# PBX and SIP Trunk using PortSIP SBC
This topic describes how to configure **PortSIP SBC** to enable interoperability between a **generic SIP trunk** and **PortSIP PBX**.\
The SBC acts as a secure SIP signaling and media boundary, interconnecting the enterprise PBX deployed in a private network with a SIP trunk service hosted on a public network.
***
### 1. Interoperability Topology
The interoperability testing between PortSIP SBC, a generic SIP trunk, and PortSIP PBX was performed using the following deployment model.
#### Deployment Scenario
* The enterprise deploys **PortSIP PBX** within its private LAN to provide internal voice communications.
* The enterprise requires PSTN connectivity and enterprise calling services through a **SIP Trunk** provided over the public Internet.
* **PortSIP SBC** is deployed at the network edge to interconnect the enterprise LAN with the SIP trunk provider and to protect the PBX from direct exposure to the public network.
#### Key Concepts
* **Session**\
A real-time voice communication session established using the Session Initiation Protocol (SIP).
* **Border**\
The IP-to-IP network boundary between the enterprise LAN (where PortSIP PBX resides) and the public network hosting the SIP trunk.
#### Call Flow Overview
The high-level call flow for this topology is:
```
Extension <-> PortSIP PBX <-> PortSIP SBC <-> SIP Trunk
```
This architecture ensures secure signaling, controlled media traversal, and protocol normalization between the PBX and the SIP trunk provider.
***
### 2. Configuring PortSIP PBX
Before configuring the SBC and SIP trunk, ensure that the PortSIP PBX is installed and operational.
#### Prerequisites
Complete the following PBX setup steps:
1. [Install PortSIP PBX](/portsip-communications-solution/portsip-pbx-administration-guide/1-installation-of-the-portsip-pbx/installation-of-portsip-pbx-v22.x/install-portsip-pbx.md)
2. Perform basic [PBX configuration, including system and tenant setup](/portsip-communications-solution/portsip-pbx-administration-guide/2-portsip-pbx-management.md)
Refer to the corresponding PBX installation and configuration guides for detailed instructions.
***
### 3. Configuring PortSIP SBC
Install and [configure the PortSIP SBC](/portsip-communications-solution/portsip-pbx-administration-guide/9-configuring-portsip-sbc.md) according to your deployment requirements.
> ❗**Note**\
> If WebRTC endpoints are used, ensure the SBC is configured for WebRTC support as described in the [*Configuring SBC for WebRTC* guide](/portsip-communications-solution/portsip-pbx-administration-guide/9-configuring-portsip-sbc/configuring-sbc-for-webrtc.md).
***
### 4. Adding the SIP Trunk to PortSIP PBX
This section describes how to add the SIP trunk to PortSIP PBX when the SBC is used as an outbound proxy.
#### Assumed SIP Trunk Parameters
* SIP trunk is reachable over the public Internet
* SIP trunk IP address: `52.214.181.141`
* SIP signaling port: `5060`
* Transport protocol: `UDP`
* Authentication mode:
* IP-based authentication **or**
* Register-based authentication
***
#### Step-by-Step Configuration
1. **Sign in to the PortSIP PBX Web Portal**
* Use **System Administrator** credentials.
* Navigate to **Call Manager > Trunks**.
2. **Add a New Trunk**
* Click the arrow button and select:
* **IP-based Trunk** or
* **Register-based Trunk**, depending on the SIP trunk type.
3. **Configure Basic Trunk Settings**
* Enter a **friendly name** for the trunk.
* Set **Host Domain or IP** to the SIP trunk IP address:
```
52.214.181.141
```
* Set **Port** to `5060`, or to the actual port provided by the SIP trunk provider if different.
4. **Configure the Outbound Proxy (SBC)**
* Set **Outbound Proxy Server** to the **private IP address of the SBC**, for example:
```
192.168.1.73
```
* Set **Outbound Proxy Server Port** to:
```
5069
```
> By default, PortSIP SBC listens on TCP port 5069 for SIP traffic from the PBX.
5. **Select Transport Protocol**
* Select **TCP** as the transport.
* Click **Next**.
> **Note**\
> PortSIP PBX communicates with the SBC using TCP by default. Ensure the selected transport matches the SBC configuration.
6. **Configure Authentication (Register-Based Trunk Only)**
* Enter the **Authorization Name** and **Password** provided by the SIP trunk service provider.
* Click **Next**.
7. **Advanced Options**
* Enable **Trunk is located in same LAN with PBX**.
* Disable **Rewrite the host IP of Via header by public IP when sending the request to trunk**.
* Click **Next**.
8. **Assign Trunk to Tenants**
* Since the trunk is created by the **System Administrator**, select one or more tenants that are allowed to use this trunk.
* For details, refer to the *Add the Trunk by System Admin* section in [Trunk Management](/portsip-communications-solution/portsip-pbx-administration-guide/7-trunk-management.md).
Now you are ready to [create the inbound & outbound rules for the call routing](/portsip-communications-solution/portsip-pbx-administration-guide/8-call-route-management.md).
---
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