diff --git a/prefab/conn_blocks/ipv4/ip_assembler.c b/prefab/conn_blocks/ipv4/ip_assembler.c
index d43137e..9269331 100644
--- a/prefab/conn_blocks/ipv4/ip_assembler.c
+++ b/prefab/conn_blocks/ipv4/ip_assembler.c
@@ -55,7 +55,7 @@ static void ipra_remove_chain(IPv4Assembler * ipra, uint16_t id) {
         return;
     }
 
-    timer_unsched(E.tmr, chainDesc->id); // remove timeout schedule
+    timer_unsched(E.tmr, chainDesc->alarmID); // remove timeout schedule
     IPv4Fragment * iter = chainDesc->fragChain; // unlink and release fragment chain
     while (iter != NULL) {
         IPv4Fragment * oldIter = iter;
@@ -66,7 +66,7 @@ static void ipra_remove_chain(IPv4Assembler * ipra, uint16_t id) {
     FragChainDesc * chainIter = ipra->chains;
     while (chainIter != NULL) { // unlink chain from chain list
         if (chainIter->next == chainDesc) { // if element is found
-            chainIter->next = chainDesc->next; // skip by looked up element by setting next properly
+            chainIter->next = chainDesc->next; // skip looked up element by setting next properly
             break; // break the loop
         }
         chainIter = chainIter->next;
@@ -104,7 +104,7 @@ static void ipra_insert_into_chain(FragChainDesc *chainDesc, const IPv4Props *ip
                 ((iter->next == NULL) || (iter->next->offset >= (frag->offset + frag->size)))) {
                 frag->next = iter->next;
                 iter->next = frag;
-            } else if ((iter == chainDesc->fragChain) && (frag->offset < iter->offset)) { // insert before the firstly received segment
+            } else if ((iter == chainDesc->fragChain) && (frag->offset < iter->offset)) { // insert before the first received segment
                 frag->next = iter;
                 chainDesc->fragChain = frag;
             }
@@ -141,8 +141,7 @@ void ipra_input(IPv4Assembler *ipra, const IPv4Props *ipProps, const uint8_t *pa
     AlarmUserData aud;
     aud.ptr = ipra;
     aud.u = chainDesc->id;
-    timer_sched_rel(E.tmr, IP_REASSEMBLY_TIMEOUT_US, ipra_timeout, aud);
-    timer_report(E.tmr);
+    chainDesc->alarmID = timer_sched_rel(E.tmr, IP_REASSEMBLY_TIMEOUT_US, ipra_timeout, aud);
 }
 
 bool ipra_try_reassemble(IPv4Assembler *ipra, uint16_t id, uint8_t **payload, uint16_t *size, PcktHeaderElement *pcktHdrLe) {
diff --git a/timer.c b/timer.c
index c6806a2..03b14b8 100644
--- a/timer.c
+++ b/timer.c
@@ -106,7 +106,6 @@ uint32_t timer_sched(Timer *tmr, const TimePoint *t, TimerAlarmCb cb, AlarmUserD
 
     // increase allocation count
     tmr->nSched++;
-    MSG("%d %s\n", tmr->nSched, __FUNCTION__);
 
     // replace nearest if needed
     if (tmr->nSched > 1) {
@@ -129,6 +128,10 @@ uint32_t timer_sched_rel(Timer *tmr, int64_t us, TimerAlarmCb cb, AlarmUserData
 }
 
 void timer_unsched(Timer *tmr, uint32_t id) {
+    if (id == 0) { // no unscheduling on receiving unknown id
+        return;
+    }
+
     ETHLIB_OS_MTX_LOCK(&(tmr->tabMtx));
 
     if (tmr->nSched > 0) {
@@ -136,7 +139,6 @@ void timer_unsched(Timer *tmr, uint32_t id) {
         if (alarm != NULL) {
             memset(alarm, 0, sizeof(AlarmAssignment));
             tmr->nSched--;
-            MSG("%d %s\n", tmr->nSched, __FUNCTION__);
             timer_update_nearest_alarm(tmr);
         }
     }
@@ -181,11 +183,12 @@ void timer_tick(Timer *tmr, int64_t us) {
 
             // decrease scheduled alarm count
             tmr->nSched--;
-            MSG("%d %s\n", tmr->nSched, __FUNCTION__);
 
             // update nearest alarm
             timer_update_nearest_alarm(tmr);
 
+            ETHLIB_OS_MTX_UNLOCK(&(tmr->tabMtx));
+
             // invoke callback
             if (alarm.cb != NULL) {
                 alarm.cb(tmr, alarm.params);
@@ -195,7 +198,6 @@ void timer_tick(Timer *tmr, int64_t us) {
                 t_alarm = time_to_us(&(tmr->nextAlarm->time));
             }
 
-            ETHLIB_OS_MTX_UNLOCK(&(tmr->tabMtx));
         }
     }
 }
diff --git a/timer.h b/timer.h
index 5c697f6..4878dfc 100644
--- a/timer.h
+++ b/timer.h
@@ -10,8 +10,8 @@
  * A single point in time
  */
 typedef struct {
-    int64_t s; ///< Seconds
-    int64_t us; ///< Microseconds
+    uint32_t s; ///< Seconds
+    uint32_t us; ///< Microseconds
 } TimePoint;
 
 /**