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The identification of a logical channel is present in every packet flowing across the X.25 interface. This identification is in the form of a field within the packet consisting of 12 bits. For SVCs, the association between a logical channel identifier and a particular virtual circuit is accomplished at call setup time when the identifier is chosen from a pool of unused identifiers. For PVCs, this association is by network subscription.
At network subscription time, the user specifies the number of logical channels needed for both SVCs and PVCs by designating ranges of logical channel numbers. NetWare Link/X.25 configuration uses the decimal equivalent of the complete 12-bit Logical Channel Identifier in terms of two subfields: the Logical Channel Group (4 bits) and the Logical Channel Number (8 bits).
Within any of the following categories, the range of available logical channels must be contiguous. Each successive range of logical channel numbers must be numerically higher than the previous range.
In increasing order, the logical channel ranges include the following:
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