Mode B.