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Technical Note: Power over Ethernet on
Business Ethernet Switches (BES)
Version: NN70000-003 issue 1.00
Date: November 28, 2008
Status: Released
Copyright © 2008 Nortel Networks. All rights reserved.
The information in this document is subject to change without notice. The statements, configurations, technical
data, and recommendations in this document are believed to be accurate and reliable, but are presented without
express or implied warranty. Users must take full responsibility for their applications of any products specified in
this document. The information in this document is the property of Nortel Networks.
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Technical Note: Power-over-Ethernet on BES products
Revision History
Revision
(Ver.Iss)
1.00 Nov. 28, 2008 Released First release of document
.
Issue Date Document
Status
Change Description
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Technical Note: Power-over-Ethernet on BES products
About this Document
This document is intended for people responsible for deployment and support of the Nortel Business Ethernet
Switch (BES) product. This may include:
• Customer System Engineering
• Channel Partner Engineering
• Nortel Solutions Engineering
• Knowledge Systems / Education Services
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Technical Note: Power-over-Ethernet on BES products
Table of Contents
Revision History..........................................................................................................................................2
About this Document..................................................................................................................................3
Table of Contents........................................................................................................................................4
1. Introduction..........................................................................................................................................5
2. Definition and Concepts.....................................................................................................................5
3. BES50 PoE capabilities.......................................................................................................................6
3.1 Number of PoE ports and PoE power budget..................................................................................6
3.2 Standards Compliance.....................................................................................................................6
3.3 Operations and Configuration ..........................................................................................................6
4. BES100/200 PoE capabilities .............................................................................................................7
4.1 Number of PoE ports and PoE power budget..................................................................................7
4.2 Standards Compliance.....................................................................................................................7
4.3 Operations and Configuration ..........................................................................................................7
5. BES1000 PoE capabilities ..................................................................................................................8
5.1 Number of PoE ports and PoE power budget..................................................................................8
5.2 Standards Compliance.....................................................................................................................8
5.3 Operations and Configuration ..........................................................................................................8
List of Acronyms.........................................................................................................................................9
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Technical Note: Power-over-Ethernet on BES products
1. Introduction
Power over Ethernet is a technology enabling efficient and simplified wiring of various Ethernet-based devices
like IP Phones, WLAN Access Points, printers, etc… It also brings the value of a centralized the power source
for network critical devices and enables efficient installation of power protection mechanisms.
The Nortel Business Ethernet Switch (BES) products include a wide range of PoE-capable Ethernet switches.
The purpose of this document is to provide information about the PoE capabilities of the various BES products
such as to facilitate the deployment and engineering of PoE solutions.
Different BES models have different PoE power budgets and capabilities. This document includes one section
for each sub-family of BES models.
2. Definition and Concepts
Guard Band
Some PoE capable switch includes a "Guard Band" which protects against an additional Powered Device (PD)
from causing the Ethernet switch to cycle a Powered Device (PD) on and off when the new connected device
brings the total power demand above total PoE power budget.
If the current power draw across all PoE devices exceeds the total power budget minus the Guard Band, then
no new devices are allowed to be power up.
PoE Watts and Current and Voltage
Per 802.3af standard, each port on a PSE device must be capable of delivering up to 350 mA of current within a
voltage range of 44 to 57V volts. For the minimum 44V, this yields 15.4 watts of power, which is the normal
documented max for a PoE Port, but this is the power at the Ethernet Switch port. The Powered Device cannot
draw more than 12.95 watts max – the difference accounts for the excepted power loss over 100m of twistedpair cable.
The 802.3af standard allows the PoE Voltage to vary from 44V to 57V. Since the voltage is a property of the
Ethernet Switch and not the Powered Device (PD), and the current draw is a property of the PD, PoE power
management is typically based off of current draw at a nominal 44V. This means that on a typical PoE
installation, where the voltage is the nominal 48V, the measured power draw on the devices, will be higher than
one would expect. For example a 15.4W max power device (based on 44V nominal) will draw 16.8W at 48V at
the Power Sourcing Equipment (PSE).
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Technical Note: Power-over-Ethernet on BES products
3. BES50 PoE capabilities
3.1 Number of PoE ports and PoE power budget
The BES50 products comes in four models as identified in the table below. All models have 12 PoE ports and
have the same PoE power budget.
Product Model Number of PoE
ports
BES50FE-12 12 84W 7W
BES50FE-24 12 84W 7W
BES50GE-12 12 84W 7W
BES50GE-24 12 84W 7W
The total PoE power budget is shared power budget for all PoE ports on the system. Per 802.3af standards, any
PoE port on the system can use (and therefore provide) a maximum of 15.4W.
3.2 Standards Compliance
The PoE capabilities of BES50 are compliant to the 802.3af standards. As such, BES50 PoE ports can provide
power to any 802.3af compliant Powered Device (PD).
The BES50 product does not support pre-standard PoE methods (like capacitive detection).
Total PoE power
budget
PoE guard-band
3.3 Operations and Configuration
Functionality Available on
BES50
Ability for administrator to shut-down PoE on a port Yes
Ability for administrator to limit the total PoE power budget to a lower value Yes
Ability for administrator to set port priority for PoE power budget allocation Yes
Presence of management LEDs providing PoE status on port basis Yes
Power budget allocation rules
If a device is connected to a switch port and the switch detects that it requires more than the power budget of
the port, no power is supplied to the device (that is, the port power remains off).
If the power demand from devices connected to switch ports exceeds the power budget set for the switch, the
port power priority settings are used to control the supplied power. For example:
• If a device is connected to a low-priority port and causes the switch to exceed its budget, port power is
not turned on.
• If a device is connected to a critical or high-priority port and causes the switch to exceed its budget, port
power is turned on, but the switch drops power to one or more lower priority ports.
Power is dropped from low-priority ports in sequence starting from port number 12 down to port 1.
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4. BES100/200 PoE capabilities
4.1 Number of PoE ports and PoE power budget
The BES100 & BES200 Fast Ethernet switch products come in eight models as identified in the table below.
The table below provides information on PoE port and budget for each of these models
Product Model Number of PoE
ports
BES110-24T 0 No PoE N/A
BES110-48T 0 No PoE N/A
BES120-24T 12 168W 10W
BES120-48T 24 168W 10W
BES210-24T 0 No PoE N/A
BES210-48T 0 No PoE N/A
BES220-24T 12 168W 10W
BES220-48T 24 168W 10W
The total PoE power budget is shared power budget for all PoE ports on the system. Per 802.3af standards, any
PoE port on the system can use (and therefore provide) a maximum of 15.4W.
Total PoE power
budget
PoE guard-band
4.2 Standards Compliance
The PoE capabilities of BES100/200 are compliant to the 802.3af standards. As such, BES100/200 PoE ports
can provide power to any 802.3af compliant Powered Device (PD).
The BES100/200 product does not support pre-standard PoE methods (like capacitive detection).
4.3 Operations and Configuration
Functionality Available on
BES50
Ability for administrator to shut-down PoE on a port Yes
Ability for administrator to limit the total PoE power budget to a lower value No
Ability for administrator to set port priority for PoE power budget allocation No
Presence of management LEDs providing PoE status on port basis Yes
Power budget allocation rules
If a device is connected to a switch port and the switch detects that it requires more than the power budget of
the port, no power is supplied to the device (that is, the port power remains off).
By default, power is allocated based on real time measurement. If the total Ethernet power budget for the
BES120/220 is exceeded, the switch sheds load by shutting down ports, starting with the highest numbered
port. The BES120/220 attempts to restore power to uppermost ports at regular intervals.
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5. BES1000 PoE capabilities
5.1 Number of PoE ports and PoE power budget
The BES1000 Gigabit Ethernet switch products come in four models as identified in the table below. The table
below provides information on PoE port and budget for each of these models
Product Model Number of PoE
ports
BES1010-24T 0 No PoE N/A
BES1010-48T 0 No PoE N/A
BES1020-24T 12 175W 0W
BES1020-48T 24 275W 0W
The total PoE power budget is shared power budget for all PoE ports on the system. Per 802.3af standards, any
PoE port on the system can use (and therefore provide) a maximum of 15.4W.
5.2 Standards Compliance
The PoE capabilities of BES1000 are compliant to the 802.3af standards. As such, BES1000 PoE ports can
provide power to any 802.3af compliant Powered Device (PD).
The BES1000 product does not support pre-standard PoE methods (like capacitive detection).
Total PoE power
budget
PoE guard-band
5.3 Operations and Configuration
Functionality Available on
BES50
Ability for administrator to shut-down PoE on a port Yes
Ability for administrator to limit the total PoE power budget to a lower value No
Ability for administrator to set port priority for PoE power budget allocation No
Presence of management LEDs providing PoE status on port basis Yes
Power budget allocation rules
If a device is connected to a switch port and the switch detects that it requires more than the power budget of
the port, no power is supplied to the device (that is, the port power remains off).
By default, power is allocated based on real time measurement. If the total Ethernet power budget for the
BES1020 is exceeded, the switch sheds load by shutting down ports, starting with the highest numbered port.
The BES1020 attempts to restore power to uppermost ports at regular intervals. One can enable or disable
power to an individual port using the Web-based management interface.
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Technical Note: Power-over-Ethernet on BES products
List of Acronyms
BES Nortel Networks Business Ethernet Switch
PD Powered Device
PoE Power over Ethernet
PSE Power Sourcing Equipment
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