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To support Voice service in 5G NR network supporting NSA (EN-DC, Option 3x), VoLTE (Voice over LTE) is used.
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VoLTE indicates a scenario where the E-UTRA network supports voice services and the EPC offers a connection to IMS.
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To support VoLTE, two EPS bearers with the following QoS Class Identifier (QCI) values are used:
–A Default Bearer for IMS signaling (QCI5)
–A Dedicated Bearer for Voice over LTE (QCI1) . -
In EN-DC configuration, The MN(Master Node) i.e. eNB prevents the voice data bearer (QCI1)from being configured as a split bearer.
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This is recommended for disallowing split bearer configuration, e.g. QCI9 (download and upload from the Internet) when the device has a VoLTE connection.
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Here I try to depict an EN-DC (Option 3x) configuration where the device has two IMS bearers (Signaling and voice) and as well as Internet connection. In this diagram split bearer configuration is allowed when UE has a VoLTE connection.
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