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AT&T SIP Trunks


SIP trunking represents a modern business phone system technology that transports voice calls over IP data networks rather than conventional PSTN lines. SIP trunks enable enterprises to unify voice, video, and data onto a single network.

AT&T offers robust SIP trunking solutions that seamlessly connect an organization’s on-premise IP PBX system to AT&T’s global VoIP and PSTN networks. This facilitates affordable voice calling integrated into wider data infrastructure.

AT&T SIP Trunking Overview

AT&T IP Flexible Reach serves as the carrier’s flagship SIP trunking product. It allows customers to utilize their existing PBX systems while taking advantage of AT&T’s IP voice network.

Key benefits promoted by AT&T include:

  • Global reach to 190+ countries for PSTN calling
  • Scalability to support evolving business needs
  • Cost savings compared to conventional trunks
  • Enhanced reliability via AT&T network failover
  • Strong SLAs for performance and uptime

AT&T SIP trunks fully support wideband audio for superior voice quality along with modern PBX features. The solution integrates securely into a company’s LAN/WAN environment.

How AT&T SIP Trunking Works

AT&T SIP trunks connect an on-premise IP PBX to AT&T’s network infrastructure. Rather than purchasing PRI trunks, the SIP protocol is used for calls over IP.

The customer’s existing PBX system connects via a session border controller (SBC) that serves as the interface point bridging the LAN and AT&T networks. The SBC manages VoIP security, interoperability, and QoS.

AT&T provides customers with SBC solutions from leading vendors like Cisco, Oracle, and AudioCodes. This ensures seamless integration with SIP trunks.

When users make outbound calls, the IP PBX routes them via the SBC and dedicated SIP trunks to AT&T’s backbone. Inbound calls traverse the same path in reverse. AT&T’s network bridges VoIP and PSTN segments to enable global reach.

Cost-Efficiency and Flexibility

Migrating to SIP trunking provides significant cost and efficiency advantages compared to conventional PRI trunks:

  • Lower per-line costs with SIP’s usage model compared to fixed PRI circuits.
  • Ability to efficiently scale up/down trunk capacity to align with changing business needs. Adding SIP lines is fast and low-cost.
  • Convergence of voice, video, and data over IP. No need to manage separate networks.
  • Native integration of advanced UC features across sites and devices.
  • Reduced hardware needs rely on software capabilities of SIP vs dedicated PRI gear.

AT&T SIP trunks deliver these benefits to help optimize spending and enable business agility.

Standout Features

AT&T augments core SIP trunking with premium capabilities:

HD Voice – SIP trunks transmit wideband audio for superior call clarity exceeding conventional phone calls.

UC Integration – Native integration with unified communications platforms enables mobility, collaboration, and productivity features.

Global Reach – AT&T’s voice network spans reach to 190+ countries to cost-effectively enable international calling.

Network Resiliency – SIP traffic instantly reroutes to AT&T’s geo-redundant PSTN network if IP connectivity fails. This prevents outages.

PSTN Fallback – Calls route over AT&T’s PSTN if the Internet isn’t available. This guarantees reliability.

Management Portal – Web-based portal assists with trunk management, monitoring usage, and generating reports.

These features optimize SIP trunking functionality, availability, and calling cost-efficiency.

Configuration and Administration

Deploying AT&T SIP trunks involves:

  1. Connecting AT&T IP Flexible Reach Service

An AT&T technician works with the customer to connect AT&T’s IP service to the premise via Ethernet handoff. AT&T provides CPE to tailor performance as needed.

  1. Configuring On-Premise SBC

The customer’s IT team configures the on-premise SBC appliance to register trunks, manage SIP traffic, and bridge networks. AT&T provides configuration guides.

  1. Linking IP Flexible Reach with IP PBX

AT&T helps connect SIP trunk groups from service to the business IP PBX. The customer manages PBX configuration for call routing, DID numbers, UC services, and more based on their system.

  1. Monitoring and Management

AT&T’s web portal allows managing the service, tracking usage, setting thresholds, and generating reports. AT&T also monitors the service proactively for optimization.

Application Notes

Here are the steps to configure AT&T SIP trunks between an Avaya IP PBX and AT&T IP Flexible Reach service:

  1. Procure AT&T IP Flexible Reach

Order the SIP trunking service from AT&T sales. Define required DIDs and expected capacity.

  1. Implement On-Premise SBC

Deploy a certified vendor SBC like the Avaya Aura Session Border Controller. Configure security, SIP protocol settings, and SIP trunk interface.

  1. Configure Avaya IP PBX

Create a SIP entity linking the SBC trunk group in Avaya Communication Manager. Assign DID numbers and dialing rules.

  1. Test End-to-End Calling

Validate outbound and inbound PSTN calls succeed via the SIP trunks. Optimize configurations as needed.

  1. Train Admins

Review management portal usage with IT admins. Monitor service quality and usage trends.

Following this process delivers a robust production SIP trunking environment. AT&T’s team can provide ongoing optimization and troubleshooting assistance.


AT&T provides enterprise-grade SIP trunking solutions to augment existing customer PBX investments with VoIP capabilities. Integrating SIP trunk infrastructure with AT&T’s global networks enables organizations to cost-effectively scale calling capacity while benefiting from IP voice networking.

With excellent service capabilities, reliability, and customer support, AT&T SIP trunks represent a compelling option for the many businesses relying on legacy Avaya, Cisco, ShoreTel, and other PBX systems. SIP trunking with AT&T provides a strategic pathway to modernize communication infrastructure.