How Does SMS Work?
Here’s the basics….
SMS stands for Short Message Service, and commonly referred to as text messaging. How does SMS work? At a high level it is very simple but the first thing you need to understand is the difference between Person to Person text messaging (P2P) vs. Application to Person text messaging (A2P). For those of you who already know the basics and want the hardcore technical details, please read on…
Person to Person (P2P) SMS and the Need for an SMSC
Text messaging is part of our everyday activities and most of us send and receive P2P text messages throughout the day. There are literally trillions of P2P text messages sent and received every year, but with mobile applications such as WhatsApp and Viber, the volume of P2P text messages is starting to dwindle and the volume of OTT (Over the Top) messages sent through mobile applications is growing. The diagram below shows how a P2P text message is sent from one mobile phone to another. Understanding the basics will help you understand how everything else works.
In the diagram above, the sender of the text message, is a mobile subscriber of operator A; while the person who the text is being sent to is a mobile subscriber of operator B. Once the person has hit “Send” on their mobile phone, the text message is sent to their home operator (e.g. AT&T). Every mobile operator has a machine called an SMSC (Short Message Service Center).
An SMSC is simply a computer system, running specific software inside of the mobile operator’s network and is designed to receive the text message from you and to deliver the SMS to your friend’s phone through their mobile operator as quickly as possible.
The mobile operator’s SMSC will deliver the message directly to your friend’s phone if the operator has reach (the ability to connect) via an SS7 network. If the operator does not have reach through an SS7 network, it will instead use what is called a P2P hub to deliver the message. A P2P hub is actually a company whose business is to pass messages between mobile operators that can’t send messages directly to each other.
Three important things to note are:
- In most cases an SMS will only be stored by one SMSC (usually the home operator) before final delivery to the intended handset
- An SMSC can deliver to any handset in the world where the home operator has reach
- In the USA all P2P messages are sent via a hub so at least two SMSC’s will be used to deliver the message.
Application to Person SMS (A2P SMS)
A2P SMS message delivery works in a similar fashion, with the key difference being instead of two people communicating through mobile phones, the communication is between a computer application and a person. An example of this is when you receive a text message from your bank or other business. To illustrate this see the following example:
The mechanics in sending an A2P SMS are similar to P2P SMS. Messages flow via the mobile operators’ SMSCs but the key difference is that the message is sent from an enterprise (a business entity) instead of a person. See the diagram below.
At this point it is worth mentioning the two directions in which an SMS message can flow. When it is sent to a mobile phone the text message is referred to as a Mobile Terminated (MT) message, subsequently when a message is sent from a mobile phone it is called a Mobile Originated (MO) message. The way in which the message is delivered is exactly as shown above. When a message is delivered by an SMSC it will return a Delivery Notification to the enterprise providing proof the message was delivered, or the reason for why it failed.
The Need for a Cloud Messaging Provider or Aggregator
An enterprise or small business could choose to directly connect to one mobile operator to handle the delivery for all their messages, but since no single mobile operator can reach every operator means there are messages that will go undelivered. On the other hand the enterprise could choose to have direct connections to several mobile operators at once, this becomes complicated real fast; see the diagram below, which shows the additional overhead and complexity.
Most enterprises would not choose to connect to multiple operators, and have the overhead of managing each one and negotiating separate commercial contracts and technical integrations, hence the need for an aggregator. So what’s an aggregator? It is a business that takes care of the technical and commercial complexities for enterprises and provides them the most cost effective price to deliver anytime, anywhere.
In some cases, an enterprise will use another partner who specializes in marketing, multi-channel communications, or a vertical specialty to send their SMS messages on their behalf, these are referred to as an Application Service Provider (ASP) or communication provider.
How to Send a Message to a Subscriber Anywhere in the World?
Most cloud messaging providers (aggregators) have two ways to send a message, either via a Web Tool or an API. A Web Tool requires no development whereas an API typically requires some basic integration development to get a 3rd party system to send messages. CLX offers both of these solutions as options.
For both the Web Tool and API option, sending an SMS is very similar to sending an Email. All that is required are the following fields:
To: (The Destination Number for the recipient of the message)
From: (Originator or Sender ID to show who the message is from)
Body: Some text to send to the recipient of the message
Once you submit that information via an API or a Web Tool, we take care of the rest of the details, and the message should arrive within a few seconds.