Thursday, November 5, 2009

About MAC - 25.321

- Coordinates te acess of physical layer
- The logical channels of higher layers are mapped to Transport channels of lower layers
- MAC selects appropriate TFS depends on Transmission Rate
- If UE uses Common Transport Channels, MAC provides unique RNTI for each UE
- When RLC in Transparent Mode MAC does encryption on user-plane data
- MAC has three SAPS - MAC-C/Sh -> Mac- Common and Shared
MAC-D -> Mac-Dedicated
MAC - B -> Mac- Broadcast

Mappings : BCCH -> Mac-B -> BCH

PCCH
CCCH
CTCH -> Mac-C/Sh -> Output as PCH, FACH, RACH, CDCH and DSCH


Mac-D -> Mapping between {DCCH, DTCH } to DCH

*in RNC there will be one mac-d entitiy for each UE
There will be one mac-b, mac-Sh/c per each cell


-> MacPDU :
Header Payload
-----------------------------------------------------------------------------
| TCTF | UE-IdType | UE-ID | C/T | MAC -SDU |
-----------------------------------------------------------------------------

TCTF : Target Channel Type , which tells whether channel carries BCH, CC , CTCH

Ue-Id Type : 00 - U-RNTI
01 - S-RNTI

UE-ID : U-RNTI (32 bits)
S-RNTI (16 bits)

C/T : Chanel Type. This helps when multiple logical channels are mapped to one same transport channel. The values would be as below
0000 Logical Chanel 1
0001 Logical Chanel 2
:
:
1110 Logical Chanel 15
1111 Logical Chanel Reserved

No comments:

Post a Comment