What are the coding methods for sending SMS by mobile phone?

The specifications related to sending and receiving SMS mainly include GSM 03.38, GSM 03.40 and GSM 07.05. The first two mainly describe the technical realization of short message (including coding mode), while the latter explains the DTE of short message in detail. There are three ways for DCE interface standard (AT command set) to send and receive short messages: block, text and PDU. Block mode is rarely used at present; Text mode is plain text mode, and different character sets can be used. Technically, it can also be used to send Chinese short messages, but domestic mobile phones basically do not support it, mainly used in Europe and America. All mobile phones support PDU mode, and any character set can be used, which is also the default coding mode of mobile phones. On the surface, the PDU string is a string of ASCII codes consisting of' 0'? ' 9 '、' A '？ F' these numbers and letters. They are 8-byte hexadecimal numbers. PDU string contains not only the message itself that can be displayed, but also many other information, such as SMS service center number, target number, coding method and so on. In PDU mode, you can use three codes to send short messages: 7-bit code, 8-bit code and 16-bit code. In the introduction of GSM, PDU consists of two parts: short message center address (SMSC) and transmission protocol data unit.