Question

How can we recognize multiple inbound SMS messages as one concatenated message?

Applies To

• Inbound SMS
• Concatenated SMS

Answer

When the receiver replies to a message with more than 160 characters, the message is stored in the Vonage API dashboard as two or more messages. Some users have a need to display the multiple messages as a single message.

To concatenate multiple inbound SMS messages you need to make use of the concat parameters passed to us by the carriers. You should be able to find 'concat', 'concat-ref', 'concat-total' and 'concat-part' in the req.query coming from the Vonage API Callback call.

This capability is dependent on the carriers supporting or sending these, though. If we receive UDH information from a carrier, we forward all the concat parameters to your application, both through GET or POST. Receiving these parameters from Vonage is not something that can be activated on our settings if they are absent.

There is not a perfect way to detect concatenated messages without UDH information being provided by carriers. If your inbound SMS carriers don't support the UDH information, it might make sense to consider messages coming from the same number and within a close timestamp as concatenated. This could be reasonably reliable, but not 100% accurate. This is only a suggestion and the configuration for this it would need to be carried out on your side.

Due to carrier limitations, carriers US Sprint and Verizon do not provide 'concat', 'concat-ref', 'concat-total' and 'concat-part' information for inbound concatenated SMS, so this information is not passed to the user.

Additional Information

More information on this is available in the developer documentation on SMS Concatenation and Encoding.