Slow response can occur if the duplex setting of the switch does not match the duplex port setting on the Cisco CallManager server.
For optimal performance, set both the switch and the server ports to 100 Mbps/Full Duplex. Cisco does not recommend using the Auto setting on either the switch or the server.
Note: You must restart the Cisco CallManager server for this change to take effect.
For more information, refer to the Mismatched Duplex Port Settings section of Cisco CallManager System Issues.
For more information on slow Cisco CallManager performance, refer to There is delay before the user receives dial tone on an IP phone