Hi John,
Please see my just-posted comments in your reply to Jim Thompson's post as well as my comments, below.
John Tully wrote:
Hello Jack,
When testing the four port card with multiple radios, problems occur when the pigtail antennas are within some inches of each other. When you have real antennas that are separated by a meter or more (and on non-overlapping frequencies), you will not see big losses in the throughput.
Yes, RF separation between the cards will minimize problems. This includes the quality of the pigtail shielding and the spacing of the pigtails and:
1. Quality of the shielding on the cards
2. Quality of the coax cable running to the antennas
3. Wi-Fi card receiver selectivity
4. Frequency spacing
5. Antenna isolation (separation distances, cleanliness of the antenna pattern, antenna F/B ratio, antenna polarization, obstructions that add additional isolation between the antennas
6. The quality of external filtering (if used) to minimize receiver overloading
7. Quality of the antenna system grounding.
I would really like to see a multi-radio capability in a Mikrotik box because it lowers the equipment cost which ultimately allows a WISP to bring service to more people but - that service has to be reliable and that means throughput can not degrade suddenly and seriously when the network becomes loaded.
As those that have tested with Atheros radios in the 5GHz band will probably know, if you don't put an antenna on the device, it sometimes won't connect even to other devices (also with no antenna) on the same table. We sometimes still get customers complaining that radios don't work in this form -- I think that is because we are all use to 2.4GHz radios that do happen to work with no antenna when on the same table. The point is, most Atheros mpci designs are better than others and have less RF leakage. Therefore, if you have good pigtails and don't mount/position the antennas close together, then you don't see a big enough problem to counter the benefits of the four or eight port setup.
It's good to hear that the Atheros cards are well shielded however I'll bet that (unless ALL the issues mentioned above are successfully addressed) the collision/overloading/throughput reduction problem will become "big enough" to worry about when traffic on the box becomes heavy - the throughput can then degrade sharply.
A simple paragraph or two addressing this issue in your documentation would provide a very valuable service to the WISP community.
Best Regards,
jack
John www.mikrotik.com
At 09:58 PM 9/29/2004, you wrote:
John,
I know you may disagree with what I'm about to say but using 8 radios that are physically spaced so close together is very likely going to lead to interference between the radios with consequent lost throughput.
If and only if the builder of an 8-radio system uses intelligent frequency planning (for example: Ch 1, 6, and 11 on 2.4 GHz and non-overlapping frequency selections on 5 GHz) will there be any chance of avoiding interference when the system is handling moderate-to-heavy traffic. Even then, it's going to take luck (and who can rely upon luck to secure their livelihood?) to keep the interference down and the throughput up.
My suggestion: Include advice and guidance on this topic in your documentation.
jack
John Tully wrote:
The eight port mpci to pci cards main use would be to easily use eight radios in you AP platform. This should be quite useful for multiradio APs with your choice of software.
John
www.mikrotik.com
RouterBOARD 18 -- 8 port mPCI to PCI board (Extreme)
http://www.routerboard.com/rb11.html#rboard18
(the back side has four ports also - tomorrow, both sides will be shown)
Price: $120 List
John www.routerboard.com www.mikrotik.com
-- Jack Unger - President, Ask-Wi.Com, Inc. Serving the License-Free Wireless Industry Since 1993 Author of the WISP Handbook - "Deploying License-Free Wireless WANs" True Vendor-Neutral WISP Consulting-Training-Troubleshooting Next 2-Day Hands-On WISP Workshop October 20-21 in Phoenix AZ [EMAIL PROTECTED] (818) 227-4220 http://www.ask-wi.com
-- Jack Unger - President, Ask-Wi.Com, Inc. Serving the License-Free Wireless Industry Since 1993 Author of the WISP Handbook - "Deploying License-Free Wireless WANs" True Vendor-Neutral WISP Consulting-Training-Troubleshooting Next 2-Day Hands-On WISP Workshop October 20-21 in Phoenix AZ [EMAIL PROTECTED] (818) 227-4220 http://www.ask-wi.com
