C1 (path loss-criterium) (GSM/DCS/PCS)
This is a parameter (ranging from -99 to 99 dBm) calculated by the phone to decide which cells to use (it uses the cell only if its C1 is positive). This value is based on:
RX
Strength of signal received in BCCH channel. If it is equal or less than RxLevAm, the phone searches for next BCCH channel. It is shown in test 1 (for current channel) and also in test 3, test 4 and test 5 (for neighbor channels). The amount of measurements of the quality of transmission with BCCH channels in neighbor cells is given in test 62
RxLevAm (Rx Level Access minimum)
Min. level of the received signal (usually from -100 dBm to -110 dBm) needed by the phone to use particular cell.
MSTxPwr
Max power, which can be transmitted by phone to get access to RACH channel (i.e. max power allowed by current cell). Actually, it is lower in towns (where cells are small) and higher outside them.
MSMaxTxPwr
Max permissible transmission power of the phone (its classes are described in TX description).
It is calculated using following formula: C1 = (RX - RxLevAm - MAX ( ( MSTxPwr - MSMaxTxPwr ), 0) ) , where MAX(x,y) is obviously a mathematical function giving the bigger one of the discussed numbers. The phone shows C1 value in test 1 (for current channel) and in test 3, test 4 and test 5 (for neighbor channels).
C2 (cell-reselection criterion) (GSM/DCS/PCS)
This parameter (-99 to 99 dBm) is calculated with following formula: C2 = C1 + Cell reselect offset - Temporary offset * H (Penalty time - T). If this value for some other cell (C2 for neighbor channels can be found in test 3, test 4 and test 5) is higher than this value for current cell (shown in test 1 and test 3) for a period of time longer than 5 seconds, the phone switches cells. There are two exceptions to the rule:
if the new cell is located on different ‘Location Area (this parameter for current cell can be checked in test 11), C2 for this cell must be (during more than 5 seconds) higher than C2+CELL_RESELECT_HYSTERESIS for old cell (where CELL_RESELECT_HYSTERESIS is a special parameter sent in BCCH channel).
if the phone switched cells during last 15 seconds, C2 for a new cell must be higher at least 5 dBm from C2 value of the old cell.
H(x) function for currently not used cells is 0 (if x<0) or 1 (if x>=0). For current cell H(x) is always equal 0.
By a skillful manipulation of this parameter (through CELL_RESELECT_HYSTERESIS), operators can direct connections to specific cells (thus lightening load of the network).
http://www.mwiacek.com/gsm/netmon/faq_net1.htm
