Basic Telephony 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.

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

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.