And why is Option 3X the preferred option in NSA?
5G NSA has mainly three options: Option 3, 3a, and 3X; Option 3x is preferred to overcome the drawback associated with options 3 and 3a.
Let’s go through each option to understand it further.
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As you can see in the below-shared figure, Option 3 has the drawbacks of tunneling all user plane data through eNodeB Legacy, and 4G Legacy has likely been dimensioned to support the air-interface speed offered by 4G; accordingly, it might limit the expected 5G Speed, or it might require extra investment to upgrade 4G BTS.
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While Option 3A has the drawback of not supporting data application transfer through the X2 interface; in other words, this means that the user plane controller is the S-GW, which will be transferring/ distributing the data randomly towards either 4G or 5G BTS without considering coverage differences between both legacies.
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While as seen in Option 3X, the user plane “Data Transfer “ is being handled through g-NodeB “ 5G BTS”, which means 5G BTS is controlling the data splitting or transfer, So in the weak coverage scenarios of 5G, the gNodeB will dynamically forward data across X2 interface towards the eNodeB.
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