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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).

As a result. and enhanced security in the operation of networks and the delivery of services. or WLAN technologies such as Wi-Fi. integrated. and it supports both Session Initiation Protocol (SIP)-based services and non-SIP-based services. and other operational support networks. The service layer is also known as the Cisco Service Exchange Framework (SEF). better control. 1 x Radio Transmission Technology (1xRTT). Evolution Data Optimized Overlay (EV-DO). and billing of the service itself. most operators also maintain a number of IT. General Packet Radio Service (GPRS). greater efficiencies. Voice. and they are slow to deploy and expensive to run on separate networks. mobile operators will have more services. In addition. SIP is specified in the IMS framework as the glue for simple mobile and wireline service transitions. To date. The complexity of operating such a network is greatly simplified. operations. and adaptive. 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. and the network becomes more resilient.Figure 1. call center. billing. a secure network layer that creates and delivers the services. features. These services often have different edge devices and different transmission types. 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 . 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. Video. adding to the complexity and time of service deployment. 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. 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).

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

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

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. 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 .

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. and they no longer need the traditional MSC. In some cases. 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 . 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. 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. As seen in Figure 7. and often it entails very high OpEx. In Figure 6. simplify network operations. The 2G and 3G voice services are converged over IP. Figure 6. the interconnects for the user plane and the control plane for all voice services beyond the MGW are based on IP technology. 3G voice is no longer handled by the MSC. The real savings and simplicity come when the MGWs transform all types of voice services into VoIP across the IP/MPLS RAN core. mobile operators will be able to reap cost savings.With this split architecture. With an IP/MPLS-based RAN and core. and accelerate time to market for new services. and mobile operators can cap their investment in circuitswitched networks. 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. This 3G Release 4 deployment stage was necessary because most vendors supported 3G Release 4 ATM solutions. eventually IP/MPLS will become the transport technology in the RAN infrastructure. 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.

introducing new VoIP services. These changes have translated to greater customer satisfaction. In six months. desktop support and billing applications was migrated onto the network. 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. This new network was implemented and tested across 34 locations throughout the United Kingdom in late 2004.Figure 7. The company will migrate all 2G voice to the architecture. 7 . This was part of a major initiative to consolidate multiple networks over an IP/MPLS core. 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. Migrating 2G voice will be the next goal. while preserving existing ATM investments. transport of all 3G voice and data services. The simplified IP network topology is providing a higher degree of stability and availability. Maintenance and fault isolation have been improved and accelerated. 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. 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.

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

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

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