Mobile Messaging Technologies and Services: SMS, EMS and MMS ...

60 Mobile Messaging Technologies and Services
Application
layer
Transfer
layer
(1)
Segmentation
Originator
SME
3.6.2 Message Structure
TPDU 1 TPDU 2 TPDU 3 TPDU n
(2) Message transport
Figure 3.9 Message structure
(3)
Concatenation
Recipient
SME
In this chapter, the following terminology is used for referring to messages.
A message refers to the subscriber’s perception of the message composed of text and/or
elements such as pictures, melodies, etc. For transport purposes and due to limitations at the
transfer layer, an application may need to segment the message into several pieces called
message segments. A one-segment message is also known as a short message. A message
segment is an element manipulated by an application.
A message segment has a limited payload size. In order to convey a large amount of data,
several message segments can be combined into a concatenated message. 5 The message
concatenation is handled at the application layer. In order to be transported, the message
segment needs to be mapped onto a TPDU at the transfer layer as shown in Figure 3.9.
In the scope of the download service, a message containing one or more objects being
downloaded is called a download message.
In this book, the word octet refers to a group of eight bits (also known as a byte) whereas a
septet refers to a group of seven bits.
3.6.3 SME-SMSC Transactions/Submit, Deliver, Report, and Command
At the transfer layer, six types of transactions can occur between an SME and an SMSC. A
TPDU type corresponds to each one of the transaction types. Figure 3.10 shows the possible
transactions between an SME and the serving SMSC.
SMS-SUBMIT: this transaction corresponds to the submission of a message segment from
the SME to the SMSC. Upon submission of the message segment, the SMSC acknowledges
the submission with the SMS-SUBMIT-REPORT transaction.
5 In several documents dealing with SMS, a concatenated message is also known as a long message