Min-SE value setting - generating warning when implementing

[Yort Mantup]

Hoping this is the correct forum.  We added a new ISR 4431 router and when adding the Min-SE config with the min value of 90 it generated the following warning:  Warning: Setting the Min-SE value allowed to a small value may
degrade router performance due to frequent re-INVITES..

Is there any real concern with setting this at the min value of 90?    Also, this site is not using SIP to the PSTN but instead using POTS lines.  Is there any need to have this built out on the router or should it be removed if this site is not using SIP?

sip
bind control source-interface GigabitEthernet0/0/0.20
bind media source-interface GigabitEthernet0/0/0.20
rel1xx disable
min-se 90
registrar server
transport switch udp tcp
options-ping 60
g729 annexb-all

[gmgarrian]

The default setting for the min-se timer is 1800 (30 minutes) so by setting it to 90 you are going to have calls refreshed at 45 second intervals as the refresh begins at half of the min-se time.  Since you're using POTS lines I can't image that the call volume is high enough for this extra traffic to be a concern.

Is this customer using CUCM? One thing to keep in mind though is that if CUCM is set for the default of 1800 then inbound calls from this gateway to CUCM would result in a "422 session timer too small" response. 

[Yort Mantup]

So the default min-se value on the router is 1800?   Yes, CUCM is used.  I checked and the sub's and pub are all set to 1800 for the SIP Min-SE Value.  I checked and all existing sites are using this command: min-se 90 session-expires 90.  with no issues.  

[gmgarrian · Accepted solution]

Since you don't have a SIP trunk to your provider you should be fine. If CUCM is sending the 422 that error message should contain it's own min-se value and the gateway will send a new invite to match that value.

Some SIP service providers may have the call fail instead of responding with a matched min-se value but you don't need to worry about that with POTS lines.

[R0g22]

What is the need to have this value set so low ? I understand that your sites use it but why ? Did you see any issues with a higher session refresher timer ?
ISR-4k can handle performance issues quite well but if you have a lot of call volume then yes, too frequent refreshers will cause CPU spikes.

[Yort Mantup]

Hello,

Thank you for the reply.  I am new to this environment and noticed the command and was asked about it.  This post is more of a "discovery" on my end.  After what I have read and from what was posted here, I feel it's best to not use the command and go with the default setting of 180.

[R0g22]

To an extent yes. The command has it's pros and cons. If you are not really sure what value needs to be there and if you need to alter it or not, leave it at the default.
Come back to it in case you face any issues related specifically to session refresher.