9.1 Protocol data units

25.3213GPPMedium Access Control (MAC) protocol specificationTS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

9.1.1 General

A MAC PDU is a bit string, with a length not necessarily a multiple of 8 bits. In the drawings in clause 9.1, bit strings are represented by tables in which the first bit is the leftmost one on the first line of the table, the last bit is the rightmost on the last line of the table, and more generally the bit string is to be read from left to right and then in the reading order of the lines.

Depending on the provided service, MAC SDUs are bit strings with any non-null length, or bit strings with an integer number of octets in length. An SDU is included into a MAC PDU from first bit onward.

In the UE for the uplink, all MAC PDUs delivered to the physical layer within one TTI are defined as Transport Block Set (TBS). It consists of one or several Transport Blocks, each containing one MAC PDU. The Transport Blocks, shall be transmitted in the order as delivered from RLC. When multiplexing of RLC PDUs from different logical channels is performed on MAC, the order of all Transport Blocks originating from the same logical channel shall be the same as the order of the sequence delivered from RLC. The order of the different logical channels in a TBS is set by the MAC protocol.

9.1.2 MAC PDU (not HS-DSCH or E-DCH)

A MAC PDU consists of an optional MAC header and a MAC Service Data Unit (MAC SDU), see figure 9.1.2-1. Both the MAC header and the MAC SDU are of variable size.

The content and the size of the MAC header depends on the type of the logical channel, and in some cases none of the parameters in the MAC header are needed.

The size of the MAC-SDU depends on the size of the RLC-PDU, which is defined during the setup procedure.

Figure 9.1.2-1: MAC PDU

9.1.3 MAC-d PDU (HS-DSCH)

For HS-DSCH the MAC-d PDU format equals the MAC PDU format for the non HS-DSCH case.

9.1.4 MAC PDU (HS-DSCH)

There are two different MAC PDU formats for HS-DSCH. Depending on configuration by higher layers the format is either MAC-hs or MAC-ehs. The MAC PDU format is determined by upper layer signalling [7].

When MAC-hs is configured, a MAC PDU for HS-DSCH consists of one MAC-hs header and one or more MAC-hs SDUs where each MAC-hs SDU equals a MAC-d PDU. A maximum of one MAC-hs PDU can be transmitted in a TTI per UE. The MAC-hs header is of variable size. The MAC-hs SDUs in one TTI belongs to the same reordering queue. If the UE receives successive MAC-hs SDUs of the same size in the MAC-hs PDU, represented by multiple (SID, N) combinations, the UE behaviour is not specified. In 1.28 Mcps TDD multi-frequency HS-DSCH cell, TSN can be extended to 9bit as indicated by RRC signalling. When TSN is extended to 9bit, the 3 least significant bits are placed after the last MAC-hs SDU.

Figure 9.1.4-1: MAC-hs PDU

When MAC-ehs is configured, a MAC PDU for HS-DSCH consists of one MAC-ehs header and one or more reordering PDUs. Each reordering PDU consists of one or more reordering SDUs belonging to the same priority queue. All reordering SDUs belonging to the same priority queue in one TTI shall be mapped to the same reordering PDU. Each reordering SDU equals a complete MAC-ehs SDU or a segment of a MAC-ehs SDU. Each MAC-ehs SDU equals a MAC-d PDU or a MAC-c PDU (FDD and 1.28 Mcps TDD only). The LCH-ID and L fields are repeated per reordering SDU. The TSN and SI fields are repeated per reordering PDU. In 1.28 Mcps TDD multi-frequency HS-DSCH cell, TSN can be extended to 9bit as indicated by RRC signalling. When TSN is extended to 9bit, the 3 least significant bits are placed after the last reordering PDU. If several TSNs is included in MAC-ehs header, the extented bits of TSN should be concatenated in the same order as that of the TSN occurrrence in the MAC-ehs header. For FDD, the size of the TSN field is configurable by upper layers [7].

The presence of the TSN_i and SI_i fields is based on the value of the LCH-ID_i; if the LCH-ID_i is mapped to the same reordering queue as LCH-ID_i-1 or if the value of LCH-ID_i-1is equal to the value of LCH-ID_i, there is no TSN_i or SI_i field. The mapping of the LCH-ID to the reordering queue is provided by upper layers [7], except for BCCH or PCCH where no reordering is applied. The TSN₁ and SI₁ fields are always present. For BCCH or PCCH the TSN field, if present, is always set to zero, the SI field, if present, is always set to ’00’ and the TSN and SI fields shall be ignored by the receiver.

Depending on the HS-DSCH physical layer category, the maximum number of MAC-ehs PDUs that can be transmitted in a TTI per UE is one or two per HS-DSCH transport channel.

The reordering SDUs in one TTI can belong to different priority queues. The MAC-ehs header is of variable size.

The UE behaviour is unspecified, if any of the following conditions are met when Multiflow is not configured or when intra-Node B Multiflow is configured:

– if reordering SDUs in one TTI belong to more than 3 priority queues,

– if the TSN field extension for MAC-ehs entity is not configured and MAC-ehs PDU(s) received during one TTI contain more than 26 reordering SDUs, or,

– if the TSN field extension for MAC-ehs entity is configured and

– up to 3 secondary serving HS-DSCH cells are configured and MAC-ehs PDU(s) received during one TTI contain more than 44 reordering SDUs; or

– more than 3 secondary serving HS-DSCH cells are configured and MAC-ehs PDU(s) received during one TTI contain more than 64 reordering SDUs.

The UE behaviour is unspecified, if any of the following conditions are met for each of the MAC-ehs entities when inter-Node B Multiflow is configured:

– if reordering SDUs in one TTI belong to more than 2 priority queues,

– if MIMO is not configured for this MAC-ehs entity and

– if one HS-DSCH cell is configured for this MAC-ehs entity and MAC-ehs PDU(s) received during one TTI contain more than 16 reordering SDUs, or,

– if more than one HS-DSCH cell is configured for this MAC-ehs entity and MAC-ehs PDU(s) received during one TTI contain more than 26 reordering SDUs, or,

– if MIMO is configured for this MAC-ehs entity and

– if one or two HS-DSCH cells are configured for this MAC-ehs entity and MAC-ehs PDU(s) received during one TTI contain more than 26 reordering SDUs; or

– if three HS-DSCH cells are configured for this MAC-ehs entity and MAC-ehs PDU(s) received during one TTI contain more than 32 reordering SDUs.

Figure 9.1.4-2: MAC-ehs PDU

Figure 9.1.4-3: MAC-hs PDU (1.28Mcps TDD multi-frequency HS-DSCH operation mode only)

Figure 9.1.4-4: MAC-ehs PDU (1.28Mcps TDD multi-frequency HS-DSCH operation mode only)

9.1.5 MAC PDU (E-DCH)

There are two different MAC PDU formats for E-DCH. Depending on configuration by upper layers the format is either MAC-e/es or MAC-i/is. The MAC PDU format is determined by upper layer signalling [7].

When MAC-e/es is configured, there are two MAC sublayers, MAC-e and MAC-es. MAC-es sits on top of MAC-e and receives PDUs directly from MAC-d. MAC-es SDUs (i.e. MAC-d PDUs) of the same size, coming from a particular logical channel are multiplexed together into a single MAC-es payload. There is one and only one MAC-es PDU per logical channel per TTI (since only one MAC-d PDU size is allowed per logical channel per TTI). To this payload is prepended the MAC-es header (see subclause 9.2.4.1). The number of PDUs, as well as the one DDI value identifying the logical channel, the MAC-d flow and the MAC-es SDU size are included as part of the MAC-e header. In case sufficient space is left in the E-DCH transport block or if Scheduling Information needs to be transmitted, an SI will be included at the end of the MAC-e PDU (see subclause 9.2.4.2). Multiple MAC-es PDUs from multiple logical channels, but only one MAC-e PDU can be transmitted in a TTI.

In the example MAC-e PDU shown in figure 9.1.5-2a, the field DDI₀ is referring to the specific DDI value that indicates that there is an SI included in the MAC-e PDU (see subclause 9.2.4.2). This header will not be associated with a new MAC-es payload. Figure 9.1.5-2b shows the MAC-e PDU format when SI is sent alone. In this case DDI₀ is not included in the MAC-e PDU and E-TFCI value 0 is used.

Figure 9.1.5-1 MAC-es PDU

Figure 9.1.5-2a: MAC-e PDU

Figure 9.1.5-2b: MAC-e PDU (SI is sent alone)

When MAC-i/is is configured, there are two MAC sublayers, MAC-i and MAC-is. MAC-is sits on top of MAC-i and receives PDUs directly from MAC-d and MAC-c (FDD and 1.28 Mcps TDD only). When MAC-i/is is configured, a MAC PDU for E-DCH consists of one MAC-i header and one or more MAC-is PDUs. Each MAC-is PDU consists of one or more MAC-is SDUs belonging to the same logical channel. Each MAC-is SDU equals a complete or a segment of a MAC-d PDU or a MAC-c PDU (FDD and 1.28 Mcps TDD only). The MAC-is SDUs can have different sizes. The LCH-ID and L fields are repeated per MAC-is SDU (see subclause 9.2.4.4). The TSN and SS fields are repeated per MAC-is PDU (see subclause 9.2.4.3). Multiple MAC-is PDUs from multiple logical channels, but only one MAC-i PDU can be transmitted in a TTI per E-DCH. In case sufficient space is left in the E-DCH transport block or if Scheduling Information needs to be transmitted, an SI will be included at the end of the MAC-i PDU (see Figure 9.1.5-4a and subclause 11.8.1.6 and subclause 11.9.1.5). If UL Control information needs to be transmitted, an UL MAC Control Information (MCI) will be included at the end of the MAC-i PDU. A MAC-i PDU can only carry either a Scheduling Information or a UL MAC Control Information.

For 1.28Mcps TDD multi-carrier E-DCH operation with more than one carrier group(defined in subclause 9.2.6.3) configured by high layer ,the sufficient space is more than 33 bits in the E-DCH transport block or if Scheduling Information needs to be transmitted, an extend SI (see Figure 9.2.6.3-1a) will be included at the end of the MAC-i PDU(see Figure 9.1.5-4a and subclause 11.9.1.5), and if the sufficient space is more than 23 bits and less than 33 bits or only one carrier group is configured by high layer, the legacy SI(see Figure 9.2.6.3-1) will be included at the end of MAC-i PDU(see Figure 9.1.5-4a and subclause 11.9.1.5). For FDD and in CELL_FACH state only, the UE’s E-RNTI can be included in the MAC-i header. Its inclusion is signalled with a reserved LCH-ID value.

Figure 9.1.5-3 MAC-is PDU.

Figure 9.1.5-4a: MAC-i PDU.

Figure 9.1.5-4b: MAC-i PDU (SI is sent alone)

Figure 9.1.5.4ba: MAC-i PDU (MCI is sent alone)

Figure 9.1.5-4c: MAC-i header part for E-RNTI transmission (FDD only)

Figure 9.1.5-4ca: MAC-i PDU (SI is sent alone before contention resolution) (FDD only)

Figure 9.1.5-4d: MAC-c PDU with CRC for CCCH transmissions (FDD and 1.28 McpsTDD only)