The technological evolution towards all IP began in the early 2000s prompted telecom operators to invest first into the architecture called NGN (Next Generation Network), then in an architecture known as IMS (IP Multimedia Subsystem) from 2007. Alongside the IMS, some telecom operators have adopted as well SDN (Software Defined Network), especially to control the routers in a centralized way as it will be discussed later.
NGN, known as next generation, hasn’t actually experienced its expansion until 2007. The network is intended for telecom operators whose architecture is based on a transfer plan packet, network capable of replacing the switched telephone network running CCITT signaling No. 7. NGN has a unique core network that allows it to provide multiple services to subscribers on different access technologies.
The IMS architecture, which replaced that of the NGN since 2007, fits the new needs of users by offering multimedia services such as IP telephony, television IPTV mode, the presence management and instant messaging. In the following article we will not talk about the NGN architecture because it is no longer up-to-date. According to the American firm ABI Research, operators worldwide will invest up to $ 4 billion in 2017 to upgrade their 4G LTE in accordance with IMS architecture, in order to introduce the voice over LTE (VoLTE). For more details on VoLTE, refer to the article on the 4G LTE in the 1st issue of this magazine published in July 2015.
Alongside the IMS architecture, a new concept is asserting itself more as well in telecoms networks and which will certainly have a great impact on the approach to the operation of telecommunications networks, but also an alternative way to offer services uses. It is the SDN (Soft Defined Network) network which aims, as is discussed in more details later, to decouple the data plan of the control plan on telecom networks. The League of the global market which was worth 816 million euros in 2014, is estimated at 7 billion euros in 2019.
Regarding the access network, there are also large developments such as the advent of FTTH (Fiber To The Home) or the evolution of mobile radio loop through the use of OFDM (Orthogonal Frequency-Division Multiplexing) for 4G. For clarification, the OFDM provides several benefits for mobile radio systems especially easier management of variable bandwidths and potentially larger ones. OFDMA was largely behind the advent of LTE.
The purpose of this article is to provide an overview of the new IMS and SDN architectures. The content of this article regarding the IMS was the subject of a presentation on the evolution of IP networks that I have recently exhibited in the Middle East with the ITU. Regarding the SDN, the presentation of Mr. Omar Cherkaoui, a professor from the University of Quebec in Montreal (UQAM) and a major expert in the world, which was held in May 2015 at the INPT, has been of great help. For this purpose, a presentation (video) of one of his students is available in the media library on SDN in this issue of Lte Magazine. If telecom operators in Morocco have already adopted the IMS, they must now prepare themselves to get accustomed with the SDN. In fact, SDN will initially allow providing bandwidth to customers depending on the daily load. Secondly, and through the integration of big data applications SDN, telecom operators will have the ability to offer premium customer services automatically according to their profitability, lifted by the algorithms of Big Data.
The IMS architecture
The IP Multimedia Subsystem (IMS), having a standardized architecture, is increasingly used by telecom operators to provide mobile and fixed multimedia services. The IMS architecture is based on SIP (Session Initiation Protocol).
IMS technology, solution for the convergence of telecom networks and services to all-IP, is used in particular to ensure video conferencing and voice over IP. IMS is suitable for both fixed networks as mobile networks. Relative to NGN, IMS has the advantage of fixed-mobile convergence and presence management. Moreover, IMS ensures interoperation with existing networks and especially those operating with SS7. With IMS technology, a single terminal would be able to be used to access the internet, watch TV and offer telephony, all using a single communications protocol.

IMS is a centralized architecture divided into several layers. Before being able to access service platforms, the users must sign in to the operator. For this purpose, the HSS (Home Subscriber Server) provides authentication and location functions. There is also the MGW (Media Gateways) and MGCF (Media Control Gateways) that will enable interconnection with existing ISDN networks operated under the CCITT No. 7 signal. The access layer allows interoperability between different access technologies and the core of the IMS network. The « Session Control » manages all SIP sessions established through the IMS architecture. It controls in particular the opening of SIP sessions and placing calls. The layer « Service » provides for the application layer services operating under SIP. The layer « Application » provides all the applications available in an IMS architecture such as the presence or videoconference.
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