Introduction
This document describes the configuration to be examined when the Packet Data Network Gateway (PGW) reports a higher quota than the assigned one.
Prerequisites
Requirements
Cisco recommends that you have knowledge of these topics:
- Long-Term Evolution (LTE)
- Online Charging
- Diameter Credit-Control Application
Components Used
This document is not restricted to specific software and hardware versions.
The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, ensure that you understand the potential impact of any command.
Problem
When the quota is exhausted, PGW reports under the Used-Service-Unit (USU) Attribute-Value Pair (AVP), more than the quota assigned by the Online Charging System (OCS) in the earlier Credit-Control-Answer Update under the Granted-Service-Unit (GSU).
Analysis Performed
Once the quota provisioned by OCS in the previous Credit-Control-Answer_UPDATE (frame 3130) is exhausted, PGW reports under the USU (frame 3142) a higher used quota. A small difference is observed between the GSU (CC-Total-Octets=11375) and USU (CC-Total-Octets=11756) octets reported.
No. Source Destination Protocol CC-Request-Type CC-Total-Octets 3GPP-Reporting-Reason Info
3130 10.30.50.36 10.125.230.100 DIAMETER UPDATE_REQUEST 11375 cmd=Credit-Control Answer(272)
3142 10.125.230.100 10.30.50.36 DIAMETER UPDATE_REQUEST 11756 QUOTA_EXHAUSTED cmd=Credit-Control Request(272)
RFC 4006 contains the behavior and interactions for this scenario. The standard states:
8.17. Granted-Service-Unit AVP
Granted-Service-Unit AVP (AVP Code 431) is of type Grouped and
contains the amount of units that the Diameter credit-control client
can provide to the end user until the service must be released or the
new Credit-Control-Request must be sent.
8.19. Used-Service-Unit AVP
The Used-Service-Unit AVP is of type Grouped (AVP Code 446) and
contains the amount of used units measured from the point when the
service became active or, if interim interrogations are used during
the session, from the point when the previous measurement ended.
Solution
When this behavior is observed, review the show configuration verbose
output from PGW and verify if quota request-trigger include-packet-causing-trigger
command is enabled under the credit-control group
configuration. Cisco StarOSĀ® Configuration Guide states concerning this configuration line:
quota request-trigger
This command configures the action on the packet that triggers the credit control application to request quota.
include-packet-causing-trigger
Includes the packet causing the threshold limit violation trigger.
If this command is enabled, the packet that triggers the QUOTA_EXHAUSTED report must be included in this report and its payload causes the USU reported value to be higher than the GSU by OCS.
Depending on your requirements, this behavior can be controlled with the quota request-trigger
by including or excluding the packet causing the threshold limit violation trigger:
quota request-trigger { exclude-packet-causing-trigger | include-packet-causing-trigger }
Note: By default, it is set to include-packet-causing-trigger
.