# MediaTailor parameter routing for ADS and origins
<a name="parameter-routing-behavior"></a>

AWS Elemental MediaTailor routes query parameters to different destinations based on their prefix and purpose. Understanding parameter routing is essential for implementing origin-specific functionality like time-shifted viewing with MediaPackage.

**Parameter routing rules**  
MediaTailor uses the following routing rules for query parameters:
+ **Origin parameters (no prefix):** Parameters without a specific prefix are passed through to the origin server for origin-specific functionality
+ **ADS parameters (`ads.` prefix):** Parameters prefixed with `ads.` are sent to the Ad Decision Server
+ **Manifest parameters (`manifest.` prefix):** Parameters prefixed with `manifest.` are used for CDN routing and authorization

**Example Parameter routing example**  
The following session initialization demonstrates parameter routing:  

```
POST /v1/session/123456789/originId/index.m3u8
{
    "adsParams": {
        "param1": "value1",
        "param2": "value2"
    },
    "manifestParams": {
        "auth_token": "abc123"
    }
}
```
In this example:  
+ `param1` and `param2` are sent to the ADS
+ `auth_token` is used for CDN routing and authorization
+ Parameters without prefixes would be passed to the origin server

## Origin server parameter behavior
<a name="origin-parameter-behavior"></a>

Parameters passed to origin servers enable origin-specific functionality such as time-shifted viewing, content filtering, and authentication.

**Common origin parameter use cases**  
Origin parameters are commonly used for:
+ **Time-shifted viewing:** `start` and `end` parameters for MediaPackage time-shifted content
+ **Content authentication:** Authentication tokens required by the origin server
+ **Content filtering:** Parameters that control which content variants are returned
+ **Origin-specific features:** Any parameters that the origin server uses for content processing

**Important**  
Parameters are processed at session initialization and maintained throughout the session. To modify parameters like time-shift windows, you must create a new session with updated values.