WiChorus reflects key trends in 4G core - integration and small cells

Among the specialists, WiChorus has been an innovator in the WiMAX core, and for a start-up, it has succeeded in adapting very quickly to changing market conditions. Like larger rivals, it has softened its stance on which of the three WiMAX Forum profiles for R6 should dominate - last year, Profile C looked set to eclipse A and B; now the interest in femtocells and other new architectures is pushing vendors to be more flexible around interfaces between the RAN and the core. And WiChorus has already managed to incorporate LTE into its system, unveiling SmartCore, which can work with WiMAX and/or LTE. For the former, it incorporates an ASN Gateway, Intelligent Home Agent, and WiMAX Mobile Internet Gateway. It will also, once LTE standards are finalized, support the equivalent functions for LTE - LTE Service Gateway, PDN Gateway, and Mobility Management Entity.

In addition, WiChorus is also reflecting the trend of the whole sector by introducing support for picocell and femtocell gateway solutions, which connect these miniature base stations to the core, and which are currently being standardized by the Femto Forum and 3GPP. As operators start to take the concept of WiMAX femtocells seriously, there has been new interest in different R6 profiles. While Profile C is geared to open, best-of-breed networks with carrier class functionality and macrocell designs, Profile B - which tightly integrates RAN and core within a "black box" and is usually proprietary to one vendor - may be more useful for operators that choose to make their first deployments based around hotzones in high value user bases, built with small cells. In this scenario, there are hundreds or thousands of base stations to link to the core, so low cost and simplicity are important, and the WiMAX or LTE network has to interoperate with the 3G network for wide area hand-off and roaming. This means operators will be more likely to start their deployments at the core, with the focus on integration and femtocells, rather than the macro RAN, as happened in 3G.

Open interfaces between the access network and the core are important to enable operators to select elements from different vendors, and this becomes even more crucial when interworking with an existing core. For best of breed strategies at the core, the critical interface is R6, which connects the WiMAX access network with the core IP network via the ASN gateway. This is the focus of activity for many specialists like Starent and Aricent, also working hard on new WiMAX core capabilities and on LTE. The major vendors will not be far behind, and this activity is certainly starting to fill some major gaps in the Mobile WiMAX offering for large scale operators and those looking to deploy mobile internet services. Until a year ago, "the focus of the WiMAX ecosystem was on fixing the radio access network," said Arnab Das, director of WiMAX product management at Aricent, in a recent interview. "Then service providers started thinking about how to deliver services, or handle hand-off and roaming, which is where the ASN (access service network) and CSN (core service network) come in."

Together the CSN and the ASN support the delivery and authentication of subscribers. The CSN sits in the core network and contains the AAA server and mobile IP Home Agent elements, and these are then connected to the RAN via the ASN Gateway, which sits between the radio and the IP elements of the WiMAX network. The ASN Gateway connects to WiMAX base stations via the R6 interface and is the most complex piece of software in an 802.16e system, and therefore the source of the greatest competitive edge for vendors and operators. It handles network entry and attachment, subscriber authentication, data session creation, handover and roaming.

There are two main ways to integrate a Mobile WiMAX network with an existing cellular network. With tight coupling, WiMAX is treated as a cellular RAN and is connected to the core by standard 3GPP interfaces; with loose coupling it is not treated as a cellular RAN and is connected by IP gateways that route WiMAX traffic to the internet without impacting the existing core. The WiMAX Forum has preferred the latter approach because it is more flexible, and allows the operator to innovate in WiMAX access without serious impact/risk in the core. Most 2G and 3G operators remain, at least in the early stages of 4G, nervous about any major disruption to the core, which has accounted for some slow uptake of technologies that would otherwise stimulate multinetwork integration, such as femtocell RANs and IP Multimedia Subsystem. However, with LTE on the horizon and mobile internet business models becoming de rigueur, this caution is declining.

Inset: SmartCore:

The newest element of WiChorus SmartCore is the WiMAX Mobile Internet Gateway, which provides all the WiMAX core functions in a single platform, simplifying initial WiMAX deployments.

"The emerging mobile internet poses unique challenges for wireless operators," said Rehan Jalil, CEO of WiChorus "Operators are faced with innovative web companies targeting premium subscribers, bandwidth demands disproportionate to average revenue per subscriber, and peer-to-peer traffic running rampant on their valuable wireless spectrum. Smart 4G networks tackle this new environment by delivering dramatically better cost per Mbps and line-rate network intelligence to help control and monetize internet traffic."

The SmartCore design distributes control and content processing functions across interconnected blades, harnessing the hardware resources across the chassis on an as-needed basis for scalability and reliability. There are three models in the family - the SC 1400, a fully redundant carrier-grade platform with 14 slots; the SC 600, a six-slot version; and the SC 20 and SC 100 appliances.

SmartCore also integrates content management, QoS and security functions on a per-subscriber, per-flow basis, and supports tracking of peer-to-peer applications by being aware of apps as well as just subscribers.

WiChorus is a two-year old outfit headquartered in Silicon Valley, which has so far raised $25 million in venture capital from Redpoint Ventures, Accel and Mayfield Fund. Its key product is its Intelligent Access Services Gateway, designed for the "fatter, flatter and smarter wireless core" that high capacity 4G will require. Content management, subscriber management and network optimization are handled from within the gateway, in line with the trend to flatten the network and apply more functionality and intelligence in a single place.
 
R6 lies at the heart of the vendor's "One Open WiMAX" slogan, under which it aims to interoperate with as many base stations, home agents, servers (AAA, IMS, policy and so on) and other ASN gateways as possible.