Gsm call flow
Since the mobile has not been informed about the ciphering, all data received from the mobile will be in error. Connected Display that the call has been connected. Click to share on Twitter Opens in new window Call flow describes the process by which a network routes a call to a mobile device.
Then the device sends a service request to the base station on the Stand Alone Dedicated Control Channel. This action will result in all BSS data being received in error.
The service request message meant for the MSC is also sent in this message. If two mobiles transmit on the channel at the same time, their messages will be lost in a collision.
Authentication call flow in gsm
If two mobiles transmit on the channel at the same time, their messages will be lost in a collision. A mobile user calling a land line subscriber is covered here. This scenario describes the call setup for a GSM originating call. This step is required so that transmissions from the mobile reach the base station at the precise time and with the correct frequency. Conversation Speech The call has entered the conversation phase. At this point, the mobile phone displays a message on the screen to indicate that call setup is being attempted. The frequency corrections correct for the Doppler shift caused by the mobile's motion. After the mobile receives this message, the mobile shall only use the specified resources for communication with the mobile network. Then the signal travels to either a packet-switched core network or to a circuit-switched core network. Enable ciphering of data transmitted to the The third and final step in the ciphering mobile handshake. The BSS enables the ciphering in transmit direction. The message also contains the time and frequency corrections. The PN code modulates the pilot channel, the first channel a mobile device will acquire when it detects a CDMA network. Any mobile can transmit on this channel whenever it wishes. The speech path has been setup between the mobile subscriber and the land-line subscriber.
This scenario describes the call setup for a GSM originating call. Dial the called person's number The user keys in the phone number for the landline subscriber and.
From this point on ciphering is enabled in both directions. The channel is ciphered so as so protect the call from eavesdropping. The authentication center AC shares a unique bit key with the mobile device and uses this key to generate a shared secret data SSD code that is used to authenticate the device.
Then the device sends to the base station the ISDN integrated service digital network number of the phone that it is trying to call, and the base station assigns a traffic channel.
Immediate assignment gsm call flow
From this point on ciphering is enabled in both directions. In a circuit-switched core network, the mobile switching center MSC uses cellular radio-telecommunications intersystem operations formerly known as IS to send the call to the home location register and the authentication center. Any mobile can transmit on this channel whenever it wishes. The network generates an address complete message ACM when the correct switching center is found. The mobiles will detect the collision via a timeout and retransmit the message after a random back off. Tune to the frequency and timeslot The mobile detunes from the AGCH and tunes to the specified radio channel. The frequency corrections correct for the Doppler shift caused by the mobile's motion. This is a slotted aloha channel that can be used at random, without any coordination between the mobiles. The message also contains the time and frequency corrections. The call is also switched from signaling to voice.
Once the device is authenticated, the MSC routes the call through the cellular and landline network to complete the call.
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