Applying QoS for Voice Traffic

QoS is very important for Voice traffic which is delay sensitive. I won’t go into details of QoS over here and will just explain the configuration we normally use on a Voice gateway for QoS.

class-map match-any Voice-RTP
match ip precedence 5
match ip dscp ef
match ip rtp 16384 16383
class-map match-any Voice-Cntl
match ip precedence 3
match ip dscp af31
match access-group name voice-signal
!
ip access-list extended voice-signal
permit tcp any any range 2000 2002
permit udp any any eq 2427
permit tcp any any eq 2428
permit tcp any any eq 1720
permit tcp any any range 11000 11999
!
!
policy-map QoS-LAN-Policy
class Voice-RTP
set dscp ef
priority 500
class Voice-Cntl
set dscp af31
bandwidth 30
class class-default
fair-queue
!

Apply it on Voice VLAN interface or towards the WAN interface if you are configuring it between sites:

!
interface FastEthernet0/1
ip address 10.0.1.1 255.255.255.0
ip rip advertise 2
ip virtual-reassembly
ip tcp adjust-mss 1360
duplex full
speed 100
service-policy output QoS-LAN-Policy
!

OR

!
interface GigabitEthernet0/0.105
description *** Voice VLAN ***
encapsulation dot1Q 105
ip address 10.60.x.x 255.255.255.0
h323-gateway voip bind srcaddr 10.60.x.x
service-policy output QoS-LAN-Policy

====

Confirmation that the voice packets are hitting the service policy:

GW#sh policy-map int fa0/1
FastEthernet0/1

Service-policy output: QoS-LAN-Policy

Class-map: Voice-RTP (match-any)
55890 packets, 11178000 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: ip precedence 5
55890 packets, 11178000 bytes
5 minute rate 0 bps
Match: ip dscp ef (46)
0 packets, 0 bytes
5 minute rate 0 bps
Match: ip rtp 16384 16383
0 packets, 0 bytes
5 minute rate 0 bps
QoS Set
dscp ef
Packets marked 55890
Queueing
Strict Priority
Output Queue: Conversation 264
Bandwidth 500 (kbps) Burst 12500 (Bytes)
(pkts matched/bytes matched) 55890/11960460
(total drops/bytes drops) 0/0

Class-map: Voice-Cntl (match-any)
605 packets, 80661 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: ip precedence 3
605 packets, 80661 bytes
5 minute rate 0 bps
Match: ip dscp af31 (26)
0 packets, 0 bytes
5 minute rate 0 bps
Match: access-group name voice-signal
0 packets, 0 bytes
5 minute rate 0 bps
QoS Set
dscp af31
Packets marked 605
Queueing
Output Queue: Conversation 265
Bandwidth 30 (kbps)Max Threshold 64 (packets)
(pkts matched/bytes matched) 605/76019
(depth/total drops/no-buffer drops) 0/0/0

Class-map: class-default (match-any)
1103573 packets, 80456575 bytes
5 minute offered rate 151000 bps, drop rate 0 bps
Match: any
Queueing
Flow Based Fair Queueing
Maximum Number of Hashed Queues 256
(total queued/total drops/no-buffer drops) 0/0/0