Implementation of NGN/IMS Technologies into Legacy Network Infrastructures Andrey Krendzel1, Sergey Lopatin2, Josep Mangues-Bafalluy1 1
Centre Tecnològic de Telecomunicacions de Catalunya (CTTC), IP Technologies Area PMT, Av. Carl Friedrich Gauss 7, B4, 08860, Castelldefels – Barcelona – Spain {andrey.krendzel, josep.mangues}@cttc.cat 2
St. Petersburg R&D Institute of Telecommunications (LONIIS), Department of Perspective Network Research 11 Warshawskaya str., 196128, St. Petersburg – Russia
[email protected]
Abstract Issues concerning implementation of Next Generation Network/IP Multimedia Subsystem (NGN/IMS) technologies into existing networks to develop a unified network infrastructure to support new services and applications are considered in this paper. In fact, legacy circuit-switched (CS) networks like Public Switched Telephone Network (PSTN) or Public Land Mobile Networks (PLMN) are oriented mainly to support narrowband voice services and have to be modernized using innovative technologies to extend a set of offered services. NGN/IMS-based technologies can enable operators of such networks to modify network infrastructures to provide an access for users to a large diversity of services to keep their market share. It will allow also reducing CapEx and OpEx using a unified IP backbone and the open IMS platform. Since implementation of the NGN/IMS technologies in the existing infrastructures represents an extremely complex process, a decomposition of the whole process into some parallel subprocesses (innovation lines) is proposed for incremental deployment of the unified full IP integrated multi-service network infrastructure on a basis of yet existing ones. The milestones of the decomposition are described in detail in the paper.
1
Introduction
Currently there are essential changes in telecommunication market realities. From one side, these changes are characterized by a very high penetration level of services in PSTN/PLMNs that is close to saturation. From other side, there are the increasing use of "the Internet" and increasing demand for multimedia services, generalized mobility, convergence of networks and services [1]. Existing CS networks are older and are due for replacement in compare with packet-switched (PS) mobile networks that have been recently deployed [2]. This generation of the legacy networks is limited by narrowband voice services and there is a risk of being displaced by mobile and Internet telephony services [2]. However, it is not reasonable “to raze to the ground” this kind of networks. NGN/IMS-based technologies can enable operators of the legacy networks to offer to their users a much wider range of services that can help to keep their share in market and to get profitability. Besides, CapEx and OpEx of the operators can be reduced through the use of a converged IP backbone and the open IMS platform [2]. However, the
NGN/IMS deployment process requests essential investment from the network operators. Thus, some issues related to the implementation of NGN/IMS technologies gradually (smoothly) into the existing CS networks like PSTN and PLMN arise. Though IMS/NGN concepts have already been put in the realization phase to reduce cost and to create new attractive services, smooth ways to implement IMS/NGN technologies into the existing network infrastructures to minimize a risk of investment loss have not yet been sufficiently studied. This paper focuses on issues concerning NGN/IMS technologies implementation into the existing infrastructures towards the incremental building of the unified full IP integrated multi-service network. The common rule to analyze and to synthesize a complex multifunctional system is to make a decomposition of its components into some subsystems. It is reasonable to apply the same approach to the extremely complex NGN/IMS deployment process as well. The main contribution of the paper is the approach for the decomposition of the whole NGN/IMS innovation process into some relatively independent subprocesses to modify
existing network infrastructures. As an idea for such decomposition, experience accumulated from the evolution process of GSM/UMTS networks towards NGN is taken into account. The rest of the paper is arranged as follows. In Section II, the main principles of network development based on NGN/IMS concepts are formulated. The principles and reasoning for the decomposition of the whole innovation process into some subprocesses (innovation lines) to modify legacy networks are considered in Section III. In the Section IV, each of the innovation lines is described in detail and some illustrations concerning the renewal of legacy infrastructures through the use of NGN/IMS technologies are presented. In Section V, economical aspects of the proposed approach are discussed. Section VI concludes the paper.
2
The main principles of NGN/IMS concepts
The concepts NGN/IMS/NGOSS are based on documents of 3GPP, IETF, ITU, ETSI TISPAN, OMA, TM Forum and other standard development organizations. In accordance with the documents, the main principles of promising network development may be defined as follows: The unified transport IPv4/IPv6 backbone (BB) for information transfer capability. The use of multiple access networks. The transport control functions to handle the switching/routing process are separated from transfer functions related to the transfer of user and network information. The service control functions by means of the IMS platform are separated from transport control functions and transfer functions. Generalized mobility, which allows consistent and ubiquitous provision of services to users across multiple access networks. Convergence of networks and services, which enables operators to launch efficiently unlimited number of NGN services. Conjugation, automation, integration of Operations (Operational) Support Systems (OSS) and Business support systems (BSS). The distribution of the NGN functional entities into some planes in accordance with these principles is presented in Figure 1. It is based on specifications ITU-T Y.2001/Y.2011, ETSI ES 282 001, 3GPP TS 23.002, TMF 053 and others. Such distribution allows obtaining a grouping convenient consisting of the certain functional components for implementation and network description. Note that in practice when deploying network infrastructures some functional entities may be combined into one physical object and vice versa, one functional component may be mapped into several physical nodes. By analyzing Figure 1, it is seen that NGN accumulates and develops the most promising ideas from the precursor
network concepts, in particular, from concepts of Intelligent Network (IN), Telecommunication Management Network (TMN), 3G networks, etc. For instance, in the IN concept, the logic of service was separated from core switch system (TDM switches) into an external node called the service control point (SCP). There is also a trigger point called the service switching point (SSP) that was added to TDM switch to forward a call related to an IN service towards SCP [3]. Since services are no longer developed in the TDM switch, service providers enable developing different value-added services (VAS) for their networks without submitting a request to the core switch manufacturers and wait for the long development process [4]. In the same manner, in NGN, service-related functions are independent from the underlying transport-related technologies [1].
AS - Application Server API - Application Programming Interface BB- Backbone BG - Border Gateway BGCF- Breakout Gateway Control Function BSS – Business Support System CSCF - Call State Control Function DNS – Domain Name Server HSS - Home Subscriber Server JAIN - Java APIs for Integrated Networks (JAIN) MGCF - Media Gateway Control Function MGW – Media Gateway NAT - Network Address translation NGOSS – New Generation Operations Systems and Software OSS – Operations (Operational) Support System R-router SCP – service control point SCS - Service Capability Server SLF - Subscriber Location Function SG – Signalling Gateway SS#7 – Signalling System#7 VoD – Video on Demand
Figure 1 NGN functional architecture overview
Besides, the IN offered an idea of service independent building blocks (SIBs) for reusable service functions. In accordance with this idea, a service is realized as a composition of various SIBs. Similarly, in accordance with the NGN/IMS concept, a service is not standardized itself, but service building blocks (service enablers in terms of OMA) that are reusable by various services are standardized. The other known concept, TMN, provides a framework for achieving interconnectivity and communication across heterogeneous operations system and telecommunication networks [5]. The Telecommunication Management (TM) Forum defines a set of principles and technical deliverables known as New Generation Operations Systems and Software (NGOSS) to integrate both OSS and BSS that currently work separately. The issues concerning the NGOSS implementation arise on each plane of the NGN architecture (Figure 1); however, they are out of the scope of this paper. The IMS concept has been developed (IMS specification began in 3GPP Rel’5, 2002) for the provision of IP multimedia applications over IP multimedia sessions to users. One can see from Figure 1 that the specifics of IMS in the context of NGN is that it involves functional components at all planes of the functional model. IMS aspects are considered more detailed in Section IV,C. It is supposed that NGN networks will be able to provide session-based services, such as IP telephony, videoconferencing and video-chatting, and non-session-based services, such as video streaming and broadcasting [6]. However, one of requirements of NGN networks is to support interworking with a set of different legacy networks, in particular, with PSTN, integrated services digital network (ISDN), 2G, and other CS networks [1]. These networks are considered as means of access to resources of NGN in order to provide the above-mentioned services to users.
3
NGN/IMS deployment process decomposition
The main objective of the innovation development of existing network infrastructures may be formulated as a smooth migration on the basis of yet existing resources towards the full IP integrated multi-service network that is able to provide a large set of different services with required QoS. To reach this objective the following principles should be fulfilled: The principle of “incremental deployment” that deals with step-by-step evaluation process from CS to PSbased technologies for supporting any kind of services. The principle of “succession” taking into account that CS telephone/mobile networks will coexist with NGN networks quite long time and interworking between them should be handled. The principle of “perspective” taking into account that the deployment process of legacy networks should be based on the NGN/IMS/NGOSS concepts.
The full IP integrated multi-service network represents a complex multifunctional system. In accordance with system theory, the design of a complex system should be broken down into simpler blocks. It allows substituting a solution of one enormous task by the solutions of some particular tasks to simplify the tangled complex system. It is worthwhile to apply the same approach here making the decomposition of the whole deployment process towards the building of the full IP integrated multi-service network (taking into account the above-mentioned principles). It is proposed to decompose the whole process into three relatively independent innovation lines: 1. Step-by-step migration of CS telephone/mobile networks towards IP-technology to process traditional telephone traffic, in particular by means of PSTN emulation based on deployment of the equipment likes SIP-based SoftSwitch (SoftSw), Mobile Switching Centre Server (MSC-S) and media gateway (MGW). 2. Modernization and extension of access networks by deployment of high speed LAN/WLANs that are able to support high bit rate data transfer, i.e., 10…100 Mb/s to the end-user (including mobile users). 3. Conjunction of a set of the existing IP-networks and renovated IP networks (see the first item) with broadband access networks (see the second item) to support unlimited number of services in combination with generalized mobility on the basis of high-throughput IP backbone and the IMS platform. In accordance with the proposed decomposition, the infrastructure of the full IP integrated multi-service network that is created in the first steps of the deployment process is shown in Figure 2.
Full IP Integrated Multi-Service Network PSTN domain PSTN emulation
Multi-service network domain IMS platform PSTN simulation
Local exchange telephone networks IP Backbone Interexchange telephone networks
CS-domain of mobile networks
Subscriber telephone equipment
PS domain of mobile network
IP-networks (LAN/WLAN)
NGN user equipment
Figure 2 First steps of network infrastructure changing towards the full IP integrated multi-service network As one can see from Figure 2, the full IP integrated multiservice network includes two main domains, namely, the PSTN domain and the multi-service network domain. The PSTN domain consists of CS telephone/mobile networks
supplemented by equipment to realize PSTN emulation. The multi-service network domain includes two blocks. The first one consists on IP backbone, PS domains of mobile networks, and the IMS platform, including entities for PSTN simulation and the second one consists of broadband access networks (LAN/WLANs). Note that PSTN emulation is a reproduction, by means of special IP-based hardware/software (SoftSwitch/MSCS/MGW), of the activity of Local Exchanges (LEs) in the real environment of the CS telephone networks. It will be needed in Europe between 2009 and 2012 [3]. At the same time, PSTN simulation is an imitation (by means of hardware/software in IP-networks) of voice services that are similar to those supported in the CS telephone networks. Thus, the proposed approach satisfies the above-mentioned principles of “incremental deployment”, “succession” and “perspective” when the going towards the full IPintegrated multi-service network by means of the three relatively independent innovation lines. Besides, QoS requirements are handled in the PSTN domain for voice services as well as in the multi-service network domain for different kind of services (by means of high-throughput IP backbone and IMS). One can notice that the proposed approach disseminates an idea taken from strategy and tactics of the development of networks based on 3GPP Rel’3/4/5/6. In fact, according to the 3G concept, a network subsystem in existing mobile GSM/UMTS networks has two domains, namely the CS and PS domains. The equipment of the CS domain is focused on supporting telephone services in real circuit switching mode (3GPP Rel’3) or virtual circuit switching mode (3GPP Rel’4/5/…) that emulates circuit switching to handle the corresponding requirements to QoS. The equipment of the PS domain, at the first steps of development (3GPP Rel’4), is focused on supporting data services and Internet access in packet-switching mode. During further evolution of the PS-domain (3GPP Rel’ 5/6/…) there is an introduction of the IMS platform to extend a set of provided services and a throughput improvement of access network technologies. In the next section, the three above-defined innovation lines of network resource modernization towards the full IP integrated multi-service network by means of NGN/IMS technologies implementation are described in detail.
4
Steps towards the full IP integrated multi-service network
A
Changes in PSTN domain
As it is shown in Figure 2, the PSTN domain in the full IP integrated multi-service network consists of CS-based networks (PSTN/ISDN, CS domain of mobile networks, etc.). The deployment process in the domain is based on emulation service (using IP-technologies) that is introduced to the existing infrastructures for the purpose of in-
heritance of telephone services, which could be provided in the networks.
IE
Local network
E1
ISUP
ISUP
Local network SIP to other
SoftSw
LE
ISUP
E1 E1
LE
LE
SoftSw
PSTN PSTN Emulation Emulation H.248 H.248
E1
MGW
E1
MGW
to other E1 MGW
Figure 3 An example of PSTN emulation The old LEs/TDM switches are substituted by flexible SoftSwitches and MGWs. Figure 3 illustrates an example of the use of a SoftSw and MGWs instead of old LEs to emulate a fragment of a local telephone network. The same emulation procedure takes place in the CS mobile networks, where Mobile Switching Centers (MSCs) are replaced by a MSC Server (MSC-S), that is, a softswitch variant of the MSC. Thus, the gradual renewal of telephone networks by means of emulation of network equipment, then fragments of network infrastructure, and finally, the entire infrastructure, allows keeping the orientation of such networks to transfer, basically, the telephone traffic. As a result, the networks are able to provide high quality telephone services, but yet on the basis of IP-technologies.
B
Development of Broadband Access Networks
Existing access networks have some limitations, e.g., LANs are mainly focused on providing access to Internet only, WLANs are not oriented to support mobility, 3G networks provide bit rate data just up to 2Mb/s to the enduser (before implementation HSPA and LTE) and even less when the load of the Base Stations is increased. The most promising technologies for operators to develop broadband access networks are LTE/LTE-Advanced and Femtocells in mobile networks, and WiMAX. These technologies will be able to provide high bit rates and throughput to support broadband services for a large number of users. Initiated in 2004 within the 3GPP standardization body, the main purpose of the LTE concept is to improve the throughput of 3GPP’s radio access up to 50/100 Mbps in the uplink/downlink correspondingly. The technology uses channel bandwidths between 1.25 and 20 MHz [7]. The
Integration of a set of IP-networks and broadband access networks on the basis of IMS resources
To support the interaction between a set of different IPnetworks and broadband IP-based access networks, it is reasonable to create and develop network resources on the basis of IPv6 transport backbone with appropriate throughput. Note that similar network resources (on the basis of IPv4) are used for interaction of PS domains to get access to the Internet and to support roaming procedures. However, the throughput of such resources now is insufficient. The interaction of a unified IP-based backbone and a variety of broadband access networks allows providing multimedia services with appropriate charging and access control by means of IMS. The IETF has standardized Internet protocols (SIP, Diameter, etc.), the 3GPP has defined the IP Multimedia Overlay platform over different underlying
PSTN/PLMN
IMS platform
NGN UEs
Admission control of network resources and services
IP access network
Other networks / Internet
Applications
IP transport backbone
Figure 4 Multi-service network domain model The gradual development of the three above-mentioned lines finally leads to the unified full IP integrated multiservice network. The model of the multi-service network domain is presented in Figure 4. IMS Platform SIP
CSCF
HSS
PSTN emulation
Admission control of network resources and services
IP Access Networks
IP backbone
IP Access Networks
SIP user equipment
C
technologies (GPRS/UMTS, WLAN, DSL) for session control based on the Internet protocols and procedures to support generalized mobility across these technologies. IMS develops the principles of IN (see Section II) using the reusable service building blocks (service enablers) to create an unlimited number of different services. In fact, it represents a uniform open functional platform for a managed IP-based infrastructure that will enable easy deployment of both basic calling services and wirelessenhanced rich multimedia services mixing telecom and data services. Rich means bundling multiple service enablers (e.g., voice/video connectivity, presence, instant messaging, conferencing, gaming, TV broadcasting) [3]. IMS offers the converged model, where different applications use common resources, like billing, authentication, Q&M, etc. instead of so-called “stovepipe” model, where applications are independent [12]. It inherits also the traditional telecommunications experience concerning guaranteed QoS, flexible charging mechanisms, etc. [13].
SIP user equipmenmt
LTE-Advanced concept (3GPP Rel’10) defines for radio access the rate 500/1000 Mbps with the channel bandwidths between 40 and 70 MHz [8]. Note that in the case of LTE-Advanced, the efficiency of bandwidth using about 15/30 bps/Hz becomes close to theoretical bounds (Shannon and Kotelnikov results) due to the use of effective transmission schemes based on OFDM (Orthogonal Frequency Division Multiplex) and MIMO (Multiple Input Multiple Output) technologies. The similar results from the viewpoint of the efficiency of bandwidths may be potentially reached in the WiMAX technology. Thus, the standard IEEE 802.16e defines full mobility support in WiMAX. It provides data rates up to 75Mbps. The IEEE is working on a new standard the IEEE 802.16m sometimes called WiMAX II, which is expected to deliver data rates up to 1Gbps. The use of the femtocell technology known also as “Home Node B” in 3GPP terms [9] allows 3G operators to extend service coverage indoors and to increase capacity of the network, especially, where access to the network is limited or unavailable. The femtocell concept has been developed mainly for 3G; however, it can be extendable for other network solutions, e.g., based on the WiMAX technology. Taking into account the bandwidth limitations and the increasing demand for higher data rates (transfer of music files, video, mobile TV, etc.) the use of these technologies in combination with mobility may be considered as the most promising ones for radio access development. To support mobility of users between multiple heterogeneous access networks (generalized mobility), including both 3GPP and non-3GPP systems (e.g. WiMAX), 3GPP Rel’8 defines a flat IP-based network IP core architecture called System Architecture Evolution (SAE) [10]. The LTE/SAE architecture supposes a fully meshed approach between access gateways (AGs) and enhanced nodes B (ENB) with tunnelling mechanism over the IP transport network [11]. It optimises 3GPP’s core network for packet mode and, in particular, for the IP-Multimedia Subsystem (IMS), which supports all access technologies [7].
End-to-end telephone services
Figure 5 End-to-end telephone services in the multiservice network
The multi-service network infrastructure is used to support all kind of services including legacy network services. Figure 5 illustrates end-to-end telephony services by means of PSTN simulation in the multi-service network domain (see Figure 2). In the next section, the economical aspects of the proposed approach are considered.
5
Economical issues of the proposed approach
NGN/IMS technologies implementation allows network operators to reduce their CapEx and OpEx. For instance, TDM switches/MSCs are replaced into the lower priced Soft Switches/Gateways (CapEx reduction). Besides, Soft Switches are less than TDM ones that can reduce expenses on the real estate, electricity consumption and operating manpower (less OpEx) [12]. A converged IP backbone also brings some economical benefits. The open IMS platform defines many common components (e.g., call control, configuration database) and reusable service enablers so less development work is required to create new services [2]. Besides, project cost and risk are decreased since new applications take less development and payback time [3]. In any case, NGN/IMS technologies implementation requires a huge investment from network operators. On the one side, network operators have to make this investment to renew their network in order not to miss their potential users. On other side, to make essential investment is a great risk, especially when it is decided to destroy all existing infrastructure and to build a new one from scratch. The proposed decomposition of the whole deployment process enables both operators of legacy public telephone networks and operators of different heterogeneous networks to realize step-by-step modernization of their network infrastructures to minimize a risk of investment loss. The operators can participate in any combination of the three lines depending on their current economical state making corresponding investment and even to frozen their investment while the crisis time. However, it is extremely important for the operators at least to keep their strategic expenditures (STRATEX) to have a possibility to fulfill a gradual innovation migration of their network infrastructures towards the extension of a set of services for end users to keep the market share.
6
Conclusion
In this paper, issues concerning the smooth implementation of IMS/NGN technologies into legacy CS networks towards building a unified full IP integrated multi-service network infrastructure have been considered. The main contribution of the paper is the approach based on a decomposition of the whole NGN/IMS implementation process into 3 innovation lines. The first innovation line is the implementation, in the CS-based telephone or mobile networks, converged IP equipment to support emulation service; the second one is the modernization of access
networks on a basis of IP-based broadband access technologies; the third one is the integration of a set of IP networks into the converged IP backbone in combination with the deployment of the IMS platform as a uniform way to support both enriched voice and multimedia services. The proposed decomposition allows: 1) to fulfill step-bystep update and development of existing network resources based on NGN/IMS technologies; 2) to minimize corresponding investments taking into account tendencies to the increasing growth of demand for the Internet and Telco services; 3) to reduce CAPEX and OPEX, while implementing NGN/IMS technologies in traditional legacy networks, like PSTN, but keeping high quality of voice communications; 4) to develop the domain of full IP-integrated multi-service network by integration of a set of IPnetworks in a unified network infrastructure that is able to use the high-speed IP backbone to support a wide set of different services in combination with generalized mobility.
Acknowledgement This work was supported in part by the Spanish Ministry of Science and Innovation under grant number TEC200806826 (ARTICO), by the Catalan Regional Government under grant 2009SGR-940, and by the Spanish Ministry of Industry, Tourism and Commerce under grant number TSI-020301-2008-13 (WIMSAT).
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