SMS Concatenation

By concatenating SMS messages, you can send long messages that exceed the standard 160 characters (140 bytes) in length. These concatenated SMS messages will be viewed by the recipient as a single SMS message.

The default maximum message parts allowed can be configured per API connection in your Developers’ Central account (defaults to three parts when you create a new API connection) or per message via an additional parameter in the API. You can view the parameters list page to see the name of the parameter for the API you are using.

How to Concatenate Long SMS Messages

  • Concatenation is achieved by adding special instructions in each SMS message part to indicate the order that the message parts should be displayed in.
  • Each message part contains this data in the form of user data headers (UDH) for the identification and ordering information.
  • As a result the space available for actual message data in each message part is reduced by six bytes but the SMS messages are combined.
  • You can view the parameters list page to see the name of the parameter for the API you are using and to see a concatenated example.

How to Concatenate Plain Text Messages

  • When concatenating plain text SMS messages, the space available in each message part is reduced by six bytes, leaving space for 153 characters per message part.
  • Please note that some characters need to be escaped (flagged with an extra character) when transmitted from the Clickatell gateway to the receiving networks, resulting in them using two characters. 

Numbers to remember:

  • Maximum message parts are 35 (if no escaping is required, else more parts can be sent)
  • 160 characters allowed in a single SMS message part
  • 153 characters used per message part when sending concatenated messages

How to Concatenate Unicode Messages

  • When messages are sent as unicode a 16-bit (two-byte) character encoding is required by the recipient's mobile handset.
  • A single Unicode SMS can thus contain a maximum of 70 characters.
  • As with standard text messaging the overall space for actual message data is reduced by three characters (six bytes) when sending concatenated SMS messages.

Numbers to remember:

  • Maximum message parts are 20
  • 70 (16-bit) characters allowed in a single SMS message part
  • 67 (16-bit) characters used per message part when sending concatenated messages

Concatenating 8-bit messages

For 8-bit concatenated messages, each SMS can support up to 140 bytes including the UDH headers. The Clickatell gateway allows up to 20 message parts.