I have a problem when I try to add switch WS-C2960-24PC-L (for IP phones) in cluster group which is defined on HSRP group of two 3550 switches. Claster group now has 16 members.
New WS-C2960-24PC-L swich and core WS-C3550-12G swich are connected over optic cable with GLC-SX-MM conector on 2960 side and WS-G5484 conector on 3550 side.
Only on new switch (this problem was never noticed on old switches) ip phones sometimes worked with problems (local and calles over PSTN were interupted very offen after several seconds,1-2 minutes).
Conigurations od central and new switch are in attachment.
IOS of core switch is c3550-i9q3l2-mz.121-13.EA1a.
How can I detect problem?