Wimax standards and Security The Wimax

TABLE 4.1
QoS Classes and Parameters


UGS rtPS nrtPS BE

√
Minimum reserved traffic rate Maximum sustained traffic rate
Maximum traffic burst _√
√ √
√ √ √
√ √

√ √
Tolerated jitter Maximum latency

• 
  Tolerated jitter: The maximum delay variation (in milliseconds) of a service flow.
  

4. 
   Admission Control
   

A connection request could be initiated by either the BS or an SS as illus- trated in Figure 4.5. IEEE 802.16 uses a mechanism of request and grant for connection-oriented services. A request is from an SS to inform the BS that it needs bandwidth. When an SS sends a request to the BS for a connection with certain QoS parameters, the BS first authenticates the SS. After authentication, the BS needs to determine if the resource is available for the request:
(all committed bandwidth) + new bandwidth request ≤ total bandwidth
In the case of UGS, the committed bandwidth is MSTR while in the case of rtPS and nrtPS the committed bandwidth is MRTR. The BE service has no committed bandwidth. An important note about IEEE 802.16 is that the UL and DL bandwidth could be dynamically allocated based on the user needs. If there are more demands for DL while many UL time slots are available, the BS can allocate more time slots from the UL to the DL.

=
Abandwidth request message is usually transmitted during a UL allocation (SS > BS), and the standard also allows an optional provision for piggyback request. It should be noted that the request is sent in the contention mode and could be lost (due to collision). As a result, the BS needs to issue the mes- sage DSX-RVD to confirm the reception of the DSA-REQ message. The BS issues the bandwidth grant in the UL-MAP that is broadcasted to all SSs, and individual SSs use CID and the UL-MAP to retrieve its own grant. After a con- nection is created with the service flow parameters, an incoming packet for the transmission enters into a priority queue to be served by the QoS scheduler.

5.