# Getting started

Use Polyester's FIX session interface with binary SBE application messages.

FIX-SBE combines institutional FIX session behavior with fixed-layout binary application messages. It is separate from tag-value FIX Classic and SBE WebSocket.

> **Use the assigned schema**
>
> Generate codecs from the versioned FIX-SBE schema assigned to your session. Internal Polyester SBE schemas and the [SBE WebSocket](https://testnet.polyester.com/docs/developer-docs/sbe-websocket/getting-started) schema are different contracts.

## When to use FIX-SBE

Use FIX-SBE when your integration can:

- operate persistent trading sessions
- implement sequence, heartbeat, resend, and recovery behavior
- generate and validate versioned SBE messages
- complete protocol conformance and certification

Use [FIX Classic](https://testnet.polyester.com/docs/developer-docs/fix-classic/getting-started) when compatibility with tag-value FIX tooling is more important than binary application encoding.

## Integration flow

1. Review the session package

   Confirm the session protocol, schema identity and version, endpoint, authentication method, enabled business workflows, and operational limits.

2. Generate and validate codecs

   Generate codecs from the assigned schema. Validate schema identity, template identity, block length, and version before decoding application messages.

3. Implement session behavior

   Implement authentication, heartbeat, sequence persistence, resend, reconnect, and recovery according to the session profile.

4. Complete certification

   Run the assigned protocol, compatibility, and recovery cases before connecting the production session.

## Recovery boundaries

## Session recovery

Persist protocol sequence and follow the session profile's resend and reset policy. Validate schema version again after reconnecting.

## Application state

Session recovery does not necessarily provide a complete trading snapshot. Reconcile application state through the assigned FIX workflow or Polyester read APIs.

See the [Connectivity matrix](https://testnet.polyester.com/docs/developer-docs/getting-started/connectivity-matrix) to compare FIX-SBE with ConnectRPC and SBE WebSocket.