diff --git a/sync/src/light_sync/downloader.rs b/sync/src/light_sync/sync_round.rs
similarity index 65%
rename from sync/src/light_sync/downloader.rs
rename to sync/src/light_sync/sync_round.rs
index dd78a3144..905e8354f 100644
--- a/sync/src/light_sync/downloader.rs
+++ b/sync/src/light_sync/sync_round.rs
@@ -21,6 +21,7 @@ use std::mem;
 
 use ethcore::header::Header;
 
+use light::client::LightChainClient;
 use light::net::{EventContext, ReqId};
 use light::request::Headers as HeadersRequest;
 
@@ -36,11 +37,20 @@ use super::response::{self, Constraint};
 const ROUND_SKIP: usize = 255;
 
 // amount of scaffold frames: these are the blank spaces in "X___X___X"
-const ROUND_FRAMES: u64 = 255;
+const ROUND_FRAMES: usize = 255;
 
 // number of attempts to make to get a full scaffold for a sync round.
 const SCAFFOLD_ATTEMPTS: usize = 3;
 
+/// Reasons for sync round abort.
+#[derive(Debug, Clone, Copy)]
+pub enum AbortReason {
+	/// Bad chain downloaded.
+	BadChain,
+	/// No incoming data.
+	NoResponses,
+}
+
 // A request for headers with a known starting header
 // and a known parent hash for the last block.
 struct Request {
@@ -86,7 +96,7 @@ impl Fetcher {
 		}
 	}
 
-	fn process_response(self, req_id: ReqId, headers: &[Bytes]) -> (Downloader, Result<(), Error>) {
+	fn process_response(self, req_id: ReqId, headers: &[Bytes]) -> (SyncRound, Result<(), Error>) {
 		unimplemented!()
 	}
 }
@@ -98,7 +108,7 @@ struct RoundStart {
 	start_block: (u64, H256),
 	pending_req: Option<(ReqId, HeadersRequest)>,
 	sparse_headers: Vec<Header>,
-	attempt: 0,
+	attempt: usize,
 }
 
 impl RoundStart {
@@ -107,65 +117,80 @@ impl RoundStart {
 			start_block: start.clone(),
 			pending_req: None,
 			sparse_headers: Vec::new(),
+			attempt: 0,
 		}
 	}
 
-	fn process_response(mut self, req_id: ReqId, headers: &[Bytes]) -> (Downloader, Result<(), Error>) {
+	fn process_response(mut self, req_id: ReqId, headers: &[Bytes]) -> (SyncRound, Result<(), Error>) {
 		let req = match self.pending_req.take() {
-			Some((id, req)) if req_id == id { req.clone() }
+			Some((id, ref req)) if req_id == id => { req.clone() }
 			other => {
 				self.pending_req = other;
-				return (self, Ok(()))
+				return (SyncRound::Start(self), Ok(()))
 			}
 		};
 
 		self.attempt += 1;
-		let headers = match response::decode_and_verify(headers, &req) {
+		let res = match response::decode_and_verify(headers, &req) {
 			Ok(headers) => {
 				self.sparse_headers.extend(headers);
 
-				if self.sparse_headers.len() == ROUND_FRAMES + 1
-					|| self.attempt >= SCAFFOLD_ATTEMPTS
-				{
+				if self.sparse_headers.len() == ROUND_FRAMES + 1 {
+					trace!(target: "sync", "Beginning fetch of blocks between {} sparse headers",
+						self.sparse_headers.len());
+
 					let fetcher = Fetcher::new(self.sparse_headers);
-					(Downloader::Fetch(fetcher), Ok(()))
+					return (SyncRound::Fetch(fetcher), Ok(()));
 				}
+
+				Ok(())
 			}
+			Err(e) => Err(e),
+		};
+
+		if self.attempt >= SCAFFOLD_ATTEMPTS {
+			(SyncRound::Abort(AbortReason::NoResponses), res.map_err(Into::into))
+		} else {
+			(SyncRound::Start(self), res.map_err(Into::into))
 		}
 	}
 }
 
-/// Downloader state machine.
-pub enum Downloader {
-	/// Waiting for peers.
-	Nothing,
-	/// Searching for common block with best chain.
-	SearchCommon,
+/// Sync round state machine.
+pub enum SyncRound {
 	/// Beginning a sync round.
-	RoundStart(RoundStart),
+	Start(RoundStart),
 	/// Fetching intermediate blocks during a sync round.
 	Fetch(Fetcher),
+	/// Aborted.
+	Abort(AbortReason),
 }
 
-impl Downloader {
-	// Process an answer to a request. Unknown requests will be ignored.
-	fn process_response(self, req_id: ReqId, headers: &[Bytes]) -> (Self, Result<(), Error>) {
+impl SyncRound {
+	fn abort(reason: AbortReason) -> Self {
+		trace!(target: "sync", "Aborting sync round: {:?}", reason);
+
+		SyncRound::Abort(reason)
+	}
+
+	/// Process an answer to a request. Unknown requests will be ignored.
+	pub fn process_response(self, req_id: ReqId, headers: &[Bytes]) -> (Self, Result<(), Error>) {
 		match self {
-			Downloader::RoundStart(round_start) => round_start.process_response(req_id, headers),
-			Downloader::Fetch(fetcher) => fetcher.process_response(req_id, headers),
+			SyncRound::Start(round_start) => round_start.process_response(req_id, headers),
+			SyncRound::Fetch(fetcher) => fetcher.process_response(req_id, headers),
 			other => (other, Ok(())),
 		}
 	}
 
-	// Return unfulfilled requests from disconnected peer. Unknown requests will be ignored.
-	fn requests_abandoned(self, abandoned: &[ReqId]) -> (Self, Result<(), Error>) {
-
+	/// Return unfulfilled requests from disconnected peer. Unknown requests will be ignored.
+	pub fn requests_abandoned(self, abandoned: &[ReqId]) -> (Self, Result<(), Error>) {
+		unimplemented!()
 	}
 
-	// Dispatch pending requests. The dispatcher provided will attempt to
-	// find a suitable peer to serve the request.
+	/// Dispatch pending requests. The dispatcher provided will attempt to
+	/// find a suitable peer to serve the request.
 	// TODO: have dispatcher take capabilities argument?
-	fn dispatch_requests<D>(self, dispatcher: D) -> (Self, Result<(), Error>)
+	pub fn dispatch_requests<D>(self, dispatcher: D) -> (Self, Result<(), Error>)
 		where D: Fn(HeadersRequest) -> Option<ReqId>
 	{
 		unimplemented!()