add some random thoughts on hopping and the oml interface

neels/jolly/new_handover
Harald Welte 13 years ago
parent eb429b7b44
commit 143f1f56d9
  1. 54
      openbsc/doc/gsm-hopping.txt
  2. 21
      openbsc/doc/oml-interface.txt

@ -0,0 +1,54 @@
according to GSM 05.02:
general parameters from CCCH:
* CA cell allocation of ARFCN's (System Information / BCCH)
* FN: TDMA frame number (t1,t2,t3') in SCH
specific parameters from channel assignment:
* MA: mobile allocation, defines set of ARFCN's, up to 64
* MAIO: index
* HSN: hopping sequence generator number (0..64)
hopping sequence generation (6.2.3):
u_int8_t rntable[114] = {
48, 98, 63, 1, 36, 95, 78, 102, 94, 73,
0, 64, 25, 81, 76, 59, 124, 23, 104, 100,
101, 47, 118, 85, 18, 56, 96, 86, 54, 2,
80, 34, 127, 13, 6, 89, 57, 103, 12, 74,
55, 111, 75, 38, 109, 71, 112, 29, 11, 88,
87, 19, 3, 68, 110, 26, 33, 31, 8, 45,
82, 58, 40, 107, 32, 5, 106, 92, 62, 67,
77, 108, 122, 37, 60, 66, 121, 42, 51, 126,
117, 114, 4, 90, 43, 52, 53, 113, 120, 72,
16, 49, 7, 79, 119, 61, 22, 84, 9, 97,
125, 99, 17, 123
};
/* mai=0 represents lowest ARFCN in the MA */
u_int8_t hopping_mai(u_int8_t hsn, u_int32_t fn, u_int8_t maio,
u_int8_t t1, u_int8_t t2, u_int8_t t3_)
{
u_int8_t mai;
if (hsn == 0) /* cyclic hopping */
mai = (fn + maio) % n;
else {
u_int32_t m, m_, t_, s;
m = t2 + rntable[(hsn xor (t1 % 64)) + t3];
m_ = m % (2^NBIN);
t_ = t3 % (2^NBIN);
if (m_ < n then)
s = m_;
else
s = (m_ + t_) % n;
mai = (s + maio) % n;
}
return mai;
}

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oml interface design notes
problems:
* there is no way how to tag a command sent to the BTS, with the response
having the same tag to identify the originator of the command
* therefore, we can have e.g. both the BSC and the OML interface send a
SET ATTRIBUTE message, where the responses would end up at the wrong
query.
the only possible solutions i can imagine:
* have some kind of exclusive locking, where the OML interface gets blocked
from the BSC and is exclusively assigned to the OML console until all commands
of the OML console have terminated. This can either be done explicitly
dynamically or on demand
* use the OML interface synchronously, i.e. always wait for the response from
the BTS before
* unilateral / unsolicited messages need to be broadcasted to both the BSC and
the OML console
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