A typical EMI/UCP exchange looks like this :
^B01/00041/R/30/A//6667778Universal Computer Protocol9:180594141236/F3^C
The start of the packet is signaled by ^B (STX, hex 02) and the end with ^C (ETX, hex 03). Fields within the packet are separated by / characters.
The first four fields form the mandatory header. the third is the operation type (O for operation, R for result), and the fourth is the operation (here 30, "short message transfer").
The subsequent fields are dependent on the operation. In the first line above, '66677789' is the recipient's address (telephone number) and '68656C6C6F' is the content of the message, in this case the ASCII string "hello". The second line is the response with a matching transaction reference number, where 'A' indicates that the message was successfully acknowledged by the SMSC, and a timestamp is suffixed to the phone number to show time of delivery.
The full specification is available on the LogicaCMG website developers' forum, but registration is required.
The two digit transaction reference number means that an entity sending text messages can only have 100 outstanding messages; this can limit performance.
The destination AdC phone number cannot contain * or # characters, although the originator OAdC can, in which case the text message could not be replied to.
As the protocol is itself text, the text of the SMS message must be encoded twice (characters packed to 7 bits, then encoded as hex), and can not be read from a dump of a message. This also applies to GSM MAP.