Wimax standards and Security The Wimax

MPDU Retransmission Scheme

The automatic retransmission (ARQ) mechanism is a part of the MAC, which is optional for implementation. When implemented, ARQ may be enabled on a per connection basis. The ARQ shall be specified and negotiated during
ACK


FIGURE 3.1
Operations of the ARQ scheme.

connection creation. A connection cannot have a mixture of ARQ and non- ARQ traffic. Similar to other properties of the MAC protocol, the scope of a specific instance of ARQ is limited to one unidirectional connection.

For ARQ-enabled connections, enabling of fragmentation is optional. When fragmentation is enabled, the transmitter may partition each MAC SDU into fragments for separate transmission based on the value of the ARQ_BLOCK_SIZE parameter. When fragmentation is not enabled, the con- nection shall be managed as if fragmentation was enabled. In this case, regardless of the negotiated block size, each fragment formed for transmission shall contain all the blocks of data associated with the parent MAC SDU. The ARQ feedback information can be sent as a stand-alone MAC management message on the appropriate basic management connection, or piggybacked on an existing connection. ARQ feedback cannot be fragmented (Figure 3.1).

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   Services Provision and Schemes
   
   1. 
      Services and Parameters
      

Scheduling services represent the data handling mechanisms supported by the MAC scheduler for data transport on a connection. Each connection is associated with a single data service. Each data service is associated with a set of QoS parameters that quantify aspects of its behavior. These parameters are managed using the dynamic service addition (DSA) and dynamic service change (DSC) message dialogs. Four services are supported: unsolicited grant

service (UGS), real-time polling service (rtPS), nonreal-time polling service (nrtPS), and best effort (BE).

The UGS is designed to support real-time data streams consisting of fixed- size data packets issued at periodic intervals, such as voice over IP without silence suppression. The mandatory QoS service flow parameters for this scheduling service are maximum sustained traffic rate, maximum latency, tolerated jitter, and request/transmission policy. If present, the minimum reserved traffic rate parameter shall have the same value as the maximum sustained traffic rate parameter.
The rtPS is designed to support real-time data streams consisting of variable-sized data packets that are issued at periodic intervals, such as mov- ing pictures experts group (MPEG) video. The mandatory QoS service flow parameters for this scheduling service are minimum reserved traffic rate, maximum sustained traffic rate, maximum latency, and request/transmission policy.
The nrtPS is designed to support delay-tolerant data streams consisting of variable-sized data packets for which a minimum data rate is required, such as FTP. The mandatory QoS service flow parameters for this scheduling service are minimum reserved traffic rate, maximum sustained traffic rate, traffic priority, and request/transmission policy.
The BE service is designed to support data streams for which no minimum service level is required and therefore may be handled on a space-available basis. The mandatory QoS service flow parameters for this scheduling service are maximum sustained traffic rate, traffic priority, and request/transmission policy.

2.