Possible delivery rates for a `https://developers.google.com/ad-manager/api/beta/reference/rest/v1/networks.lineItems#LineItem`. It dictates the manner in which the LineItem is served.

| Enums ||
|---|---|
| `LINE_ITEM_DELIVERY_RATE_TYPE_UNSPECIFIED` | No value specified. |
| `AS_FAST_AS_POSSIBLE` | The booked impressions may delivered well before the end time. Other lower-priority or lower-value LineItems will be stopped from delivering until the LineItem meets the number of impressions or clicks it is booked for. |
| `EVENLY` | LineItems are served as evenly as possible across the number of days specified in a LineItem's duration. |
| `FRONTLOADED` | LineItems are served more aggressively in the beginning of the flight date. |