Below is a sh interface s0/2/0 from my router indicating that packets are being dropped. I am trying to figure out why the packets are dropped. I checked the buffers and memory but can't find any problems there. The line is not flapping. No errors. No acl's & QoS. On router2 that connects to this router via the s0/2/0 interface there was 2 QoS applied to the interfaces on the serial and the ethernet. I thought that was causing a bottleneck and removed it, but still no joy. Router2 also indicates that packets are dropped although not as many as with router1 (output below).
Serial0/2/0 is up, line protocol is up
Hardware is GT96K Serial
Internet address is 172.16.16.1/21
MTU 1500 bytes, BW 128 Kbit, DLY 20000 usec,
reliability 255/255, txload 67/255, rxload 33/255
Encapsulation HDLC, loopback not set
Keepalive set (10 sec)
Last input 00:00:00, output 00:00:00, output hang never
Last clearing of "show interface" counters 00:00:02
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 12
Queueing strategy: weighted fair
Output queue: 55/1000/64/12 (size/max total/threshold/drops)
Conversations 10/42/256 (active/max active/max total)
Reserved Conversations 0/0 (allocated/max allocated)
Available Bandwidth 96 kilobits/sec
5 minute input rate 17000 bits/sec, 21 packets/sec
5 minute output rate 34000 bits/sec, 20 packets/sec
149 packets input, 17668 bytes, 0 no buffer
Received 1 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
137 packets output, 39404 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 output buffer failures, 0 output buffers swapped out
0 carrier transitions
DCD=up DSR=up DTR=up RTS=up CTS=up
Beside Martin's information, understand some drops are routine. One general rule of thumb is a up to 1% is usually okay. However, your stats show 12 drops for only 137 packets, about 8.8%, which is worth reviewing.
First thing you might do, let the stats accumulate longer and see how the drop ratios holds.
Second, while the link is busy, try a "show queue s 0/2/0", and see if all flows are experiencing drops, or just one. If just one, if it's just some background file transfer, is a higher drop rate for it acceptable?
Third, you can often adjust the default FQ settings, try "fair-queue 2000".
Lastly, you can get very involved in managing this congestion with advanced QoS configurations, but at only 128 Kbps, might be worthwhile attempting to obtain a more bandwidth first.