Link Slow

Answered Question
Dec 22nd, 2008

We use Cisco1310 at our customer location; the units are installed in the outdoor for a distance of 4 KMS, with external antenna. The link is slow and the TTL on the Ethernet is not stable, the SSID and the WEP key is applied for 40 BIT encryption, tried different channels there were no improvements please suggest



Attachment: 
Correct Answer by srosenthal about 8 years 2 months ago

You might want to verify your alignment. I would put both units in install mode and verify the signal levels you are getting.


The signal levels that you are seeing are not in percentage, but are the actual signal levels. Your SNR shows 9dB, and should be at least 20dB. You can see that your data is mostly going out at 1M. You need to improve your SNR.


Even if you had your power at 1mW, your distance for using parabolic dishes is 2.27Km. You must be at least 21 feet above all obstructions at 1mW.


Here is a document that shows what the RSSI lights should be when the unit is in install mode. Again, because of the nature of the parabolic dish, alignment is critical and should be on a very stable mast.



  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 5 (2 ratings)
Loading.
srosenthal Tue, 12/23/2008 - 05:26

What type of external antenna are you using? You SNR is down in the dumps. You data is mostly going at 1Meg rate based on your spreadsheet. This shows that your are not getting a very good signal which is why you have poor speed.


For your distance given, in order to get 54M you will need to be using parabolic dish antenna's. If you are using them, they are extremely sensitive to align which is very critical to get the best signal level.


Seth

ignatiusrajkumar Tue, 12/23/2008 - 05:57

Thanks for your responce, we use a Parabolic dish Antenna with 24dbi and as rightly said we have a signal strength of 76-77 and even goes to 81 %

Please let me know your views

Correct Answer
srosenthal Tue, 12/23/2008 - 06:10

You might want to verify your alignment. I would put both units in install mode and verify the signal levels you are getting.


The signal levels that you are seeing are not in percentage, but are the actual signal levels. Your SNR shows 9dB, and should be at least 20dB. You can see that your data is mostly going out at 1M. You need to improve your SNR.


Even if you had your power at 1mW, your distance for using parabolic dishes is 2.27Km. You must be at least 21 feet above all obstructions at 1mW.


Here is a document that shows what the RSSI lights should be when the unit is in install mode. Again, because of the nature of the parabolic dish, alignment is critical and should be on a very stable mast.



dennischolmes Wed, 12/24/2008 - 16:42

Check for alignment of the parabolic. They are highly directional. Next look for cable loss to the bridge. A bad connector or bad cable will cause problems. Next, insure that the distance is keyed into the gui to insure proper timing issues.

ignatiusrajkumar Fri, 01/02/2009 - 07:18

We have noted that there was signal interference and we changed our external antennas polarization from Horizontal to Vertical and then we were able to choose

Alternative Radio Link Channels (we were able to connect only in channel 11 in Horizontal Polarization) when moved the polarization

We had an option of others channels were in Ch 7 and Ch 8 we found very less Interference

By running carrier busy test.

I have attached the latest Link Report need your views on the same


The Link is stable for the past 4 days




Attachment: 
srosenthal Fri, 01/02/2009 - 07:40

Based on your report, you are only working at 5M or slower. You may still be experiencing too much interference or it still could be your antenna alignment.


dennischolmes Fri, 01/02/2009 - 08:11

As I stated above and the other guys have as well, check antennae alignments. The best way to align parabolics at long distance is to use a survey theodolite or a high powered spotting scope then tweak in millimeters. Parabolics are extremely directional in their nature. You might also need to do a Fresnel Zone clearance calculation to insure at least 60% of the Fresnel Zone is occlusion free. There are excellent tools available from Cisco on bridge links, Fresnel Zones, and free space attenuation. For a good overview of RF propagation go to the Cisco Antenna Reference page on the website.


http://www.cisco.com/en/US/prod/collateral/wireless/ps7183/ps469/product_data_sheet09186a008008883b.html


You should verify signal strength with Airmagnet or Spectrum Expert at each end after verification of alignment and Fresnel.


Lastly, 1300 Series bridges are in the 2.4 spectrum which is highly oversubscribed at this time. With 802.11n becoming more prevalent, 5ghz will soon suffer the same. I would still consider 5ghz (more non overlapping channels) or a alternative licensed spectrum solution depending on the mission criticality of the applications that depend on the bridge. We offer several alternative solutions at our company and I am sure that your partner or one in your area should offer the same.

CFayNTAdmin83 Fri, 01/02/2009 - 08:18

Yes, based on the RSSI values your antenna alignment hopefully can be improved. Technically you can have a working connection around -80dBm, but this means that your connection is very weak. This is why you are seeing the "POOR" link test result. It is telling you that you have a high rate of packet retries. If possible, please try and get your RSSI signal closer to -65dBm or better. I would make very small movement changes to the antenna and then stop moving it when you notice a better RSSI signal. Also, you mentioned that you had less interference with channels 7 and 8. I would recommend to use channel 6 if possible. Channels 1,6, and 11 should only be used in 2.4Ghz as general practice. Of course you can use the other channels, but they'll be more prone to interference with other 2.4 Ghz networks.

Actions

This Discussion

 

 

Trending Topics: Other Wireless Mobility

client could not be authenticated
Network Analysis Module (NAM) Products
Cisco 6500 nam
reason 440 driver failure
Cisco password cracker
Cisco Wireless mode