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Correlation b/w Gx, Gy and Sy

+4 votes
3,436 views

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).

posted Dec 28, 2015 by Pdk

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3 Answers

+2 votes
 
Best answer

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.
answer Dec 29, 2015 by Rathnakumar Kayyar
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
+2 votes

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.

answer Dec 29, 2015 by Rathnakumar Kayyar
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
+1 vote

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

answer Dec 31, 2015 by Peeyush Sharma
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.
Similar Questions
+1 vote

Hi all,

We have complexity linked to Gy and Gx interfaces.

Let's say that we have two rules configured as static on PGW with :

Rule1= Reports RatingGroup1
Rule2= Reports RatingGroup2

When PCRF install Rule 1 on Gx, the ratingGroup reported by PGW to OCS is RatingGroup1
When PCRF uninstal Rule1 then install Rule2, the ratingGroup reported by PGW remain RatingGroup1 till a Gy trigger is reached (revalidation time, GSU consumption...).
Then the problem on our system is that when PCRF change the rules on Gx interface the PGW keep reporting the old rating group on Gy interface ie: Gx change do not lead to a Gy change similtanously. I m wondering if there is a standard behaviour for such a use case?

Thanks a lot

+2 votes

I have a question regarding the mapping the Policy counter to Bearers.

Does Policy counter relates to subscriber or it relates to services. I mean how the OCS manages the poilicy counter..
And how it maps to bearers

Lets say we have default bearer which is used for the internet browsing and dedicated bearer for voice.

Now lets say we have Policy counter id1 for subscriber 1, which says the "service as Internet" ..And lets say APN-AMBR (for internet is 5 Mbps upto 5GB ) and 2 Mbps for more than 5GB.

Now in the OCS , we configure for
subscriber1:
Policy counterid1: status 5 Mbps upto 5GB and 2 Mbps for more than 5GB.

And on registration, CCR is sent by PGW to PCRF, which inturn sends the SLR with Policy counter id1 with session Id lets say Sysession1

Now the PCRF sends the CCA to PGW with "service type as Internet", Metering method as "volume" and Rating Group some random value. But there is no way to indicate to PGW about the details of counter like on counting 5Mb, it needs to send the CCR-U to OCS. Or lets say on every 2MB PGW indicates to OCS. The Gy session is created for each bearer ? (i.e one for default bearer here and may be another for dedicated bearer related to that..)

On reaching the 5MB limit, the OCS, sends the SNR to PCRF with the Sysession1.

And when the IP CAN is terminated, CCR-T is sent to OCS and also to PCRF by PGW. PCRF inturn sends the STR to OCS.

Now my Q is about a for 2nd APN for the same subsribers, whatabout the Gy and Sy interfaces, are they reused ?

And whatabout the dedicated bearers related to first APN, will they be using the same Gy and Sy interfaces ?

thanks a lot. Any help or any hints in this very helpful for me to correct my understanding and which will correct my code and finally test it !!!

+5 votes

Hi,
What is the difference between Gx and Gz interface.
As we know the interface between P-GW and OFCS is Gz interface and P-GW to PCRF is Gx.
Why both the interfaces are considered as Offline Charging

+1 vote

Hi ,
How Reporting-Reason AVP reporting is decided by GGSN/P-GW in Gy Interface.
There are different Reporting-Reason AVP parameters are present. My doubt is let say at same time Quota_Exhausted and Validity_Time got expired , so how GGSN/P-GW will choose which parameter need to be reported to OCS.
Is their any priority or ordering concepts?

Appreciate your help.

Thanks

+1 vote

I am going through the 32.299 and trying to figure out the contents of the CCR message.

Section 6.4.2 lists the AVPS in that message, I am looking for how the PCEF sends the "used bytes" to OCS. The "Multiple services credit control" looks like the one. But need some inputs and help on this AVP. Or please correct me if I am wrong.

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