E (Normative)  Verbal forms for the expression of provisions  Word‑p. 41

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.1: Requirement

Verbal form

Equivalent expressions for use in exceptional cases (see clause 6.6.1)

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shall

is to

is required to

it is required that

has to

only ... is permitted

it is necessary

shall not

is not allowed [permitted] [acceptable] [permissible]

is required to be not

is required that ... be not

is not to be

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Do not use "must" as an alternative for "shall". (This will avoid any confusion between the requirements of a standard and external statutory obligations).

Do not use "may not" instead "shall not" to express a prohibition.

To express a direct instruction, for example referring to steps to be taken in a test method, use the imperative mood (e.g. "switch on the recorder").

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The verbal forms shown in table E.2 shall be used to indicate that among several possibilities one is recommended as particularly suitable, without mentioning or excluding others, or that a certain course of action is preferred but not necessarily required, or that (in the negative form) a certain possibility or course of action is deprecated but not prohibited.

Table E.2: Recommendation

Verbal form

Equivalent expressions for use in exceptional cases (see clause 6.6.1)

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should

it is recommended that

ought to

should not

it is not recommended that

ought not to

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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)

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may

is permitted

is allowed

is permissible

need not

it is not required that

no ... is required

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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.

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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)

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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

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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.

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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

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will

will not

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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.

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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

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is

Any verb in the indicative mood, present tense.

is not

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Distinguish from "shall" / "shall not". Do not use present indicative of verbs for expressing requirements.

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F  Checklist concerning quantities and units to be used in 3GPP TSs or 3GPP TRs  Word‑p. 44

Void.

G  Example layout of a typescript