mirror of https://github.com/sipwise/sems.git
SEMS parsed b= lines in incoming SDP and copied them into generated
SDP, but could not manage them: there was no way to add or compute
bandwidth modifiers for offers SEMS generates, which 3GPP
interoperability (VoLTE/RCS, TS 26.114 6.2.7.2) often requires.
Add AmSdpBandwidth: computes b=AS from the selected codec and
a=ptime (including IP/UDP/RTP overhead) and derives b=RS/RR per
RFC 3556 defaults (1.25% / 3.75%). Controlled by a global config
parameter sdp_bandwidth={off|auto} (off by default, preserving
current behavior) and a per-session SdpBandwidthCtl override for
applications.
In 'auto' mode:
- in answers, b= lines received in the offer are echoed back;
- in offers initiated by SEMS, b=AS/RS/RR are computed from the
negotiated codec and ptime; no value is generated for codecs
not covered by the internal rate table;
- relayed (B2BUA) bodies always pass the endpoints' b= lines
through unchanged, independent of the global setting.
Signed-off-by: Vadim Saranov <vadim.saranov@gmail.com>
pull/16/head
Vadim Saranov
2 months ago
parent
d950dc5e44
commit
59e83b5006
@ -0,0 +1,240 @@
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/*
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* Copyright (C) 2026 Vadim Saranov
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*
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* This file is part of SEMS, a free SIP media server.
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*
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* SEMS is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version. This program is released under
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* the GPL with the additional exemption that compiling, linking,
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* and/or using OpenSSL is allowed.
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*
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* For a license to use the SEMS software under conditions
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* other than those described here, or to purchase support for this
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* software, please contact iptel.org by e-mail at the following addresses:
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* info@iptel.org
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*
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* SEMS is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*/
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/** @file AmSdpBandwidth.cpp - SDP bandwidth modifiers (b=AS/RS/RR) */
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#include <cstdlib>
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#include <cctype>
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#include <cstring>
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#include "AmSdpBandwidth.h"
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#include "AmConfig.h"
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static inline int ceil_div(int a, int b) { return (a + b - 1) / b; }
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/** speech bits per channel mode, see 3GPP TS 26.171 (AMR-NB) /
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TS 26.201 / TS 26.202 (AMR-WB), per 20 ms frame */
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static const int amr_nb_bits[8] = { 95, 103, 118, 134, 148, 159, 204, 244 };
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static const int amr_wb_bits[9] = { 132, 177, 261, 285, 317, 365, 397, 461, 477 };
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/**
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* Get a codec parameter from an fmtp string ("key=value" entries separated
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* by ';'). Returns false if the parameter is not present.
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*/
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static bool get_fmtp_param(const string& fmtp, const char* key, string& val)
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{
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size_t klen = strlen(key);
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size_t pos = 0;
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while (pos < fmtp.size()) {
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size_t end = fmtp.find(';', pos);
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if (end == string::npos) end = fmtp.size();
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size_t s = pos;
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while (s < end && isspace(fmtp[s])) s++;
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size_t e = end;
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while (e > s && isspace(fmtp[e-1])) e--;
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if (e > s + klen && fmtp.compare(s, klen, key, klen) == 0
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&& fmtp[s+klen] == '=') {
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val = fmtp.substr(s+klen+1, e-s-klen-1);
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return true;
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}
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pos = end + 1;
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}
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return false;
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}
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/**
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* Highest AMR/AMR-WB channel mode from the "mode-set" fmtp parameter
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* ("0,1,2" or "0-7" forms). Defaults to the highest supported mode.
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*/
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static int amr_max_mode(const string& fmtp, int n_modes)
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{
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string ms;
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if (!get_fmtp_param(fmtp, "mode-set", ms) || ms.empty())
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return n_modes - 1;
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int max_mode = -1;
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size_t pos = 0;
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while (pos < ms.size()) {
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size_t end = ms.find(',', pos);
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if (end == string::npos) end = ms.size();
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int lo = atoi(ms.substr(pos, end-pos).c_str());
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size_t dash = ms.find('-', pos);
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int hi = lo;
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if (dash != string::npos && dash < end)
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hi = atoi(ms.substr(dash+1, end-dash-1).c_str());
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if (lo > max_mode) max_mode = lo;
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if (hi > max_mode) max_mode = hi;
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pos = end + 1;
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}
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if (max_mode < 0 || max_mode >= n_modes)
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return n_modes - 1;
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return max_mode;
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}
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/**
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* AMR/AMR-WB RTP payload size in bytes for one ptime interval.
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* Bandwidth-efficient framing (default) adds CMR (4) + ToC (6) bits;
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* octet-aligned framing adds a single ToC byte (octets-pc mode is ignored).
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*/
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static int amr_frame_bytes(const int* bits_table, int n_modes,
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const string& fmtp)
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{
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int bits = bits_table[amr_max_mode(fmtp, n_modes)];
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string oa;
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if (get_fmtp_param(fmtp, "octet-align", oa) && atoi(oa.c_str()) == 1)
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return ceil_div(bits, 8) + 1;
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return ceil_div(bits + 10, 8);
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}
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/**
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* RTP payload (no RTP/UDP/IP headers) size in bytes for one ptime interval.
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* @return bytes or -1 for codecs not covered by the table
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*/
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static int codec_payload_bytes(const SdpPayload& p, int ptime)
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{
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string name = p.encoding_name;
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for (size_t i = 0; i < name.size(); i++)
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name[i] = toupper(name[i]);
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if (name == "PCMU" || name == "PCMA" || name == "G722")
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return 8 * ptime; // 64 kbit/s
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if (name == "L16" && p.clock_rate > 0 && (p.clock_rate % 1000) == 0)
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return p.clock_rate / 1000 * 2 * ptime; // 16 bit/sample, mono
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if (name == "GSM")
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return 33 * ceil_div(ptime, 20); // 33 B / 20 ms frame
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if (name == "ILBC") {
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string mode_s;
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int mode = (get_fmtp_param(p.sdp_format_parameters, "mode", mode_s)
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&& atoi(mode_s.c_str()) == 30) ? 30 : 20;
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return (mode == 30 ? 50 : 38) * ceil_div(ptime, mode);
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}
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if (name == "AMR")
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return amr_frame_bytes(amr_nb_bits, 8, p.sdp_format_parameters);
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if (name == "AMR-WB")
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return amr_frame_bytes(amr_wb_bits, 9, p.sdp_format_parameters);
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if (name == "EVS" && p.clock_rate == 16000) {
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string br_s;
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int bitrate = 16400;
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if (get_fmtp_param(p.sdp_format_parameters, "max-bitrate", br_s)) {
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int v = atoi(br_s.c_str());
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if (v > 0) bitrate = v;
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}
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// 10 ms frames: bitrate/100 bits per frame, padded to a byte boundary
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// + 1 class byte, see 3GPP TS 26.445/26.448
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return ceil_div(ptime, 10) * (ceil_div(bitrate, 800) + 1);
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}
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return -1;
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}
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int AmSdpBandwidth::computeAsKbps(const SdpMedia& m)
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{
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const SdpPayload* sel = NULL;
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for (std::vector<SdpPayload>::const_iterator it = m.payloads.begin();
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it != m.payloads.end(); ++it) {
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if (it->encoding_name == "telephone-event")
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continue;
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sel = &*it;
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break;
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}
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if (sel == NULL || sel->encoding_name.empty())
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return -1;
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int ptime = 20;
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for (std::vector<SdpAttribute>::const_iterator it = m.attributes.begin();
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it != m.attributes.end(); ++it) {
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if (it->attribute == "ptime") {
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int v = atoi(it->value.c_str());
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if (v > 0) ptime = v;
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break;
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}
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}
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int payload_bytes = codec_payload_bytes(*sel, ptime);
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if (payload_bytes < 0)
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return -1;
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// IP (20) + UDP (8) + RTP (12); RTCP excluded (TS 26.114 6.2.7.2)
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int total_bytes = payload_bytes + 40;
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// kbit/s = bytes * 8 / ptime, rounded up
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return ceil_div(total_bytes * 8, ptime);
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}
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void AmSdpBandwidth::apply(SdpMedia& m, const SdpBandwidthCtl& ctl,
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const SdpMedia* offer)
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{
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m.bandwidth.clear();
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if (m.type != MT_AUDIO)
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return;
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// b=AS describes the maximum bandwidth for the receiving direction
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// (3GPP TS 26.114 6.2.7.2): do not emit for sendonly/inactive media.
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if (!m.recv)
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return;
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SdpBandwidthCtl::Mode mode = ctl.mode;
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if (mode == SdpBandwidthCtl::Inherit)
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mode = (AmConfig::SdpBandwidth == AmConfig::SdpBwAuto)
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? SdpBandwidthCtl::Auto : SdpBandwidthCtl::None;
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if (mode == SdpBandwidthCtl::None)
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return;
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if (mode == SdpBandwidthCtl::Custom) {
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if (ctl.as >= 0) m.bandwidth.push_back("AS:" + std::to_string(ctl.as));
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if (ctl.rr >= 0) m.bandwidth.push_back("RR:" + std::to_string(ctl.rr));
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if (ctl.rs >= 0) m.bandwidth.push_back("RS:" + std::to_string(ctl.rs));
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return;
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}
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// Auto: in an answer echo the offer's b= lines as-is (no recomputation
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// on codec downgrade); in a locally generated offer compute AS+RS+RR.
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if (offer != NULL && !offer->bandwidth.empty()) {
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m.bandwidth = offer->bandwidth;
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return;
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}
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int as = computeAsKbps(m);
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if (as < 0)
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return; // no value is invented for codecs not covered by the table
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m.bandwidth.push_back("AS:" + std::to_string(as));
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int rr = computeRr(as);
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int rs = computeRs(as);
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if (rr > 0) m.bandwidth.push_back("RR:" + std::to_string(rr));
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if (rs > 0) m.bandwidth.push_back("RS:" + std::to_string(rs));
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}
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@ -0,0 +1,98 @@
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/*
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* Copyright (C) 2026 Vadim Saranov
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*
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* This file is part of SEMS, a free SIP media server.
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*
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* SEMS is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version. This program is released under
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* the GPL with the additional exemption that compiling, linking,
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* and/or using OpenSSL is allowed.
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*
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* For a license to use the SEMS software under conditions
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* other than those described here, or to purchase support for this
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* software, please contact iptel.org by e-mail at the following addresses:
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* info@iptel.org
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*
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* SEMS is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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||||
* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*/
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/** @file AmSdpBandwidth.h - SDP bandwidth modifiers (b=AS/RS/RR) */
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#ifndef __AmSdpBandwidth_h__
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#define __AmSdpBandwidth_h__
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#include <vector>
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#include <string>
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#include "AmSdp.h"
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/**
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* Per-session control of SDP bandwidth modifiers (b=AS/RS/RR, RFC 4566/3556).
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*
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* Four states:
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* Inherit - resolved through global AmConfig::SdpBandwidth
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* None - never emit b= lines for this session
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* Auto - echo b= from the offer if present, otherwise compute
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* b=AS from codec + ptime and RS/RR from AS
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* Custom - explicit values (as in kbps, rr/rs in bps, -1 = unset)
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*
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* Precedence: session control > global config. Applications are expected to
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* set this per session/call.
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*/
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struct SdpBandwidthCtl {
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enum Mode { Inherit = 0, None, Auto, Custom };
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Mode mode;
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int as; // kbps, -1 unset
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int rr; // bps, -1 unset
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int rs; // bps, -1 unset
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SdpBandwidthCtl() : mode(Inherit), as(-1), rr(-1), rs(-1) {}
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};
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class AmSdpBandwidth
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{
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public:
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/**
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* Computes b=AS (application maximum bandwidth, kbps, integer) for a
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* media descriptor from its first non-telephony payload (codec name,
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* clock rate and fmtp) and a=ptime (default 20 ms).
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*
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* AS includes IP(20)/UDP(8)/RTP(12) overhead and excludes RTCP
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* (3GPP TS 26.114 6.2.7.2, receiving direction).
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*
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* @return AS in kbps or -1 if the codec is not covered
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* (no value is invented for unknown codecs).
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*/
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static int computeAsKbps(const SdpMedia& m);
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/** RTCP bandwidth from b=AS, RFC 3556 default shares:
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b=RS = 1.25% and b=RR = 3.75% of the session bandwidth, in bps. */
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static int computeRs(int as_kbps) { return as_kbps < 0 ? -1 : as_kbps * 125 / 10; }
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static int computeRr(int as_kbps) { return as_kbps < 0 ? -1 : as_kbps * 375 / 10; }
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/**
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* Applies the bandwidth policy to a media descriptor, replacing all
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* of its b= lines.
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*
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* @param m media to modify (answer or locally generated offer)
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* @param ctl per-session control
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* @param offer matching offer media to echo b= from, or nullptr
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*
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* b= lines describe the maximum bandwidth for the receiving direction,
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* so nothing is applied for media we do not receive (sendonly/inactive).
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* Audio media only.
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*/
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static void apply(SdpMedia& m, const SdpBandwidthCtl& ctl,
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const SdpMedia* offer);
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};
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#endif
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Loading…
Reference in new issue