RFWiMAX CID vs SFID: Connection ID and Service Flow ID Explained
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This page explains the fundamental differences between CID (Connection ID) and SFID (Service Flow ID) parameters used in WiMAX systems. Service flows are a core element of the 802.16 WiMAX standard.
A service flow represents a unidirectional data stream. To transmit bi-directional traffic, two service flows must be defined: one for the uplink and another for the downlink. These service flows can have distinct QoS (Quality of Service) settings. For more details, refer to the WiMAX QoS page.
The WiMAX base station allows multiple service flows to be configured for each subscriber station within a sector. This enables network service providers to offer diverse services and segregate traffic flows with varying QoS requirements. Data packets are forwarded by the base station based on classification rules.
Classification rules involve examining each packet for pattern matches, such as destination address, source address, or VLAN tag. All classification is defined at the WiMAX base station, and the classification parameters are downloaded to the subscriber station. Base Station (BS) manufacturers typically provide an interface for adding and deleting service flow configurations.
CS specification follows 802.3. There will be provision to set SFID for downlink and uplink with SS MAC ID setting.
A service flow in WiMAX is partially characterized by the following attributes:
- Service Flow ID (SFID): A 32-bit identifier assigned to all existing service flows. The SFID acts as the principal identifier for the Service Flow and has an associated direction (uplink or downlink).
- Connection ID (CID): A 16-bit identifier associated with each active SFID (i.e., when the connection is active).
- QoS Parameters (Required): A set of QoS parameters specifying the resources required by the service flow. The primary resource is bandwidth, but the specification may also include latency requirements.
- QoS Parameters (Provided): A set of QoS parameters defining the level of service being provided.
Service flows are defined and stored in the base station. To establish a service flow, the base station sends a setup message to the subscriber station, specifying the required set of QoS parameters. The subscriber station responds to each request by accepting or rejecting the setup message.
A service flow may be pre-provisioned or dynamically created and deleted without service interruption. This is useful for supporting multiple subscribers in a single sector. New subscribers can be added, and existing subscribers can be removed or have service levels modified.
Setup messages are sent by the base station following any subscriber station power-cycle, loss and recovery of the wireless link to a subscriber station, or any service flow add/delete operation at the WiMAX base station.
Fig-1: Event log or network log in WiMAX system
Figure 1 above shows an event log captured by a WiMAX-compliant base station, indicating “service flow creation success” between the Base Station (BS) and Subscriber Station (SS). There are two SFIDs, each having a unique CID. This refers to the uplink and downlink connection.
WiMAX CID Table
| CID Value | Description |
|---|---|
| 0x0000 | Initial Ranging: Used by SS and BS during the initial ranging procedure. |
| 0x0001-m | Basic CID: The same value is assigned to both downlink and uplink connection. |
| m+1 to 2m | Primary Management CID: The same value is assigned to both downlink and uplink connection. |
| 2m+1 to 0xFEFE | Transport CIDs and Secondary Management CIDs: For the secondary management connection, the same value is assigned to both downlink and uplink connection. |
| 0xFFFF | Broadcast CID: Used for broadcast information which is transmitted on the downlink to all the SSs. |
