module GPRS_TBF { /* GPRS TBF Routines, intended as minimal MS-Side GPRS implementation * * (C) 2018 by Harald Welte * All rights reserved. * * Released under the terms of GNU General Public License, Version 2 or * (at your option) any later version. * * SPDX-License-Identifier: GPL-2.0-or-later */ import from GSM_Types all; import from Osmocom_Types all; import from General_Types all; import from Misc_Helpers all; import from RLCMAC_CSN1_Types all; import from RLCMAC_Types all; import from RLCMAC_Templates all; import from LLC_Types all; import from GPRS_Context all; private const integer RLC_GPRS_SNS := 128; private const integer RLC_GPRS_WS := 64; private const integer RLC_EGPRS_MIN_WS := 64; private const integer RLC_EGPRS_MAX_WS := 1024; private const integer RLC_EGPRS_SNS := 2048; private const integer RLC_EGPRS_MAX_BSN_DELTA := 512; private const integer RLC_MAX_SNS := RLC_EGPRS_SNS; private const integer RLC_MAX_WS := RLC_EGPRS_MAX_WS; private const integer RLC_MAX_LEN := 74 /* MCS-9 data unit */ private const integer sns_half := (RLC_MAX_SNS / 2); private const integer mod_sns_half := (RLC_MAX_SNS / 2) - 1; /*********************************************************************** * Uplink TBF handling ***********************************************************************/ /* input parameters into TBF (mostly mode/cs + LLC PDUs */ type record UlTbfPars { /* Acknowledged mode (true) or unacknowledged (false) */ boolean ack_mode, /* Coding Scheme for transmission, determines block size */ GprsCodingScheme initial_cs, /* list of abstract/decoded LLC PDUs */ record of PDU_LLC llc_pdus optional, /* possibly computed: list of encoded LLC PDUs */ record of octetstring llc_pdus_enc } type record RlcEndpointTx { /* send state variable V(S) (9.1.1): 0 .. SNS-1 */ integer v_s, /* acknowledge state variable V(A) (9.1.2): BSN value of oldest RLC data block that has not * been positively acknowledged by peer. */ integer v_a, /* acknowledge state array V(B) (9.1.3) */ bitstring v_b } private function f_RlcEndpointTx_init(inout RlcEndpointTx ep) { ep.v_s := 0; ep.v_a := 0; ep.v_b := int2bit(0, 128); /* FIXME: EGPRS 2048 bits length */ } type record UlTbfState { /* "const" input state with TBF Data */ UlTbfPars tbf, uint8_t num_ts, RlcEndpointTx et, integer tfi, /* total length of all encoded LLC PDUs */ integer llc_pdu_totlen, /* index of current/next PDU in llc_pdus_enc */ integer cur_pdu, /* byte offset into current/next PDU; next byte to transmit */ integer cur_index, /* block sequence number of next block within TBF */ integer bsn_p, /* total number of bytes remaining in TBF */ integer total_bytes_remain, /* list of already-sent RLC/MAC Blocks */ record of RlcmacUlBlock rlc_sent } function f_UlTbfState_init(inout UlTbfState us, in UlTbfPars utpars) { var RlcmacUlBlock blk; us.tbf := utpars; us.num_ts := 1; f_RlcEndpointTx_init(us.et); us.tfi := 0; /* FIXME */ us.cur_pdu := 0; us.cur_index := 0; us.bsn_p := 0; us.total_bytes_remain := 0; us.rlc_sent := {}; /* encode all LLC PDUs from their abstract type to octetstring */ us.cur_pdu := 0; /* currently processed PDU */ us.cur_index := 0; /* next to-be transmitted index */ if (ispresent(us.tbf.llc_pdus)) { us.tbf.llc_pdus_enc := {}; us.llc_pdu_totlen := 0; for (var integer i := 0; i < sizeof(us.tbf.llc_pdus); i := i+1) { var octetstring cur_enc := enc_PDU_LLC(us.tbf.llc_pdus[i]); us.tbf.llc_pdus_enc := us.tbf.llc_pdus_enc & { cur_enc }; us.llc_pdu_totlen := us.llc_pdu_totlen + lengthof(cur_enc); } us.total_bytes_remain := us.llc_pdu_totlen; } } private function f_UlTbf_ack_one_block(inout UlTbfState us, integer n) { /* compute index into v_b */ var integer idx := n - us.et.v_a; if (idx < 0 or idx > lengthof(us.et.v_b)) { setverdict(fail, "UlTbf: Cannot ACK ", n, " while V(A) is ", us.et.v_a); mtc.stop; } /* set the bit in the acknowledge state array */ us.et.v_b[idx] := '1'B; } /* check if V(B) contains '1' at lower end: if yes, advance V(A) and shift V(B) */ private function f_UlTbf_check_advance_v_a(inout UlTbfState us) { log("FIXME: Implement this"); } /* copy 'len' number of bytes from current pending LLC PDU */ private function f_copy_from_llc(inout UlTbfState us, integer len) return octetstring { var integer pdu_len := lengthof(us.tbf.llc_pdus_enc[us.cur_pdu]) var octetstring ret; ret := substr(us.tbf.llc_pdus_enc[us.cur_pdu], us.cur_index, len); us.cur_index := us.cur_index + len; us.total_bytes_remain := us.total_bytes_remain - len; /* if we completed this PDU, move on to the next, resetting the index */ if (us.cur_index >= pdu_len) { us.cur_pdu := us.cur_pdu +1; us.cur_index := 0; log("copy_from_llc (incrementing pdu)"); } return ret; } /* generate one LlcBlock (maximum size 'max_len') */ private function f_ul_tbf_pull_one(out LlcBlock ret, inout LlcBlockHdr prev_hdr, inout UlTbfState us, integer max_len, boolean is_final) return boolean { /* if we've already pulled all data from all LLC PDUs: nothing to do */ if (us.cur_pdu >= sizeof(us.tbf.llc_pdus_enc)) { log("pull_one: No more data", us); return false; } var integer pdu_len := lengthof(us.tbf.llc_pdus_enc[us.cur_pdu]) var integer cur_llc_remain_len := pdu_len - us.cur_index; var integer len; var LlcBlock lb; if (us.cur_index == 0) { /* start of a new LLC PDU */ prev_hdr.more := true; } if (cur_llc_remain_len > max_len) { log("Chunk with length ", cur_llc_remain_len, " larger than space (", max_len, ") left in block"); len := max_len; lb := { hdr := omit, payload := f_copy_from_llc(us, len) } } else if (cur_llc_remain_len == max_len and is_final) { /* final RLC block of TBF and LLC remainder fits exactly */ len := max_len; lb := { hdr := omit, payload := f_copy_from_llc(us, len) } prev_hdr.e := true; } else if (cur_llc_remain_len == max_len) { /* LLC remaineder would fit exactly -> "singular case" with L=0 */ len := max_len - 1; lb := { hdr := { length_ind := 0, more := false, e := true }, payload := f_copy_from_llc(us, len) } prev_hdr.e := false; } else { /* normal case: cur_llc_remain_len < max_len */ len := cur_llc_remain_len; lb := { hdr := { length_ind := len, more := false, e := true }, payload := f_copy_from_llc(us, len) } prev_hdr.e := false; } ret := lb; return true; } /* return encoded size of one given LlcBlock */ private function f_LlcBlock_enc_len(LlcBlock blk) return integer { if (isvalue(blk.hdr)) { return 1 + lengthof(blk.payload); } else { return lengthof(blk.payload); } } /* return encoded size of given record of LlcBlock */ private function f_LlcBlocks_enc_len(LlcBlocks blks) return integer { var integer sum := 0; for (var integer i := 0; i < sizeof(blks); i := i+1) { sum := sum + f_LlcBlock_enc_len(blks[i]); } return sum; } private function f_ul_tbf_pull_multi(out LlcBlocks ret, inout UlTbfState us, integer max_len, boolean is_final) return boolean { var integer space_left; var boolean rc; ret := {}; /* loop as long as we have pending LLC data and space left in the current block... */ for (space_left := max_len; space_left > 0; space_left := max_len - f_LlcBlocks_enc_len(ret)) { var LlcBlock lb; var integer ret_size := sizeof(ret); if (ret_size > 0) { rc := f_ul_tbf_pull_one(lb, ret[ret_size-1].hdr, us, space_left, is_final); } else { var LlcBlockHdr dummy_hdr; rc := f_ul_tbf_pull_one(lb, dummy_hdr, us, space_left, is_final); } if (rc == false) { /* we couldn't fill the full RLC block, insufficient LLC Data */ if (sizeof(ret) == 0) { /* we couldn't obtain any LlcBlocks at all */ return false; } else { /* we have some LlcBlocks from earlier iterations */ return true; } } ret := ret & {lb}; } return true; } /* Determine 'K' value for given CS (TS 44.060 9.3.1.1) */ private function f_k_for_cs(GprsCodingScheme cs) return integer { /* FIXME: EGPRS */ return 1; } /* TS 44.060 9.3.1.1 */ private function f_calc_cv(integer nbc, integer bsn_p, integer nts, GprsCodingScheme cs, integer bs_cv_max) return integer { var integer dividend := nbc - bsn_p - 1; var integer k := f_k_for_cs(cs); var integer divisor := nts * k; var integer x := f_div_round_up(dividend, divisor); if (x <= bs_cv_max) { return x; } else { return 15; } } private function f_rlcmac_hdr_size(boolean tlli_needed) return integer { var integer ret := 2; if (tlli_needed) { ret := ret + 4; } return ret; } /* determine countdown value based on remaining length pending */ private function f_ul_tbf_get_cv(inout UlTbfState us, GprsCodingScheme cs, boolean tlli_needed) return integer { var integer hdr_size := f_rlcmac_hdr_size(tlli_needed); /* FIXME: PFI, ... */ var integer blk_len_net := f_gprs_blocksize(cs) - hdr_size; var integer num_remain := f_div_round_up(us.total_bytes_remain, blk_len_net); var integer cv := f_calc_cv(num_remain + sizeof(us.rlc_sent), us.bsn_p, us.num_ts, us.tbf.initial_cs, 14 /* FIXME */); return cv; } function f_ul_tbf_get_next_block(out RlcmacUlBlock blk, inout UlTbfState us, inout MmContext mmctx, boolean tlli_needed := false) return boolean { var integer hdr_size := f_rlcmac_hdr_size(tlli_needed); /* FIXME: TLLI, PFI, ... */ var integer len_remain := f_gprs_blocksize(us.tbf.initial_cs) - hdr_size; var octetstring payload; var integer cv; var LlcBlocks llc_blocks; cv := f_ul_tbf_get_cv(us, us.tbf.initial_cs, tlli_needed); /* potentially get multiple payload chunks of multiple LLC PDUs */ if (f_ul_tbf_pull_multi(llc_blocks, us, len_remain, false) == false) { return false; } /* include TLLI when needed */ if (tlli_needed) { blk := valueof(t_RLCMAC_UL_DATA_TLLI(CS_1, us.tfi, cv, us.et.v_s, llc_blocks, false, mmctx.tlli)); } else { blk := valueof(t_RLCMAC_UL_DATA(CS_1, us.tfi, cv, us.et.v_s, llc_blocks, false)); } /* Increment Block Sequence Number */ us.bsn_p := us.bsn_p + 1; us.et.v_s := us.bsn_p mod 128; /* FIXME: EGPRS SNS: 2048 */ /* append to list of sent blocks */ us.rlc_sent := us.rlc_sent & { blk }; return true; } function f_ul_tbf_process_acknack(inout UlTbfState us, RlcmacDlCtrlBlock db) { if (ispresent(db.payload.u.ul_ack_nack.gprs)) { var UlAckNackGprs uan_gprs := db.payload.u.ul_ack_nack.gprs; if (ispresent(uan_gprs.cont_res_tlli)) { /* FIXME: check for contention resolution */ } var integer i; /* iterate over received bitmap, ACK each block in our TBF state */ for (i := lengthof(uan_gprs.ack_nack_desc.receive_block_bitmap)-1; i >= 0; i := i-1) { if (uan_gprs.ack_nack_desc.receive_block_bitmap[i] == '1'B) { var integer seq := uan_gprs.ack_nack_desc.starting_seq_nr + i; f_UlTbf_ack_one_block(us, seq); } } f_UlTbf_check_advance_v_a(us); } } /*********************************************************************** * Downlink TBF handling ***********************************************************************/ type record RlcEndpointRx { /* receive state variable V(R) (9.1.5): BSN one higher than highest BSN yet received (mod SNS) */ integer v_r, /* receive window state variable V(Q) (9.1.6): Lowest BSN not yet received (mod SNS) */ integer v_q, /* receive state array V(N) (9.1.7) */ bitstring v_n } private function f_RlcEndpointRx_init(inout RlcEndpointRx ep) { ep.v_r := 0; ep.v_q := 0; ep.v_n := int2bit(0, 128); /* FIXME: EGPRS 2048 bits length */ } type record DlTbfPars { /* Acknowledged mode (true) or unacknowledged (false) */ boolean ack_mode, /* Coding Scheme for transmission, determines block size */ GprsCodingScheme initial_cs, /* Sequence Number Space */ integer sns, /* Window Size */ integer ws } type record DlTbfState { /* "const" input state with TBF Data */ DlTbfPars tbf, uint8_t num_ts, RlcEndpointRx er, integer tfi, /* list of abstract/decoded RLC PDUs */ record of RlcmacDlBlock rlc_received } function f_dl_tbf_mod_sns(DlTbfState ds, integer val) return integer { return (val mod ds.tbf.sns); } function f_dl_tbf_is_in_window(integer bsn) return boolean { Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail, "please implement me"); return false; } function f_dl_tbf_is_received(inout DlTbfState ds, integer bsn) return boolean { var integer offset_v_r; if (not f_dl_tbf_is_in_window(bsn)) { return false; } /* offset to the end of the received window */ offset_v_r := f_dl_tbf_mod_sns(ds, ds.er.v_r - 1 - bsn); if (not (offset_v_r < ds.tbf.ws)) { return false; } if (ds.er.v_n[bsn mod sns_half] == '1'B) { return true; } return false; } function f_dl_tbf_mark_received(inout DlTbfState ds, integer bsn) { ds.er.v_n[bsn mod sns_half] := '1'B; f_dl_tbf_raise_v_r(ds, bsn); } /* Raise V(Q) if possible */ function f_dl_tbf_raise_v_q(inout DlTbfState ds, integer bsn) return integer { var integer count := 0; while (ds.er.v_q != ds.er.v_r) { var integer v_q_old := ds.er.v_q; if (not f_dl_tbf_is_received(ds, v_q_old)) { break; } ds.er.v_q := f_dl_tbf_mod_sns(ds, ds.er.v_q + 1) log("RLCMAC: Taking block ", v_q_old, " out, raising V(Q) to ", ds.er.v_q); count := count+1; } return count; } function f_dl_tbf_raise_v_r(inout DlTbfState ds, integer bsn) { var integer offset_v_r := f_dl_tbf_mod_sns(ds, bsn + 1 - ds.er.v_r); if (offset_v_r < (ds.tbf.sns / 2)) { for (var integer i := offset_v_r; i > 0; i := i-1) { /* mark as missing */ ds.er.v_n[bsn mod sns_half] := '0'B; //raise_v_r_to(1); } log("RLCMAC: Raising V(R) to ", ds.er.v_r); } } /* process the actual data and update TbfState */ function f_dl_tbf_process_dl_data(inout DlTbfState ds, RlcmacDlDataBlock db) { var integer bsn := db.mac_hdr.hdr_ext.bsn; if (db.mac_hdr.hdr_ext.tfi != ds.tfi) { setverdict(fail, "Unexpected TFI of DL Data Block ", db); mtc.stop; } f_dl_tbf_mark_received(ds, bsn); if (ds.tbf.ack_mode) { /* In RLC acknowledged mode, the receive window is defined by the receive window * state variable V(Q) in the following inequality[ V(Q) ≤ BSN < V(Q)+ WS ] modulo * SNS */ if (bsn < ds.er.v_q or bsn > ds.er.v_q + ds.tbf.ws) { setverdict(fail, "Unexpected BSN outside of window ", bsn); mtc.stop; } /* In RLC acknowledged mode, the value of V(Q) shall be updated when the RLC * receiver receives the RLC data block whose BSN is equal to V(Q). The value of * V(Q) shall then be set to the BSN value of the next RLC data block in the receive * window (modulo SNS) that has not yet been received, or it shall be set to V(R) if * all RLC data blocks in the receive window have been received */ f_dl_tbf_mark_received(ds, bsn); } else { /* In RLC unacknowledged mode, if [V(R) - V(Q)] modulo SNS > WS after updating V(R), * then V(Q) is set to [V(R) - WS] modulo SNS. */ /* FIXME */ } } }