Tag Archives: Power over Ethernet

How Much Do You Know About PoE?

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For many network devices, like IP cameras, two connections would normally be needed—an electrical connection and the actual network connection. The electrical connection offers the necessary power for the device, and the network connection allows the device to communicate with the network. It’s obvious that cost will be increased if both of the connections are installed at the same time. However, PoE (Power-over-Ethernet) provides a cost-effective way for this kind of problem. Here are some basic introductions about PoE that you may be interested in.

poe

Do You Really Know Clearly About PoE?

Maybe most people know that PoE is a technology that enables powered devices such as surveillance camera and VoIP phone to receive electrical power and data over the same Ethernet cable, supporting the same 100m transmission distance, which eliminating the need for another electrical connection and power lines. However, do you really know clearly about PoE? Here, in order to get further understanding of PoE, I’d like to list several most common misconceptions, which offers a new way to help you know clearly about PoE in some degree.

PoE Has Compatibility Problems.

In the early days of PoE, it’s true that many proprietary schemes needed to get power on network cables. However, with the development of PoE, the IEEE 802.3af standard has achieved universal adoption, which means that the compatibility issue between all PoE equipment is assured.

Power Is Forced into Devices.

This misconception is the most common one. But what we should keep in mind that the power ratings marked by manufacturers is not fixed. Plugging a 5 watt camera into a 15 watt injector does not result in 10 watts of power being lost somewhere. Instead the camera will simply draw as much electrical power as it needs.

PoE Requires Special Wires.

This conception is not right at all. Because common cables used in networks such as Cat 5e, Cat 6 and Cat6a, and RJ45 connectors are also can be deployed for PoE-enabled local area networks. Besides, power-sourcing equipment such as a PoE switch or PoE Injector utilizes a power supply and help network link to a powered device.

Where Is PoE Used?

Apart from data communications between two devices, PoE also enables an Ethernet switch/Hub to power a remote device over an existing LAN cable. Without PoE, any remote device needs to be powered independently. And PoE also has many other applications. Here are three major applications of PoE: network cameras, wireless access points (WAPs) and voice-over-IP phones (VoIPs). Following is a simple diagram of PoE application.

poe-applications

What’s the Major Advantages of PoE?

Installing PoE to your network will bring lots of advantages that you cannot ignore.

Time and Cost Saving

By deploying the PoE, there is no need to install conduit, electrical wiring and outlets throughout the facility, which provides a significantly reduction on investment. What’s more, as PoE runs via one cable directly, it also takes less time to install.

Increased Reliability

In terms of the nature of systems, fewer electrical cords and power plugs mean more reliable, for there is less chance for a malfunction or other problems. For example, power maybe need to be cut down by an electrician who was called to rewire the electrical circuits.

More Flexibility

When planning out the location of access points, designers know there are always existing different problems. However, PoE enables designers to have more flexibilities, because they are not limited by the need for proximity to electrical outlets. And this also makes the deployment easier and cheaper for future modifications such as relocating access points or increasing network capacity.

Enhanced Operational Support

Many PoE devices utilize the simple network management protocol (SNMP), which offers the electrical power supplied to access points in remote management. For instance, the power to a PoE-enabled access point can be shut off remotely following detection of a security breach. Therefore, other SNMP-based features allow the power supply and consumption levels to be monitored by systems, which effectively ensures the network operations.

Summary

In summary, it is no doubt that PoE is an innovative technology that provides a more convenient, flexible and cost-efficient method for powering network devices. And there are many products supporting PoE in the market such as injectors, PoE switches, PoE media converters and network interface cards. For more information, please visit FS.COM.

Fundamentals of Power over Ethernet (PoE)

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With the introduction of new Ethernet-enabled devices expanding geometrically, the need to power these devices from standard AC power outlets has become a limiting factor. IP telephones, wireless access points, IP cameras and device servers are examples of devices limited by the need to have an AC power outlet nearby to plug in a DC power adapter. At best, power supply installation and wiring adds labor and results in the mess of extra wiring; worst case, the lack of nearby AC power means devices cannot be installed where they are needed.

In response to this need, IEEE developed IEEE802.3af to standardize a system of supplying low voltage power to networked devices via the communications line. It is more commonly referred to as Power over Ethernet (POE). This article focus on introducing some fundamental elements about PoE.

Basic Concepts of PoE

PoE is defined across a single network link that includes three basic components. The first one is an equipment delivering power to the cable (often referred to as a PSE, which stands for power sourcing equipment). The second component is a device receiving power from the cable (also known as a powered device, or PD). The third is the cable itself.

Typical PDs include IP cameras, wireless access points, and the PSE would normally be a PoE switch or a midspan power injector, patched in to add PoE capability to a non-PoE network switch channel or similar. These two configurations are shown in the following picture.

PoE

Advantages of PoE

The most prominent advantages of PoE are time saving and cost effective. By reducing the time and expense of having electrical power cabling installed, network cables do not require a qualified electrician to fit them, thus it can be located anywhere. Besides, it has great flexibility. Without being tethered to an electrical outlet, the PDs (IP cameras, wireless access points) could be located wherever they are needed most. Safety is the third advantage. PoE delivery is intelligent and it is designed to protect network equipment from overload, or incorrect installation. Also it has reliability and scalability. PoE power comes from a central and universally compatible source, rather than a collection of distributed wall adapters. It can be backed-up by an uninterruptible power supply, or controlled to easily disable or reset devices.

Applications of PoE

The original PoE application is VoIP phones, which have a single connection to a wall socket, and can be remotely powered down, just like with the older analog systems. PoE could also be used in IP cameras. It is ubiquitous on networked surveillance cameras where it enables fast deployment and easy repositioning. Wifi and bluetooth APs and RFID (radio frequency identification devices) readers are commonly PoE-compatible, to allow remote location away from AC outlets, and relocation following site surveys.

How PoE Works

PoE is designed to operate over standard network cable: Cat 3, Cat 5, Cat 5e or Cat 6 (often collectively referred to as Cat 5), using conventional RJ45 connectors. The principles of carrying electrical power over Cat5 are of no difference to those of other power distribution systems, but as the power is being transferred over light-duty cable for long distances, the effects of the power loss and voltage drop become significant.

The arrangement and connection to the cabling used for PoE also differ slightly from conventional power wiring, in order to work around the existing standard for Ethernet data. Cat 5 network cables contain a bundle of eight wires, arranged as four twisted pairs shown in the following picture. In the most common type of Ethernet, 100BASE-T or Fast Ethernet, only two of the four pairs are used to carry data; each pair carrying a signal in one direction. These are known as the data pairs, and the remaining two are unused and are referred to as the spare pairs.

PoE working

Although each data signal can be carried within a single pair, PoE treats each pair of wires as a single conductor (a reason for this is that using both wires halves the overall resistance). As electrical current must flow in a loop, two pairs are required to allow power to be carried by the cable, and either the data or spare pairs can be used for this. The PD must be able to accept power from whichever pairs the PSE delivers it to.

Conclusion

PoE is a convenient and now ubiquitous method for delivering power to a wide variety of loads on standard Cat 5 Ethernet cables. It is no doubt that Power over Ethernet will become increasingly important in the near future.