What is bulk SMS or bulk SMS service?

Bulk SMS is the process of sending a large volume of SMS or text messages in a short duration of time. The sender of bulk SMS is a bulk SMS service user.  Service user sends the same or different SMS to multiple subscribers. In normal SMS, a user sends a text to another user form a mobile device. While in bulk SMS, an application sends the text to mobile devices. An SMS or text is a message encoded according to the gsm specifications in a fixed protocol format. SMS application or software and handset uses the same GSM protocol standards. This enables an SMS to be visible on any handset in a human-readable format. Network protocols are gsm map over ss7.  The following are the classification of SMS according to various flows.

A2P or Application to person messaging is the type of messaging where an application of software, sends SMS to mobile devices. Sending an SMS from the web portal is an example of A2P messaging.  Useful for the companies requires to send a text from a back-end software to the service user, e.g a bank sends the OTP, from its central system to authorize a transaction.

P2P or Person to Person messaging is basic and legacy messaging, that a mobile operator provides to its subscribers a basic service along with Voice call. In p2p messaging, a  mobile subscriber sends text or SMS  to another mobile subscriber. Sending an SMS from your phone to a friend’s phone is an example of P2P messaging. Sender and receiver may belong to the same or different mobile network operators. Mobile operator charges for an SMS, based on the sender and receiver location. For example, if a subscriber wants to send international SMS, then charges are higher as compared to a local SMS.

P2A or Person to Application messaging is a service where a mobile subscriber sends a text to an application. Sending SMS for voting or any other service (bank account balance check) on short a code (e.g 515151) is the example of P2A messaging.

What is SMS:

SMS or short message is the service provided by a mobile operator to send and receive text messages.  In GSM, SMS is a basic service. controlled by a mobile operator. When a new SIM card is provisioned in HLR, SMS service is also provisioned along with other services.

SS7 is the network protocol for SMS. An SMS text on the wire is 160 bytes long. For sending a long message, the SMS segments the long SMS and the mobile phone reassembles the SMS. This is the basic service which runs on all mobile phones. There are other applications for sending the text but requires an internet connection.

Bulk SMS Service: 

There are vendors that provide a platform for sending and receiving a text. The service platform is reachable over the internet.  Service providers expose SMS APIs. APIs can be integrated by an SMS user in an SMS software application. This enables a user to send bulk text, without deploying an SMS gateway software and connecting to a complex telecom network.

Advantages of bulk SMS service:

  1. SMS service is the basic service on all mobile phones.  In many countries, most of the population is living in a rural area and doesn’t have internet.  This enables the advertisement on mobile phones without an active internet connection.
  2. People read SMS more often than reading emails. SMS gives alert to the user and then the user checks SMS in most of the 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 sender id based on the brand he wants to promote.
  5. Huge coverage. These days almost everyone carrying a mobile. To advertise business mobile phones are the biggest platform to reach the target audience.
  6. SMS gateway hides the complex structure of the telecom network. This enables a service user to easily develop a bulk SMS application.
  7. Almost every business model has a use case for bulk SMS service. Banks, stores, schools, etc. have a need for bulk SMS.

Bulk SMS software or SMS Gateway:

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

Connecting To the SMSCs of mobile operators over SMPP.

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

Short Code and long code for SMS:

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 short code, the Short  Code routing is set in the telecom network in such a way that an SMS is sent to the SMS gateway which is serving node for the code. A content provider can rent out a Short Code from an SMS service provider.  Content/service provider can get queries from the market on Short Code and a web-based panel connects to, shows the full inbox. SMS received have a sending party, a mobile number which is useful for business. No need to buy a database for target customers and get a pool of interested customers for the business.

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 differentiate based on KEYWORD. This option is a low cost than have 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 sending 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 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 the 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 the 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 remover the phone number from the list.

If IMSI and MSC number present in 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 code or Short Code, roaming MSC sends mo SMS to SMSC of 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.

E-Mail to SMS service:

This service provides the capability of sending email text 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 service:

In this, a service provider can get SMS input in excel with a fixed format. The excel has thousands of SMS for an 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 SMS, a service provider provides a delivery report.

SDK For bulk SMS APIs:

SDK is a software development kit. It is a library of already developed functions to support interaction between user and gateway. Bulk SMS providers provide 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 easily 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 when a user can get a response code, text, etc.

Bulk SMS API selection:

Bulk SMS provider provides the 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 very important factor, 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 for a city.

HLR Lookup:

Bulk SMS senders use HLR lookup service, to clean invalid numbers, get mobile number portability information 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 of 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 important 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.  Choose SMS provider, giving more validity time for a bulk SMS package. This will help you to decide the quality of the service.

Bulk SMS Reseller: 

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 will also lose the coverage. Seller maintains multiple accounts for many resellers. Each has own dashboard to check the statics of the account. A reseller may get connections from multiple sellers, based on coverage and cost a seller gateway decided for sending SMS.

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