Edge Computing Division Users Forum

Overview

Many devices are now equipped to use Power Over Ethernet (POE) as their power source. Such devices include VOIP telephones, iP cameras, wireless access points, and a growing variety of embedded devices. Fitlet, due to its miserly power requirements, is an ideal candidate for headless POE operation.




Some POE Basics

The most common forms of Power over Ethernet are specified by IEEE Standard 802.3. There are 2 prevalent variants of IEEE802.3 POE which are Type 1 Low Power covered by IEEE 802.3af (2003) and the newer Type 2 High Power covered by IEEE 802.3at (2009).

Any item of equipment used in POE applications can be classified as either Power Sourcing Equipment (PSE) or a Powered Device (PD). As their names imply, PSE's inject power into the systems and PDs use that power.

Some specfics about the POE variants are included in the table shown below.
Since Fitlet's specified power consumption is 10.5 watts or less, it is very suitable for use with both 802.3af low power and 802.3at high power systems. However, if you will operate your Fitlet with the BIOS TDP set significantly above 4500 in conjunction with multiple USB peripherals, it would be preferable to utilize the higher power PoE option.




The System

The Fitlet POE sysytem I tested is detailed in the following block diagram. Note that Fitlet is operating in a headless configuration and is controlled using VNC via a Compulab fitPC3 Pro running Windows 7.

For simplicity, I elected to run Fitlet in a headless configuration using a Compulab fit-Headless HDMI monitor adapter. This approach gives good headless results and does not require any changes to my Linux Mint OS.

Hardware

The hardware used in this test is as follows:

Power Sourcing Equipment

1. Intellinet Model 560436 PoE+ Power Injector


Powered Devices/VNC Server

1. Intellinet Model 560443 PoE+ Splitter
2. Compulab Fitlet (Linux Mint) running X11VNC
3. Compulab fit Headless HDMI Monitor Emulator
4. Custom Power Cable Fabricated using Compulab fitPC DC Cable

VNC Client

1. Compulab fitPC3 Pro (Windows 7) running VNC Viewer

Assembled Test System

Here is the assembled test system. It was compressed using short cables so that everything would fit in 1 picture. Obviously, in a real world application the POE Data/Power Cable would be much longer - up to 100 meters.



VNC Server Setup

1. Install Software

a. X11VNC (Available in Repository)
b. openbsd-inetd (Available in Repository)
c. tcpd (Available in Repository)

2. Configure X11VNC to start on bootup

a. Add the line
5900 stream tcp4 nowait root /usr/sbin/tcpd /usr/local/bin/x11vnc.sh
to the file /etc/inetd.conf

b. Create the file /usr/local/bin/x11vnc.sh

c. Add the following 3 lines (red text only) to the file x11vnc.sh you created in step b above
>#!/bin/sh
>/usr/bin/x11vnc -inetd -passwd "Your Password Goes Here" -o /var/log/x11vnc.log -display :0 \
>-auth /var/lib/mdm/:0.Xauth -many -bg

d. Make the script x11vnc.sh executable using the command:
sudo chmod +x /usr/local/bin/x11vnc.sh

e. Make the file /var/log/x11vnc.log writeable using the command
sudo chmod 766 /var/log/x11vnc.log

f. Restart Fitlet

g. Verify Port 5900 is open and listening using the command:
nmap -sT -O localhost




VNC Client

1. Connect VNC Client Machine to Fitlet VNC Server IP:Port 5900 and enter password

2. Control Fitlet remotely using your VNC Client Machine

Wndows 7 Based VNC Client


Results

Fitlet operates perfectly using Power Over Ethernet. There was no discernible difference in performance as compared to operating from the standard power supply.





Conclusions

1. If you have a need for operating a headless Fitlet in a location where a physical ethernet connection is available but mains power is not availalble, then POE may offer an alternative provided the ethernet cabling is adequate and the run isn't too long.

2. For a new headless Fitlet installation where both data and power cabling must be run, POE may provide a cost savings by eliminating the need to run power cabling.

3.Fitlet again demonstrates its versatility in fullfilling many different roles.