RRC Connection Management & Radio Bearer Control Procedures

The RRC connection Management & Radio Bearer control procedures are as described in pictures below. The other RRC connection Management & Radio Bearer control procedures that are not described here resemble to the ones listed below.

The procedures listed below are:

• RRC Channel Switching from CELL_FACH to CELL_DCH
• RRC Channel Switching from CELL_DCH to CELL_FACH [64/64 - BE]
• RRC Channel Switching from CELL_DCH to CELL_DCH [64/64 - 0/0] - Multi Service
• RRC Channel Switching from CELL_DCH to CELL_DCH [0/0 - 64/64] - Multi Service
  

Author: Kabeer Ahmed, http://skabeer.ahmed.googlepages.com/ Last Updated: November 4th, 2006

Network Assisted Cell Change - NACC

Definition

In the GPRS, it is usually the MS that takes the decision to change the cell in the idle and dedicated mode or call it a Packet Transfer Mode. Release 4 presents another feature wherein Network can assist a MS in this procedure. This is known as NACC and is defined clearly in the 44.060 specification from the 3GPP.

These are few important points to be noted regarding the NACC:

When doing cell reselection -
A PBCCH description for the target cell may be received in the packet system information (neighbour cell information in PSI3 and 3bis) in the old serving cell, or in a BCCH message (SI13) in the target cell.

If the old cell does not support CCN, the operation in the old cell shall be aborted when one of the following conditions
are met:

• the mobile station starts to receive information on PBCCH in the target cell;
• the mobile station has received the SI13 message (see 3GPP TS 44.018) and there is no PBCCH present in the target cell; or
• the criteria for camping on the old cell are no longer fulfilled (see 3GPP TS 45.008).

During this process, the data transfer in both Packet Idle Mode and Packet Transfer Mode might be suspended to receive necessary System Information.

Before we venture out into the details of these things, there are often certain definitions that need to be in mind. I often tend to forget these and get confused. Here is the link that will help one recollect the definitions of Network Control Mode and Network Mode of Operation.

Abbreviations Used

PCCC - Packet Cell Change Continue
PCCN - Packet Cell Change Notification
PCCO - Packet Cell Change Order

Procedures in Various Conditions

There are different scenarios that might occur in the NACC procedure which can be divided in to the following types:

1. Cell Reselection with NACC support in NC1 mode (with PMR), the proposed cell from the MS is accepted by the Network
2. Cell Reselection with NACC support in NC1 mode (with PMR), the proposed cell from the MS is not accepted. Other neighbour cell from the network is accepted.
3. Cell Reselection with NACC support in NC1 mode (with PMR), the proposed cell from the MS is not accepted. No other neighbour cells are available.
4. Cell Reselection with NACC support in NC0 mode (no PMR), the propsed cell from the MS is accepted from the network (PCCC).
5. Cell Reselection with NACC support in NC0 mode (no PMR), the propsed cell from the MS is not accepted. Other neighbour cell is accepted from the network.
6. Cell Reselection with NACC support in NC0 mode (no PMR), the proposed cell from the MS is not accepted. No other neighbour cells are available.

Scenario 1: Cell Reselection with NACC support in NC1 mode (with PMR), the proposed cell from the MS is accepted by the Network

The picture below depicts this scenario clearly. Well I have some doubt casted on the sending of 'Packet Measurement Report' on the PDTCH/U.

It should be noted that PMR is a continuous message all throughout this procedure. It is indicated here only once for clarity and to maintain sanity of the picture.

Scenario 2: Cell Reselection with NACC support in NC1 mode (with PMR), the proposed cell from the MS is rejected by the Network. The Cell Proposed by the Network is selected by the MS

MS might suggest a cell that it considers strong. But it might so happen that Network might already know that the cell being proposed by the MS is congested. So in this case, the Network instructs the MS to reselect to a cell that NW considers better than the current serving cell.

Scenario 3: Cell Reselection with NACC support in NC1 mode (with PMR), the proposed cell from the MS is rejected by the Network. There are no other cells that are available

This scenario is very similar to the scenario 2. The cell proposed by the MS is known to the Network as a congested cell and there are no other cells available. Henceforth, the MS stays on the same cell. In this scenario, PCCN messages can still be seen from the MS.

After sending PCCN, the Network indicates NC2 mode in the PMO.

Scenario 4, 5 and 6 are similar to 1,2 and 3 respectively. Except that in these scenarios as the Network Control Mode is NC0, PMR is absent.

References:

1. 3GPP 45.008
2. 3GPP 44.018
3. 3GPP 44.060
   

Questions:

1. How is CCN support for a cell indicated by the Network?

• This information is relayed by the network in System Information on BCCH or PBCCH. Or, the network might also send this in the PMO - Packet Measurement Order, to the MS.
  

_{Copyright 2006 - Kabeer Ahmed}