# Call Model and Test-Verification Methods for PS-LTE Core Equipment
## 2 Call Model and Test Result for Core Equipment
### SAE-GW Core System Test Model  
SAE-GW is one of the NEs constituting LTE core and is integrated equipment in a serving gateway (S-GW) and a packet data network gateway (P-GW). The main functions of S-GW include inter-eNB handover, packet buffering, packet routing and forwarding, and transport-level packet marking. The main functions of P-GW include IP routing/forwarding, per-service data flow (SDF)/per-user-based packet filtering, IP address allocation to UE, and policy and charging control (PCC) rule processing. SAE-GW has an active-standby structure, and the interface comprises a small form-factor pluggable (SFP) + 12-port supporting 10-gigabit ethernet (GE) and RJ-45 8-port supporting 1 GE. The requirements for DSCNs are based on 400,000 subscribers, 16,000 TPS, and 10 Gbps (PCC on, deep packet inspection (DPI) on, row manager on). The call model for calculating the capacity and performance of SAE-GW is shown in Table 3.  
The simulator load conditions for the SAE-GW test have used the fixed calls of 346,000 subscribers, floating calls of 10,000 subscribers, and traffic calls of 44,000 subscribers as inputs. Per subscriber, subscribers:session:bearer ratio (1:3:6) is calculated as 400,000 (subs): 1,200,000 (session):2,400,000 (bearer). As for fixed-call subscribers, attach/PDN conn./bearer activation is performed. The simulator setting for floating call bulk subscribers is approved as 2400 CPS as a scenario of attach and detach, and attach/detach transaction is calculated as CPS \(\times\) 7 (CSR, DSR, MBR, CCR-I, CCR-T, ACR_START, ACR_STOP), which is 16,800 TPS. As for UE traffic, traffic of 8 Gbps is applied to 44,000 subscribers, which is approximately 10% of 400,000 subscribers, using a commercial traffic generator, and the packet size is set by mixing 128, 512, and 1024 bytes. The total number of bearers is calculated as the number  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Items**} & **Number of** & **BHCA/** & **Transactions** \\  & **Transactions** & **Subscriber** & **per Hour** \\ \hline Attach/Detach & 7 & 0.53 & 3.71 \\ \hline \multirow{4}{*}{TAU} & w/SGW & \multirow{2}{*}{0} & \multirow{2}{*}{0} \\  & relocation & & \\  & w/MME and & & \\  & SGW relocation & 1 & 0.1 & 0.1 \\  & No change & 0 & 0 & 0 \\ \hline Periodic TAU & 1 & 0.12 & 0.12 \\ \hline Bearer activation & 1 & 2.08 & 2.08 \\ \hline \multirow{4}{*}{X2} & w/o SGW & \multirow{2}{*}{1} & \multirow{2}{*}{5.06} & \multirow{2}{*}{5.06} \\  & relocation & & \\  & w/SGW & & \\  & relocation & & \\ \hline S1 & w/MME & \multirow{2}{*}{1} & \multirow{2}{*}{0} & \multirow{2}{*}{0} \\  & relocation & & \\ \hline UE init request (idle \(\rightarrow\) active) & 1 & 18.88 & 18.88 \\ \hline UE init request (idle \(\leftarrow\) active) & 2 & 37.76 & 75.52 \\ \hline S1 release (active \(\rightarrow\) idle) & 1 & 38.33 & 38.33 \\ \hline PDN connection/disconnection & 5 & 0.63 & 3.15 \\ \hline TPH per subscriber & & 149.13 \\ \hline TPS per subscriber & & 0.0414 \\ \hline TPS based on 400,000 subscribers & & 16,570 \\ \hline Throughput (Kbps) per subscriber & & 20.85 \\ \hline Throughput (Gbps) based on 400,000 subscribers & & 8.34 \\ \hline \hline \end{tabular}
\end{table}
Table 3: SAE-GW call model: assuming 400,000 subscriber base.  
of fixed call bearers + the number of traffic call bearers, and the numbers of sessions and subscribers must be checked equally.  
Figure 4 shows the test results applying the SAE-GW call model as shown in Table 3, and it can be seen that performance test is possible with the proposed call model by confirming the performance of 17,559 TPS and 16.9 Gbps (8.2 + 8.7 Gbps), which are higher than the requirements of 16,000 TPS and 10 Gbps.