QoS on isdn line

Question

Hello,
I have an isdn line as a backup with the following policy
policy-map backup
class preced-5
priority 45
class preced-4
bandwidth remaining percent 30
class preced-3
bandwidth remaining percent 30
class preced-2
bandwidth remaining percent 20
class preced-1
bandwidth remaining percent 10
class class-default
bandwidth remaining percent 10
I can see drops at the critical class even when the offered rate is 1000 or 5000bps, while it should allow untill 45Kbps.
Virtual-Access1
Service-policy output: backup
Class-map: preced-5 (match-any)
354 packets, 252724 bytes
30 second offered rate 1000 bps, drop rate 1000 bps
Match: ip precedence 5
354 packets, 252724 bytes
30 second rate 1000 bps
Queueing
Strict Priority
Output Queue: Conversation 40
Bandwidth 45 (kbps) Burst 1125 (Bytes)
(pkts matched/bytes matched) 354/252724
(total drops/bytes drops) 141/156991
Class-map: preced-5 (match-any)
268 packets, 189684 bytes
30 second offered rate 3000 bps, drop rate 3000 bps
Match: ip precedence 5
268 packets, 189684 bytes
30 second rate 3000 bps
Queueing
Strict Priority
Output Queue: Conversation 40
Bandwidth 45 (kbps) Burst 1125 (Bytes)
(pkts matched/bytes matched) 268/189684
(total drops/bytes drops) 114/130919

Answer 1

It should allow an /average/ of 45kbps. If your traffic is bursty you are going to see drops even though the 30 second offered rate is low.
If you are putting Voice into your LLQ make sure you are provisioning for the layer 3 header as well as the traffic. This will be about 80kbps for a standard G.711 call and 24kbps for a single G.729 call.
You may want to change the interface to
if#max-reserved-bandwidth 90
This shouldn't be affecting your problem, but it could eliminate any problems with the default-class percent versus the other non-priority classes.