---
title: Packet Data
sidebar_label: Packet Data
sidebar_position: 4
slug: /how-it-works/packet-data
---

import HighlightTag from '@site/src/components/HighlightTag';

# Packet Data Structure

<HighlightTag type="advanced"/><HighlightTag type="protocol"/>

The data that is sent over an IBC channel is called a packet. The packet data is defined by the IBC application module
that is sending the packet. In the case of `cw-ica-controller`, the packet data is defined by the ICS-27 specification.

```rust reference
https://github.com/srdtrk/cw-ica-controller/blob/v0.5.0/src/ibc/types/packet.rs#L18-L44
```

The data field is encoded as protobuf bytes using the following function:

```rust reference
https://github.com/srdtrk/cw-ica-controller/blob/6843b80b29af97b9c4561ad487420e2f54857553/src/ibc/types/packet.rs#L90-L96
```

## From CosmosMsg to Packet Data

Since this contract also provides an execute message to send `CosmosMsg`s as ICA packets, we have a helper function
that converts a `CosmosMsg` to a packet data:

```rust reference
https://github.com/srdtrk/cw-ica-controller/blob/6843b80b29af97b9c4561ad487420e2f54857553/src/ibc/types/packet.rs#L98-L133
```

The specific conversion of each `CosmosMsg` variant into a protobuf any can be found in
[`cosmos_msg.rs`](https://github.com/srdtrk/cw-ica-controller/blob/v0.5.0/src/types/cosmos_msg.rs).

## Acknowledgement Data

For each packet that is sent, the receiving module must respond with an acknowledgement packet. The acknowledgement
packet is used to signal whether or not the ICA packet was successfully executed. The acknowledgement data is defined by the ICS-27 specification.

```rust reference
https://github.com/srdtrk/cw-ica-controller/blob/v0.5.0/src/ibc/types/packet.rs#L169-L177
```

`cw-ica-controller` includes the acknowledgement packet in the [callbacks](../contract-api/04-callbacks.mdx) that
it makes to the external contract.