N26 is an inter-CN interface between AMF and MME in order to enable interworking between the 5G core and EPC. Support of N26 interface in the network is optional. Interworking procedures using N26 interface enable the exchange of MM and SM states between the source and target networks. Handover procedures are supported through N26 interface.
The support for N26 interface between AMF in 5GC and MME in EPC is required to enable seamless session continuity for inter-system handover which will be critical for voice services. And let me tell you about a practical trail done by one operator during HO between 5G (VoNR) to 4G (VoLTE), so with N26 interface we had a voice interruption time ≈ 70ms, while without N26 interface, the interruption time ≈ 700ms, however the recommended limit for a voice call = 300ms.
Also N26 is based on GTPv2 and Not Httpv2 and is required to enable seamless session continuity for inter-system handover which will be critical for voice services
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