Hello Hari,
i had the "same" problem. We updateded a CUCM form 6.1.2 to 7.1.2. So we also updated the SRST Gateways to 12.4(24)T1.
After this our 3825 Gateways with 256 MB Mem refused the command max-dn. It still worked, but only for very low numbers. (up to 23). So I opend a TAC Case and the anser was
#########################################
The system is now
telling you that there is not enough memory to add dial-peers into the
system. Note that the threshold is 80% for 256M or less, 85% for
256-512M and 90% for > 512M of processor memory. The system will not let
you add ephone-dn's (dial-peers) when it's available processor memory is
below that threshold.
Below is two relevant URL that discuss this:
How to determine the maximum number of dial-peers that can be configured
on a router
http://www.ciscotaccc.com/kaidara-advisor/voice/showcase?case=K34857008
When calculating the memory requirements for the number of dial-peers
required you can use the following:
Router>show memory summary
Head Total (b) Used (b) Free (b) Lowest (b)
Largest (b)
Processor 60AB4ED0 5550384 2082996 3467388 3464996
3454608
I/O 40000000 16777216 1937280 14839936 14839936
14838908
Total = the total amount of memory available after the system image
loads and builds its data structures.
#########################################
We also saw in the following document that 512 MB of memory are recommended.
http://www.cisco.com/en/US/docs/voice_ip_comm/cusrst/requirements/guide/srs71spc.html
Bye
Jo
