diff --git a/TODO.md b/TODO.md
index d3530e4..b4f5243 100644
--- a/TODO.md
+++ b/TODO.md
@@ -167,6 +167,25 @@ Follow-up:
 - Capture and expose backend exit status where possible.
 - Consider direct CUPS integration only if MARS_NWE needs CUPS job IDs, cancellation, or status polling. Do not add a hard CUPS dependency for basic queue compatibility.
 
+### Transaction Tracking System (TTS)
+
+Current status:
+
+- `NCP 0x22/0x00 TTS Is Available` reports the WebSDK-documented
+  unavailable status.
+- MARS-NWE does not currently implement TTS rollback semantics, transaction
+  files, transaction status tracking, or the begin/end/abort transaction
+  state machine.
+- Other TTS subfunctions remain unsupported instead of pretending to succeed
+  without real transaction tracking.
+
+Follow-up:
+
+- Implement TTS only if a concrete client requires it.
+- Treat this as a real transaction subsystem, not as a completion-code shim:
+  the WebSDK TTS calls include begin/end/abort transaction, status, threshold,
+  and control/statistics operations.
+
 ## Deferred / optional protocol work
 
   * Basic Packet Burst file transfer support is implemented and verified with a
diff --git a/src/nwconn.c b/src/nwconn.c
index 93cf99b..a0ab1a2 100644
--- a/src/nwconn.c
+++ b/src/nwconn.c
@@ -2359,10 +2359,27 @@ static int handle_ncp_serv(void)
                   }
                   break;
 
-      case 0x22 : { /* div TTS Calls */
+      case 0x22 : { /* Transaction Tracking System (TTS) calls */
                     int ufunc = (int) *requestdata;
-                    if (!ufunc) completition=0; /* TTS not availible */
-                    else completition=0xfb;     /* request not known */
+                    /*
+                     * WebSDK / headers:
+                     *   NCP 0x2222/34/00 TTS Is Available has no reply data.
+                     *   Its completion code is the status value: 0x00 means
+                     *   Transaction Tracking Unavailable, 0xfd means Disabled,
+                     *   and 0xff means Available.  The SDK headers expose this
+                     *   as NWTTSIsAvailable().
+                     *
+                     * MARS-NWE does not implement transaction tracking.  Report
+                     * the documented unavailable status for the availability
+                     * probe, but keep the state-changing TTS subfunctions
+                     * unsupported rather than pretending to begin, end, or abort
+                     * transactions without rollback semantics.
+                     *
+                     * Cross-check: lwared and the Rust nwserver code do not
+                     * provide a fuller TTS transaction implementation to mirror.
+                     */
+                    if (!ufunc) completition=0;  /* TTS unavailable */
+                    else completition=0xfb;      /* request not known */
                   } break;
 
       case 0x23 : { /* div AFP Calls */