Bulk SMS | SMS Gateway | MMSC | SMSC

What is an SMS Bulk service? What are the different forms of bulk SMS and how do they work?


Bulk SMS is a service that allows you to send a huge number of SMS or text messages to a targeted audience in a short period of time. The text is sent by an application, and the recipients are mobile phone users.

The service user may send identical or distinct SMS to the specified recipients. A bulk SMS sender loads the target phone numbers into either a web portal or a software application.

After defining a target list, he can schedule various campaigns.

What is Bulk SMS Service?

How an SMS works in the GSM network?

A sender must have an active SIM card on a mobile device in order to send a usual SMS. The process involves tying a text, choosing a recipient, and pressing the send button. While in the case of bulk SMS the sender is an application. If the target number is active, the network delivers the text otherwise, the application gets an error response.

What is a text message as per the GSM standards?

An SMS is a message that has been encoded in accordance with the gsm standards. Both the sender and the recipient need to follow the same format and procedures mentioned in the protocol specifications for the service. The use of standard protocol enables an SMS text to be displayed in a human-readable format on any handset. GSM map is the message format protocol that encapsulates text and other details in a standard format.

What types of messaging flows are there?

Application to Person (A2P) messaging is the type of messaging where the software or web application sends SMS to mobile devices. The sender application uses APIs of the bulk SMS service provider. Sending an SMS from the web portal is an example of A2P messaging. 

The companies such as banks integrate APIs into the software application for sending a text from a back-end software to the service user. OTP message is one of the examples where an online money transfer transaction authorizes a bank customer.

Person to Person (P2P) messaging is the primary and essential messaging service that a mobile operator provides to its subscribers, along with Voice. In p2p messaging, a  mobile subscriber sends a text or SMS  to another mobile subscriber. Sending an SMS from your phone to a friend’s phone is an example of P2P messaging. The sender and receiver may belong to the same or different mobile network operators.

Mobile operator bills the service user for SMS. The cost is based on the location of the sender and receiver. For example, if a subscriber wants to send international SMS, then prices are higher as compared to a local SMS.

Person to Application (P2A) is a scenario where a mobile user sends a text to a software application. Using a short code (e.g., 515151) to send an SMS for voting or any other service (such as checking your bank account balance) is an example of P2A.

What is Short Messaging Service in Bulk?

Sending and receiving a text is an essential function in the GSM network. It is under the control of a mobile operator. The facility gets active with the provisioning of a sim card on HLR.

SS7 is the transport network that encloses text inside the protocol messages in an encoded byte stream. The maximum allowed length is 160 bytes. If a message is too long and exceeds the maximum length. It is segmented at the source and afterward assembled at the destination.

What is Bulk Messaging Service? 

Some companies are providing platforms for sending and receiving texts using the web or a software application. The platform offers a bulk messaging service. A service user can connect to the platform over the internet. 

The platform exposes the APIs to use the service APIs that can be integrated by an SMS user in an SMS software application. Enables a user to send bulk text, without deploying an SMS gateway software and connecting to a complex telecom network.

What are the advantages of a bulk SMS service?

  1. Being a basic service, SMS works on all types of devices.  In many countries, most of the population is living in rural areas and doesn’t have smartphones. Enables the advertisement on mobile phones without an active internet connection.
  2. People read SMS more often than reading emails. SMS gives an alert to the user, and then the user checks SMS in most cases.
  3. SMS can be targeted based on the current location, while any other service does not have a real-time subscriber location.
  4. Alphanumeric sender id provides better brand awareness.  Sending an SMS from the mobile device displays the sender’s mobile number. With SMS API, a service user gets an option to set a sender id based on the brand he wants to promote.
  5. Extensive coverage with messaging. These days almost everyone carries a mobile phone. To advertise any business, mobile phones are the biggest platform to reach the target audience.
  6. SMS gateway hides the complex structure of the telecom network. Enables a service user to develop a bulk SMS application quickly.
  7. Almost every business model has a use case for bulk SMS service. Banks, stores, schools, etc. require bulk SMS.

How to use a software application and gateway for bulk SMS?

If a company or person wants to develop software for bulk SMS, there are different options.

Connecting Directly To Mobile Operators over SS7/Sigtran:

For direct mobile operator connection, the SS7 or SIGTRAN protocol is the option. The SMS gateway or bulk SMS application connects to all operators over the ss7 or Sigtran (SS7 over IP) link. For service users, the app provides SMPP or HTTP-based bulk SMS APIs. The SMS gateway hides all protocol-level difficulties. Direct connection to ss7 or Sigtran, enables the bulk SMS service providers,  fast and accurate delivery of SMS. It’s a cheaper option, as this offloads the mobile operator’s SMSC.

Connect to the SMSCs of mobile operators over SMPP.

With this option, the bulk SMS service application connects network operator SMSCs over SMPP Protocol.  For sending and receiving a text.

Using Aggregators over SMPP or HTTP-based APIs:

With this option, an SMS gateway service provider connects to other agree-gators for sending SMS to mobile phones.

What is a Long and Short Code used for messaging?

Shortcode is a 5 or 6 digits number (e.g., 344512), which is easy to remember. A mobile device can send an SMS to a shortcode.

Telecom networks route the shortcode towards the serving gateway for that shortcode. Gateway routes messages to the serving bulk SMS receiver application or content provider.

A content provider can rent out a Short Code from an SMS service provider. 

Using a shortcode a business can get queries from mobile subscribers. Later a web portal can show all received questions.

SMS received has a sending party contact number. No need to buy a database for target customers and get a pool of interested customers for the company. A long code is a 10 digits number.

Shared long or Short Code for bulk SMS:

A number can be shared between many content providers. Providers can be differentiated based on the KEYWORD. This option is a low cost than having a full dedicated short or long code.

MT-SMS Call flow by bulk SMS service user: 

Mt SMS call flow or A2P SMS call flow, is for messages sent by a user or content provider from a software to a mobile device. The application submits SMS (text, mobile number, source number) over SMPP or HTTP, to the bulk SMS gateway.

Bulk SMS gateway does an HLR lookup over  SS7/Sigtran to get the IMSI and MSC numbers of the subscriber. An HLR lookup over ss7, SRI-SM GSM MAP level message is sent over ss7 to the HLR of the subscriber.

If an error response is present in response to the HLR lookup, an error is sent to the SMS application software from the gateway in the delivery report. If the error is for temporary problems (e.g. subscriber not reachable), the application may retry after some time.

If the error is permanent (e.g. unknown subscriber), the application may remove the phone number from the list for a more accurate database.

If IMSI and MSC numbers are present in the HLR lookup response. The gateway sends MT Forward SM  to the MSC with IMSI, and the delivery report is sent back to the application upon receiving the MT Forward SM response.

MO-SMS  Call flow for short or long code:

  1. P2A is a type of MO-SMS.
  2. The mobile subscriber sends an SMS to a long or ShortCode. The roaming MSC sends mo SMS to the SMSC of the serving mobile operator.
  3. SMSC address is derived from the SMSC number stored in the phone.
  4. The SMSC sends a text to the gateway serving the short/long code over SS7.
  5. The gateway sends the application, which is serving the short/long code.

What are the services provided by a bulk SMS provider?

E-Mail to SMS service:

This service provides the capability of sending email texts to the mobile device in SMS. A mobile subscriber may subscribe to this service from an SMS gateway service provider. By using this facility, a person can see email text even if there is no internet connectivity.

Excel to SMS:

In this, a service provider can get SMS input in excel with a fixed format. Excel has thousands of SMS for SMS campaign marketing. To send bulk SMS, a service user uploads the excel to the service provider portal for sending SMS to all numbers mentioned in excel. After sending an SMS, a service provider provides a delivery report.

What is SDK for bulk messaging service integration?

SDK is a software development kit. It is a library of already developed functions to support interaction between user and gateway. Bulk SMS providers expose API to the service user. The SMS service may require complex encoding/decoding of messages.  To hide the complexity, SMS service companies provide the SDK. By including SDK in an application, the user can quickly develop SMS applications. The SDK might be in java, PHP, etc.  For example, it is difficult to parse the response to a message from the hex stream. SDK may provide a call-back function for a response. Where a user can get a response code, text, etc.

How to select suitable APIs for a messaging service?

Bulk SMS provider offers APIs for sending content in SMS. APIs are accessible via the internet from the SMS gateway of the service providers. One can choose any provider across the globe. The following factors help in choosing a bulk SMS provider.

SMS Coverage:

A significant factor is if a provider doesn’t have coverage in an area where SMS needs to be sent then no use of APIs. SMS Coverage might be for a country or a city.

HLR Lookup:

Bulk SMS senders use the HLR lookup service to clean invalid numbers, It gets mobile number portability and real-time location information for a mobile user before sending an SMS. 

This saves cost and can target SMS on the basis of the current location and the serving mobile operator. If a mobile user of country A is roaming in country B, and SMS is targeted to country A  offers, then no use in sending SMS to the user. From mobile number portability, an SMS can be targeted to the subscribers of a particular mobile operator. This is possible from the information obtained by the HLR lookup.

SMS Delivery Reports:

The accuracy and latency are essential for sending SMS. Before buying, get a test account and check the delivery reports and latency.

SMS Cost :

Choose the package which is most suitable for you. An SMS provider gives more validity time for a bulk SMS package. This will help you to decide the quality of the service.

How does a Bulk SMS reseller work?

A bulk SMS provider buys SMS in large quantities from mobile operators. Now it can act as an SMS gateway for other bulk SMS providers. For starting a business, a vendor can get connected to another bulk SMS provider and can provide SMS service to the end-users. This provider is called a reseller. This chain may grow further. The reseller always depends on the original seller. If the seller lost the coverage in an area, the reseller would also lose the coverage. Seller maintains multiple accounts for many resellers. Each has its dashboard to check the statics of the report. A reseller may get connections from various sellers. Based on coverage and cost a seller gateway decided for sending SMS.

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