Out-of-Band SHAKEN: What the new FCC Proposal Means for TDM Networks

On April 29^th, the FCC proposed new rules aimed at solving a persistent problem: how to verify the identity of callers when part of the call path runs through legacy TDM systems. The proposal puts a spotlight on out-of-band SHAKEN, a method that could help close the gaps left by traditional in-band approaches.

While STIR/SHAKEN has made strong progress in SIP-based environments, many networks still include older, inflexible TDM components, making full implementation challenging from a technical standpoint. Let’s explore what out-of-band SHAKEN really means, how it compares to in-band alternatives, and why it’s becoming a key focus in the effort to build more secure and trustworthy voice communication.

Why the FCC Is Talking About Out-of-Band SHAKEN

STIR/SHAKEN is one of the most effective tools for verifying caller identity, helping curb spoofed calls by allowing the receiving carrier to confirm the origin of the call. It’s already well-established in SIP networks, but TDM networks remain a challenge due to legacy constraints.

The FCC’s NPRM is currently seeking feedback on how to implement SHAKEN across these TDM environments. While still in the proposal stage, many past FCC actions have shaped international regulation. That’s why global service providers should take note and stay ahead by preparing for potential changes.

STIR/SHAKEN: A Quick Recap

STIR/SHAKEN relies on digital certificates to verify the identity of the calling party. When a call is initiated, the originating service provider signs the call with an attestation level:

• A: Full attestation – the provider knows the caller and the number.

• B: Partial attestation – the provider knows the customer but not the number.

• C: Gateway attestation – the provider can’t verify the source.

These attestations are inserted into SIP headers, allowing downstream systems to validate the caller and take appropriate action — such as allowing, flagging, or blocking the call.

You can find a more detailed overview of STIR/SHAKEN here.

The Roadblocks to Modernizing TDM Networks

SIP networks are natively compatible with STIR/SHAKEN. Custom headers can be added and carried across the network. But TDM, governed by rigid standards dating back to the 1970s, doesn’t allow for that flexibility. Many TDM-based switches lack the software capacity to handle these newer identity fields, making direct STIR/SHAKEN implementation nearly impossible.

To address this, two in-band methods have emerged for inserting SHAKEN identity information into TDM signaling:

1. UUI Field (User-to-User Information):
   Encrypted attestation info can be inserted into the UUI field, one of the few flexible elements in TDM protocols. However, not all networks will pass UUI reliably, especially across intermediary carriers.

2. Trunk Group Segmentation:
   Calls with SHAKEN attestations can be routed through specific trunk groups. But this approach requires coordination across every hop in the call path, making it operationally complex and fragile.

Out-of-Band SHAKEN: A More Scalable Option

Out-of-band SHAKEN offers a more robust path forward. Instead of embedding attestation data within TDM signaling, it’s sent to a centralized service (sometimes called a Call Placement Service). This modern, cloud-based system stores the SHAKEN data separately, allowing the terminating service provider to query it and validate the caller.

Some key things to consider:

• Low latency: The data must reach the service quickly, before the call arrives.

• Time-bound validity: The data is temporary — typically destroyed within 20 seconds — to prevent misuse.

• No reliance on TDM modifications: Ideal for legacy networks where changes aren’t feasible.

While no global standard exists yet for out-of-band SHAKEN, several service providers have already begun implementation using third-party attestation services. However, adoption has been inconsistent, and that’s exactly why the FCC decided to step in. They aim to establish clearer guidelines and ensure interoperability across SIP and TDM domains.

How TelcoBridges Supports Out-of-Band SHAKEN

Whether through our Tmedia gateways or ProSBC, TelcoBridges enables out-of-band SHAKEN with minimal network disruption. Here’s how:

• Data extraction: We capture relevant call data and send it to a third-party attestation provider.

• Flexible signaling: Our platforms insert SHAKEN identity headers for SIP calls or populate UUI fields for TDM where needed.

• Out-of-band enablement: We facilitate seamless interaction with external call placement services — no changes needed on the TDM leg.

Our scripting capabilities, previously discussed in detail here, make all this configurable and adaptable, even as standards continue to evolve.

Preparing for What’s Next

While it’s too early to know exactly where the FCC’s rulemaking will land, the message is clear: SHAKEN needs to work across all networks — SIP and TDM alike.

With TelcoBridges’ proven adaptability and integration with multiple SHAKEN service providers, your network can stay compliant and fraud-resilient. No forklift upgrade required.

Curious about how out-of-band SHAKEN fits into your current setup?
Contact us to explore implementation options tailored to your network environment.