Concatenated SMS messages allow a phone to send messages longer than 160 characters. The sender composes a message normally, however, behind the scenes, the phone detects the message length. If the message is less than or equal to 160 characters, the phone sends a one standard SMS message. However, if the message is greater than 160 characters, the phone automatically divides the longer message into multiple, shorter SMS messages which are then transmitted to the recipient separately.
The recipient’s phone takes these multiple, shorter SMS messages and recombines them into the original message which was sent. Because the individual segments of the complete message need to be recombined in this way, this is referred to as ‘concatenated SMS’. In order to achieve this seamless delivery, additional information is added to each individual concatenated SMS message. This additional information, referred to as the user data header (UDH), provides identification and ordering information. For example, the UDH could relate the three individual concatenated SMS messages to each other, and indicate the order for recombination.
Character Count Thresholds
The character limits for individual concatenated SMS messages results in various thresholds for which additional individual concatenated SMSmessages will be required to support sending a larger overall message:
GSM encoding:
- 1 standard SMS message = up to 160 characters
- 2 concatenated SMS messages = up to 306 characters
- 3 concatenated SMS messages = up to 459 characters
- 4 concatenated SMS messages = up to 612 characters
- 5 concatenated SMS messages = up to 765 characters
- etc. (153 x number of individual concatenated SMS messages)
UTF-16 encoding (including special characters):
- 1 standard SMS message = up to 70 characters
- 2 concatenated SMS messages = up to 134 characters
- 3 concatenated SMS messages = up to 201 characters
- 4 concatenated SMS messages = up to 268 characters
- 5 concatenated SMS messages = up to 335 characters
- etc. (67 x number of individual concatenated SMS messages)
These thresholds are an important consideration for a number of reasons including billing, and the programmatic interfacing with SMSgateways.
Generally, telephone companies count individual concatenated SMS text messages separately even though they are being recombined at the phone into a single message. This means a message containing 180 characters could potentially invoke a charge for two SMS text messages, even if the sender/recipient only sees a single message.
The TeleMessage platform lets you choose up to the maximum number of concatenated SMS messages you would like to send. Note that if you send a message with more characters than the threshold limit, your message will be cut off. For example, if you send a message with more than 459 characters, but only allow up to 2 concatenated messages, your message will be cut off at 306 characters and the recipient will not receive the entire message.