Hi everyone, I have an interesting QoS issue, and while I've found a solution, I wonder if there's a better way.
Background:
This is for a radio station that is sending audio from the station to the transmitter on a mountain via a T1. Historically they've used a device that will divide the T1's time-slots up to deliver digital audio (not IP audio), and use the remaining time-slots to extend a LAN to the other side.
They're now switching over to use IP audio codec appliances to deliver a one-way UDP stream from the station to the mountain top. I have now been given all 24 time-slots (1.544 mbps) for IP traffic, and need to ensure as close to 0% packet loss on the UDP stream as possible. The catch being that I need to use the existing LAN extender equipment, whereas normally I'd want to put in a pair of routers with serial cards in place.
The IP audio codec tags its UDP packets with a DSCP value of "ef". I tried several policy-maps based on that, giving priority to "ef", but I was still able to create a massive packet loss rate by doing things like FTPing files up. In this case, packet loss means dead air on the radio station.
Eventually I came up with the following policy-map that polices "ef" traffic, giving a hard 700 kbps. All other traffic gets 715 kbps, with anything exceeding that getting dropped. It works. It's solid. I've flooded that link with non-DSCP "ef" traffic, and I'm getting no packet loss.
The question is, could this be done better? Right now if the station wanted to add another IP Audio Codec, I'd need to adjust the policing on my policy-map. Is there a way to make prioritization more dynamic?
Network diagram:
Policy map and interface config on CoreSW01:
class-map match-any AUDIO
match ip dscp ef
!
policy-map MNT-UPLINK
class AUDIO
bandwidth 700
police 700000 conform-action transmit exceed-action transmit
class class-default
bandwidth 715
police 715000 conform-action transmit exceed-action drop
!
interface GigabitEthernet2/48
description LAN extender to mountaintop
switchport access vlan 200
switchport mode access
bandwidth 1415
service-policy output MNT-UPLINK
Show policy-map int output from CoreSW01, taken during a traffic flood test:
CoreSW01#show policy-map interface gigabitEthernet 3/19
GigabitEthernet3/19
Service-policy output: MNT-UPLINK
Class-map: AUDIO (match-any)
18027176 packets
Match: ip dscp ef (46)
18027176 packets
Queueing
queue limit 264 packets
(queue depth/total drops) 0/196
(bytes output) 3877438140
bandwidth 700 kbps
police:
cir 700000 bps, bc 21875 bytes
conformed 3869345110 bytes; actions:
transmit
exceeded 0 bytes; actions:
transmit
conformed 671000 bps, exceeded 0000 bps
Class-map: class-default (match-any)
4114839 packets
Match: any
Queueing
queue limit 1848 packets
(queue depth/total drops) 0/34
(bytes output) 1074097063
bandwidth 715 kbps
police:
cir 715000 bps, bc 22343 bytes
conformed 987031146 bytes; actions:
transmit
exceeded 222510411 bytes; actions:
drop
conformed 227000 bps, exceeded 2000 bps
CoreSW01#
Thanks!
-Ian
