How monitoring subscriber activity affects the operator's business

What is subscriber activity monitoring?

Subscriber activity monitoring is an L2 BRAS feature that allows operators to monitor subscriber connection availability and, if necessary, regulate or terminate their session. FastDPI has two mechanisms for monitoring subscriber activity based on outgoing traffic from subscribers to the Internet:

1. Cutting off incoming traffic without terminating the session: a reactive method that monitors packets arriving at the subscriber from the Internet. This type of activity control limits incoming traffic to the subscriber in case of inactivity, but does not terminate the subscriber’s session.
2. Closing the session when inactive: a proactive method that monitors the status of DHCP sessions and terminates them when they are inactive for a long time. SHCV (Subscriber Host Connectivity Verification) is similar to Nokia BNG control — since DHCP does not have a mechanism for maintaining activity, alternative methods of checking the availability of DHCP nodes are used.

These mechanisms are compatible and can work together.

Application scenarios

Scenario 1. Monitoring subscriber activity with incoming traffic cutoff without closing the session

Set the following parameters in the fastdpi.conf configuration file:

• bras_subs_activity_timeout — sets the activity interval in seconds.
  The default value is 0 — disable activity monitoring.
• bras_subs_activity_ping_timeout — timeout in seconds for pinging the subscriber with an ARP request.
  The default value is 0 — disable ARP pinging of the subscriber.

Subscriber activity monitoring cuts inet → subs traffic if there is no subs → inet traffic. The subscriber becomes inactive when bras_subs_activity_timeout seconds have passed since the last subs → inet packet was received.

The subscriber is also pinged: a unicast ARP request is sent once every bras_subs_activity_ping_timeout seconds. If a response to the request is received, the bras_subs_activity_timeout activity interval is updated and the subscriber is considered active again.

Scenario 2. Monitoring subscriber activity with session termination in case of inactivity

Set the following parameters in the fastdpi.conf configuration file:

• bras_dhcp_shcv_interval — subscriber inactivity interval, seconds.
  Default = 0 (SHCV disabled).
• bras_dhcp_shcv_retry_timeout — ARP request response wait time, in seconds.
  Default = 3 seconds.
• bras_dhcp_shcv_retry_count — number of ARP requests without response.
  Default = 3 requests.

Subscriber activity monitoring closes the subscriber’s DHCP session in case of prolonged inactivity and no response to a unicast ARP request:

1. If there is no subs → inet traffic for bras_dhcp_shcv_interval seconds after sending the last subs → inet packet, fastDPI pings the subscriber with unicast ARP requests. The response timeout is bras_dhcp_shcv_retry_timeout seconds.
2. If there is no response to bras_dhcp_shcv_retry_count (pcs) ARP requests or the ARP response contains a different MAC, the subscriber is considered inactive.
3. The session is closed. Mechanism:
   • Sending Acct Stop;
   • Deannouncing the subscriber’s IP address;
   • Updating the session status to released. At the same time, the reauthorization time does not change so that there are no parasitic L3 authorizations if the subscriber becomes active before the lease time expires and sends something other than DHCP;
   • Deleting the DHCP session (in the DHCP database).

For more information on configuring subscriber activity control and its mechanisms, see the VAS Experts documentation.

Impact on the operator’s business process

1. Monitoring subscriber activity with incoming traffic cutoff without closing the session is especially relevant for subscribers with a static public address—if such a subscriber becomes inactive but traffic continues to flow to them, it is cut off by BRAS and does not reach the subscriber. This removes unnecessary load from the operator’s equipment.
2. Subscriber activity monitoring with session closure (Subscriber Host Connectivity Verification) allows for quick de-announcement of a subscriber’s public IP address from one BRAS to another. This procedure is very often performed by the operator in case of an accident or network maintenance.
3. In both cases, when using activity monitoring, the subscriber’s status is transmitted to billing more quickly. This allows you to quickly detect a problem if the session was closed by mistake and start fixing it.

Conclusion

Subscriber activity control is an important tool for operators seeking to improve service quality and optimize the use of their resources. This mechanism reduces the load on equipment, allows resources to be freed up more quickly, and transfers information to the billing system, which ultimately has a positive impact on the operator’s business.