Wimax standards and Security The Wimax

FIGURE 4.3
WiMAX protocol stacks.

Downlink Guard Uplink

(Ti

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^Fk2

^Fk1

Frame k

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FIGURE 4.4
Time division duplex (TDD) framing.

2. 
   Service Flow
   

When the BS receives a connection request from an SS, it calls for an autho- rization module to determine if the user has the proper authorization for the service. The BS then determines if the physical resource (i.e., RF bandwidth) is available to support the request. If yes, the BS associates the connection request with a service flow with the requested QoS parameters. Each connec- tion is identified by a 16-bit connection ID (CID). Note that IEEE 802.16 does not use source or destination MAC addresses in the MAC frame. A service flow has the following attributes:

1. 
   Service flow ID (SFID): Each service flow has an SFID with its transmission direction (DL or UL).
   
2. 
   CID: A CID is mapped to an SFID after the connection is admitted.
   
3. 
   Provisioned QoS parameters: QoS is provisioned via a network management system.
   
4. 
   Admitted QoS parameters: QoS parameters for which the BS is reserving the resources. The primary resource to be reserved is the bandwidth.
   
5. 
   Active QoS parameters: QoS parameters actually provided for the service flow. Only active service flow may send packets over the wireless link.
   

A service flow could be statically provisioned through the network man- agement system or dynamically created by the following IEEE 802.16 control messages:

• 
  Dynamic service addition (DSA): to create a new service flow
  
• 
  Dynamic service change (DSC): to change an existing service flow
  
• 
  Dynamic service deletion (DSD): to delete an existing service flow
  

These MAC control messages allow a service provider to add new sub- scribers, modify QoS for existing customers, allocate more resource (i.e., RF bandwidth) to existing links, and reclaim unused resources. All this can be accomplished during the operation without interfering with the active services of existing customers.
A dynamic service request can be initiated by either the BS or an SS. In the case of SS-initiated request, a DSA-REQ (request) message is sent from an SS with a service flow reference and the QoS parameter set. When the BS receives the DSA-REQ message, it sends a DSX-RVD (received) message to inform the SS of receiving the request. After that, the BS sends DSA-RSP (response) message to indicate the acceptance or rejection of the request. The SS then sends an acknowledgment (DSA-ACK) . The complete message flow diagram is illustrated in Figure 4.5. The BS-initiated request is similar except that there is no need to send a DSX-RVD.