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

White Paper

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).

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.

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).

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.

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.

Figure 5 3G Release 4 Architecture with ATM Voice and Media Gateways

With this split architecture, 3G voice is no longer handled by the MSC, and mobile operators can cap their investment in circuit- switched networks. 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 some cases, the circuit-switched gear is approaching end of life, and often it entails very high OpEx. 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. 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. This 3G Release 4 deployment stage was necessary because most vendors supported 3G Release 4 ATM solutions.

The real savings and simplicity come when the MGWs transform all types of voice services into VoIP across the IP/MPLS RAN core. In Figure 6, the interconnects for the user plane and the control plane for all voice services beyond the MGW are based on IP technology. The 2G and 3G voice services are converged over IP, and they no longer need the traditional MSC. 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.

Figure 6 3G Release 4 Architecture with Media Gateway Voice Interconnect

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. As seen in Figure 7, eventually IP/MPLS will become the transport technology in the RAN infrastructure. With an IP/MPLS-based RAN and core, mobile operators will be able to reap cost savings, simplify network operations, and accelerate time to market for new services.

Figure 7 3G Release 5 and Beyond – IP/MPLS-Based RAN and Core

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. This was part of a major initiative to consolidate multiple networks over an IP/MPLS core. The company will migrate all 2G voice to the architecture, introducing new VoIP services, while preserving existing ATM investments. 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.

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. In six months, transport of all 3G voice and data services, desktop support and billing applications was migrated onto the network. Migrating 2G voice will be the next goal. The simplified IP network topology is providing a higher degree of stability and availability. Maintenance and fault isolation have been improved and accelerated. 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.

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. Design considerations vary based on the transmission technology or technologies in use, the location of core sites, and the sources of voice and data. Capacity planning and active monitoring are also very important activities to maintain QoS and high availability. It is important to know how much of the network is being utilized and, in the event of failure, whether enough capacity is still available for failover scenarios.

Cisco IOS® Software and Cisco IOS-XR Software technologies and tools support a variety of converged network management best practices, 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, delay, jitter, and packet loss. Scalability is achieved by the mechanisms of policing, shaping, and marking at the edge and then implementing efficient queuing in the core. Different classes such as voice, multimedia, signaling, business data, and best effort can be defined and supported with tight service-level agreements (SLAs) for latency, delay, convergence, and loss.

• Cisco Traffic Engineering can be used to provide a point-to-point QoS guarantee when combined with DiffServ. 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. When combined with policy servers, such as a bandwidth manager, this also has the potential to enable networkwide Connection Admission Control (CAC) by interaction with a softswitch.

• Cisco Fast Convergence techniques evolved because initially routing protocols were developed to converge in a matter of seconds or even minutes. This was considered acceptable for data traffic but is unacceptable with voice traffic. Because of increasing control- plane processor speeds and the ability to develop adaptive routing protocols able to react quickly while remaining stable under link flaps, convergence times have been significantly reduced. Cisco supports fast convergence techniques for Interior Gateway Protocol (IGP) (Intermediate System-to-Intermediate System [IS-IS] Protocol, Open Shortest Path First [OSPF]), Label Switched Path (LSP), Border Gateway Protocol (BGP), Multiprotocol BGP (MP-BGP), and VPNs.

• Cisco IP/MPLS Traffic Engineering Fast Reroute (FRR) is another technology that contributes to guaranteed bandwidth. It allows for extremely quick recovery if a node or link fails. Such fast recovery prevents end-user applications from timing out and also prevents loss of data. 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, which is competitive with SONET and SDH.

Cisco is often asked to provide a network topology that will support 99.999 percent network availability (or the equivalent of five minutes of downtime per year). In a CPN over IP/MPLS, there are different resiliency requirements based on different kinds of services. In the event of a failure, it might be acceptable for IP user data to sustain a failover time of 3 seconds. For signaling, an outage of 60 seconds might be acceptable. For voice services, however, an outage of less than 300 to 500 milliseconds may be required; otherwise, voice services will be seriously affected.

• Cisco IP Solution Center is a carrier-class management solution that includes a family of network management applications to help mobile operators plan, provision, and manage ATM, Frame Relay, TDM, Ethernet, Point-to-Point Protocol (PPP), and High-Level Data Link Control (HDLC) traffic and Layer 2 and Layer 3 VPNs across multiple sites through a unified IP/MPLS backbone. Simplified provisioning and automated troubleshooting lower the total cost of ownership of mobile networks. The four primary management modules of the Cisco IP Solution Center are Layer 3 IP/MPLS VPNs, Layer 2 VPNs, AToM MPLS Traffic Engineering, and MPLS Troubleshooting. The Cisco IP Solution Center lets mobile operators plan offline, troubleshoot conflicts, and then deploy new services in a controlled manner.

• 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. It can coexist and integrate with the Cisco IP Solution Center Layer 3 VPN Management product. In the growing and competitive MPLS VPN market, many providers and enterprises are under pressure to improve the operational efficiency of their network operations centers to reduce costs, contain headcount growth, and provide better customer support. Troubleshooting an MPLS VPN is often a manual task, requiring complex procedures not supported in traditional fault-management tools. Cisco IP/MPLS Diagnostics Expert is designed around a knowledge base of MPLS VPN failure scenarios, based on Cisco experience in worldwide MPLS VPN deployments. 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). If a VPN is not working properly, a network administrator can define the source and destination IP addresses, and the tool then automatically runs a series of tests to diagnose exactly where the problem is within the network, speeding up the solution to the problem.

Measuring QoS in the Network Two tools available within Cisco IOS Software can help measure QoS in a converged IP/MPLS network. They include:

• Cisco IP SLA measures availability and performance through active probes or pings. It sends probes out across the network, and it can measure jitter, delay, and application responsiveness. It can even go out to HTTP and Domain Name System (DNS) servers and measure how quickly they are reacting. Over time, these statistics can tell network administrators how well the network is performing. Alarms can be set to give feedback if a problem occurs.

• Cisco NetFlow can determine the source, destination, port, and QoS class of a traffic problem on the network. It can determine the top 10 talkers on a network and what users might be creating problems, and it can facilitate trend analyses to define when transmission upgrades might be required.

Conclusion Mobile operators can greatly benefit from providing converged 2G and 3G voice and data services over an IP/MPLS backbone. Cisco has tested solutions, which closely conform to 3G Release 4 specifications, and has deployed them in enterprises and mobile operator networks around the world. The right planning tools for deployment and monitoring are also available to help ensure that the converged packet network is a success.

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, network security, scalability, resiliency, and management enhancements for deploying data, voice, and video services. These carrier-class, industry-leading features run on powerful Cisco platforms, ranging from the Cisco CRS-1 Carrier Routing System to Cisco 12000 Series edge routers, which can scale from DS-0 on channelized interfaces up to multiple OC-192/STM- 64 or 10 Gigabit Ethernet, to the high-performing Cisco 7600 Series routers, for provider edge and enterprise metropolitan-area networks (MANs) and WANs.

Contact your Cisco account representative or partner today to learn more about converged voice and data services over an IP/MPLS backbone network.

For More Information Vodafone UK Converged Packet Network Case Study: http://www.cisco.com/go/ibsg

Video on Demand: Cisco IP/MPLS Core Solutions for Mobile Operators: http://www.cisco.com/pcgi-bin/sreg2/register/regmenu.pl

Cisco IP/MPLS Solutions for Mobile Operators: http://www.cisco.com/go/mobile

Cisco CRS-1 Carrier Routing System: http://www.cisco.com/go/crs

Cisco XR12000/12000 Series routers: http://www.cisco.com/go/12000

Cisco 7600 Series routers: http://www.cisco.com/go/7600

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