Structure of the scheduling center

 Structure of the scheduling center

• MO process
  In the MO process, after a mobile subscriber submits an SM to the SMCAPP, the BillCreater generates an MO bill, and the SMCAPP determines whether SMs to be delivered to the called party are stored in the FDB. If yes, the SMCAPP saves the SM to the FDB. Otherwise, the SMCAPP attempts to deliver the SM.
• MT process
  In the MT process, the SMCAPP attempts to deliver an SM to a mobile subscriber, and the BillCreater generates an MT bill. If the SM fails to be delivered and is pending redelivery, or is successfully delivered but requires a status report, the SMCAPP saves the SM to the FDB. If the SM is deleted after the final delivery attempt fails, or is successfully delivered but requires no status report, the BillCreater generates a charging bill and history bill, and the DBDaemon saves the SM to the history database.

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Functions of the SMS System

This section describes the functions of the SMSC.

The functions of the SMSC are as follows:

• Providing value-added services (VASs) and obtaining profits
  As a basic telecom service of the mobile communication network, the SMS enables subscribers to transmit information through SMs and obtain such useful information as stock market, weather, sports and bank information, which greatly facilitates subscribers in getting information and gets subscribers into a better and closer relationship with operators. At the same time, operators can get direct revenue by providing VASs based on the SMS service.
  
  
• Improving quality of service (QoS)
  Mobile subscribers have high requirements for timely information transfer. In many cases such as channel busy, masking or network coverage problems, communication is difficult and information cannot be exchanged. With the SMSC, subscribers can get information at the earliest time and smooth information transmission is ensured.
  
  
• Improving connectivity and reducing congestion of the mobile network
  According to statistics, over 30% of calls or faxes cannot be charged due to busy line or no reply, resulting in the waste of network resources. As a solution to this problem, the SMSC can connect incoming calls manually or automatically and record the information subscribers want to transmit, thus dredging the GSM network. In addition, the SMSC can reduce false load which is caused by repetitive dialing to an MS switched off, thus reducing network congestion.

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Position of the SMS System in the GSM Network

Position of the SMS System in the GSM

The position of the SMSC in the GSM network. The physical entities related to the SMSC are the MSC, VLR and the HLR. Their functions in the SM transmission are as follows:

• MSC
  
  • The SMs submitted by the MS pass the BSS and reach the MSC. Then the MSC forwards them to the corresponding SMSC.
    
  • After receiving the SMs delivered by the SMSC, the MSC queries the VLR and the HLR for the related routing and subscriber information, and then delivers them to subscribers through BSS.
    
    
• VLR
  The VLR stores the temporary information of a subscriber roaming in the local MSC area. The subscriber must pass the authentication through the VLR before sending an SM, and the MSC queries the route of a subscriber through the VLR before delivering an SM.
  
  
• HLR
  The HLR is a database for mobile subscriber management. It stores the subscription information, position information, mobile station international ISDN number (MSISDN), and international mobile station identity (IMSI) of a subscriber. Before delivering SM, the SMSC finds which MSC the subscriber belongs to through the HLR.
  

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Structure of the SMS-GSM System

Structure of the GSM System

This section describes the architectures of the GSM, CDMA, and TDMA networks, as well as the position and functions of the SMSC in the three networks.
The system architectures of the CDMA, TDMA, and GSM networks are quite similar. Each of the three network systems is composed of the following four parts:

• Network subsystem (NSS)
  
• Base station subsystem (BSS)
  
• Operation and maintenance center (OMC)
  
• A great many mobile stations (MSs)
  

There are interfaces between various subsystems and functional entities within the subsystems. The specifications in the CDMA, TDMA, and GSMnetworks stipulate standard interfaces and communication protocols through which the functional entities can implement communications coordinately. Adopting different interface specifications and protocols, the three mobile networks are independent of each other.

Figure 1 Mobile network

SMSC: Short Message Service Center	NSS: Network SubSystem
HLR: Home Location Register	AUC: Authentication Center
EIR: Equipment Identity Register	MSC: Mobile Switching Center
VLR: Visitor Location Register	OMC: Operation & Maintenance Center
BSS: Base Station Subsystem	DCN:Data Communication Net
BSC: Base Station Controller	PSTN: Public Switched Telephone Network
BTS: Base Transceiver Station	MS: Mobile Station

NSS

In the mobile network, the NSS mainly implements the switching function and database function. The database function is necessary for subscriber data management, mobility management and security management. The NSS includes the following functional entities:

• MSC
  The MSC controls calls, manages the communication service of MSs within the local network and with other networks (such as PSTN/ISDN/PSPDN, and other mobile networks), and provides the charging information. Besides, in order to set up call routes to MSs, the MSC can also function as the GMSC, that is, querying location information of MSs.
  Short messages submitted by the MS pass the BSS and reach the MSC. Then the MSC forwards them to the corresponding SMSC.
  After receiving the SMs delivered by the SMSC, the MSC queries the VLR and the HLR for the related routing and subscriber information, and then delivers them to subscribers through BSS.
• VLR
  The visitor location register (VLR) stores the relevant information of registered subscribers in the control area, and provides the mobile subscribers with necessary conditions for call connection. It can be regarded as a dynamic database.
  
• HLR
  The home location register (HLR) is the central database of a mobile network. It stores the information of all mobile subscribers in the control area. The HLR stores two kinds of information: subscriber data, and location information of MSs for setting up call routes to the MSs.
  
• AuC
  The AuC stores authentication algorithm and encryption key, which prevent illegal subscribers from accessing the system, thus ensuring the security of the mobile subscribers' communications through the radio interface.
  
• EIR
  The EIR stores the International Mobile Equipment Identity (IMEI.). Generally the AuC and the EIR are integrated physically.
  
  NOTE:
  

  Generally, the MSC and the VLR are integrated physically; and the AUC, EIR and HLR are integrated physically.

BSS

The BSS is the system equipment, which is controlled by the MSC and communicates with MSs in the specific radio coverage area. It is responsible for radio transmission and reception, and radio resource management. The BSS consists of the following two functional entities:

• Base station controller (BSC)
  
• The BSC is responsible for radio network resource management, cell configuration data management, power control, location and switchover. It implements powerful communication control function.
  
• Base transceiver station (BTS)
  
• The BTS is the radio interface equipment, which is controlled by the BSC. It handles the radio connection, conversion between radio signals and landline signals, radio diversity, radio channel encryption, frequency hopping, and so on.
  

OMC

The OMC is responsible for managing and controlling the whole GSM and CDMA networks.

MS

The MS is the mobile subscriber's device. It consists of the following two parts:

• Mobile terminal (MT)
  The MT implements such functions as voice coding, channel coding, information encryption, information modulation and demodulation, information transmission and reception.
  
• Subscriber identity module/user identity module card (SIM/UIM card)
  The SIM/UIM card is an intelligent card, which keeps the subscriber identity information and the management data related to the subscriber and network. An MT with an SIM/UIM card inside can access the telecom network.
  

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Basic concepts of the SMSC

Basic Concepts

Describes the basic concepts of the SMSC.

SM

The short message (SM) is the non-real-time and reliable data packet transmitted on the PLMN (Public Land Mobile Network) network through a signaling channel. The short message service (SMS) provides peer-to-peer, non-real-time and reliable data transmission by storing and forwarding messages.

SME

The short message entity (SME) is the sender or recipient of SMs, including mobile subscribers, automatic systems and manual systems. The SP can also be called external short message entity (ESME).

MO

The mobile originated (MO) SM refers to the SM which is originated from the mobile station (MS). The MO process refers to the process of the MS sending an SM to the SMSC and then receiving the acknowledgement from the SMSC.

MT

The mobile terminated (MT) SM refers to the SM which is terminated at the MS. The MT process refers to the process of the SMSC sending an SM to the MS according to a certain rule and then receiving the acknowledgement from the MS.

Account

All connections between ESME and SMSC use the same account. The account stores such data as interface authority, authentication attribute and basic flow control information.

Interface

An interface is an object of recording the connection between the ESME and the SMSC. The ESME logs in to the SMSC with the account and the SMSC creates an interface to manage this connection. The attributes of an interface include local IP address, opposite IP address, protocol parameter, flow control parameter, and so on.

Route Table

The route table is the mapping table which stores the relationship between the original address, destination address, SM protocol type and account. The SMSC (Short Message Service Center) delivers an SM to the designated account according to the information set in the route table.

SP

The service provider (SP) is the provider of the SMS. After contracting with operators, the SP provides various SMSs such as on-demand and customization for subscribers.

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