Correlation b/w Gx, Gy and Sy

Question

I am trying to comeout with the basic AVPs in Gx (to initiate the counting functionality in the PGW.).
- Lets say when the Default bearer is created initially (lets take ims apn as example). In this case, what information is sent to PGW so it starts to count the number of bytes used up for this bearer.
- When the multiple dedicated bearers are created for that particular user, how is this info will differentiate it from the counts the bytes different from the one for each bearers.
- what kind of counters can be implemented in PCRF. Like lets say, the counter which is applicable only for the GBR bearers etc ? (like there is a generic counter for each subscriber or at bearer level for each subscriber)
- Im also looking to comeout with the basic sequence chart ..(or may be wireshark related to mapping Gx, Gy and sy).

Answer 1

Priya, since you are already going through 32.299 and 29.219, my advice is - just continue. It takes multiple readings but you will get most of the questions answered. But you also need to look at the product documentation of the OCS and PCRF products you are targeting. For example, while 29.219 (Sy) defines how the Policy Counter status information is exchanged between OCS and PCRF, standard doesn't dictate how OCS should create and maintain them. We have seen vendor implementations differing considerably (to the extent that it doesn't remain standard compliant anymore...)

Specific question: Starting of reporting to OCS - Look at CCR Initial request of Gy. 32.299 indicates the possible PDU structure but specific OCS may impose restrictions. Further, domain specific charging considerations apply (PS Information, IMS Information etc.)

Maintaining the relationship between Gx and Gy Diameter sessions is your application's responsibility. OCS and PCRF don't care about it. Subscription-Id is available to them anyway - for example when PCRF registers for Policy Counter Status updates.

• Gy session also should terminate when UE detaches, by sending CCR-Terminate. OCS should know that the UE is not consuming services any more.
• Sy termination - yes, it is logical for PCRF to terminate the Sy session when subscriber is not connected any more.

Comments

Thanks a lot. yes I think multiple reading help me.
Basically I come from lower layer (l3 esp RRC and l2 UE development background, so sometimes get lost in the vast network side.)
I work for a small company, so initially i need to come up with changes in most of the modules in this area. So bit difficult scenario, than from where we have a third party component and access to their integration test specs.
As per Gx, once it worked internally, we had thirdparty PGW, so it was easier to validate what i had achived internally works with other modules too..

Thanks a lot again and your hints will surely eases my spec understandings

Answer 2

Pdk, not sure if I understand the question correctly, but let me give my take on it. Tracking of traffic volume is essentially a data plane functionality, and PGW will be doing it (or has to do it) for each IP CAN session, independent of control plane.

Correlation of Gx, Rx, Gxx, S9 sessions (if any) is done based on the corresponding IP CAN session. Note that IP CAN session can be identified based on attributes like Subscriber Id (may be IP4/v6 address) and called -PN. This is Diameter Routing Agent (DRA -see 29.213) functionality. This essentially involves correlating Diameter sessions over different interfaces (Gx, Rx,..) based on the IP CAN session they serve.

Same idea is applicable to correlating Gx, Gy , Sy traffic. Since a single Diameter session over any of these interfaces would be for a single subscriber, logically it is more meaningful to correlate Diameter sessions rather than individual command/responses. For example for Gx, this would mean a CCR Initial followed by zero or more CCR -Updates followed by CCR-Terminate (along with corresponding answers.) Clearly in OCS, Gy traffic would have direct impact on the Policy Counters it maintains for the subscriber, in trun resulting in Sy notifications to PCRF.

Comments

Rathnakumar: Thanks a lot for replying and very helpful hints. I do understand my Q is bit vague as I am just reading the Gy and Sy specs without any prior knowledge. So please forgive me, i am still in the way of getting some basic idea. It is difficult just reading specs as I am not able to find any books related to this area.

Regarding your answers
- I thought PGW will count the number of bytes without any trigger on IPCAN session est. But without any trigger , how can it start reporting the number of bytes consumed back to OCS. Either there is some paramteter ( Is it Rating group ?) in the Initial CCA message to inform PGW about this . This is needed as in Dynamic rule configuration, the PGW is not preconfigured with any parameter.

- I thought there is anIP CAN session for the subscriber for each APN. I am talking about only the Gx interface. So PCRF can have a map of Gx sessionId with Apn and subscriber Id. But now when Gy and Sy is created, how are the sessions maintained ?

-In case of Gx, the session is maitained till the UE detaches. Will the same applicable to others like Gy and Sy ?.

- Yes, i understand the IP-CAN session est is control side (i,e done during the attach) and later during the data session, the PGW User side, keeps count of utilised bytes. But my query is is the Policy counter applicable to all dedicated bearers related to IP-CAN session ?

thanks
Priya

Answer 3

Hi Priya,

In case PCRF wants to do the monitoring on how much data is consumed then it can use Usage-Monitoring-Information AVP to do it.
It will grant a quota to PGW and when PGW will use that much quota it should report the same to PCRF.
With the help of Monitoring key it can control if the monitoring is to be done at PCC Rule Level or Session Level.

Let's look at Gy interface now.
In case PCRF wants to implement charging for any rule or bearer it provides the Service-Id and Rating-Group along with the charging method in CCA or RAR.
Based on the information recevied(mentioned in the above line) PGW will then initiate a Gy session with OCS (Note that for every bearer there is a different Gy session in LTE)

Regards,
Peeyush Sharma

Comments

Thanks a lot Peeyush.
This is exactly what i was trying to figure out ( basic AVPs) :) . It is difficult, to find these details, when I try to read the whole of specs . ( confusing to get my head around it )
Thanks a lot again and much appreciate your valuable inputs, as always helped me alot.