1. What is SDAP?
– SDAP (Service Data Adaptation Protocol) is a layer introduced in 5G NR architecture
– Primary functions:
– Mapping QoS flows to DRBs
– Handling various traffic types (video, VoIP, browsing) per their QoS requirements
– SDAP is specific to 5G Core (5GC) architecture
2. What Happens When NR Connects to EPC?
– Known as Option 3 or NSA (Non-Standalone) deployment
– NR used only for high-speed radio; core remains EPC (4G)
– LTE handles control signaling and bearer anchoring
– 5G QoS and SDAP are not used
– NR user plane: PDCP-RLC-MAC-PHY stack (same as LTE)
– SDAP skipped since EPC does not support 5G QoS model
3. Summary Table
| Deployment | Core Used | SDAP Used? | Reason |
|---|---|---|---|
| Option 3 (NSA) | EPC (4G) |  No |
EPC doesn’t support 5G QoS or SDAP |
| Option 2 (SA) | 5GC (5G) |  Yes |
SDAP required for 5G QoS flow mapping |
4. Protocol Stack Overview
– NSA (NR + EPC):
App
|
IP
|
PDCP
|
RLC
|
MAC
|
PHY
– SA (NR + 5GC):
App
|
IP
|
SDAP ← new layer!
|
PDCP
|
RLC
|
MAC
|
PHY
In Summary:
– SDAP is not used in NSA because EPC lacks support for the 5G QoS model
– SDAP is only present in SA deployments using 5G Core
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