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wimax SS network entry procedure

In this page we will go through wimax network entry procedure between SS(Subscriber station) and BS(Base Station). The procedure helps wimax subscriber camp on to wimax compliant base station. Following are the summarized steps for network entry. Please note that this procedure is as per IEEE 802.16-2004 OFDM PHY and MAC layer specifications. This version of wimax is also referred as fixed wimax due to non-mobility of subscriber stations. The procedure for mobile version of wimax i.e. mobile wimax is similar to this but there are few changes to MAPs/channel descriptors and header format as well as addition in MAC messages.

Step-1: WiMAX subscriber station(SS) scans for downlink RF channel frequency and establish synchronization with the wimax Base station(BS).

Step-2: Subscriber station will obtain information regarding where to transmit in the wimax frame based on UCD message. UCD message is carried in the broadcast message transmitted by base station. The modulation-code rate information of the broadcast message is carried in the FCH or DLFP. Hence SS need to decode FCH which is always BPSK1/2 in order to get information about broadcast message.

WiMAX frame structure

Step-3: Subscriber station will perform ranging which maintains RF link between BS and SS. There are various types of ranging messages. The messages used are RNG REQ(from SS to BS) and RNG RSP(from BS toSS) . There will be dedicated slot reserved for ranging messages to be exchanged between BS and SSs. The wimax frame structure outlines this reserved slot.

Step-4: WiMAX SS informs BS of its basic capabilities. BS adjusts the parameters as informed by SS. The messages used to perform this are SBC REQ (from SS to BS) and SBC RSP(from BS to SS). The position for SBC in the frame is informed to the SS in response to bandwidth request message received at the BS. BS informs about it in the subsequent broadcast message.

Step-5: Authorization of SS is done by BS and key is exchanged between BS and SS for encryption. This is done using PKM-REQ and PKM-RSP messages.

Step-6: SS follows registration procedure and hence it will become manageable by BS. REG REQ and REG RSP messages are used for this purpose.

Step-7: A managed SS will establish secondary management connection and will configure its IP connectivity. This is done by SS using DHCP protocol by obtaining IP address and other parameters required for IP connection. At this stage it is assumed that provisioned service flow is created between BS and SS using DSA REQ, DSA RSP and DSA ACK messages exchanged between them.

Step-8: Establish time of day is done for retrieving time stamping logged events.

Step-9: Operational parameters are transferred between BS and SS. When configuration file is successfully downloaded by SS, SS will notify BS by transmission of TFTP-CPLT message on its primary management connection. BS will respond with TFTP-RSP message. TFTP-RSP is the short form of config file TFTP complete response.

Step-10:Data transfer takes place between BS and SS.

wimax network entry procedure used by SS

Figure-2 mentions messages logged in event log screen of popular wimax compliant base station device. It shows wimax network entry messages as mentioned below in the sequence.

1. Initial Ranging Success
2. Basic Capability Success
3. SS Registered
4. Service Flow Creation success for downlink(say)
5. Service Flow Creation success for uplink.

For more information also refer article on wimax MAC protocol. This article describes wimax MAC layers viz. convergence sub layer, MAC common part sublayer and security sublayer. It covers various MAC layer messages exchanged between BS and SS which include Broadcast message (DLMAP, ULMAP, UCD and DCD), Ranging request(RNG REQ), Bandwidth request(BW REQ), DSA REQ and DSA ACK.

Links to WiMAX MAC Layer resources

WiMAX Ranging Procedure
WiMAX Bandwidth Request procedure
WiMAX Network Entry Procedure
WiMAX FCH header format
WiMAX TLV Format basics
WiMAX Timers
WiMAX Network Interface types
WiMAX QoS Classes

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