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Converged IP/MPLS Backbone Networks for 2G and 3G Voice Services Integration

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Converged IP/MPLS Backbone Networks for 2G and 3G Voice Services Integration White Paper Converged IP/MPLS Backbone Networks for 2G and 3G Voice Services Integration With Release 4 of the third-generation (3G) architectural standards for mobile networks, mobile operators can now reduce costs, enhance revenues, and decrease time to market for new voice-over-IP (VoIP) and traditional voice services. When mobile operators deploy a new split architecture to support voice, and consolidate 2G and 3G voice over an IP/Multiprotocol Label Switching (IP/MPLS) backbone network, existing 2G and newer 3G voice traffic can greatly benefit from simplified operations, multigigabit speeds, transport efficiency, quality of service (QoS), traffic engineering, and all of the features required of carrier-class networks. This paper describes how IP/MPLS technologies support the emerging VoIP infrastructure in mobile networks to facilitate the convergence of 2G and 3G mobile voice services, including the evolution of the VoIP network from the split architecture in 3G Release 4 to the introduction of the IP-enabled media gateway, and how available technologies from Cisco Systems® can help operators effectively manage converged IP/MPLS mobile networks. Summary Most mobile operators are now firmly focused on consolidating transmission and management of a broad range of mobile services deployed on disparate networks to reduce their capital expenses (CapEx) and operating expenses (OpEx), increase business agility, and more easily deploy new 3G IP-based services. Cisco® has helped both wireless and wireline carriers accomplish such consolidation while greatly enhancing performance and network features by converging disparate networks into one common IP/MPLS core to support both existing and future services. The Cisco IP Next-Generation Network (IP NGN) architecture for mobile operators is a roadmap to realize the vision of next-generation mobile services – the delivery of data, voice, and video anywhere and anytime across virtually any access technology. The Cisco IP NGN provides a migration path to an IP foundation and support for both IP Multimedia Subsystem (IMS) and non-IMS applications to achieve more services, better control, and greater network efficiencies. It offers a superior platform for converged services and support for flexible billing and service plans. Furthermore, it allows interoperability with different radio access technologies, and open and distributed support for multiple-vendor implementations. The goal is a network environment where multiple types of services can be continuously deployed to meet customer demands in 3G and miscellaneous service environments. This is possible with an extremely powerful and flexible architecture that features convergence at application, service control, and network layers (Figure 1). Cisco Systems, Inc. All contents are Copyright © 1992–2006 Cisco Systems, Inc. All rights reserved. Important Notices and Privacy Statement. Page 1 of 11 Figure 1 Cisco IP Next-Generation Network Architecture for Mobile Operators Mobile operators need an application layer that interfaces with the customer; a secure network layer that creates and delivers the services; and between them both a service layer that orchestrates the delivery, operations, features, and billing of the service itself. The service layer is also known as the Cisco Service Exchange Framework (SEF), and it supports both Session Initiation Protocol (SIP)- based services and non-SIP-based services. SIP is specified in the IMS framework as the glue for simple mobile and wireline service transitions. Intelligent networking with the Cisco IP NGN for mobile architecture and associated technologies and platforms makes it possible to connect all three layers to make next-generation mobile services a reality. The complexity of operating such a network is greatly simplified, and the network becomes more resilient, integrated, and adaptive. As a result, mobile operators will have more services, greater efficiencies, better control, and enhanced security in the operation of networks and the delivery of services. To date, many mobile operators using either Global System for Mobile Communications (GSM) or Code Division Multiple Access (CDMA) cellular technology standards have already enhanced their 2G networks to deliver high-speed data services using Enhanced Data Rates for GSM Evolution (EDGE), General Packet Radio Service (GPRS), 1 x Radio Transmission Technology (1xRTT), Evolution Data Optimized Overlay (EV-DO), or WLAN technologies such as Wi-Fi. These services often have different edge devices and different transmission types, and they are slow to deploy and expensive to run on separate networks. Cisco Systems, Inc. All contents are Copyright © 1992–2006 Cisco Systems, Inc. All rights reserved. Important Notices and Privacy Statement. Page 2 of 11 In addition, most operators also maintain a number of IT, billing, call center, and other operational support networks, adding to the complexity and time of service deployment. IP/MPLS VPNs have been used to collapse the disparate networks down in a very effective way, giving them their own IP addressing space on the same converged platform, as seen in Figure 2. This implementation has, thus far, generally included data services but not VoIP. Figure 2 Migration of Disparate Networks to a Single IP/MPLS Core At left, Figure 2 shows various separate mobile data networks, including GPRS internal packet network (Gn) interface, Gateway GPRS Support Node (GGSN) interface (Gi), and billing and Internet access networks used by the same mobile operator. At right is the convergence of these services at separate sites through IP/MPLS VPNs. The benefits include lower transmission costs per megabit, fewer maintenance contracts, a single management solution, and the enhanced ability to quickly deploy new services within the same topology. Now, with Release 4 specifications to 3G standards, mobile operators can further reduce their costs and simplify their architecture as they deploy VoIP. A new split architecture allows mobile operators to reduce OpEx and cap investments through the eventual retirement of existing mobile switching centers (MSCs). Cisco Systems, Inc. All contents are Copyright © 1992–2006 Cisco Systems, Inc. All rights reserved. Important Notices and Privacy Statement. Page 3 of 11 Challenge The Evolution of 2G to 3G Releases for Voice Services In the evolution from 2G to 2.5G to 3G specifications, ATM has figured prominently as a requirement for Release 99 of 3G. The introduction of ATM was meant to be a solution for integrated voice, data, and video. But scalability and management are not optimal to support increasing traffic on mobile networks while the 2G time-division multiplexing (TDM) network continues to be costly to maintain and operate. Converging 2G and 3G voice over a packet-switched IP/MPLS network is the path forward to reduce costs and gradually retire expensive TDM equipment in the network. This requires multiple Gigabit Ethernet speeds, greater capacity, and other features such as QoS to support the latency-sensitive characteristics of voice end to end. Figure 3 shows a 2G TDM voice architecture. Voice traffic is seen moving from each base transceiver station (BTS) at the Radio Access Network (RAN) edge to a base station controller (BSC) and moving to the RAN core to an MSC and a gateway MSC (GMSC) to the public switched telephone network (PSTN). Only voice services are shown. All of the voice is backhauled, and the switching and interconnect take place through the MSCs. There are no IP or ATM services here. Instead, there is a TDM-based T1/E1 infrastructure supported by an underlying SONET/SDH layer in the RAN. This infrastructure supports circuit-switched voice services and some data services as well. Figure 3 2G TDM Voice Solution 3G voice services have been possible with Release 99 of the 3G standards (Figure 4), in which the RAN carries 2G voice over TDM (gold line) and 3G Release 99 voice over ATM (blue line). The media gateway (MGW) was also introduced to do voice-over-ATM to TDM conversion and some signaling. All of the back-end switching continues to be handled by MSCs. The radio network controller (RNC) is a 3G version of the BSC, responsible for routing calls and regulating bandwidth. As voice traffic continues to grow, the scaling of MSC-based core networks becomes more costly and lengthy in implementation. The challenge for mobile operators is to move away from circuit switching and harness the efficiency provided by new packet technologies, including IP, while maintaining the same service quality. Cisco Systems, Inc. All contents are Copyright © 1992–2006 Cisco Systems, Inc. All rights reserved. Important Notices and Privacy Statement. Page 4 of 11 Figure 4 2G Voice with 3G Release 99 Voice The media gateway is an important step on the way to the IMS standard reference architecture defined by the Third-Generation Partnership Project (3GPP) and Third-Generation Partnership Project 2 (3GPP2). The IMS architecture defines standards for session control, connection control, and an applications services framework, along with subscriber and services data for a core network for IP telephony and IP multimedia services. The Cisco IP NGN for Mobile Operators is being developed in conjunction with the evolution of these standards. Leading mobile suppliers, including Ericsson, Motorola, Nokia, and Siemens, are bringing forward their roadmaps for media gateways to support VoIP. Solution The next deployment of voice services in mobile networks is 3G Release 4, which introduces a split architecture. For 3G voice traffic, the connection between the MGWs has a control plane and a user plane. The control plane is IP based, and Signaling System 7 (SS7) is enabled through the MSC server. The user plane can handle TDM, ATM, or IP traffic. In the ATM example shown in Figure 5, it is also possible to carry 3G ATM voice traffic over IP/MPLS in the RAN core using Cisco Any Transport over MPLS (AToM) technologies. Previously, the user plane and control plane used TDM in a traditional MSC voice network. Cisco Systems, Inc. All contents are Copyright © 1992–2006 Cisco Systems, Inc. All rights reserved.
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