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TTL values
30-03-2012, 11:32 AM (This post was last modified: 30-03-2012 12:16 PM by simoncn.)
Post: #1
TTL values
I've been debugging a problem where a device sometimes couldn't see another device if the two devices were on separate wireless networks (but the same subnet).

Eventually I discovered that the M-SEARCH TTL value defaults to 2 if not set in InitParams, but the TTL for SSDP notifications is set to a fixed value of 4. For devices on separate wireless networks, the TTL=4 messages were being received, but the TTL=2 messages weren't being received.

I can fix this by setting MsearchTtl=4 in InitParams, but I'm not sure why
a) the default M-SEARCH TTL value isn't the same as the SSDP notify TTL fixed value
b) the SSDP notify TTL value isn't configurable as well as the M-SEARCH TTL value

Is there any scenario where it makes sense to have these TTL values be different? If not, perhaps the same configurable value should be used for both.
(30-03-2012 11:32 AM)simoncn Wrote:  I've been debugging a problem where a device sometimes couldn't see another device if the two devices were on separate wireless networks (but the same subnet).

Eventually I discovered that the M-SEARCH TTL value defaults to 2 if not set in InitParams, but the TTL for SSDP notifications is set to a fixed value of 4. For devices on separate wireless networks, the TTL=4 messages were being received, but the TTL=2 messages weren't being received.

I can fix this by setting MsearchTtl=4 in InitParams, but I'm not sure why
a) the default M-SEARCH TTL value isn't the same as the SSDP notify TTL fixed value
b) the SSDP notify TTL value isn't configurable as well as the M-SEARCH TTL value

Is there any scenario where it makes sense to have these TTL values be different? If not, perhaps the same configurable value should be used for both.

I set the MsearchTtl value to 4, but the messages still aren't getting through to the other wireless network. I'll have a closer look at my network setup to try to find out what's causing the problem.
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30-03-2012, 01:06 PM
Post: #2
RE: TTL values
After stopping and restarting everything a few times, the M_SEARCH messages are arriving successfully on the second wireless network most of the time (but not every time). I've gone back to the default MsearchTtl=2 and this doesn't seem to make things any worse or better.

I'd still be interested to know why the M-SEARCH and NOTIFY TTL values are different, though. Smile
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02-04-2012, 10:15 AM
Post: #3
RE: TTL values
(30-03-2012 01:06 PM)simoncn Wrote:  After stopping and restarting everything a few times, the M_SEARCH messages are arriving successfully on the second wireless network most of the time (but not every time). I've gone back to the default MsearchTtl=2 and this doesn't seem to make things any worse or better.

Thanks for the update. I was curious about why a ttl of 4 was necessary in your setup. I'd be interested to hear if you figure out what the problem is.

Quote:I'd still be interested to know why the M-SEARCH and NOTIFY TTL values are different, though. Smile

That was a mistake. I've updated our local copy to use the user-defined value in both cases now. (The API still refers to MsearchTtl though. I won't change this just yet as it'd be more disruptive.)
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