How SignalWire Works with Carriers to Send Messages

The process of how messages get to the end-users from a bird's eye view.

The process in which a phone call, message, or fax between a SignalWire customer and the overall end-user can be tricky to explain given the number of moving parts and the complexity of the telecommunication industry as a whole. To better explain this process and SignalWire’s role in it, here is a diagram to illustrate it.

This diagram explains how the system works. It’s easiest to first explain what upstream carriers are. Upstream carriers are SignalWire’s carrier peers who own phone numbers and are responsible for the transmission of your message from the sender (SignalWire’s customers) to the downstream carrier peers. SignalWire, being an API company, provides a simple to use portal which allows you to purchase phone numbers from the upstream carrier peers and also allows you to configure those numbers to be able to accomplish your business’s use case. Whether that be setting up an IVR, building conference calls, marketing through SMS, or anything else. That being said, it is important to note here that SignalWire is not a carrier. SignalWire does not own any of the phone numbers in your SignalWire Space and currently will not block any traffic, unless your messaging is found to be against our messaging code of conduct. Under this circumstance, SignalWire will notify you and request more information so that your SignalWire Space can be verified and your account’s block can be lifted.

When a message is sent by the sender, it is transferred from the sender to SignalWire’s APIs, to the upstream carrier, and then to the downstream carrier. The downstream carrier is then tasked, in the case of messaging, with handling an initial vetting of content messaging. Downstream carriers and their algorithms primarily vet for content correlated with high amounts of spam. Such content includes, but is not limited to:

  • Social Marketing
  • Collections
  • Financial Services**
  • Auto Loans
  • Mortgages
  • Payday Loans
  • Short-Term Loans
  • Student Loans
  • Debt Consolidation, Reduction, or Forgiveness
  • Insurance***
  • Gambling, Casino, and Bingo
  • Gift Cards
  • Sweepstakes
  • Free Prizes
  • Investment Opportunities
  • Lead Generation
  • Recruiting
  • Commission Programs
  • Credit Repair
  • Tax Relief
  • Illicit or Illegal Substances (Including Cannabis)****
  • Work From Home
  • Get Rich Quick
  • Uggs or RayBan Campaigns
  • Phishing
  • Fraud or Scams
  • Deceptive Marketing
  • SHAFT Content (Sexual, Hate, Alcohol, Firearms, or Tobacco)

While there are situations in which some of these use cases are legitimate, because of the high correlation of spam associated with them, they are often blocked by the downstream carrier peers. The best recommendation SignalWire can give to make sure your legitimate business that falls under one of these use cases still gets passed is to have the traffic pre-approved by the carriers. This can be achieved by registering your brand and all 10DLC campaigns (whether they are included in this list of use cases or not) through the Campaign Registry, which can be done within your SignalWire Space. It is important to note that because the Campaign Registry’s goal is to reduce spam being sent to the end-users, approval is not guaranteed if the carriers do not believe your traffic is legitimate. It is also important to note that outside of sending your registration information to the carriers for approval, SignalWire has no control or influence over the final verdict of the Campaign Registry.

When the message has been received by and approved by the downstream carrier, it is then sent to the Mobile Network Operator (otherwise known as the MNO). The MNO then proceeds with one final vetting process to check for spam, and then on approval, sends the message to the end-user. MNOs are perhaps best thought of as the “cellphone carriers” most people know of (Verizon, T-Mobile, AT&T, US Cellular, etc.). It is possible, albeit rare, to have pre-approved traffic on the Campaign Registry be blocked by filters and a given MNO’s algorithms. In these cases, the sender would have to contact the MNO to get those filters lifted. Upon MNO approval, the content is then sent from the MNO to the end-user.


*The Campaign Registry, which is a third-party vetting process, only applies to 10DLC messaging traffic. No phone calls, faxes, or messaging coming from either phone number types such as toll-free or shortcode run through the Campaign Registry's vetting process.

**Financial services include, but are not limited to, account notifications, marketing, collections, or billing for high-risk, subprime lending, or credit card companies as a whole.

***Insurance messaging includes car, home, disaster, or health insurance.

****While SignalWire acknowledges the state-level legality of cannabis in certain areas, it should be taken as a blanket statement that because cannabis is not legal at the federal level, content explicitly reflecting the marketing of cannabis is not allowed.

SignalWire in Seconds

If you want to see a live explanation of how SignalWire works with our carriers to send a message, call, or fax, feel free to watch this SignalWire in Seconds video. If you want to learn more concepts about SignalWire in just a few short minutes each, check out our YouTube Channel!

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