> For the complete documentation index, see [llms.txt](https://smsc.revicom.ltd/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://smsc.revicom.ltd/how-to-work-with-smsc/concatenated-sms-sending.md).

# Concatenated SMS sending

According to the SMPP protocol specification, the maximum length of one SMS to be sent is:

* for messages in Latin: 160 characters;
* for messages in Cyrillic: 70 characters.

SMS exceeding the maximum length are called **multipart or concatenated SMS** and are usually split into parts when sent. The length of one part is:

* for messages in Latin: 153 characters;
* for messages in Cyrillic: 67 characters.

To send concatenated SMS, one of the following three technologies is employed:

* UDH (user data header) is a special header at the beginning of the text of the SMS;
* SAR is analogue of the UDH header; due to the location in TLV fields, it will not reduce the size of one part of an SMS
* message\_payload is TLV field hosting the entire message content

Detailed information about the above technologies can be found in the [SMPP protocol specification.](https://smpp.org/SMPP_v3_4_Issue1_2.pdf)

:warning:**IMPORTANT:**

In each part of a multipart SMS, the values of the following fields must match:

* service\_type;
* source\_addr\_ton;
* source\_addr\_npi;
* source\_addr;
* dest\_addr\_ton;
* dest\_addr\_npi;
* destination\_addr;
* esm\_class;
* protocol\_id;
* priority\_flag;
* validity\_period;
* registered\_delivery;
* data\_coding.

A message cannot be delivered until all of its parts have been received.

The wait time for all parts of a concatenated message is 10 minutes. If all parts are not received after this period, the message will not be sent.