Fiber Optic Networks

If all systems are down, check the main power source. If that checks out OK then begin troubleshooting using the process of elimination.  Proceed as follows: Begin with transmitters and receivers – Use a power meter to measure the optical power being received at the receiver. If that tests out OK, you know that the problem is likely the receiver. If no light is being received by the receiver, ensure that the  transmitter has power. Check for breaks or severe bends in the fiber. Do this only after ensuring that the transmitter and receiver are OK.  A fault finder and OTDR are useful tools at this stage of testing. Hint: Begin checking fiber where people have the most contact with it, such  as patch panels, under desks, etc.

Wireless Office Networks
If experiencing problems while connecting a PC or other wireless host to the office network:

1. Check all physical connections
2. Ensure that the wireless adapter in connected and configured properly
3. Ensure that the LAN port is active on the router
4. Check the IP address of the wireless adapter
5. Verify reachability using a “ping” command
6. Check that firewall protection is disabled on the host
7. Router and adapter should have the same settings for SSID, channel, wireless mode and security.
8. To locate a parameter mismatch for security, temporarily disable security for both the router and adapter.
9. Debug and resolve any issues regarding current protocols, including possible mismatches with Extensible Authentication Protocol  (EAP).
10. Check for sources of RF interference

Various companies are offering alternatives to the smart grid for controlling energy consumption by appliances. For example, RLtec manufactures appliances that use Dynamic Demand Management (DDM) technology. These appliances sense energy fluctuations in the
grid and adjust their electrical consumption accordingly.

DDM appliances don’t offer the comprehensive solutions of the smart grid. On the other hand, they don’t need to communicate with the utility company for instructions. That means they can react very quickly to changes in the grid. Some people suggest that these self-regulating devices do a better job of conserving energy, so there is no need to relinquish control of appliances to the smart grid.

Niche Market

DDM appliances will likely find a niche within smart grid homes. This is particularly true for large appliances if DDM’s faster response time can be shown to produce more savings than similar appliances that are controlled by the grid.

A happy compromise may be to have these appliances monitored by the grid, but left to operate on their own under normal circumstances.

The HAN zone is connected to the Nan zone. The NAN zone is connected to the WAN zone. Like the old Fats Waller song, connectivity is the key when it comes to the smart grid. Every “zone” (area network) within the smart grid is interconnected to form a cohesive hole.

Home Area Network (HAN)
Within the home HAN connects appliances, computers, and other electrical devices to the Smart Meter, an emergency monitor is also the home’s principal Smart Grid energy interface.

Neighborhood Area Network (NAN)
Outside the home, the Smart Meter connects to other Smart Meters within the NAN, typically as a “mesh” network.

Wide Area Network (WAN)
NAN interfaces with the WAN, which integrates local networks with the smart grid on the national level.

Overview:

• In a DWDM System, multiple wavelengths are transmitted down a single fiber. Dense Wavelength Division Multiplexing (DWDM) allows higher data rates and increased bandwidth to be transmitted over existing networks.
• The wavelengths are transmitted along the fiber in tightly spaced intervals. Due to Chromatic Dispersion, these tightly spaced signals will spread out as they travel down the fiber. They can spread out to the point that they blend into each other, causing errors in the transmission.
• Optical Spectrum Analyzers (OSA) can separate and display the multiple wavelengths combined on a DWDM system and create a graph of Power vs. Wavelength. Analysis can be performed on each individual wavelength within the signal. The power and bandwidth of each wavelength can be measured as well as its interaction with other wavelengths.
• OSA testing is performed during installation, commissioning and maintenance.

Certification:

• Verify transmission integrity over distance
• Determine where signal regeneration is required in an
optical network
• Uses PC software for documentation/certification reporting

Recommended Equipment:

Anritsu CMA 5000A OSA Analyzer
EXFO FTB-5240B OSA Analyzer

Bit Error Rate Testing (BERT)

Overview:

• A Bit Error Rate Tester measures the performance of a communication system. Bit Error Rate testing involves sending simulated data through a communication system and comparing the input data to the output data.

• Bit Error Rate is the percentage of bits that have an error compared to the total number of bits received. The Bit Error Rate (BER) represents how often a data packet has to be re-transmitted due to errors.

• A high Bit Error Rate increases the number of re-transmissions. This in turn increases the amount of time needed to send data through the system, slowing transmission speeds.

Troubleshooting & Certification:

• Measure network performance – verify number of re-transmissions

• Use test data to determine optimal data rate for the communication system

• Bit Error Rate Testing is used to determine the sources of Bit Errors in a system and to re-verify the BER after actions have been taken to remedy the issues.

• Uses PC software for documentation and certification reporting

Recommended Equipment

Anritsu MP1800 Signal Quality Analyzer

Overview:

• Measure the length and overall loss of an optical fiber
• Provide the location and loss value of any event along a fiber
• Create a graphical display of the fiber under test
• Certify and troubleshoot optical networks during Construction,
Maintenance and Restoration
• Has the ability to measure Optical Return Loss (ORL)

Certification:

• Verify integrity of cable reels prior to installation
• Measure splice loss during construction – verify splice meets specs.
• Measure End to End loss to certify fiber span meets loss budget
• Verify connector reflectance meets spec.
• PC Emulation Software – Generate Certification Reports
• Certify that Optical Return Loss (ORL) meets specs.

Troubleshooting:

• Fault Location – Locate a break in the fiber
• Detect Macrobends
• Pinpoint high loss splice events
• Locate highly reflective connections
• Compare traces to detect changes that
occur in a fiber system over time

Recommended Equipment:

FIS Deluxe Mini OTDR
FIS Advanced Mini OTDR
Anritsu MT9083A
EXFO FTB-150

Testing Procedure Overview:

• Minimal Equipment needed ( Power Meter & Light Source)
• Measure End-to-End loss of an optical fiber
• Some Units:
• Have the ability to measure Optical Return Loss (ORL)
• Have user adjustable Pass / Fail Thresholds – quickly verify if a span is within specs.
• Are capable of providing automated Bi-Directional Testing

Certification:

• Certify that End-to-End loss of a fiber span meets loss budget
• Certify that Optical Return Loss (ORL) meets specs.
• Uses PC software for documentation and certification reporting

Troubleshooting:

• Verify continuity of a fiber span
• Verify correction of ORL issues

Recommended Equipment:

FIS Fiber Optic Test Set Kit
EXFO 930 Max Tester

Overview:

• A Laser pulse contains several wavelengths, which travel down the fiber at different speeds. This difference in speed causes the laser pulse to spread out and bits to overlap making it difficult for the receiver to interpret.
• Chromatic Dispersion degrades signal quality, and limits the network’s ability to transmit at higher speeds.
• Chromatic Dispersion increases with fiber link distance and bit rate, which makes it a critical factor in upgrading to 40 gig and 100 gig systems.

Certification:

• Measure Chromatic Dispersion to help verify performance of an installed fiber span. Determine if the span is qualified to be upgraded to transmit at higher bit rates.
• Use test results to create a dispersion compensation plan for each link tested.
• Re-verify the span after CD compensation has been
deployed.
• Uses PC software for documentation and certification
reporting

Recommended Equipment:

Anritsu CMA 5000A CD OTDR Module
EXFO FTB-5800 CD Analyzer Module

Q. I see that many test devices sold today include PC software. What is the purpose of this software?

A. Most of today’s test equipment is very compact to provide for easy portability on the job. There’s no room for a printer, and the number of buttons on the keyboard is limited to those required to perform the tests at hand. The software enables
the user to download test data to a PC for further analysis, as well as to print test results and documentation. Also, the PC’s large display screen and full size keyboard make it easy to navigate through the data.

There have been many advancements in standard multimode fiber over the years. The ISO 11801 standard provides the following system of classification for multimode fibers, The system is based on the bandwidth of various fibers and classifies them as either OM1, OM2, OM3 or OM4.

OM1 Fiber

62.5 um fiber introduced. This fiber had a larger core than the 50 um fiber that it replaced, enabling more of the light from an LED to be injected into the fiber’s core. 62.5 multimode fiber was able transmit over 2 km campuses at 10 Mb/s. Also, the new fiber was easier to install due to its higher numerical aperture.

OM2 Fiber

As data rates increased, 62.5 fiber could not keep pace due to its lower bandwidth at the 850 nm wavelength. In 1995 the new 100 Mb/s Fast Ethernet standard advocated the use of LEDs operating at 1300 nm wavelength which resulted in less attenuation. As a result, 50 um fiber was reintroduced, providing up to ten times the bandwidth of 62.5 um fiber. The newer 1 Gb/s and 10Gb/s transmitters used smaller spot-size lasers, which eliminated the issue relating to LED power coupling losses that was previously associated with 50um fiber.

OM3 Fiber

Laser optimized 50μm fiber was introduced as a cost-effective solution for short-range applications that had to support 1Gb/s or multi-gigabit speeds. OM 3 fiber also offered significant cost savings in terms of electronics when upgrading networks to higher speeds. OM3 became the preferred multimode fiber for LANs, SANs, as well as data center interconnects and access applications.

OM4 Fiber

This is 50μm fiber similar to OM 3 but operating a higher bandwidth. OM 4 is cost effective in that savings can be achieved by using 850 nm VCSELs with long building backbones and medium size campus backbones. Supports 10 Gb/s Ethernet, Fibre Channel, and OIF applications over distances up to 550 meters.