# How capacity works

A DID number can use channels included with the DID number service, Capacity assigned directly to the DID number, or
Capacity shared through a Capacity group. These resources allow DID numbers to handle more simultaneous inbound calls,
support temporary traffic increases, and control how inbound call resources are allocated across one or more DID
numbers.

Capacity is evaluated automatically when inbound calls arrive. DIDWW checks the available Capacity resources for the DID
number and uses the highest-priority resource that is available.

For example, a DID number can use included channels first, then dedicated channels, then shared channels, and finally
metered channels if higher-priority resources are already in use.

The following example shows how DIDWW evaluates available Capacity resources when an inbound call arrives.

```
        ---
config:
  layout: dagre
---
flowchart LR
    classDef decision stroke:#fb923c,fill:#fef3c7,stroke-width:2px
    classDef action stroke:#22c55e,fill:#dcfce7,stroke-width:2px
    classDef outcome stroke:#ef4444,fill:#fee2e2,stroke-width:2px
    classDef input stroke:#38bdf8,fill:#e0f2fe,stroke-width:2px

    A([Incoming call]):::input
    B{"Included channels available?"}:::decision
    C["Use included channels"]:::action
    D{"Dedicated channels available?"}:::decision
    E["Use dedicated channels"]:::action
    F{"Shared channels available?"}:::decision
    G["Use shared channels"]:::action
    H{"Metered channels available?"}:::decision
    I["Use metered channels"]:::action
    J["Call rejected"]:::outcome

    A --> B
    B -->|YES| C
    B -->|NO| D
    D -->|YES| E
    D -->|NO| F
    F -->|YES| G
    F -->|NO| H
    H -->|YES| I
    H -->|NO| J
```

The flow starts with the Capacity that belongs most directly to the DID number and then moves through the remaining
configured resources. If no Capacity resource is available, the inbound call cannot be delivered using Capacity
resources.

This priority model allows different Capacity resources to work together while keeping call delivery predictable.

For Capacity type definitions and priority order, see [Channel types](capacity-reference.html#capacity-channel-types)
and [Capacity priority](capacity-reference.html#capacity-priority-values).

## Capacity types

Capacity can be provided through included channels, dedicated channels, shared channels, metered channels, or a
combination of these resources.

Some resources belong to the DID number service, some are assigned directly to one DID number, and others are made
available through a Capacity group. Capacity resources can also use different billing models depending on how they are
configured.

For Capacity type definitions, see [Channel types](capacity-reference.html#capacity-channel-types).

## DID included channels

Some DID numbers include inbound voice channels as part of the DID number service. These channels are the first Capacity
resource used for inbound calls.

When included channels are already in use, other configured Capacity resources can provide additional concurrent call
handling.

For capacity mode values, see [DID capacity modes](capacity-reference.html#capacity-mode-values).

## Dedicated channels

Dedicated channels are flat-rate channels assigned directly to one DID number. They are reserved for that DID number and
are used after included channels.

For a detailed explanation of dedicated flat-rate behavior, see [Flat-rate channels](flat-rate-channels.html).

To assign or unassign dedicated channels, see [Manage dedicated channels](how-to-guides/manage-dedicated-channels.html).

## Shared channels

Shared channels are flat-rate channels assigned to a Capacity group. DID numbers in the group can use the shared
channels when higher-priority Capacity resources are unavailable.

For a detailed explanation of shared flat-rate behavior, see [Flat-rate channels](flat-rate-channels.html) and [Capacity
groups](capacity-groups.html).

To assign or unassign shared channels, see [Manage shared channels](how-to-guides/manage-shared-channels.html).

## Metered channels

Metered channels are pay-per-minute channels assigned to a Capacity group. They provide usage-based Capacity and are
used after higher-priority resources are unavailable.

For a detailed explanation of metered Capacity behavior, see [Pay-per-minute channels](pay-per-minute-channels.html) and
[Capacity groups](capacity-groups.html).

To assign or unassign metered channels, see [Manage metered channels](how-to-guides/manage-metered-channels.html).

## Capacity priority

When multiple Capacity resources are available, inbound calls use available resources according to a predefined priority
order.

This ensures that Capacity resources are consumed consistently and that higher-priority resources are used before
lower-priority resources.

For example, a DID number may have included channels, dedicated channels assigned directly to the DID number, and shared
channels available through a Capacity group. Inbound calls use the available resources according to Capacity priority
until no Capacity remains available.

For priority values and resource order, see [Capacity priority](capacity-reference.html#capacity-priority-values).

## Capacity groups

A Capacity group allows multiple DID numbers to use shared channels, metered channels, or both. Groups are used when
Capacity should be allocated to a set of DID numbers instead of directly to one DID number.

For Capacity group behavior, fields, and limits, see [Capacity groups](capacity-groups.html). To create or manage a
group, see [Create a capacity group](how-to-guides/create-capacity-group.html) and [Manage DID(s) in a
group](how-to-guides/manage-dids-in-group.html).

## Hybrid capacity

Hybrid Capacity combines multiple Capacity resource types within the same Capacity configuration.

This allows inbound calls to move between available Capacity resources as call volume increases.

For example, a DID number may use included channels during normal traffic levels, dedicated or shared Capacity during
higher traffic periods, and metered Capacity when all other available resources have been consumed.

The exact behavior depends on the Capacity resources assigned to the DID number and any associated Capacity groups.

For hybrid capacity priority by capacity mode and channel combination, see [Hybrid capacity
combinations](capacity-reference.html#capacity-hybrid-combinations).

## When capacity is exceeded

Inbound calls use available channels according to Capacity priority. If no configured channel is available, the inbound
call cannot be delivered using Capacity resources.

Use [View capacity usage](view-capacity-usage.html) to review concurrent call usage, capacity exceeded events, and
reports.

## Related resources

- [Capacity reference](capacity-reference.html) - Review Capacity types, modes, priorities, pools, fields, and limits.
- [Flat-rate channels](flat-rate-channels.html) - Learn how flat-rate Capacity resources work.
- [Pay-per-minute channels](pay-per-minute-channels.html) - Learn how usage-based Capacity resources work.
- [Capacity groups](capacity-groups.html) - Understand Capacity group behavior and allocation.
- [Capacity billing](capacity-billing.html) - Understand how Capacity affects billing.

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