Outbound SIP Trunk Requirements

Overview

This article covers the requirements for configuring an outbound SIP trunk from Sharpen to a remote customer endpoint. For requirements related to inbound SIP traffic coming from a remote destination into Sharpen, refer to Inbound SIP Trunk Requirements.

1. Customer SIP Endpoints

To get started, the following information must be provided to your Sharpen Client Success Manager:

• One or more publicly accessible IP addresses for your SIP endpoints. For security reasons, IP whitelisting must be performed by Sharpen; customers cannot add whitelisted IPs directly.

• SIP and RTP port numbers, if different from Sharpen's default ports listed in Section 3.

• Expected call concurrency estimates, including average and maximum concurrent calls.

Once Sharpen has configured your IP addresses, they will appear in Admin > SIP Trunks, where you can assign them friendly names. From there, you can create a SIP Trunk Group on the same page and add your available SIP trunks in the order you want them used (see Section 4 for routing behavior).

2. Authentication and IP Whitelisting

Sharpen will whitelist your provided IP addresses on our outbound Session Border Controllers (SBCs). You will also need to whitelist the following Sharpen outbound gateway IPs on your endpoint. Contact your Client Success Manager if you are unsure which IP list applies to your organization.

Main Outbound Gateways

• 107.23.194.169

• 107.23.195.119

• 107.23.101.107

Condo IZ1 Outbound Gateways

• 18.204.61.135

• 184.73.214.192

• 54.157.9.182

3. Ports and Traffic Requirements

Configure your endpoint to allow the following traffic from Sharpen:

4. Routing Strategy

Sharpen uses an active/backup routing strategy for SIP Trunk Groups. Calls are attempted in the order that trunks are listed within the group.

How failover works:

• Every call first attempts the first IP address in the trunk group.

• If that IP does not respond or returns a 500 error, Sharpen immediately tries the next IP in the group.

• If a connection succeeds on a secondary or tertiary IP, the call proceeds normally.

• Any IP that fails is marked offline. Sharpen will attempt to restore it every 15 minutes. If the attempt succeeds, the trunk is returned to its position in the active order. If it fails again, it remains offline and continues to be retried every 15 minutes until it recovers or is manually removed from the group.

• If a customer endpoint accepts IP traffic but does not respond with SIP signals ("soft down"), there will be a delay of up to 60 seconds before Sharpen proceeds to the next IP. To avoid this delay, the trunk can be manually removed from the group. Note that trunk group order changes are cached on a 15-minute interval and may take up to 15 minutes to take effect.

• If all IPs in the group are exhausted without a successful connection, the call is disconnected. Sharpen has internal alerting in place to notify customers if this becomes an ongoing issue.

5. Dial Plan Configuration

Outbound call formatting is controlled through Sharpen's Dial Plan and SIP Line configurations in the Admin module. This is enabled on a per-organization basis as customers onboard their own SIP trunking.

Sharpen uses SIP OPTIONS messages to verify that a remote endpoint is reachable before sending calls to it. When using a SIP Trunk Group with multiple trunks, Sharpen will detect unavailable trunks and automatically fail over to the next available trunk in the group. Even with a single-IP trunk group, Sharpen can detect a service disruption and fail over to the next dial plan entry.