---
title: FAQs
slug: dynamic-sip-trunking/faqs
docTags: 
createdAt: 2026-01-24T09:02:46.432Z
---

# FAQ – Exotel SIP Trunking



### 1. What is Exotel SIP Trunking?

Exotel SIP Trunking connects your PBX, Contact Center, or Voice AI system to the telephone network over SIP.
 It supports inbound, outbound, and bi-directional calling.

### 2. What systems can I connect using SIP Trunking?

Any SIP-compliant system such as Asterisk, FreePBX, SBCs, Contact Centers, or Voice AI platforms can be connected.

### 3. What are inbound and outbound calls?

Outbound calls go from your SIP system to phone numbers.
 Inbound calls come from phone numbers to your SIP system.

### 4. What is mode: pstn?

pstn routes calls to and from the telephone network.
 This is the default mode for standard calling.

### 5. What is mode: flow?

flow routes calls to Exotel Flows such as Voicebot or App Bazaar applets.
It is required for Voicebot and non-Connect applets.

### 6. Do I need to set a Destination URI even when using Flow?

Yes. A Destination URI is mandatory on the trunk for routing and validation, even if the call later goes to Flow.

### 7. Do I need a static IP?

A static IP is required for outbound calls and StreamKit.
 Inbound calls can use either IP or FQDN.

### 8. Can I use FQDN instead of IP?

Yes, FQDN is supported only for inbound calls (PSTN → SIP).
 Outbound calls require IP-based whitelisting.

### 9. Do I need to whitelist IPs for inbound calls?

No. For inbound calls, Exotel initiates the connection and you only need to allow Exotel source IPs in your firewall.

### 10. Do I need to whitelist IPs for outbound calls?

Yes. Your SIP server IP must be whitelisted using the Map ACL API, otherwise outbound calls will fail.

### 11. Which ports should I open on my firewall?

Open  443 (TLS) or 5070 (TCP) for signaling and UDP 10000–40000 for RTP media.

### 12. Do I need to fix source ports for inbound calls?

No. Source ports are dynamic by design.
 You only need to expose a fixed destination port on your SIP server.

### 13. Calls are connecting but there is no audio. Why?

This usually means RTP ports are blocked.
 Ensure UDP ports 10000–40000 are open in your firewall.

### 14. What does “Duplicate resource” error mean?

It means the configuration already exists (IP, number, or trunk).
This error is safe to ignore.

### 15. Which audio codec should I use in India?

Use G.711 (India standard).
 Avoid configuring unnecessary codecs.