we have a 500M Metro-E link terminated on the fiber 1G port on SUP720 itself (C6500). The switch sees the link as 1G instead of 500M.
The challenge is how to achieve QoS for VoIP traffic (dscp EF) without feature support of "shaping" on LAN ports. We don't have FlexWAN/SIP/SPA cards.
so I can't do:
1. shaping down to 500M
2. WRR since the port will never see egree queue filled up
Since DSCP marking is configured and we basically have two classes of traffics:
1. dscp 0 for data
2. dscp 46 for voice
I want your views on this "creative" QoS design in place of WRR queuing because the LAN port will never see the congestion at 500M.
Here is my plan:
1. implement egress policing on the LAN port connected to this 500M WAN link
2. police dscp 0 at 450M
3. implicitly IPT dscp 46/EF traffic can have 50M bandwidth when there is congestion on 500M WAN link
is it a valid design?
class-map match-all data
match ip dscp default
police 450000000 800000 800000 conform-action transmit exceed-action drop
desc 500M WAN link
service-policy output dropdata
If I recall correctly, the general recommendation is to keep within 150 ms, so you might start with a Tc of 50 ms or less.
That should be 280,000,000 b/s * .05 /8 = 1,750,000 bytes.
Also keep in mind, recall shaper/policer doesn't account for Ethernet overhead, so probably should reduce that by about 10 to 15%.
BTW, the default often may have been 25 ms, not 250 ms (.25 s). 12.4(20)T now uses, I think, a 4 ms default.