diff --git a/src/tablist/index.ts b/src/tablist/index.ts
index c0f4d0e..72cddce 100644
--- a/src/tablist/index.ts
+++ b/src/tablist/index.ts
@@ -1,4 +1,5 @@
 import {BehaviorSubject, Observable, timer} from "rxjs";
+import {pubsub} from "../pubsub";
 import type {PubSub} from "../pubsub/types";
 
 const enum CHANNEL {
@@ -8,15 +9,23 @@ const enum CHANNEL {
   LIST,
   /** Notify other tabs that this tab is alive. */
   PING,
+  /** Call another tab. Establish a bi-directional private channel. */
+  CALL,
 }
 
 type HelloMessage = number;
 type PingMessage = number;
 type ListMessage = [id: number, peers: PeerList];
+type CallMessage = [caller: number, callee: number];
 
 type PeerList = Record<number, number>;
 
-/**  */
+export interface TabListDependencies {
+  readonly bus: PubSub;
+  readonly newBus: (name: string) => PubSub;
+  readonly clock?: number;
+}
+
 export class TabList {
   /** Unique ID of the current browser tab instance. Zero is not allowed. */
   public readonly id: number = Math.ceil(Math.random() * 0xFFFFFFFFFFFFFF);
@@ -25,58 +34,67 @@ export class TabList {
   protected readonly clock$: Observable<number>;
   protected pingTimeout: number
 
+  /** Send other tabs a heartbeat. This is sent automatically in a loop. */
   public ping = () => {
-    this.pubsub.pub(CHANNEL.PING, this.id);
+    this.deps.bus.pub(CHANNEL.PING, this.id);
   }
 
-  public constructor(protected readonly pubsub: PubSub, clock: number = 200) {
+  public constructor(protected readonly deps: TabListDependencies) {
+    const {bus, clock = 200} = deps;
     this.clock$ = timer(clock, clock);
     this.pingTimeout = clock * 5;
 
     // Listen for new peers joining.
-    pubsub.sub$<HelloMessage>(CHANNEL.HELLO).subscribe((id) => {
+    bus.sub$<HelloMessage>(CHANNEL.HELLO).subscribe((id) => {
       const now = Date.now();
       this.mergePeers({[id]: now}, now);
-      pubsub.pub<ListMessage>(CHANNEL.LIST, [this.id, this.peers]);
+      bus.pub<ListMessage>(CHANNEL.LIST, [this.id, this.peers]);
     });
 
     // Listen for peer list updates.
-    pubsub.sub$<ListMessage>(CHANNEL.LIST).subscribe(([id, peers]) => {
+    bus.sub$<ListMessage>(CHANNEL.LIST).subscribe(([id, peers]) => {
       const now = Date.now();
       peers[id] = now;
       this.mergePeers(peers, now);
     });
 
     // Join the swarm.
-    this.pubsub.pub<HelloMessage>(CHANNEL.HELLO, this.id);
+    bus.pub<HelloMessage>(CHANNEL.HELLO, this.id);
 
     // Send heartbeats to other tabs.
     this.clock$.subscribe(this.ping);
 
     // Listen to heartbeats from other tabs.
-    pubsub.sub$<PingMessage>(CHANNEL.PING).subscribe((id) => {
+    bus.sub$<PingMessage>(CHANNEL.PING).subscribe((id) => {
       const now = Date.now();
       this.mergePeers({[id]: now}, now);
     });
   }
 
-  public mergePeers(peers: PeerList, now: number = Date.now()): number {
-    let leader = 0;
-    const localList = this.peers;
-    for (const [key, time] of Object.entries(peers)) {
-      const id = Number(key);
-      if ((time + this.pingTimeout < now) || (id === this.id)) continue;
-      if (!localList[id]) localList[id] = time;
-      else if (localList[id] < time) localList[id] = time;
-      if (leader < id) leader = id;
-    }
-    for (const [key, time] of Object.entries(localList)) {
+  protected mergePeers(peers: PeerList, now: number = Date.now()): number {
+    let leader = this.id;
+    Object.assign(this.peers, peers);
+    for (const [key, time] of Object.entries(this.peers)) {
       const id = Number(key);
-      if ((time + this.pingTimeout < now) || (id === this.id)) delete localList[id];
+      if ((time + this.pingTimeout < now) || (id === this.id)) delete this.peers[id];
       if (leader < id) leader = id;
     }
-    if (this.id > leader) leader = this.id;
     if (leader !== this.leader$.getValue()) this.leader$.next(leader);
     return leader;
   }
+
+  private getCallNumber(tabId: number): string {
+    let id1 = this.id;
+    let id2 = tabId;
+    if (id1 > id2) [id1, id2] = [id2, id1];
+    return `${id1.toString(36)}-${id2.toString(36)}`;
+  }
+
+  /** Establish a bi-directional channel with another tab. */
+  public async call(tabId: number): Promise<PubSub> {
+    const callNumber = this.getCallNumber(tabId);
+    const channel = pubsub(callNumber);
+    this.deps.bus.pub<CallMessage>(CHANNEL.CALL, [this.id, tabId]);
+    return channel;
+  };
 }
diff --git a/stories/tablist.stories.js b/stories/tablist.stories.js
index 13aa170..f60ca41 100644
--- a/stories/tablist.stories.js
+++ b/stories/tablist.stories.js
@@ -7,8 +7,10 @@ export default {
   title: 'tab list',
 };
 
-const channel = pubsub('test');
-const list = new TabList(channel);
+const bus = pubsub('test');
+const list = new TabList({
+  bus,
+});
 
 list.leader$.subscribe((leader) => {
   console.log('leader:', leader);
@@ -16,7 +18,7 @@ list.leader$.subscribe((leader) => {
 
 export const Default = () => {
   const incoming$ = new BehaviorSubject([]);
-  channel.sub$(4).subscribe((data) => {
+  bus.sub$(4).subscribe((data) => {
     console.log('data received:', data);
     incoming$.next(incoming$.getValue().concat(data));
   });