diff options
| author | Holger Hans Peter Freyther <zecke@selfish.org> | 2011-06-23 17:53:27 -0400 |
|---|---|---|
| committer | Holger Hans Peter Freyther <zecke@selfish.org> | 2012-01-06 18:52:05 +0100 |
| commit | faf1f64a2d0a54d37616a8bec8691346ab792cde (patch) | |
| tree | cf9f5052348eae7207bceeb9803967686ca3e692 /openbsc/include | |
| parent | 26d0fe3c89042ed4008903dbe12c5110d8f9fc48 (diff) | |
gprs: Honor GSM 04.64 8.4.2 Receipt of unacknowledged information
GSM 04.64 8.4.2 asks to ignore UI frames if the DLCI is not known,
or if the "(V(UR)- 32) <= N(U) < V(UR)". E.g. if we want to have
V(UR) == 511 and this frame is dropped, we would ignore N(U)'s
0 to 510. Calculate the delta.
The code is based on Jonathan Santos's "LLC UI window" fix but the
issue was discovered independly.
Diffstat (limited to 'openbsc/include')
| -rw-r--r-- | openbsc/include/openbsc/gprs_llc.h | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/openbsc/include/openbsc/gprs_llc.h b/openbsc/include/openbsc/gprs_llc.h index f905473a1..e3fc82ef9 100644 --- a/openbsc/include/openbsc/gprs_llc.h +++ b/openbsc/include/openbsc/gprs_llc.h @@ -179,4 +179,20 @@ int gprs_llgmm_assign(struct gprs_llc_llme *llme, int gprs_llc_init(const char *cipher_plugin_path); int gprs_llc_vty_init(void); +/** + * \short Check if N(U) should be considered a retransmit + * + * Implements the range check as of GSM 04.64 8.4.2 + * Receipt of unacknowledged information. + * + * @returns Returns 1 if (V(UR)-32) <= N(U) < V(UR) + * @param nu N(U) unconfirmed sequence number of the UI frame + * @param vur V(UR) unconfirmend received state variable + */ +static inline int gprs_llc_is_retransmit(uint16_t nu, uint16_t vur) +{ + int delta = (vur - nu) & 0x1ff; + return 0 < delta && delta < 32; +} + #endif |