Читать книгу Mobile Communications Systems Development - Rajib Taid - Страница 103

The LTE and 5G NR MAC layer facilitates the exchange of air interface Layer 2 information in terms of a PDU between a UE and LTE E‐UTRAN or between UE and 5G NG‐RAN. A MAC PDU consists of a MAC header and MAC SDU, which is received from the RLC layer. The method of description and encoding of the MAC layer PDU is similar to the method used by the LTE and NR RLC layers as described above. Similar to the RLC layer, the encoded bit strings of LTE or 5G NR MAC layer is an octet (8 bits) aligned.

Also, note that unlike the air interface Layer 3 message header, the MAC header and the MAC SDU are variable in size. For more information on the MAC layer protocol header, its different parameters, and their encoding requirements, refer to TS 36.321 [93] for LTE and TS 38.321 [113] for 5G NR. NR air interface MAC layer and its PDU formats are described later in Chapter 19.