C1 coding scheme is mainly used for signaling traffic and C2,
C3 and C4 coding schemes are used for user data traffic. The
C2 scheme corresponding with a transmission rate of 13.4
kb/s is assumed to be used. The GPRS message size is
exponentially distributed with means of 2~13.4 kb, 5~13.4 kb,
10x1 3.4 kb respectively, corresponding to the mean service
time (Up) of 2s, 5s and 10s with single slot transmission. The
approximation results of single slot service are calculated
from (6) and (8).