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Most phone companies sell phones from third-party manufacturers. Personal information such as contact numbers of friends and family can also be stored on the SIM by the subscriber. The phone then identifies itself to the network through the control channel. Once this is successfully completed, the phone is said to be attached to the network. The key feature of a mobile phone is the ability to receive and make calls in any area where coverage is available. This is generally called roaming from a customer perspective, but also called visiting when describing the underlying technical process.
Location Register to obtain the details for that phone. Every SIM card contains a secret key, called the Ki, which is used to provide authentication and encryption services. This is useful to prevent theft of service, and also to prevent “over the air” snooping of a user’s activity. If not, the call is rejected.
If the call is allowed to continue, 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. 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. Number, then this number is stored in the Home Location Register. If that is the case, then the CFU number is returned to the Gateway MSC for immediate routing to that destination.
Gateway MSC, and the call is forwarded there. The mobile phone may sometimes override the default setting. This number is relayed back to the Gateway MSC, and then used to route the call to the MSC where the called phone is roaming. IMSI is registered in order to inform the phone that there is an incoming call for it. It is also possible that the phone call is not answered. A roaming user may want to avoid these forwarding services in the visited network as roaming charges will apply.
In the United States and Canada, callers pay the cost of connecting to the Gateway MSC of the subscriber’s phone company, regardless of the actual location of the phone. For outgoing calls, any long distance charges are billed as if they originate at the GMSC, even though it is the visiting MSC that completes the connection to the PSTN. Australia, and Argentina only charge their subscribers for outgoing calls. Incoming calls are free to the mobile subscriber with the exception of receiving a call while the subscriber is roaming as described below. However, callers typically pay a higher rate when calling mobile phones. Special prefixes are used to designate mobile numbers so that callers are aware they are calling a mobile phone and therefore will be charged a higher rate. From the caller’s point of view, it does not matter where the mobile subscriber is, as the technical process of connecting the call is the same.
International roaming calls are often quite expensive, and as a result some companies require subscribers to grant explicit permission to receive calls while roaming to certain countries. However, some networks’ GMSCs connect unanswered calls directly, keeping the voice signal entirely within the home country and thus avoiding the double charge. Wideband AMR also known as HD voice. All codecs except AMR operate with a fixed data rate and error correction level. The GSM standard also provides separate facilities for transmitting digital data. The AT commands can control anything from ring tones to data compression algorithms.
These types of connections are typically charged on a per-second basis, regardless of the amount of data sent over the link. This is because a certain amount of bandwidth is dedicated to the connection regardless of whether or not it is needed. It is backwards-compatible with systems that use pre-1997 versions of the standard. Multiple GPRS users can share a single unused channel because each of them uses it only for occasional short bursts. The advantage of packet-switched connections is that bandwidth is only used when there is actually data to transmit.
4 billion people by the end of 2007. SMS text messages may be sent by mobile phone users to other mobile users or external services that accept SMS. The SMSC is a central routing hubs for Short Messages. This GSM service estimates the call cost for display on the user’s mobile phone. However, in practice, this GSM service is rarely used because the calculation is more complex than the standard allows. These notifications may be read out loud using a speech-synthesis system, or may be transmitted in textual form.