> ASN Paging Controller and Location Registry Overview
> The ASN Paging Controller and Location Registry (PC/LR) provides paging and location updates to WiMAX subscribers in IEEE 802.16 Mobile WiMAX radio access networks. This service can be used as a standalone product or in combination with ASN Gateway as co-located services on the same chassis.
> Introduction
> ASN Paging Controller and Location Registry (PC/LR) supports connection management and mobility across cell sites and inter-service provider network boundaries by processing subscriber control and bearer data traffic.
> Each ASN Gateway can concentrate traffic from many radio base stations. This reduces the required number of devices under management and minimizes connection set-up latency by decreasing the number of call hand-offs in the network.
> Paging and Idle Mode Operation maintains a track and alert for MSs when they are in idle mode to save battery power. Paging is executed to alert MSs when there is an incoming message. Figure 8 illustrates the paging operation and paging and idle mode elements in the WiMAX network system.
> ASN Paging Controller and Location Registry in WiMAX Networks
> In WiMAX networks, a mobile station is tracked when it is in idle mode. The information is stored to a location register (LR). The tracking area is larger than the cell size because a paging group (PG) comprises multiple cells. When a mobile station moves across paging groups, its location is updated via R6 and/or R4. The paging controller (PG) in ASN-GW retrieves the location from the LR and alerts the paging agent in (PA) in the base station to signal to the mobile station.
> Location information for idle mode subscribers is maintained in a location register central database that is co-located on an anchor paging controller. Idle mode can be initiated by the mobile device or the network. The paging controller retains subscriber session context information in addition to supervising paging activities. It also represents an authentication liaison between the user device and the AAA server. As the subscriber roams across cell sites, it is associated with a group of base stations known as a paging group. Location updates to the LR database are conveyed over R6 and R4 messages between the relay paging controller serving ASN and the A-PC/LR. When a remote host attempts to reach an idle mode subscriber device, the anchor paging controller alerts the paging group members when it receives downlink traffic by requesting the paging agent in the base station to signal the idle mode subscriber.
> Description of PC/LR Support
> The PC/LR runs as a stand-alone function in a separate chassis or as an integrated service on same chassis as the Anchor Authenticator (A-PC)/Anchor Datapath (A-DP) ASN Gateway. The idle mode LR database uses distributed software architecture and provides an LR manager task that partitions smaller database volumes across separately running session manager tasks in the system. The implementation is based on a topologically unaware paging scheme in which the A-PC does not have global awareness of all member base stations in a paging group. The A-PC uses a single-step paging operation where paging notifications are sent to the last-reported serving paging controller or directly attached base station.
> Idle mode operation is very important in order for any cellular system to keep the mobile device reachable when it is inactive. It enables mobility in addition to conserving battery life. Idle mode paging also eliminates the requirements of independent VLRs/HLRs, when it is supported as an integrated function in the ASN Gateway system.
> Licenses
> The ASN PC/LR service is a separate product from the ASN Gateway. You must purchase the WiMAX Paging Controller/Location Register product license separately to enable this service.
> Paging and Location Update Procedures
> This section provides an overview of the ASN Gateway’s paging and location update procedures.
> The system provides following components for the paging controller, paging group and location registry functionality.
> Paging Controller (PC)
> The paging controller is a functional entity that administers the activity of idle mode mobile stations in the network. It is identified by PC ID, which maps to the address of a functional entity in a WiMAX network. In this implementation, the PC is co-located with ASN Gateway. There are two types of PCs:

> • | Anchor PC: For each idle mode MS, there is a single anchor PC that contains the updated location information of the MS.

> • | Relay PC: There are one or more other PCs in the network, called relay PCs, that participate in relaying paging and location management messages between the paging agent and the anchor PC.

> Paging Agent (PA)
> The paging agent is a functional entity, implemented in an ASN base station, that handles the interaction between PC- and paging-related functionality.
> Paging Group (PG)
> A paging group is a logical entity comprising one or more paging agents. A paging group resides entirely within a NAP boundary. Paging groups are managed by the network management system and provisioned per the access network operator’s provisioning requirements.
> Location Register (LR)
> A location register is a distributed database, with each instance corresponding to an anchor PC. Location registers contain information about idle mode MSs. The information for each MS includes:

> • | MS paging information about each MS that has registered in the past in the network but is currently in idle mode

> • | Current paging group ID (PGID)

> • | PAGING_CYCLE

> • | PAGING_OFFSET

> • | Last reported BSID

> • | Last reported relay PCID

> • | MS service flow information

> • | Idle mode retention information for each MS in idle mode

> • | Information about the service flows associated with the MS

> An instance of a location register is associated with every anchor PC.
> Paging Controller and Location Update functionality supports following operation and procedures in ASN Gateway:
> Location Update Procedure
> Location Update with Paging Controller Relocation
> Paging Operation
> MS Initiated Idle Mode Entry
> MS Initiated Idle Mode Exit
> Location Update Procedure
> This section describes the secure location update procedure for a WiMAX MS.
> The following figure and table provides a high-level view of the steps involved in a secure location update.
> Location Update Flow
> Location Update Procedure Flow Description

> Step | Description
> 1 | The MS initiates a secure Location Update procedure by sending a RNG-REQ message to serving ASN BS, which includes the Ranging Purpose Indication TLV set to indicate Idle Mode Location Update, the PC ID TLV which points to the anchor ASN Gateway acting as the anchor PC function for the MS, and the HMAC/CMAC tuple.
> 2 | The serving ASN BS sends an R6 LU_Req message to the serving ASN Gateway and starts timer TR6_LU_Req. The message may include the PG ID, Paging Offset, and Paging Cycle TLVs if the serving ASN BS proposes an update to these parameters.
> 3 | The serving ASN Gateway (associated with the local Paging Controller) sends an R4 LU_Req message to the anchor PC (associated with Anchor ASN Gateway) and starts timer TR6_LU_Req. The message may include the PG ID, Paging Offset, and Paging Cycle TLVs if the serving ASN Gateway proposes an update to these parameters. Note: This message may be relayed by several intermittent ASNs before reaching the anchor PC (Anchor ASN Gateway).
> 4 | If the anchor PC retains context information for the MS including its Authenticator ID, the anchor PC initiates a Context Request procedure with the anchor authenticator/ASN Gateway. If the anchor authenticator/ASN Gateway has valid key material for the MS, it returns AK context for the MS to the Anchor PC.
> 5 | Upon successful retrieval of the AK context, the anchor PC sends an R4 LU_Rsp message back to the serving ASN Gateway and starts timer TR4_LU_Conf. The message includes the MSID, BSID, Authenticator ID, assigned PGID, Paging Offset, Paging Cycle, Anchor PC ID TLVs, and Location Update Status TLV set to Accept. Upon receipt of the R4 LU_Rsp message, the serving ASN Gateway stops timer TR4_LU_Req.
> 6 | Upon receipt of the R4 LU_Rsp message, the serving ASN Gateway stops timer TR4_LU_Req, sends an R6 LU_Rsp message to the serving ASN BS, and starts timer TR6_LU_Conf. The message includes the Location Update Status TLV set to Accept, AK Context TLVs, as well as the assigned Paging Information TLV if they were included in the corresponding R4 message.
> 7 | Based on the AK and AK context received from the anchor PC, the serving BS (associated with Local PC/Relay PC in serving ASN Gateway) successfully authenticates the RNG_REQ message received from the MS and sends a RNG_RSP message with HMAC/CMAC and Successful LU_Rsp indication to the MS.
> 8 | The serving ASN BS initiates an R6 CMAC Key Count Update procedure with the ASN Gateway. The serving ASN Gateway initiates an R4 CMAC Key Count Update procedure with the authenticator ASN to update it with the latest CMAC Key Count.
> 9 | The serving ASN BS sends an R6 LU_Cnf message to the serving ASN Gateway with Location Update TLV indicating success. Upon receipt of the message, the serving ASN Gateway stops timer TR6_LU_Conf.
> 10 | The serving ASN Gateway sends an R4 LU_Cnf message with a successful LU indication to the anchor PC and stops timer TR6_LU_Req. Upon receipt of the message, the anchor PC updates the LR with MS Idle Mode information and stops timer TR4_LU_Conf.

> ‌
> Location Update with Paging Controller Relocation
> This section describes the secure location update with PC relocation procedure for a WiMAX MS.
> The following figure and table provides a high-level view of the steps involved in a secure location update with PC relocation.
> Location Update with PC Relocation - Procedure Flow

> Step | Description
> 1 | The MS initiates a secure Location Update procedure by sending a RNG-REQ message to the serving ASN BS, which includes the Ranging Purpose Indication TLV set to indicate Idle Mode Location Update, the PC ID TLV which points to the anchor ASN Gateway acting as the anchor PC function for the MS, and the HMAC/CMAC tuple.
> 2 | The serving BS sends an R6 LU_Req message to the serving ASN Gateway and starts timer TR6_LU_Req. The message may include the PG ID, Paging Offset, and Paging Cycle TLVs if the serving BS proposes an update to these parameters.
> 3 | The serving ASN Gateway (associated with the serving BS and local PC) sends an R4 LU_Req message to the anchor PC ASN associated and starts timer TR4_LU_Req. The message may include the PG ID, Paging Offset, and Paging Cycle TLVs if the serving ASN proposes an update to these parameters. Note that this message may be relayed by several intermittent ASNs before reaching the current anchor PC ASN. The serving ASN or any intermittent ASN along the path may request PC relocation.
> 4 | Upon receipt of the R4 LU_Req message, a relay PC ASN adds the anchor PC Relocation Destination TLV to initiate PC relocation. The message is forwarded to the anchor PC ASN. The new anchor PC ASN starts timer TR4_LU_Request.
> 5 | If the current anchor PC ASN retains context information for the MS, including its authenticator ID, the current anchor PC ASN initiates a Context Request procedure with the anchor authenticator ASN. If the anchor authenticator ASN has valid key material for the MS, it returns AK context for the MS to the anchor PC ASN.
> 6 | The current anchor PC ASN sends an R4 LU_Rsp message back to the new anchor PC ASN and starts timer TR4_LU_Conf. The message includes the MSID, BSID, authenticator ID, assigned PGID, Paging Offset, Paging Cycle, Anchor PC ID TLVs, and Location Update Status TLV set to Accept. The anchor PC Relocation Request Response TLV is set to Accept to indicate that the current anchor PC ASN accepted the PC_Relocation_Req and the anchor PC ID TLV is set to the identifier of the new anchor PC ASN ID which was received in the anchor PC Relocation Destination TLV in the R4 LU_Req message. The R4 LU_Rsp message also includes MS Info TLV containing the MS context for transfer to the new anchor PC ASN. If the new anchor PC ASN does not request PC Relocation, the current anchor PC MAY still request to perform the procedure by including the PC Relocation Indication TLV. If the new anchor PC does not accept the relocation, it reports a failure in step 17.
> 7 | Upon receipt of the R4 LU_Rsp message from current anchor PC ASN, the new anchor PC ASN stops timer TR4_LU_Req, stores the MS context received from current anchor PC ASN, updates the paging information (Paging Group ID, Paging Cycle, Paging Offset), forwards the R4 LU_Rsp message on to the serving ASN, and starts timer TR4_LU_Conf.
> 8 | Upon receipt of the R4 LU_Rsp message, the serving ASN-GW stops timer TR4_LU_Req, sends an R6 LU_Rsp message to the S-BS, and starts timer TR6_LU_Conf. The message includes the Location Update Status TLV set to Accept, MS Info, AK Context, anchor PC ID, and the old anchor PC ID TLV. The message may include the paging information TLVs if they were included in the corresponding R4 message.
> 9 | Based on the AK and AK context received from the current anchor PC, the serving BS (associated with local PC/relay PC) successfully authenticates the RNG_REQ message received from the MS. The serving BS sends a RNG_RSP message with HMAC/CMAC and Successful Location Update Response indication to the MS.
> 10 | The serving BS sends an R6 LU_Cnf message to the serving ASN-GW with Location Update TLV indicating success. Upon receipt of the message, the serving ASN-GW stops timer TR6_LU_Conf.
> 11 | The serving ASN sends an R4 LU_Cnf message with a successful LU indication to new anchor PC ASN (as indicated by the anchor PC ID received from the BS) and stops timer TR6_LU_Req. Alternatively, the relay PC ASN forwards LU_Cnf to the ASN associated with new anchor PC with the result indication reassigned by the relay PC. Upon receipt of the message, new anchor PC ASN stops timer TR4_LU_Conf.
> 12 | Upon receipt of the LU_Cnf message, the new anchor PC ASN sends an R4 PC_Relocation_Ind to the anchor DP/FA ASN, and starts timer TR4_PC_Reloc_Upd_ADP.
> 13 | The anchor DP/FA ASN updates the anchor PC for the MS with the new anchor PC ASN ID and responds with an R4 PC_Relocation_Ack message confirming the anchor PC update. Upon receipt of the message, the new anchor PC ASN stops timer TR4_PC_Reloc_Upd_ADP. The new anchor PC ASN hosts the anchor PC function and becomes the new current anchor PC ASN for the MS. The anchor PC is de-allocated from the old current anchor PC ASN.
> 14 | Simultaneous with sending PC_Relocation_Ind to the anchor DP/FA, the new anchor PC sends an R4 PC Relocation Indication to the anchor authenticator ASN to inform the change of the anchor PC, and starts timer TR4- PC_Reloc_Upd_AA.
> 15 | The anchor authenticator ASN updates the anchor PC for the MS with the new anchor PC ASN ID and responds with an R4 PC_Relocation_Ack message confirming the anchor PC update. Upon receipt of the message, the new anchor PC ASN stops timer TR4-PC_Reloc_Upd_AA. At this point, new anchor PC ASN hosts the anchor PC function and becomes the new current Anchor PC ASN for the MS. The anchor PC is de-allocated from the old current anchor PC ASN.
> 16 | The new anchor PC ASN sends an R4 LU_Cnf message with a successful LU indication to the current anchor PC ASN and stops timer TR4_LU_Conf. The old current anchor PC ASN clears its LR context for the MS.
> 17 | This step is optional. If the anchor PC ASN receives CMAC Key Count TLV update in LU_Cnf message, it should perform an R4 CMAC Key Count Update procedure with the authenticator ASN to update it with the latest CMAC Key Count. Refer to section 4.13 for the call flow.

> ‌
> Paging Operation
> This section describes the paging operation for a WiMAX MS.
> The following figure and table provides a high-level view of the steps involved in the paging operation call flow of an MS.
> Paging Operation Procedure Flow
> Paging Operation Procedure Flow Description

> Step | Description
> 1 | Data from HA arrives through the tunnel at the FA and its associated DPF. The anchor DPF buffers the data.
> 2 | Anchor Data Path Function (DPF) sends an R4 Initiate_Paging_Req message to the anchor PC/LR to request paging. Optionally the R4 Initiate_Paging_Req message contains the QoS parameters of the flow for which the data arrived at the anchor DPF. This helps set priority treatment of the paging operation based on the QoS parameters and flow types. The anchor DPF may have policies for triggering paging based on the QoS parameters for the data received. The anchor DP Function starts timer TInit_Page_Req.Note: When MS is in Idle Mode, if data not belonging to any saved Service Flow (SF) of the MS arrives, the decision to initiate paging or not is on the basis of operator’s setting.
> 3 | The anchor PC/LR retrieves the information related to the MS and sends an R4 Initiate_Paging_Rsp to Anchor Data Path function. This message indicates whether the MS context as contained in the PC/LR is correct and the requested paging action is authorized. Exclusion of the Response Code TLV indicates intent to page the MS. Upon receipt of this message the anchor DP Function starts timer TInit_Page_Req if running.
> 4 | If paging action is authorized, the anchor PC retrieves the MS paging information and constructs Paging_Announce message. The anchor PC issues one or more Paging_Announce messages based on its knowledge of the paging region topology. The anchor PC starts a timer TR4_Paging_Announce when it sends out the first Paging_Announce message and waits for the paging response. The anchor PC sets a paging re-transmission counter N. If the anchor PC does not receive a paging response, it retransmits the Paging_Announce message prior to the expiration of the timer TR4_Paging_Announce. If the anchor PC is topologically aware of the defined Paging Group (PG), including the last BS from which the MS performed location update, the anchor PC directly issues Paging_Announce messages to all or some subset of the paging group members. The members consist of BSs and/or relay PCs in the region. If the anchor PC is topologically unaware of the paging region or the BSs defined in the paging group, the Paging_Announce messages are sent to the known relay PC(s). The relay PC(s) forwards the announce message to one or more BSs in the paging region.
> 5 | The ASN Gateway that contains the local/relay PC function for the MS initiates the paging operation and sends the R6 Paging_Announce message to the BS(s) associated with the Paging Group ID (PGID) received in R4 Paging_Announce. The ASN Gateway performs single- or multi-step paging based on whether the BS ID TLV or the L-BSID TLV is present. Associated with each R4 Paging_Announce message, the ASN Gateway starts timer TR6_Paging_Announce.
> 6 | Once the Paging Agent (PA) at the BS receives the Paging_Announce message with the requested action set to Start, it extracts the relevant paging parameters for the MS (Paging Cycle, Paging Offset). It then initiates the paging action requested by sending out MOB-PAG_ADV message over the airlink as per the indicated paging cycle and the paging offset. The optional SF Flow info in the message helps the BS implement a paging priority scheme for faster call setup when bandwidth is constrained or for resource allocation. The PA continues to page the MS for the duration specified by the Paging Announce Timer TLV, until the appropriate response is received from the MS, or a stop page indication is received from the Local PC.
> 7 | Upon being successfully paged the MS performs a Idle Mode Exit or a location update procedure. If any Paging Agent (PA) receives a successful reply from the paged MS, the Paging Agent notifies the Local PC by sending an R6 LU_Req message, or an R6 IM_Exit_State_Change_Req message, in the case of data delivery to MS in idle mode. Upon receipt of a such a message the Local PC stops timer TR6_Paging_Announce if running, and sends the appropriate R4 LU_Req or R4 IM_Exit_State_Change_Req message to the anchor PC. Upon receipt of such a message, the anchor PC stops timer TR4_Paging_Announce, if running. The anchor PC also initiate stop paging procedures as described at step 8 and onward.
> 8 | Upon receipt of a response from the MS as mentioned at step 7, and anchor PC wants to initiate stop paging procedure, the anchor PC sends a R4 Paging_Announce message to all BSs in the PG. The R4 Paging_Announce message has the Paging Start/Stop TLV set to 0.
> 9 | The local PC sends a R6 Paging_Announce message to the BSs. The R6 Paging_Announce message has the Paging Start/Stop TLV set to 0.
> 10 | Upon receipt of the R6 Paging_Announce message with Paging Start/Stop = 0, the BS terminate/cease a MOB_PAG-ADV messages over the air.

> MS Initiated Idle Mode Entry
> This section describes the MS-initiated idle mode entry procedure for a WiMAX subscriber.
> The following figure and table provides a high-level view of the steps involved in MS-initiated idle mode entry call flow of an SS/MS.
> MS Initiated Idle Mode Entry Procedure Flow
> MS Initiated Idle Mode Entry Procedure Flow Description

> Step | Description
> 1 | MS decides to enter Idle Mode and sends DREG_REQ formatted as described in IEEE 802.16e.The De-Registration Request code is set to 0x01 indicating that the MS intends to enter Idle Mode.
> 2 | Based on the MS’s request, the serving ASN BS (Paging Agent) in serving ASN sends an R6 IM_Entry_State_Change_Req message to its ASN Gateway. Timer TR4_IM_Entry_Req is started to monitor R6 IM_Entry_State_Change_Rsp at the serving ASN BS(PA).
> 3 | The local Relay PC in Serving ASN Gateway chooses an anchor PC for the MS and sends inter-ASN R4 IM_Entry_State_Change_Req message to the Anchor ASN associated with the chosen anchor PC. Timer TR4_IM_Entry_Req_ASN is started to monitor the R4 IM_Entry_State_Change_Rsp.
> 4 | The anchor PC/LR, sends R4 IM_Entry_State_Change_Req to the anchor authenticator to verify whether the MS is allowed to go into Idle mode. Timer TR4_IM_Entry_Req_APC is started at this time to monitor the R4 IM_Entry_State_Change_Rsp from the anchor authenticator. This step is optional if the anchor authenticator and anchor PC/LR are collocated in the same ASN Gateway.
> 5 | The anchor authenticator checks if the MS is allowed to enter Idle Mode and saves necessary information if allowed, then sends back R4 IM_Entry_State_Change_Rsp to the anchor PC/LR including MSID, IDLE mode authorization indication. If the anchor authenticator rejects the Idle mode entry request, the Idle Mode Authorization TLV contains the rejection code. When R4 IM_Entry_State_Change_Rsp for MS entering Idle Mode is send successfully, The anchor authenticator stores the anchor PC ID for this MS. Upon receipt of this message at the anchor PC, the TR4_IM_Entry Req_APC is stopped. This step is optional if the anchor authenticator and anchor PC/LR are collocated in the same ASN Gateway.
> 6 | According to the reported information in R4 IM_Entry_State_Change_Rsp, based on the content of Idle mode authorization indication IE, the anchor PC updates the LR with current MS location information (PGID) and other parameters, and sends back R4 IM_Entry_State_Change_Rsp message to the serving ASN Gateway. When this message is received at the serving ASN Gateway, timer TR4_IM_Entry_Req_ASN is stopped.
> 7 | Serving ASN Gateway forwards the R6 IM_Entry_State_Change_Rsp to serving BS (PA) including IDLE Mode authorization indication and accepted Paging parameters. Upon receipt of this message at the BS, timer TR6_IM_Entry_Req is stopped.
> 8 | Serving ASN BS sends DREG_CMD to the MS. The DREG_CMD conveys PC ID field pointing to the anchor PC for the MS and allocated Idle mode parameters.
> 9 | After sending the DREG_CMD to the MS, the serving ASN BS (PA) acknowledges the successful delivery of DREG_CMD to the local relay PC in the serving ASN Gateway by sending R6 IM_Entry_State_Change_Ack.
> 10, 11 | The local relay PC in the serving ASN Gateway forwards the successful entry of MS to Idle mode to the anchor PC in the anchor ASN Gateway by sending an R4 IM_Entry_State_Change_Ack. Upon receipt of this message at the anchor PC, timer TR4_IM_Entry_Rsp is stopped.
> 12 | The anchor ASN Gateway associated with the anchor PC/LR updates the information of MS into LR database and sends an Anchor PC Indication message to the anchor DPF/FA to reflect the success of MS entering Idle Mode. Timer TR4_APC_Ind is started at this time when the anchor PC Indication is sent, to monitor the response.
> 13 | The anchor DPF/FA finally updates the information of MS, including the anchor PC ID of this MS, and acknowledges to the anchor PC/LR by an Anchor PC Ack message. When the Anchor PC Ack is received at the anchor ASN Gateway, timer TR4_APC_Ind is stopped.
> 14 | After the expiration of the Management Resource Holding Timer (an 802.16e parameter), the serving BS initiates the related R6 data Path Dereg procedure by sending R6 Path_Dereg_Req to the anchor ASN Gateway.
> 15 | The serving ASN Gateway completes the data path de-registration from its side and sends an R4 Path_Dereg_Ack to the anchor DPF/FA. Upon receipt of this message, the anchor ASN Gateway stops timer TPath_Dereg_Rsp_ADPFt and the serving BS (PA) updates the anchor authenticator with the CMAC Key count for the MS via the serving ASN Gateway as per the CMAC Key count update procedure. The anchor authenticator acknowledges the CMAC update for the MS. Optionally this procedure may be invoked anytime after step 11.

> ‌
> MS Initiated Idle Mode Exit
> This section describes the MS-initiated idle mode exit procedure for a WiMAX subscriber.
> The following figure and table provides a high-level view of the steps involved in MS- initiated idle mode exit call flow of an SS/MS.
> MS Initiated Idle Mode Exit Procedure Flow
> MS Initiated Idle Mode Exit Procedure Flow Description

> Step | Description
> 1 | MS initiates exit procedure from IDLE mode and sends RNG_REQ to the serving ASN BS. The Ranging Purpose Indication TLV is set to 1 and the PC ID TLV is included, thus indicating that the MS intends to Re-Entry from Idle Mode.
> 2 | The ASN BS receives the RNG_REQ message from MS indicating Idle mode exit and sends R6 IM_Exit_State_Change_Req to the relay PC in the ASN Gateway, indicating that the MS wants to become active. Timer TR6_IM_Exit_Ctx_Req is started at this point by the BS to monitor the response for this message.
> 3 | The relay PC in the serving ASN Gateway receives the R6 IM_Exit_State_Change_Req from the BS indicating Idle mode exit and sends R4 IM_Exit_State_Change_Req to the anchor PC/LR in the anchor ASN Gateway, indicating that the MS wants to become active. Timer TR4_IM_Exit_Ctx_Req is started at this point by the anchor ASN Gateway to monitor the response for this message. In the event that the relay PC is the anchor PC, this step is not required.
> 4 | On receiving the R4 IM_Exit_State_Change_Req, the anchor PC/LR proceeds to request the security context from the anchor authenticator in the anchor ASN Gateway using the R4 IM_Exit_State_Change_Req. Timer TR4_lMexit_ctx_req_PC is started at this point by the anchor PC to monitor the response for this message. This step is optional if the anchor authenticator and anchor PC/LR are co-located in the same ASN Gateway.
> 5 | The anchor authenticator responds with the security context back to the anchor PC/LR with R4 IM_Exit_State_Change_Rsp message. Once the anchor PC receives this message, Timer TIM_Exit_Ctx_Req_PC is stopped. This step is optional if the anchor authenticator and the anchor PC/LR are collocated in the same ASN Gateway.
> 6 | The anchor PC/LR, sends R4 IM_Exit_State_Change_Rsp to the relay PC. Once the relay PC receives this message, Timer TR4_IM_Exit_Ctx_Req is stopped.R4 IM_Exit_State_Change_Rsp contains the stored information for the MS at the anchor PC.
> 7 | The serving ASN Gateway retrieves the MS context from anchor PC ASN and forwards the MS context to the serving BS on the R6 interface. Once the BS receives this message, timer TR6_IM_Exit_Ctx_Req is stopped. The AK fetched from the authenticator is used to verify the RNG-REQ.
> 8 | After successful authentication, the BS starts data path establishment across the serving BS, serving ASN Gateway, relay PC, anchor PC, authenticator, and DPF.
> 9 | The serving BS uses MS service and operational information indicated by IDLE Mode Retain Info obtained by step 7 to construct HO Process Optimization TLV settings in the RNG-RSP based on local policy, then sends RNG_RSP message to the MS formatted according to IEEE 802.16e specification. This message delivers all the required information to resume service in accordance with Idle Mode Retain information.
> 10 | When R4 Path_Reg_Ack is received at the anchor DPF, the Data Path function associated with FA sends a Delete_MS_Entry_Req message to PC/LR in order to delete the Idle mode entry associated with the MS. If the MS is exiting Idle mode due to a network initiated Idle mode exit, the PC/LR will cease all Paging Announce operations.
> 11 | The serving BS updates the anchor authenticator with the CMAC Key count for the MS via the serving ASN Gateway. The anchor authenticator acknowledges the CMAC update for the MS.

> ‌
> Supported Platforms and Software
> ASN PC-LR is available for all chassis running StarOS Release 8.0 or later.

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