Figure: DE aware 802.1ad access network shows an example of a topology where the new DE feature may be used: a DE aware, 802.1ad access network connected via a regular SAP to a router PE.
In the following example, PE1 can ensure coherent processing of the DE indication between the 802.1ad and the MPLS networks. For example, for packets ingressing the SAP connected to 802.1ad access, read the DE indication and perform classification, color aware metering/policing, marking of the related backbone QoS fields, and selective discarding of the frames throughout the queueing system, based on their discard eligibility. In addition, packets egressing the SAP toward the 802.1ad access provide correct DE indication by marking the new DE bit in the S-TAG.
Figure: DEI processing ingress into the PE1 SAP shows an example of the QoS processing of the DEI processing steps for the IEEE 802.1ad use case for both ingress and egress directions (from a PE1 SAP perspective).
The following steps related to DEI are involved in the QoS processing as the packet moves from left to right:
The QinQ access device sets the DE bit from the S-TAG based on the QoS classification or on the results of the metering/policing for the corresponding customer UNI.
The SAP on PE1 may use the DE bit from the customer S-TAG to classify the frames as in/out-of-profile. Color aware policing/metering can generate additional out-of-profile packets as the result of packet flow surpassing the CIR.
When the packet leaves PE1 via SDP, the DE indication must be copied onto the appropriate tunnel QoS fields (outer VLAN ID and, or EXP bits) using the internal PHB (per hop behavior) of the packet (for example, the FC and Profile).
As the packet arrives at PE2, on ingress into the related SDP, the DE indication is used to classify the packets into an internal PHB.
On egress from the PE2 SAP, the internal PHB may be used to perform marking of the DE bit.
A combination of two access networks can be possible. If PBB encapsulation is used, the configuration used for DE in SAP and SDP policies applies to both BVID and ITAG DE bits. When both fields are used, the BVID takes precedence.