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Recent advances in mobile technology have made it possible for mobile network operators (MNOs) to decrease their operational expenses (OpEx). As the wireless subscriber base grows, MNOs can quickly reduce costs by offloading Special Call traffic onto their cost-efficient IP networks. Special Call traffic includes calls types such as international and domestic long distance, voice mail, customer support, sports scores, weather updates, and stock quotes. Mobile operators are realizing these costs savings and achieving tremendous benefits by deploying the industry-leading Special Call Offload application offered by Cisco Systems®.
This paper will present the business case behind why mobile operators should offload Special Call traffic onto their IP networks and how they can use the Cisco® Special Call Offload application to reduce operating expenses and evolve toward a Next-Generation Network (NGN) Architecture.
Summary
Mobile communication technology is evolving rapidly to provide multiple services and applications to today's subscribers. Over the past several years, the growth in wireless subscribers has been phenomenal worldwide. As the subscriber base of MNOs grows, so does the Special Call traffic they must carry. Special Call traffic is growing exponentially, straining existing mobile operators' signaling networks and infrastructure. With the slower-than-expected deployments of third-generation (3G) mobile technology and the increasing demand for fast-to-market data applications over existing wireless networks, mobile operators need more than ever for their IP networks to provide cost-effective and value-added services.
Existing Global System for Mobile Communications (GSM) and Code Division Multiple Access (CDMA) mobile networks use their signaling networks to route the Special Call traffic either to interactive voice response (IVR) systems or to the voice-mail servers. To complete the calls, MNOs typically use the public switched telephone network (PSTN), often at a very high cost. In fact, the interconnect charges for the PSTN can cost in the range of US$200,000 to $2M per month (estimated cost for the MNOs to terminate the Special Call traffic). The high cost of PSTN interconnects coupled with the inability of the existing TDM equipment to support the new data-centric applications have forced MNOs to look for cost-saving alternatives. Figure 1 shows the MNO's average revenue per user (ARPU) as well as their backhaul spending for the interconnect.
Figure 1
Mobile Operator ARPU and Backhaul Spending
Challenge
In traditional GSM and CDMA networks, Special Calls are handled by terminating the bearer traffic at the Mobile Switch Center (MSC). When a subscriber dials 611 for customer support in the United States, for example, after the initial number analysis, the call is routed out of the originating MSC to the PSTN. The call is then directed to an IVR or a call center. When an IVR or operator answers the call, a voice path is established and network resources are committed. In this model, not only do MNOs have to have interconnection agreement with the interexchange carriers (IXCs), but a valuable resource, a DS-0, is tied up at the MSC. Figure 2 shows a typical 611 call as it traverses through the network.
Figure 2
Special Call Offload - Traditional Approach
As the Special Call traffic increases, more and more DS-0s are tied up at the MSC, which could otherwise be used to connect regular voice calls, and MNOs are forced to pay high interconnect costs to terminate those calls. This generates a real need for offloading Special Calls onto IP networks, which provides the capacity boost and ultimately increases the MSC's ability to better serve subscribers. MNOs have two choices: They can add old-architecture-based switching and port capacity, or they can "offload" the traffic from their TDM MSC switch to free up network resources. The incremental costs associated with increasing the capacity of an older infrastructure are rarely justified. Cisco Special Call Offload is a better and less costly alternative. Besides providing cost efficiency, Cisco Special Call Offload is often one of the first applications in a migration strategy toward the NGN architecture.
Solution
Cisco Special Call Offload is a cost-effective solution to overcome the problems created by increased Special Call traffic in the MNO's network. MNOs, with the help of Cisco PGW 2200 PSTN Gateway, Cisco MGX® 8800 Media Gateway, and IP Transfer Point (ITP) Signaling Gateway, can quickly deploy the Cisco Special Call Offload application to offload their Special Call traffic onto their IP networks for immediate OpEx savings (Figure 3).
Figure 3
Cisco Special Call Offload in an IP Network
Figure 3 shows how, when a subscriber dials a 611 customer service number, the switch serving that subscriber (MSC) launches a call setup request through the Signaling System 7 (SS7) network. The SS7 network routes that request to the Cisco ITP over an SS7 link. ITP sends that request to the Cisco PGW 2200 over IP. The Cisco PGW 2200 translates the SS7 call request and sets up a connection on the Cisco MGX 8800 Media Gateway, eliminating the need for the PSTN interconnect. Instead, the IP network is used to connect the caller to the 611 server. This is done by the Cisco PGW 2200 sending SIP INVITE to the 611 server. The SDP information is exchanged between the media gateway and the 611 server through the Cisco PGW 2200 and upon answer the resources are committed.
Why Cisco
Based on the Cisco IP Next-Generation Network (IP NGN) architecture, the Cisco Special Call Offload application features separate signaling, bearer, and service planes. The application includes the following components:
• Cisco PGW 2200 PSTN Gateway, which functions as a media gateway controller (MGC)
• Cisco MGX 8800 IP-ATM Multiservice Switch with voice interworking service modules (VISM), which functions as a media gateway
• Cisco ITP Signaling Gateway, which functions as an SS7-to-IP signaling gateway
Figure 4 illustrates the Cisco Special Call Offload application configuration with all its required components. Cisco PGW 2200 is running in the call-control mode, which controls the Cisco MGX 8850 through MGCP signaling. The Cisco ITP is connected to Cisco PGW 2200 through IP, which in turn talks to the MSC through the SS7 network.
Figure 4
Cisco Special Call Offload Configuration
Solution Architecture
Cisco PGW 2200 - Media Gateway Controller
Cisco PGW 2200 PSTN Gateway is a flexible, multiprotocol MGC that provides a bridge between traditional GSM and CDMA networks and next-generation packet networks - supporting simple SS7 interconnect or providing intelligent call control and routing functions. Cisco PGW 2200 supports a continuous service architecture with no single point of failure. All critical components are deployed in redundant configurations, and all stable calls are preserved in the event of a switchover. The application software runs on Network Equipment Building Systems (NEBS) Level 3-certified UNIX open-computing platforms. These carrier-grade servers, along with the continuous service software design, enable carrier-class availability.
Cisco PGW 2200 can be configured in two modes: signaling mode and call-control mode. In the Cisco Special Call Offload application, Cisco PGW 2200 is configured in call-control mode. In the signaling mode, call control resides in the gateways and Cisco PGW 2200 provides the SS7 interconnect. In the call-control mode, Cisco PGW 2200 provides both the SS7 interconnect and intelligent call control and routing functions for voice gateways such as the Cisco MGX 8800. When configuring for call control, Cisco PGW 2200 terminates the SS7 links from the PSTN, performs number analysis and routing decisions, and communicates with the media gateways through MGCP while providing signaling to the SIP server.
Cisco PGW 2200 is designed to provide maximum support for different IP network architectures. This flexibility enables it to provide both an SS7 interconnect for H.323- or SIP-based networks where the call control resides in the H.323 or SIP core (signaling mode), or it can provide intelligent call control and routing functions for MGCP-based gateways (call-control mode) while concurrently providing an H.323 and/or SIP interface for maximum flexibility and interoperability.
Cisco MGX Platform - Media Gateway
Cisco MGX 8800 Series multiservice switches provide industry-leading scalability, scaling from 1.2-Gbps to 180-Gbps switching capacity and from DS-0 to OC-192/STM-64 interface capacity. This scalability provides exceptional savings and efficiency for network operations and services growth. The Cisco MGX Family includes Cisco MGX 8800 Series edge concentrators and Cisco MGX 8800 Series multiservice switches. The Cisco MGX Family supports the following services through the addition of individual modules: Frame Relay, ATM, voice over ATM, voice over IP, circuit emulation, IP, wireless aggregation, DSL aggregation, ATM service backbones, and VPNs.
The Cisco MGX 8880 Media Gateway enables a range of packet voice applications for wireless service providers. In the Cisco Special Call Offload application, the Cisco MGX 8800 terminates IMT trunk from MSCs and transports bearer traffic over IP to a remote gateway.
Cisco IP Transfer Point - Signaling Point
The Cisco ITP transports SS7 traffic over IP networks. The Cisco ITP allows mobile operators to efficiently transport increasing volumes of SS7 traffic by offloading the traffic from the existing SS7 network to an SS7-over-IP network. Cisco ITP also positions the mobile operator for enhanced return on investment (ROI) and profits by providing the infrastructure for IP-enabled service control points and revenue-generating IP services.
For the Cisco Special Call Offload application, the Cisco ITP connects to the MSC via A-links and performs MTP3 routing to Cisco PGW 2200. The Cisco ITP also offers service providers access to various IP application servers such as HLR, VLR, and MAP gateways, which enable enhanced wireless services support. Cisco ITP fully supports the Signaling Transport (SIGTRAN) architecture as defined in RFC 2710. The Cisco ITP using SIGTRAN provides a common signaling transport protocol called Stream Control Transport Protocol (SCTP - RFC 2960) that enables reliable communication to IP-based application servers while adhering to the stringent loss and delay requirements of a traditional SS7 network. Using the SS7-over-IP (SIGTRAN) functions of the Cisco ITP, a service provider can reduce the need for physical TDM signaling links for all SS7 communications.
Cisco ITP supports the following protocols:
• Stream Control Transmission Protocol (SCTP, RFC 2960)
• MTP2-User Peer-to-Peer Adaptation (M2PA, RFC 4165)
• MTP3-User Adaptation (M3UA, RFC 3332)
• SCCP-User Adaptation (SUA, RFC 3868)
Evolution Toward Next-Generation Network Architecture
One of the primary features that the Cisco Special Call Offload application introduces is its capability to take advantage of the inherent benefits of SIP. Cisco PGW 2200 uses SIP to communicate to the end devices such as a call-center IVR or a voice-mail server. With SIP already turned on in the network, MNOs can easily insert other next-generation products such as the Cisco Name Resolution Server (NRS). The combination of Cisco PGW 2200 and Cisco NRS provides highly flexible routing, capable of routing on SIP and telephony parameters. It also addresses issues such as Cisco PGW 2200 scaling, route management, and centralized versus distributed architecture. Figure 5 shows how Cisco NRS can interwork with Cisco PGW 2200 to provide next-generation services.
Figure 5
Cisco NRS Interworks with Cisco PGW 2200
Conclusion
Mobile network operators are looking for ways to boost revenues by offering new IP-based services and cutting costs by reducing OpEx. As the Special Call traffic grows, it is becoming increasingly important for MNOs to offload the traffic onto their cost-efficient and easy-to-manage IP networks. The Cisco Special Call Offload application implements offload services based on industry-supported, open Cisco architecture without disrupting network operations. Collaborating with the leading MNOs, Cisco Systems is helping to transform the design, profitability, and cost-effectiveness of wireless networks. Cisco offers an innovative and evolutionary solution based on its Cisco PGW 2200 PSTN Gateway, Cisco MGX 8800 Media Gateway, and Cisco ITP Signaling Gateway, which MNOs can deploy to offload their Special Call traffic and reduce high interconnect costs. In doing so, MNOs build intelligence into their networks to support the evolution toward a converged IP Next-Generation Network that can deliver advanced, revenue-generating multimedia services.
Benefits of the Cisco Special Call Offload application include:
• Infrastructure cost reduction
• Improved scalability
• Extremely compelling ROI
• Optimized environment for deploying revenue-generating, IP-based applications
• Network investment protection
Although the market consensus is an all-IP network, until that becomes reality, MNOs need to look at the most efficient and cost-effective ways to resourcefully manage their networks and provide new revenue-generating services. Cisco Special Call Offload is one such application that not only enables MNOs to cut costs and offer new services, but also prepares them for the gradual evolution toward next-generation networks. Cisco's goal is to help MNOs migrate toward an IP NGN by providing value in the deployable applications every step of the way. The Special Call Offload application provides an essential starting point for MNOs to realize the benefits of a next-generation architecture.
For More Information
Cisco PGW 2200 PSTN Gateway: http://www.cisco.com/en/US/products/hw/vcallcon/ps2027/index.html
Cisco MGX Family: http://www.cisco.com/en/US/products/hw/switches/ps1938/index.html
Cisco ITP Signaling Gateway: http://www.cisco.com/en/US/products/sw/wirelssw/ps1862/index.html