From a carrier perspective is there a natural migration path from 'Voice over DSL' to later provide

From a carrier perspective, is there a natural migration path from 'Voice over DSL' to later provide 'Quality of Serice VoIP'?

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Some VoDSL implementations are based upon voice over ATM over DSL and others are Ethernet based IP over DSL solutions. The problem with the ATM based voice over DSL solutions is that the voice traffic typically uses AAL2 and the data traffic uses AAL5. Most implementations set the ATM cell loss priority to 0 for AAL2 voice and 1 for AAL5 data. The problem is that if you use an IP phone behind an ATM based IAD, the VoIP traffic will sent as data. The VoIP traffic may very well have the IP ToS byte set for a high priority, however, it won't matter if there is congestion at the ATM layer.

If you're using an Ethernet based IP over DSL solution (such as this), QoS can be enabled at the Ethernet layer using IEEE 802.1p/q.

This was first published in August 2004

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