Hello,
input drops basically mean that you interface is receiving too much traffic to handle and that subsequentially packets are being dropped. Check the document below for detailed troubleshooting info. The only way to get rid of the input drops is to reduce the amount of input traffic. In your case, you could apply some sort of (frame relay) traffic shaping to prioritize certain traffic (which in your situation would probably be most suitable for the VoIP traffic). Have a look at the following Frame Relay Traffic Shaping configuration:
interface Serial1/0
frame-relay traffic-shaping
frame-relay interface-dlci 102
class DLCI_102
!
class-map NO_VoIP
match not access-group VoIP
!
policy-map FRTS
class NO_VoIP
set fr-de
!
map-class frame-relay DLCI_102
frame-elay cir 512000
frame-relay bc 5120
service-policy output FRTS
frame-relay fragment 640
!
ip access-list extended VoIP
permit tcp any any eq 1720
permit udp any any range 16384 32767
This configuration would prioritize all VoIP traffic by setting the frame relay discard eligible (DE) bit on all non-essential traffic. In addition, the maximum packet size is being reduced, minimizing the possible delay for real time traffic packets.
The example is based on a frame relay CIR of 512000, which might not reflect what you have.
Let me know if you run into problems when configuring this.
Cisco - Troubleshooting Input Queue Drops and Output Queue Drops
http://www.frameip.com/dos_cisco/queue_drops.pdf
HTH,
GP
