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authorAlexander Couzens <lynxis@fe80.eu>2019-06-16 17:05:40 +0200
committerAlexander Couzens <lynxis@fe80.eu>2019-07-11 18:38:45 +0200
commit210ccf4a1da89da9a32745d38ee518c144715ddb (patch)
tree97c00ae8bffa59d9651be787f52cf89de0b427b1
parent5c3a9880cadc29ab8f4354ad2205563ab51201d7 (diff)
Encoding: ACK/NACK: always encode with length field present
In most cases the length field was present and this field takes 7 bits of the maximum available 110 rest bits. The length field was only removed when encoding huge bitmaps usually only happen on lossy connections with packet lost. However the cases without length field were encoded incorrect, because all remaining bits must be used by the uncompressed bitmaps, but the PCU violates this by encoding always the "release 5" bit. Rather than fixing the encoding without length field, simply remove it and always encode with length field. This also reduces the code complexity. Change-Id: I7bc2e18d647b72b8f17ba7a5c9c5e421d88275fb
-rw-r--r--src/encoding.cpp82
1 files changed, 39 insertions, 43 deletions
diff --git a/src/encoding.cpp b/src/encoding.cpp
index 48f3829..ca9e906 100644
--- a/src/encoding.cpp
+++ b/src/encoding.cpp
@@ -828,6 +828,17 @@ static void write_packet_uplink_ack_gprs(
bitvec_write_field(dest, &wp, 0, 1); // 0: don't have REL 5
};
+/* Encode the Ack/Nack for EGPRS. 44.060
+ * The PCU encodes to receive block bitmap to the following rules:
+ * - always encode the lenght field
+ * - use compressed receive block bitmap if it's smaller than uncompressed
+ * receive block bitmap
+ * - use the remaining bits for an uncompressed receive block bitmap if needed
+ *
+ * Note: The spec also defines an Ack/Nack without length field, but the PCU's
+ * doesn't support this in UL. It would require a lot more code complexity
+ * and only saves 7 bit in lossy sitations.
+ */
static void write_packet_ack_nack_desc_egprs(
bitvec * dest, unsigned& wp,
gprs_rlc_ul_window *window, bool is_final, unsigned rest_bits)
@@ -849,12 +860,12 @@ static void write_packet_ack_nack_desc_egprs(
bitvec ucmp_vec;
bitvec crbb_vec;
uint8_t uclen_crbb = 0;
- bool len_coded = true;
uint8_t crbb_start_clr_code;
uint8_t i;
/* static size of 16 bits
- ..0. .... = ACKNACK: (Union)
+ ..1. .... = ACKNACK: (Union)
+ 0 0000 000 Length
Desc
...0 .... = FINAL_ACK_INDICATION: False
@@ -865,8 +876,9 @@ static void write_packet_ack_nack_desc_egprs(
.... ..10 0101 0001 1... .... = STARTING_SEQUENCE_NUMBER: 1187
- .0.. .... = CRBB Exist: 0 */
- rest_bits -= 16;
+ .0.. .... = CRBB Exist: 0
+ minimal size is 24 rest_bits */
+ rest_bits -= 24;
if (num_blocks > 0)
/* V(Q) is NACK and omitted -> SSN = V(Q) + 1 */
@@ -903,47 +915,31 @@ static void write_packet_ack_nack_desc_egprs(
crbb_len = crbb_vec.cur_bit;
}
- if (is_compressed == 0) {
- /* length field takes 8 bits*/
- if (num_blocks > rest_bits - 8) {
- eow = false;
- urbb_len = rest_bits;
- len_coded = false;
- } else if (num_blocks == rest_bits) {
- urbb_len = rest_bits;
- len_coded = false;
- } else
- urbb_len = num_blocks;
- len = urbb_len + 15;
+ if (is_compressed) {
+ /* 8 = 7 (CRBBlength) + 1 (CRBB starting color code) */
+ rest_bits -= 8;
} else {
- if (num_blocks > uclen_crbb) {
- eow = false;
- urbb_len = num_blocks - uclen_crbb;
- }
- /* Union bit takes 1 bit */
- /* Other fields in descr of compresed bitmap takes 23 bits
- * -8 = CRBB_STARTING_COLOR_CODE + CRBB_LENGTH */
- if (urbb_len > (rest_bits - crbb_len - 8)) {
- eow = false;
- len_coded = false;
- urbb_len = rest_bits - crbb_len - 8;
- /* -16 = ACKNACK Dissector length + CRBB_STARTING_COLOR_CODE + CRBB_LENGTH */
- } else if (urbb_len > (rest_bits - crbb_len - 16)) {
- eow = false;
- len_coded = false;
- urbb_len = rest_bits - crbb_len - 16;
- }
- len = urbb_len + crbb_len + 23;
+ uclen_crbb = 0;
+ crbb_len = 0;
}
- /* EGPRS Ack/Nack Description IE */
- if (len_coded == false) {
- bitvec_write_field(dest, &wp, 0, 1); // 0: don't have length
- } else {
- bitvec_write_field(dest, &wp, 1, 1); // 1: have length
- bitvec_write_field(dest, &wp, len, 8); // length
- }
+ if (num_blocks > uclen_crbb + rest_bits) {
+ eow = false;
+ urbb_len = rest_bits - crbb_len;
+ } else
+ urbb_len = num_blocks - uclen_crbb;
+
+ if (is_compressed)
+ len = urbb_len + crbb_len + 23;
+ else
+ len = urbb_len + 15;
+
+
+ /* EGPRS Ack/Nack Description IE
+ * do not support Ack/Nack without length */
+ bitvec_write_field(dest, &wp, 1, 1); // 1: have length
+ bitvec_write_field(dest, &wp, len, 8); // length
bitvec_write_field(dest, &wp, is_final, 1); // FINAL_ACK_INDICATION
bitvec_write_field(dest, &wp, bow, 1); // BEGINNING_OF_WINDOW
@@ -973,9 +969,9 @@ static void write_packet_ack_nack_desc_egprs(
}
LOGP(DRLCMACUL, LOGL_DEBUG,
"EGPRS URBB, urbb len = %d, SSN = %u, ESN_CRBB = %u, "
- "len present = %s,desc len = %d, "
+ "desc len = %d, "
"SNS = %d, WS = %d, V(Q) = %d, V(R) = %d%s%s\n",
- urbb_len, ssn, esn_crbb, len_coded ? "yes" : "No" , len,
+ urbb_len, ssn, esn_crbb, len,
window->sns(), window->ws(), window->v_q(), window->v_r(),
bow ? ", BOW" : "", eow ? ", EOW" : "");