# Call Model and Test-Verification Methods for PS-LTE Core Equipment
## 2 Call Model and Test Result for Core Equipment
### MME Core System Test Model  
The MME for DSCNs is designed with a capacity of 400,000 simultaneous subscribers, and the detailed requirements for services are 3200 calls per second (CPS), 1,200,000 sessions (average of three sessions per subscriber), 2,400,000 bearers (average of six bearers per subscriber), 30,000 eNB, and 44,300 transactions per second (TPS). MME is installed as a virtual machine (VM) configuration on the two units of HP DL380, and it is provided as a virtualization system. In the performance test, the environment of the simulator and measuring instrument for each subsystem is set up, and the capacity and performance are measured by applying call connection/disconnection and voice/video call and general traffic to each subsystem. Because commercial measuring instruments do not support both user equipment (UE) and eNB, performance is measured using a self-developed simulator and a commercial packet generator for testing. System statistics confirm the number of subscribers, traffic, load, fail/drop and load status of CPU, and memory for each VM. It is assumed that 1 (subs):3 (session):6 (bearer) is created per subscriber. For a scenario for generating both 3200 CPS and 44,300 TPS, 370,000 fixed call subscribers are attached, and for 30,000 floating call subscribers, a scenario is created by attach \(\rightarrow\) public data network (PDN) connectivity \(\rightarrow\) X2 handover \(\rightarrow\) tracking area update (TAU) \(\rightarrow\) S1 release (S1 REL) \(\rightarrow\) scheduling request (SR) \(\rightarrow\) PDN disconnect (PDN DISCON) \(\rightarrow\) detach. As 16 tracking area codes (TAC) are assigned per tracking area list, the number of eNBs within 1 TAC is not limited. Terminal emulation for services was used for MCPTT group voice and video calls by 10 units, respectively, and for VoLTE voice and video calls, by two units. Initial attach CPS means as the average (AVG) CPS \(\times\) the number of transactions per attach. PDN connectivity CPS refers to total AVG CPS \(\times\) the number of transactions per PDN connection (CON). X2 HO Connectivity CPS is confirmed as total attempt/60 ch (CPS) \(\times\) the number of transactions per PDN CON. TAU CPS refers to AVG CPS \(\times\) the number of transactions per TAU. S1 REL CPS transmits radio access bearer (RAB) request (REQ) message when S1 REL occurs, and it is confirmed that total RAB REQ/60 ch (CPS) \(\times\) the number of transactions per S1 REL. SR CPS refers to total AVG CPS \(\times\) the number of transactions per SR. PDN disconnect CPS is calculated as PDN disconnect = bearer deactivation per node (BDN)--DTACH and PDN DISCON CPS = BDN (attempt--DTACH attempt)/60. PDN DISCON TPS is calculated as PDN DISCON CPS \(\times\) the number of transactions per SR. Detach TPS is calculated as AVG_CPS \(\times\) the number of transactions per DTACH. Figure 3 shows the performance test results applying the call model set in Table 2, and it confirms the processing capacity of 48,807 TPS, which is higher than the requirement of 44,300 TPS. Therefore, the performance test is possible using the call model defined in Table 2. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Items** & **Type** & \begin{tabular}{c} **Number of** \\ **Transactions** \\ \end{tabular} & **BHCA/User** & \begin{tabular}{c} **Transactions** \\ **per Hour** \\ \end{tabular} \\ \hline Attach & INIT & 10 & 0.4 & 4 \\ \hline \multirow{2}{*}{Detach} & \
\begin{tabular}{c} Detach UE \\ Detach NW \\ \end{tabular} & 3 & 0.09 & 0.27 \\  &
\begin{tabular}{c} Detach NW \\ \end{tabular} & 1 & 0.04 & 0.04 \\ \hline Preservation & eNB init S1 REL & 2.5 & 38.33 & 95.83 \\ \hline \multirow{2}{*}{Service request} & UE & 2.5 & 18.88 & 47.2 \\  & NW & 3 & 37.76 & 113.28 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: MME call model: assuming 400,000 subscriber base.