Connection ID (CID)
WiMAX logical channels are identified by a connection identifier (CID). A CID is a unique name or number that is used to identify a specific logical connection path in a communication system. Some connection channel IDs are reserved for control (management connection) and other connections are used for transporting user data.
Each type of connection has its own CID. A two-way connection requires two CIDs. For basic, primary and secondary connections, CID codes are assigned in pairs and they are the same for the downlink and uplink connections.
An initial ranging connection identifier is a code that is used during the initial connection to a wireless system to determine how much transmission timing adjustment is required. For WiMAX systems, the initial ranging CID is 0000 for standard transmission systems and FEFF for adaptive antenna systems.
A basic CID is a logical channel that is assigned during the initial ranging process. Basic CID connections are used for time sensitive MAC control messages such as RF power control and time alignment. The range of CIDs that can be assigned for basic CIDs is from 0001 to some number (m) selected by the operator.
A primary management CID is a logical channel that is used to transfer link control messages. The range of CIDs that are assigned as primary CIDs ranges from the address above the highest basic CID (m+1) to double the number of basic CIDs (2m).
A secondary management CID is a logical channel that is used for upper layer control messages such as DHCP and TFTP messages. The range of CIDs that is assigned as secondary management CIDs ranges from the address above the highest primary management CID (2m+1) up to connection ID FEFE.
A transport CID is a logical channel that is used to transfer user data. The range of CIDs that are assigned as transport CIDs ranges from the address above the highest primary management CID (2m+1) up to connection ID FEFE. Transport connections can use different CIDs in the uplink and downlink directions.
Multicast polling connection identifiers are used to prompt subscriber stations which are part of a multicast group that have data to transmit to attempt to transmit their data using a contention control process. The multicast polling CIDs range from FF00 to FFFC.
A broadcast connection identifier is used to transfer broadcast messages to all devices that are listening to the radio channel. The broadcast CID is FFFF.
Figre 1 outlines some of the CID codes that are used in the WiMAX system. The table shows that CID 0000 is reserved for initial ranging and the basic, primary, secondary and transport CIDs are dynamically assigned as needed. Other reserved CIDs include FEFF for adaptive antenna initial ranging, FF00 through FFFC for multicast polling, FFFD for fragmental broadcast messages, FFFE for padding messages and FFFF for broadcast messages.
Service Flow ID (SFID)
A service flow identifier is a unique number that is assigned by a system that is used to identify the flow of a communication channel that is used for a specific service type. A WiMAX device may have multiple SFIDs per connection (per CID).
Figure 2 illustrates that the WiMAX system has logical connection and service flow channels. Each subscriber station has at least one connection channel and service flows may be assigned to the connections. In this diagram, a WiMAX base station has setup connections with 3 WiMAX subscriber stations. For home #1, the WiMAX transceiver connection is providing one type of service flow for an Internet web browser over a single connection. For home #2, the WiMAX base station has setup a single connection with two services flows; one for a web browsing computer and the other for an IP telephone. For the office user, the WiMAX base station has setup 3 connections on a single subscriber device (3 CIDs). Of these, 2 connections have 2 service flows providing web browsing and IP telephone service and the 3rd connection has a single service flow for web browsing service.
