Mobile Telephone Switching Office
Encyclopedia
The Mobile Telephone Switching Office (MTSO) is the mobile equivalent to a PSTN Central Office. The MTSO contains the switching equipment or Mobile Switching Center (MSC) for routing mobile phone calls. It also contains the equipment for controlling the cell sites that are connected to the MSC.
The systems in the MTSO are the heart of a cellular system. It is responsible for interconnecting calls with the local and long distance landline telephone companies, compiling billing information (with the help of its CBM/SDM), etc. It also provides resources needed to efficiently serve a mobile subscriber such as registration, authentication, location updating and call routing. Its subordinate BSC/RNC are responsible for assigning frequencies
to each call, reassigning frequencies for handoffs, controlling handoffs so a mobile phone
leaving one cell (formally known as BTS)'s coverage area, can be switched automatically to a channel
in the next cell.
All cellular systems have at least one MTSO which will contain at least one MSC. The MSC is responsible for switching calls to mobile units as well as to the local telephone system, recording billing data and processing data from the cell site controllers.
The MSC is connected to a close telephone exchange by a trunk group. This provides an interface to the (Public Switched Telephone Network
) (PSTN). It also provides connectivity to the PSTN. The region to be served by a Cellular Geographic Serving Area(CGSA) is split into geographic cells. These cells are ideally hexagonal in shape and they are initially laid out with their centers about 4 to 8 miles apart from each other. Other MTSO equipment, the cell site controllers provide control functions for a group of cell sites and actions of mobile phones through command and control data channels. To achieve this, there has to be a method of connectivity between the MTSO and the cell site. This may be by DS1, DS3, OCn or Ethernet circuits.
. When a mobile phone is turned on, it listens for the network operator's SID (System Identification Code) on the control channel. If it cannot find any control channels to listen to then it assumes it is outside the range and displays a message indicating no service. If it finds a control channel to listen to, receives the SID and then compares it to the SID programmed into the phone. If both SIDs match then it knows that it is communicating with a cell in its home system.
The phone also transmits a registration request along with the SID. If the subscriber has previously registered to a particular MSC
then the MSC
will have a record in its VLR and will therefore know the subscriber last registered location. If the subscriber is unknown to the MSCs VLR, it will query the HLR
to obtain the subscriber's profile and save it for a set length of time in its VLR. Anytime a MSC successfully registers a subscriber the HLR record is also updated. This will help when a call is received outside of the MSC's coverage area or for an incoming PSTN call.
A subscriber's VLR profile has a LAC(Location Area Code - Area server by cluster of BTS/cell sites) CID (Cell ID) as well as a list of allowed and disallowed services/features and other information.
With the subscriber's VLR Profile the MSC can determine the last known LAC/CID for this subscriber and knows which BTS to use when it needs to ring/page that phone for an incoming call. When the MSC gets the call, it checks its database for the location of the phone. Then it picks a frequency pair the phone will use in that cell to take the call. The MSC communicates with the phone over the control channel to tell it which frequencies to use, and once the phone and the tower switch on those frequencies, the call is connected.
and its signal weakens, the BSC(GSM) or RNC
(3G UMTS) will automatically instruct it to tune to a different frequency, one assigned to the newly entered BTS. This process is called handoff. place by analyzing measurements of radio signal strength made by the present controlling cell site and by its neighbors. The returning instructions for handoff sent during a call must use the voice channel. The data regarding the new channel are sent rapidly (in about 50 milliseconds), and the entire returning process takes only about 300 milliseconds. After handoff, if the SID on the control channel does not match the SID programmed into the phone, then the phone assumes that it is roaming.
The MSC
also performs handovers/handoffs which occurs when a call needs to be handed off to a different BSC/RNC it serves or to completely new MSC. A MSC can serve many BSCs/RNCs which in turn server many BTS. As a result a MSC can serve a large are typically hundreds of miles. Highly populated areas require more BTSs and BSCs/RNCs which will in turn obviously, will reduce the geographic coverage of a DMSC. The above in a MSC is what's considered as it's mobility management. The BTS, BSC/RNC are the RAN/UTRAN (Radio Access Network & UMTS Radio Access Network) subset in the mobile network. The remaining functions of a MSC are identical to a PSTN switch.
The systems in the MTSO are the heart of a cellular system. It is responsible for interconnecting calls with the local and long distance landline telephone companies, compiling billing information (with the help of its CBM/SDM), etc. It also provides resources needed to efficiently serve a mobile subscriber such as registration, authentication, location updating and call routing. Its subordinate BSC/RNC are responsible for assigning frequencies
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
to each call, reassigning frequencies for handoffs, controlling handoffs so a mobile phone
Mobile phone
A mobile phone is a device which can make and receive telephone calls over a radio link whilst moving around a wide geographic area. It does so by connecting to a cellular network provided by a mobile network operator...
leaving one cell (formally known as BTS)'s coverage area, can be switched automatically to a channel
Channel (communications)
In telecommunications and computer networking, a communication channel, or channel, refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel...
in the next cell.
All cellular systems have at least one MTSO which will contain at least one MSC. The MSC is responsible for switching calls to mobile units as well as to the local telephone system, recording billing data and processing data from the cell site controllers.
The MSC is connected to a close telephone exchange by a trunk group. This provides an interface to the (Public Switched Telephone Network
Public switched telephone network
The public switched telephone network is the network of the world's public circuit-switched telephone networks. It consists of telephone lines, fiber optic cables, microwave transmission links, cellular networks, communications satellites, and undersea telephone cables, all inter-connected by...
) (PSTN). It also provides connectivity to the PSTN. The region to be served by a Cellular Geographic Serving Area(CGSA) is split into geographic cells. These cells are ideally hexagonal in shape and they are initially laid out with their centers about 4 to 8 miles apart from each other. Other MTSO equipment, the cell site controllers provide control functions for a group of cell sites and actions of mobile phones through command and control data channels. To achieve this, there has to be a method of connectivity between the MTSO and the cell site. This may be by DS1, DS3, OCn or Ethernet circuits.
Subscriber Registration
The MSC also plays a major role in call routingRouting
Routing is the process of selecting paths in a network along which to send network traffic. Routing is performed for many kinds of networks, including the telephone network , electronic data networks , and transportation networks...
. When a mobile phone is turned on, it listens for the network operator's SID (System Identification Code) on the control channel. If it cannot find any control channels to listen to then it assumes it is outside the range and displays a message indicating no service. If it finds a control channel to listen to, receives the SID and then compares it to the SID programmed into the phone. If both SIDs match then it knows that it is communicating with a cell in its home system.
The phone also transmits a registration request along with the SID. If the subscriber has previously registered to a particular MSC
MSC
- Computers:* Mario Strikers Charged* Microsoft Common Console Document, file for the Microsoft Management Console* Microelectronics Support Centre* Microsoft Corporation* MIDI Show Control* Message Sequence Chart...
then the MSC
MSC
- Computers:* Mario Strikers Charged* Microsoft Common Console Document, file for the Microsoft Management Console* Microelectronics Support Centre* Microsoft Corporation* MIDI Show Control* Message Sequence Chart...
will have a record in its VLR and will therefore know the subscriber last registered location. If the subscriber is unknown to the MSCs VLR, it will query the HLR
HLR
HLR may refer to:* Hoffmann-La Roche, a Swiss global health-care company* Home Location Register, a central database that contains details of each mobile phone subscriber that is authorized to use the GSM and or WCDMA core network of this PLMN....
to obtain the subscriber's profile and save it for a set length of time in its VLR. Anytime a MSC successfully registers a subscriber the HLR record is also updated. This will help when a call is received outside of the MSC's coverage area or for an incoming PSTN call.
A subscriber's VLR profile has a LAC(Location Area Code - Area server by cluster of BTS/cell sites) CID (Cell ID) as well as a list of allowed and disallowed services/features and other information.
With the subscriber's VLR Profile the MSC can determine the last known LAC/CID for this subscriber and knows which BTS to use when it needs to ring/page that phone for an incoming call. When the MSC gets the call, it checks its database for the location of the phone. Then it picks a frequency pair the phone will use in that cell to take the call. The MSC communicates with the phone over the control channel to tell it which frequencies to use, and once the phone and the tower switch on those frequencies, the call is connected.
Handovers
As a mob unit engaged in a call moves away from a cell site or formally known as Base transceiver stationBase Transceiver Station
A base transceiver station or cell site is a piece of equipment that facilitates wireless communication between user equipment and a network. UEs are devices like mobile phones , WLL phones, computers with wireless internet connectivity, WiFi and WiMAX gadgets etc...
and its signal weakens, the BSC(GSM) or RNC
Radio Network Controller
The Radio Network Controller is a governing element in the UMTS radio access network and is responsible for controlling the Node Bs that are connected to it. The RNC carries out radio resource management, some of the mobility management functions and is the point where encryption is done before...
(3G UMTS) will automatically instruct it to tune to a different frequency, one assigned to the newly entered BTS. This process is called handoff. place by analyzing measurements of radio signal strength made by the present controlling cell site and by its neighbors. The returning instructions for handoff sent during a call must use the voice channel. The data regarding the new channel are sent rapidly (in about 50 milliseconds), and the entire returning process takes only about 300 milliseconds. After handoff, if the SID on the control channel does not match the SID programmed into the phone, then the phone assumes that it is roaming.
The MSC
MSC
- Computers:* Mario Strikers Charged* Microsoft Common Console Document, file for the Microsoft Management Console* Microelectronics Support Centre* Microsoft Corporation* MIDI Show Control* Message Sequence Chart...
also performs handovers/handoffs which occurs when a call needs to be handed off to a different BSC/RNC it serves or to completely new MSC. A MSC can serve many BSCs/RNCs which in turn server many BTS. As a result a MSC can serve a large are typically hundreds of miles. Highly populated areas require more BTSs and BSCs/RNCs which will in turn obviously, will reduce the geographic coverage of a DMSC. The above in a MSC is what's considered as it's mobility management. The BTS, BSC/RNC are the RAN/UTRAN (Radio Access Network & UMTS Radio Access Network) subset in the mobile network. The remaining functions of a MSC are identical to a PSTN switch.