> For a complete documentation index, fetch https://docs.voximplant.ai/llms.txt
# Example: Context history with ApplicationStorage
> This example answers an inbound call and uses ApplicationStorage to persist a small “memory” per caller across calls, then injects it into the next Deepgram Voice Agent session via agent.context.messages.
For the complete documentation index, see llms.txt.
This example answers an inbound call and uses `ApplicationStorage` to persist a small “memory” per caller across calls, then injects it into the next Deepgram Voice Agent session via `agent.context.messages`.
For a full breakdown of session setup, media bridging, barge-in, and event handling, see [Example: Answering an incoming call](inbound).
**⬇️ Jump to the [Full VoxEngine scenario](#full-voxengine-scenario).**
## Prerequisites
* Set up an inbound entrypoint for the caller:
* Phone number: [https://voximplant.com/docs/getting-started/basic-concepts/phone-numbers](https://voximplant.com/docs/getting-started/basic-concepts/phone-numbers)
* WhatsApp: [https://voximplant.com/docs/guides/integrations/whatsapp](https://voximplant.com/docs/guides/integrations/whatsapp)
* SIP user / SIP registration: [https://voximplant.com/docs/guides/calls/sip](https://voximplant.com/docs/guides/calls/sip)
* App user: [https://voximplant.com/docs/getting-started/basic-concepts/users](https://voximplant.com/docs/getting-started/basic-concepts/users) (see also [https://voximplant.com/docs/guides/calls/scenarios#how-to-call-a-voximplant-user](https://voximplant.com/docs/guides/calls/scenarios#how-to-call-a-voximplant-user))
* Create a routing rule that points the destination (phone number / WhatsApp / SIP username / app user alias) to this scenario: [https://voximplant.com/docs/getting-started/basic-concepts/routing-rules](https://voximplant.com/docs/getting-started/basic-concepts/routing-rules)
* Store your Deepgram API key in Voximplant [Secrets](/platform/voxengine/secrets) under `DEEPGRAM_API_KEY`.
## How cross-call history works
### 1) Pick a user identity and storage key
The example uses the inbound caller ID (`call.callerid()`) as a simple “user identity”, and stores history under a key like `dgva_history:+15550123456`.
Caller ID can be missing, blocked, spoofed, or shared (for example, a PBX).
### 2) Load stored history and pass it to Deepgram
On call start, the scenario reads the stored JSON array from `ApplicationStorage` and passes it directly to the agent:
* `SETTINGS_OPTIONS.agent.context.messages`: prior turns to preload into the session
### 3) Append new turns and persist on hangup
During the call, Deepgram emits `Deepgram.VoiceAgentEvents.History` events containing history items suitable for `context.messages`. The example appends those items to a `rollingHistory` array, trims it to a max size, and then saves it back to `ApplicationStorage` when the call ends.
`ApplicationStorage` values are size-limited (up to 2000 characters per key), so store only what you need (for example last 10–20 items) and enforce a TTL to avoid unbounded growth. See [https://voximplant.com/docs/references/voxengine/applicationstorage#put](https://voximplant.com/docs/references/voxengine/applicationstorage#put).
## Notes
[See the VoxEngine API Reference for more details](https://voximplant.com/docs/references/voxengine/deepgram).
## Full VoxEngine scenario
```javascript title={"voxeengine-deepgram-ctx-history.js"} maxLines={0}
/**
* Voximplant + Deepgram Voice Agent connector demo
* Feature highlighted: CROSS-CALL CONTEXT HISTORY using ApplicationStorage + agent.context.messages
*/
require(Modules.Deepgram);
require(Modules.ApplicationStorage);
const HISTORY_TTL_SECONDS = 14 * 24 * 3600; // 2 weeks
const MAX_HISTORY_ITEMS = 10;
const SYSTEM_PROMPT = `
You are a helpful English-speaking voice assistant for phone callers.
Keep your turns short and telephony-friendly (usually 1–2 sentences).
If conversation history is present, start by briefly summarizing what the caller asked last time in 1 sentence, then ask how you can help.
`;
function safeParseJsonArray(value) {
if (!value) return [];
try {
const parsed = JSON.parse(value);
return Array.isArray(parsed) ? parsed : [];
} catch (error) {
void error;
return [];
}
}
VoxEngine.addEventListener(AppEvents.CallAlerting, async ({call}) => {
let voiceAIClient;
// Caller ID is used as a simple "user identity" for the demo.
const callerId = call.callerid() || null;
const historyKey = callerId ? `dgva_history:${callerId}` : null;
let rollingHistory = [];
async function saveHistory() {
if (!historyKey) return;
await ApplicationStorage.put(historyKey, JSON.stringify(rollingHistory), HISTORY_TTL_SECONDS);
Logger.write("===CROSS_CALL_HISTORY_SAVED===");
Logger.write(JSON.stringify({callerId, messages: rollingHistory.length}));
}
async function terminate() {
try {
await saveHistory();
voiceAIClient?.close();
} catch (error) {
Logger.write(`===CROSS_CALL_HISTORY_SAVE_ERROR===> ${JSON.stringify(error)}`);
}
VoxEngine.terminate();
}
try {
call.answer();
// -------------------- Load cross-call history --------------------
if (historyKey) {
const stored = await ApplicationStorage.get(historyKey);
rollingHistory = safeParseJsonArray(stored?.value);
Logger.write("===CROSS_CALL_HISTORY_LOADED===");
Logger.write(JSON.stringify({callerId, messages: rollingHistory.length}));
} else {
Logger.write("===CROSS_CALL_HISTORY_DISABLED=== Missing caller ID");
}
// -------------------- Deepgram Voice Agent settings --------------------
const SETTINGS_OPTIONS = {
tags: ["voximplant", "deepgram", "voice_agent_connector", "cross_call_history_demo"],
agent: {
language: "en",
greeting: "Hi! I'm Voxi. How can I help today?",
context: {
messages: rollingHistory,
},
listen: {
provider: {
type: "deepgram",
model: "flux-general-en",
},
},
think: {
provider: {
type: "open_ai",
model: "gpt-4o-mini",
temperature: 0.6,
},
prompt: SYSTEM_PROMPT,
},
speak: {
provider: {
type: "deepgram",
model: "aura-2-cordelia-en",
},
},
},
};
// Create client and wire media
voiceAIClient = await Deepgram.createVoiceAgentClient({
apiKey: VoxEngine.getSecretValue('DEEPGRAM_API_KEY'),
settingsOptions: SETTINGS_OPTIONS,
});
VoxEngine.sendMediaBetween(call, voiceAIClient);
call.addEventListener(CallEvents.Disconnected, () => {
terminate();
});
call.addEventListener(CallEvents.Failed, () => {
terminate();
});
// -------------------- Update rolling history --------------------
// Deepgram emits history items suitable for agent.context.messages.
voiceAIClient.addEventListener(Deepgram.VoiceAgentEvents.History, (event) => {
const item = event?.data?.payload;
if (!item) return;
rollingHistory.push(item);
rollingHistory = rollingHistory.slice(-MAX_HISTORY_ITEMS);
});
// Optional: log transcript
voiceAIClient.addEventListener(Deepgram.VoiceAgentEvents.ConversationText, (event) => {
const {role, text} = event?.data?.payload || {};
if (role && text) Logger.write(`===TRANSCRIPT=== ${role}: ${text}`);
});
} catch (error) {
Logger.write("===UNHANDLED_ERROR===");
Logger.write(error);
terminate();
}
});
```