Steel-Belted Radius Carrier 7.2.x Administration and Configuration Guide > Overview of the WiMAX Mobility Module > WiMAX Post-Paid (Offline) Accounting

WiMAX Post-Paid (Offline) Accounting

Accounting in WiMAX is based on a subscription that is identified through the subscription's NAI. A single subscriber can have multiple subscriptions. The WiMAX mobility module supports the following post-paid (offline) accounting features:

• Flow-based accounting
• IP-session-based accounting

For a diagram depicting accounting events within a home network, see Figure 170.

Accounting events for the ASN-GW, home agent, and DHCP server in either the home network or visited network are recorded in accounting log files. Accounting log files are named yyyymmdd.act, where yyyy is the 4-digit year, mm is the month, and dd is the day on which the log file was created. Accounting events include START messages, which indicate the beginning of a connection; STOP messages, which indicate the termination of a connection; and INTERIM messages, which indicate a connection is ongoing.

For more details about logging and reconciling accounting records, see Using the Accounting Log File.

Flow-Based Accounting

Flow-based accounting sessions are defined by starting and stopping flows. An Account-Start (defined with its proper attributes) marks the start of a flow and an Account-Stop (defined with its proper attributes) marks the end of a flow.

An Account-Start is received for each WiMAX packet flow. Flows are identified at the PDSN (Packet Data Serving Node) using packet filters. Packet filters are used to map forward traffic and for per-flow accounting in the forward and reverse direction.

Flow-based accounting messages do not create or destroy sessions, but will create entries in the accounting log file. These messages are received by the SQL accounting plug-in. For more details about using the SQL accounting plug-in, see Chapter 19, Configuring SQL Accounting.

The attributes in Table 53 are used to determine the state of the flow:

Table 53: WiMAX Packet Flow Attributes

Attribute	Description
WiMAX-Session-Continue	Specifies whether the WiMAX packet flow continues or reaches the final stop of an accounting session. If set to 0 (False) or if the attribute is missing, indicates that the WiMAX packet flow has reached the final stop of the accounting session. If set to 1 (True), indicates that the WiMAX packet flow is not at the end of an accounting session (an Account-Stop is immediately followed by another Account-Start).
WiMAX-Beginning-Of-Session	Specifies whether the WiMAX packet flow is starting a new accounting flow or continues with a previous accounting flow. If set to 0 (False) or if the attribute is missing, indicates that the WiMAX packet flow is a continuation of a previous accounting session. If set to 1 (True), indicates that the WiMAX packet flow is starting a new flow of an accounting session.

Flows are preprovisioned and are described in the Packet-Flow-Descriptor attribute. A packet flow may describe a unidirectional flow and bidirectional flow. The Packet-Flow-Descriptor attribute is attached to the initial Access-Accept. Each (potential) flow is identified by a package data flow ID (PDFID) and announces when a flow has started. Its value matches all records from the same packet data flow. The PDFID correlates all accounting records, and is assigned by the connectivity services network (CSN) and remains constant through all handover scenarios.

For each flow that has started within an accounting session, before the accounting session can be closed (stopped), each flow within that accounting session must be stopped. A CSN can restart a flow by sending an existing PDFID in a new Account-Start.

IP-Session-Based Accounting

The WiMAX-Session-Continue attribute (as described in Table 53) defines when an accounting session actually ends. Each Accounting Start/Stop packet delineates the following:

• A complete session or flow
• A segment of a session or flow

A session or flow may consist of several accounting segments. Accounting segmentation occurs due to:

• Handover with accounting client relocation
• Change in status such as hot-line state

The accounting attributes WiMAX-Beginning-Of-Session and WiMAX-Session-Continue, determine the interpretation of the Accounting-Request packets as shown in Table 54:

Table 54: Interpretation of Accounting-Request Packets

Acct-Status-Type	WiMAX-Beginning-Of-Session	WiMAX-Session-Continue	Description
Start	True	N/A	Beginning of the first accounting segment for a session or flow.
Start	False (or missing)	N/A	Beginning of a subsequent accounting segment of a session or flow.
Start	N/A	True	The end of the accounting segment. Another accounting segment is starting; expect an Accounting-Request (Start).
Stop	N/A	False	This is the end of the session or flow.

Each accounting session is identified by an Acct-Multi-Session-Id attribute. Flows within an accounting session are identified by the Acct-Multi-Session-Id. The Acct-Multi-Session-Id attribute contains the same value as the AAA-Session-Id attribute. The identifier is set to the value of the AAA-Session-Id which is generated by the AAA server after successful authentication and delivered to the ASN-GW in an Access-Accept message. The AAA-Session-Id is unique per AAA server, but is used for all flows.

The Acct-Multi-Session-Id correlates accounting records for a device session on a particular device for a given subscription.