FSO vs. RF
Licensed and unlicensed radio frequency links (RF) have been used successfully for wireless connectivity for a long time now. And the RF link "state of the art" in terms of throughput, reliability and distance have progressed substantially, particularly in the past few years.
We have gone over all of the technology options, different makes/models, and varying requirements hundreds if not thousands of times.
So, just as an example of some of the issues and relevant criteria, let's sort out what can be a confusing set of variables in terms of which is best for a few specific application scenarios:
Application #1:
| Distance point A to point B: |
10-200m |
|
| Throughput required: | 1.25 Gbps | |
| Full duplex req. (Voice): | Y | |
| Low Latency req. (Voice): | Y | |
| Security is important: | Y | |
| Slightly less than 5-9's is OK: | Need 100% availability for voice | |
| Low Budget is critical: | Y | |
| Needs to be running in <1 month: | Y | |
| Temporary / Permanent / DR Link: | Permanent | |
| Protocol is: | GigE |
Recommendation: This is the one application where Free-Space Optics is nearly a "Silver Bullet" for a number of reasons:
- Gigabit FSO is very low cost ($12-18k) at short distances, thousands less than any other choice.
- It is full Duplex, virtually zero latency, secure, and at this short distance, there are no fog/rain/snow weather issues.
- For same variables except FastE instead of GigE, FSO has all the same advantages, and cost drops to around $4-5k.
2 x GigE Hybrid
Application #2:
| Distance point A to point B: |
200-1000m |
|
| Throughput required: | 1.25 Gbps | |
| Full duplex req. (Voice): | Y | |
| Low Latency req. (Voice): | Y | |
| Security is important: | Y | |
| Slightly less than 5-9's is OK: | Need 100% availability for voice | |
| Low Budget is critical: | Y | |
| Needs to be running in <1 month: | Y | |
| Temporary / Permanent / DR Link: | Permanent | |
| Protocol is: | GigE |
Recommendation: Over 200m, bad fog can take a Free-space Optics link down. Most moderate fogs in North America hit FSO in the 50 dB/km range, but can be up to +100 dB/km. Most FSO links have 30-60 dB optical margin available depending on model and actual deployed distance, so you can see fog can be a problem (rain and snow somewhat less so). To accommodate both GigE performance, and full availability for longer distances, combining FSO with RF (hybrid link) can be a good choice:
- Full availability for all weather events
- Mitigates potential for any hardware failures on primary link (mimics double-trenched fiber).
- Can be low cost ($30k), as you have the option to provide the redundant path at lesser throughput (10-20 Mbps) to reduce cost if you anticipate a relatively low incidence of fail-down.
- Still highly secure as data will be on RF just a few hours per year.
- In many cases, especially if voice is not deployed across the link, minor weather related outages of non-hybrid Free-space Optics links are acceptable, and deemed < historic Telco service interruptions. The hybrid decision is very individualized, and usually determined by budget vs. availability tradeoffs.
Application #3:
| Distance point A to point B: |
5km |
|
| Throughput required: | 10Mbps | |
| Full duplex req. (Voice): | N | |
| Low Latency req. (Voice): | N | |
| Security is important: | N | |
| Slightly less than 5-9's is OK: | N | |
| Low Budget is critical: | Y | |
| Needs to be running in <1 month: | Y | |
| Temporary / Permanent / DR Link: | Permanent | |
| Protocol is: | 10BaseT Ethernet |
Recommendation: This scenario is a clear 802.11"x" type RF application. For longer link deployments where throughput, latency, and security requirements are low, unlicensed RF is an easy choice. It is cheap ($2-3k), easy to install, and a good alternative to a Telco T1 if more than 1.5Mbps is required (for 1.5Mbps just call your Telco).
Application #4:
| Distance point A to point B: |
1000m |
|
| Throughput required: | 1.25Gbps | |
| Full duplex req. (Voice): | Y | |
| Low Latency req. (Voice): | Y | |
| Security is important: | Y | |
| Slightly less than 5-9's is OK: | Need 100% availability for voice | |
| Low Budget is critical: | Y | |
| Needs to be running in <1 month: | Y | |
| Temporary / Permanent / DR Link: | Permanent | |
| Protocol is: | GigE |
Recommendation: Let's assume for this scenario you can't do a hybrid link as a budget consideration. Very recently, an ultra-high frequency (60GHz) unlicensed RF link with extended range has been introduced. It provides >5-9's availability at 1km for $25k. A perfect fit for this application.
As you can see, if you are after a high speed FastE or GigE link, there are quite a few things to consider when picking your technology, and configuration.
One good way to resolve all the issues on a preliminary basis is to take advantage of the QuickQuote feature on our commercial web site. It's free, and in most cases yields an optimal recommendation.
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What's HOT☺, what's not...
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FSO vs. RF? >>
Security? >>
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>>
Where does Free-space Optics fit best? >>
Where does Free-space Optics not fit? >>
Competitive comparison of the major Free-Space Optics solutions. >>
Free-Space Optics White Papers. >>
Who are we, and what’s our motivation for supporting this web site? >>
And last but not least…here’s our Free-Space Optics commercial website for specific product and/or service inquiries. >>
...and our refurbished FSO equipment site. >>