You think about making a phone call to someone, pull out your cell phone, enter

Question

You think about making a phone call to someone, pull out your cell phone, enter a phone number, and hit the dial button. Assuming that your attempt to make this phone call was a success, that is, you spoke with the intended person for a while and hung up, describe with as many details as possible, all the sequence of events. You may include, for example, the protocol stack on your phone, details about the mobile communications stan- dard your phone is using, details about your cell phone providers network (nearest cell-tower, etc), details about A/D on your phone, etc.

Explanation / Answer

Before a mobile phone can establish a call, it first needs to establish a connection to the available service providers network. We are assuming that phone is connected to the strongest available network.

Let's start :

1. After user dials the no, a call initiation request is sent on the reverse control channel.

2. That request also contains Mobile Identification Number (MIN), Electronic Serial Number (ESN) and the dialled telephone number.

3. The base station receives this data and sends it to the Mobile Switching Center (MSC).

4. The MSC checks the MIN with the records on its database and validates it.

5. If the MIN is valid, a connection to the called party is made through Public switched Telephone network (PSTN).

6. Now, MSC requests the base station to move the mobile phone to an unused voice channel so that the conversation can begin.

7. Once a call is in progress, the MSC adjusts the power transmitted by the mobile phone as it moves in and out of the coverage area of each base station.

8. When a mobile phone with a call in progress moves from one base station to another, the process is called handoff.

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