📘 SIP Trunk Specifications

🔍 Overview

Customers can securely connect their own PBX systems via our SIP Trunk.
Each SIP Trunk is redundant, offering two SIP registrations to ensure failover in case of outages or connectivity issues.

If your PBX becomes unreachable, malfunctions, or all concurrent channels are in use, our Trunk Failover feature automatically reroutes all incoming calls to the designated failover dial plan.

🧠 Summary

Category	Value
Protocol	SIP/UDP
Authentication	SIP DIGEST
Codecs	G.711A / G.711U
DTMF	RFC2833
T.38	Not supported
Caller ID	P-Asserted-Identity
Failover	Dual SIP Trunks
Expiry Timer	1800 seconds
Format	E.164+
Keepalive	OPTIONS

✨ Key Features

✅ Limit concurrent calls
✅ Restrict access by IP or subnet
✅ Restrict destinations by country or prefix
✅ Limit total calls per hour/day/week to prevent fraud
✅ One SIP Trunk = two SIP accounts for redundancy
✅ Handle multiple incoming numbers per trunk
✅ Use multiple Caller IDs per trunk

⚙️ Specifications & Technical Considerations

📡 Protocol

SIP/UDP

SIP over UDP is supported — TCP is not supported.

📜 Related Standards

RFC2833, RFC3261, RFC3264, RFC3325, RFC3326, RFC4566

While we aim for full standards compliance, minor deviations may occur to maintain compatibility with specific devices.

🧩 Supported SIP Methods

ACK, BYE, INVITE, OPTIONS, REGISTER

Other SIP methods may be ignored.

🎧 Supported Codecs

G.711A (preferred), G.711U

Other codecs may function on certain routes but are not officially supported.

🔢 DTMF

RFC2833 only

SIP INFO and in-band signaling may work, but are not officially supported.

📠 Fax (T.38)

❌ Not supported

T.38 passthrough may work in isolated cases, but support is not guaranteed.

🔐 Authentication

SIP Digest Authentication

SIP REGISTER with DIGEST authentication
SIP INVITE with DIGEST authorization

☎️ Number Format

E.164+ International Format

Example: +3120202020
All SIP headers (Request-URI, From, To) must follow this format.

⏱️ Expiry Timer

Session Expiry (Min-SE): 1800 seconds

👤 Caller ID Configuration

Use P-Asserted-Identity (PAI) header.

The From header should match, and Remote-Party-ID may be used as a fallback (unsupported).
Calls missing valid Caller ID headers may be ignored.

🙈 Anonymous Calling

To hide your Caller ID, use the Privacy header:

Privacy: id

Both From and P-Asserted-Identity headers must still contain valid numbers.

💓 Keepalive

We periodically send OPTIONS packets to check if your trunk is active.

Always respond with 200 OK.
We also reply with 200 OK to received OPTIONS packets.

🔁 Failover

Each customer receives two trunks:

This ensures seamless continuity even during outages or maintenance.