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Why is one mobile application able to download a cellular network?

In a recent topic, “Is one mobile application capable of downloading a cellular network? ” A question was raised about downloading one application of a cellular network. In this post I would like to briefly explain how this is possible.

Cellular communication networks at the radio communication level between the base station and the subscriber are built on the principle of channels. That is, the entire available radio interface is divided into channels. It can be broken differently: in time ( TDMA in GSM ), in frequencies ( FDMA in old standards, for example, NMT-450 ), in codes ( CDMA in UMTS , IS-95 ). The number of such channels is limited by the physical capabilities of the equipment on which the cellular network is built.

In order not to be unfounded I will give the simplest example of such a division into channels.

This is a GSM channel structure for a cell in which one frequency is used.
B + D channel reserved for 2 types of traffic: Broadcasting (broadcast information in a cell about various logical parameters) and Dedicated — connections are established on this type of dedicated channel. That is, when you press the green button you are put on this channel and there you are given further instructions.
T is a traffic channel; conversations are made here.
G - channel reserved for GPRS / EDGE.
With this configuration of channels in a cell, it turns out that 6 subscribers can talk at the same time, there is always GPRS traffic, but it is not enough and there is some resource for establishing new connections.

This is usually sufficient, but variations may occur depending on the needs:

If there is an ATM in a cell, it will often establish new connections and will consume a signaling resource. It is necessary to allocate a separate channel for establishing connections.

If there are a lot of voice subscribers in a cell, then you can remove a fixed channel under GPRS and then users will be able to receive packet access only when not all channels are busy with voice.

There may be such a function on the equipment of a certain manufacturer, when the channel for establishing connections dynamically eats away the resource that it needs, but for this the operator usually has to pay a certain amount to the equipment supplier.

Further more - it is possible to include one more frequency in this cell and there will be 2 times more channels. The coolest thing I heard about - 32 frequencies in one cell. In Russia, we usually have no more than 4. Another thing is to make 2 users on the same traffic channel at once, this slightly degrades the voice quality, but increases the network capacity. If we talk about the network UMTS (3G), then there is a very similar situation.

So I wanted to explain that the cellular network resource is limited by how it was built by the planning and optimization engineers. If no one could have imagined that suddenly such a program would appear that would constantly establish a connection, then the network from it would “fall on a signal” —the overload at the stage of establishing a connection. The person whose letter is referred to in the original post is the head of the department responsible for tracking such incidents and solving such problems.

Source: https://habr.com/ru/post/107347/

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