RRC, RLC, MAC, and PHY [Under UMTS]
» Radio
interface layer - 25.301 «
» RRC -
25.331 «
» RLC -
25.322 «
» MAC -
25.321 «
In earlier articles, we looked at number of aspects of access stratum like MAC and PHY interface (described in terms of TF/TFC), PHY structures of few initial channels (SCH, P-CCPCH, PRACH etc.), Logical to Transport to Physical channel mapping, RLC modes for channels, RRC states, RRC connection establishment etc. We know roughly: channel mapping is done based on RRC state, RLC take care of acknowledged/unacknowledged modes, MAC uses TF/TFC for multiplexing of logical channels, PHY works on concept CCTrCh, due to TF/TFC/CCTrCh UMTS can support various kinds of services.
In our flow of discussion, we have seen RRC signaling during RRC Signaling Connection establishment. Next step is how radio bearers are setup (you may want to take a quick look at article on signaling briefly).
But before we do that, we will list down some of the major functions (few of which we have already seen) of RRC, RLC, MAC, and PHY from UE point of view (refer diagram from article on radio layers).
RRC
- Managing RRC connection
- Mobility handling during RRC
connected mode
- Cell selection and re-selection
-
Interpreting broadcast system information
- Managing radio
bearers
- Measurement reporting and control
- Ciphering
control
- Outer loop power control (setting rough target
for closed loop power control)
- Overall configuration and
control of access stratum
RLC
- Support of
Acknowledged/Unacknowleded/Transparent modes
- Segmentation and
reassembly (PDU size can match to TF sizes) for larger size SDUs
-
Concatenation of smaller RLC SDUs
- Padding (when required)
-
Ciphering for non-transparent modes (Ack/Unack)
- Flow control
-
Re-transmission if error detected for Ack mode
MAC
- Providing transport for logical channels or
mapping of logical channels to transport channels
-
Multiplexing/demultiplexing higher layer PDUs onto/from transport
blocks given to/taken from PHY
- Selecting appropriate TF/TFC
-
Deciding ASC for RACH (except for RRC Connection Request)
-
Identification of UEs on common transport channels
- Ciphering
for transparent RLC mode
- HARQ for HS-DSCH
PHY
- Scanning, Synchronisation
- Multiplexing
of transport channels onto CCTrCh and reverse of it
- Rate
matching
- Coding, Interleaving, Spreading, Modulation and
reverse of it
- Mapping of CCTrCh onto physical channels
-
Measurement reporting to RRC
- Closed loop power control
References: UMTS by Sanchez and Thioune, and WCDMA for UMTS by Holma and Toskala.
| Copyright © Samir Amberkar 2010 | § |
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