> ## Documentation Index
> Fetch the complete documentation index at: https://docs.leamout.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Core concepts

> The resource and deployment model behind Leamout communications.

## Organizations

An organization is the tenant boundary for customer-owned resources. Telecom APIs resolve an organization before reading or mutating calls, numbers, trunks, carrier connections, SIP domains, subscribers, webhooks, and related resources.

## Voice applications

A voice application groups programmable voice behavior. It can define values such as ring timeout, caller ID, voice URL, and callback URL. Bindings connect a voice application to a phone number, SIP domain, or subscriber for inbound routing.

## Carrier connections and trunks

A **carrier connection** describes an organization's relationship and authentication boundary with a SIP carrier. It can hold inbound source-IP policy, inbound/outbound authentication, codec capabilities, and admission limits.

A **trunk** is a routable SIP service attached to connectivity. BYOC trunks reference a carrier connection and contain one or more physical SIP endpoints. Endpoint priority, weight, health, and cooldown state are part of route selection.

## Numbers

A number is an organization-owned phone-number resource. BYOC numbers can be assigned to a carrier connection. Voice applications can bind to numbers to select inbound behavior.

## Calls

Calls are durable organization-scoped resources. Leamout records direction, state, media state, SIP call ID, route attribution, timestamps, and hangup reason. The public API controls the durable Leamout call rather than exposing internal runtime session identifiers.

## SIP domains and subscribers

A SIP domain defines an organization-owned SIP namespace. Subscribers belong to a SIP domain and authenticate using SIP credentials. Browser clients use the same subscriber model over secure WebSocket.

## Runtime placement vs connectivity ownership

These are independent choices:

| Runtime       | Connectivity    |
| ------------- | --------------- |
| Self-hosted   | BYOC            |
| Self-hosted   | Leamout-managed |
| Leamout Cloud | BYOC            |
| Leamout Cloud | Leamout-managed |

The current product work is centered on the **Self-hosted + BYOC** path. The model is designed so moving runtime placement does not require redesigning communications resources, and changing carrier ownership does not redefine the runtime.