47
4. Call Forward
Unreachable
Forward Num
Forward calls when the GSM channel cannot register to the carrier.
This specifies the phone number to receive forwarded calls under this
condition.
Not Set
5.3.12 IMEI
This section allows IMEI modifications. Each GSM channel is programmed with an IMEI. It is a 15-digit number
with the format described below.
TAC
SERIAL
CHECK DIGIT
AA BBBBBB
CCCCCC
D
The first two digits, “AA”, of the TAC are the
(RBI), which identifies the
-approved
group that allocated the TAC. The RBI numbers are allocated by the Global Decimal Administrator. The first
two digits are always decimal (i.e., less than 0xA0), allowing IMEI numbers to be distinguished from an
which will always have 0xA0 or larger as its first two digits.
The next six digits, “BBBBBB”, signifies the manufacturer and the brand/model.
The following six digits, “CCCCCC”, are the serial number.
The last digit is the check digit which is calculated according to Luhn formula. The Check Digit is calculated of all
other digits in the IMEI. The purpose of the Check Digit is to help guard against the possibility of incorrect entries
to the CEIR (Central Equipment Identity Register) and EIR equipment.
The check digit is validated in three steps:
1. Starting from the right, double a digit every two digits (e.g., 7 → 14).
2. Sum the digits (e.g., 14 → 1 + 4).
3. Check if the sum is divisible by 10.
Conversely, one can calculate the IMEI by choosing the check digit that would give a sum divisible by 10. For the
example IMEI =
35 780502 398494 ?
IMEI number
3
5
7 8
0 5
0 2 3 9
8 4 9 4 ?
Double every other digit
3
10
7
16
0
10
0
4
3
18
8
8
9
8
?
Sum all digits
3 + (
1 + 0
) + 7 + (
1+6
) + 0 + (
1+0
)+ 0 +
4
+ 3 + (
1+8
) + 8 +
8
+ 9 +
8
+ ? =
68
+
?
Sum of all digits is
68
. We need to make it divisible by 10. We need to add
2
to our Sum of
68
and this addition is
our check digit. Our complete IMEI is
35 780502 398494 2
.
Summary of Contents for GoIP
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