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 networks Architecture
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.
Gateways are planned to pass from SS7based RTC networks to SIP based IMS network
The SDN architecture
The SDN (Software Defined Network) was developed by the Open Networking Foundation (ONF). Operational since 2011, it aims to decouple in telecom networks the data plan of the control plan part. Some experts said SDN was a weapon against routers manufacturers, as they will lose their power against telecom operators in terms of control. For illustration, Cisco will provide routers without the control function and it is up to the operators to manage the control function routers in a centralized way. In fact, without SDN, control was performed at each router. The SDN will thus relegate to second place router manufacturers. The control function will be provided by operators to control different brands of equipment as long as they conform to the ONF. In other words, the SDN leaves only the switch packages to the routers. Intelligent control functions such as the allocation of priorities or routing decisions will be decided in a common controller to multiple devices.
Several experts indicate that the majority of mobile operators think about introducing in the next three years connectivity solutions based on SDN. Investment in SDN by operators for the year 2019 is 7 billion estimated.
In a network without SDN, at the arrival of a packet on the port on a router, the latter applies the rules of routing or switching programmed into its operating system. But this program can be modified or adapted manually by the administrator.
With SDN, these routing rules can be changed remotely in a programmable manner. The administrator defines the rules in the MCU so that they are instantly broadcasted in the network equipment. For example, we can offer more bandwidth during the day (or night) to a company as needed. Thus SDN enables automation of these configurations in a centralized controller without interfering with each router.
The controller is actually a software system that replaces the control software located at each network node. Therefore, it becomes possible to fully control the network of an operator, heterogeneous or not, without having to touch every router. At the 2016 Mobile World Congress in Barcelona, representatives of an operator of South Korea indicated to me that Korea is already considering the possibility of offering a quality service according to the user profile through the application of big data and the SDN architecture.
Before 2002, the IP has not experienced any significant developments on the telecom network because of the complexity of existing servers at the time, the cost of bandwidth and low broadband penetration in enterprises.
All players in the telecom ecosystem were betting on the development of ATM technology (Asynchronous Transfer Mode) during the 90s and early 2000. ATM technology has precisely been designed for a network that could support a synchronous traffic as well as traffic using packets. However, ATM technology has failed to spread over its networks. Its complexity and the investment that it requires have been obstacles to its development, which enabled, accordingly, the IP to impose itself.
As of 2002, the IP has had a real acceleration especially with the emergence of new protocols such as SIP. The IMS is a standardized NGN type architecture used by phone operators to provide fixed and mobile multimedia services. This architecture allows, among others, to use VoIP technology and a standardized implementation, by the 3GPP, the SIP protocol compatible IP standard protocols (IPv4 and IPv6). The purpose of the introduction of IMS is to provide other services in addition to those offered by the NGN such as the presence and convergence. In fact, IMS allows to coalesce the Internet and the telephony world, whether fixed or mobile. On SDN networks, decoupling mechanism between the hardware side and the software one is not reminiscent of the IMS architecture (IP Multimedia Subsystem), which introduced two distinct levels on telecom equipment, one for data and one for control.
By Ahmed Khaouja Telecommunications Consultant and ICTs and ITU expert.