VG450 SRST partial SRST registering

[mleboeuf]

Hi,

I have the following:

• ISR4331 - 100 phones SRST capacity
• VG450 - 144 SCCP configured for analog basic phones
• 40 x Cisco 8851

We configured all 8851 in a device pool with ISR4331 as SRST reference.  We configured all VG450 ports (except two) in a different device pools with no SRST reference.  Two ports are configured in the device pool with SRST reference.

I use the CUCM as a config server for the VG.

All ports of the VG receive a fallback-dn configuration from CUCM.  Hence all 144 ports will try to register with the ISR when SRST occurs and battle with the 8851's for the 100 spots available.

Is there a way to restrict some VG ports to register with the ISR when SRST occurs and let some other ports register?  I removed the fallback-dn configuration but as soon there a reset of SCCP, the configuration comes back.  Is the only solution not to use CUCM as a config server?

Thank you!

[Nithin Eluvathingal]

Assign the ports which you dont want to register with the ISR 4331 in a different Device pool which has no SRST preference. 

[Roger Kallberg]

@Nithin Eluvathingal This is already done by the OP.

”We configured all 8851 in a device pool with ISR4331 as SRST reference.  We configured all VG450 ports (except two) in a different device pools with no SRST reference.  Two ports are configured in the device pool with SRST reference.”

AFAIK the SCCP controlled ports will not get the SRST reference from the device pool. For these to register with SRST you’ll need to add a SCCP reference that has a higher preference than the CMs. So if you have 3 CPE CMs that would be used for normal operations you’ll add a 4:th SCCP reference that points to your router that runs SRST with a preference of 4.

With this the answer to your question would be AFAIK you cannot control what ports that can register with SRST.

[mleboeuf]

Thank you @Roger Kallberg , I configured the router as preference 4 in the SCCP config indeed.  You are telling me what I was thinking: the VG is a whole device and its ports will battle for SRST with no control.  And they will battle with the 8851.

[Nithin Eluvathingal]

Restrictions for Enabling Fallback to Cisco Unified SRST for Call Control on Analog FXS Ports

• Switchover and switchback are supported using the graceful method only. Other switchover and switchback methods are not supported.
• Cisco Unified SRST supports basic calls only; it does not support supplementary features.
• Cisco Unified SRST does not provide fallback for analog endpoints in Cisco Unified Communications Manager Express (Cisco Unified CME).
• In an actual Cisco Unified SRST scenario, when a Cisco Unified IP phone registers with a Cisco Unified CM, the Cisco Unified CM pushes Cisco Unified SRST information (using the selected device pool) to the Cisco Unified IP phone and the phone stores the information. However, in the case of an analog phone connected to Cisco IOS SCCP voice gateways, like the VG224, that provision is not available. These voice gateways do not perform autoconfiguration through the TFTP download of XML configuration files. The ports of these voice gateways do not receive or store any Cisco Unified SRST information from Cisco Unified CM so selective fallback is not possible with VG224 and similar voice gateway ports.

This docuemnt is for iOS 15.X, I didn't find  an updated  document for IOS Xe. so I hope the same policy gets applied to Vg450.

https://www.cisco.com/c/en/us/td/docs/ios/voice/fxs/configuration/guide/15_1/fxs_15_1_cg_book/fxssrst.html

[mleboeuf]

Thank you @Nithin Eluvathingal, this is good information.  That is confirming with no doubt that the whole VG will try to register to SRST gateway.

[Nithin Eluvathingal]

I missed that in the OP.