SMS is also known as ‘Short Messaging Service’ which is basically a two way service that sends and receives text messages over a wireless communication system. It was basically designed for GSM network technology. But the pace at which it gained fame among the user base, it was later adopted by other networks and service providers as well.
Under this service a text message sent by a user is transmitted to the recipient through SMSC (Short Message Service Centre) of the service providers. If for any reason, the recipient is unavailable, the message is placed in a queue and is delivered to the recipients when they are available.
One of the defining characteristics of SMS messages is the maximum length of 160 7-bit characters (140 octets). Although early drafts of the specification did not specify any standardized methods for concatenating SMS messages, SMS messages can be concatenated to form longer messages by following the concatenation method based on the header in the TP-User Data field as specified in 3GPP TS 23.040 although compliance to this protocol is not required. It is up to the user agent to decide whether to limit the length of the message, and how to indicate this limit in its user interface if necessary