Version

Sy AVPs

Sy (application id: 16777302)

The Sy interface is a critical reference point within the Diameter protocol architecture, primarily designed to facilitate communication between the Policy and Charging Rules Function (PCRF) and the Online Charging System (OCS). This interface plays a vital role in managing policy control and charging for subscribers based on their spending limits.

The primary purpose of the Sy interface is to enable the PCRF to make informed policy decisions by retrieving subscriber spending limit information from the OCS. It supports functions such as requesting policy counter statuses, subscribing to or unsubscribing from spending limit reports, and receiving notifications of changes in spending limit statuses.
The Sy interface is essential in scenarios where the PCRF needs to adjust policy decisions dynamically based on a subscriber's spending behavior, ensuring that the network enforces appropriate charging rules and quality of service (QoS) settings.

In the overall PCC (Policy and Charging Control) architecture, the Sy interface connects the PCRF and the OCS. The PCRF acts as a client that requests and utilizes policy counter status information, while the OCS serves as the server that maintains these counters and provides the necessary data.
The Sy interface is implemented over the Diameter protocol, utilizing Diameter commands and Attribute-Value Pairs (AVPs) specific to the Sy application. 

Sy interface workflow:

Initial Spending Limit Report Request: 

  • When the PCRF determines that it needs information about a subscriber's spending limit to make a policy decision, it sends an Initial Spending Limit Report Request to the OCS over the Sy interface.
  • The request includes details about which policy counters are required. If necessary, the PCRF may also subscribe to ongoing updates regarding these counters.

Spending Limit Report Provisioning:

  • Upon receiving the request, the OCS processes it and retrieves the requested policy counter statuses.
  • The OCS then sends a Spending Limit Report Answer back to the PCRF, providing the current statuses of the requested counters.
  • If the PCRF has subscribed to updates, the OCS will notify the PCRF of any changes in these counters over time.

Intermediate and Final Spending Limit Reports:

  • As the subscriber's spending changes, the OCS generates intermediate reports to update the PCRF with the latest status of the counters.
  • Once the subscriber reaches a specific spending threshold or a billing cycle completes, the OCS sends a final report to the PCRF, summarizing the final status of the counters.

Policy Decision and Enforcement:

  • The PCRF uses the information provided by the OCS to make real-time policy decisions. These decisions could involve adjusting the subscriber's QoS settings, modifying access policies, or triggering specific charging rules.
  • The PCRF then communicates these decisions to other network elements, such as the Policy and Charging Enforcement Function (PCEF), to enforce the new policies.

Session Termination:

  • Once the PCRF determines that it no longer needs updates from the OCS (e.g., the subscriber session ends or the required information is no longer relevant), it sends a request to terminate the Sy session.
  • The OCS acknowledges this request and ceases to send further updates.

For complete technical specification of Sy interface in Diameter protocol please refer to: [3GPP TS 29.219]

package com.mobius.software.telco.protocols.diameter.primitives.sy;

Name

AVP Code

Data Type

Vendor

Pending-Policy-Counter-Change-Time

2906

Time

3GPP

Represents the Network Time Protocol (NTP) timestamp at which the pending policy counter status becomes the current status of a policy counter.

Pending-Policy-Counter-Information

2905

Grouped

3GPP

Contains pending policy counter status along with the scheduled time when the status will become active. If multiple pending policy counter AVPs are included,  they shall be sorted in order of change time.

The AVP structure is defined as follows:

Policy-Counter-Status (Mandatory): Defines the pending policy counter status that will become active at the specified change time. 

Pending-Policy-Counter-Change-Time (Mandatory): Represents the Network Time Protocol (NTP) timestamp at which the pending policy counter status will take effect.

Note: The valid values for the Pending-Policy-Counter-Information AVP are specific for each Policy-Counter-Identifier value.

Policy-Counter-Identifier

2901

UTF8String

3GPP

Identifies a policy counter maintained per subscriber within the Online Charging System (OCS).

Policy-Counter-Status

2902

UTF8String

3GPP

Defines the status of a specific policy counter for a given subscriber. It is used to indicate whether a policy counter is valid, invalid, or in another state based on operator-defined criteria.

Note: The valid values for the Policy-Counter-Status AVP are specific for each Policy-Counter-Identifier value. 

The values (e.g. valid, invalid or any other status) are not specified. The interpretation and actions related to the defined values are out of scope of 3GPP.

Policy-Counter-Status-Report

2903

Grouped

3GPP

Used by the Online Charging System (OCS) to report the status of a specific policy counter to the Policy and Charging Rules Function (PCRF). It allows for the synchronization of policy counter values and ensures that policy-based charging, restrictions, and entitlements are correctly enforced.

The AVP structure is defined as follows:

Policy-Counter-Identifier (Mandatory): Uniquely identifies the policy counter being reported.

Policy-Counter-Status (Mandatory): Indicates the current status of the policy counter (e.g., "active," "exhausted," "suspended," etc.). The exact values are operator-defined and vary based on the specific policy control framework.

Pending-Policy-Counter-Information (Optional, Multiple): Contains future policy counter status changes that will take effect at a specified time. If no Pending-Policy-Counter-Information AVPs are included, it indicates that previously stored pending statuses should be removed.

If new pending statuses are included, they overwrite previously provided ones.

SL-Request-Type

2904

Enumerated

3GPP

Indicates whether the Spending Limit Report (SLR) command is being sent as part of the initial or intermediate spending limit report request procedure. 

Enumerated Values:

0: INITIAL_REQUEST: Indicates that the SLR command is the first request in the Diameter session. Used when the spending limit reporting procedure is just beginning.

1: INTERMEDIATE_REQUEST: Indicates that the SLR command is a subsequent request in the same Diameter session. Used when additional reports need to be sent to update the OCS on spending limit consumption.

SN-Request-Type

2907

Unsigned32 (Bitmask)

3GPP

Used to indicate the type of Spending-Status-Notification-Request (SNR) being sent in the Sy interface between the Policy and Charging Rules Function (PCRF) and the Online Charging System (OCS). This AVP allows the PCRF to determine whether the request is a normal spending status notification or an abort session request.

Multiple bits may be set in combination, allowing flexibility in spending status notifications.

Bitmask Definition:

Bit 0: Normal Request: If this bit is set, the SNR is only used to convey a spending limit report. This is the default value if the SN-Request-Type AVP is not included in the SNR.

Bit 1: Abort Session Request: If this bit is set, the SNR is used to request the termination of the Sy session. Indicates that the OCS wants to end the session between the PCRF and OCS due to policy or spending limit exhaustion.


 

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