R- GSM extended
2.3 GPRS Function
The GPRS functions supported by BSS include:
Radio link management and radio resources management.
Access control over the MS.
Provision of routes for the transfer of packet data.
The radio link management function involves mainly establishment, maintenance and release of the radio links. The radio resources management function involves mainly coding/decoding of radio packet channels, configuration of radio packet channels, multiplexing of radio channels, switchover of radio channels between the circuit switched traffic channel and the packet switched traffic channel and allocation of channels to the MS.
The access control function serves primarily to solve the issue of channel contention and allocate radio resources to the MS according to the requested QoS.
The routes serve to transfer the uplink data to Serving GPRS Support Node (SGSN) properly and receive the downlink data from the SGSN.
2.3.1 Supported Packet System Information
I. Overview
The packet system information broadcast in the cell serves mainly for the MS to access the network. If the cell supports GPRS, the System Information 13 (SI13) shall be added to the BCCH, if not, SI13 will not be broadcast. The cell can either be configured with the PBCCH channel or without it. This will be notified to the MS via SI13. The main
message broadcast on the PBCCH are the dedicated packet system information of GPRS.
II. Technical description
There are following types of packet system information:
1) Packet System Information Type 1 (PSI1)
This information is sent by the network on the PBCCH or PACCH, giving information for Cell selection, for control of the PRACH, for description of the control channel(s) and optional global power control parameters. This information shall not be segmented across more than one RLC/MAC control block.
2) Packet System Information Type 2 (PSI2)
This information is sent by the network on PBCCH and PACCH, giving information of reference frequency lists, cell allocation, GPRS mobile allocations and PCCCH descriptions being used in the cell. PSI2 also contains Non-GPRS cell options applicable for non-packet access. This message shall not be segmented across more than one RLC/MAC control block.
3) Packet System Information Type 3 (PSI3)
This information is sent by the network on the PBCCH or PACCH, giving information of the BCCH allocation (BA_GPRS) in the neighboring cells and cell selection parameters for serving cell and non-serving cells. This information shall not be segmented across more than one RLC/MAC control block.
4) Packet System Information Type 3 bis (PSI3bis)
This information is sent by the network on the PBCCH and PACCH giving information of the BCCH allocation in the neighboring cells and cell selection parameters for non-serving cells. This information shall not be segmented across more than one RLC/MAC control block. If not all information fits into one instance of the PSI3bis, the PSI3bis can be repeated.
5) Packet System Information Type 4 (PSI4)
This information is optionally sent by the network on the PBCCH and PACCH giving information directing the mobile station to make measurements on a list of serving cell PDCHs, during the idle frame of those PDCHs. This information shall not be segmented across more than one RLC/MAC control block.
6) Packet System Information Type 5 (PSI5)
This optional information is sent by the network on the PBCCH giving information for measurement reporting and network controlled cell reselection. If not all information fits into one information, the remaining information will be sent in other instances of the
This information may be broadcast by the network on the PACCH. The information provides the mobile station with GPRS cell specific access-related information. The information in this information shall be the same as provided in the PSI13 on BCCH.
PSI1~PSI4 can either be broadcast on the PBCCH or sent on the PACCH. PSI5 can be broadcast only on the PBCCH. PSI13 can be sent only on the PACCH. When there is PBCCH in the cell, no PSI13 will be transferred on the PACCH, but PSI1 will be broadcast periodically on it. When there is no PBCCH in the cell, only the PSI13 will be broadcast periodically on the PACCH.
M900/M1800 BSS can transfer all the GPRS-related packet system information, provide such functions as controlled re-transmission, high-speed re-transmission and low-speed retransmission, and control the transfer of packet system information on the PACCH based on the configuration of the PBCCH/PCCCH in a cell.
III. Parameter
At present, the PBCCH and PCCCH are not configured. Therefore, PSI13 is usually broadcasted on PACCCH.
The configuration of PSI13 is realized with the command pcu add gprs. The following parameters are involved.
1) NMO
Description: network operation mode.
Value range: 0~3. 0 - network operation mode I, 1 - network operation mode II, 2 - network operation mode III, 3 – reserved.
Default: At present, the GPRS network usually has neither Gs interface nor PCCCH configured. Therefore, this parameter is usually set as "1".
2) T3168
Description: T3168 timer overtime value. The duration for MS to wait for the packet uplink assignment message.
Value range: 500 ms, 1000 ms,↑, 4000 ms Default: 1000ms
T3192
Description: T3192 timer overtime value. The duration for the MS to wait for TBF release after receiving the last data block.
Value range: 500 ms, 1000 ms, 1500 ms, 0 ms, 80 ms, 120 ms, 160 ms and 200 ms Default: 500 ms
Description: maximum duration of non-DRX. The maximum duration for executing non-DRX mode when MS is switching from packet transfer mode to packet idle mode.
Value range: no – enter DRX mode immediately, 1 s – 1 s, 2 s – 2 s, ↑64 s – 64 s Default: 4 s, i.e., enter DRX mode after 4 seconds
4) AccBurst
Description: the access burst format used by MS in PRACH, PTCCH/U or packet control acknowledge message.
Value range: 8 bit, 11bit
Default: Some MSs do not support 11 bit access burst type, so it is recommended to set it as "8 bit".
5) CtrlAckType
Description: control acknowledge message type. The format adopted by MS in the control acknowledge message.
Value range: 0, 1. 0 – 4 access burst used (TA can be obtained without sending
"polling" message), 1 - RLC/MAC control block used (TA can be obtained only after sending "polling" message).
Default: 0 6) BsCvMax
Description: maximum value of MS countdown timer Value range: 0~15
Default: 4 7) PanDec
Description: PAN_DEC used by MS N3102 counter. When MS T3182 times out, N3102 will reduce the value of PAN_DEC.
Value range: 0~7, nouse Default: 3
8) PanInc
Description: PAN_INC used by MS N3102 counter. When MS activates T3182 and receives the corresponding acknowledge message from packet uplink, N3102 will increase the value of PAN_DEC.
Value range: 0~7, nouse
Description: PAN_MAX of MS N3102 counter, i.e. the maximum value of N3102.
Value range: 4, 8, ↑ 32, nouse Default: 12