diff --git a/src_mtln/generators.F90 b/src_mtln/generators.F90
index 74b568ad..83c9cc9d 100644
--- a/src_mtln/generators.F90
+++ b/src_mtln/generators.F90
@@ -46,22 +46,26 @@ function generatorCtor(index, conductor, gen_type, resistance, path, layer_indic
         if (present(layer_indices)) then
             call MPI_COMM_SIZE(SUBCOMM_MPI, sizeof, ierr)
             if (sizeof > 1) then
-                res%in_layer = .false.
-                do i = 1, size(layer_indices,1) 
-                    if (index >= layer_indices(i, 1) .and. index <= layer_indices(i,2)+1) then 
-                        res%in_layer = .true.
-                        slice = i
-                    end if
-                end do
-
-                layer_index = 0
-                if (res%in_layer) then 
-                    do i = 1, slice - 1
-                        layer_index = layer_index + layer_indices(i,2) + 1 - (layer_indices(i,1) - 1)
+                if (size(layer_indices,1) == 0) then
+                    res%in_layer = .true.
+                else
+                    res%in_layer = .false.
+                    do i = 1, size(layer_indices,1)
+                        if (index >= layer_indices(i, 1) .and. index <= layer_indices(i,2)+1) then
+                            res%in_layer = .true.
+                            slice = i
+                        end if
                     end do
-                    layer_index = layer_index + res%index - layer_indices(slice,1) + 1
+
+                    layer_index = 0
+                    if (res%in_layer) then
+                        do i = 1, slice - 1
+                            layer_index = layer_index + layer_indices(i,2) + 1 - (layer_indices(i,1) - 1)
+                        end do
+                        layer_index = layer_index + res%index - layer_indices(slice,1) + 1
+                    end if
+                    res%index = layer_index
                 end if
-                res%index = layer_index
             end if
         end if
 #endif
diff --git a/src_mtln/mtl.F90 b/src_mtln/mtl.F90
index daf889ea..a3eddcc9 100644
--- a/src_mtln/mtl.F90
+++ b/src_mtln/mtl.F90
@@ -137,6 +137,8 @@ function mtl_shielded(lpul, cpul, rpul, gpul, &
                 allocate(res%segments(0))
                 allocate(res%mpi_comm%comms(0))
             end if
+            res%layer_indices = layer_indices
+            if (present(bundle_in_layer)) res%bundle_in_layer = bundle_in_layer
         else
             res%step_size =  step_size
             allocate(res%layer_indices(0,0))
@@ -153,9 +155,13 @@ function mtl_shielded(lpul, cpul, rpul, gpul, &
         res%number_of_conductors = size(lpul, 1)
         call res%initDirections()
         call res%allocatePULMatrices()
-        call res%initLC(lpul, cpul)
-        call res%initRG(rpul, gpul)
-        call res%checkTimeStep(getMax = (lpul(1,1) /= 0.0), dt = dt)
+        if (size(res%step_size) /= 0) then
+            call res%initLC(lpul, cpul)
+            call res%initRG(rpul, gpul)
+            call res%checkTimeStep(getMax = (lpul(1,1) /= 0.0), dt = dt)
+        else
+            res%dt = dt
+        end if
         res%parent_name = parent_name
         res%conductor_in_parent = conductor_in_parent
         res%transfer_impedance = transfer_impedance
@@ -192,7 +198,7 @@ function mtl_unshielded(lpul, cpul, rpul, gpul, &
                 allocate(res%mpi_comm%comms(0))
             end if
             res%layer_indices = layer_indices
-            res%bundle_in_layer = bundle_in_layer 
+            if (present(bundle_in_layer)) res%bundle_in_layer = bundle_in_layer
         else
             res%step_size =  step_size
             allocate(res%layer_indices(0,0))
@@ -217,9 +223,11 @@ function mtl_unshielded(lpul, cpul, rpul, gpul, &
             else 
                 call res%initLC(lpul, cpul)
             end if
+            call res%initRG(rpul, gpul)
+            call res%checkTimeStep(getMax = (lpul(1,1) /= 0.0), dt = dt)
+        else
+            res%dt = dt
         end if
-        call res%initRG(rpul, gpul)
-        call res%checkTimeStep(getMax = (lpul(1,1) /= 0.0), dt = dt)
         res%lumped_elements = dispersive_lumped_t(res%number_of_conductors, 0, size(res%step_size), res%dt)
     end function
 
diff --git a/src_mtln/mtl_bundle.F90 b/src_mtln/mtl_bundle.F90
index d830ae9c..9286b5b8 100644
--- a/src_mtln/mtl_bundle.F90
+++ b/src_mtln/mtl_bundle.F90
@@ -1,12 +1,13 @@
 module mtl_bundle_m
 
     use mtln_utils_m
-    use probes_m
+    use probes_m, only: probe_t, probeCtor, PROBE_TYPE_CURRENT
     use generators_m
     use dispersive_m
     use mtl_m
 #ifdef CompileWithMPI
     use FDETYPES_m, only: SUBCOMM_MPI, REALSIZE, INTEGERSIZE, MPI_STATUS_SIZE
+    use mpi
 #endif
     use mtln_types_m, only: SOURCE_TYPE_CURRENT, SOURCE_TYPE_VOLTAGE
     use FDETYPES_m, only: RKIND, RKIND_TIEMPO
@@ -38,6 +39,8 @@ module mtl_bundle_m
 #ifdef CompileWithMPI
         integer(kind=4), allocatable, dimension(:,:) :: layer_indices
         type(comm_t) :: mpi_comm
+        ! Owner rank of each physical current segment.
+        integer(kind=4), allocatable :: segment_owner(:)
 #endif
 
     contains
@@ -57,6 +60,8 @@ module mtl_bundle_m
 #ifdef CompileWithMPI
         procedure :: Comm_MPI_V
         procedure :: Comm_MPI_Fields
+        procedure :: Comm_MPI_I
+        procedure :: initMPIStateOwnership
 #endif
 
 
@@ -70,6 +75,10 @@ module mtl_bundle_m
         integer, dimension(3) ::position
         integer :: direction = 0
         real(kind=rkind) , pointer  :: field => null()
+        ! True only on the rank that updates this FDTD field cell.
+        logical :: field_is_local = .false.
+        ! True on the geometric FDTD owner even when the cell is PEC/lossy.
+        logical :: field_is_owned = .false.
     end type
 
 contains
@@ -401,10 +410,52 @@ subroutine bundle_updateGenerators(this, time, dt)
 
     end subroutine
 
+#ifdef CompileWithMPI
+    subroutine initMPIStateOwnership(this)
+        class(mtl_bundle_t) :: this
+        integer :: i, ierr, rank, n
+        integer, allocatable :: candidate(:), owner(:)
+
+        n = this%number_of_divisions
+        allocate(candidate(n), owner(n), source = -1)
+        call MPI_COMM_RANK(SUBCOMM_MPI, rank, ierr)
+        do i = 1, n
+            if (this%external_field_segments(i)%field_is_owned) candidate(i) = rank
+        end do
+        call MPI_Allreduce(candidate, owner, n, MPI_INTEGER, MPI_MAX, SUBCOMM_MPI, ierr)
+        if (any(owner < 0)) error stop "MTLN MPI ownership missing for a current segment"
+        if (allocated(this%segment_owner)) deallocate(this%segment_owner)
+        call move_alloc(owner, this%segment_owner)
+        do i = 1, n
+            this%external_field_segments(i)%field_is_local = this%external_field_segments(i)%field_is_local .and. &
+                this%segment_owner(i) == rank
+        end do
+        do i = 1, size(this%probes)
+            if (this%probes(i)%type == PROBE_TYPE_CURRENT) then
+                this%probes(i)%in_layer = this%segment_owner(this%probes(i)%index) == rank
+            else
+                this%probes(i)%in_layer = this%segment_owner(min(this%probes(i)%index, n)) == rank
+            end if
+        end do
+        do i = 1, size(this%generators)
+            this%generators(i)%in_layer = this%segment_owner(this%generators(i)%index) == rank
+        end do
+    end subroutine initMPIStateOwnership
+#endif
+
     subroutine bundle_advanceVoltage(this)
         class(mtl_bundle_t) ::this
         integer :: i
+#ifdef CompileWithMPI
+        integer :: ierr, rank
+        call MPI_COMM_RANK(SUBCOMM_MPI, rank, ierr)
+#endif
         do i = 2,this%number_of_divisions
+#ifdef CompileWithMPI
+            if (allocated(this%segment_owner)) then
+                if (this%segment_owner(i) /= rank) cycle
+            end if
+#endif
             this%v(:, i) = matmul(this%v_term(i,:,:), this%v(:,i)) - &
                            matmul(this%i_diff(i,:,:), (this%i(:,i) - this%i(:,i-1)) + matmul(this%du(i,:,:), this%i_source(:,i)))
         end do
@@ -417,17 +468,20 @@ subroutine bundle_advanceCurrent(this)
         integer :: i
         real(kind=rkind) :: eps_r
 #ifdef CompileWithMPI
-        integer(kind=4) :: sizeof, ierr
-
-#endif
-#ifdef CompileWithMPI
+        integer(kind=4) :: sizeof, ierr, rank
         call MPI_COMM_SIZE(SUBCOMM_MPI, sizeof, ierr)
+        call MPI_COMM_RANK(SUBCOMM_MPI, rank, ierr)
         if (sizeof > 1) call this%Comm_MPI_V()
 #endif
         call this%transfer_impedance%updateQ3Phi()
         this%i_prev = this%i
 
         do i = 1, this%number_of_divisions
+#ifdef CompileWithMPI
+            if (allocated(this%segment_owner)) then
+                if (this%segment_owner(i) /= rank) cycle
+            end if
+#endif
             this%i(:,i) = matmul(this%i_term(i,:,:), this%i(:,i)) - &
                           matmul(this%v_diff(i,:,:), (this%v(:,i+1) - this%v(:,i)) - &
                                                       this%e_L(:,i) * this%step_size(i) - &
@@ -435,57 +489,81 @@ subroutine bundle_advanceCurrent(this)
                           matmul(this%v_diff(i,:,:), matmul(this%du(i,:,:), this%transfer_impedance%q3_phi(i,:)))
         enddo
         call this%transfer_impedance%updatePhi(this%i_prev, this%i)
+#ifdef CompileWithMPI
+        if (sizeof > 1) call this%Comm_MPI_I()
+#endif
     end subroutine
 
     subroutine bundle_setExternalLongitudinalField(this)
         class(mtl_bundle_t) :: this
         integer :: i, j
 #ifdef CompileWithMPI
-        integer :: sizeof, ierr
-
-        call MPI_COMM_SIZE(SUBCOMM_MPI, sizeof, ierr)
-        if (sizeof > 1) call this%Comm_MPI_Fields()
+        integer :: ierr, rank
+        call MPI_COMM_RANK(SUBCOMM_MPI, rank, ierr)
 #endif
-
+        this%e_L = 0.0_rkind
         do j = 1, this%conductors_in_level(1)
             do i = 1, size(this%e_L,2)
-                    this%e_L(j,i) = this%external_field_segments(i)%field * &
-                                    this%external_field_segments(i)%direction/abs(this%external_field_segments(i)%direction)
-                                    
+#ifdef CompileWithMPI
+                if (allocated(this%segment_owner)) then
+                    if (this%segment_owner(i) /= rank) cycle
+                end if
+#endif
+                this%e_L(j,i) = this%external_field_segments(i)%field * &
+                                  this%external_field_segments(i)%direction / abs(this%external_field_segments(i)%direction)
             end do
         end do
-
     end subroutine
 
 #ifdef CompileWithMPI
     subroutine Comm_MPI_V(this)
         class(mtl_bundle_t) :: this
-        integer :: number_of_conductors, i, c
-        integer :: ierr, rank, status(MPI_STATUS_SIZE)
+        integer :: i, ierr, rank, nreq, source_rank, destination_rank
+        integer, allocatable :: requests(:), statuses(:,:)
+
+        if (.not. allocated(this%segment_owner)) return
         call MPI_COMM_RANK(SUBCOMM_MPI, rank, ierr)
-        number_of_conductors = size(this%v,1)
-        do i = 1, size(this%mpi_comm%comms)
-            if (this%mpi_comm%comms(i)%comm_type == COMM_V .or. this%mpi_comm%comms(i)%comm_type == COMM_BOTH) then
-                if (this%mpi_comm%comms(i)%comm_task == COMM_SEND) then
-                    do c = 1, number_of_conductors
-                        call MPI_send(this%v(c, this%mpi_comm%comms(i)%v_index),1, REALSIZE, &
-                                      rank+this%mpi_comm%comms(i)%delta_rank, &
-                                      200*(rank+this%mpi_comm%comms(i)%delta_rank+1)+c, &
-                                      SUBCOMM_MPI, ierr)
-                    end do
-                end if
-                if (this%mpi_comm%comms(i)%comm_task == COMM_RECV) then
-                    do c = 1, number_of_conductors
-                        call MPI_recv(this%v(c, this%mpi_comm%comms(i)%v_index),1, REALSIZE, &
-                                      rank+this%mpi_comm%comms(i)%delta_rank, &
-                                      200*(rank+1)+c, &
-                                      SUBCOMM_MPI, status, ierr)
-                    end do
-                end if
+        allocate(requests(2 * max(0, this%number_of_divisions - 1)), &
+                 statuses(MPI_STATUS_SIZE, 2 * max(0, this%number_of_divisions - 1)))
+        nreq = 0
+        do i = 2, this%number_of_divisions
+            source_rank = this%segment_owner(i)
+            destination_rank = this%segment_owner(i-1)
+            if (source_rank == destination_rank) cycle
+            if (rank == source_rank) then
+                nreq = nreq + 1
+                call MPI_Isend(this%v(:,i), size(this%v,1), REALSIZE, destination_rank, 501, SUBCOMM_MPI, requests(nreq), ierr)
+            else if (rank == destination_rank) then
+                nreq = nreq + 1
+                call MPI_Irecv(this%v(:,i), size(this%v,1), REALSIZE, source_rank, 501, SUBCOMM_MPI, requests(nreq), ierr)
             end if
         end do
+        if (nreq > 0) call MPI_Waitall(nreq, requests, statuses, ierr)
+    end subroutine
 
+    subroutine Comm_MPI_I(this)
+        class(mtl_bundle_t) :: this
+        integer :: i, ierr, rank, nreq, source_rank, destination_rank
+        integer, allocatable :: requests(:), statuses(:,:)
 
+        if (.not. allocated(this%segment_owner)) return
+        call MPI_COMM_RANK(SUBCOMM_MPI, rank, ierr)
+        allocate(requests(2 * max(0, this%number_of_divisions - 1)), &
+                 statuses(MPI_STATUS_SIZE, 2 * max(0, this%number_of_divisions - 1)))
+        nreq = 0
+        do i = 2, this%number_of_divisions
+            source_rank = this%segment_owner(i-1)
+            destination_rank = this%segment_owner(i)
+            if (source_rank == destination_rank) cycle
+            if (rank == source_rank) then
+                nreq = nreq + 1
+                call MPI_Isend(this%i(:,i-1), size(this%i,1), REALSIZE, destination_rank, 502, SUBCOMM_MPI, requests(nreq), ierr)
+            else if (rank == destination_rank) then
+                nreq = nreq + 1
+                call MPI_Irecv(this%i(:,i-1), size(this%i,1), REALSIZE, source_rank, 502, SUBCOMM_MPI, requests(nreq), ierr)
+            end if
+        end do
+        if (nreq > 0) call MPI_Waitall(nreq, requests, statuses, ierr)
     end subroutine
 
         subroutine Comm_MPI_Fields(this)
diff --git a/src_mtln/mtln_solver.F90 b/src_mtln/mtln_solver.F90
index 0b5526c8..034fc5d0 100644
--- a/src_mtln/mtln_solver.F90
+++ b/src_mtln/mtln_solver.F90
@@ -59,9 +59,10 @@ module mtln_solver_m
 
 contains
 
-    function mtlnCtor(parsed, alloc) result(res)
+    function mtlnCtor(parsed, alloc, sweep) result(res)
         type(parsed_mtln_t) :: parsed
         type(XYZlimit_t), dimension(1:6), intent(in), optional :: alloc
+        type(XYZlimit_t), dimension(1:6), intent(in), optional :: sweep
         type(mtln_t) :: res
         integer :: i
         type(preprocess_t) :: pre
@@ -74,7 +75,11 @@ function mtlnCtor(parsed, alloc) result(res)
         call mpi_barrier(subcomm_mpi, ierr)
 #endif
         if (present(alloc)) then 
-            pre = preprocess(parsed, alloc)
+            if (present(sweep)) then
+                pre = preprocess(parsed, alloc, sweep)
+            else
+                pre = preprocess(parsed, alloc)
+            end if
         else  
             pre = preprocess(parsed)
         end if
diff --git a/src_mtln/preprocess.F90 b/src_mtln/preprocess.F90
index 00c85cf5..224bfc81 100644
--- a/src_mtln/preprocess.F90
+++ b/src_mtln/preprocess.F90
@@ -53,9 +53,10 @@ module mtln_preprocess_m
 contains
 
 
-    function preprocess(parsed, alloc) result(res)
+    function preprocess(parsed, alloc, sweep) result(res)
         type(parsed_mtln_t), intent(in):: parsed
         type(XYZlimit_t), dimension(1:6), intent(in), optional :: alloc
+        type(XYZlimit_t), dimension(1:6), intent(in), optional :: sweep
         type(preprocess_t) :: res
         type(fhash_tbl_t) :: cable_name_to_bundle_id
         type(transmission_line_bundle_t), dimension(:), allocatable :: line_bundles
@@ -81,7 +82,11 @@ function preprocess(parsed, alloc) result(res)
 #endif
         ! Create mtl objets from cables
         if (present(alloc)) then 
-            line_bundles = buildLineBundles(cable_bundles, res%dt, alloc)
+            if (present(sweep)) then
+                line_bundles = buildLineBundles(cable_bundles, res%dt, alloc, sweep)
+            else
+                line_bundles = buildLineBundles(cable_bundles, res%dt, alloc)
+            end if
         else 
             line_bundles = buildLineBundles(cable_bundles, res%dt)
         end if
@@ -335,16 +340,17 @@ subroutine addEndConnector(line, connector)
 
     end function
 
-    function buildLineBundles(cable_bundles, dt, alloc) result(res)
+    function buildLineBundles(cable_bundles, dt, alloc, sweep) result(res)
         type(cable_bundle_t), dimension(:), allocatable :: cable_bundles
         type(transmission_line_bundle_t), dimension(:), allocatable :: res
         real(kind=RKIND_TIEMPO), intent(in) :: dt
         type(XYZlimit_t), dimension(1:6), intent(in), optional :: alloc
+        type(XYZlimit_t), dimension(1:6), intent(in), optional :: sweep
         integer :: i, j, k
         integer :: nb, nl, nc
         integer(kind=4), allocatable, dimension(:,:) :: layer_indices
         logical :: bundle_in_layer = .false.
-        integer(kind=4), dimension(2) :: alloc_z
+        integer(kind=4), dimension(2) :: alloc_z, sweep_z
         if (present(alloc)) then
             alloc_z(1) = alloc(3)%zi
             alloc_z(2) = alloc(3)%ze
@@ -354,13 +360,16 @@ function buildLineBundles(cable_bundles, dt, alloc) result(res)
         do i = 1, nb
             if (present(alloc)) then
                 if (allocated(layer_indices)) deallocate(layer_indices)
-                bundle_in_layer = isBundleInLayer(cable_bundles(i)%levels(1)%cables(1)%ptr, alloc_z)
-                if (bundle_in_layer) then 
-                    layer_indices = findIndicesInLayer(cable_bundles(i)%levels(1)%cables(1)%ptr, alloc_z)
-                else 
-                    allocate(layer_indices(0,2), source = 0)
+                if (present(sweep)) then
+                    sweep_z(1) = sweep(iHz)%zi
+                    sweep_z(2) = sweep(iHz)%ze
+                    bundle_in_layer = isBundleInLayer(cable_bundles(i)%levels(1)%cables(1)%ptr, alloc_z, sweep_z)
+                    if (bundle_in_layer) layer_indices = findIndicesInLayer(cable_bundles(i)%levels(1)%cables(1)%ptr, alloc_z, sweep_z)
+                else
+                    bundle_in_layer = isBundleInLayer(cable_bundles(i)%levels(1)%cables(1)%ptr, alloc_z)
+                    if (bundle_in_layer) layer_indices = findIndicesInLayer(cable_bundles(i)%levels(1)%cables(1)%ptr, alloc_z)
                 end if
-                ! if (layer_indices(1,1) ==  layer_indices(1,2) ) bundle_in_layer = .false.
+                if (.not. bundle_in_layer) allocate(layer_indices(0,2), source = 0)
             end if
             nl = size(cable_bundles(i)%levels)
             allocate(res(i)%levels(nl))
@@ -378,15 +387,16 @@ function buildLineBundles(cable_bundles, dt, alloc) result(res)
         end do
 
     contains
-        logical function isBundleInLayer(cable, alloc_z)
+        logical function isBundleInLayer(cable, alloc_z, sweep_z)
             integer(kind=4), dimension(2), intent(in) :: alloc_z
+            integer(kind=4), dimension(2), intent(in), optional :: sweep_z
             class (cable_t), pointer, intent(in) :: cable
             integer :: n, i
             logical :: in_layer
             in_layer = .false.
             n = 0
             do i = 1, size(cable%segments)
-                if (isSegmentWithinAllocBox(cable%segments, i, alloc_z)) then 
+                if (isSegmentWithinAllocBox(cable%segments, i, alloc_z, sweep_z)) then
                     if (.not. in_layer) then 
                         in_layer = .true.
                     end if
@@ -401,8 +411,9 @@ logical function isBundleInLayer(cable, alloc_z)
             isBundleInLayer = (n/=0)
         end function
 
-        function findIndicesInLayer(cable, alloc_z) result(res)
+        function findIndicesInLayer(cable, alloc_z, sweep_z) result(res)
             integer(kind=4), dimension(2), intent(in) :: alloc_z
+            integer(kind=4), dimension(2), intent(in), optional :: sweep_z
             class (cable_t), pointer, intent(in) :: cable
             integer(kind=4), allocatable, dimension(:,:) :: res
             integer :: n, i, direction, position(1:3)
@@ -411,7 +422,7 @@ function findIndicesInLayer(cable, alloc_z) result(res)
             ! precount
             n = 0
             do i = 1, size(cable%segments)
-                if (isSegmentWithinAllocBox(cable%segments, i, alloc_z)) then 
+                if (isSegmentWithinAllocBox(cable%segments, i, alloc_z, sweep_z)) then
                     if (.not. in_layer) then 
                         in_layer = .true.
                     end if
@@ -428,7 +439,7 @@ function findIndicesInLayer(cable, alloc_z) result(res)
             n = 1 
             in_layer = .false.
             do i = 1, size(cable%segments)
-                if (isSegmentWithinAllocBox(cable%segments, i, alloc_z)) then 
+                if (isSegmentWithinAllocBox(cable%segments, i, alloc_z, sweep_z)) then
                     if (.not. in_layer) then 
                         res(n,1) = i
                         in_layer = .true.
@@ -446,15 +457,29 @@ function findIndicesInLayer(cable, alloc_z) result(res)
             end if
         end function
 
-        logical function isSegmentWithinAllocBox(segs, i,  z)
+        logical function isSegmentWithinAllocBox(segs, i, alloc_z, sweep_z)
             type(segment_t), intent(in), dimension(:), allocatable :: segs
-            type(segment_t) :: prev
             integer :: i
-            integer(kind=4), dimension(2), intent(in) :: z
-            isSegmentWithinAllocBox = (segs(i)%z >= z(1)) .and. (segs(i)%z <= z(2))
+            integer(kind=4), dimension(2), intent(in) :: alloc_z
+            integer(kind=4), dimension(2), intent(in), optional :: sweep_z
+            if (present(sweep_z)) then
+                isSegmentWithinAllocBox = isSegmentOwnedByMTLNRank(segs(i), alloc_z, sweep_z)
+            else
+                isSegmentWithinAllocBox = (segs(i)%z >= alloc_z(1)) .and. (segs(i)%z <= alloc_z(2))
+            end if
         end function
 
     end function
+    logical function isSegmentOwnedByMTLNRank(segment, alloc_z, sweep_z)
+        type(segment_t), intent(in) :: segment
+        integer(kind=4), dimension(2), intent(in) :: alloc_z, sweep_z
+
+        if (abs(segment%orientation) == ZPOS) then
+            isSegmentOwnedByMTLNRank = (segment%z >= alloc_z(1)) .and. (segment%z <= alloc_z(2))
+        else
+            isSegmentOwnedByMTLNRank = (segment%z > sweep_z(1)) .and. (segment%z <= sweep_z(2))
+        end if
+    end function
 
     function buildCableBundleFromParent(parent, cables) result(res)
         type(cable_abstract_t), intent(in) :: parent
diff --git a/src_mtln/probes.F90 b/src_mtln/probes.F90
index 3776ec6d..f5182172 100644
--- a/src_mtln/probes.F90
+++ b/src_mtln/probes.F90
@@ -67,22 +67,26 @@ function probeCtor(index, probe_type, dt, name, position, layer_indices) result(
         if (present(layer_indices)) then
             call MPI_COMM_SIZE(SUBCOMM_MPI, sizeof, ierr)
             if (sizeof > 1) then
-                res%in_layer = .false.
-                do i = 1, size(layer_indices,1) 
-                    if (index >= layer_indices(i, 1) .and. index <= layer_indices(i,2)+1) then 
-                        res%in_layer = .true.
-                        slice = i
-                    end if
-                end do
-
-                layer_index = 0
-                if (res%in_layer) then 
-                    do i = 1, slice - 1
-                        layer_index = layer_index + layer_indices(i,2) + 1 - (layer_indices(i,1) - 1)
+                if (size(layer_indices,1) == 0) then
+                    res%in_layer = .true.
+                else
+                    res%in_layer = .false.
+                    do i = 1, size(layer_indices,1)
+                        if (index >= layer_indices(i, 1) .and. index <= layer_indices(i,2)+1) then
+                            res%in_layer = .true.
+                            slice = i
+                        end if
                     end do
-                    layer_index = layer_index + res%index - layer_indices(i,1) + 1
+
+                    layer_index = 0
+                    if (res%in_layer) then
+                        do i = 1, slice - 1
+                            layer_index = layer_index + layer_indices(i,2) + 1 - (layer_indices(i,1) - 1)
+                        end do
+                        layer_index = layer_index + res%index - layer_indices(i,1) + 1
+                    end if
+                    res%index = layer_index
                 end if
-                res%index = layer_index
             end if
         end if
 #endif
diff --git a/src_wires_pub/wires_mtln.F90 b/src_wires_pub/wires_mtln.F90
index 6988fe7c..023368fb 100644
--- a/src_wires_pub/wires_mtln.F90
+++ b/src_wires_pub/wires_mtln.F90
@@ -53,13 +53,14 @@ subroutine InitWires_mtln(sgg,Ex,Ey,Ez, sggMiEx, sggMiEy, sggMiEz, sggMiHx, sggM
       logical :: thereAreMTLNbundles
       real(kind=rkind_tiempo), intent(inout) :: dtcritico
 #ifdef CompileWithMPI
-      integer(kind=4) :: ierr
+      integer(kind=4) :: ierr, m
 #endif
       eps0 = eps00
       mu0 = mu00
 
 #ifdef CompileWithMPI
-      mtln_solver = mtlnCtor(mtln_parsed, sgg%alloc)
+      ! Keep the MTLN state whole on every rank; field samples are synchronized in mtl_bundle_t.
+      mtln_solver = mtlnCtor(mtln_parsed)
       call mpi_barrier(subcomm_mpi,ierr)
 #else
       mtln_solver = mtlnCtor(mtln_parsed)
@@ -73,6 +74,11 @@ subroutine InitWires_mtln(sgg,Ex,Ey,Ez, sggMiEx, sggMiEy, sggMiEz, sggMiHx, sggM
       end if
       if (mtln_solver%dt < dtcritico) dtcritico = mtln_solver%dt
       call pointSegmentsToFields()
+#ifdef CompileWithMPI
+      do m = 1, mtln_solver%number_of_bundles
+         call mtln_solver%bundles(m)%initMPIStateOwnership()
+      end do
+#endif
       call mtln_solver%updatePULTerms()
 
    contains
@@ -88,24 +94,33 @@ subroutine pointSegmentsToFields()
             if (mtln_solver%bundles(m)%bundle_in_layer) then 
                do n = 1, ubound(mtln_solver%bundles(m)%external_field_segments,1)
                   call readGridIndices(i, j, k, mtln_solver%bundles(m)%external_field_segments(n))
+                  mtln_solver%bundles(m)%external_field_segments(n)%field_is_local = .false.
+                  mtln_solver%bundles(m)%external_field_segments(n)%field_is_owned = segmentIsOwnedByThisRank(mtln_solver%bundles(m)%external_field_segments(n))
+                  if (.not. mtln_solver%bundles(m)%external_field_segments(n)%field_is_owned) then
+                     mtln_solver%bundles(m)%external_field_segments(n)%field => mtln_solver%null_field
+                     cycle
+                  end if
                   select case (abs(mtln_solver%bundles(m)%external_field_segments(n)%direction))
                      case(DIRECTION_X_POS)
                         if (isEmbeddedInPECorLossy(sggmiEx(i,j,k))) then 
                            mtln_solver%bundles(m)%external_field_segments(n)%field => mtln_solver%null_field
                         else
                            mtln_solver%bundles(m)%external_field_segments(n)%field => Ex(i, j, k) 
+                           mtln_solver%bundles(m)%external_field_segments(n)%field_is_local = .true.
                         end if
                      case(DIRECTION_Y_POS)     
                         if (isEmbeddedInPECorLossy(sggmiEy(i,j,k))) then 
                            mtln_solver%bundles(m)%external_field_segments(n)%field => mtln_solver%null_field
                         else
                            mtln_solver%bundles(m)%external_field_segments(n)%field => Ey(i, j, k) 
+                           mtln_solver%bundles(m)%external_field_segments(n)%field_is_local = .true.
                         end if
                      case(DIRECTION_Z_POS)        
                         if (isEmbeddedInPECorLossy(sggmiEz(i,j,k))) then 
                            mtln_solver%bundles(m)%external_field_segments(n)%field => mtln_solver%null_field
                         else
                            mtln_solver%bundles(m)%external_field_segments(n)%field => Ez(i, j, k) 
+                           mtln_solver%bundles(m)%external_field_segments(n)%field_is_local = .true.
                         end if
                      end select
                end do
@@ -113,6 +128,30 @@ subroutine pointSegmentsToFields()
          end do
       end subroutine
 
+      logical function segmentIsOwnedByThisRank(field_segment)
+         type(external_field_segment_t), intent(in) :: field_segment
+         integer :: field_component
+
+         select case (abs(field_segment%direction))
+         case (DIRECTION_X_POS)
+            field_component = iEx
+         case (DIRECTION_Y_POS)
+            field_component = iEy
+         case (DIRECTION_Z_POS)
+            field_component = iEz
+         case default
+            segmentIsOwnedByThisRank = .false.
+            return
+         end select
+
+         segmentIsOwnedByThisRank = field_segment%position(1) >= sgg%sweep(field_component)%xi .and. &
+                                    field_segment%position(1) <= sgg%sweep(field_component)%xe .and. &
+                                    field_segment%position(2) >= sgg%sweep(field_component)%yi .and. &
+                                    field_segment%position(2) <= sgg%sweep(field_component)%ye .and. &
+                                    field_segment%position(3) >= sgg%sweep(field_component)%zi .and. &
+                                    field_segment%position(3) <= sgg%sweep(field_component)%ze
+      end function
+
       logical function isEmbeddedInPECorLossy(media)
          integer(kind=INTEGERSIZEOFMEDIAMATRICES), intent(in) :: media
          isEmbeddedInPECorLossy = (media == 0 .or. sgg%med(media)%is%pec .or. sgg%med(media)%is%lossy)
@@ -136,6 +175,7 @@ subroutine AdvanceWiresE_mtln(sgg,Idxh, Idyh, Idzh, eps00,mu00)
       do m = 1, mtln_solver%number_of_bundles
          if (mtln_solver%bundles(m)%bundle_in_layer) then 
             do n = 1, ubound(mtln_solver%bundles(m)%external_field_segments,1)
+               if (.not. mtln_solver%bundles(m)%external_field_segments(n)%field_is_local) cycle
                punt => mtln_solver%bundles(m)%external_field_segments(n)%field
                punt = real(punt, kind=rkind_wires) - computeFieldFromCurrent(m,n)
             end do
diff --git a/test/mtln/mtln_tests.h b/test/mtln/mtln_tests.h
index e77b803d..5731195b 100644
--- a/test/mtln/mtln_tests.h
+++ b/test/mtln/mtln_tests.h
@@ -4,6 +4,8 @@
 extern "C" int test_mtl_init_homogeneous();
 extern "C" int test_mtl_time_step();
 extern "C" int test_mtl_wrong_dt();
+extern "C" int test_mtl_inactive_mpi_slice();
+extern "C" int test_mtl_replicated_mpi_probe();
 //test_mtl_bundle.F90
 extern "C" int test_mtl_bundle_init();
 extern "C" int test_mtl_bundle_generator();
@@ -44,6 +46,7 @@ extern "C" int test_preprocess_conductors_before_cable();
 extern "C" int test_preprocess_conductors_in_level();
 extern "C" int test_preprocess_zt_conductor_ranges_2();
 extern "C" int test_preprocess_zt_conductor_ranges();
+extern "C" int test_preprocess_mpi_segment_ownership();
 // extern "C" int test_coaxial_line_paul_8_6_square();
 // extern "C" int test_coaxial_line_paul_8_6_triangle();
 // extern "C" int test_2_conductor_line_paul_9_6();
@@ -61,6 +64,8 @@ extern "C" int test_preprocess_zt_conductor_ranges();
 TEST(mtln, mtl_homogeneous)   { EXPECT_EQ(0, test_mtl_init_homogeneous()); }
 TEST(mtln, mtl_time_step) { EXPECT_EQ(0, test_mtl_time_step()); }
 TEST(mtln, mtl_wrong_dt) { EXPECT_EQ(0, test_mtl_wrong_dt()); }
+TEST(mtln, mtl_inactive_mpi_slice) { EXPECT_EQ(0, test_mtl_inactive_mpi_slice()); }
+TEST(mtln, mtl_replicated_mpi_probe) { EXPECT_EQ(0, test_mtl_replicated_mpi_probe()); }
 TEST(mtln, mtl_bundle_init) { EXPECT_EQ(0, test_mtl_bundle_init()); }
 TEST(mtln, mtl_bundle_generator) { EXPECT_EQ(0, test_mtl_bundle_generator()); }
 
@@ -73,6 +78,7 @@ TEST(mtln, preprocess_conductors_before_cable) { EXPECT_EQ(0, test_preprocess_co
 TEST(mtln, preprocess_conductors_in_level) { EXPECT_EQ(0, test_preprocess_conductors_in_level()); }
 TEST(mtln, preprocess_zt_conductor_ranges_2) { EXPECT_EQ(0, test_preprocess_zt_conductor_ranges_2()); }
 TEST(mtln, preprocess_zt_conductor_ranges) { EXPECT_EQ(0, test_preprocess_zt_conductor_ranges()); }
+TEST(mtln, preprocess_mpi_segment_ownership) { EXPECT_EQ(0, test_preprocess_mpi_segment_ownership()); }
 
 TEST(mtln, math_eigvals) { EXPECT_EQ(0, test_math_eigvals()); }
 TEST(mtln, math_matmul_broadcast) { EXPECT_EQ(0, test_math_matmul_broadcast()); }
diff --git a/test/mtln/test_mtl.F90 b/test/mtln/test_mtl.F90
index 30dc56d5..c182d0ce 100644
--- a/test/mtln/test_mtl.F90
+++ b/test/mtln/test_mtl.F90
@@ -96,4 +96,75 @@ integer function test_mtl_time_step() bind(C) result(error_cnt)
         error_cnt = error_cnt +1
     end if
 
-end function
\ No newline at end of file
+end function
+
+integer function test_mtl_inactive_mpi_slice() bind(C) result(error_cnt)
+    use mtl_m
+    use mtln_types_m, only: DIRECTION_X_POS
+    implicit none
+
+    type(mtl_t) :: shielded_line, unshielded_line
+    type(transfer_impedance_per_meter_t) :: zt
+    type(multipolar_expansion_t), dimension(:), allocatable :: multipolar_expansion
+    real(kind=rkind), dimension(1,1) :: lpul, cpul, rpul, gpul
+    real(kind=rkind), dimension(2) :: step_size
+    type(segment_t), dimension(:), allocatable :: segments
+#ifdef CompileWithMPI
+    integer(kind=4), dimension(:,:), allocatable :: layer_indices
+#endif
+    integer :: i
+    real(kind=rkind_tiempo), parameter :: dt = 1e-11_rkind_tiempo
+
+    error_cnt = 0
+#ifdef CompileWithMPI
+    lpul = reshape([4.4712610e-7_rkind], [1,1])
+    cpul = reshape([2.242e-10_rkind], [1,1])
+    rpul = 0.0_rkind
+    gpul = 0.0_rkind
+    step_size = [20.0_rkind, 20.0_rkind]
+    zt%inductive_term = 0.0_rkind
+    zt%resistive_term = 0.0_rkind
+    allocate(zt%poles(0), zt%residues(0), multipolar_expansion(0), segments(2), layer_indices(0,2))
+    do i = 1, size(segments)
+        segments(i)%x = i
+        segments(i)%y = 1
+        segments(i)%z = 1
+        segments(i)%orientation = DIRECTION_X_POS
+    end do
+
+    shielded_line = mtl_shielded(lpul, cpul, rpul, gpul, step_size, 'inactive', segments, dt, &
+                                 'parent', 1, zt, layer_indices, .false.)
+    unshielded_line = mtl_unshielded(lpul, cpul, rpul, gpul, step_size, 'inactive', segments, dt, &
+                                     multipolar_expansion, 0.0_rkind, layer_indices, .false.)
+
+    if (shielded_line%bundle_in_layer) error_cnt = error_cnt + 1
+    if (size(shielded_line%step_size) /= 0) error_cnt = error_cnt + 1
+    if (shielded_line%dt /= dt) error_cnt = error_cnt + 1
+    if (unshielded_line%bundle_in_layer) error_cnt = error_cnt + 1
+    if (size(unshielded_line%step_size) /= 0) error_cnt = error_cnt + 1
+    if (unshielded_line%dt /= dt) error_cnt = error_cnt + 1
+#endif
+end function
+
+integer function test_mtl_replicated_mpi_probe() bind(C) result(error_cnt)
+    use probes_m, only: probe_t, probeCtor
+    use mtln_types_m, only: PROBE_TYPE_CURRENT
+    use FDETYPES_m, only: RKIND, RKIND_TIEMPO
+    implicit none
+
+    type(probe_t) :: probe
+    character(len=:), allocatable :: name
+#ifdef CompileWithMPI
+    integer(kind=4), dimension(:,:), allocatable :: layer_indices
+#endif
+
+    error_cnt = 0
+#ifdef CompileWithMPI
+    allocate(layer_indices(0,0))
+    name = "replicated"
+    probe = probeCtor(2, PROBE_TYPE_CURRENT, 1.0e-12_RKIND_TIEMPO, name, &
+                      [0.0_RKIND, 0.0_RKIND, 0.0_RKIND], layer_indices)
+    if (.not. probe%in_layer) error_cnt = error_cnt + 1
+    if (probe%index /= 2) error_cnt = error_cnt + 1
+#endif
+end function
diff --git a/test/mtln/test_preprocess.F90 b/test/mtln/test_preprocess.F90
index 8f10e1f4..42f9f489 100644
--- a/test/mtln/test_preprocess.F90
+++ b/test/mtln/test_preprocess.F90
@@ -216,3 +216,29 @@ integer function test_preprocess_zt_conductor_ranges_2() bind(C) result(error_cn
 
 end function
 
+
+integer function test_preprocess_mpi_segment_ownership() bind(C) result(error_cnt)
+    use mtln_preprocess_m, only: isSegmentOwnedByMTLNRank
+    use mtln_types_m, only: segment_t, DIRECTION_X_POS, DIRECTION_Z_POS
+    implicit none
+
+    type(segment_t) :: segment
+    integer(kind=4), dimension(2) :: rank0_alloc, rank0_sweep, rank1_alloc, rank1_sweep
+
+    error_cnt = 0
+    rank0_alloc = [-1_4, 34_4]
+    rank0_sweep = [0_4, 34_4]
+    rank1_alloc = [33_4, 68_4]
+    rank1_sweep = [34_4, 67_4]
+
+    segment%z = 33
+    segment%orientation = DIRECTION_X_POS
+    if (.not. isSegmentOwnedByMTLNRank(segment, rank0_alloc, rank0_sweep)) error_cnt = error_cnt + 1
+    if (isSegmentOwnedByMTLNRank(segment, rank1_alloc, rank1_sweep)) error_cnt = error_cnt + 1
+
+    segment%z = 34
+    segment%orientation = DIRECTION_Z_POS
+    if (.not. isSegmentOwnedByMTLNRank(segment, rank0_alloc, rank0_sweep)) error_cnt = error_cnt + 1
+    segment%z = 33
+    if (.not. isSegmentOwnedByMTLNRank(segment, rank1_alloc, rank1_sweep)) error_cnt = error_cnt + 1
+end function