MAC-ehs PDU Structure with Example

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There are two different types of MAC HSDPA PDU format depending upon the upper layer configuration.

• MAC-hs
• MAC-ehs

In this tutorial only MAC-ehs is covered.

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In this case the MAC HSDPA PDU is consists of

• MAC-ehs header
• One or more reordering PDUs

Each reordering PDU consists of one or more reordering SDU belonging to the same priority queue.

Header Elements

LCH-ID (Logical Channel Identifier): 4 bits

The LCH-ID field provides identification of the logical channel at the receiver and the re-ordering buffer destination of a reordering SDU.

LCH-ID	Designation
0000	Logical Channel 1
0001	Logical Channel 2
. . . . . . .	. . . . . . . . . . . . . . . .
1110	Logical Channel 15
1111	Logical Channel 16

TSN (Transmission Sequence Number): 6 bits

The TSN field provides an identifier for the transmission sequence number on the HS-DSCH. The TSN field is used for reordering purposes to support in-sequence delivery to higher layers.

SI (Segmentation Indicator): 2 bits

The SI field indicates is MAC-ehs SDU has been segmented.

SI Field	Segmentation indication
00	The first reordering SDU of the reordering PDU is a completeMAC-ehs SDU. The last reordering SDU of the reordering PDU is a complete MAC-ehs SDU.
01	If there are more than one reordering SDUs in the reordering PDU, the last reordering SDU of the reordering PDU is a complete MAC-ehs SDU. The first reordering SDU of the reordering PDU is the last segment of a MAC-ehs SDU.
10	If there are more than one reordering SDUs in the reordering PDU, the first reordering SDU of the reordering PDU is a complete MAC-ehs SDU. The last reordering SDU of the reordering PDU is the first segment of a MAC-ehs SDU.
11	If there are more than one reordering SDUs in the reordering PDU, the first reordering SDU of the reordering PDU is the last segment of a MAC-ehs SDU and the last reordering SDU of reordering PDU is the first segment of a MAC-ehs SDU. If there is only one reordering SDU in the reordering PDU, the reordering SDU is a middle segment of a MAC-ehs SDU.

L (Length): 11 bits

The L field provides the length of the reordering SDU in octets. The reordering SDU size can vary for each reordering SDU in the MAC-ehs PDU, and is set for each reordering SDU individually.

F (Flag): 1 bit

The F field is a flag indicating if more fields are present in the MAC-ehs header or not.

• 0: the F field is followed by an additional set of LCH-ID and L fields and optionally TSN and SI fields.
• 1: the F field is followed by a reordering PDU. Each header extension corresponds to one reordering SDU.

Example in Decoding

e0 f4 11 80 06 01 10 10 a0 01 01 0d 59 06 11 5f ad d0 cb 6f 01 1c d6 21 10 a9 06 5f 0c 10 1f 50 f9 01 c1 11 91 22 d0 5c 66 c6 0a 50 a1 1a 00 1f 22 16 0a d0 b9 df f1 b1 19 02 11 fb 1c 20 21 12 c0 10 12 c9 00 1b 01 b1 00 bb 5a 1f 09 06 0c fd 0f b1 b6 9a 56 09 c1 aa 10 1d b6 10 1d 19 0f 92 1a 51 f2 61 d1 d5 10 bf 10 ba 1f 6f 5b 11 92 1d cb 09 d6 11 12 a1 11 00 2f c1 60 61 20 00 00

Header In Bits

1110 00001111010 000010 00 1

MAC-ehs PDU Header

LCH ID: 1110 (14)
L: 00001111010 (122)
TSN: 000010
SI: 00 (Complete Segment)
F: 1 (Reordering PDU Follows)

Reordering PDU :

0x80 06 01 10 10 a0 01 01 0d 59 06 11 5f ad d0 cb 6f 01 1c d6 21 10 a9 06 5f 0c 10 1f 50 f9 01 c1 11 91 22 d0 5c 66 c6 0a 50 a1 1a 00 1f 22 16 0a d0 b9 df f1 b1 19 02 11 fb 1c 20 21 12 c0 10 12 c9 00 1b 01 b1 00 bb 5a 1f 09 06 0c fd 0f b1 b6 9a 56 09 c1 aa 10 1d b6 10 1d 19 0f 92 1a 51 f2 61 d1 d5 10 bf 10 ba 1f 6f 5b 11 92 1d cb 09 d6 11 12 a1 11 00 2f c1 60 61 20

Padding : 0x

0000

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Reference

• Medium Access Control (MAC) specification: http://www.3gpp.org/ftp/Specs/archive/25_series/25.321/
• WCDMA Design Handbook
• UMTS Signaling: UMTS Interfaces, Protocols, Message Flows and Procedures Analyzed and Explained

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