It is possible to take calls from any location because, the mobile phone keeps the network/cellular operator informed about its location. This in-turn enables the mobile operator to route the calls to you anywhere.
HLR is the most important database maintained by the operator. The subscriber info is created by the operator in HLR at the time of purchase of subscription by an user.
VLR is a database that contains temporary information about the subscriber. It is used to service the visiting subscribers.
Location area refers to group of cells. If the mobile moves from one location area to a cell in different location area, it shall perform a location update to the network/cellular operator about its location. The mobile performs a location update to inform the operator about its exact location by checking the location area of the old cell and new cell. If the location area is different, the mobile will definitely perform a location udpate.
In the new location area, the VLR shall check its database for the subscriber information for authentication. If the subscriber information is not present in its database, it shall check with the HLR and get the copy of the subscription information via the location update. In this entire process, only a copy is made available to VLR and the HLR will not delete the subscriber information. The HLR shall infact update its records such that the subscriber information is updated with current VLR serving the mobile.
In scenario where a mobile moves from first VLR(eg - first location area) to a cell in second VLR(eg - second location area), the subscriber information that was copied into the first VLR shall be deleted once the mobile moves out of that first location area and the subscriber information in the recent VLR(second VLR) shall be retained. Once the mobile moves towards the second VLR (second location area), the HLR shall request the first VLR(old VLR) to remove the subscriber record. Note that only the subscriber information in the first VLR(old VLR) is deleted. The HLR updates its database with the current VLR serving the mobile.
From the above scenarios, you will observe that addition/deletion of subscriber info happens in VLR and only updation of subscriber info happens in HLR.
However, the HLR data is stored only as long as the subscriber uses the service of the cellular operator. That is, if the user opts to move with different cellular operator due to an attractive plan or any other reason, then obviously it implies that he is closing his subscription and only in that case, the subscriber information shall be deleted from HLR.
Don't confuse layer-1 broadcast (sending a signal everywhere) to a layer-2 or layer-3 broadcast (sending frames or packets addressed for every host).
The original ethernet was on coax, a broadcast medium. Every host could hear everything on the network segment. That is why ethernet adopted MAC (Media Access Control). An ethernet host only listens to frames addressed to it (including unicast to its MAC address, broadcast, and multicast for groups to which it has subscribed), even though all the frames reach every host on the link. The medium has nothing to do with how the frames are addressed.
Think about your cable television. All the channels are being broadcast on the medium all the time, but the cable provider doesn't send each channel individually to all the homes; it sends each video frame on each channel once, and a television in any home can display it if it is listening to that channel.
The cable ISP also only sends a data frame once, the way it happens in ethernet. The shared medium may deliver it to all the sites on a segment the way cable video is sent once to all the homes on a segment. A cable modem only listens to frames destined to its specific address, ignoring all the others. The same thing happens when your cable modem sends something back to the ISP. The frame may received by all the cable modems on the segment, but only the ISP equipment is listening to frames addressed to it.
For your ethernet broadcast, a switch only sends the frame once to each switch interface. It doesn't make a copy for each host on the LAN, and it is no more onerous for a switch to copy broadcast frames to every interface than it is for the switch to switch a single frame to a single other interface. There can be multiple hosts on each switch interface (think hubs or switches connected to a switch interface). The problem with broadcast on ethernet is that it interrupts every host on the LAN, and it uses bandwidth on every switch interface. You may be thinking about a broadcast storm, where bridged (switches are bridges) ethernet has a bridging loop, so that broadcast frames never die, they just accumulate until the LAN collapses.
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