From b356e893c025e31ecfd71604cb158fe763267da4 Mon Sep 17 00:00:00 2001
From: Sam Machin <sam@sammachin.com>
Date: Wed, 29 Jul 2026 10:42:12 +0100
Subject: [PATCH] Update call-session.js

---
 lib/session/call-session.js | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/lib/session/call-session.js b/lib/session/call-session.js
index 6499caff..794486f2 100644
--- a/lib/session/call-session.js
+++ b/lib/session/call-session.js
@@ -1779,6 +1779,32 @@ class CallSession extends Emitter {
       this.logger.info('CallSession:_lccDtmf - invalid command as we do not have a stable call');
       return;
     }
+
+    /* Prefer media-path DTMF: have the media server generate RFC 2833 tones directly into the
+     * media stream (via send_dtmf), which the SBC/rtpengine simply forwards. This is reliable
+     * regardless of whether rtpengine is transcoding the call. Sending SIP INFO to the SBC
+     * instead relies on rtpengine 'play DTMF' injection, which silently no-ops on calls that
+     * are not being transcoded (rtpengine has no DSP to synthesize the tone into). We fall back
+     * to SIP INFO only when we have no endpoint in the media path for the targeted leg, e.g. when
+     * media has been released to the SBC.
+     * this.ep is the endpoint facing the caller (A) leg; this.currentTask.ep is the endpoint
+     * facing the dialed (B) leg.
+     */
+    const ep = callSid === this.callSid ? this.ep : this.currentTask?.ep;
+    if (ep?.connected) {
+      try {
+        this.logger.debug(`CallSession:_lccDtmf - sending ${digit}@${duration} via send_dtmf on ${ep.uuid}`);
+        await ep.execute('send_dtmf', `${digit}@${duration}`);
+        return;
+      } catch (err) {
+        this.logger.error({err},
+          'CallSession:_lccDtmf - error sending DTMF via send_dtmf, falling back to SIP INFO');
+      }
+    }
+
+    /* fallback: signal the SBC to inject DTMF via SIP INFO (used when media is released
+     * and we have no endpoint in the media path for the targeted leg)
+     */
     try {
       const dlg = callSid === this.callSid ? this.dlg : this.currentTask.dlg;
       const res = await dlg.request({