Re: [lwip-users] PPP LCP echo interval u8

[Sylvain Rochet]

Hi Nikolas,

On Mon, Oct 10, 2022 at 04:17:11AM +0000, Nikolas Karakotas wrote:
> Hi,
> 
> Is there a reason why the LCP echo data type size is u8?

Yes, memory footprint. I am not against changing it but at first I would 
like to understand why an LCP echo interval over 255 seconds would be 
necessary.


> In Iot devices the transmission interval can be high from 5 minutes to 
> an hour + or event driven.
> 
> Wouldn't it be more flexible if this was a u16 to allow for a larger 
> echo interval to be set?

I guess you are using a cellular modem with PPP. In this case LCP 
packets are not sent over the air and LCP echo probes are only used as a 
serial link check between the MCU and the modem. Cellular modems being 
all buggy as hell this serial link check does not do a true check that 
the modem is still alive as the RF part can be in a dead end but not the 
serial part, making the check unreliable.

It would make much more sense to me to disable LCP echo at all by 
setting lcp_echo_interval to 0 instead of setting it to more than 5 
minutes or even hours.

Also, PPP can be attached and detached ("reconnected" and 
"disconnected") without changing the RF state. On cellular modems, RF 
state is managed through AT commands (AT+CGDCONT, AT+CGACT, …).

Sylvain

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