With IPHost Network Monitor you can run simple snmp requests against a Cisco device in your network.
frxCktDiscards
Cisco 90i Circuit Discards
1.3.6.1.4.1.1570.1.6.2.1.10
The number of input frames from the subscriber port on the addressed permanent virtual circuit that were discarded due to congestion (lack of buffer space or congestion control.
Back to CISCO-90-MIB MIB page.
IPHost Network monitor allows you to monitor frxCktDiscards on Cisco device via the SNMP protocol. Download IPHost Network Monitor (500 monitors for 30 days, 50 monitors free forever) to start monitoring Cisco optical switches right now.