11.2.6b Packet DBPSCH Downlink Ack/Nack

3GPP44.060General Packet Radio Service (GPRS)Mobile Station (MS) - Base Station System (BSS) interfaceRadio Link Control / Medium Access Control (RLC/MAC) protocolRelease 17TS

This message is sent on FACCH, SACCH or SDCCH from the mobile station to the network to indicate the status of downlink RLC data blocks received.

Message type: PACKET DBPSCH DOWNLINK ACK/NACK

Direction: mobile station to network

Table 11.2.6b.1: Packet DBPSCH Downlink Ack/Nack information elements

< Packet DBPSCH Downlink Ack/Nack message > ::=

< MESSAGE_TYPE : bit (6) == 000010 >

< RB Id : bit (5) >

{ 0 — TCH TBF mode

{ 0 – All data blocks acknowledged, no retransmission requested

| 1 < STARTING_SEQUENCE_NUMBER : bit (8) >

< RECEIVED_BLOCK_BITMAP : bit (128) > }

| 1 — DCCH TBF mode

{ 0 – All data blocks acknowledged, no retransmission requested

| 1 < STARTING_SEQUENCE_NUMBER : bit (4) >

< RECEIVED_BLOCK_BITMAP : bit (8) > } }

<padding bits > ;

Table 11.2.6b.2: Packet DBPSCH Downlink Ack/Nack information element details

RB Id (5 bit field)
This field contains the radio bearer identity of the mobile station’s radio bearer for which the downlink data transfer is acknowledged. This field is encoded as a binary number with range 0-31.

STARTING_SEQUENCE_NUMBER (8 or 4 bit field)
The SSN contains the value of V(R) when this information element was transmitted. This field is encoded as the binary representation of V(R).
Range 0 to 255 (8 bit field)
Range 0 to 15 (4 bit field)

RECEIVE_BLOCK_BITMAP (RBB) (128 or 8 bit field)
The RBB is a bitmap representing Block Sequence Numbers. The bitmap is indexed relative to SSN as follows:

BSN = (SSN – bit_number) modulo 256, for bit_number = 1 to 128 (128 bit field).

BSN = (SSN – bit_number) modulo 16, for bit_number = 1 to 8 (8 bit field).

The BSN values represented range:

from (SSN – 1) mod 256 to (SSN – 128) mod 256 (128 bit field)

from (SSN – 1) mod 16 to (SSN – 8) mod 16 (8 bit field)

The value of each bit represents the acknowledgement status of the RLC data block with:

BSN = (SSN – bit_number) mod 256 (128 bit field)
BSN = (SSN – bit_number) mod 16 (8 bit field),

it is encoded as follows:

0 Negative acknowledgement

1 Positive acknowledgement