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Troubleshooting Q&A - January 22, 2004

Power over Ethernet vs. Powerline Technology

Keeping current with the multitude of home networking technologies can be quite a challenge. It's all too easy to get confused as new acronyms and technologies pop up right and left. This week's Q&A compares and contrasts a couple of commonly misunderstood technologies – Powerline and PoE.

By Ron Pacchiano

Q. I was hoping you could settle a disagreement between me and some of my co-workers. I was talking with a couple of them about a home networking problem I was having when one of them suggested that I look into possibly setting up a Power over Ethernet network. I had never heard of this before and thought that he had actually meant to say a Powerline network. His response was, “They are the same thing.” I disagreed.

So we brought our disagreement to some of the other technicians for their input. Most of them hadn’t even heard of either one, and a few of them agreed with my associate that the two are in fact the same. I still insist that they are different and was hoping that you could set the record straight. Are they the same? If not, then what is Power over Ethernet? I have $60 bucks riding on this, so please don’t let me down. Thanks!

A. I have to tell you, there’s almost nothing I enjoy more than taking money off of my co-workers when they tell me that I’m wrong in my interpretation of a technical issue. Fortunately, today you get to share in that feeling!

You are indeed correct in your assertion that Powerline networks are in fact different from Power over Ethernet (PoE). Powerline, or HomePlug, networks use the electrical cabling already running throughout your house to carry data between your systems. They have a throughput rating of 14Mbps and support 56-bit DES encryption for security and privacy. They don’t use any device drivers, which makes them easy to install, and many Powerline solutions can be purchased for about $100.

Power over Ethernet (PoE), also known as IEEE 802.3af, is a technology standard designed for wired Ethernet LANs (local area networks) that allows the ELECTRICAL CURRENT necessary for the operation of a network device to be carried by the Ethernet cables rather than through separate power cords. The most significant benefit of PoE is that it minimizes the number of wires that must be strung in order to install the network. This results in lower cost, less downtime, easier maintenance, and greater installation flexibility than you have with traditional wiring.

For PoE to work, the electrical current must go into the data cable at the power supply end (usually referred to as a "power hub") and come out at the device end in such a way that the current is kept separate from the data signal so that neither interferes with the other. The current enters the cable by means of a component called an injector. If the device at the other end of the cable is PoE-compatible, then that device will function properly without modification. If the device is not PoE-compatible, then a component called a picker or tap must be installed to remove the current from the cable. This 'picked-off' current is then routed to the power jack.

To minimize the possibility of damage to equipment in the event of a malfunction, the more sophisticated PoE systems employ a kind of surge protection. This feature shuts off the power supply if an excessive current or a short circuit is detected.

Even with the recent standardization of Power over Ethernet as IEEE 802.3af, it is still an evolving technology with many hurdles to overcome. However, it has the potential to create a whole new world of smart networked appliances (e.g. internet-enabled Refrigerators) because of its unique ability to provide power as well as data over nothing more than an existing Ethernet cable.

Jim Geier, an associate of mine at Wi-Fi Planet, wrote a fantastic story about Power over Ethernet. It discusses in much greater detail the benefits of this promising new technology and what equipment you need in order to successfully implement it. If you’re interested, the full story can be found at http://www.wi-fiplanet.com/tutorials/article.php/1404631.

Enjoy your new found cash and try not to gloat too much when you take it!

Q. I’m experiencing kind of a strange problem with my broadband router. I can connect to the Internet just fine. However, on some websites where a login is required, I get a bunch of error messages on the screen that prevent me from logging in. When I can finally enter my username and password, I usually get a message from Internet Explorer saying “Access Denied.”

I initially thought that my router was the cause of my problem due to somehow blocking the site I was trying to log into, but I can’t find any area within my router’s firewall to support this theory. Do you have any suggestions that might help me resolve this problem? Thank you!

A. First of all, whenever you ask a question of this nature it’s always helpful to supply the router make and model and one or two websites where you have experienced this problem. However, with the information you did provide, I can offer a few words of advice that may help.

For starters, I'm reasonably sure that the router is not your problem. Although many broadband routers have the capability to block entire Web sites based on the URL or IP address, they are usually pretty expensive and, in some cases, a bit complicated to configure. Additionally, it would be next to impossible for this block to have been enabled accidentally; you would have had to specifically enabled it.

A more likely possibility is that there is (or was) a site error or scripting error on the page you were trying to access. It's not uncommon for sites to have these kinds of errors, which are usually unwittingly introduced when the site is updated or content is somehow changed. Sometimes these can manifest themselves as permissions errors. If the problem is intermittent or clears up after a while, this is most likely the case.

You didn't say what version of Internet Explorer you are using, but I would check to make sure you’re using the latest version with all of the service packs installed. It’s also reasonable to think that your IE settings were inadvertently changed or corrupted. I've seen this occur on many occasions. You can reset your settings under Tools, Internet Options. Choose the Security tab and click Default Level, then choose Advanced and click Restore defaults. You might also try deleting your cookies and temporary files.

One last thought — there is the possibility that this could just be human error. You mentioned that this typically happens on sites where you need to supply a login name and password to gain access. It’s possible that you just might have entered this information incorrectly. Perhaps you inadvertently left the cap lock key on. I know it’s unlikely, but don’t rule it out. Anyway, I hope this helps. Good Luck!


Use our feedback form to submit your questions on home or SOHO networking issues. We cannot guarantee to answer every question we get, but we’ll consider them all.



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