**1.1 WiMAX core network system architecture**

In the last few years, worldwide interoperability for microwave access (WiMAX) has been proposed as a promising wireless communication technology due to the fact that it can provide high data rate communications in metropolitan area networks (MANs). Until now, a number of specifications for WiMAX were standardized by the IEEE 802.16 working group. In this chapter, the architecture of WiMAX core network, all-IP mobile network, and optical integrative switching are introduced . It also tells the accounting of WiMAX in detail.

#### **1.2 Mobile network core network architecture**

WiMAX network structure mainly includes WiMAX Access Service Network and WiMAX Connectivity Service Network. CSN is the core network of WiMAX. It provides the IPconnection service for the users. Its connection modules are shown in the figure below:

Fig. 1. CSN connection modules

As you can see in CSN, it includes the router, location register, home agent and AAA-server. Router connects CSN with the other modules. Location register record the user's login and location information. In order to support the mobility, CSN provides mobile IP function. Home agent is responsible for maintaining MS position imformation and sending the packets to the network of MS.AAA proxy/ server provide authentication, authorization and accounting services. As to connect Internet or any other IP network, CSN may also include user database and interworking gateway devices, DHCP server and DNS server.

CSN is defined as the combination of network function . It includes these performances:


ASN and CSN are not belong to the same operator. CSN can use several ASNs and it is the same to ASN. Several CSNs can share the services that just one ASN provides. In this case, it will change information between ASN and MS to let ASN know that which CSN is connected with MS.

If WiMAX is arranged alone, CSN can be used as independent network construction. If it constructed with the other network, they can share some function entity .

#### **1.2.1 All-IP mobile network**

The mobile broadband wireless industry is in the midst of a significant transition in terms of capabilities and means of delivering multimedia IP services anytime, anywhere. So the all-IP mobile network specification is being defined by the Network Working Group (NWG) in the WiMAX Forum. The ip-based WiMAX architecture is shown in the figure below :

Fig. 2. IP-based WiMAX architecture

And its reference model is shown in the figure below :

It gives the reference network model interfaces:

Rl Interface between the MS and the ASN. Functionality : air interface .

R2 Interface between the MS and the CSN. Functionality : AAP, IP host configuration, mobility management.

R3 Interface between the ASN and the CSN. Functionality: AAP, policy enforcement, mobility management.

R4 Interface between ASNs. Functionality : mobility management.

RS Interface between CSNs. Functionality : intemetworking, roaming .

R6 Interface between BS and ASN gateway. Functionality : IP tunnel management to establish and release MS connection .

RS Interface between BSs. Functionality: handoffs.

R7 is the interface in ASN gateway . It is not shown in figur e 3.

Fig. 3. IP-based WiMAX network model

A prominent feature of the NWG specification is the extensive use of IP and IETF-standard protocols. The focus is on enabling IP access for mobile devices. Networking functionality requirements for client devices consist of just standard IP protocols like DHCP, Mobile IP, EAP protocols. IP connectivity is assumed between all interacting entities in the network. Mobile IP used as the mechanism for redirection of the data as a mobile device moves from one ASN to another ASN, crossing IP subnet/ prefix boundaries. Mobility support for mobiles that are not Mobile-IP capable is provided by the use of Proxy Mobile IP. On the network side, IP address pool management provided through IETF standard mechanisms like DHCP or AAA. Decomposition of protocols across reference points enables interoperability while accommodating flexible implementation choices for vendors and operators.

WiMAX network architecture utilizes a combination of the IETF-standard Mobile IP protocol and special protocols defined by WiMAX NWG to handle mobility. The use of standard Mobile IP makes it possible to leverage off-theshelf components such as Home Agent in addition to simplifying the interface to the rest of the IP world.Alongside IETF Mobile IP, WiMAX specific protocols are used to allow for optimizations and to provide

flexibility in handling mobility. For a given MS, the Mobile IP Home Agent (HA) resides in a CSN and one or more Foreign Agents (FA) resides in each ASN. Data for this MS is transported through the Mobile IP tunnel, which is terminated at an FA in an ASN. Once Mobile IP tunnel is terminated at the FA, WiMAX specific protocols (i.e. Data Path Functions) take over and transport the data from the FA to the serving base station, to which the MS is attached.This design offers multiple levels of anchoring for the user data plane path during handovers . Mobile IP is used to provide a "top" level of anchoring of the data flow for a mobile. WiMAX specific Data Path Function (DPF) to provide further levels of anchoring "below" Mobile IP.

Note that many mobile clients today such as PDAs and laptops are not Mobile-IP capable; instead they work with simple IP. WiMAX network architecture assures that those clients, together with Mobile-IP capable clients, are fully able to use services offered by the network. This is achieved by employing Proxy Mobile IP Client (PMIP Client), which acts as a proxy for the mobile client, in the network and handles the Mobile IP procedures in lieu of the mobile client in a transparent fashion.
