G.4 Message extension using ‘padding bits’

04.603GPPGeneral Packet Radio Service (GPRS)Mobile Station (MS) - Base Station System (BSS) interfaceRadio Link Control / Medium Access Control (RLC/MAC) protocolRelease 1999TS

The bit ‘0’ in the first bit position of the ‘padding bits’, see sub-clause 11, may be altered into a bit ‘1’ in future versions of the present document, in order to indicate an extension of the message content. When a message is received with bit ‘1’ in this position, a receiver implemented according to the current version of the present document shall ignore the remaining part of the message.

The example show how a message can be extended, relying on the fact that the ‘padding bits’ are defined with bit ‘0’ in the first bit position.

< Packet UUU message content > ::= — Current version of this EN

< contents defined in current version >

< padding bits > ;

The presence of the extension of the message content is indicated by bit ‘1’. The transmitter shall send a bit ‘1’ in this position if any content is defined for the remaining part of the message. If a bit ‘0’ is received in this position by a receiver in the new version, it shall ignore the remaining part of the message.

< Packet UUU message content > ::= — Future version of this EN

< contents defined in current version >

{ null | 0 bit** = < no string > — Receiver backward compatible with earlier version

| 1 — Bit ‘1’ sent by transmitter in new version

< contents defined in a future version >

< padding bits > } ; — New ‘padding bits’ allows further extension

Annex H (informative):
Examples of ALLOCATION_BITMAP encoding principles

This annex depicts ALLOCATION_BITMAP encoding principles in case of blocks encoding and block periods encoding. References are made to sub-clause 12.4 definitions.