VSC7440 datasheet(128/444 Pages) MICROSEMI

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Functional Descriptions

VMDS-10492 VSC7440 Datasheet Revision 4.2

111

The VLAN classification determines the following set of VLAN parameters for all frames:

•

Priority Code Point (PCP). The PCP is carried internally in the IFH field IFH.VSTAX.TAG.CL_PCP.

•

Drop Eligible Indicator (DEI). The DEI is carried internally in the IFH field IFH.VSTAX.TAG.CL_DEI.

•

VLAN Identifier (VID). The VID is carried internally in the IFH field IFH.VSTAX.TAG.CL_VID.

•

Tag Protocol Identifier (TPID) type, which holds information about the TPID of the tag used for

classification. The TPID type is carried internally in IFH field IFH.VSTAX.TAG.TAG_TYPE. Extended

information about the tag type is carried in IFH.DST.TAG_TPID.

The device recognizes five types of tags based on the TPID, which is the EtherType in front of the tag:

•

Customer tags (C-tags), which use TPID 0x8100.

•

Service tags (S-tags), which use TPID 0x88A8 (IEEE 802.1ad).

•

Custom service tags (S-tags), which use one of three custom TPIDs programmed in

ANA_CL::VLAN_STAG_CFG. Three different values are supported.

For customer tags and service tags, both VLAN tags (tags with nonzero VID) and priority tags (tags with

VID = 0) are processed.

It is configurable, which of the five recognized TPIDs are valid for the VLAN classification

(VLAN_TPID_CTRL.BASIC_TPID_AWARE_DIS). Only VLAN tags with valid TPIDs are used by the

VLAN classification. The parsing of VLAN tags stops when a VLAN tag with an invalid TPID is seen.

The VLAN tag information is either retrieved from a tag in the incoming frame or from default port-based

configuration. The port-based VLAN tag information is configured in ANA_CL:PORT:VLAN_CTRL.

For double tagged frames (at least two VLAN tags with valid TPIDs), there is an option to use the inner

tag instead of the outer tag (VLAN_CTRL.VLAN_TAG_SEL). Note that if the frame has more than two

valid VLAN tags, the inner tag refers to the tag immediately after the outer tag.

The following illustration shows the flow chart for basic VLAN classification.

ANA_CL::VLAN_STAG_CFG

Configures custom S-tag TPID value.

ANA_CL:PORT:PCP_DEI_TRANS_CFG

Port-based translation of (DEI, PCP) to basic classified

(DEI, PCP).

Per port per

DEI per PCP

(16 per port)

ANA_CL:PORT:VLAN_TPID_CTRL.

BASIC_TPID_AWARE_DIS

Configures valid TPIDs for VLAN classification. This

configuration is shared with routing tag control.

Per port

Table 70 •

VLAN Configuration Registers (continued)

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