feat: add PCF charging design docs

docs/guide/3-install-free5gc.md

@@ -17,13 +17,13 @@ You will not be able to run most of the tests in [Test](./4-test-free5gc.md) pag
 
 2\. Golang Version
 
-* As noted above, free5gc is built and tested with Go 1.18.10
+* As noted above, free5gc is built and tested with Go 1.21.8
 * To check the version of Go on your system, from a command prompt:
 ```
 go version
 ```
 
-* If another version of Go is installed, remove the existing version and install Go 1.18.10:
+* If another version of Go is installed, remove the existing version and install Go 1.21.8:
 
 ```bash
 # this assumes your current version of Go is in the default location:

docs/guide/Chf/design.md

@@ -97,4 +97,5 @@ Charging on PDU Session is achieved by **FBC charging, with specific rating grou
 - For ULCL deployment, only the data usage of the PSA-UPF will be charged (it avoids charging the same data packet twice).
 - In our implementations, UPF is composed of the `go-upf` (Controller) and `gtp5g` (Executor).
     - `gtp5g` sends the usage report to `go-upf` via unix socket.
-    - `gtp5g` is able to send multiple reports at once, which reduces the communication effort in UPF.
+    - `gtp5g` is able to send multiple reports at once, which reduces the communication effort in UPF.
+- [PCF Charing Design](./../PCF/charging.md)

docs/guide/PCF/charging.md

@@ -0,0 +1,60 @@
+# PCF Charging Software Design Architecture
+
+>[!NOTE]
+> Author: [Andy Chen (CTFang)](https://www.linkedin.com/in/tsung-fang-chen-437a71191/)
+> Date: 2024/05/07
+
+
+
+**PCF:  Policy Control Function**
+
+Relative specs:
+
+- *TS 29.507 Access and Mobility Policy Control Service*
+- *TS 23.503 Policy and Charging Control Framework for the 5G System (5GS)*
+- *Ts 29.513 Policy and Charging Control Signalling flows and QoS parameter mapping*
+- *Ts 23.255 Telecommunication management; Charging management; 5G data connectivity domain charging* 
+
+
+
+The 3GPP defines the FBC(Flow-Based Charging) and QBC (QoS-Based Charging). 
+
+However, *free5GC v3.4.1* supports **FBC** only. 
+
+
+
+## RatingGroup Allocate
+
+![PDU session establishment](./../Chf/image-1.png)
+
+> PDU session establishment, described in *3GPP TS 32.255 clause 5.2.2.2.2*
+
+Charging on PDU Session is achieved by **FBC charging, with specific rating group/service identifier**:
+
+- The **rating group** would be allocated by PCF during SM Policy Authorization (Step 6).
+    - Get chargingData from MongoDB collection `policyData.ues.chargingData`.
+    - Allocate **rating group** to each charging rule.
+    - Create new chargingData with rating group in MongoDB. 
+    - Create PCC Rule for charging with rating group, SDF template, and charging method.
+    - Make Decision from PCC Rule to SMF. 
+
+- When PCF `HandleDeleteSmPolicyContextRequest`, the new chargingData with rating group would be deleted. 
+
+
+
+## CHF
+
+CHF would use rating group from MongoDB (`policyData.ues.chargingData`) to calculate the usage and grant quota. 
+
+- ABMF (Account Balance Management Function)
+- Rating Function
+
+
+
+![pcf_charging](./images/pcf_charging.png)
+
+
+
+## Others
+
+- [CHF design document](./../Chf/design.md)

docs/guide/contribute.md

@@ -32,6 +32,7 @@ We maintain the design documents to help people started contributing to the free
 - [UPF (GTP5G)](./Gtp5g/design.md)
 - [UPF (PFCP)](./Upf_PFCP/design.md)
 - [CHF](./Chf/design.md)
+- [PCF (Charging)](./PCF/charging.md)
 - [OAuth2 on SBI](./OAuth2/OAuth2Design.md)
 - [Problem Details](https://github.com/free5gc/free5gc.github.io/tree/main/docs/guide/ProblemDetails)