Settings and Message Storage in the SIM

The internal architecture of a SIM card is organized around a processor and there are the following three different types of memory:
1- Read Only Memory (ROM): this memory contains the card operating system along with one or more applications.
2- Electrically Erasable Programmable Read Only Memory (EEPROM): this memory contains all parameters defined by the GSM/3GPP technical specifications and data manipulated by applications. Information saved in this memory is persistently stored even if the mobile station has been powered off.
3- Random Access Memory (RAM): this memory contains data manipulated by applications. Information stored in this memory is lost when the mobile station is powered off.

The storage structure of a SIM card is based on a hierarchy of folders and files. The root folder is known as the Master File (MF), a normal folder is known as a Dedicated File (DF), and a file is known as an Elementary File (EF).

Structure of a Message Segment

Transport Protocol Data Unit


Message Types
SMS-SUBMIT, SMS-SUBMIT-REPORT, SMS-DELIVERY-REPORT, SMS-STATUS-REPORT, SMS-COMMAND.
Text Coding Schemes
The two text coding schemes that can be used in SMS are the GSM 7-bit default alphabet defined in [3GPP-23.038] and the Universal Character Set (UCS2) defined in [ISO-10646].








Text Compression In theory, the text part of a message may be compressed [3GPP-23.042]. However, none of the handsets currently available on the market support text compression. A message with compressed text cannot be displayed properly by an MS that does not support text decompression.

Message Classes
In addition to its type, a message belongs to a class. The TP-Data-Coding-Scheme (TP-DCS) parameter of the TPDU indicates the class to which the message belongs. It has to be noted that in most cases, a message does not belong to any of the four classes. In this situation the message is known as a no-class message and is usually handled as a class 1 or 2 message by the receiving SME.













Coding Groups
A message may belong to one of three coding groups. The coding group indicates what the receiving SME should do with the message once it has been read or interpreted.














Protocol Identifiers
The protocol identifier indicates how the receiving messaging application should handle an incoming Message (normal case, ME data download, SIM data download, etc.).

SMS - Protocol Layers

The SMS protocol stack is composed of four layers: the application layer, the transfer layer, the relay layer, and the link layer. The application layer is implemented in SMEs in the form of software applications that send, receive, and interpret the content of messages (e.g., message editor, games, etc.). The application layer is also known as SM-AL for Short-Message-Application-Layer. At the transfer layer, the message is considered as a sequence of octets containing information such as message length, message originator or recipient, date of reception, etc. The transfer layer is also known as the SM-TL for Short-Message-Transfer-Layer. The relay layer allows the transport of a message between various network elements. The relay layer is also known as the SM-RL for Short-Message-Relay-Layer. The link layer allows the transmission of the message at the physical level. For this purpose, the message is protected to cope with low-level channel errors. The link layer is also known as the SM-LL for Short-Message-Link-Layer. For transport purposes, an application maps the message content and associated delivery instructions onto a Transfer Protocol Data Unit (TPDU) at the transfer layer. ATPDU is composed of various parameters indicating the type of the message, specifying whether or not a status report is requested, containing the text part of the message, etc.

SMS Interworking between Mobile Networks
For this purpose, operators have commercial agreements. Each mobile network counts the number of messages being sent from another network. After a given period of time, these counts are compared and there is a commercial settlement between operators.

Message Structure
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.


SME-SMSC Transactions/Submit, Deliver, Report, and Command
At the transfer layer, six types of transactions can occur between an SME and an 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.

• SMS-DELIVER: this transaction corresponds to the delivery of a message segment from the SMSC to the SME. Upon delivery of the message segment, the SME acknowledges the delivery with the SMS-DELIVER-REPORT transaction.

• SMS-STATUS-REPORT: this transaction corresponds to the transfer of a status report from an SMSC back to an SME.

• SMS-COMMAND: this transaction corresponds to the request from an SME, usually an external SME, for the execution of a specific command by the SMSC.

SMS Basic Features

SMS encompasses a number of basic features. This includes message submission, message delivery, handling of status reports, requests for command execution, reply path, etc. These features are presented in the following sections.

Message Submission and Delivery
Message Sending: Mobile-originated messages are messages which are submitted from an MS to an SMSC. These messages are addressed to other SMEs such as other mobile users or Internet hosts. This feature is also known as the Short Message-Mobile Originated (SM-MO).
Message Delivery: Mobile-terminated messages are messages delivered by the SMSC to the MS. Nearly all GSM handsets support message reception. This feature is also known as Short Message Mobile Terminated (SM-MT). In GSM, messages are sent over SDCCH or SACCH channels whereas, in GPRS, short messages are sent over PDTCH channels.

Status Reports
It is possible for an originator SME to request that a status report be generated upon delivery of the short message to the recipient SME. The status report indicates to the originator whether or not the short message has been successfully delivered to the recipient SME.

Reply Path
This feature is sometimes used by operators to allow the message recipient to provide a reply message ‘‘free of charge’’ for the message recipient. Additionally, for networks supporting several SMSCs, operators sometimes use this feature to get reply messages to be returned to a particular SMSC. For example, an operator could have several SMSCs but only one connected to the Email gateway. In this configuration, if a message is originated from the Internet domain, then the operator uses the reply path to indicate that any message reply associated with this Email-originated message should be submitted to the SMSC connected to the Email gateway.

Addressing Modes
With SMS, several modes are possible for addressing message recipients. The most common addressing mode consists of using the Mobile Station ISDN Number (MSISDN) in the [ITU-E.164] format (e.g., ?33612345678). An optional addressing feature of SMS consists of conveying sub-addressing information as part of a message. For instance, a mobile handset may request a weather forecast update by sending a message to an application server. The identification of the requested service (e.g., service 64) can be specified as part of the sub-addressing information.

Validity Period
A message originator has the possibility of indicating a validity period for a message. This validity period defines the deadline after which the message content is to be discarded. If a message has not been delivered to the message recipient before the expiry date, then the network usually discards the message without further attempts to deliver it to the recipient.

SMS Use Cases

Short Message Service

The Short Message Service (SMS) is a basic service allowing the exchange of short text messages between subscribers. The first short text message is believed to have been transferred in 1992 over signaling channels of a European GSM network.

Service Description
Developed as part of the GSM Phase 1 ETSI technical specifications, the Short Message Service (SMS) allows mobile stations and other network-connected devices to exchange short text messages.

SMS Use Cases
SMS was intended to be a means of exchanging limited amounts of information between two mobile subscribers. This limited capability has become a building block for the development of more compelling services ranging from the download of ringtones to professional applications such as remote monitoring or fleet tracking.

Consumer Applications Based on SMS
Person-to-Person Messaging: This is the original use case for which SMS has been designed. This use case relates to the exchange of a short text message between two mobile subscribers. With SMS, the two most well known predictive text input algorithms are T9 from Tegic and ZI from ZI corporation.
Information Services: This is probably one of the most common use cases in the machine-to-person scenario. With information services, weather updates and financial reports can be prepared by value-added service providers and pushed to mobile handsets with SMS.
Voice Message and Fax Notifications: This use case is widely supported in GSM mobile networks. This use case relates to the reception of messages containing notifications for voice messages and fax waiting in a remote message inbox.
Internet Email Alerts: With Email alerts via SMS, subscribers are notified that one or more Email messages are waiting to be retrieved. Such an alert usually contains the address of the message originator along with the message subject and the first few words from the Email message body.
Download Services: It has become popular for mobile subscribers to customize their mobile handset. This can be done by associating ringtones to persons in the phone contact directory.
Chat Applications: During a chat session, several users can exchange messages in an interactive fashion. All messages exchanged during a session are kept in chronological order in a chat history. In the chat history, messages sent from a recipient are differentiated from messages sent from other users. Several existing mobile chat applications are based on SMS for the transport of messages.
Smart Messaging: Smart Messaging is a proprietary service developed by Nokia. This service enables the exchange of various objects via SMS. This includes the transfer of Internet configuration
parameters, business cards for PIM updates, etc.

Corporate Applications Based on SMS
Vehicle Positioning: The Global Positioning System (GPS) is a technology for determining global positions on Earth. A GPS receiver coupled to a handset, built-in or as an accessory, can provide the location of a person or equipment. This location information can be formatted in a short message and sent to a remote server via SMS. The server interprets locations received from several handsets and displays them on associated geographical maps.
Remote Monitoring: Messages can transport information about the state of remote devices. For instance, system administrators can be notified by a short message that a server is running low of resources or that a fault has been detected on a remote computer.

Operator Applications Based on SMS
Operators have used SMS as a building block for enabling the realization of several services including the ones listed below.
SIM Lock: Operators sometimes require handsets to be locked and usable with only one specific SIM. After a minimal subscription period, the user may request the operator to deactivate the lock in order to be able to use the mobile handset with another SIM (from the same operator or from another operator). If the operator agrees on the lock being deactivated, then the operator sends a short message containing a code allowing the device to be unlocked.
SIM Updates: With SMS, operators can remotely update parameters stored in the SIM. This is performed by sending one or more messages with new parameters to a mobile device. In the past, operators have used this method for updating voice mail access numbers, customer service profiles (determining which network services are accessible to the subscriber), operator name for display in idle mode on the device screen, and address book entries.
Message Waiting Indicator: Operators have used SMS as a simple way to update message waiting indicators on the receiving handset. With this mechanism, a short message contains the type of indicator (voice mail, etc.) to be updated along with the number of waiting messages.
WAP Push: The SMS can be used as a bearer for realizing theWAP push. With this configuration, a WSP protocol data unit or the URI of the content to be retrieved is encoded in a short message and sent to the receiving device. Upon reception of such a message, the WAP microbrowser intercepts the message, interprets the pushed content, and presents the content to the subscriber.