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Wednesday, December 17, 2008
What Is SGSN ?
A Serving GPRS Support Node (SGSN) is responsible for the delivery of data packets from and to the mobile stations within its geographical service area. Its tasks include packet routing and transfer, mobility management (attach/detach and location management), logical link management, and authentication and charging functions. The location register of the SGSN stores location information (e.g., current cell, current VLR) and user profiles (e.g., IMSI, address(es) used in the packet data network) of all GPRS users registered with this SGSN.
What Is SMSC ?
A Short Message Service Center (SMSC) is a network element in the mobile telephone network which delivers SMS messages.
All SMS sent by a mobile subscriber are first submitted to SMSC of his mobile network. After submission SMSC find the location of destination mobile subscriber and deliver the SMSC to that subscriber. SMSC works on store and forward mechanism. If for some reasons SMSC is unable to deliver SMS to destination subscriber, SMSC can store this SMS for longer durations and keep retrying to deliver this SMS at regular interval.
All SMS sent by a mobile subscriber are first submitted to SMSC of his mobile network. After submission SMSC find the location of destination mobile subscriber and deliver the SMSC to that subscriber. SMSC works on store and forward mechanism. If for some reasons SMSC is unable to deliver SMS to destination subscriber, SMSC can store this SMS for longer durations and keep retrying to deliver this SMS at regular interval.
What Is MSC ?
The Mobile Switching Center or MSC is the primary service delivery node for GSM, responsible for handling voice calls and SMS as well as other services (such as conference calls, FAX and circuit switched data). The MSC sets up and releases the end-to-end connection, handles mobility and hand-over requirements during the call and takes care of charging and real time pre-paid account monitoring.
In the GSM mobile phone system, in contrast with earlier analogue services, fax and data information is sent directly digitally encoded to the MSC. Only at the MSC is this re-coded into an "analogue" signal (although actually this will almost certainly mean sound encoded digitally as PCM signal in a 64-kbit/s timeslot, known as a DS0 in America).
There are various different names for MSCs in different contexts which reflects their complex role in the network, all of these terms though could refer to the same MSC, but doing different things at different times.
A Gateway MSC is the MSC that determines which visited MSC the subscriber who is being called is currently located. It also interfaces with the Public Switched Telephone Network. All mobile to mobile calls and PSTN to mobile calls are routed through a GMSC. The term is only valid in the context of one call since any MSC may provide both the gateway function and the Visited MSC function, however, some manufacturers design dedicated high capacity MSCs which do not have any BSSes connected to them. These MSCs will then be the Gateway MSC for many of the calls they handle.
The Visited MSC is the MSC where a customer is currently located. The VLR associated with this MSC will have the subscriber's data in it.
The Anchor MSC is the MSC from which a handover has been initiated. The Target MSC is the MSC toward which a Handover should take place. An MSC Server is a part of the redesigned MSC concept starting from 3GPP Release 5.
In the GSM mobile phone system, in contrast with earlier analogue services, fax and data information is sent directly digitally encoded to the MSC. Only at the MSC is this re-coded into an "analogue" signal (although actually this will almost certainly mean sound encoded digitally as PCM signal in a 64-kbit/s timeslot, known as a DS0 in America).
There are various different names for MSCs in different contexts which reflects their complex role in the network, all of these terms though could refer to the same MSC, but doing different things at different times.
A Gateway MSC is the MSC that determines which visited MSC the subscriber who is being called is currently located. It also interfaces with the Public Switched Telephone Network. All mobile to mobile calls and PSTN to mobile calls are routed through a GMSC. The term is only valid in the context of one call since any MSC may provide both the gateway function and the Visited MSC function, however, some manufacturers design dedicated high capacity MSCs which do not have any BSSes connected to them. These MSCs will then be the Gateway MSC for many of the calls they handle.
The Visited MSC is the MSC where a customer is currently located. The VLR associated with this MSC will have the subscriber's data in it.
The Anchor MSC is the MSC from which a handover has been initiated. The Target MSC is the MSC toward which a Handover should take place. An MSC Server is a part of the redesigned MSC concept starting from 3GPP Release 5.
What Is VLR?
Visitor Location Register (VLR) is a database - part of the GSM mobile phone system - which stores information about all the mobiles that are currently under the jurisdiction of the MSC (Mobile Switching Center) which it serves. Of all the information it stores about each MS (Mobile Station), the most important is the current LAI (Location Area Identity). LAI identifies under which BSC (Base Station Controller) the MS is currently present. This information is vital in the call setup process.
Whenever an MSC detects a new MS in its network, in addition to creating a new record in the VLR, it also updates the HLR of the mobile subscriber, apprising it of the new location of that MS.
Whenever an MSC detects a new MS in its network, in addition to creating a new record in the VLR, it also updates the HLR of the mobile subscriber, apprising it of the new location of that MS.
What Is HLR ?
The Home Location Register or HLR is a central database that contains details of each mobile phone subscriber that is authorized to use the GSM core network. There is one logical HLR per PLMN, although there may be multiple physical platforms.
The HLR stores details of every SIM card issued by the mobile phone operator. Each SIM has a unique identifier called an IMSI which is the primary key to each HLR record.
The next important items of data associated with the SIM are the MSISDNs, which are the telephone numbers used by mobile phones to make and receive calls. The primary MSISDN is the number used for making and receiving voice calls and SMS. Each MSISDN is also a primary key to the HLR record.
Examples of other data stored in the HLR against an IMSI record is:
The HLR stores details of every SIM card issued by the mobile phone operator. Each SIM has a unique identifier called an IMSI which is the primary key to each HLR record.
The next important items of data associated with the SIM are the MSISDNs, which are the telephone numbers used by mobile phones to make and receive calls. The primary MSISDN is the number used for making and receiving voice calls and SMS. Each MSISDN is also a primary key to the HLR record.
Examples of other data stored in the HLR against an IMSI record is:
- GSM services that the subscriber has requested or been given, like can he make call, can he receive call , can he make sms, can he roam etc
- GPRS settings to allow the subscriber to access packet services
- Current Location of subscriber (VLR and SGSN), i.e where is this subscriber currently.
- Call divert settings applicable for each associated MSISDN.
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