System Information Overview: System information (SYS INFO) contains network parameters sent to MS through Um interface network identity parameters: CGI=LAI+CI LAI= MCC+MNC+LAC BSIC=NCC+BCC

CGI: Cell global identity MCC: Mobile Country Code (EX:002(Egypt)) international mobile subscriber identity (IMSI) Location area identity (LAI). Temporary Mobile Subscriber Identity (TMSI) MNC: Mobile Network Code (EX: 010 (Vodafone)). LAC: Location Area Code (The whole area covered by each GSM PLMN is divided into different location areas LACs). LAC contain of LAIs (Location Area Indication) of MSs. CI : Cell Identity

BSIC :base station identity code: The code is needed because it is possible that mobile stations receive the broadcast channel of more than one base station on the same frequency. This is due to frequency re-use in a cellular network As long as base stations use different frequencies for their broadcasting channel, there is no problem in using the same Base Station Identity Code NCC: Network Color CodeBCC: Base station Color Code

Signal StrengthThe first and arguably most important consideration in radio link management is signal strength. In GSM (and most other RF communications) the standard measure of signal strength is dBm (decibels in milliwatts). The term received signal strength indicator (RSSI) is often used but in GSM the term received-signal level (RXLEV) is preferred. The distinction is that the term RSSI was generally used on analog networks and RXLEV is used on digital networks. On this website RSSI will be used for general reference to signal strength and RXLEV for the actual value that is passed over the network. RXLEVRXLEV is a number from 0 to 63 that corresponds to a dBm value range. 0 represents the weakest signal and 63 the strongest.

RSSI below -110 dBm are generally considered unreadable in GSM. RSSI in the area of -50 dBm are rarely seen and would indicate that the MS is right next to the BTS. The main factor that affects RSSI is distance from the tower. However, other factors such as terrain, elevation, and large objects such as buildings can dampen signal strength.RXQUALAlthough a strong RSSI is desirable, it does not guarantee a quality signal. RXQUAL is a value that represents the quality of the received signal. The MS determines the Bit Error Rate (BER) of the signal and reports it back to the network. The BER is simply a percentage of the number of bits it receives that did not pass error checking. The bits may have been garbled along the RF path or lost due to fading or interference. The higher the BER the lower the signal quality. RXQUAL is given as a number from 0 to 7 and represents a percentage range of BER.

Cell Selection and ReselectionCell selection refers to the initial registration that a MS will make with a network. This normally only occurs when the phone powers up or when the MS roams from one network to another.Cell reselection refers to the process of a MS choosing a new cell to monitor once it has already registered and is camped on a cell. It is important to distinguish that selection and reselection are done by the MS itself and not governed by the network. The network would only be responsible for this function when the MS is in a Traffic Channel (TCH). When the MS reselects a new cell it will not inform the network that it has done so unless that new cell is in a new Location Area (LA). There are many parameters involved in selection and reselection of a new cell. The MS must ensure it is getting the best signal and the network must ensure that the MS does not cause unneeded strain on the network by switching cells when unnecessary or undesired. C1C1 is the path-loss parameter that is used to determine the strongest cell for selection. The MS will calculate a C1 for each tower it can see and select the cell tower with the highest C1. The C1 uses the following parameters for calculation:

The formula for calculating C1 is given as: C1 = (A) - Max(B,0) where:A = (RXLEV - RLAM) B = MS Transmit Power Max CCH -Max RF Output of MSAt first this may seem complicated but if we examine the various parameters and how they affect the C1 score then it becomes more clear.A - This value is merely a dB value for the difference between what RSSI is required to select that cell and what signal strength the MS sees the tower at. If the RLAM is -110dB and the MS sees the tower at -90dB then the value of A is 20dB. The higher the value of A the higher the C1 and the more attractive this tower will be to the MS. B - Just because a MS can receive a tower's signal does not mean that the MS has enough power to reach that tower. The tower tells the MS what maximum power level that the MS may use to transmit to that tower. If the phone is capable of transmitting at this power than there is no problem. However, what if the phone can not transmit at that power level? The signal from the MS may not have enough power to reach the tower. Any lack in transmitting power of the MS must be taken into account when calculating C1. B is essentially the value of this difference. Let's say a cell tower requires the MS to be able to transmit at a 30dB power level but this MS is only capable of transmitting at 26dB. In this case the value of B would be 4dB. This value is subtracted from the value of A which has the result of lowering the value of C1. If the MS is capable of transmitting at the required power or higher then B will be zero and no adjustments to C1 will be made.In summary, the two main factors in determining C1 are the strength of the received signal and the transmission power the MS is capable of. C1 alone is only used for cell selection. When a MS is already camped on a cell and it wants to move to another cell it will reselect it. Cell reselection uses a different criteria C2.C2C2 is the parameter used for cell reselection. Once a MS is camped on a cell it will continuously monitor the strength of neighbor cells. Every BCCH sends out a BCCH Allocation (BA) List. This is a list of neighbor cells (ARFCNs) that the MS must monitor while camped on a particular cell. The MS will monitor these ARFCNs for signal strength and only reselect a cell that is on this list. The MS will calculate a C2 value for each cell on the BA list. The cell tower with the highest C2 wins and the MS will move to that cell and camp on it. Keep in mind the C2 is calculated by the MS and the MS decides which cell tower to camp on. The cell that the MS camps on is known as the serving cell. As long as the losing cell and the gaining cell are both in the same Location Area the MS will not notify the network that is is selecting a new cell. The MS only needs to notify the network if it is reselecting the cell that is in a new location area in which case it will do a location update.The C2 is calculated using the following parameters:

The formula for calculating C2 is:C2 = C1 + CRO - (Temp_Offset * H(T-PT))H = 1 if the MS has been monitoring a particular cell for less than the penalty time.H(x) =1 if x