366 lines
10 KiB
Plaintext
366 lines
10 KiB
Plaintext
module GPRS_TBF {
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/* GPRS TBF Routines, intended as minimal MS-Side GPRS implementation
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*
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* (C) 2018 by Harald Welte <laforge@gnumonks.org>
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* All rights reserved.
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*
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* Released under the terms of GNU General Public License, Version 2 or
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* (at your option) any later version.
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*/
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import from GSM_Types all;
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import from Osmocom_Types all;
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import from General_Types all;
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import from RLCMAC_Types all;
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import from RLCMAC_CSN1_Types all;
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import from LLC_Types all;
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import from GPRS_Context all;
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/* input parameters into TBF (mostly mode/cs + LLC PDUs */
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type record UlTbfPars {
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/* Acknowledged mode (true) or unacknowledged (false) */
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boolean ack_mode,
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/* Coding Scheme for transmission, determines block size */
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GprsCodingScheme initial_cs,
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/* list of abstract/decoded LLC PDUs */
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record of PDU_LLC llc_pdus optional,
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/* possibly computed: list of encoded LLC PDUs */
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record of octetstring llc_pdus_enc
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}
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type record RlcEndpointTx {
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/* send state variable V(S) (9.1.1): 0 .. SNS-1 */
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integer v_s,
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/* acknowledge state variable V(A) (9.1.2): BSN value of oldest RLC data block that has not
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* been positively acknowledged by peer. */
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integer v_a,
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/* acknowledge state array V(B) (9.1.3) */
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bitstring v_b
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}
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private function f_RlcEndpointTx_init(inout RlcEndpointTx ep) {
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ep.v_s := 0;
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ep.v_a := 0;
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ep.v_b := int2bit(0, 128); /* FIXME: EGPRS 2048 bits length */
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}
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type record RlcEndpointRx {
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/* receive state variable V(R) (9.1.5): BSN one higher than highest BSN yet received (mod SNS) */
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integer v_r,
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/* receive window state variable V(Q) (9.1.6): Lowest BSN not yet received (mod SNS) */
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integer v_q,
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/* receive state array V(N) (9.1.7) */
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bitstring v_n
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}
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private function f_RlcEndpointRx_init(inout RlcEndpointRx ep) {
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ep.v_r := 0;
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ep.v_q := 0;
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ep.v_n := int2bit(0, 128); /* FIXME: EGPRS 2048 bits length */
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}
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type record UlTbfState {
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/* "const" input state with TBF Data */
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UlTbfPars tbf,
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uint8_t num_ts,
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RlcEndpointTx et,
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integer tfi,
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/* total length of all encoded LLC PDUs */
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integer llc_pdu_totlen,
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/* index of current/next PDU in llc_pdus_enc */
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integer cur_pdu,
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/* byte offset into current/next PDU; next byte to transmit */
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integer cur_index,
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/* block sequence number of next block within TBF */
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integer bsn_p,
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/* total number of bytes remaining in TBF */
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integer total_bytes_remain,
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/* list of already-sent RLC/MAC Blocks */
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record of RlcmacUlBlock rlc_sent
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}
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function f_UlTbfState_init(inout UlTbfState us, in UlTbfPars utpars) {
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var RlcmacUlBlock blk;
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us.tbf := utpars;
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us.num_ts := 1;
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f_RlcEndpointTx_init(us.et);
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us.tfi := 0; /* FIXME */
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us.cur_pdu := 0;
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us.cur_index := 0;
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us.bsn_p := 0;
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us.total_bytes_remain := 0;
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us.rlc_sent := {};
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/* encode all LLC PDUs from their abstract type to octetstring */
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us.cur_pdu := 0; /* currently processed PDU */
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us.cur_index := 0; /* next to-be transmitted index */
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if (ispresent(us.tbf.llc_pdus)) {
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us.tbf.llc_pdus_enc := {};
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us.llc_pdu_totlen := 0;
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for (var integer i := 0; i < sizeof(us.tbf.llc_pdus); i := i+1) {
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var octetstring cur_enc := enc_PDU_LLC(us.tbf.llc_pdus[i]);
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us.tbf.llc_pdus_enc := us.tbf.llc_pdus_enc & { cur_enc };
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us.llc_pdu_totlen := us.llc_pdu_totlen + lengthof(cur_enc);
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}
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us.total_bytes_remain := us.llc_pdu_totlen;
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}
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}
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private function f_UlTbf_ack_one_block(inout UlTbfState us, integer n) {
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/* compute index into v_b */
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var integer idx := n - us.et.v_a;
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if (idx < 0 or idx > lengthof(us.et.v_b)) {
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setverdict(fail, "UlTbf: Cannot ACK ", n, " while V(A) is ", us.et.v_a);
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self.stop;
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}
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/* set the bit in the acknowledge state array */
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us.et.v_b[idx] := '1'B;
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}
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/* check if V(B) contains '1' at lower end: if yes, advance V(A) and shift V(B) */
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private function f_UlTbf_check_advance_v_a(inout UlTbfState us) {
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log("FIXME: Implement this");
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}
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/* copy 'len' number of bytes from current pending LLC PDU */
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private function f_copy_from_llc(inout UlTbfState us, integer len) return octetstring
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{
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var integer pdu_len := lengthof(us.tbf.llc_pdus_enc[us.cur_pdu])
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var octetstring ret;
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ret := substr(us.tbf.llc_pdus_enc[us.cur_pdu], us.cur_index, len);
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us.cur_index := us.cur_index + len;
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us.total_bytes_remain := us.total_bytes_remain - len;
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log("copy_from_llc: ", ret, " us: ", us);
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/* if we completed this PDU, move on to the next, resetting the index */
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if (us.cur_index >= pdu_len) {
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us.cur_pdu := us.cur_pdu +1;
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us.cur_index := 0;
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log("copy_from_llc (incrementing pdu)");
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}
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return ret;
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}
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/* generate one LlcBlock (maximum size 'max_len') */
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private function f_ul_tbf_pull_one(out LlcBlock ret, inout LlcBlockHdr prev_hdr,
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inout UlTbfState us, integer max_len,
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boolean is_final) return boolean
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{
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/* if we've already pulled all data from all LLC PDUs: nothing to do */
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if (us.cur_pdu >= sizeof(us.tbf.llc_pdus_enc)) {
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log("pull_one: No more data", us);
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return false;
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}
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var integer pdu_len := lengthof(us.tbf.llc_pdus_enc[us.cur_pdu])
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var integer cur_llc_remain_len := pdu_len - us.cur_index;
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var integer len;
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var LlcBlock lb;
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if (us.cur_index == 0) {
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/* start of a new LLC PDU */
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prev_hdr.more := true;
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}
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if (cur_llc_remain_len > max_len) {
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log("Chunk with length ", cur_llc_remain_len, " larger than space (",
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max_len, ") left in block");
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len := max_len;
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lb := {
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hdr := omit,
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payload := f_copy_from_llc(us, len)
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}
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} else if (cur_llc_remain_len == max_len and is_final) {
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/* final RLC block of TBF and LLC remainder fits exactly */
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len := max_len;
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lb := {
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hdr := omit,
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payload := f_copy_from_llc(us, len)
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}
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prev_hdr.e := true;
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} else if (cur_llc_remain_len == max_len) {
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/* LLC remaineder would fit exactly -> "singular case" with L=0 */
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len := max_len - 1;
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lb := {
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hdr := {
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length_ind := 0,
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more := false,
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e := true
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},
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payload := f_copy_from_llc(us, len)
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}
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prev_hdr.e := false;
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} else {
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/* normal case: cur_llc_remain_len < max_len */
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len := cur_llc_remain_len;
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lb := {
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hdr := {
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length_ind := len,
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more := false,
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e := true
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},
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payload := f_copy_from_llc(us, len)
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}
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prev_hdr.e := false;
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}
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ret := lb;
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return true;
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}
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/* return encoded size of one given LlcBlock */
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private function f_LlcBlock_enc_len(LlcBlock blk) return integer {
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if (isvalue(blk.hdr)) {
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return 1 + lengthof(blk.payload);
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} else {
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return lengthof(blk.payload);
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}
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}
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/* return encoded size of given record of LlcBlock */
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private function f_LlcBlocks_enc_len(LlcBlocks blks) return integer {
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var integer sum := 0;
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for (var integer i := 0; i < sizeof(blks); i := i+1) {
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sum := sum + f_LlcBlock_enc_len(blks[i]);
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}
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return sum;
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}
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private function f_ul_tbf_pull_multi(out LlcBlocks ret, inout UlTbfState us, integer max_len,
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boolean is_final) return boolean
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{
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var integer space_left;
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var boolean rc;
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ret := {};
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/* loop as long as we have pending LLC data and space left in the current block... */
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for (space_left := max_len; space_left > 0; space_left := max_len - f_LlcBlocks_enc_len(ret)) {
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var LlcBlock lb;
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var integer ret_size := sizeof(ret);
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if (ret_size > 0) {
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rc := f_ul_tbf_pull_one(lb, ret[ret_size-1].hdr, us, space_left, is_final);
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} else {
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var LlcBlockHdr dummy_hdr;
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rc := f_ul_tbf_pull_one(lb, dummy_hdr, us, space_left, is_final);
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}
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if (rc == false) {
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/* we couldn't fill the full RLC block, insufficient LLC Data */
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if (sizeof(ret) == 0) {
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/* we couldn't obtain any LlcBlocks at all */
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return false;
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} else {
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/* we have some LlcBlocks from earlier iterations */
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return true;
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}
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}
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ret := ret & {lb};
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}
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return true;
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}
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/* Determine 'K' value for given CS (TS 44.060 9.3.1.1) */
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private function f_k_for_cs(GprsCodingScheme cs) return integer {
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/* FIXME: EGPRS */
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return 1;
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}
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/* TS 44.060 9.3.1.1 */
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private function f_calc_cv(integer nbc, integer bsn_p, integer nts, GprsCodingScheme cs,
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integer bs_cv_max) return integer {
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var integer dividend := nbc - bsn_p - 1;
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var integer k := f_k_for_cs(cs);
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var integer divisor := nts * k;
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var integer x := f_div_round_up(dividend, divisor);
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if (x <= bs_cv_max) {
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return x;
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} else {
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return 15;
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}
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}
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private function f_rlcmac_hdr_size(boolean tlli_needed) return integer {
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var integer ret := 2;
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if (tlli_needed) {
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ret := ret + 4;
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}
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return ret;
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}
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/* determine countdown value based on remaining length pending */
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private function f_ul_tbf_get_cv(inout UlTbfState us, GprsCodingScheme cs, boolean tlli_needed)
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return integer {
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var integer hdr_size := f_rlcmac_hdr_size(tlli_needed); /* FIXME: PFI, ... */
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var integer blk_len_net := f_gprs_blocksize(cs) - hdr_size;
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var integer num_remain := f_div_round_up(us.total_bytes_remain, blk_len_net);
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var integer cv := f_calc_cv(num_remain + sizeof(us.rlc_sent), us.bsn_p, us.num_ts, us.tbf.initial_cs, 14 /* FIXME */);
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log("CV=", cv, ", num_rmain=", num_remain, " from ", us);
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return cv;
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}
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function f_ul_tbf_get_next_block(out RlcmacUlBlock blk, inout UlTbfState us, inout MmContext mmctx,
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boolean tlli_needed := false) return boolean {
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var integer hdr_size := f_rlcmac_hdr_size(tlli_needed); /* FIXME: TLLI, PFI, ... */
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var integer len_remain := f_gprs_blocksize(us.tbf.initial_cs) - hdr_size;
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var octetstring payload;
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var integer cv;
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var LlcBlocks llc_blocks;
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cv := f_ul_tbf_get_cv(us, us.tbf.initial_cs, tlli_needed);
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/* potentially get multiple payload chunks of multiple LLC PDUs */
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if (f_ul_tbf_pull_multi(llc_blocks, us, len_remain, false) == false) {
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return false;
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}
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/* include TLLI when needed */
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if (tlli_needed) {
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blk := valueof(t_RLCMAC_UL_DATA_TLLI(us.tfi, cv, us.et.v_s,
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llc_blocks, false, mmctx.tlli));
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} else {
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blk := valueof(t_RLCMAC_UL_DATA(us.tfi, cv, us.et.v_s, llc_blocks, false));
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}
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/* Increment Block Sequence Number */
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us.bsn_p := us.bsn_p + 1;
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us.et.v_s := us.bsn_p mod 128; /* FIXME: EGPRS SNS: 2048 */
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/* append to list of sent blocks */
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us.rlc_sent := us.rlc_sent & { blk };
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return true;
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}
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function f_ul_tbf_process_acknack(inout UlTbfState us, RlcmacDlCtrlBlock db) {
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if (ispresent(db.payload.u.ul_ack_nack.gprs)) {
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var UlAckNackGprs uan_gprs := db.payload.u.ul_ack_nack.gprs;
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if (ispresent(uan_gprs.cont_res_tlli)) {
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/* FIXME: check for contention resolution */
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}
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var integer i;
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/* iterate over received bitmap, ACK each block in our TBF state */
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for (i := lengthof(uan_gprs.ack_nack_desc.receive_block_bitmap)-1; i >= 0; i := i-1) {
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if (uan_gprs.ack_nack_desc.receive_block_bitmap[i] == '1'B) {
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var integer seq := uan_gprs.ack_nack_desc.starting_seq_nr + i;
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f_UlTbf_ack_one_block(us, seq);
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}
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}
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f_UlTbf_check_advance_v_a(us);
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}
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}
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}
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