04.043GPPLayer 1 - General RequirementsRelease 1999TS
The physical layer implements a peer‑to‑peer protocol for the control of timing advance and power control at the operation on dedicated physical channels, and further, for the control of timing advance at the operation on packet data physical channels. For this purpose a two octet physical header is defined on all blocks transferred via the SACCH, a logical channel always present on a dedicated physical channel. Further more, a 16 octet information field is defined on downlink blocks transferred via the PTCCH, a logical channel present on a packet data physical channel.
6.1 Physical layer protocol fields and procedures
Procedures for handling the ordered and actual power level fields are specified in 3GPP TS 05.05 and 05.08. The ordered MS power level field and the actual MS power level field are coded as the binary representation of the "power control level", see 3GPP TS 05.05.
Procedures for handling the ordered and actual timing advance fields are specified in 3GPP TS 05.10. The numbers corresponding to the timing advance steps in 3GPP TS 05.10 are included binary coded in the 7 bit or in case of GSM 400 8 bit ordered and actual timing advance fields of the physical layer header.
For all the bands except GSM 400, the values 0 – 63 are valid TA values. The bit pattern "1111111" indicates that the field does not contain a timing advance value. All other bit combinations (64 to 126 decimal) are reserved. For all bands except GSM 400 bit 8 is set to spare.
For GSM 400, the values 0 to 219 decimal are valid TA values. The bit pattern "11111111" indicates that the field does not contain a timing advance value. The remaining values 220 to 254 are reserved.
A MS in packet transfer state which is assigned a TAI shall, when receiving a PTCCH downlink block on the packet data physical channel containing PACCH, read the corresponding ordered timing advance field in that PTCCH block. The ordered timing advance fields corresponding to other TAIs than the assigned one shall be ignored.