---
title: "Basic Telephony Concepts"
description: "Documentation for Concepts"
---

## 📖 Introduction

Before configuring Ring2All, it helps to understand basic telephony terms and concepts.

---

## 📞 Key Terms

### Extensions

An **extension** is a phone line inside your organization. Usually a 3-4 digit number like 1001, 1002, etc.

| Property | Example |
|----------|---------|
| Extension Number | 1001 |
| User | John Smith |
| Device | Desk phone, softphone |

### DID (Direct Inward Dialing)

A **DID** is an external phone number that people dial to reach you. 

| DID | Routes To |
|-----|-----------|
| +1-555-123-4567 | Main IVR |
| +1-555-123-4568 | John's Extension (1001) |

### SIP Trunk / Gateway

A **SIP Trunk** (also called Gateway) connects your PBX to the outside world through a VoIP provider like Twilio or Telnyx.

```mermaid
sequenceDiagram
    autonumber
    actor Caller as 👤 Caller (External PSTN)
    participant Carrier as 🌐 SIP Carrier
    participant SBC as 🛡️ Ring2All SBC
    participant Engine as ⚙️ Ring2All PBX Engine
    actor Extension as 🎧 Extension 1001

    Caller->>Carrier: Dial +1-555-123-4567
    Carrier->>SBC: SIP INVITE
    Note over SBC: Validate IP, Pike Anti-flood & ACL
    SBC->>Engine: Authenticated SIP INVITE
    Engine->>Extension: Ringing (SIP 180)
    Extension-->>Engine: Answer (SIP 200 OK)
    Engine-->>SBC: 200 OK
    SBC-->>Carrier: 200 OK
    Note over Caller,Extension: 🎙️ Active RTP Media Session (2-Way Audio)
```

### IVR (Interactive Voice Response)

An **IVR** is an automated phone menu:
- "Press 1 for Sales"
- "Press 2 for Support"
- "Press 0 for Operator"

### Queue

A **Queue** holds callers until an agent is available. Used for support lines, sales teams, etc.

### Ring Group

A **Ring Group** rings multiple extensions simultaneously or sequentially until someone answers.

---

## 📊 Call Flow Example

```mermaid
flowchart TD
    Call["📞 Incoming Call (+1-555-123-4567)"] --> Route["🔀 Inbound Route (Matches DID)"]
    Route --> Time{"⏰ Time Condition (Business Hours?)"}
    Time -->|Yes| IVR["🗣️ Main IVR Menu"]
    Time -->|No| Closed["🌙 After Hours Announcement"] --> VM["📼 Voicemail"]
    
    IVR -->|"Press 1"| Sales["👥 Sales Queue"] --> Agent1["🎧 Sales Agent"]
    IVR -->|"Press 2"| Support["🛠️ Support Queue"] --> Agent2["🎧 Support Tech"]
    IVR -->|"Press 0"| Reception["🛎️ Operator (Ext 1000)"]
```

---

## 🔗 SIP Basics

### SIP (Session Initiation Protocol)

The protocol that makes VoIP calls work. You'll see these terms:

| Term | Meaning |
|------|---------|
| **SIP Server** | The PBX IP address |
| **SIP Port** | Usually 5060 (UDP) or 5061 (TLS) |
| **Username** | Extension number |
| **Password** | SIP password |
| **Register** | Phone connects to server |

### Registration

When a phone "registers," it tells the PBX:
- "I'm extension 1001"
- "Reach me at this IP address"

This allows the PBX to route calls to the phone.

---

## 📞 Call Types

| Type | Description |
|------|-------------|
| **Internal** | Extension to Extension (1001 → 1002) |
| **Inbound** | Outside caller → Extension |
| **Outbound** | Extension → Outside number |

---

## 💡 Tips

> [!TIP]
> **Test internally first**: Make extension-to-extension calls before testing external calls.

> [!TIP]
> **Check registration**: Most problems are phone registration issues.

---

## 🔗 Related

- [Getting Started](getting-started.md)
- [Extensions](../pbx/extensions/extensions.md)
- [Gateways](../pbx/routing/gateways.md)