diff --git a/examples/capture-test.rs b/examples/capture-test.rs
index 07f2380f4..19b00a354 100644
--- a/examples/capture-test.rs
+++ b/examples/capture-test.rs
@@ -153,7 +153,7 @@ pub mod kafka {
     use differential_dataflow::lattice::Lattice;
 
     /// Creates a Kafka source from supplied configuration information.
-    pub fn create_source<G, D, T, R>(scope: G, addr: &str, topic: &str, group: &str) -> (Box<dyn std::any::Any>, Stream<G, (D, T, R)>)
+    pub fn create_source<G, D, T, R>(scope: G, addr: &str, topic: &str, group: &str) -> (Box<dyn std::any::Any + Send + Sync>, Stream<G, (D, T, R)>)
     where
         G: Scope<Timestamp = T>,
         D: ExchangeData + Hash + for<'a> serde::Deserialize<'a>,
diff --git a/src/operators/arrange/agent.rs b/src/operators/arrange/agent.rs
index 8016c12cc..63f950bc7 100644
--- a/src/operators/arrange/agent.rs
+++ b/src/operators/arrange/agent.rs
@@ -423,19 +423,26 @@ where
         Tr: TraceReader,
     {
         // This frontier describes our only guarantee on the compaction frontier.
-        let frontier = self.get_logical_compaction().to_owned();
-        self.import_frontier_core(scope, name, frontier)
+        let since = self.get_logical_compaction().to_owned();
+        self.import_frontier_core(scope, name, since, Antichain::new())
     }
 
-    /// Import a trace advanced to a specific frontier.
-    pub fn import_frontier_core<G>(&mut self, scope: &G, name: &str, frontier: Antichain<Tr::Time>) -> (Arranged<G, TraceFrontier<TraceAgent<Tr>>>, ShutdownButton<CapabilitySet<Tr::Time>>)
+    /// Import a trace restricted to a specific time interval `[since, until)`.
+    ///
+    /// All updates present in the input trace will be first advanced to `since`, and then either emitted,
+    /// or if greater or equal to `until`, suppressed. Once all times are certain to be greater or equal
+    /// to `until` the operator capability will be dropped.
+    ///
+    /// Invoking this method with an `until` of `Antichain::new()` will perform no filtering, as the empty
+    /// frontier indicates the end of times.
+    pub fn import_frontier_core<G>(&mut self, scope: &G, name: &str, since: Antichain<Tr::Time>, until: Antichain<Tr::Time>) -> (Arranged<G, TraceFrontier<TraceAgent<Tr>>>, ShutdownButton<CapabilitySet<Tr::Time>>)
     where
         G: Scope<Timestamp=Tr::Time>,
         Tr::Time: Timestamp+ Lattice+Ord+Clone+'static,
         Tr: TraceReader,
     {
         let trace = self.clone();
-        let trace = TraceFrontier::make_from(trace, frontier.borrow());
+        let trace = TraceFrontier::make_from(trace, since.borrow(), until.borrow());
 
         let mut shutdown_button = None;
 
@@ -458,18 +465,27 @@ where
 
                     let mut capabilities = capabilities.borrow_mut();
                     if let Some(ref mut capabilities) = *capabilities {
-
                         let mut borrow = queue.1.borrow_mut();
                         for instruction in borrow.drain(..) {
-                            match instruction {
-                                TraceReplayInstruction::Frontier(frontier) => {
-                                    capabilities.downgrade(&frontier.borrow()[..]);
-                                },
-                                TraceReplayInstruction::Batch(batch, hint) => {
-                                    if let Some(time) = hint {
-                                        if !batch.is_empty() {
-                                            let delayed = capabilities.delayed(&time);
-                                            output.session(&delayed).give(BatchFrontier::make_from(batch, frontier.borrow()));
+                            // If we have dropped the capabilities due to `until`, attempt no further work.
+                            // Without the capabilities, we should soon be shut down (once this loop ends).
+                            if !capabilities.is_empty() {
+                                match instruction {
+                                    TraceReplayInstruction::Frontier(frontier) => {
+                                        if timely::PartialOrder::less_equal(&until, &frontier) {
+                                            // It might be nice to actively *drop* `capabilities`, but it seems
+                                            // complicated logically (i.e. we'd have to break out of the loop).
+                                            capabilities.downgrade(&[]);
+                                        } else {
+                                            capabilities.downgrade(&frontier.borrow()[..]);
+                                        }
+                                    },
+                                    TraceReplayInstruction::Batch(batch, hint) => {
+                                        if let Some(time) = hint {
+                                            if !batch.is_empty() {
+                                                let delayed = capabilities.delayed(&time);
+                                                output.session(&delayed).give(BatchFrontier::make_from(batch, since.borrow(), until.borrow()));
+                                            }
                                         }
                                     }
                                 }
diff --git a/src/trace/wrappers/frontier.rs b/src/trace/wrappers/frontier.rs
index ec321b71e..cb0865c49 100644
--- a/src/trace/wrappers/frontier.rs
+++ b/src/trace/wrappers/frontier.rs
@@ -1,8 +1,10 @@
 //! Wrapper for frontiered trace.
 //!
-//! Wraps a trace with a frontier so that all exposed timestamps are first advanced by the frontier.
-//! This ensures that even for traces that have been advanced, all views provided through cursors
-//! present deterministic times, independent of the compaction strategy.
+//! Wraps a trace with `since` and `upper` frontiers so that all exposed timestamps are first advanced
+//! by the `since` frontier and restricted by the `upper` frontier. This presents a deterministic trace
+//! on the interval `[since, upper)`, presenting only accumulations up to `since` (rather than partially
+//! accumulated updates) and no updates at times greater or equal to `upper` (even as parts of batches
+//! that span that time).
 
 use timely::progress::Timestamp;
 use timely::progress::{Antichain, frontier::AntichainRef};
@@ -17,7 +19,10 @@ where
     Tr: TraceReader,
 {
     trace: Tr,
-    frontier: Antichain<Tr::Time>,
+    /// Frontier to which all update times will be advanced.
+    since: Antichain<Tr::Time>,
+    /// Frontier after which all update times will be suppressed.
+    until: Antichain<Tr::Time>,
 }
 
 impl<Tr> Clone for TraceFrontier<Tr>
@@ -28,7 +33,8 @@ where
     fn clone(&self) -> Self {
         TraceFrontier {
             trace: self.trace.clone(),
-            frontier: self.frontier.clone(),
+            since: self.since.clone(),
+            until: self.until.clone(),
         }
     }
 }
@@ -51,8 +57,9 @@ where
     type Cursor = CursorFrontier<Tr::Cursor>;
 
     fn map_batches<F: FnMut(&Self::Batch)>(&self, mut f: F) {
-        let frontier = self.frontier.borrow();
-        self.trace.map_batches(|batch| f(&Self::Batch::make_from(batch.clone(), frontier)))
+        let since = self.since.borrow();
+        let until = self.until.borrow();
+        self.trace.map_batches(|batch| f(&Self::Batch::make_from(batch.clone(), since, until)))
     }
 
     fn set_logical_compaction(&mut self, frontier: AntichainRef<Tr::Time>) { self.trace.set_logical_compaction(frontier) }
@@ -62,8 +69,9 @@ where
     fn get_physical_compaction(&mut self) -> AntichainRef<Tr::Time> { self.trace.get_physical_compaction() }
 
     fn cursor_through(&mut self, upper: AntichainRef<Tr::Time>) -> Option<(Self::Cursor, <Self::Cursor as Cursor>::Storage)> {
-        let frontier = self.frontier.borrow();
-        self.trace.cursor_through(upper).map(|(x,y)| (CursorFrontier::new(x, frontier), y))
+        let since = self.since.borrow();
+        let until = self.until.borrow();
+        self.trace.cursor_through(upper).map(|(x,y)| (CursorFrontier::new(x, since, until), y))
     }
 }
 
@@ -73,10 +81,11 @@ where
     Tr::Time: Timestamp,
 {
     /// Makes a new trace wrapper
-    pub fn make_from(trace: Tr, frontier: AntichainRef<Tr::Time>) -> Self {
+    pub fn make_from(trace: Tr, since: AntichainRef<Tr::Time>, until: AntichainRef<Tr::Time>) -> Self {
         TraceFrontier {
             trace,
-            frontier: frontier.to_owned(),
+            since: since.to_owned(),
+            until: until.to_owned(),
         }
     }
 }
@@ -86,10 +95,11 @@ where
 #[derive(Clone)]
 pub struct BatchFrontier<B: BatchReader> {
     batch: B,
-    frontier: Antichain<B::Time>,
+    since: Antichain<B::Time>,
+    until: Antichain<B::Time>,
 }
 
-impl<B: BatchReader> BatchReader for BatchFrontier<B>
+impl<B> BatchReader for BatchFrontier<B>
 where
     B: BatchReader,
     B::Time: Timestamp+Lattice,
@@ -102,7 +112,7 @@ where
     type Cursor = BatchCursorFrontier<B>;
 
     fn cursor(&self) -> Self::Cursor {
-        BatchCursorFrontier::new(self.batch.cursor(), self.frontier.borrow())
+        BatchCursorFrontier::new(self.batch.cursor(), self.since.borrow(), self.until.borrow())
     }
     fn len(&self) -> usize { self.batch.len() }
     fn description(&self) -> &Description<B::Time> { &self.batch.description() }
@@ -114,10 +124,11 @@ where
     B::Time: Timestamp+Lattice,
 {
     /// Makes a new batch wrapper
-    pub fn make_from(batch: B, frontier: AntichainRef<B::Time>) -> Self {
+    pub fn make_from(batch: B, since: AntichainRef<B::Time>, until: AntichainRef<B::Time>) -> Self {
         BatchFrontier {
             batch,
-            frontier: frontier.to_owned(),
+            since: since.to_owned(),
+            until: until.to_owned(),
         }
     }
 }
@@ -125,14 +136,16 @@ where
 /// Wrapper to provide cursor to nested scope.
 pub struct CursorFrontier<C: Cursor> {
     cursor: C,
-    frontier: Antichain<C::Time>,
+    since: Antichain<C::Time>,
+    until: Antichain<C::Time>
 }
 
 impl<C: Cursor> CursorFrontier<C> where C::Time: Clone {
-    fn new(cursor: C, frontier: AntichainRef<C::Time>) -> Self {
+    fn new(cursor: C, since: AntichainRef<C::Time>, until: AntichainRef<C::Time>) -> Self {
         CursorFrontier {
             cursor,
-            frontier: frontier.to_owned(),
+            since: since.to_owned(),
+            until: until.to_owned(),
         }
     }
 }
@@ -157,12 +170,15 @@ where
 
     #[inline]
     fn map_times<L: FnMut(&Self::Time,&Self::R)>(&mut self, storage: &Self::Storage, mut logic: L) {
-        let frontier = self.frontier.borrow();
+        let since = self.since.borrow();
+        let until = self.until.borrow();
         let mut temp: C::Time = <C::Time as timely::progress::Timestamp>::minimum();
         self.cursor.map_times(storage, |time, diff| {
             temp.clone_from(time);
-            temp.advance_by(frontier);
-            logic(&temp, diff);
+            temp.advance_by(since);
+            if !until.less_equal(&temp) {
+                logic(&temp, diff);
+            }
         })
     }
 
@@ -181,14 +197,16 @@ where
 /// Wrapper to provide cursor to nested scope.
 pub struct BatchCursorFrontier<B: BatchReader> {
     cursor: B::Cursor,
-    frontier: Antichain<B::Time>,
+    since: Antichain<B::Time>,
+    until: Antichain<B::Time>,
 }
 
 impl<B: BatchReader> BatchCursorFrontier<B> where B::Time: Clone {
-    fn new(cursor: B::Cursor, frontier: AntichainRef<B::Time>) -> Self {
+    fn new(cursor: B::Cursor, since: AntichainRef<B::Time>, until: AntichainRef<B::Time>) -> Self {
         BatchCursorFrontier {
             cursor,
-            frontier: frontier.to_owned(),
+            since: since.to_owned(),
+            until: until.to_owned(),
         }
     }
 }
@@ -212,12 +230,15 @@ where
 
     #[inline]
     fn map_times<L: FnMut(&Self::Time,&Self::R)>(&mut self, storage: &Self::Storage, mut logic: L) {
-        let frontier = self.frontier.borrow();
+        let since = self.since.borrow();
+        let until = self.until.borrow();
         let mut temp: B::Time = <B::Time as timely::progress::Timestamp>::minimum();
         self.cursor.map_times(&storage.batch, |time, diff| {
             temp.clone_from(time);
-            temp.advance_by(frontier);
-            logic(&temp, diff);
+            temp.advance_by(since);
+            if !until.less_equal(&temp) {
+                logic(&temp, diff);
+            }
         })
     }