The changing demands on mobile networks, which are now responsible for transporting growing volumes of high-speed data and video traffic along with voice, are pushing mobile infrastructures beyond their traditional bandwidth capacities. More bandwidth is needed to support more concurrent users with a variety of mobile, multimedia devices. New broadband technologies such as High-Speed Packet Access (HSPA) are providing 20 to 30 Mbps data speeds in an environment of falling equipment prices and decreasing cost-per-transported-bit.
This paper explores the dramatic and continuing increase in data traffic within mobile service provider networks - specifically traffic based on HSPA and associated standards - and presents a solution for cost-effectively providing more bandwidth in the Radio Access Network (RAN) for backhaul of data traffic. The Cisco® solution, Mobile Transport over Packet (MToP), is presented. A description of how a mobile service provider can make a smooth migration over time from a legacy infrastructure to 3G IP infrastructures and beyond to 4G or Long Time Evolution (LTE) is also included.
Challenge
The 3.5G mobile wireless broadband technology HSPA has emerged as a popular means of transporting mobile data traffic among Global System for Mobile Communications (GSM) operators. Its speed - providing more than 80 percent faster downloads compared to Global Packet Radio Service (GPRS) and Universal Mobile Telecommunications System (UMTS) - allows mobile operators to keep up with the rapidly growing numbers of mobile data subscribers while utilizing most of the same infrastructure. HSPA and its variants, including High Speed Uplink Packet Access (HSUPA), High Speed Downlink Packet Access (HSDPA), and the proposed High Speed Orthogonal Frequency Division Multiplexing Packet Access (HSOPA), compete with Evolution Data Optimized (EV-DO), which is used for high-speed data service on Code Division Multiple Access (CDMA) mobile networks.
As shown in Figure 1, according to a study by Gartner in 2007, HSPA connections are growing. The most dramatic increase is in Europe, where the most mature 3G mobile networks and the highest concentration of HSPA exist. A recent Ovum study forecasts 199 percent HSPA growth worldwide between 2006 and 2010, while ARPU for this service will decline during that period to -1 percent.
Figure 1. HSPA Connections by Geography
In North America, adoption of HSPA began in earnest in 2007. The summer 2008 introduction of the Apple iPhone 3G for AT&T's HSDPA network is expected to bring in millions of new mobile broadband users. The phone will only connect at a maximum of 1.4 Mbps, even though the AT&T HSDPA network will be able to handle 7.2 Mbps by the end of 2008. The reason: concern over cell site congestion and backhaul.
The increased speed possible with HSPA requires a correspondingly large increase in bandwidth for backhaul of the data traffic from the RAN. A 2006 Yankee Group study found that backhaul had risen to 52 percent of mobile network operational costs. Many operators saw their costs for backhaul spike up 15 to 25 percent in 2007 for HSPA and EV-DO alone. With the average revenue per user (ARPU) for data service much lower than for voice and text messaging services, due to highly competitive rates from both wireline and mobile operators, mobile operators must find a cost-efficient way to scale RAN backhaul bandwidth. Scaling traditional backhaul solutions for SDH/SONET or ATM environments that were originally designed for voice services has involved the addition of expensive E1 or T1 access lines, usually leased from fixed service providers. As the volume of 3G traffic grows as expected, over the next few years the costs for this type of backhaul will render the service highly unprofitable. Therefore an alternative, cost-efficient backhaul solution, in keeping with the evolution of the mobile architecture, is vitally needed.
Interim Solutions
To cope with backhaul demands for increasing HSPA traffic, mobile operators in Europe have been adding multiple E1 lines. This strategy, used in the past to scale backhaul for 2G traffic, requires many more lines to handle HSPA traffic. Telecommunications Magazine estimates that HSPA may increase the number of E1 or T1 lines required per 3G cell site from one or two to eight to sixteen on average. Some European operators have extended DSL lines from the aggregation site to the cell site, where HSPA traffic is backhauled over ATM to the Base Station Controller (BSC) and the Radio Network Controller (RNC) as "best effort" backhaul. This is seen as an overly costly, interim fix that will not easily scale. There is also a high rate of bit errors, poor reliability, lack of quality of service (QoS) north of the DSL Access Multiplexer (DSLAM), and problems with overbooking with this approach.
Mobile operators, faced with the convergence of multiple services, are embracing IP and often Multiprotocol Label Switching (MPLS) due to the enhanced ability of these technologies to provision, scale, and manage multiple services. The move to IP and MPLS has occurred in the network core outward and the RAN has still not been adapted to efficiently handle IP broadband traffic due to the high costs of replacing aggregation and cell site infrastructures. Many mobile operators are therefore looking into intermediate solutions to ease the cost of eventually evolving to an all-IP RAN.
The Cisco Mobile Transport over Packet Solution for Mobile Data Backhaul
Cisco has developed a viable, highly cost-effective solution to the high-speed data backhaul challenge for mobile operators. The solution requires the addition of Cisco Circuit Emulation over Packet (CEoP) shared port adapter (SPA) cards to Cisco routers in aggregation or pre-aggregation sites. These cards enable the Cisco Mobile Transport over Packet (MToP) solution for RAN backhaul. Cisco MToP uses standards-based MPLS technology to extend the packet-based core already deployed at many carriers to the edge of the network. This solution provides an IP-based platform that can transport native IP and Ethernet-based Node B traffic as well as TDM and ATM traffic through the addition of CEoP SPA cards.
The MToP solution is flexible and cost-effective. It allows operators to evolve to a packet-based network while still maintaining the easy operational familiarity and resiliency of the existing TDM- and ATM-based network. Capital expenditures may be more productively applied to IP technologies instead of older TDM and ATM platforms.
As shown in Figure 2, previous RAN backhaul solutions have relied on T1 or E1 lines transporting backhaul traffic from the Base Transceiver Station (BTS) and Node B at the cell tower to the core or to an aggregation site where an ATM switch transports the traffic to the network core over fiber. In the core, the traffic is received by another ATM switch and then the data traffic is separated from the voice traffic and sent to the Serving GPRS Support Node (SGSN), a data gateway.
Figure 2. Traditional RAN Backhaul in a GSM Network
By contrast, with the MToP solution, the ATM switches are replaced by a Cisco 7600 Series Router that can transport all types of traffic and interface with all legacy equipment in the RAN, Figure 3. A "zero touch" deployment feature for the cell site router reduces installation costs. Each Cisco 7600 Series Router has a CEoP SPA card that provides the intelligence for connecting to ATM and TDM interfaces and backhaul transport over pseudowires. Pseudowires are MPLS virtual circuit "tunnels" that aggregate and transport TDM, IP, Ethernet, and ATM traffic, as well as clock synchronization, from the RAN to the network core.
The MToP solution increases bandwidth available for backhaul and other services by an order of magnitude but at a tenth of the cost per bit when compared to T1 and E1 service. It is fast and easy to deploy. Another benefit is that MToP uses the existing MPLS infrastructure for the highest levels of traffic grooming and network management, and QoS for assigning different classes of service.
Figure 3. MToP in the RAN Backhaul in a GSM Network
The pseudowires generally provide a Carrier Ethernet connection between the core and aggregation or pre-aggregation sites for much greater bandwidth at a fraction of the cost of T1 and E1 lines in a TDM network. The pre-aggregation site is an economical way of aggregating multiple cell sites and transporting the data backhaul traffic using Carrier Ethernet over a pseudowire to the core.
The MToP solution can also accommodate the DSL-to-the-cell-site solution that many mobile operators are using in Europe to offload HSPA traffic, Figure 4. Also, in Europe, the MToP solution can encompass DSL to the cell site, backhauling HSPA using pseudowires. HSPA data is offloaded to a Carrier Ethernet network using pseudowires.
Figure 4. Cisco HSPA Offload Solution Using MToP
Wholesale wireline service providers can use their existing T1 and E1 infrastructure to provide HSPA backhaul for mobile operators using the Cisco MToP solution. Using Cisco IP SLA, wholesalers can keep track of and report on the end-to-end services they are providing. Service providers are already pursuing this wholesale model, reselling the bandwidth as a managed service. Some are placing cell site routers in the cell sites of mobile operators, routing traffic over their own network and then dropping it at the aggregation sites or core of the mobile operator. This solution keeps the HSPA traffic separate and IP SLA keeps careful track of its efficiency.
The Cisco Service Exchange Framework and Related Products
The Cisco Service Exchange Framework (SEF) is an integral part of Cisco IP Next-Generation Network (IP NGN) architecture. In mobile networks, the SEF provides a standards-based framework that links the RAN to the IP network, bringing many value-added IP services. These include access and service control, classification, prioritization, easy mobility, and deep packet inspection. The Cisco SEF also takes advantage of the proven performance and carrier-class reliability of Cisco switch and router platforms at the network layer of the Cisco IP NGN. Cisco Mobile SEF is an open platform for service creation and management that interfaces with the control elements in the IP network. It has proven its compatibility with all major third-party RAN, AAA, content billing, and content filtering and compression solutions.
Key products that make up the Cisco Mobile SEF environment include:
• Cisco 7600 Series Routers
• Cisco Content Services Gateway 2 (CSG2)
• Cisco Gateway GPRS Support Node (GGSN)
• Cisco Packet Data Serving Node (PDSN)
• Cisco Mobile Wireless Home Agent
• Cisco Service Control Engine (SCE)
• Cisco PGW 2200 Softswitch
• Cisco IP Transfer Point (ITP)
• Cisco Session Border Controller (SBC)
Collectively, these Cisco Mobile SEF components successfully address many of the challenges operators face while seeking profitability from 2G, 2.5G, and 3G mobile packet infrastructures. This is of particular importance when mobile operators are looking to partner efficiently with the new Internet "over-the-top" players to provide their customers with a variety of innovative packages, competitive services, and brand new experiences.
Calculating Return on Investment with MToP
Costs for network connections vary throughout the world, but Table 1 contains an approximate cost comparison of high-speed data backhaul using E1 or T1 lines versus Ethernet connections over pseudowires, as in the Cisco MToP solution. The tremendous savings possible using Cisco MToP is clear. (Note: Five E1 or T1 lines equal one 10-Mbps Ethernet connection. For high-speed data service for LTE backhauling, one 100-Mbps Ethernet connection is presumed necessary.)
Table 1. Table Names Use the TableCaption Style
Migration to All-IP, Carrier Ethernet in the RAN
The Next Generation Mobile Networks (NGMN) Alliance is defining requirements from leading operators for a 4G, all-IP network, providing guidance to the 3rd Generation Partnership Project (3GPP). Cisco is a member of both 3GPP and NGMN and contributing to the IP RAN architecture definition based on Carrier Ethernet and MPLS.
With the increasing diversity of services traveling across mobile networks, all traffic is not the same. It varies based on characteristics such as burstiness, volume, end-to-end delay, variance, and tolerance for dropped packets. It is vital to be able to identify, classify, and prioritize traffic across the transport network.
Additionally, mobile operators should be able to enforce different levels of service for pre-paid customers, roaming customers, local customers, or business customers paying different subscription rates and with different service bundles. With Node Bs able to classify traffic at the edge of the network, mobile operators can prioritize traffic appropriately. And wholesalers should be able to prove that they can enforce strict SLAs for customers.
Advanced features from Cisco that take advantage of a common MPLS core transport environment include:
• IP SLA
• Traffic Engineering
• Fast Reroute
• Traffic Shaping
• Policing
• Rate Limiting
• Classification
• Prioritization
Migration to an all-IP, Ethernet RAN will be a multi-year process for most mobile operators who typically have 2G and 2.5G networks in place today. Ultimately, mobile networks will collapse backhaul technologies in favor of IP MPLS services running from the cell site all the way back to the network core and the NOC, Figure 5.
Figure 5. All-IP RAN Using Cisco MToP
In the all-IP RAN, pseudowires are no longer needed because Ethernet connections with IP/MPLS services will carry backhaul from the cell site to the core. Shown at the cell sites are Cisco Mobile Wireless Routers (MWRs), which provide optimization of 2G and 3G radio traffic. Cisco 7600 Series and 7604 Routers at the aggregation and pre-aggregation sites transmit the groomed data traffic to the network core with full clocking, traffic handling, and other IP/MPLS features.
The Cisco Advantage
With MToP and other solutions, Cisco is working to extend the many capabilities of IP MPLS out to the RAN. While some competitors have focused on redesigning only specific facets of the mobile network to better scale high-speed data services, others have attempted an end-to-end, all-IP approach similar to Cisco. Yet Cisco has gone beyond concept to full-featured solutions that have been deployed in mobile networks worldwide.
Cisco MToP is also based on the popular Cisco 7600 Series Router and this one platform supports every transport media. Therefore, migration from copper to optical, for example, only requires a card change and not a new platform. Cisco's end-to-end solution extends the capabilities of IP MPLS from core routers to the edge and out to the RAN. Customers who already enjoy the benefits of the Cisco 7600 Series in their core and edge can insert the CEoP SPA card and transform their existing network using MToP as they scale either HSPA or EV-DO services.
Beyond increased bandwidth and reduced operational expenses with pseudowires, the Cisco MToP solution also takes advantage of service delivery assurance with a variety of technologies that promote high availability, IP security, and the most robust traffic engineering in the industry, all available in Cisco IOS® Software. While other RAN backhaul solutions using pseudowires may sound attractive, they may not match the scalability, service handling, low total cost of ownership, and network assurance of Cisco MToP.
Conclusion
The growing volumes of HSPA traffic that are forecast to increase dramatically in the next few years are putting tremendous pressure on mobile operators to scale their bandwidth to and from cell sites to keep up with demand. To maintain profitability for HSPA services, operators need an alternative backhaul solution; scaling bandwidth by adding more leased T1 and E1 lines is prohibitively expensive.
While the ultimate vision embraced by many mobile operators and industry analysts is to replace TDM and ATM equipment and bring IP services over Carrier Ethernet to the cell site, a complete retrofit of infrastructure to make this possible would also incur huge capital costs. Instead, a growing number of mobile operators are deploying viable solutions that separate HSPA traffic for backhaul over highly cost-effective pseudowires from either aggregation or pre-aggregation sites. This solution, pioneered by Cisco, requires minimal capital expenditures and can be quickly deployed to reduce operational expenses dramatically while boosting bandwidth to scale services profitably. The MToP solution can also work with cell site routers offloading HSPA traffic using DSL to a router at the aggregation site, where the traffic is then transmitted over pseudowire back to the RNC.
Only Cisco has the MToP solution, the end-to-end IP MPLS NGN architecture with the Cisco SEF for service creation and management, and the range of technologies to help ensure the highest levels of traffic engineering, security, QoS, availability, and management. And Cisco MToP is aligned with both 3G and evolving 4G IP infrastructure standards to maintain the longevity of any investment.
For More Information
MToP in the RAN
Alternative Backhaul HSDPA
Cisco IP NGN for Mobile Operators