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Towards successful VoLTE and VoWiFi deployment: network function virtualization solutions’ benefits and challenges

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Abstract

The Recent decades have witnessed intensive efforts from operators to implement methods enabling better control over network utilization, service usage, and service monetization. Nevertheless, they report significant growth in Diameter signaling traffic, especially policy management signaling traffic. More specifically, operators offering long term evolution (LTE) data-only services and planning for a massive introduction of voice over LTE (VoLTE) and voice over WiFi (VoWiFi) services need to tackle the enormous growth in Diameter signaling traffic. The biggest challenge for those operators is to find an appropriate solution, scalable enough to handle the unpredictable growth of Diameter signaling traffic; as the VoLTE and VoWiFi services will reshape the landscape of LTE policies. Throughout this paper, we propose a network function virtualization (NFV) based model, mature enough to tackle the challenges of those operators planning to launch VoLTE and VoWiFi, without impacting existing services and without jeopardizing current revenues. In our approach we first used standard VoLTE and VoWiFi message flow and referenced users’ behavior; then we considered NFV architecture characteristics. We finally referred to the latest experiments and test results related to NFV maturity cycle.

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Correspondence to Youness Jouihri.

Appendix: Model description

Appendix: Model description

Functions to model the subscribers growth:

The \(N_v (x)\) is the function presenting the evolution of the number of VoLTE users:

$$\begin{aligned} N_v(x) = \frac{S_{max}}{(1+{e^{-\lambda _1(x-x_0)}})} \end{aligned}$$
(1)

where \(S_{max}, x_0\) and \(\lambda _1\) are respectively the maximum number of subscribers, the inflection year (convexity change in subscriber forecast), and the slope parameter for subscribers forecast.

The \(N_d (x)\) is the function presenting the evolution of the number of data-only subscribers:

$$\begin{aligned} N_d (x)= & {} \frac{n_1}{\sigma _1\sqrt{2\pi }}e^{\frac{-(x-\mu _1)^{2}}{2\sigma _1^{2}}}+\frac{n_2}{\sigma _2\sqrt{2\pi }}e^{\frac{-(x-\mu _2)^{2}}{2\sigma _2^{2}}} \end{aligned}$$
(2)

where \(n_1\) and \(n_2\) are calculated based on the initial and target values of LTE data-only subscriber’s growth. \(\sigma _1\), \(\sigma _2\), are the standard deviation, and \(\mu _1\), \(\mu _2\) are the the means.

In our use case, \(S_{max} = 20(Millions), x_0\) = 3(years), \(\lambda _1\)= 2.5, \(n_1\) = 25, \(n_2\) = 8, \(\sigma _1\) = 2, \(\sigma _2\) = 1.6, \(\mu _1\)= 6, and \(\mu _2= -0.1\).

Table 2 Network attach parameters description
Table 3 VoWiFi specific parameters description
Table 4 VoLTE call parameters description
Table 5 Network detach parameters description

Diameter transactions calculation

The average number of Diameter signaling transactions per second during the busy hour at year x, \(S_{total} (x)\), generated by LTE subscribers (VoLTE, VoWiFi and LTE data-only) was calculated based on the sum of signaling Diameter transactions generated by the activities associated to the below functions \(A_i\), with \(1 \le i \le 10\), where the first element of the function \((A_{i1})\) represents the number of transactions related to the Internet default bearer, the second \((A_{i2})\) corresponds to the number of transactions pertaining to VoLTE and VoWiFi default bearer. The third \((A_{i3})\) is association with the number of VoLTE and VoWiFi dedicated bearer transactions.The parameters used of those functions are described in Tables 2, 3, 4, and 5.

$$\begin{aligned} {S_{total}(x)=\frac{1}{3600}\sum _{j=1}^{j=3}\sum _{i=1}^{i=10} A_{ij}} \end{aligned}$$
(3)

\(A_1(x)\): number of Diameter transactions to establish default bearers (Internet and VoLTE/VoWiFi):

$$\begin{aligned} A_1(x)= & {} \frac{1}{3600}\left[ \begin{matrix} A_{11}&\quad A_{12}&\quad A_{13}\end{matrix} \right] \\ A_1(x)= & {} \frac{p_2}{3600}\left[ \begin{matrix} t_1.(N_v(x)+N_d(x))&\quad t_2.N_v(x)&\quad 0 \end{matrix}\right] \end{aligned}$$

\(A_2(x)\): number of Diameter transactions to authenticate an LTE subscriber (VoLTE and LTE data-only):

$$\begin{aligned} A_2(x)= & {} \frac{1}{3600}\left[ \begin{matrix} A_{21}&\quad A_{22}&\quad A_{23} \end{matrix}\right] \\ A_2(x)= & {} \frac{p_2}{3600}\left[ \begin{matrix} t_5.N_d(x)&\quad t_5.(1-p_6).N_v(x)&\quad 0 \end{matrix}\right] \end{aligned}$$

\(A_3(x)\): number of transactions to download the spending limit report from online charging system:

$$\begin{aligned} A_3(x)= & {} \frac{1}{3600}\left[ \begin{matrix} A_{31}&\quad A_{32}&\quad A_{33} \end{matrix}\right] \\ A_3(x)= & {} \frac{p_2}{3600}\left[ \begin{matrix} t_6.N_d(x)&\quad t_6.N_v(x)&\quad 0 \end{matrix}\right] \end{aligned}$$

\(A_4(x)\): number of Diameter transactions to charge LTE data services:

$$\begin{aligned} A_4(x)= & {} \frac{1}{3600}\left[ \begin{matrix} A_{41}&\quad A_{42}&\quad A_{43} \end{matrix}\right] \\ A_4(x)= & {} \frac{p_2}{3600}\left[ \begin{matrix} t_7.N_d(x)&\quad t_7.(1-p_6).N_v(x)&\quad 0 \end{matrix}\right] \end{aligned}$$

\(A_5(x)\): number of Diameter transactions to register a VoLTE or VoWiFi subscriber in IMS:

$$\begin{aligned} A_5(x)= & {} \frac{1}{3600}\left[ \begin{matrix} A_{51}&\quad A_{52}&\quad A_{53} \end{matrix}\right] \\ A_5(x)= & {} \frac{p_5}{3600}\left[ \begin{matrix} 0&\quad t_8.N_v(x)&\quad 0 \end{matrix}\right] \end{aligned}$$

\(A_6(x)\): number of Diameter transactions to release a default bearer (VoLTE or VoWiFi and Internet):

$$\begin{aligned} A_6(x)= & {} \frac{1}{3600}\left[ \begin{matrix} A_{61}&\quad A_{62}&\quad A_{63} \end{matrix}\right] \\ A_6(x)= & {} \frac{p_3}{3600}\left[ \begin{matrix} t_4.N_d(x)&\quad t_4.N_v(x)&\quad 0 \end{matrix}\right] \end{aligned}$$

\(A_7(x)\): number of Diameter transactions to de-register a VoLTE or a VoWiFi subscriber from IMS:

$$\begin{aligned} A_7(x)= & {} \frac{1}{3600}\left[ \begin{matrix} A_{71}&\quad A_{72}&\quad A_{73}\end{matrix}\right] \\ A_7(x)= & {} \frac{p_3}{3600}\left[ \begin{matrix} 0&\quad t_9.N_v(x)&\quad 0 \end{matrix}\right] \end{aligned}$$

\(A_8(x)\): number of Diameter transactions to establish and release dedicated bearer:

$$\begin{aligned} A_8(x)= & {} \frac{1}{3600}\left[ \begin{matrix} A_{81}&\quad A_{82}&\quad A_{83} \end{matrix}\right] \\ A_8(x)= & {} \frac{p_1}{3600}\left[ \begin{matrix} 0&\quad 0&\quad t_3.N_v(x) \end{matrix}\right] \end{aligned}$$

\(A_9(x)\): number of Diameter transactions to charge a prepaid VoLTE or VoWiFi call:

$$\begin{aligned} A_9(x)= & {} \frac{1}{3600}\left[ \begin{matrix} A_{91}&\quad A_{92}&\quad A_{93} \end{matrix}\right] \\ A_9(x)= & {} \frac{p_1}{3600}\left[ \begin{matrix} 0&\quad 0&\quad p_4.t_{10}.N_v(x) \end{matrix}\right] \end{aligned}$$

\(A_{10}(x)\): number of Diameter transactions to authenticate a VoWiFi subscriber:

$$\begin{aligned} A_{10}(x)= & {} \frac{1}{3600}\left[ \begin{matrix} A_{101}&\quad A_{102}&\quad A_{103} \end{matrix}\right] \\ A_{10}(x)= & {} \frac{p_2}{3600}\left[ \begin{matrix} 0&\quad 0&\quad p_6.(t_{11}+t_{12)}.N_v(x) \end{matrix}\right] \end{aligned}$$

Calculation of the total Diameter signaling transactions moved to the NFV

The average number of Diameter transactions per second during busy hour at year x moved to our virtualized architecture, \(S_{NFV}(x)\), is calculated by adding an NFV weighting factor \(\delta _{ij}\) to the Eq. (3):

$$\begin{aligned} S_{NFV}(x)=\frac{1}{3600}\sum _{j=1}^{j=3}\sum _{i=1}^{i=10} \delta _{ij}A_{ij} \end{aligned}$$
(4)
$$\begin{aligned}&S_{NFV}(x) =\frac{1}{3600}.[\delta ].\left[ \begin{matrix} A_{11}&{}\quad A_{12}&{}\quad A_{13}\\ A_{21}&{}\quad A_{22}&{}\quad A_{23}\\ A_{31}&{}\quad A_{32}&{}\quad A_{33}\\ A_{41}&{}\quad A_{42}&{}\quad A_{43}\\ A_{51}&{}\quad A_{52}&{}\quad A_{53}\\ A_{61}&{}\quad A_{62}&{}\quad A_{63}\\ A_{71}&{}\quad A_{72}&{}\quad A_{73}\\ A_{81}&{}\quad A_{82}&{}\quad A_{83}\\ A_{91}&{}\quad A_{92}&{}\quad A_{93}\\ A_{101}&{}\quad A_{102}&{}\quad A_{103} \end{matrix}\right] \\&S_{NFV}(x)=\frac{1}{3600}.[\delta ].(N_d(x)\left[ \begin{matrix} p_2.t_1&{}\quad 0&{}\quad 0\\ p_2.t_5&{}\quad 0 &{}\quad 0\\ p_2.t_6&{}\quad 0&{}\quad 0\\ p_2.t_7&{}\quad 0&{}\quad 0\\ 0&{}\quad 0&{}\quad 0\\ p_3.t_4&{}\quad 0&{}\quad 0\\ 0&{}\quad 0&{}\quad 0\\ 0&{}\quad 0&{}\quad 0\\ 0&{}\quad 0&{}\quad 0\\ 0&{}\quad 0&{}\quad 0 \end{matrix}\right] \\&\quad +\,N_v(x)\left[ \begin{matrix} p_2.t_1&{}\quad p_2.t_2&{}\quad 0\\ 0&{}\quad p_2.t_5.(1-p_6)&{}\quad 0\\ 0&{}\quad p_2.t_6&{}\quad 0\\ 0&{}\quad p_2.t_7.(1-p_6)&{}\quad 0\\ 0&{}\quad p_5.t_8&{}\quad 0\\ 0&{}\quad p_3.t_4&{}\quad 0\\ 0&{}\quad p_3.t_9&{}\quad 0\\ 0&{}\quad 0&{}\quad p_1.t_3\\ 0&{}\quad 0&{}\quad p_1.p_4.t_{10}\\ 0&{}\quad 0&{}\quad p_2p_6(t_{11}+t_{12}) \end{matrix}\right] \end{aligned}$$

The matrix \([\delta ]\) is the matrix grouping the entire weighting factors, defined as below:

$$\begin{aligned}{}[\delta ] = \left[ \begin{matrix} \delta _{11}&{}\quad \delta _{21}&{}\quad \delta _{31}&{}\quad \delta _{41}&{}\quad \delta _{51}&{}\quad \delta _{61}&{}\quad \delta _{71}&{}\quad \delta _{81}&{}\quad \delta _{91}&{}\quad \delta _{101}\\ \delta _{12}&{}\quad \delta _{22}&{}\quad \delta _{32}&{}\quad \delta _{42}&{}\quad \delta _{52}&{}\quad \delta _{62}&{}\quad \delta _{72}&{}\quad \delta _{82}&{}\quad \delta _{92}&{}\quad \delta _{102}\\ \delta _{13}&{}\quad \delta _{23}&{}\quad \delta _{33}&{}\quad \delta _{43}&{}\quad \delta _{53}&{}\quad \delta _{63}&{}\quad \delta _{73}&{}\quad \delta _{83}&{}\quad \delta _{93}&{}\quad \delta _{103} \end{matrix}\right] \nonumber \\ \end{aligned}$$
(5)

We calculated the elements \(\delta _{ij}\) (\(1 \le i \le 10\) and \(1 \le j \le 3\)) of the matrix \([\delta ]\) using the following rules:

\(\delta _{ij} = 1\), when: 100 % of transactions migrated to the virtualized model when the activities happen into the model.

\(\delta _{ij} = 0.5\), when: 50 % of transactions migrated to the virtualized model when the activities occur between two elements one of them in our model.

\(\delta _{ij} = 0.5\), when: 0 % of transactions migrated to our virtualized model if the activities occur between elements out of our model.

$$\begin{aligned} {[}\delta _{Model}] \!=\! \left[ \begin{matrix} 0 &{}\quad 0 &{}\quad 0 &{}\quad 0 &{}\quad 0 &{}\quad 0 &{}\quad 0 &{}\quad 0 &{}\quad 0 &{}\quad 0 \\ 1 &{}\quad 0 &{}\quad 0.5 &{}\quad 0.5 &{}\quad 0.5 &{}\quad 1 &{}\quad 0.5 &{}\quad 0 &{}\quad 0 &{}\quad 0 \\ 0 &{}\quad 0 &{}\quad 0 &{}\quad 0 &{}\quad 0 &{}\quad 0 &{}\quad 0 &{}\quad 1 &{}\quad 0.5 &{}\quad 0 \end{matrix}\right] \nonumber \\ \end{aligned}$$
(6)

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Jouihri, Y., Guennoun, Z., Chagh, Y. et al. Towards successful VoLTE and VoWiFi deployment: network function virtualization solutions’ benefits and challenges. Telecommun Syst 64, 467–478 (2017). https://doi.org/10.1007/s11235-016-0186-y

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