Avaya Power Over Ethernet Instruction Manual

A Practical Guide to Power Over Ethernet
(PoE) by Avaya
Release 1.1 Avaya Labs
ABSTRACT
This paper will discuss the highlights in the Power over Ethernet standard (IEEE 802.3af) and the earlier
pre-standard PoE implementations. Common implementation issues are also addressed to help you avoid
unpleasant surprises.
External posting: www.avaya.com.
Application Note
October 2006
COMPAS ID 122875
MJK Copyright © 2006 Avaya Inc. All Rights Reserved. 1

Copyright ©2006 Avaya, Inc.
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MJK Copyright © 2006 Avaya Inc. All Rights Reserved. 2

A Practical Guide to Power over Ethernet (PoE)
Document Summary
This document contains basic, but practical information concerning Power over Ethernet. Powering devices
like Access Points (APs), IP Telephones, Web Cameras, etc. through the Ethernet cable is a natural
evolution in the networking industry. The Central Office in the PSTN historically powered analog phones for
many decades. The PBX has also powered digital phones through the wires. Appliances, like Access
Points and Web-based Cameras are positioned in hard to reach locations, like ceilings, and are therefore
prime candidates for power through the Ethernet cable that connects them. There are benefits in powering
IP telephones through the Ethernet cable. One is convenience and another is the ability to monitor devices.
This paper will discuss the highlights in the Power over Ethernet standard (IEEE 802.3af) and the earlier
pre-standard PoE implementations. Common implementation issues are also addressed to help you avoid
unpleasant surprises.
The first part of this paper describes the basics of the IEEE 802.3af standard that was ratified in June 2003.
The second part of this paper describes practical differences in Power over Ethernet (PoE) implementations
of Avaya and Cisco equipment compared to the standard and to each other. This paper is not intended to
point out shortcomings of any other vendor, but it is beneficial to reveal subtle issues in vendor specific
implementations of PoE that can cause issues during and after installation. Since many customers use a
Cisco data infrastructure, Cisco specific examples are cited and compared to Avaya’s products. A PoE
checklist is included in Appendix A as a quick check to aid your implementations.
Table of Contents
A Practical Guide to Power over Ethernet (PoE) Document Summary .........................................3
A Practical Guide to Power over Ethernet (PoE) Paper .................................................................4
1Introduction.............................................................................................................................4
2Definitions...............................................................................................................................4
3IEEE 802.3af – how it works ...............................................................................................5
4Static vs. Dynamic Power Allocation..................................................................................7
5 PoE Implementation Details ................................................................................................9
6Avaya Configuration ...........................................................................................................12
7Cisco Configuration.............................................................................................................14
8 Future Directions .................................................................................................................22
MJK Copyright © 2006 Avaya Inc. All Rights Reserved. 3

A Practical Guide to Power over Ethernet (PoE)
1 Introduction
Voice over Internet Protocol (VoIP) is the convergence of traditional voice onto an IP data network to
provide better application integration by using common protocols. This lowers costs by using one network
infrastructure and even melding separate support staffs into one. Other real-time traffic streams, such as
uncompressed video and streaming audio are also converging onto data networks.
Convergence began with basic VoIP and, over time, has expanded traditional features and functions
including powering IP endpoints. The idea to send power through cables to an end device is not new.
Home analog telephones have been powered from the Central Office (CO) for scores of years. PBX type
switches have also provided power to analog and digital phones in business offices for decades. The
evolution to send power over a Cat-5 type cable is then a natural extension of an existing idea applied to a
new platform – the data network.
It is interesting that the IEEE eventually based their standard on the Avaya (Lucent Technologies at that
time) PoE scheme. This means that all Avaya products have been standards compliant even before the
standard was ratified. This also means that proprietary implementations of PoE, like Cisco, had to convert
from their vendor specific methods to the standards-based protocol. Older Cisco chassis-based switch
blades required daughter cards or total blade replacement to provide compliant power to the newer
standard. Adhering to the standard, titled IEEE 802.3af, is important because it allows power
interoperability from any vendor’s products. You can have confidence in Avaya’s products knowing that
Avaya led the IEEE standards committee with the ultimate solution for Powering devices over the Ethernet
cable. No one implements Power over Ethernet (PoE) better than Avaya. Avaya can intelligently and
dynamically apply the right amount of power to ANY vendor’s products that are standards compliant.
Please see section 5 of this paper for details.
2 Definitions
Before technologies are discussed, some important definitions must be learned.
End-Span. An End-Span, or Endpoint PSE is an Ethernet switch that is capable of sending Power over
Ethernet up to 100 meters over copper twisted pair to an endpoint device like an IP telephone.
Mid-Span. A device that lies between the Ethernet switch (or hub) and injects Power through the Ethernet
(copper) cable to the endpoint device. A Mid Span is not an access device like a switch or a hub. Its only
purpose is to inject power from the middle of the link between an access device (switch) and the endpoint –
hence the name “Mid” span.
Ohm. A measure of resistance using the Omega symbol - Ω
PD – Powered Device. A powered device is an endpoint that requires power. Many devices can
accommodate power in more than one way such as a local transformer or Power over Ethernet. Examples
of devices include IP telephones, Access Points, Web Cameras, magnetic card readers, etc.
PoE – Power over Ethernet is any scheme, either proprietary or standards-based, that defines how to send
power through an Ethernet cable.
PSE – Power Sourcing Equipment. A PSE is a device that sends Power over Ethernet to the PD. End-
Span and Mid-Span provide PoE, but there can also be other devices that send power to PDs.
Watt. A measure of power derived by multiplying current (Amperes) with resistance (Ohms). One Watt
equals one Ampere across one Ohm’s worth of resistance.
MJK Copyright © 2006 Avaya Inc. All Rights Reserved. 4

3 IEEE 802.3af – how it works
The phases between connecting a PD, power flow to the PD and power termination are:
PD (Powered Device) Detection
PD Classification or actual power determination
Power management, termination and PD re-discovery
PD Detection: The goal of this phase is to detect a valid PD. When a PD is connected to a PSE (Power
Sourcing Equipment), a small DC current is sent from the PSE. A PSE is typically a switch (End-Span) or a
power injector (Mid Span). If the resistive load of a PD is sensed at 25K Ω(+/- 1.25K Ω), the device may
meet the 802.3af requirements for power. Not only does the resistive load need to meet the 25K Ωlevel,
but the PD must also meet the resistance range during a short voltage ramp-up period. The idea is to only
power devices that are valid PDs and to protect non-PDs that could be damaged if they received power.
In a short amount of time, voltage is increased from 2.7 Volts to 10.1 Volts in 1.0 Volt increments. The
resistance must remain between the range of 23.75K Ωand 26.25K Ωor power is removed almost
immediately. This is generally known as the 802.3af resistive signature – adhering to both an initial
resistive range and that same range during a voltage ramp-up period. Any device that does not present this
resistive signature, will not receive power from the PSE. Additionally, any “signature” in the zones beyond
23.75 – 26.25 K Ωpresents an invalid or non-compliant signature and power will not be applied. See
appendix B for specifics on invalid and non-compliant signatures. Capacitance and inductance values are
also measured when validating a PD to the IEEE 802.3af standard.
Table 1 – Parameters for a valid PD power signature
Valid PD Detection Ramp-up Conditions Resistive Signature Range
Initial Resistive load for a potential PD 23.75K Ω– 26.25K Ω
Required resistance during voltage ramp-up 2.7V – 10.1V 23.75K Ω– 26.25K Ω
Input capacitance 2.7V – 10.1V 0.05µF – 0.12µF
Input Inductance 2.7V – 10.1V ≤100µH
Note: Power in the 802.3af standard is expressed in watts assuming 48 volts to the PD. By design, a PD
must accept a voltage variance. The standard mandates that “any PD will withstand 0 to 57 volts
indefinitely without damage”.
The IEEE 802.3af standard allows power on either the spare pairs or the signaling pairs. Ethernet uses
signaling wire pairs 1,2 & 3,6. Power over these used pairs is sometimes called phantom power or inline
power. Most End-Span PSEs (switches) use the inline power scheme, but they can also use the spare
pairs 4,5 & 7,8 as an option.
Mid-Span PSEs use only the spare pairs 4,5 & 7,8 to transmit power. All PDs are required to accept power
on either spare or signaling pairs. All Avaya products comply with this requirement and can be powered
three ways; from the signal pair, the spare pair or one pair (7,8) as a further option to support external
power supplies like a “brick” type transformer.
PD Classification: After detection, the goal of this next phase is to supply appropriate power. This can be
done based on the IEEE 802.3af power class of the PD, or more intelligent algorithms can sense how much
power is actually needed.
MJK Copyright © 2006 Avaya Inc. All Rights Reserved. 5

The IEEE 802.3af standard defines, but does not mandate, the use of power classes. This means a PD
may advertise one, and only one power class. This is important for non-Avaya PSEs that logically allocate
power from the total power pool and is discussed later in this paper. The following chart describes power
(in watts) required by PDs and provided by PSEs.
Table 2 – IEEE 802.3af power definitions for each class of PSE and PD devices
Class Usage Minimum Power from PSE Power Range at PD
0 Default 15.4w 0.44w – 12.95w
1 Optional 4.0w 0.44w – 3.84w
2 Optional 7.0w 3.84w – 6.49w
3 Optional 15.4w 6.49w – 12.95w
4 Reserved Treat as Class 0 Future Use
The preceding chart not only describes the power ranges for endpoints, but also the power minimums for
PSEs. The difference between the maximum PD power and the maximum PSE delivered power is needed
to “push” the power across a potential 100 meters (328 feet) of copper twisted pair between the PSE and
the PD. There is a natural attenuation of power from the PSE to the PD as the power encounters the
impedance of the copper wire. Therefore, more power is needed from the PSE so the full PoE class
maximum wattage is delivered to the PD.
IEEE 802.3af PD power class is derived from a classification signature measured in milli-Amps. The chart
below describes the values that a PD presents to a current under a constant voltage. The values returned
to the PSE then classify that PD into an IEEE power class.
Table 3 – Values used to assign PDs into IEEE 802.3af classes
Classification Signature Conditions Values
Current for Class 0 14.5V – 20.5V 0 – 4 mA
Current for Class 1 14.5V – 20.5V 9 – 12 mA
Current for Class 2 14.5V – 20.5V 17 – 20 mA
Current for Class 3 14.5V – 20.5V 26 – 30 mA
Current for Class 4 14.5V – 20.5V 36 – 44 mA
PD Management, Termination and Rediscovery: This final stage is steady state power management
including continual power parameter sensing and detecting PD absence or violation of required parameters.
Steady state powering involves a continual sensing of valid parameters. An example is a sudden short
circuit of the wire pairs carrying power. This condition is detected and power is almost instantly halted by
the PSE. If a PD is drawing power and is removed from the PSE port, power is again halted because
another device could use that same PSE port and be damaged by erroneously receiving power. Lastly, if
resistance, capacitance or inductance lies in the values listed in Appendix B, power is removed because the
signature is now invalid or non-compliant. This is the end of the 802.3af material. The remaining sections
are vendor specifics on implementing IEEE 802.3af PoE.
MJK Copyright © 2006 Avaya Inc. All Rights Reserved. 6

4 Static vs. Dynamic Power Allocation
Static Power Allocation
This method is used by many vendors because it is cheaper to implement. If a device advertises itself as a
class-1 endpoint but needs only 1-Watt of power, the PSE will allocate 4-Watts of power to the port serving
that device. This is done by logically allocating 4-Watts from the available power pool. Similarly, a class-3
device needing 8-Watts will be allocated 15.4-Watts of power. The problems with allocating the top of the
class range power are:
More power is reserved than is needed. A 1-Watt device will be allocated 4-Watts because the top of the
range for class-1 is 3.84-Watts plus a little more to travel over a possible 100 meters of Cat-5 cable.
Reserved power can deplete the total power pool even though it is not used. The resulting penalty from
logically reserving more power than the PD requires is that available power is “logically” exhausted before
all physical switch ports are used. For example, if a customer is using IP phones and those phones are
PoE class-3, each physical port will be ready to send out 15.4-watts. If each phone only requires 7-watts,
but 15.4-watts are reserved, 8.4-watts per port will logically consume part of the total power pool. Ten of
these physical ports used will strand 84 watts of power from the power pool. 24 ports will strand 201.6
Watts. 96 ports will strand 806.4 Watts. This is a worst case example.
The assumption that each port connected to a Class-3 device should be ready to provide 15.4-Watts at any
time doesn’t make sense with IP telephones or any known standards compliant device. Very few if any
devices operationally vary in power needs more than one Watt. An on-hook phone taking 8 watts will
almost never require more than 9-Watts in the off-hook state. Very few if any PDs require more than 11
watts, so the assumption of having to apply 15.4 watts rarely happens.
Static power allocation results in a brute-force application that is wasteful and unintelligent. It is easy to
calculate and deliver power based on the top of the power class, but it results in wasting or “stranding”
power logically from the total power pool. The practical results are:
9Incurring low port density. A 48-port switch or switch blade may only provide power to 32 ports
because power was logically exhausted.
9Buy larger power supplies. Systems with more than one power supply or chassis based switches
usually have options to buy higher wattage supplies. A larger power supply can mitigate or even
overcome the logical reservation limit, but at a cost of needlessly buying a large power supply you
don’t really need. Larger power supplies also cost more to run.
9Buy more switches. If larger power supplies don’t solve the problem, buying more switches may be
an alternative but can be very expensive. Many fixed switches have an internal power supply that
cannot be upgraded, so buying more may be a solution to low port density.
9Manually configure a power ceiling for each port. Today, many vendors have implemented a
feature that allows the administrator to manually set a power limit for each port. While this stops
the wasting of stranded logical power, it is a manual process requiring the switch administrator to
know the power needs of every device. Furthermore, the administrator must manually apply the
power limit to each port and be ready to change that limit as devices move or are changed with
other PDs.
Note: As you will see, Cisco and others use Static power allocation, but Cisco has created commands that
can put a power limit on any number of ports to solve issues of low port density, buying larger power
supplies or buying more switches. Manual configuration and maintenance is still a cost using this method.
MJK Copyright © 2006 Avaya Inc. All Rights Reserved. 7

Dynamic Power Allocation
This method is more expensive to implement in a switch or Mid-Span, but is less expensive to operate and
allows full port density. Dynamic power allocation senses how much power is required and delivers that
exact amount of power to the port leading to the PD. Dynamic, means that as the power requirements
change, the power delivered to that port also changes accordingly. Since dynamic power allocation doesn’t
depend on the advertised PD class, the algorithm isn’t confined to delivering 15.4-Watts for every port.
Therefore, the size of the power supply can be smaller than a static power allocation design.
Unlike the preceding section on static power allocation, if a device advertises itself as a class-1 endpoint but
needs only 1-Watt of power, the PSE will allocate 1-Watt of power to the port serving that device. There is
no logical reservation from the available power pool. Similarly, a class-3 device needing 8-Watts will be
allocated 8-Watts of power. There are no known problems with dynamically allocating the exact amount of
power needed. In fact the advantages over the static allocation scheme are:
No more power is reserved than is needed. A 1-Watt device will be allocated 1-Watt.
The total power pool is not affected by reservations. There is no wasted power because there is no concept
of reserving power from a pool. There is no logical pool to consider. Each device is given the amount of
power it requires.
The assumption that each port connected to a Class-3 device should be ready to provide 15.4-Watts at any
time still doesn’t make sense with IP telephones or any other standards compliant device. Again, very few if
any devices operationally vary in power needs more than one Watt. A phone taking 8 watts will almost
never require more than 9-Watts. If a PD required 12.95 watts, 15.4-Watts would be supplied by the
802.3af specification. If, theoretically, all ports required 15.4-Watts, you could run out of available power
due to a smaller power supply. This is not a known event in industry to date because very few if any Class-
3 PDs require a full 12.95-Watts.
Dynamic power allocation results in an intelligent application that is applied to any vendor’s PD. The
practical results of this method are:
9Full port density. A 48-port switch or Mid-Span will provide power to all 48 ports.
9No need to buy larger power supplies. Operational costs are lower.
9No need to buy more switches to compensate for a logical reservation of power. The equipment
footprint and operational/maintenance requirements are kept to a minimum.
9There is no manual configuration needed by a network administrator. Errors are avoided and time
is saved because there is no manual effort required to administer power for PDs. Changes can be
administered automatically or with a minimum of administrator effort.
MJK Copyright © 2006 Avaya Inc. All Rights Reserved. 8

5PoE Implementation Details
Avaya’s Implementation
The best method to provide PD power is not by PoE classification, but by delivering the exact amount of
power required by the PD. Avaya uses dynamic power allocation in all of its products – Mid-Spans, P330,
C360 and C460 switches and gateways like the G350 and G250.
All Avaya PSE devices detect the actual power requirements from the PD and can increase or decrease the
power amounts dynamically. No proprietary protocol is needed to assess and calculate the power needs of
an Avaya or other vendor’s PD as long as the PD is 802.3af compliant. For Avaya products, this means a
PD that has been powered for an hour, say an Avaya 4620SW IP phone, and an EU-24 Expansion Button
module is then attached to that phone, the PSE power is almost instantly increased to the PD to cover the
additional power needed by the EU-24. For Non-Avaya products, as a fictitious example, if a Logitech web
camera required 3.9 Watts, a PoE class-based PSE would have to reserve and be ready to supply 7.0
Watts because the camera would be classified as class-2. If that same camera was connected to an Avaya
PSE, the camera would receive 3.9 Watts plus an additional half Watt to traverse a potential 100 meters.
The Avaya PSE would not have reserved 7-Watts because Avaya PSEs intelligently deliver the right
amount of power to any vendor’s PD. Avaya also powers dynamically. This means if any vendor’s PD
requires varying power over time, the Avaya PSE follows the changing demand and delivers exact power at
any point in time.
Cisco’s Implementation
Cisco provided proprietary power before the PoE standard was ratified. After ratification of IEEE 802.3af,
Cisco supported both their legacy PoE scheme as well as the standard. Cisco uses CDP, a proprietary
discovery protocol, to discover Cisco IP telephones. After discovering which Cisco phone type is connected
to a switch port, the exact amount of power for that phone is logically reserved from a total pool of power
available. If a non-Cisco PD is attached to the same switch port, the power class from the PD is read and
the power limit at the top of the power class range is reserved from the same total power pool.
Cisco uses the advertised power class from non-Cisco PDs because the PD cannot participate in the
proprietary CDP protocol and because Cisco does not sense exact power needs. The resulting penalty
from logically reserving more power than the PD requires is listed in the previous “Static Power Allocation”
section.
Please remember, vendors other than Cisco also use static allocation of power based on advertised PoE
class and present the same implementation difficulties of low port density, requiring larger (or more) power
supplies, purchasing more switches or as we will see, need manual administration to place a power cap for
each port.
Another implementation detail for non-Cisco PDs using a Cisco Catalyst 6500 PoE platform is an
approximate 11% power loss when using the IEEE 802.3af method of powering PDs. Cisco has details on
this issue found here (see figure 7 in Cisco document):
http://www.cisco.com/en/US/products/hw/switches/ps708/products_white_paper0900aecd80233a77.shtml
No power supply is 100% efficient. Heat results from the inefficiency of power supplies. The approximate
11% loss is in addition to the natural inefficiency. Power loss occurs traveling from the power supplies,
along the back-plane and through the PoE switch card of this chassis-based system. The result of this
power loss is that a class-3 non-Cisco PD will have 17.3 Watts logically reserved to yield 15.4 Watts to the
Ethernet cable to make up for the loss on this larger Cisco chassis-based switch.
MJK Copyright © 2006 Avaya Inc. All Rights Reserved. 9

Below is a worst-case example of an 800-Watt power supply (not including power consumed by the switch
itself), powering class-3 PDs. Assume each non-Cisco PD requires 7-Watts to operate and is therefore a
class 3 device in terms of power.
Of the available 800 Watts, only 46 PDs can be powered because 17.3 Watts is reserved for each PD
(800W / 17.3W = 46). The actual power demand is 322 Watts (46 * 7W = 322W). Therefore, 478 Watts is
stranded because each PD has an additional 10.3 Watts reserved but never used (800W – 322W = 478W).
If the class-3 PDs were Cisco phones, CDP would discover them and apply the exact amount of power they
need for operation.
Cisco has addressed this issue with commands like “power inline allocation” and others.
Details are in section 7.
Avaya’s PSEs
The next natural question concerns implementation issues using Avaya’s PSEs. Avaya uses best-in-class
methods for all PSE equipment. There are no power transport inefficiencies to consider, no logical
reservation of power, no additional money spent to upgrade power supplies, no unintelligent static allocation
of power and no penalties when using any vendor’s standards compliant PD. Another benefit of dynamic
power allocation is the small number of commands needed to configure and maintain the switch or Mid-
Span. As you will see, there are fewer commands and command options using Avaya PSE products.
All ports can be used on all of Avaya’s PSE equipment – even with the most power hungry Avaya PDs
listed in the table below. This table lists very conservative power consumption numbers for Avaya IP
phones.
Values in the worst case row are not achievable in any customer environment. Values in the typical row are
conservative and the actual power draw may be lower. Using the worst case values will prevent issues
caused by switch configuration and is discussed earlier in this section.
Table 4 Avaya 46xx IP Phone Power Consumption in Watts assuming 48 volts.
Model
Notes
4601/02 4602SW 4606/12/24 4610 4620
Mfg
Disc.
4620SW
< 9/2004
4620SW
>9/2004
4621SW
4622SW
4625SW
PoE Class Class 2 Class 2 Class 0 Class 2 Class 3 Class 3 Class 2 Class 2 Class 3
Typical 3.5 4.1 5.0 4.0 7.7 5.9 4.6 4.9 7.8
Worst
Case 4.6 5.0 6.4 6.0 9.9 8.0 5.75 6.45 9.42
MJK Copyright © 2006 Avaya Inc. All Rights Reserved. 10

Table 5 Avaya 96xx IP Phone Power Consumption in Watts assuming 48 volts.
Model 9610 9620 9630 9630G 9640 9650 SMB-24 Gig-E
Adapter
PoE Class Class 2 Class 2 Class 2 Class 2 Class 2 Class 2 N/A Class 3
Typical (Not Backlit) * 4.6 4.6 * * * 0.35 *
Typical (Backlit) * 4.9 5.2 * * * 0.6 *
Worst Case * 5.30 5.58 * * * 0.9 *
Notes for table 5:
•Some 96xx models are not in production at the time this document was updated; therefore power
values are not available at this time. These future power values are marked with ( * )
•SBM24 is an additional 24-button button module that is powered from its associated phone. It is
not recognized as a standalone PD, but still draws power as listed in the table. The addition of this
module will NOT cause a class-2 phone to become a class-3 phone.
•The Gig-E adapter is a module that fits into all 96ss models except the 9610 and 9630G to allow
Gigabit Ethernet data flow through the phone. The 9630G phone model has Gigabit Ethernet
capability natively – that is without the Gig-E adapter.
Avaya’s PSEs include:
Switches: P333T-PWR, C363T-PWR, C364T-PWR, C460 with PoE blades
Gateways: G250, G350
Mid Spans: 1152A1/X, 1152A2/X, 1152A3/X
MJK Copyright © 2006 Avaya Inc. All Rights Reserved. 11

6 Avaya Configuration
Avaya has PoE in both a chassis based switch (C460) and fixed switches (C360, P330) as well as 802.3af
capability in the G250 and G350 gateways. They all function the same way using the same CLI. The
output is slightly different and is shown in tables below. PoE is enabled by default, so there is no
configuration needed unless PoE was previously disabled. The P330 (actually called the P333T-PWR) has
two internal power supplies – one for the switching functions and one to provide 802.3af power to the ports.
Redundant power for switching and powering ports is an option using external power supplies. Note that no
power is available to ports on the optional expansion module (X330T16).
To check the PoE state, use the “show powerinline” command.
There are four states under the Operational Status column.
Delivering power means detection has taken place and power is being supplied
Searching means a non-PoE capable device is attached and the switch keeps “searching” for a valid PD
signature.
Off means powering that port has been administratively disabled using the “set port powerinline”
command
Fault means a problem has been detected and no power is supplied.
The power allocated class column will always display class0. The Cajun switches do not rely on class to
deliver power. This may be used in the future.
To enable or disable power to a port, use the “set port powerinline” command.
The “set port powerinline priority” command can change the default value of low in the
powering priority. This column is used in the rare case where PD power requests exceed the capacity of
the internal power supply for those ports. Low, high and critical are valid options. If all ports are set to low
priority and more power is requested than can be delivered, power is removed from the highest physical
MJK Copyright © 2006 Avaya Inc. All Rights Reserved. 12

port. If that doesn’t bring the total power into the power budget, power is removed from the next highest
physical port and so until requested power is within the capability of the internal power supply.
The C360 series of Avaya switches have similar commands to the P330. The “show powerinline”
command display is slightly different from the P330 in that it doesn’t show the power allocated class
column. Again, Avaya switches, Mid-Spans and gateway power schemes do not require or rely on an
advertised class of power.
All ports have power enabled by default. Commands are:
Enable or disable power to a port or group of ports
Set port powerinline <mod/port> enable | disable
Assign a priority in case over-subscription requires shutting down port power
Set port powerinline priority <mod/port> <priority>
Low – (Default setting) standard priority for standard devices
High – higher priority than low for important devices
Critical – highest priority for critical devices like APs
Describe the PD for each port
Set port powerinline type <mod/port> “string”
The string is a text description of the PD.
MJK Copyright © 2006 Avaya Inc. All Rights Reserved. 13

7 Cisco Configuration
There are basically two different classes of Cisco switch PSEs, fixed and chassis. A fixed switch has very
little hardware configuration ability if any after it is purchased. Fixed switches generally don’t have
redundant power supplies, few features and flexibility compared to chassis-based switches. Examples of
fixed switches include the Catalyst 3560 and 3750. These are relatively inexpensive switches used for
access to the network.
Chassis-based switches have a cabinet that houses cards or blades. These cards can be replaced with
other cards to meet the changing needs of a business such as migrating from copper ports to fiber ports.
Although more expensive, they offer more features, redundancy, and again, can be reconfigured to meet
business changes or growth. Examples of enterprise switches are the Catalyst 4500 and 6500 series.
Some chassis-based switches can operate with either one of two operating systems (OS) – Cat-OS and
IOS. Cisco is migrating from Cat-OS to IOS and over time will only support IOS. But many enterprises still
use Cat-OS and the command syntax is different than using IOS. This section does not list all possible
commands for one or both OS platforms – just the most important commands to control PoE.
Fixed Switch Configuration
Fixed switches like the Catalyst 3560 and 3750 have power sensing enabled on all ports by default. This
means all ports continually sense for a valid PD and if found, will provide power based on class for non-
Cisco PDs. The show power inline command will display the total amount of power, the power used
and power remaining for that switch.
There are three states under the Admin column, Auto, Never and Static. The syntax to apply one of these
commands is: power inline {auto[max max-wattage]|never|static[max max-wattage]}
Auto is an automatic mode that senses the PoE class and then delivers the maximum power of that class’s
range if enough power is available. The example above displays 7.0 Watts for port fa/01 because it is a
class 2 PD. Port fa0/2 displays 15.4 Watts because the PD on that port is a class 3 device. When all
available power is allocated, no remaining ports can be powered.
Never is used to disable power and power sensing on that port (interface). Non-PDs like desk-top PCs are
good candidates for this command.
Static is used to pre-allocate power to a port even before the switch senses a valid PD. This is a priority
scheme to make sure the most important PDs always receive power.
MJK Copyright © 2006 Avaya Inc. All Rights Reserved. 14

The max max-wattage option for the Auto and Static states is used to restrict the use of higher power
Cisco PDs. This command should not be applied to Avaya or other vendor PDs. Be careful when using
this option because there are two reasons fixed switches will remove power from a port:
A PD requires more power than the Max option is set to provide
The Max option is set lower than the PoE class maximum value for a non-Cisco PD
You can detect if one of the two conditions listed above happens by using the show power inline
command. If you see “power-deny” instead of “on”, in the oper column, either the PD requested too much
power or the max max-wattage value was lower than the IEEE class maximum value. You cannot use the
max max-wattage option to save logical power to increase the number of PDs on a switch.
The Catalyst 3750 has a command to reclaim logical power for non-Cisco PDs beginning with IOS
12.2(25)SEC. This command sets a power ceiling that is more than the device will draw, but less than the
max value of the PoE class range. The command is power inline consumption default
[wattage value]. This command can be applied in “global configuration mode” for the entire switch or
individual values for each interface (port).
A global setting of 6 watts for every port would be:
Switch (config)# power inline consumption default 6000
An individual port setting for port 2 at 11 watts would be:
Switch (config)# interface gigabitethernet 1/0/2
Switch (config-if)# power inline consumption default 11000
This command is extremely useful if you are deploying non-Cisco class-3 PDs. The value is greatly
diminished when deploying class 2 or class 1 PDs because the difference between the actual power-draw
and the class maximum value is much smaller than with the class-3 range for IP telephones. Remember to
allocate enough power for a worst case PD power draw and to traverse 100 meters of cable. Table 2 can
help you decide how much additional power is needed to travel over 100 meters.
Catalyst 3560 and 3750 IOS Common Notes:
The “power inline” command was added to IOS 12.1(19)EA1
The “static” and “max” features were added to IOS 12.2(25)SE
Never use IOS earlier than 12.2(20)SE1 because power could still flow through a port even after the
valid PD was removed. This could damage a non-PD device.
Catalyst 3750 IOS Specific Note:
The “power inline consumption” feature was added to IOS 12.2(25)SEC
End of Fixed Switch section
MJK Copyright © 2006 Avaya Inc. All Rights Reserved. 15

Chassis-Based Switch Configuration
A chassis-based switch like the Catalyst 4006, 4506 and 6509 can provide standards-based power if the
correct line card (blade) is installed and the proper IOS or Cat-OS is running. This subsection focuses on
the Catalyst 6509 since it is the widest deployed platform amongst businesses that use Cisco switches.
IEEE 802.3af capable line cards have power sensing enabled on all ports by default. This means all ports
continually sense for a valid PD and if found, will provide power based on PoE class for non-Cisco PDs.
These larger switches are more complex in both hardware and software and will require more commands to
verify and configure than the smaller fixed access switches.
Examples shown are for the 4006 using IOS. The troubleshooting method is the same for 4500 and 6500
switches, but some of the commands may differ slightly.
There are basically four commands to use to assess the state of an existing PoE switch:
Show system [to verify the number of power supplies and their status]
Show environment power (or show power) [to verify consumed power and reserve power]
Show module [to verify the line (model) and daughter card (sub-model)]
Show port inline power [to verify power used and allocated per port on a blade]
These commands start at the system level and go to the port level.
The power supplies should be verified before configuration takes place. Use the “show system”
command to verify the power supply status. Verify how many power supplies are installed, their status, the
total watts supplied and the total watts delivered.
If total power should suddenly decrease, as in the case of a failed power supply, power is removed from the
line cards beginning at the bottom of the chassis moving upwards until the actual load is within the
remaining power budget. If a line card supports PDs, ports begin removing power beginning at the highest
port down to the lowest port before power is removed from that line card. This is another reason the show
system command can be very useful.
MJK Copyright © 2006 Avaya Inc. All Rights Reserved. 16

Next, use the show environment power command to check the power consumption status. The bottom
line will show the total available power to the line card, the amount used by the line card and the maximum
wattage allotted to each port on that line card.
Use the command show module to check the status of the PoE line card installed and the daughter card if
applicable. Note the sub-model at the bottom of the display shows the inline power daughter card (WS-
F6K-GE48-AF) installed on the line card (model) WS-X6148-GE-TX. The status should be “OK”.
MJK Copyright © 2006 Avaya Inc. All Rights Reserved. 17

Finally, use the show port inline power command to verify line card variables.
Column definitions:
Admin mode (auto, never). Auto will detect the PD class and apply power based on the top of that class.
Never disallows port power and the searching algorithm for a PD on that port.
Oper mode (on, off, faulty or deny). Operational mode is the actual state of a port compared to the admin
column which is the administered state. On means power is supplied by the port. Off means power is not
being supplied by the port. Faulty means the port is unable to power the PD. Deny means the port cannot
supply power because the system doesn’t have enough power.
From PS is the logical power reserved from the available power pool.
To PD is the power level leaving the line card to the PD
Device type either IEEE or Cisco phone model number
The class of PD connected to each port
The third line showing the “Total power drawn by module x” displays the amount of power consumed by the
PDs attached to it and does NOT include the power needed to run the module itself.
Don’t assume that a PoE capable line card can support all ports with up to 15.4 watts. Each line card slot in
the chassis is allocated about 1,000 watts regardless of the port density on any specific card. Cisco
introduced the WS-X6196-RJ-21, a 96-port PoE line card. IEEE 802.3af support on this line card requires a
PoE daughter card to manage 960 Watts for all ports. Again, worst-case, if class-3 PDs are used, only 62
ports could supply power. But using class-2 PDs, all 96 ports would give power.
MJK Copyright © 2006 Avaya Inc. All Rights Reserved. 18

Specific Commands for the Catalyst 4500 and 6500
4500 series:
The preceding 4 steps describe how many power supplies are active, total wattage available, total wattage
used, wattage used per module (blade) and which ports are delivering power, etc. The following commands
enable 802.3af PoE at the port level and apply a method for that port’s power.
IOS release 12.1(19)EW and higher:
Switch(config-if)# power inline {auto [max[milli-watts] | never | static
[max[milli-watts] | allocation}
Power inline sets the interface (port) to sense for and apply power if a PD is connected.
Auto will sense the class of a non-Cisco PD and apply power of the top of the class range
Max[milli-watts] allows you to specify a power ceiling that is lower than the class maximum, but higher than
the PD requires. Valid range is 2000 to 15400 milli-watts. This option will reduce the amount of logically
reserved power and is especially important when using class-3 PDs.
Static acts the same as auto except that it pre-allocates power to that port during startup. This is useful for
important PDs like access points and critical phones because it gives them priority over other PDs by pre-
allocating power.
Max[milli-watts] allows you to specify a power ceiling that is lower than the class maximum, but higher than
the PD requires. Valid range is 2000 to 15400 milli-watts. This option will reduce the amount of logically
reserved power and is especially important when using class-3 PDs.
Never disallows power to a port – even if a PD is connected.
Allocation works much like the “max[milli-watt]” option of auto and static where you can specify a power
ceiling for a port or globally for the entire switch. This command option allows you to specify a power value
independently from the PD class. Therefore PD class value is not determined and no errors result from
specifying a value that is above the class range for that PD. This can save time if more than one PD class
is used. An example is having class-2 and class-3 PDs on a switch and setting the allocation value to 9-
Watts. Class-2 ceiling is 7-watts, so using power inline auto 9000 would not work for class-2 PDs
because it exceeds the class limit. However, using power inline allocation 9000 would work for
both class-2 and class-3 phones because class limits are not considered. Valid values are 2000 to 15200
milliwatts. This option will reduce the amount of logically reserved power and is especially important when
using class-3 PDs.
MJK Copyright © 2006 Avaya Inc. All Rights Reserved. 19

Cat-OS 8.3(1)GLX or higher
set port inlinepower mod/port {off | {auto | static} [max-wattage]}
Power inline - sets the interface (port) to sense for and apply power if a PD is connected.
Off – removes power and sensing from a port or group of ports.
Auto – delivers class-based power if a valid IEEE PD is connected
Static – powers a port to a specified value if a valid PD is connected. This value is lower than the class
ceiling, but higher than minimum requirements of the PD.
Max-Wattage – a value of the maximum power used with auto or static mode. Valid range is 2000 through
15400 milli-watts. This option will reduce the amount of logically reserved power and is especially important
when using class-3 PDs.
set port inlinepower mod/port consumption {wattage | auto}
Consumption – specifies power consumption limit on a per port basis and can be used instead of the
previous command that used “auto” or “static”. This command is not based on the PD’s power class. This
option will reduce the amount of logically reserved power and is especially important when using class-3
PDs.
Wattage – range is 2000 through 15400 milli-watts
Auto – uses IEEE or CDP limits without administrator knowing PD requirements
set inlinepower defaultallocation value
This command pre-allocates a default wattage value as a global command and can cause problems if not
well understood and paired with another command. This command is only for Cisco phones – do not use
this command for Avaya phones.
Notes for Catalyst 4500
IOS
12.1(11)EW Support “power inline” command was introduced on the Catalyst 4500 series switch.
12.1(19)EW Support added for static power allocation.
12.1(20)EW Support added for Power over Ethernet.
CatOS
8.3(1)GLX support for “set port inlinepower” command expanded for all options listed.
MJK Copyright © 2006 Avaya Inc. All Rights Reserved. 20