Access Service Network Functional Protocols
Protocol Layering of WiMAX considers end-to-end protocol layering. Data and control packets are forwarded from the MS to the CSN in uplink. The traffic is concentrated in the ASN-GW and forwarded to the CSN and same way, concentrated in the ASN-GW for downlink and distributed to the MSs residing in different BSs. IP packets use IP convergence sublayer (IP-CS) or Ethernet convergence sublayer (ETH-CS) over IEEE 802.16e. The IP-CS with IP-in-IP encapsulation between BS and ASN-GW is considered in most designs. Bridging is also another way of routing packet within ASN.
Network Discovery and Selection implements manual or automatic selection of the appropriate network. MS first discovers all the NAPs where each has an Operator ID embedded into Base Station ID and transmitted with DL-MAP of each frame. And MS continue to listen the channel for SII-ADV signal which system identity information advertisement to advertise NSP IDs. The MS selects one NSP from the list according to an algorithm and performs network entry and provide its identity and its home NSP domain with a network access identifier (NAI). The ASN selects the next AAA hop from the realm portion of the NAI.
IP Address Assignment is done through DHCP or AAA: ASN hosts DHCP relay or DHCP proxy respectively. In order to deliver the point of attachment IP address to MS. For IPv6 there is access router in ASN to obtain globally routable IP address. The MS gets the care-of-address (CoA) from ASN and home address (HoA) from CSN.
Authentication and Security Architecture implements 802.16e security with IETF EAP framework. AAA framework is used for service flow authorization, mobility management and policy control. AAA framework is based on pull model in which supplicant sends a request to ASN and ASN forwards it to AAA server. The AAA return with appropriate response to ASN which set up the service and inform the MS. The elements are depicted in Figure 5.
User and device authentication is supported with PKMv2 and EAP. PKMv2 is between MS and BS and BS relays this EAP messages to ASN-GW where AAA client encapsulates the EAP and forwards to AAA server in the CSN over RADIUS. EAP-AKA, EAP-TLS, EAP-SIM, EAP-PSK, EAP-TTLS are the supported EAP types. Both user and device authentication is performed with double-EAP and device credentials are in the form of digital certificate, secret key, or X.509 certificate.
Quality of Service Architecture in WiMAX complements the QoS framework in IEEE 802.16e-2005 QoS model. The QoS provides rich set of variety: per user and per service flow basis differentiated levels; admission control; bandwidth optimization. QoS provides static and dynamic service flow creation. For each service there is provisioned, admitted, and active states. When flow is in active state it starts getting the service. Entities are Policy function and AAA server residing in CSN, Service flow management residing in BS, and Service flow authorization residing in ASN-GW. QoS functional architecture is depicted in Figure 6.
Mobility Management implements mobility with the ASN and across the ASNs as seen in Figure 7. ASN-anchored mobility is when MS moves within the same Foreign Agent domain residing in ASN-GW. Control signals use R6 and R8 reference points and data path shift happens in ASN-GW with new R6 to target BS when handover is complete. CSN-anchored mobility additional to ASN-anchored mobility triggers the FA change through Home Agent. Now, R3 and R4 reference points also become active.
Radio Resource Management is responsible to fully utilize the network by information gathering and implementing decisions. The information such as radio-related measurements; base station spare capacity reports are concentrated to assist handover decision and load balancing decisions.
Paging and Idle Mode Operation is responsible to maintain a track and alert for MS when it is in idle mode for battery power saving reasons. Paging is executed to alert MS when there is an incoming message. Figure 8 illustrates the paging operation along with paging and idle mode elements in the system. MS is tracked when it is in the idle mode and information is stored to a location register (LR). Granularity of track is bigger than cell size since a paging group (PG) is composed of multiple cell and when a MS moves across paging groups, location update occurs via R6 and/or R4. Paging Controller (PG) in ASN-GW retrieves the location from LR and alerts the paging agent in (PA) in BS to signal to MS.