Propagation Delay

helloworld · 10-01-2005

I noticed there are multiple threads on setting up long haul wireless links after proper RF considerations. I understand the calculations would take care of attenuation, multipath etc. However, I have difficulty in understanding why links over 1000m should work at all because the round trip 802.11 ACK delay is more than 6microseconds and the 802.11 timeouts are smaller. So propagation delay is a factor. What is it that I am missing? Thanks in advance.

dakkon2k · 10-01-2005

Check out this: 125 mile WiFi link
There are some links at the bottom of the page that may help.

helloworld · 10-01-2005

These are modified Prism chipsets with no hardware ACKs and carrier-sense backoffs during SynTx turned off.

So given that the RF is well designed, is it true that only some configurable chipsets can be used for the long haul links?

dakkon2k · 10-01-2005

Wish I could help more, but I'm not even a neophyte to long distance WiFi

Perhaps some of the other regulars will wander threw and offer up some words of wisdom.

wrzwaldo · 10-02-2005

About the only thing I'll offer up is...

It's all about the proper tool for the job.

helloworld · 10-02-2005

All the discussion in these forums for e.g. http://netstumbler.org/showthread.php?t=17243
pertains to proper tools for RF rather than proper MAC. Are these common equipment like WRT54g already configured correctly for long haul links?

If yes, how can they perform well with the same settings in indoor (<20m) environments?

Roy_M · 10-02-2005

Would the WRTG's automatically adjust the IFS (Interframe Space) timings based on whether they are in bridge or AP mode? I believe SIFS (short IFS) is responsible for ACKs so perhaps it lengthens this timing.

10-01-2005	#1 (permalink)
helloworld Registered Member Join Date: Oct 2005 Posts: 25	Propagation Delay I noticed there are multiple threads on setting up long haul wireless links after proper RF considerations. I understand the calculations would take care of attenuation, multipath etc. However, I have difficulty in understanding why links over 1000m should work at all because the round trip 802.11 ACK delay is more than 6microseconds and the 802.11 timeouts are smaller. So propagation delay is a factor. What is it that I am missing? Thanks in advance.

10-01-2005	#2 (permalink)
dakkon2k proselyte Join Date: Jul 2005 Location: Quite a bit EAST & a smidgen south of the world famous Rat. 2 miles from the beach or 1/2 a mile from a golf course and liquor store, or 2 miles from a Gun store or 5 miles from a hooters or a "adult nightclub" Posts: 894	Check out this: 125 mile WiFi link There are some links at the bottom of the page that may help. __________________ Unable to apply patch, Please install M$ Outlook to continue. A journey of a thousand posts begins with How To Ask Questions The Smart Way

10-01-2005	#4 (permalink)
dakkon2k proselyte Join Date: Jul 2005 Location: Quite a bit EAST & a smidgen south of the world famous Rat. 2 miles from the beach or 1/2 a mile from a golf course and liquor store, or 2 miles from a Gun store or 5 miles from a hooters or a "adult nightclub" Posts: 894	Wish I could help more, but I'm not even a neophyte to long distance WiFi Perhaps some of the other regulars will wander threw and offer up some words of wisdom. __________________ Unable to apply patch, Please install M$ Outlook to continue. A journey of a thousand posts begins with How To Ask Questions The Smart Way

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10-01-2005	#3 (permalink)
helloworld Registered Member Join Date: Oct 2005 Posts: 25	These are modified Prism chipsets with no hardware ACKs and carrier-sense backoffs during SynTx turned off. So given that the RF is well designed, is it true that only some configurable chipsets can be used for the long haul links?

10-02-2005	#5 (permalink)
wrzwaldo I amuse you? Join Date: Dec 2003 Posts: 9,147	About the only thing I'll offer up is... It's all about the proper tool for the job.

10-02-2005	#6 (permalink)
helloworld Registered Member Join Date: Oct 2005 Posts: 25	All the discussion in these forums for e.g. http://netstumbler.org/showthread.php?t=17243 pertains to proper tools for RF rather than proper MAC. Are these common equipment like WRT54g already configured correctly for long haul links? If yes, how can they perform well with the same settings in indoor (<20m) environments?

10-02-2005	#7 (permalink)
Roy_M Registered Member Join Date: Jun 2005 Posts: 72	Would the WRTG's automatically adjust the IFS (Interframe Space) timings based on whether they are in bridge or AP mode? I believe SIFS (short IFS) is responsible for ACKs so perhaps it lengthens this timing.