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White Paper

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

With Release 4 of the thirdgeneration (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 carrierclass 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).

a secure network layer that creates and delivers the services. Cisco IP Next-Generation Network Architecture for Mobile Operators Application Layer Self Service Identity Policy Billing Open Framework for Enabling “Triple Play on the Move” (Data. SIP is specified in the IMS framework as the glue for simple mobile and wireline service transitions. or WLAN technologies such as Wi-Fi. In addition.Figure 1. integrated. mobile operators will have more services. and between them both a service layer that orchestrates the delivery. 2 Security • Service Assurance Bandwidth Management • Traffic Engineering Push to Talk VoIP over Mobile Mobile Gaming Picture Messaging Mobile TV Operational Layer Service Layer . 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). and billing of the service itself. and other operational support networks. and they are slow to deploy and expensive to run on separate networks. most operators also maintain a number of IT. The service layer is also known as the Cisco Service Exchange Framework (SEF). Video. These services often have different edge devices and different transmission types. operations. and adaptive. call center. Evolution Data Optimized Overlay (EV-DO). Voice. greater efficiencies. billing. To date. The complexity of operating such a network is greatly simplified. As a result. and enhanced security in the operation of networks and the delivery of services. adding to the complexity and time of service deployment. features. 1 x Radio Transmission Technology (1xRTT). General Packet Radio Service (GPRS). better control. Mobility) Service Exchange Framework Mobility Network Layer Radio Access Cell Site Aggregation IP/MPLS Backbone Signaling over IP Cisco Intelligent IP Transport Intelligent Networking Mobile operators need an application layer that interfaces with the customer. and the network becomes more resilient. and it supports both Session Initiation Protocol (SIP)-based services and non-SIP-based services. 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.

This requires multiple Gigabit Ethernet speeds. as seen in Figure 2. At right. 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. The introduction of ATM was meant to be a solution for integrated voice. generally included data services. and billing and Internet access networks used by the same mobile operator. a single management solution. Now. Figure 2 shows various separate mobile data networks. A new split architecture allows mobile operators to reduce OpEx and cap investments through the eventual retirement of existing mobile switching centers (MSCs). including GPRS internal packet network (Gn) interface. At right is the convergence of these services at separate sites through IP/MPLS VPNs. Challenge The Evolution of 2G to 3G Releases for Voice Services In the evolution from 2G to 2. data. 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 implementation has. Figure 2.5G to 3G specifications. ATM has figured prominently as a requirement for Release 99 of 3G. greater capacity. and the enhanced ability to quickly deploy new services within the same topology. thus far. Gateway GPRS Support Node (GGSN) interface (Gi). with Release 4 specifications to 3G standards. giving them their own IP addressing space on the same converged platform. but not VoIP. mobile operators can further reduce their costs and simplify their architecture as they deploy VoIP.IP/MPLS VPNs have been used to collapse the disparate networks down in a very effective way. fewer maintenance contracts. The benefits include lower transmission costs per megabit. and video. Migration of Disparate Networks to a Single IP/MPLS Core Gn Site 2 Site 4 Gi IP/MPLS Core Billing Site 1 Site 6 Internet Site 2 Site 1 Site 3 Site 5 Site 4 Site 6 Site 3 Site 5 Many Networks on Common Sites with Different Edge Devices and Transmission Single Network over High-Capacity Transmission Carrying All Services 3 . and other features such as QoS to support the latency-sensitive characteristics of voice end to end.

Instead. responsible for routing calls and regulating bandwidth. which introduces a split architecture. there is a TDM-based T1/E1 infrastructure supported by an underlying SONET/SDH layer in the RAN. The radio network controller (RNC) is a 3G version of the BSC. while maintaining the same service quality. As voice traffic continues to grow. the scaling of MSC-based core networks becomes more costly and lengthy in implementation. All of the voice is backhauled. Solution The next deployment of voice services in mobile networks is 3G Release 4. 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. The Cisco IP NGN for Mobile Operators is being developed in conjunction with the evolution of these standards. or IP traffic. 3G voice services have been possible with Release 99 of the 3G standards (Figure 4).Figure 3 shows a 2G TDM voice architecture. The control plane is IP based. All of the back-end switching continues to be handled by MSCs. There are no IP or ATM services here. 2G TDM Voice Solution RAN Edge BTS BSC RAN Core MSC GMSC PSTN BTS BSC SONET/SDH MSC 4 . and an applications services framework along with subscriber and services data for a core network for IP telephony and IP multimedia services. 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). and the switching and interconnect take place through the MSCs. ATM. connection control. in which the RAN carries 2G voice over TDM (gold line) and 3G Release 99 voice over ATM (blue line). Previously. including IP. Leading mobile suppliers. the user plane and control plane used TDM in a traditional MSC voice network. Motorola. For 3G voice traffic. the connection between the MGWs has a control plane and a user plane. and Siemens. In the ATM example shown in Figure 5. including Ericsson. 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 media gateway (MGW) was also introduced to do voiceover-ATM to TDM conversion and some signaling. Nokia. Only voice services are shown. The user plane can handle TDM. This infrastructure supports circuit-switched voice services and some data services as well. The IMS architecture defines standards for session control. are bringing forward their roadmaps for media gateways to support VoIP. and Signaling System 7 (SS7) is enabled through the MSC server. Figure 3. The challenge for mobile operators is to move away from circuit switching and harness the efficiency provided by new packet technologies.

3G Release 4 Architecture with ATM Voice and Media Gateways RAN Edge BTS BSC Node B RNC BTS BSC Node B RNC RAN Core MSC GMSC PSTN MGW ATM Over MPLS MSC Server MSC MGW ATM ATM IP/MPLS SONET/SDH 5 . 2G Voice with 3G Release 99 Voice RAN Edge BTS BSC Node B RNC BTS BSC Node B RNC RAN Core MSC GMSC PSTN MGW MSC MGW ATM SONET/SDH Figure 5.Figure 4.

With an IP/MPLS-based RAN and core. Some operators are also deploying the Release 4 split architecture for 2G-only solutions to retire the exiting MSC networks and make use of alternate IP-based interconnects. and mobile operators can cap their investment in circuitswitched networks. and accelerate time to market for new services. This 3G Release 4 deployment stage was necessary because most vendors supported 3G Release 4 ATM solutions. Interest in this split architecture for voice is based on the desire of mobile operators to retire their traditional MSCs over time and offer VoIP. In Figure 6. As seen in Figure 7.With this split architecture. The 2G and 3G voice services are converged over IP. the interconnects for the user plane and the control plane for all voice services beyond the MGW are based on IP technology. eventually IP/MPLS will become the transport technology in the RAN infrastructure. mobile operators will be able to reap cost savings. 3G Release 4 Architecture with Media Gateway Voice Interconnect RAN Edge BTS BSC Node B RNC BTS BSC Node B RNC RAN Core GMSC MGW PSTN ATM Over MPLS IP/MPLS MSC Server MGW ATM ATM IP/MPLS SONET/SDH 6 . and often it entails very high OpEx. Figure 6. VoIP is also considered much less expensive when mobile operators use a 10-Gigabit converged IP network instead of traditional transport over T1/E1 lines. the circuitswitched gear is approaching end of life. simplify network operations. and they no longer need the traditional MSC. In some cases. Few mobile operators want to invest further in what is seen as a traditional technology of circuit switches while they continue to add 3G services. The real savings and simplicity come when the MGWs transform all types of voice services into VoIP across the IP/MPLS RAN core. 3G voice is no longer handled by the MSC. Increased use of IP/MPLS to the RAN edge with 3G Release 5 and beyond will simplify and accelerate the introduction of VoIP over the converged IP network end to end.

7 . The simplified IP network topology is providing a higher degree of stability and availability. 3G Release 5 and Beyond—IP/MPLS-Based RAN and Core RAN Edge BTS BSC Node B RNC BTS BSC Node B RNC RAN Core GMSC MGW PSTN IP/MPLS MSC Server MGW IP/MPLS DWDM Mobile operator Vodafone UK was one of the first to deploy 3G voice and data traffic using the split architecture in an ATM-over-IP/MPLS network. Vodafone estimates that it has cut its time to market for new services in half and saved more than 20 percent in operational costs with a converged IP/MPLS network while gaining Gigabit speeds. In six months. while preserving existing ATM investments. This new network was implemented and tested across 34 locations throughout the United Kingdom in late 2004. Migrating 2G voice will be the next goal. Maintenance and fault isolation have been improved and accelerated. introducing new VoIP services. This was part of a major initiative to consolidate multiple networks over an IP/MPLS core. transport of all 3G voice and data services. Vodafone UK deployed a converged packet network (CPN) that converged multiple data networks carrying customer services traffic and Vodafone UK enterprise IT services and support functions. desktop support and billing applications was migrated onto the network. These changes have translated to greater customer satisfaction. Vodafone Group plans to introduce the CPN and the split architecture for IP and traditional services to other Vodafone operating companies around the world as part of the One Vodafone program.Figure 7. The company will migrate all 2G voice to the architecture.

TDM. and marking at the edge and then implementing efficient queuing in the core. troubleshoot conflicts. The Cisco IP Solution Center lets mobile operators plan offline. The four primary management modules of the Cisco IP Solution Center are Layer 3 IP/MPLS VPNs. provision. Multiprotocol BGP (MPBGP). and tools support a variety of converged network management best practices. this also has the potential to enable networkwide Connection Admission Control (CAC) by interaction with a softswitch. Scalability is achieved by the mechanisms of policing. Label Switched Path (LSP). however. such as a bandwidth manager. For signaling. including: • Cisco Differentiated Services (DiffServ) is fully compliant with the industry standard DiffServ architecture and offers application-level QoS and traffic management in an architecture that incorporates mechanisms to control bandwidth. Design considerations vary based on the transmission technology or technologies in use. there are different resiliency requirements based on different kinds of services. business data. and the sources of voice and data. and best effort can be defined and supported with tight service-level agreements (SLAs) for latency. Cisco supports fast convergence techniques for Interior Gateway Protocol (IGP) (Intermediate System-to-Intermediate System [IS-IS] Protocol. Simplified provisioning and automated troubleshooting lower the total cost of ownership of mobile networks. This allows operators to deploy guaranteed bandwidth services for voice traffic along with planning tools (such as Cisco IP Solution Center Traffic management) to help ensure that even under failures the same capacity is available for critical services. and VPNs. shaping. multimedia. it might be acceptable for IP user data to sustain a failover time of 3 seconds. convergence. whether enough capacity is still available for failover scenarios. and packet loss. an outage of 60 seconds might be acceptable. • Cisco IP Solution Center is a carrier-class management solution that includes a family of network management applications to help mobile operators plan. It is important to know how much of the network is being utilized and. For voice services. • Cisco Fast Convergence techniques evolved because initially routing protocols were developed to converge in a matter of seconds or even minutes. signaling. Open Shortest Path First [OSPF]). AToM MPLS Traffic Engineering. Layer 2 VPNs. an outage of less than 300 to 500 milliseconds may be required. Cisco is often asked to provide a network topology that will support 99. delay. and then deploy new services in a controlled manner. Cisco IOS Software and Cisco IOS-XR Software technologies ® develop adaptive routing protocols able to react quickly while remaining stable under link flaps. This was considered acceptable for data traffic but is unacceptable with voice traffic. Border Gateway Protocol (BGP). voice services will be seriously affected. In the event of a failure. jitter. otherwise. When combined with policy servers. the location of core sites. • Cisco Traffic Engineering can be used to provide a point-topoint QoS guarantee when combined with DiffServ. In a CPN over IP/MPLS. in the event of failure. Capacity planning and active monitoring are also very important activities to maintain QoS and high availability. Point-to-Point Protocol (PPP). and loss. delay.Design Considerations for the Converged IP/MPLS Mobile Network Getting the physical network topology and structure of a converged IP/MPLS network correct goes a long way toward significantly reducing complexity and subsequent problems. Because of increasing control-plane processor speeds and the ability to 8 . Different classes such as voice. convergence times have been significantly reduced. and MPLS Troubleshooting. • Cisco IP/MPLS Traffic Engineering Fast Reroute (FRR) is another technology that contributes to guaranteed bandwidth. Cisco IP/MPLS FRR can locally patch traffic onto a backup tunnel in case of a link or node failure with a failover time of 50 milliseconds. Frame Relay.999 percent network availability (or the equivalent of five minutes of downtime per year). Such fast recovery prevents end-user applications from timing out and also prevents loss of data. It allows for extremely quick recovery if a node or link fails. which is competitive with SONET and SDH. Ethernet. and High-Level Data Link Control (HDLC) traffic and Layer 2 and Layer 3 VPNs across multiple sites through a unified IP/MPLS backbone. and manage ATM.

which closely conform to 3G Release 4 specifications.com/pcgi-bin/sreg2/register/regmenu. voice. If a VPN is not working properly. and provide better customer support. scalability. a network administrator can define the source and destination IP addresses.com/go/ibsg Video on Demand: Cisco IP/MPLS Core Solutions for Mobile Operators www. network security. They include: • Cisco IP SLA measures availability and performance through active probes or pings. In the growing and competitive MPLS VPN market. contain headcount growth. and it can facilitate trend analyses to define when transmission upgrades might be required. industry-leading features run on powerful Cisco platforms. ranging from the Cisco CRS-1 Carrier Routing System to Cisco 12000 Series edge routers.cisco. • Cisco NetFlow can determine the source. speeding up the solution to the problem. requiring complex procedures not supported in traditional fault-management tools. port.cisco.cisco. many providers and enterprises are under pressure to improve the operational efficiency of their network operations centers to reduce costs. these statistics can tell network administrators how well the network is performing. and management enhancements for deploying data.• Cisco IP/MPLS Diagnostics Expert is an automated.com/go/12000 Cisco 7600 Series routers ww. It sends probes out across the network. It is the only MPLS VPN diagnostic tool on the market that includes built-in domain knowledge from Cisco IOS Software MPLS development experts and the Cisco Technical Assistance Center (TAC).com/go/7600 9 .cisco. workflow-based network management application that helps network operators troubleshoot and diagnose problems in IP/MPLS VPN deployments.cisco. It can coexist and integrate with the Cisco IP Solution Center Layer 3 VPN Management product. Mobile operators are at different stages of migrating to 3G and 4G mobile network services and architectures and new IP services and applications. delay. Alarms can be set to give feedback if a problem occurs. and the tool then automatically runs a series of tests to diagnose exactly where the problem is within the network. Cisco IP/MPLS Diagnostics Expert is designed around a knowledge base of MPLS VPN failure scenarios.com/go/mobile Cisco CRS-1 Carrier Routing System www. and QoS class of a traffic problem on the network. and application responsiveness. which can scale from DS-0 on channelized interfaces up to multiple OC-192/STM-64 or 10 Gigabit Ethernet. These carrier-class. The right planning tools for deployment and monitoring are also available to help ensure that the converged packet network is a success. Contact your Cisco account representative or partner today to learn more about converged voice and data services over an IP/MPLS backbone network. and it can measure jitter. Cisco has tested solutions. Over time.cisco. Troubleshooting an MPLS VPN is often a manual task.com/go/crs Cisco XR12000/12000 Series routers www. Measuring QoS in the Network Two tools available within Cisco IOS Software can help measure QoS in a converged IP/MPLS network. resiliency.pl Cisco IP/MPLS Solutions for Mobile Operators www. and video services. based on Cisco experience in worldwide MPLS VPN deployments. to the highperforming Cisco 7600 Series routers. The Cisco IP NGN architecture and products for mobile operators—tested with successful deployments worldwide—provide the end-to-end QoS. and has deployed them in enterprises and mobile operator networks around the world. Conclusion Mobile operators can greatly benefit from providing converged 2G and 3G voice and data services over an IP/MPLS backbone. For More Information Vodafone UK Converged Packet Network Case Study www. destination. It can determine the top 10 talkers on a network and what users might be creating problems. for provider edge and enterprise metropolitan-area networks (MANs) and WANs. It can even go out to HTTP and Domain Name System (DNS) servers and measure how quickly they are reacting.

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