Francesco Usseglio Gaudi wrote:
My little experience is that cell phones are in the most of cases nearly congenstion: a simple crow of people calling all together can shut down or delay every calls and sms
GSM networks running TFR or EFR audio codecs have 8 timeslots on a cell. Usual 900MHz frequency allocation plans allow for 4-5 usable cells but most handsets try only the two with best reception to get an available timeslot. If you happen to be in a neighborhood with 850/1900 or 900/1800 service, the odds of having more capacity available are better. This translates to 16 people with the same network dialing simultaneously can congest the two local cells. Almost all GSM networks implement emergency priority where a call with the bit set will pre-empt capacity in the primary cell. Some handset firmware can be modified to set the neccessary bit on demand. Not sure how long one would get away with it or if the BTS firmware would check the number dialed before granting pre-emption. Pete