Monday, October 5, 2009

Addressing | WiMAX Radio

Each WiMAX radio is configured at the factory with a unique 48 bit medium access control address (MAC address) as identified in IEEE standard 802-2001. The first few bits of the MAC address indicate the manufacturer of the device. The remaining bits are a unique serial number of the device. While it is possible for a single subscriber device to have more than one 48 bit physical MAC address, most devices have a single MAC address.

The 48 bit MAC address is not part of the transmitted packet (MPDU). Instead, the device is identified by a 16 bit connection identifier (CID) that is assigned after the device has connected to the system. The MAC address is transferred during the device registration or authentication process to allow the system to identify the specific user. A single WiMAX device may contain 1 or more globally unique MAC addresses.

Each WiMAX device typically has several CIDs assigned. Some of the CIDs are used for controlling information and some are used to identify user data transmission channels (traffic channels).

The 16 bit CID is used to identify and categorize traffic (a maximum of 65,535 CIDs can exist per RF channel). Some CIDs are pre-assigned for specific functions (such as initial ranging) and others are unique to a specific connection.

A single CID may be shared by several services (logical channels). Each of these channels is a service flow and is identified by a service flow identifier (SFID).

To reduce the amount of overhead on a WiMAX radio channel (bits dedicated for control purposes), a shortened version of a CID (called a reduced connection identifier) may be used. A reduced connection identifier (RCID) can be 11, 7 or 3 bits long.

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