Media Conversion

Choosing the right backbone

• By Susan Stanley
• Jun 01, 2014

When a successful European toy manufacturer outgrew its facilities, it built a new, three-facility campus that included an office along with manufacturing and warehouse space. It would have been impractical to network the new campus with copper Ethernet cable, since it has a range limitation of about 100 yards. While that could have been increased to 1,900 yards with Ethernet extenders and DSL technology, the bandwidth would have been limited at the longer ranges. Instead, the manufacturer chose multi-mode fiber as the network backbone.

Multi-mode is less expensive than single-mode fiber as it typically employs lower-cost electronics, like LEDs and vertical cavity surface emitting lasers (VCSELs). It has a smaller range than single-mode fiber, which can reach up to 64 miles, but multi-mode can still carry data several miles at speeds of up to one Gigabit. Multi-mode shares single-mode fiber’s immunity to Electromagnetic Interference (EMI), and both fiber types are inherently secure because the data travels on a beam of light, meaning outsiders can’t hack in via Wi-Fi.

Security was an important consideration since the facility received daily visits from toy sales representatives, vendors and other outsiders. The factory owners wanted to establish 24/7 video surveillance for the campus, but IP cameras are typically installed in inconvenient locations—you’ll see them on top of light poles, for example. These cameras need a power supply of some sort, and because IP cameras usually have 100 MBps copper interfaces, they would also need media conversion before they could connect to the campus’ fiber infrastructure.

Standard copper-to-fiber media converters could convert the signals from IP cameras, but they wouldn’t solve the power problem. And, because the cameras would be outdoors, the company needed media converters with extended temperature specs, along with the ability to observe and report faults on remote copper and fiber connections. The manufacturer ultimately chose a PoE media converter, the B&B Electronics PoE+ Giga-MiniMc.

Power over Ethernet (PoE)

While concurrently supporting the Ethernet data stream, PoE devices greatly simplify installation by letting network switches and other “injectors” provide power to connected devices over the Ethernet cable. This works because a copper RJ-45 cable has four wires: Two support the data stream, and the other two are available for PoE. A PoE copper port’s ability to carry power will not impact or reduce the efficacy of the data stream. Low-power devices can use Cat-3 cables, but devices that draw more power require Cat- 5, Cat-5e or Cat-6 cables.

There are two types of PoE power sourcing equipment (PSE) that support point-to-multipoint power distribution: endspan and midspan. An endspan PSE is typically a switch and can be placed anywhere a switch or router would normally be required. Midspan devices, like PoE-enabled media converters, inject power inline and are often used when upgrading an existing network to PoE standards. A midspan device is placed between an existing legacy switch and a powered device, which could be an IP camera, a wireless access point, a serial device server or any other IP device that requires power.

On initial power up, the PSE is designed to detect and supply power to only the network devices that it identifies as being PoE-enabled. The PSE initiates this signature detection process by using low probing voltages to sense the type of connected power device. PSEs are able to detect several undesirable load conditions, including shorted communications cables, disconnected powered devices and the connection of non-PoE devices.

The original IEEE 802.3af-2003 PoE standard provided up to 15.4 W DC—minimum 44 V DC and 350 mA—to each device, with 12.95 W available at the powered device after cable loss. But some devices, such as heated remote cameras, need more. So, the newer IEEE 802.3at-2009 PoE standard (referred to as either PoE+ or PoE plus) nearly doubles the available power, providing up to 25.5 W while remaining compatible with the older 802.3af PoE standard.

PoE+ switches and injectors will recognize 802.3af powered devices and source power to them accordingly. The reverse is also true: PoE+ powered devices will recognize 802.3af PoE injectors and are designed to restrict how much power they draw, preventing damage to the equipment.

With PoE’s low voltage, it is considered to be safe enough that it doesn’t bring strict building codes into play, which lowers installation costs. Note that AC power standards, plugs and outlets vary from one region to another, but PoE equipment works everywhere.

Hot Swappable Transceivers and Remote Diagnostics

In addition to the twin 10/100/1000 MBps PoE copper ports, the media converters provided a small form pluggable (SFP) fiber port. SFP fiber ports future proof an installation by supporting both 100 MBps and 1000 MBps connections. Currently, the toy factory only requires 100 MBps connectivity to meet its needs. If, at a later date, the owners wish to upgrade the system to gigabit (1,000 MBps), the transition from multimode to single-mode fiber would be easy. There would be no need to replace the media converters; the hot swappable SFP transceiver is the only component that would need to be changed.

The media converters provide a useful diagnostic feature called Link Fault Pass Through (LFPT). LFPT means that the state of the 100BASE-TX copper receiver is passed to the 100BASEFX fiber transmitter. Imagine a situation in which a remote device stops communicating. The LFPT function lets the media converter detect the lost copper link and alert the network manager.

By deploying devices that combine PoE, remote management features and wide temperature specs, this toy manufacturer was able to establish video surveillance in all desired locations while simultaneously retaining the option to upgrade to single-mode fiber, should the need arise.

This article originally appeared in the June 2014 issue of Security Today.