GSM System information messages

This page covers GSM System information messages which include SI1,SI2,SI3,SI4,SI5,SI6,SI7,SI8,SI9 and SI13 transmitted on BCCH/SACCH.

System information messages are transmitted on either BCCH normal or BCCH extended or on SACCH.

SI messages are transmitted in TC=0 to 7 in a cyclic order repeating every eight TCs of the 51 frame multi frame. TC is the sequence number of the 51 frame MF.
SI1 to SI4 - Transmitted on BCCH
SI5 / SI6 - associated with SACCH
SI7 / SI8 -BCCH Extended
SI-2quater and SI13 - BCCH Normal or BCCH extended

Table-System Information messages

GSM System Information message type SI Description
System information-1(SI1) Cell ARFCN, RACH parameters required to access the system by MS and hopping related information are sent in this SI message.
System information-2(SI2) Neighbour BCCH frequencies and PLMN information are sent in this SI. MS uses these frequencies for signal strength measurements required for handover.
System information-2bis(SI-2bis) RACH control and BCCH extension on neighbor cells
System information-2ter(SI-2ter) Information of BCCH extended allocated on which neighbor cells are provided in this SI. Broadcasted optionally on BCCH by the network to all the MSs.
System information-2 Quarter (SI-2Quater) 3G neighbor cell related information
System information-3 (SI3) Carry following : 1. LAI of the current location area, 2. Cell identity, 3. Control channel information required to calculate paging group, 4. Cell options to achieve good performance in the cell, 5. cell selection parameters required by MS.
System information-4 (SI4) CBCH and CBCH related frequency information, LAI, Cell selection parameters and RACH control information are carried by this SI4 message.
System information-5 (SI5) It carries neighbor cell informations. In active mode, MS sends measurement reports in the uplink and output power/timing advance information in the downlink (on SACCH). Also gets BCCH carrier related information of the neighbor cells.
System information-6 (SI6) Information on LAI, cell options, Cell identity and PLMN permitted or not is transmitted on this SI.
System information-7 (SI7) Cell re-selection parameters needed by MS are sent on this SI.
System information-8 (SI8) Cell re-selection parameters needed by MS are sent on this SI.
System information-9 (SI9) Scheduling related some of the informations are sent on this SI.
System information-13 (SI13) Carry GPRS related information needed for PS call.

This table on system information messages in gsm is useful to analyze gsm UE related issues. In case of any issues related to SIs mentioned above, following need to be observed.

• First it need to be checked which SIs are transmitted by BS and the same have been received by UE or not.
• After this, it has to be checked whether the SIs are decoded correctly without any RF or physical layer (i.e. lower layer) issues.

GSM Channels

Following links are useful for more study on GSM channels of different types:

RF and Wireless Terminologies