Content for TS 38.323 Word version: 18.3.0
B Uplink Data Compression Protocol
B.1 UDC general description
B.2 UDC packet format and parameters
B.2.1 UDC Header and UDC Data Block format
B.2.2 UDC parameters
B.2.2.1 FU
B.2.2.2 FR
B.2.2.3 Checksum
B.2.3 An example of UDC Checksum calculation
$ Change history
B (Normative) Uplink Data Compression Protocol |R17| p. 51
B.1 UDC general description p. 51
A UDC packet consists of a UDC header and a UDC data block. A UDC data block contains either DEFLATE compressed blocks generated by UDC protocol or original PDCP SDU for SDU not compressed by UDC protocol; the type is specified in FU field (details see Annex B.2.2.1) in UDC header. The FR field (details see Annex B.2.2.2) and the Checksum field (details see Annex B.2.2.3) in UDC header are used only if FU field is set to 1.
If reset procedure is triggered, after performing the reset, the FR field in UDC header of the first compressed PDU shall be set to 1.
B.2 UDC packet format and parameters p. 51
B.2.1 UDC Header and UDC Data Block format p. 51
Figure B.2.1-1 shows the format of UDC Header and UDC Data Block.
B.2.2 UDC parameters p. 52
B.2.2.1 FU p. 52
Length:
1 bit
Indication of whether this packet is compressed by UDC protocol or not. Value '1' means the packet is compressed by UDC protocol.
| Bit | Description |
|---|---|
| 0 | Packet is not compressed using UDC protocol |
| 1 | Packet is compressed using UDC protocol |
B.2.2.2 FR p. 52
Length:
1 bit
Indication of whether UDC compression buffer is reset or not. Value '1' means this is the first compressed packet after UDC buffer reset.
| Bit | Description |
|---|---|
| 0 | Compression buffer is not reset. |
| 1 | Compression buffer has been reset. |
B.2.2.3 Checksum p. 52
Length:
4 bits
This field contains the validation bits for the compression buffer content: The checksum is calculated by the content of current compression buffer before the current packet is put into buffer.
The checksum is derived from the values of the first 4 bytes and the last 4 bytes in the whole compression buffer. The calculation is described as follows:
- Each byte is divided into two 4-bit numbers.
- The 16 4-bit numbers are added together to obtain a sum;
- The checksum is one's complement of the right-most 4 bits (i.e. 4 LSB) of the sum.
B.2.3 An example of UDC Checksum calculation p. 52
The current UDC compression/decompression buffer has the following binary values for example:
Header <1,1,0,0,0,1,0,1,0,0,1,1,1,1,1,1,0,0,0,1,1,0,0,1,0,1,0,1,0,0,0,1, …, 0,1,1,1,1,1,0,1,1,0,0,0,1,0,1,0,1,0,0,1,1,1,1,1,1,0,0,1,1,1,0,0> Tail
The sum of the first 4 bytes and the last 4 bytes can be calculated:
1100+0101+0011+1111+0001+1001+0101+0001+0111+1101+1000+1010+1001+1111+1001+1100 = 10000110;
And checksum value will be one's complement of the right-most 4 bits (i.e. 4 LSB) of the above sum. Hence checksum is 1001.
$ Change history p. 53
