diff --git a/src/simplerenderer.tsx b/src/simplerenderer.tsx
index 05dfed284..552d8ac07 100644
--- a/src/simplerenderer.tsx
+++ b/src/simplerenderer.tsx
@@ -36,7 +36,7 @@ class SimpleBlobRendererModel {
         this.savedHeight = params.savedHeight;
         this.ptyDataSource = params.ptyDataSource;
         if (this.isDone.get()) {
-            this.reload(0);
+            setTimeout(() => this.reload(0), 10);
         }
     }
 
@@ -74,6 +74,10 @@ class SimpleBlobRendererModel {
             this.loading.set(true);
         })();
         let rtnp = this.ptyDataSource(this.context);
+        if (rtnp == null) {
+            console.log("no promise returned from ptyDataSource (simplerenderer)", this.context);
+            return;
+        }
         rtnp.then((ptydata) => {
             setTimeout(() => {
                 this.ptyData = ptydata;
diff --git a/src/term.ts b/src/term.ts
index a0c541d1d..7636173da 100644
--- a/src/term.ts
+++ b/src/term.ts
@@ -109,7 +109,7 @@ class TermWrap {
         if (opts.customKeyHandler != null) {
             this.terminal.attachCustomKeyEventHandler((e) => opts.customKeyHandler(e, this));
         }
-        this.reload(0);
+        setTimeout(() => this.reload(0), 10);
     }
 
     getUsedRows() : number {
@@ -281,6 +281,10 @@ class TermWrap {
         this.reloading = true;
         this.terminal.reset();
         let rtnp = this.ptyDataSource(this.termContext);
+        if (rtnp == null) {
+            console.log("no promise returned from ptyDataSource (termwrap)", this.termContext);
+            return;
+        }
         rtnp.then((ptydata) => {
             setTimeout(() => {
                 this._reloadThenHandler(ptydata);
diff --git a/src/types.ts b/src/types.ts
index fd65c3bdc..9a035ae7a 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -535,9 +535,11 @@ type WebCmd = {
 };
 
 type WebFullScreen = {
+    screenid : string,
     screen : WebScreen,
     lines : WebLine[],
     cmds : WebCmd[],
+    cmdptymap : Record<string, number>,
     vts : number,
 }
 
@@ -548,16 +550,6 @@ type PtyDataUpdate = {
     data : string,
 };
 
-type WebScreenUpdate = {
-    type : string,
-    screenid : string,
-    screen : WebScreen,
-    lines : WebLine[],
-    cmds : WebCmd[],
-    ptydata : PtyDataUpdate[],
-    removedlines : string[],
-};
-
 type WebShareWSMessage = {
     type : string,
     screenid : string,
@@ -589,4 +581,4 @@ type RendererContainerType = {
 
 type LineHeightChangeCallbackType = (lineNum : number, newHeight : number, oldHeight : number) => void;
 
-export type {SessionDataType, LineType, RemoteType, RemoteStateType, RemoteInstanceType, HistoryItem, CmdRemoteStateType, FeCmdPacketType, TermOptsType, CmdStartPacketType, CmdDataType, ScreenDataType, ScreenOptsType, PtyDataUpdateType, ModelUpdateType, UpdateMessage, InfoType, CmdLineUpdateType, RemotePtrType, UIContextType, HistoryInfoType, HistoryQueryOpts, WatchScreenPacketType, TermWinSize, FeInputPacketType, RemoteInputPacketType, RemoteEditType, FeStateType, ContextMenuOpts, RendererContext, WindowSize, RendererModel, PtyDataType, BookmarkType, ClientDataType, PlaybookType, PlaybookEntryType, HistoryViewDataType, RenderModeType, AlertMessageType, HistorySearchParams, ScreenLinesType, FocusTypeStrs, HistoryTypeStrs, RendererOpts, RendererPluginType, SimpleBlobRendererComponent, RendererModelContainerApi, RendererModelInitializeParams, RendererOptsUpdate, ClientMigrationInfo, WebShareOpts, RemoteStatusTypeStrs, WebFullScreen, WebScreen, WebLine, WebCmd, RemoteTermContext, TermContextUnion, WebRemote, WebScreenUpdate, PtyDataUpdate, WebShareWSMessage, LineHeightChangeCallbackType, LineFactoryProps, LineInterface, RendererContainerType};
+export type {SessionDataType, LineType, RemoteType, RemoteStateType, RemoteInstanceType, HistoryItem, CmdRemoteStateType, FeCmdPacketType, TermOptsType, CmdStartPacketType, CmdDataType, ScreenDataType, ScreenOptsType, PtyDataUpdateType, ModelUpdateType, UpdateMessage, InfoType, CmdLineUpdateType, RemotePtrType, UIContextType, HistoryInfoType, HistoryQueryOpts, WatchScreenPacketType, TermWinSize, FeInputPacketType, RemoteInputPacketType, RemoteEditType, FeStateType, ContextMenuOpts, RendererContext, WindowSize, RendererModel, PtyDataType, BookmarkType, ClientDataType, PlaybookType, PlaybookEntryType, HistoryViewDataType, RenderModeType, AlertMessageType, HistorySearchParams, ScreenLinesType, FocusTypeStrs, HistoryTypeStrs, RendererOpts, RendererPluginType, SimpleBlobRendererComponent, RendererModelContainerApi, RendererModelInitializeParams, RendererOptsUpdate, ClientMigrationInfo, WebShareOpts, RemoteStatusTypeStrs, WebFullScreen, WebScreen, WebLine, WebCmd, RemoteTermContext, TermContextUnion, WebRemote, PtyDataUpdate, WebShareWSMessage, LineHeightChangeCallbackType, LineFactoryProps, LineInterface, RendererContainerType};
diff --git a/src/webshare-elems.tsx b/src/webshare-elems.tsx
index c38152de7..d6a5b56e8 100644
--- a/src/webshare-elems.tsx
+++ b/src/webshare-elems.tsx
@@ -24,7 +24,6 @@ type OMap<K,V> = mobx.ObservableMap<K,V>;
 let foo = LinesView;
 
 // TODO reshare
-// TODO debounce some of the updates
 
 function makeFullRemoteRef(ownerName : string, remoteRef : string, name : string) : string {
     if (isBlank(ownerName) && isBlank(name)) {
@@ -624,7 +623,7 @@ class WebScreenView extends React.Component<{}, {}> {
     }
     
     render() {
-        let fullScreen = WebShareModel.screen.get();
+        let fullScreen = WebShareModel.fullScreen.get();
         if (fullScreen == null || fullScreen.lines.length == 0) {
             return this.renderEmpty();
         }
@@ -643,7 +642,7 @@ class WebShareMain extends React.Component<{}, {}> {
     }
             
     render() {
-        let screen = WebShareModel.screen.get();
+        let screen = WebShareModel.fullScreen.get();
         let errMessage = WebShareModel.errMessage.get();
         let shareName = "";
         if (screen != null) {
diff --git a/src/webshare-model.ts b/src/webshare-model.ts
index 51f9261a4..247e40f19 100644
--- a/src/webshare-model.ts
+++ b/src/webshare-model.ts
@@ -14,6 +14,10 @@ type OArr<V> = mobx.IObservableArray<V>;
 type OMap<K,V> = mobx.ObservableMap<K,V>;
 type CV<V> = mobx.IComputedValue<V>;
 
+type PtyListener = {
+    receiveData(ptyPos : number, data : Uint8Array, reason? : string);
+};
+
 function isBlank(s : string) {
     return (s == null || s == "");
 }
@@ -30,7 +34,7 @@ class WebShareModelClass {
     viewKey : string;
     screenId : string;
     errMessage : OV<string> = mobx.observable.box(null, {name: "errMessage"});
-    screen : OV<T.WebFullScreen> = mobx.observable.box(null, {name: "webScreen"});
+    fullScreen : OV<T.WebFullScreen> = mobx.observable.box(null, {name: "webScreen"});
     terminals : Record<string, TermWrap> = {};        // lineid => TermWrap
     renderers : Record<string, T.RendererModel> = {};   // lineid => RendererModel
     contentHeightCache : Record<string, number> = {};  // lineid => height
@@ -39,12 +43,17 @@ class WebShareModelClass {
     selectedLine : OV<number> = mobx.observable.box(0, {name: "selectedLine"});
     syncSelectedLine : OV<boolean> = mobx.observable.box(true, {name: "syncSelectedLine"});
     lastScreenSize : T.WindowSize = null;
+    activePtyFetch : Record<string, boolean> = {}; // lineid -> active
+    localPtyOffsetMap : Record<string, number> = {};
+    remotePtyOffsetMap : Record<string, number> = {};
+    activeUpdateFetch : boolean = false;
+    remoteScreenVts : number = 0;
     
     constructor() {
         let urlParams = new URLSearchParams(window.location.search);
         this.viewKey = urlParams.get("viewkey");
         this.screenId = urlParams.get("screenid");
-        setTimeout(() => this.loadFullScreenData(), 10);
+        setTimeout(() => this.loadFullScreenData(false), 10);
         this.wsControl = new WebShareWSControl(getBaseWSUrl(), this.screenId, this.viewKey, this.wsMessageCallback.bind(this));
         document.addEventListener("keydown", this.docKeyDownHandler.bind(this));
     }
@@ -59,7 +68,7 @@ class WebShareModelClass {
         mobx.action(() => {
             this.syncSelectedLine.set(val);
             if (val) {
-                let fullScreen = this.screen.get();
+                let fullScreen = this.fullScreen.get();
                 if (fullScreen != null) {
                     this.selectedLine.set(fullScreen.screen.selectedline);
                 }
@@ -103,7 +112,7 @@ class WebShareModelClass {
     }
 
     getServerSelectedLine() : number {
-        let fullScreen = this.screen.get();
+        let fullScreen = this.fullScreen.get();
         if (fullScreen != null) {
             return fullScreen.screen.selectedline;
         }
@@ -116,7 +125,7 @@ class WebShareModelClass {
     }
 
     updateSelectedLineIndex(delta : number) : void {
-        let fullScreen = this.screen.get();
+        let fullScreen = this.fullScreen.get();
         if (fullScreen == null) {
             return;
         }
@@ -209,14 +218,20 @@ class WebShareModelClass {
         fullScreen.cmds.push(newCmd);
     }
 
-    mergeUpdate(msg : T.WebScreenUpdate) {
+    mergeUpdate(msg : T.WebFullScreen) {
         if (msg.screenid != this.screenId) {
-            console.log("bad WebScreenUpdate, wrong screenid", msg.screenid);
+            console.log("bad WebFullScreen update, wrong screenid", msg.screenid);
             return;
         }
-        console.log("merge", msg);
+        console.log("merge screen-update", "vts=" + msg.vts);
+        // console.log("merge", "vts=" + msg.vts, msg);
         mobx.action(() => {
-            let fullScreen = this.screen.get();
+            let fullScreen = this.fullScreen.get();
+            if (fullScreen.vts >= msg.vts) {
+                console.log("stale merge", "cur-vts=" + fullScreen.vts, "merge-vts=" + msg.vts);
+                return;
+            }
+            fullScreen.vts = msg.vts;
             if (msg.screen) {
                 fullScreen.screen = msg.screen;
                 if (this.syncSelectedLine.get()) {
@@ -225,6 +240,10 @@ class WebShareModelClass {
             }
             if (msg.lines != null && msg.lines.length > 0) {
                 for (let line of msg.lines) {
+                    if (line.archived) {
+                        this.removeLine(fullScreen, line.lineid);
+                        continue;
+                    }
                     this.mergeLine(fullScreen, line);
                 }
             }
@@ -233,33 +252,118 @@ class WebShareModelClass {
                     this.mergeCmd(fullScreen, cmd);
                 }
             }
-            if (msg.ptydata != null && msg.ptydata.length > 0) {
-                for (let data of msg.ptydata) {
-                    let termWrap = this.getTermWrap(data.lineid);
-                    if (termWrap == null) {
-                        continue;
-                    }
-                    let dataArr = base64ToArray(data.data);
-                    termWrap.receiveData(data.ptypos, dataArr, "ws:ptydata");
-                }
+            this.handleCmdPtyMap(msg.cmdptymap);
+         })();
+    }
+
+    handleCmdPtyMap(ptyMap : Record<string, number>) {
+        if (ptyMap == null) {
+            return;
+        }
+        for (let lineId in ptyMap) {
+            let newOffset = ptyMap[lineId];
+            this.remotePtyOffsetMap[lineId] = newOffset;
+            let localOffset = this.localPtyOffsetMap[lineId];
+            if (localOffset != null && localOffset < newOffset) {
+                this.runPtyFetch(lineId);
             }
-            if (msg.removedlines != null && msg.removedlines.length > 0) {
-                for (let lineid of msg.removedlines) {
-                    this.removeLine(fullScreen, lineid);
+        }
+    }
+
+    runPtyFetch(lineId : string) {
+        let prtn = this.checkFetchPtyData(lineId, false);
+        let ptyListener = this.getPtyListener(lineId);
+        if (ptyListener != null) {
+            prtn.then((ptydata) => {
+                ptyListener.receiveData(ptydata.pos, ptydata.data, "model-fetch");
+                if (ptydata.data.length > 0) {
+                    setTimeout(() => this.checkFetchPtyData(lineId, false), 100);
                 }
+            });
+        }
+    }
+
+    getPtyListener(lineId : string) {
+        let termWrap = this.getTermWrap(lineId);
+        if (termWrap != null) {
+            return termWrap;
+        }
+        let renderer = this.getRenderer(lineId);
+        if (renderer != null) {
+            return renderer;
+        }
+        return null;
+    }
+
+    receivePtyData(lineId : string, ptyPos : number, data : Uint8Array, reason? : string) : void {
+        let termWrap = this.getTermWrap(lineId);
+        if (termWrap != null) {
+            termWrap.receiveData(ptyPos, data, reason);
+        }
+        let renderer = this.getRenderer(lineId);
+        if (renderer != null) {
+            renderer.receiveData(ptyPos, data, reason);
+        }
+    }
+
+    checkFetchPtyData(lineId : string, reload : boolean) : Promise<T.PtyDataType> {
+        let lineNum = this.getLineNumFromId(lineId);
+        if (this.activePtyFetch[lineId]) {
+            // console.log("check-fetch", lineNum, "already running");
+            return;
+        }
+        if (reload) {
+            this.localPtyOffsetMap[lineId] = 0;
+        }
+        let ptyOffset = this.localPtyOffsetMap[lineId];
+        if (ptyOffset == null) {
+            // console.log("check-fetch", lineNum, "no local offset");
+            return;
+        }
+        let remotePtyOffset = this.remotePtyOffsetMap[lineId];
+        if (ptyOffset >= remotePtyOffset) {
+            // up to date
+            return Promise.resolve({pos: ptyOffset, data: new Uint8Array(0)});
+        }
+        this.activePtyFetch[lineId] = true;
+        let viewKey = WebShareModel.viewKey;
+        // console.log("fetch pty", lineNum, "pos=" + ptyOffset);
+        let usp = new URLSearchParams({screenid: this.screenId, viewkey: viewKey, lineid: lineId, pos: String(ptyOffset)});
+        let url = new URL(getBaseUrl() + "/webshare/ptydata?" + usp.toString());
+        return fetch(url, {method: "GET", mode: "cors", cache: "no-cache"}).then((resp) => {
+            if (!resp.ok) {
+                throw new Error(sprintf("Bad fetch response for /webshare/ptydata: %d %s", resp.status, resp.statusText));
             }
-        })();
+            let ptyOffsetStr = resp.headers.get("X-PtyDataOffset");
+            if (ptyOffsetStr != null && !isNaN(parseInt(ptyOffsetStr))) {
+                ptyOffset = parseInt(ptyOffsetStr);
+            }
+            return resp.arrayBuffer();
+        }).then((buf) => {
+            let dataArr = new Uint8Array(buf);
+            let newOffset = ptyOffset + dataArr.length;
+            console.log("fetch pty success", lineNum, "len=" + dataArr.length, "pos => " + newOffset);
+            this.localPtyOffsetMap[lineId] = newOffset;
+            return {pos: ptyOffset, data: dataArr};
+        }).finally(() => {
+            this.activePtyFetch[lineId] = false;
+        });
     }
 
     wsMessageCallback(msg : any) {
         if (msg.type == "webscreen:update") {
-            this.mergeUpdate(msg);
+            console.log("[ws] update vts", msg.vts);
+            if (msg.vts > this.remoteScreenVts) {
+                this.remoteScreenVts = msg.vts;
+                setTimeout(() => this.checkUpdateScreenData(), 10);
+            }
             return;
         }
-        console.log("ws message", msg);
+        console.log("[ws] unhandled message", msg);
     }
 
     setWebFullScreen(screen : T.WebFullScreen) {
+        console.log("got initial screen", "vts=" + screen.vts);
         mobx.action(() => {
             if (screen.lines == null) {
                 screen.lines = [];
@@ -267,7 +371,9 @@ class WebShareModelClass {
             if (screen.cmds == null) {
                 screen.cmds = [];
             }
-            this.screen.set(screen);
+            this.handleCmdPtyMap(screen.cmdptymap);
+            screen.cmdptymap = null;
+            this.fullScreen.set(screen);
             this.wsControl.reconnect(true);
             if (this.syncSelectedLine.get()) {
                this.selectedLine.set(screen.screen.selectedline);
@@ -303,6 +409,10 @@ class WebShareModelClass {
             onUpdateContentHeight: (termContext : T.RendererContext, height : number) => { this.setContentHeight(termContext, height); },
         });
         this.terminals[lineId] = termWrap;
+        if (this.localPtyOffsetMap[lineId] == null) {
+            this.localPtyOffsetMap[lineId] = 0;
+        }
+        this.localPtyOffsetMap[lineId] = 0;
         if (this.getSelectedLine() == line.linenum) {
             termWrap.giveFocus();
         }
@@ -358,6 +468,7 @@ class WebShareModelClass {
             term.dispose();
             delete this.terminals[lineId];
         }
+        delete this.localPtyOffsetMap[lineId];
     }
 
     getUsedRows(context : T.RendererContext, line : T.WebLine, cmd : T.WebCmd, width : number) : number {
@@ -391,11 +502,26 @@ class WebShareModelClass {
         return this.renderers[lineId];
     }
 
-    registerRenderer(cmdId : string, renderer : T.RendererModel) {
-        this.renderers[cmdId] = renderer;
+    registerRenderer(lineId : string, renderer : T.RendererModel) {
+        this.renderers[lineId] = renderer;
+        if (this.localPtyOffsetMap[lineId] == null) {
+            this.localPtyOffsetMap[lineId] = 0;
+        }
     }
 
-    loadFullScreenData() : void {
+    checkUpdateScreenData() : void {
+        let fullScreen = this.fullScreen.get();
+        if (fullScreen == null) {
+            return;
+        }
+        // console.log("check-update", "vts=" + fullScreen.vts, "remote-vts=" + this.remoteScreenVts);
+        if (fullScreen.vts >= this.remoteScreenVts) {
+            return;
+        }
+        this.loadFullScreenData(true);
+    }
+
+    loadFullScreenData(update : boolean) : void {
         if (isBlank(this.screenId)) {
             this.setErrMessage("No ScreenId Specified, Cannot Load.");
             return;
@@ -404,20 +530,53 @@ class WebShareModelClass {
             this.setErrMessage("No ViewKey Specified, Cannot Load.");
             return;
         }
-        let usp = new URLSearchParams({screenid: this.screenId, viewkey: this.viewKey});
+        if (this.activeUpdateFetch) {
+            // console.log("there is already an active update fetch");
+            return;
+        }
+        // console.log("running screen-data update");
+        this.activeUpdateFetch = true;
+        let urlParams : Record<string, string> = {screenid: this.screenId, viewkey: this.viewKey};
+        if (update) {
+            let fullScreen = this.fullScreen.get();
+            if (fullScreen != null) {
+                urlParams.vts = String(fullScreen.vts);
+            }
+        }
+        let usp = new URLSearchParams(urlParams);
         let url = new URL(getBaseUrl() + "/webshare/screen?" + usp.toString());
         fetch(url, {method: "GET", mode: "cors", cache: "no-cache"}).then((resp) => handleJsonFetchResponse(url, resp)).then((data) => {
-            mobx.action(() => {
-                let screen : T.WebFullScreen = data;
+            let screen : T.WebFullScreen = data;
+            if (update) {
+                this.mergeUpdate(screen);
+            }
+            else {
                 this.setWebFullScreen(screen);
-            })();
+            }
+            setTimeout(() => this.checkUpdateScreenData(), 300);
         }).catch((err) => {
             this.errMessage.set("Cannot get screen: " + err.message);
+        }).finally(() => {
+            this.activeUpdateFetch = false;
         });
     }
 
+    getLineNumFromId(lineId : string) : number {
+        let fullScreen = this.fullScreen.get();
+        if (fullScreen == null) {
+            return -1;
+        }
+        for (let i=0; i<fullScreen.lines.length; i++) {
+            let line = fullScreen.lines[i];
+            if (line.lineid == lineId) {
+                return line.linenum;
+            }
+        }
+        return -1;
+    }
+
     getLineIndex(lineNum : number) : number {
-        let fullScreen = this.screen.get();
+        let fullScreen = this.fullScreen.get();
         if (fullScreen == null) {
             return -1;
         }
@@ -431,7 +590,7 @@ class WebShareModelClass {
     }
 
     getNumLines() : number {
-        let fullScreen = this.screen.get();
+        let fullScreen = this.fullScreen.get();
         if (fullScreen == null) {
             return 0;
         }
@@ -439,7 +598,7 @@ class WebShareModelClass {
     }
 
     getCmdById(lineId : string) : T.WebCmd {
-        let fullScreen = this.screen.get();
+        let fullScreen = this.fullScreen.get();
         if (fullScreen == null) {
             return null;
         }
@@ -468,22 +627,7 @@ function getTermPtyData(termContext : T.TermContextUnion) : Promise<T.PtyDataTyp
     if ("remoteId" in termContext) {
         throw new Error("remote term ptydata is not supported in webshare");
     }
-    let ptyOffset = 0;
-    let viewKey = WebShareModel.viewKey;
-    let usp = new URLSearchParams({screenid: termContext.screenId, viewkey: viewKey, lineid: termContext.lineId});
-    let url = new URL(getBaseUrl() + "/webshare/ptydata?" + usp.toString());
-    return fetch(url, {method: "GET", mode: "cors", cache: "no-cache"}).then((resp) => {
-        if (!resp.ok) {
-            throw new Error(sprintf("Bad fetch response for /webshare/ptydata: %d %s", resp.status, resp.statusText));
-        }
-        let ptyOffsetStr = resp.headers.get("X-PtyDataOffset");
-        if (ptyOffsetStr != null && !isNaN(parseInt(ptyOffsetStr))) {
-            ptyOffset = parseInt(ptyOffsetStr);
-        }
-        return resp.arrayBuffer();
-    }).then((buf) => {
-        return {pos: ptyOffset, data: new Uint8Array(buf)};
-    });
+    return WebShareModel.checkFetchPtyData(termContext.lineId, true);
 }
 
 let WebShareModel : WebShareModelClass = null;
diff --git a/src/webshare-ws.ts b/src/webshare-ws.ts
index 030723f60..af7508ebe 100644
--- a/src/webshare-ws.ts
+++ b/src/webshare-ws.ts
@@ -23,7 +23,7 @@ class WebShareWSControl {
         this.viewKey = viewKey;
         this.open = mobx.observable.box(false, {name: "WSOpen"});
         this.closed = true;
-        setInterval(this.sendPing, 15000);
+        setInterval(this.sendPing, 20000);
     }
 
     close() : void {