July 21, 2009

Mobile WiMAX System Architecture

The Mobile WiMAX network architecture is defined by WiMAX Forum’s Network Working Group (NWG). It has been planned to offer capable mobility mutually at micro and macro network levels as well as providing inter-technology roaming and handovers through the use of standard interfaces. Since Mobile WiMAX implements standard interfaces for interoperability between equipment, it is key to understand the basic network architecture.

The Mobile WiMAX network architecture has been designed to support network sharing through a variety of standardized interfaces. The network architecture supports different business models, allowing a logical separation between the following functions:

The Network Access Provider (NAP): Entity that owns and/or operates the access network.

The Network Service Provider (NSP): Entity that owns the subscriber and provides the broadband access service.

The Application Service Providers (ASP): Entities that provide the value added services.

The architecture supports the concept of a virtual network operator,
enabling a Mobile WiMAX access network to be shared by multiple NSPs or indeed NSPs using access networks from multiple NAPs. In conjunction with these models, the architecture supports the ability for the Mobile Subscriber (MS) to discover and select service from one or more of the available NSPs.

The Mobile WiMAX end-to-end network architecture model follows the Network Reference Model (NRM), the first release of which is shown below.
The Network Reference Model contains reference points, which reflect defined interfaces within the architecture. A summary of reference points is provided below.

R1: Interface between the MS and the ASN. Functionality: air interface.
R2: Interface between the MS and the CSN. Functionality: AAA, IP host configuration, mobility management.
R3: Interface between the ASN and CSN. Functionality: AAA, policy enforcement, mobility management.
R4: Interface between ASNs. Functionality: mobility management.
R5: Interface between CSNs (home & visited networks) Functionality: internetworking, roaming.
R6: Interface between BS and ASN-GW. Functionality: IP tunnel management to establish and release MS connection.
R8: Interface between Base stations. Functionality: Mobile handoffs.

The mobile WiMAX NRM calls for the ability to manage subscriber mobility at a number of layers as well as providing authentication, accounting and policy control on a per subscriber basis. This is achieved by dividing the WiMAX network into two main parts:

* Access Service Network (ASN)
* Connectivity Service Network (CSN)


The ASN logically consists of a complete set of functions in order to provide radio access to the WiMAX subscriber. The ASN provides the following mandatory functions:

* WiMAX Layer 2 connectivity to the Mobile Subscriber
* Transfer of AAA messages from the MS to the WiMAX subscriber’s Home Network Service Provider (H-NSP)
* Network Discovery & Selection of the WIMAX subscriber’s preferred Network Service Provider (NSP)
* Relay for establishing Layer 3 connectivity with the MS device
* Radio Resource Management
* ASN to CSN tunneling
* Mobility and Paging / Location Management

A key element of the ASN is the ASN GW, which controls and aggregates the traffic from one or more WiMAX base stations. It manages handover of MS devices between them as well as coordinating authentication, service flows and key distribution between base stations.


The CSN logically consists of a complete set of network functions to provide IP connectivity services to the WiMAX subscriber. The CSN provides the following functions:

* Mobile Station IP address
* End point parameter allocations for user sessions
* Internet Access
* AAA proxy or server
* Policy and admission control (based on user subscription profiles)
* ASN-CSN tunneling support
* WiMAX subscriber billing and inter-operator settlement
* Inter-CSN tunneling for roaming
* Inter-ASN mobility
* Services; for example location based services

The key elements of the CSN are the Home Agent and AAA server. The Home agent provides an anchor point for Mobile IP nodes (MS), providing a care-of-address for communication to the device. The Home Agent uses tunneling to forward traffic to the MS through the Foreign Agent in the ASN-GW. This tunnel ensures that the MS does not need to change IP address as it moves around the network.


hoha said...


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