Quality of Service

From Zenitel Wiki

The AlphaCom uses the UDP ports 61000 to 61150 for VoIP audio.

Quality of Service (QoS) is by default set on all VoIP audio packages, using Diffserv bit class EF (

The TOS byte in the IP header is set to DSCP (Diffserv) (

Additional information

The Linux Console can be used to check if QoS is active. SSH to the AMC-IP with standard user (alpha/com), then:

$ su -
(root passord)
# iptables –t mangle –L –v 

To change QoS settings:

# nano /opt/amc/scripts/networking

The following lines configures QoS:

# set DSCP class EF on all outgoing VoIP packages  
iptables -t mangle -A OUTPUT --protocol udp --destination-port 61000:61150 -j DSCP --set-dscp-class EF

The rule "udp dpts:61000:61150 DSCP set 0x2e" on the chain "OUTPUT" tells the linux kernel to set the DSCP field in the IP-header to hex 0x2e for all outgoing UDP packets within the port range 61000:61150. You can from the iptables command read out the number of packages and bytes this rule has been applied to.

The DSCP value 0x2e is also called Expedited Forwarding (EF). For details on the bits of the DSCP field in the IP header see: