[OZAPRS] HF Gateways

Ray Wells vk2tv at exemail.com.au
Tue Jun 30 07:41:26 EST 2009


You've just reminded me of my days of Linux on a busy network, and 
waiting for forever for the next RR to be sent. I eventually learned to 
change the default to linear. Somehow the fresh country air of Kempsey 
has made me forgetful :-)

Ray vk2tv

Ray Wells wrote:
> James,
> Excuse my ignorance of TTL and thank you for the explanation.
> Re exponential backoff and ax25, I know that Linux has either 
> exponential or linear as a user selectable option. It's a long time 
> (1994) since I used JNOS but I "think" it also offered the option. I 
> don't know about other implementations of ax25.
> Ray vk2tv
> James Cameron VK2LQZ wrote:
>> On Mon, Jun 29, 2009 at 06:06:32PM +1000, Ray Wells wrote:
>>> With numbered ax25 frames the "within reason" is determined by 
>>> RETRY  which is typically 10. Is the TCP/IP equivalent the TTL (Time 
>>> To Live)  parameter?
>> No.  TTL determines how many times a single packet is repeated by
>> internet routers and gateways before it is no longer repeated.
>> The amount of time a TCP connection may be stalled doing retries is
>> determined by (a) any keep-alive setting of the operating system or
>> application, or (b) any timer in the application that eventually gives
>> up and announces a timeout.
>> TCP retries use an exponential backoff.  I'm not yet sure what AX.25
>> uses.  Still learning AX.25.
>> APRS uses "if it didn't get through, don't worry, we'll send another one
>> soon."  ;-)
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