Where to apply qos

Question

We have this:
src/dst---ORtr1---100Mbps---SPRtr---512kbps---Ortr2---T1---Ortr2---src/dst
Where should we apply qos? We don't have access to SPRtr(service provider) and here is sample config on our router 1 (Ortr1):
interface FastEthernet0/0
service-policy output OUR-POLICY
Class-map voice-signaling
match access-group 102
class-map voice-traffic
match access-group 101
policy-map OUR-POLICY
class voice-traffic
priority 64
class voice-signaling
bandwidth 16
class class-default
fair-queue
access-list 101 permit udp any any range 16384 32767
access-list 102 permit tcp any eq 1720 any
access-list 102 permit tcp any any eq 1720

Answer 1

Hi,
Qos should be applied to ORtr1 FE, ORtr2 512k, ORtr3 (?) T1.
On ORtr2 and ORtr3 - connected through T1 - you can use f.e. your posted policy.
The tricky one is ORtr1 and your policy will not work. The underlying reason is: you are configuring queueing and it will only be involved IF the physical interface is overloaded. This means that there should be more than 100 Mbps traffic before your config is involved. Obviously the problem occurs already if there is more than 512k.
The solution to the problem is called "nested policy". It would look like this taking your initial policy:
interface FastEthernet0/0
service-policy output Shape512k
Class-map voice-signaling
match access-group 102
class-map voice-traffic
match access-group 101
policy-map OUR-POLICY
class voice-traffic
priority 64
class voice-signaling
bandwidth 16
class class-default
fair-queue
policy-map Shape512k
class class-default
shape 500
service-policy output OUR-POLICY
access-list 101 permit udp any any range 16384 32767
access-list 102 permit tcp any eq 1720 any
access-list 102 permit tcp any any eq 1720
The policy Shape512k will only allow 500 kbps to pass through the F0/0 interface. Once this SHAPER is overloaded you apply the policy OUR-POLICY to prioritize voip.
The idea is never overload your SPRtr interface. Thus you should not shape to 512k exactly to account for OSI layer2 overhead.
Hope this helps! Please rate all posts.
Regards, Martin