5G NSA 3.x Architecture
5G NR, initial deployments are based on 5G NSA, also known as Option-3. There are multiple variants of Option-3 namely option 3, Option 3a and Option 3x.
Option-3/3a/3x are transparent to 4G Core network (MME and P-GW).
- Option-3: User Plane Traffic is split at eNodeB.
- Option-3a: User Plane Traffic is split at EPC (S-GW).
- Option-3x: User Plane Traffic is split at 5G gNB.
Following figure show Option-3x deployment architecture. It is based on LTE assisted signaling, which is done through the LTE eNB to the Mobile. The 5G gNB will only provides user plane connection to the EPC core via signaling from the LTE eNB.
As per NSA 3.x deployment architecture we will have following available interfaces.
- S1-U: Provides user plane connectivity to EPC for eNB and gNB.
- S1-C: Provides control plane (signalling) connectivity to EPC for eNB and gNB.
- X2-U: Provide user plane connectivity between eNB and gNB
- X2-C: Provides control plane between eNB and gNB
Interface Bandwidth requirement depends on following factors:
- Number of Users Supported
- Average Data Throughput/User in DL and UL(Mbps)
- Use Ratio between X2-U and S1-U
- Support of VLAN and IPSec
- OAM and IP Sync Bandwidth
- Control Plane to User Plane Ratio
- Payload Packet Size
- Packet Header Overhead
Interface Bandwidth Calculation
Interface calculation is very important for network architecture and dimensioning .
Assumptions or Inputs
- Number of Users = 700
- Average DL Data Throughput = 100 Mbps
- Average UL Data Throughput = 50 Mbps
- X2U to S1U Use Ratio = 10%
- Peak to Avg Traffic Ratio = 1
- Control Plane to User Plane Ratio = 1%
- OAM Bandwidth= 1 Mbps
- IP Sync Clock BW = 0 Mbps
Full Transport Packet Size Calculation:
Transport packet contains data payload + headers. The data payload is a single air interface packet and headers includes following.
- MAC header – 18 Bytes
- VLAN header – 4 Bytes , optional applicable only when VLAN tagging is enabled
- IPsec header – 70 Bytes, optional applicable only when IPsec is implemented in operator’s network for security
- IP header – 20 Bytes
- UDP header – 8 Bytes
- GTP-U header – 12 Bytes
- Payload is the user data, it can varies from 256 Bytes to 4096 Bytes. For our calculation lets assume it to be 1400 bytes
- Full Packet Size= 1400 + 132 = 1532 Bytes
S1-U Interface DL Bandwidth
Following formula can be used to calculate the S1-U interface Downlink bandwidth.
S1-U Interface UL Bandwidth
Following formula can be used to calculate the S1-U interface UL bandwidth.
S1-C Interface Peak Bandwidth
X2 Interface Peak Bandwidth
Peak throughput for X2 Interface is the sum of control and user plane.
- X2-U Interface Peak Bandwidth
- X2-C Interface Peak Bandwidth
gNB Total Bandwidth
gNB base station total throughput is the sum of S1-U peak BW, X2-C peak BW, O&M BW and IP sync clock BW.
eNB Total Bandwidth
LTE eNB base station total throughput is the sum of X2 Peak BW and S1 interface control plane BW.
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