Combining 802.1p with ATM QoS

The number of customers using 802.1p on their switched Ethernet LANs is growing rapidly, and many of those same customers now want to map that prioritization to Quality of Service over their high-speed ATM switch uplinks. While this is quite possible, it does require that the ATM uplink support both 802.1p and PNNI.

Ethernet switches that support IEEE 802.1p prioritization can queue packets according to their priority. The ATM uplink (running LANE and PNNI) can request QoS Available Bit Rate (ABR) for those packets destined to travel across the ATM fabric. ABR allows a connection to use whatever bandwidth is currently available. In theory, in an uncongested network, the switch could request different ABR QoS profiles for different 802.1p priorities at the time of request.

While all of this may sound a bit complex, the end result is that customers can leverage ATM QoS to leverage existing performance benefits of IEEE 802.1p to further enhance the performance characteristics of their networks. Of course, this approach doesn't bring all of ATM's QoS back to Ethernet, but it does port Ethernet prioritization over to ATM. Given the obvious benefits of maintaining such control over traffic prioritization, customers who interconnect their Ethernet switches with ATM uplinks should look for switches that support both PNNI and LANE on the uplinks.

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