Different control messages defined by IEEE 802.16 for Mac management are:

• Uplink and downlink channel descriptor: Transmits characteristics of the physical channel.

• Uplink and downlink access definition: Allocates access to the uplink and downlink channels.

• Ranging request and response: The request is used by the subscriber to deter- mine network delay and to request power and/or modulation adjustment. The response from the BS contains the requested parameters.

• Registration request, response, and acknowledge: The request is transmitted by the subscriber at initialization time and contains various relevant parameters.The base station replies with a response, and the subscriber sends an acknowledge to complete the handshake.

• Privacy key management request and response: Used to exchange information about encryption keys.

• Dynamic service addition request, response, and acknowledge: The request is sent by a subscriber to request a new service flow.

• Dynamic service change request, response, and acknowledge: The request is sent by a subscriber or the base station to dynamically change the parameters of an existing service flow.

• Dynamic service deletion request and response: The request is sent by the base station or subscriber to delete an existing service flow.

• Multicast polling assignment request and response: Sent by a subscriber to request inclusion in a multicast polling group.

• Downlink data grant type request: Sent by the base station to the subscriber to dictate the modulation method and FEe technique to be used on a particular connection, to enhance performance.

• ARQ acknowledgment: Used to acknowledge successful receipt of one or more packets from the peer MAC entity.