Blueprint: Network Architecture

Migrating to Flatter, All-IP Wireless Networks

by Eric Andrews, Vice President of Product Management

1/16/2008

To address consumer demands for better voice and data communications and more advanced services, wireless technology standards have evolved over the last decade from 1G systems to the currently deployed 3G systems. Despite the growth of carrier networks and the evolution of standards, voice and data communications have not evolved in synch. Carriers have historically added data communications as an afterthought to voice network architectures originally conceived in the circuit-switched era, resulting in complex hierarchical networks that support both voice and data.

This type of architecture is expensive, leading to high operating and capital expenditures for service providers and significantly lowering margins in a highly competitive industry. In addition, networks employing cobbled-together voice and data communications systems simply do not have the capacity to provide the rich multimedia services and omnipresent Internet access that today's wireless customers demand.

To address these limitations, service providers are moving toward emerging all-IP wireless technologies that promise to reduce complexity, simplify the wireless core, and decrease service providers' operational and capital expenses. Currently there are several initiatives that operators are considering for building wireless IP networks:

� WiMAX End-to-End Network Systems Architecture: Defined by the WiMAX Forum Network Working Group (NWG) and leveraging the IEEE 802.16e WiMAX interface.

� Long Term Evolution (LTE): Being defined by the Third Generation Partnership Project (3GPP) and targeted as a successor to GSM-based technologies.

� Ultra Mobile Broadband (UMB): Being defined by the Third Generation Partnership Project 2 (3GPP2) and targeted as a successor to CDMA-based technologies.

All three of these architectures are similar in that they leverage a flat, user-plane, all-IP network architecture with fewer nodes that enables mobile operators to integrate the core with the access network, providing real-time multimedia and broadband IP services from the core to the mobile station. This flatter architecture results in reduced latencies and thus optimizes performance for real-time services such as voice and video.

In addition, all three architectures consist of base stations and Access Services Gateways interconnected by IP and employ high-performance Orthogonal Frequency-Division Multiple Access (OFDMA) air interfaces. The high performance of OFDMA-based technology, coupled with a lower cost of deployment, promises to bring voice, data, and multimedia services to customers at much more affordable prices while maintaining telecom operators' required gross margins.

The Gateway Is a Critical Network Component

The Access Service Gateway is now emerging as the critical network component in the flatter, all-IP network. The Access Service Gateway consolidates multiple functions from previous architectures, including the Radio Network Controller (RNC), Packet Data Serving Node (PDSN), Gateway General Support Node (GGSN), and Serving GRPS Support Node (SGSN). Called an Access Services Network (ASN) Gateway in WiMAX, or an Access Gateway in LTE, this new element knits base stations together to create a scalable, feature-rich, end-to-end network.

A look at the role of ASN Gateways for WiMAX networks clearly shows how important and strategic the gateways are. An ASN Gateway provides visibility across all subscribers and subscriber flows, and is the obvious point to apply intelligence to the network. Service providers can use the gateway to manage their subscribers, enable differentiated services, and optimize network resources.

The ASN Gateway provides a number of critical functions, including subscriber authentication and addressing support, service flow-authorization, mobility management, billing and accounting services, and load balancing. In addition to the functions required by the WiMAX standard, vendors can implement value-added features within the ASN Gateway to further enhance the network for service providers. These features can include peer-to-peer traffic management, advanced billing and charging models, granular QoS policing and shaping, advanced content management, security, backhaul optimization and spectral optimization.

Until quite recently, however, service providers have been forced to piece together ASN Gateway-like functionality with little more than repurposed routers or Linux appliances that lack the performance, scalability, and wireless intelligence needed to deliver large-scale, profitable WiMAX services. As vendors begin to introduce ASN Gateways, it is important to consider the requirements needed to deploy successful WiMAX services.

Open Standards Protect Investment and Spark Innovation

An important first step to creating a successful WiMAX service is to ensure that network elements are based on open standards. With its origins in IEEE and IP, and its commitment to reasonable intellectual property rights, the WiMAX industry is poised to bring the benefits of open markets to the traditionally closed carrier environment. As has happened with WiFi and enterprise technologies, embracing open interfaces can help drive competitive cost structures, broad market adoption, increased innovation, and best-of-breed choices for service providers.

The WiMAX Forum's NWG group has defined specifications for end-to-end WiMAX networks that allow for interoperability of the core network infrastructure and the access network. Building on the IEEE's 802.16e air interface, the Forum's NWG specification covers interfaces among ASN Gateways, Home Agents, AAA servers, Base Stations, and Subscriber Stations. To reap the benefits that come with openness and standards compliance, service providers need to ensure that their base stations and ASN Gateways are fully compliant with the WiMAX Forum NWG specifications. It is particularly important to ensure that base stations and ASN Gateways support an open R6 interface, such as profile C, and not a proprietary interface, such as profile B. Support for R6 profile C enables providers to choose best-of-breed products and ensures network-wide service enablement.

Requirements for Supporting a High-Value, Tiered-Services Structure

WiMAX networks are inherently designed to handle high-value applications such as multimedia services and other content. The OFDMA-based base stations carriers use to build WiMAX network have Multiple Input Multiple Output (MIMO) and Adaptive Antenna Systems (AAS) enhancements that generate ten times more bandwidth than current base stations. As a result, mobile operators require an ASN Gateway that can accommodate this increased bandwidth, plus perform all of the required subscriber functions at line rate.

Flatter, all-IP wireless networks require gateways that support a large number of dynamic service flows to support tiered services. They must provide extensive support for creating and processing per-subscriber, per-service flows to ensure optimal network performance. These processing requirements can be very taxing for platforms that have not been optimized for emerging wireless architectures. Before selecting an ASN Gateway, carriers need to consider total number of Generic Routing Encapsulation (GRE) tunnels it supports, the total number of service flows that are possible, the total number of flows per subscriber, and the rate at which service flows can be created (new entries per minute).

Any individual subscriber may have several active service flows, each with a unique QoS profile. For effective delivery of voice, video and other real-time services, therefore, service providers need to ensure their networks have robust, end-to-end, QoS support. Leveraging WiMAX, carriers can provision QoS parameters on a per-subscriber, per-flow basis for granular control of traffic. While ASN Gateways are not required to enforce these QoS policies, gateways that provide full classification, policing, and shaping enable service providers to offer a better end-to-end experience for their customers. Furthermore, the ASN Gateway provides an ideal location to provide advanced service differentiation based on a variety of characteristics, such as application type or source/destination address - enabling service providers to create additional revenue streams.

Because it provides visibility across all subscriber flows, the ASN Gateway is a critical resource for gathering accounting information and enabling advanced charging models. Service providers should look for gateways that can provide real-time per-subscriber, per-flow statistics, as well as additional accounting capabilities based on real-time content. In addition, ASN Gateways can also enable hot-lining and prepaid services to provide maximum flexibility in billing models.

Managing and Securing Subscriber Services

With growing customer demand for ubiquitous internet access, service providers are faced with pragmatic challenges as well as new potential revenue opportunities. Leveraging an intelligent ASN Gateway with extensive deep-packet-processing capabilities, service providers can carefully manage this traffic and fully exploit monetization opportunities. For example, an ASN Gateway can identify and manage peer-to-peer traffic so it does not overwhelm the network and degrade service quality for other users. Providers can use intelligent processing of real-time content together with subscriber profile information to create new and unique services, such as location-based ad insertion. These value-added features have a direct impact on the service provider's bottom line.

Since most of the backhaul links currently used for 3G networks do not have the bandwidth needed for next-generation broadband wireless networks, service providers want to use these links in the most efficient manner possible. By implementing compression and advanced traffic management in the ASN Gateway, service providers can optimize use of their backhaul links. Spectral resources are also a precious commodity for service providers. With visibility of base stations throughout the ASN, intelligent ASN Gateways can assist with load balancing and other optimizations to ensure maximum efficiency of spectral resources and a premium user experience.

To ensure secure connections between subscribers and the network, the WiMAX Forum has adopted an Extension Authentication Protocol (EAP)-based authentication model. The ASN Gateway plays a key role in the admission and authentication of wireless subscribers, working in conjunction with the AAA server. Given its strategic location in the network, the ASN Gateway is also an obvious location to enforce additional security policies, such as content-based filtering, mobility restriction, or encryption of traffic.

Access Services Gateway: A Key Component for Migration to an All-IP Network

The wireless infrastructure market is poised for a significant migration from a primarily voice-centric hierarchal model to a flatter, all-IP based architecture that can readily accommodate advanced data services along with real-time traffic. This transition is similar to what has already occurred in the wireline market, which had to overhaul the infrastructure as internet traffic quickly outstripped voice traffic.

By reducing the complexity of the network, service providers can reduce not only the amount of capital required to deploy the network but also the ongoing expenses associated with managing and operating it. Whether an ASN Gateway for WiMAX or an Access Gateway for LTE, these new access services gateways are a critical component of these emerging flatter networks. Due to its unique position in the network, the access services gateway sees all the subscribers and their associated traffic flows. It is therefore the ideal location to deploy value-added intelligence for enabling new services, optimizing network resources, and providing advanced subscriber management. These solutions will allow carriers to deploy large scale, profitable WiMAX and 4G networks.

About the Author

Eric Andrews is Vice President of Product Management at WiChorus. He brings over 20 years of marketing and executive management experience in the networking industry to WiChorus. Prior to WiChorus, Eric was Vice President of Marketing for NetDevices (now part of Alcatel), a startup company delivering integrated networking and security solutions for the enterprise market. Prior to NetDevices, Eric was Vice President of Marketing for Turnstone Systems, a pioneer in local-loop management for DSL carriers, where he managed all aspects of marketing from the company's inception, to profitability, and launching a successful IPO. Prior to Turnstone, Eric held various marketing and product management roles at networking companies such as Newbridge Networks and Penril DataComm Networks. Eric holds an MS and BS in Computer Science and Electrical Engineering from the Massachusetts Institute of Technology.

About WiChorus

WiChorus is the provider of new class of intelligent and massively scalable platforms for WiMAX and 4G core networks. Leveraging this platform, the company's Intelligent Access Services Network (ASN) Gateway, provides advanced service and subscriber management, service aggregation, content management and network optimization. It enables fixed and mobile service providers to deploy scalable WiMAX networks, capitalize on service differentiation opportunities and streamline capital and operational costs. Through its One Open WiMAX� initiative, WiChorus is accelerating the availability of an end-to-end open WiMAX ecosystem - ensuring service providers have the option to combine best-of-breed solutions. Headquartered in San Jose , Calif. , WiChorus is backed by leading Silicon Valley investors Accel Partners, Mayfield Fund, and Redpoint Ventures. For more information, please visit www.wichorus.com.

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