Telephone Network

Connection between Mobile to Telephone Network

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The telephone network is the network of the world's public circuit-switched telephone networks. These standards allow different networks in different countries tointerconnect seamlessly. There is also a single global address space for telephone numbers based on the E.163 and E.164 standards. Originally a network of fixed-line analog telephone systems, the PSTN is now almost entirely digital in its core and includes mobile as well as fixedtelephones.

The technical operation of the PSTN utilizes standards created by the ITU-T. It consists oftelephone lines, fiber optic cables, microwave transmission links, cellular networks, communications satellites, and undersea telephone cables, all inter-connected by switching centers, thus allowing any telephone in the world to communicate with any other. The combination of the interconnected networks and the single numbering plan make it possible for any phone in the world to dial any other phone.

Mobile Network :
A mobile network is a radio network distributed over land areas called cells, each served by at least one fixed-location transceiver known as a cell site or base station. When joined together these cells provide radio coverage over a wide geographic area. to communicate with each other and with fixed transceivers and telephones anywhere in the network, This enables a large number of portable transceivers (mobile phones.) via base stations, even if some of the transceivers are moving through more than one cell during transmission.

Cellular networks offer a number of advantages over alternative solutions:

§ increased capacity

§ reduced power use

§ larger coverage area

§ reduced interference from other signals

Mobile To Telephone Network depends on three things:

§ A billing relationship with a mobile phone operator. This is usually either where services are paid for in advance of them being consumed (prepaid), or where bills are issued and settled after the service has been consumed (postpaid) to Telephone.

§ A mobile phone that is GSM compliant and operates at the same frequency as the operator. It passes the signal and telephone network captured it to itz own operator.

§ A Signal are passes network to network in the mobile phone without wiring and telephone system used some time time wiring to adjacent the call.

Mobile Outgoing to Telephone
Once a mobile phone has successfully attached to a GSM network as described above, calls may be made from the phone to any other phone on the global Telephone Network.

The call setup request message is handled next by the Mobile Switching Center, which checks the subscriber's record held in the Visitor Location Register to see if the outgoing call is allowed. If so, the MSC then routes the call in the same way that a telephone exchange does in a fixed network.

The user dials the telephone number, presses the send or talk key, and the mobile phone sends a call setup request message to the mobile phone network via the nearest mobile phone base transceiver station (BTS).

If the subscriber is on a prepaid tariff (sometimes known as Pay As You Go (PAYG) or Pay & Go), the call is rejected. If the call is allowed to continue, then an additional check is made to see if the subscriber has enough credit to proceed. If not, then it is continually monitored and the appropriate amount is decremented from the subscriber's account. When the credit reaches zero, the call is cut off by the network. The systems that monitor and provide the prepaid services are not part of the GSM standard services, but instead an example of intelligent network services that a mobile phone operator may decide to implement in addition to the standard GSM ones.

Incoming calls
When someone places call Telephone to a mobile phone, they dial the mobile number (also called a MSISDN) associated with the mobile user and the call is routed to the mobile phone operator's Gateway Mobile Switching Centre. The Gateway MSC, as the name suggests, acts as the "entrance" from exterior portions of the Public Switched Telephone Network onto the provider's network.

As noted above, the phone is free to roam anywhere in the operator's network or on the networks of roaming partners, including in other countries. So the first job of the Gateway MSC is to determine the current location of the mobile phone in order to connect the call. It does this by consulting the Home Location Register (HLR), which, as described above, knows which Visitor Location Register (VLR) the phone is associated with, if any.
How speech is encoded during mobile to Telephone calls

During a GSM call, speech is converted from analogue sound waves to digital data by the phone itself, and transmitted through the mobile phone network by digital means. (Though older parts of the fixed Telephone Network may use analog transmission.)

The digital algorithm used to encode speech signals is called a codec. The speech codecs used in GSM are called Half-Rate (HR), Full-Rate (FR), Enhanced Full-Rate (EFR) and Adaptive Multirate (AMR). All codecs except AMR operate with a fixed data rate and error correction level.

How Data transmitted mobile to Telephone Network
The GSM standard also provides separate facilities for transmitting digital data. This allows a mobile phone connect to telephone network act like any other computer on the Internet, sending and receiving data via the Internet Protocol.

The mobile may also be connected to a desktop computer, laptop, or PDA, for use as a network interface (just like a modem or Ethernetcard, but using one of the GSM data protocols described below instead of a PSTN-compatible audio channel or an Ethernet link to transmit data). Some GSM phones can also be controlled by a standardised Hayes AT command set through a serial cable or a wireless link (usingIRDA or Bluetooth). The AT commands can control anything from ring tones to data compression algorithms.
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