Background: Know: Recognize: VLAN, 802.1q standard

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Extract of 802.1q PICSEdit

The picture shown below is the general structure of the PICS proforma.

The main component of the PICS proforma is a fixed-format questionnaire, divided into several subclauses, each comprising of a number of individual items. Answers to the questionnaire items are given in the rightmost column, either by simply providing an answer to indicate a restricted choice (usually Yes or No) or by entering a value or a set or range of values.

From the picture below, we can see there are five columns in PICS table:


  • Item column: In this column, each item is identified by an item reference.
  • Feature column: This column contains the questions to be answered.
  • Status column: This column marks the status of the item,including mandatory, optional or conditional. The following notations are status symbols:

M mandatory - the capability is required to be supported.

O optional - the capability may be supported or not.

O.n optional, but support of at least one of the group of options labeled by the same numeral n is required.
X prohibited (excluded) - there is a requirement not to use this capability in the given context.

pred conditional-item symbol, including predicate identification

- logical negation, applied to a conditional item's predicate

  • Reference column: It contains the reference or references to the material that specifies the item in the main body of this standard.
  • Support column: This column provides the space for the answers. The support column shall be filled in by the supplier of the implementation. The following common notations are used for the support column:
Y or y supported by the implementation.
N or n not supported by the implementation.
N/A, n/a or - no answer required (allowed only if the status is n/a, directly or after evaluation of a conditional


IEEE Std. 802.1Q-2005, Virtual Bridged Local Area Networks