Juniper: QoS and traffic shaped ports causing tail dropped packets

We have a newly installed 200mb link between 2 data centres. Prior to this we have had 10gb core links between all our MX devices so have not seen this issue before.

W have shaped the traffic on the port to match the carrier's 200mb:

set class-of-service interfaces ge-1/0/2 shaping-rate 200m

​

Now what we are seing is tail-dropped packets due to (what i believe) trafic entering device on 1gb/10gb ports, and hitting the queue and not leaving immediately due to the shaping-rate we have applied.

The buffer on this queue is relatively low:

buffer-size temporal 3k;

This is due to the queue being used for VOIP traffic so we did not want packets buffered as it could affect call quality.

Transmitted:

Packets : 2073757 0 pps

Bytes : 3201880808 0 bps

Tail-dropped packets : 459156 0 pps

​

Im looking for advice on how we can stop these tail dropped packets. Would it be best to remove the shaping-rate on the interface and instead hard set the rate-limit as a numerical value in the QoS policy?

MPLS_TCLASS_VOICE_MEDIA {

transmit-rate percent 55;

buffer-size temporal 3k;

priority high;

​

From the way i read the conig, 55% of 200m should be 110mb for voice_media, but its obvious that the buffer is too small to cope with the transition from 1gb to 200mb.

​

Using iperf we get about 80mbps before packet loss kicks in (which im guessing is the tail dropped packets):

[ 3] local 172.22.4.164 port 5001 connected with 216.111.92.111 port 52005

[ 3] 0.0-10.0 sec 97.0 MBytes 81.3 Mbits/sec 0.158 ms 83800/152958 (55%)

[ 3] 0.00-10.00 sec 62 datagrams received out-of-order

​

Just looking for some advice on how best to amend the configuration