VSC7440 datasheet(129/444 Pages) MICROSEMI

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Functional Descriptions

VMDS-10492 VSC7440 Datasheet Revision 4.2

112

Figure 26 •

Basic VLAN Classification Flow Chart

In addition to the classification shown, the port decides the number of VLAN tags to pop at egress

(VLAN_CTRL.VLAN_POP_CNT). If the configured number of tags to pop is greater than the actual

number of valid tags in the frame, the number is reduced to the number of actual valid tags in the frame.

A maximum of three VLAN tags can be popped. The VLAN pop count is carried in IFH field

IFH.TAGGING.POP_CNT.

Finally, the VLAN classification sets IFH field IFH.VSTAX.TAG.WAS_TAGGED if the port is VLAN aware

and the frame has one or more valid VLAN tags. WAS_TAGGED is used the rewriter to make decision on

whether tag information from existing tags can be used for rewriting.

”Frame has valid outer tag” and

VLAN_AWARE_ENA[port]

”Frame has valid inner tag” and

VLAN_TAG_SEL[port]

TAG_TPID = VLAN_CTRL.PORT_TAG_TYPE

PCP = VLAN_CTRL.PORT_PCP

DEI = VLAN_CTRL.PORT_DEI

VID = VLAN_CTRL.PORT_VID

TAG_TPID = TPID(Frame.InnerTPID)

PCP = Frame.InnerPCP

DEI = Frame.InnerDEI

VID = Frame.InnerVID

VID == 0

VID = VLAN_CTRL.PORT_VID

Basic Classified Tag information

TAG_TPID = TPID(Frame.OuterTPID)

PCP = Frame.OuterPCP

DEI = Frame.OuterDEI

VID = Frame.OuterVID

VLAN_PCP_DEI_TRANS_ENA

PCP = PCP_TRANS_VAL[port][8 x DEI + PCP]

DEI = DEI_TRANS_VAL[port][8 x DEI + PCP]

A tag is valid for VLAN classification when:

- the TPID is one of 5 known TPIDs, and

- BASIC_TPID_AWARE_DIS[tag number, TPID] is cleared.

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