BACKGROUND


SMS allows users to send/receive text messages up to 160 characters long to/from mobile phones that support GSM. It is a store and forward service, meaning that if a recipient's mobile phone is not active or is not within range, the message is stored and delivered at a later time when the phone is active and within range. This is achieved by the use of a short message service center (SMSC) that acts as a store and forward center.

Among typical SMS applications are:

  • Notifying a mobile phone owner of a voice mail message;

  • Enabling a user to check for a traffic summons;

  • Advertising, e.g., concert tickets, special promotion at a music store, etc.;

  • Providing inventory information to traveling salespersons;

  • Marketing communications strategy.

Currently, SMS has an extremely high consumer usage but a low business adoption. In other words, while billions of SMS messages are delivered between individual consumers each month, the use of SMS as part of business strategies is still relatively low (Clickatell, 2002). Despite the other communications media such as television, radio, Internet, e-mail, and others (see Table 1) that are available to marketers and advertisers, SMS has the following characteristics: high reach, low cost, and high retention, which make it a powerful part of an organization's marketing tool.

Table 1: Comparison between standard communication media (Clickatell, 2002)

Medium

Reach

Cost

Retention

Television

One of the highest

Very high

Good

Radio

Medium

Medium

Poor

Internet
(Banners)

High

Medium

Dropping

E-mail

High

Extremely
Low

Extremely
Low

Print Media

Low

High

High

Billboard

Medium

Medium

Medium

Moving
Media

Medium

High

Medium

Telephone

Medium

High

Medium

Fax

Low

Medium

Low

Standard
Mailers

High

High

Medium

Personal
Interaction

Low

High

High

SMS

High

Low

High

Before we proceed to discuss existing SMS applications, a brief overview of how the service is provided based on the European Telecommunication Standard Institute GSM 03.40 specification (ETSI, 1996) is given below.

Point-to-Point Service

SMS is defined as two point-to-point services, i.e., mobile originated short message (MO-SM) and mobile terminated short message (MT-SM). Messages originating from a mobile station (MS) are transported to an SMSC while messages terminating at an MS are transported from an SMSC to the MS. An MS is a wireless terminal with the capability to send and receive short messages in addition to sending and receiving voice calls. An active MS is able to send/ receive a short message regardless of whether or not there is a speech or data call in progress. For an MT-SM, a report is returned to the SMSC confirming that the MS has received the short message or that it is not possible to deliver the message to the MS along with the reason for the failure. Likewise for MO-SM, a report is returned to the MS either confirming that the SMSC has received the short message or informing it of a delivery failure plus the reason for the failure. In addition to MO-SM, a message submitted to the SMSC may also originate from voice mail systems, paging networks, or operators.

SMS Architecture

A short message originating from an MS is first delivered to a short message service interworking MSC (IWMSC) and then forwarded to a short message service center (SMSC). An SMSC is connected to the GSM network via a short message service gateway MSC (SMS GMSC). An SMSC may connect to more than one GSM network via a number of SMS GMSCs. The SMS GMSC is the point of contact between a mobile network and other networks. It determines the recipient's current MSC and delivers the message to the MSC. The MSC broadcasts the message to the base station systems (BSSs), and the base transceiver stations (BTSs) page the intended recipient. If the intended recipient is active, the message is delivered to the recipient. Even though Figure 2 shows that the recipient is an MS, the recipient can also be a fax machine or a PC connected to the Internet.


Figure 2: GSM short message service network architecture

SMS Elements

There are seven SMS elements related to the receipt and delivery of messages:

  1. A validity period specifies for how long a message is held in the SMSC before it is delivered to the recipient. The validity period varies between five minutes to one week and is counted from the time the message arrives at the SMSC.

  2. A service center time stamp is a parameter that is included in the message by the SMSC to inform the recipient when the message arrived at the SMSC.

  3. A protocol identifier specifies either the higher layer protocol being used or indicates the interworking of the telematic device.

  4. A more message to send element is used by the SMSC to inform the mobile user that there is more than one message waiting to be delivered.

  5. An SMSC indicates the priority of a message to the public land mobile network (PLMN). For non-priority messages, message delivery is not attempted if the MS has been identified as being absent; otherwise , message delivery is attempted even if the MS has been identified as not having enough free memory capacity (the message that is delivered is stored in the subscriber identification module (SIM) card or the memory of the MS). For priority messages, delivery is attempted even if MS has been identified as being absent or not having enough free memory capacity.

  6. If message delivery fails due the temporary absence of an MS, the message waiting element is used by the PLMN to provide the home location register (HLR) and visitor location register (VLR) currently associated with the MS with information that there is a message waiting to be delivered at the originating SMSC. An HLR is a database that holds information about a subscriber that subscribes to a mobile network service. It stores and manages all mobile subscriptions of an operator. HLR acts as a location register that holds information such as directory number, profile information, current location, and validation period. A VLR stores subscription information for visiting subscribers so that the corresponding MSC can provide service. It is a location register used to retrieve information for handling calls to/from visiting subscribers.

  7. An alert is used by the GSM PLMN to inform an SMSC of a delivery attempt failure because an MS is not reachable or because the MS memory capacity has been exceeded. It is also used to inform an SMSC that a previously absent/unreachable MS is now active or that the MS now has sufficient memory. Upon receiving the alert, the SMSC may initiate a delivery attempt.

Reliability of Message Delivery

There are a variety of SMS applications; some are noncritical applications that do not require guaranteed message delivery while others depend on reliable message delivery to ensure correctness of the operations performed by the application. How does SMS guarantee message delivery for critical applications such as mobile banking?

When a user sends a short message, a report is returned to the MS to either confirm the message delivery to the SMSC or to inform it of delivery failure. Likewise, when an SMSC attempts to deliver a message to an MS, a report is returned to the SMSC either confirming the message delivery or informing it of delivery failure. In the latter case, the reason for the failure is also included.

Figure 3 shows the process of delivering a message from an MS:

  1. The MS sends the message to the MSC.

  2. The MSC queries the VLR to verify that the message transfer does not violate any restrictions imposed.

  3. The MSC sends the short message to the SMSC using the forwardShortMessage operation.

  4. The SMSC delivers the message to the intended recipient.

  5. The SMSC sends an acknowledgement to the MSC that the forwardShortMessage operation is successful.


Figure 3: MO-SM message delivery

Figure 4 shows the process of delivering a message to an MS:

  1. The SMSC receives a message from a service center (SC).

  2. The SMSC queries the HLR to obtain routing information for the recipient MS.

  3. The SMSC sends the message to the MSC using the forwardShortMessage operation.

  4. The MSC retrieves the subscriber information from the VLR. If required, authentication if performed at this stage.

  5. The MSC transfers the message to the recipient MS.

  6. The MSC returns the outcome of the forwardShortMessage operation to the SMSC.

  7. If requested , the SMSC returns a status report indicating the delivery status to the originating MS.


Figure 4: MT-SM message delivery

The SC has the capability to inform the MS of the message delivery status. If an MS wishes to receive a status report it may indicate so in the MO-SM. The status is either the message has been successfully delivered or the SC is unable to forward the message to the SME due to an error. There are two types of error, namely, permanent error (e.g., validity period expired , invalid SME address) or temporary error (e.g., SME temporarily unavailable, SC-SME connection currently down).

The support for reporting the delivery status is important, especially for critical applications such as mobile banking, where, for example, a user wishes to be assured that his instruction for a fund transfer has been received and executed accordingly by the bank.

Supplementary Service for SMS

Barring service is available as a supplementary service. If an operator identifies that a message is undeliverable because the originator has been barred, an error message is returned to the originator.

Multiple Message Transfer

If an SMSC has more than one message to transfer, it may indicate this to the gateway MSC for short message service (GMSC) to avoid having to page and authenticate the MS for each message delivery.




Mobile Commerce Applications
Mobile Commerce Applications
ISBN: 159140293X
EAN: 2147483647
Year: 2004
Pages: 154

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