Content for TR 21.801 Word version: 17.0.0

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E (Normative) Verbal forms for the expression of provisions p. 42

The verbal forms shown in Table E.1 shall be used to indicate requirements strictly to be followed in order to conform to the standard and from which no deviation is permitted.

Table E.2: Recommendation

Verbal form	Equivalent expressions for use in exceptional cases (see clause 6.6.1)
should	it is recommended that ought to
should not	it is not recommended that ought not to

The verbal forms shown in Table E.3 are used to indicate a course of action permissible within the limits of the 3GPP TS or 3GPP TR.

Table E.3: Permission

Verbal form	Equivalent expressions for use in exceptional cases (see clause 6.6.1)
may	is permitted is allowed is permissible
need not	it is not required that no ... is required
Do not use "possible" or "impossible" in this context. Do not use "can" instead of "may" in this context. Do not use "may" or "may not" to indicate a possibility or lack of possibility - see Table E.4 below. NOTE: "May" signifies permission expressed by the standard, whereas "can" refers to the ability of a user of the standard or to a possibility open to him.

The verbal forms shown in Table E.4 are used for statements of possibility and capability, whether material, physical or causal.

Table E.4: Possibility and capability

Verbal form	Equivalent expressions for use in exceptional cases (see clause 6.6.1)
can	be able to there is a possibility of it is possible to
cannot	be unable to there is no possibility of it is not possible to
Do not use "may" instead of "can" in this context. Do not use "may not" in this context. NOTE: "May" signifies permission expressed by the standard, whereas "can" refers to the ability of a user of the standard or to a possibility open to him. If there is uncertainty about whether an event will or will not happen, in particular where the normally expected behaviour will sometimes be impossible, a formulation such as "cannot always" should be used.

The verbal forms shown in Table E.5 shall be used to indicate behaviour of equipment or sub-systems outside the scope of the document in which they appear. For example, in a standard specifying the requirements of terminal equipment, these forms shall be used to describe the expected behaviour of the network or network simulator to which the terminal is connected.

Table E.5: Inevitability

Verbal form	Equivalent expressions
will
will not
Distinguish from "shall" / "shall not". Use to express behaviour of equipment or systems outside the scope of the document being drafted, where description of such behaviour is essential to the correct understanding of the requirements pertaining to equipment within the scope of the current document.

EXAMPLE:

Extract from standard specifying behaviour of terminal equipment: "… On expiry of timer T3, the terminal shall send a TIMEOUT message to the network and start timer T4. The network will respond with a TIMOUT-ACKNOWLEDGE message. On receipt of a TIMEOUT-ACKNOWLEDGE message, the terminal shall stop timer T4 …"; thus is distinguished the strong future ("the terminal shall") used for requirements and the normal future ("the network will") used to indicate expected events.

The verbal forms shown in Table E.6 shall be used to indicate statements of fact.

Table E.6: Fact

Verbal form	Equivalent expressions
is	Any verb in the indicative mood, present tense.
is not	Any verb in the indicative mood, present tense.
Distinguish from "shall" / "shall not". Do not use present indicative of verbs for expressing requirements.

F Checklist concerning quantities and units to be used in 3GPP TSs or 3GPP TRs p. 45

Void.

G Example layout of a typescript p. 45

Void.