Allied Telesis AR440S manual How to make voice traffic high priority

How to make voice traffic high priority

This is an optional enhancement to the configuration of the routers. It prioritises outgoing voice traffic higher than other outgoing traffic on each VPN, to maximise call quality.

Use the configuration in this section if you expect your VPN client or branch office users will be using VoIP over a VPN. The configuration consists of the following sections:

z"How to prioritise outgoing VoIP traffic from the headquarters router"

z"How to prioritise outgoing VoIP traffic from the branch office 1 router"

z"How to prioritise outgoing VoIP traffic from the branch office 2 router"

This enhancement prioritises outgoing voice traffic rather than incoming voice traffic, because the link to the ISP is the most likely point of congestion.

We recommend you configure prioritisation on both peers in each VPN, not just on the headquarters router, because the link from either peer to its ISP could become a point of congestion.

Note: This enhancement only prioritises outgoing VoIP traffic at the routers you configure it on. Of course, you cannot control the quality of service on routers in the Internet, such as your ISP’s routers.

Classifying In the following configurations, the router classifies voice traffic by checking packets’ IP DSCP VoIP traffic values. If the originating VoIP appliance does not mark packets with a DSCP value, you can

instead select the voice traffic by:

zclassifying on the range of destination ports that the appliance uses for RTP (Real Time Protocol—the protocol that carries voice data), or

zuse the Dynamic Application Recognition (DAR) system, which dynamically determines the ports

If you also need to classify the signalling traffic (call setup etc) and the signalling traffic is not DSCP-marked, then create classifiers for the appropriate ports. For example, H.323 signalling traffic uses TCP ports 1720 and 1721, and SIP uses UDP port 5060. To create classifiers for

H.323 signalling packets, use the following commands:

create classifier=<id> tcpd=1720

create classifier=<id> tcpd=1721

For more information, including information about DAR, see the following:

zthe “Software Quality of Service (QoS)” and “Generic Packet Classifier” chapters of the Software Reference

zHow To Configure Software QoS For Some Specific Customer Scenarios. This How To Note is available from www.alliedtelesis.com/resources/literature/howto.aspx.

Page 30 AlliedWare™ OS How To Note: VPNs for Corporate Networks