Network Engineering Asked on December 30, 2021
I’m struggling to understand the need for frame aggregation into the multiframe and other higher level frames.
What exactly do we gain with the aggregation? Is this for synchronisation purposes across all the channels? Is this simplifying slot addressing?
There are two kinds of multiframes in GSM. They are:
So multiframes help with scheduling and synchronization.
To make the timing of traffic multiframes and control multiframes unfirom, we have the superframe. It is 51 traffic multiframes long, i.e., it is 26 control multiframes long. Notice how a multiframe is 51*26 frames long, so it is an integer multiple of both the control multiframes and traffic multiframes, so it helps to align traffic and control multiframes in one superframe.
Last but not least, the biggest is the hyperframe, which is 2048 superframes long. That is over 3 hours. A few functions are designed to use this periodicity of the hyperframe. For example, the encryption counter is unique only within a hyperframe and then repeats in the next hyperframe. It would be best to never repeat the counter, but as a practical tradeoff, GSM uses the hyperframe for that periodicity.
Answered by auspicious99 on December 30, 2021
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