Accounting modes of operation

This section is applicable to the 7750 SR or the 7450 ESS. There are three basic accounting models:

Per queue-instance
Per Host
Per Session

Each of the basic models can optionally be enabled to send interim-updates. Inclusion/exclusion of interim-updates depends on whether volume based (start/interim-updates/stop) or time-based (start/stop) accounting is required.

The difference between the three basic accounting models is in its core related to the processing of the acc-session-id for each model. The differences are related to:

acct-session-id generation within each model
outcome in response to the CoA action relative to the targeted acct-session-id

The counters for volume-based accounting are collected from queues or policers that are instantiated per SLA profile instance (SPI). This is true regardless of which model of accounting (or combination of models) is deployed. Within the accounting context, the SPI equates to queue-instance.

The following table summarizes the key differences between various accounting modes of operation that are supported. Interim-updates for each individual mode can be enabled or disabled through configuration (keyword as an extension to the commands that enable three basic modes of accounting). This is denoted by the IU-Config keyword under the ‛I-U’ column in the table. The table also shows that any two combinations of the three basic models (including their variants for volume and time- based accounting) can be enabled simultaneously.

Table: Accounting modes of operation
Accounting mode	Accounting entity	START	I-U	STOP	Acct-session-id	Acct-multi-session-id
queue-instance-accounting	queue-instance	X	IU-config	X	X
	session
	host
session-accounting	queue-instance
	session	X	IU-config	X	X	queue-instance
	host
host-accounting	queue-instance
	session
	host	X	IU-config	X	X	queue-instance
queue-instance-accounting + host-accounting	queue-instance	X	IU-config	X	X	queue-instance
	session
	host	X	IU-config	X	X	queue-instance
queue-instance-accounting + session-accounting	queue-instance	X	IU-config	X	X	queue-instance
	session	X	IU-config	X	X	queue-instance
	host
session-accounting + host-accounting	queue-instance
	session	X	IU-config	X	X	queue-instance
	host	X	IU-config	X	X	session

Note: Hosts within the targeted CoA entity are affected as follows:

If the CoA target is the session, both constituting members (IPv4 and IPv6) of the dual-stack host are affected.
If the CoA target is the queuing-instance, up to 32 hosts that are sharing that SPI are affected.

The same principle applies to LI.

The accounting behavior (accounting messages and accounting attributes) in case that the SPI is changed with CoA depends on the accounting mode of operation. The behavior is the following:

SPI change in conjunction with per queuing instance accounting triggers a STOP for the old SPI and a START for the new SPI with corresponding counters. Acct-session-id/Acct-Multi-Session-Id is unique per SPI. Note that Acct-Multi-Session-Id is only generated if per queuing-instance accounting mode of operation is combined with some other mode of operation (host or session).
SPI change in conjunction with per host or per session accounting (no interim updates for either method) does not trigger any new accounting messages. In other words, SPI change goes unnoticed from the perspective of the accounting server until the host/session is terminated. When the host/session is terminated a STOP is sent with the VSA carrying the latest SPI name and the acct-multi-session-id attribute of the latest SPI. Acct-session-id stays the same during the lifetime of the host. Counters are not included in STOP (interim-update not enabled).

SPI change in conjunction with per host accounting with interim-updates or per session accounting with interim-updates triggers two interim-update messages:
- One with the old counters (terminated queues) and the old SPI name VSA. This behavior is similar to the triggered STOP message in per queuing-instance accounting upon SPI change.
- One with the new counters (new queues instantiated), the VSA carrying the new SPI name and the new acct-multi-session-id referencing the new SPI. This behavior is similar to the triggered START message in per queuing-instance accounting when SPI is changed.