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What is the use of Sy interface?

+5 votes

Can someone provide me some high level detail and good pointer :)

posted Nov 6, 2014 by Harshita Dhaliwal

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2 Answers

0 votes

Sy Interface exist between PCEF and OCS whichenables transfer of information relating to subscriber spending from OCS to PCRF and supports the following functions:

  1. Request of policy counter status reporting from PCRF to OCS.
  2. Notification of policy counter status change from OCS to PCRF.
  3. Cancellation of policy counter status reporting from PCRF to OCS.

Sy Interface Overview


answer Nov 6, 2014 by Salil Agrawal
0 votes

For the prepaid subscriber,charging will be taken care by OCS.Sy maintains Policy counter identifier and its status.

At the time of initial attach,PCEF sends CCR-I to PCRF for default policy of subscriber. PCRF makes LDAP query to SPR and gets default policy identifier(Lets say D which means apn-ambr(UL/DL)=256 Kbs.At the same time PCRF will ask OCS on Sy interface about the status of the policy counter identifier D in SLR-initial. OCS sends the status of this Policy Identifier D(apn-ambr(UL/DL)=256 Kbs) in SLA-Initial.After this PCRF seds CCA-I to PCEF having apn-ambr(UL/DL)=256 Kbs.If suppose in the mid session the status of the policy counter identifier changes to B(apn-ambr(UL/DL)=128 Kbs),Then OCS will notify this in SNR to PCRF and PCRF convey the same information to PCEF through RAR and PGW will in turn update the bearer Qos.

Messages exchanges between PCRF and OCS on Sy interface are as:

OCS------- SLA-----------PCRF



Hope it will provide the basics info of Sy interface.

For more details see ETSI TS 129 219 V11.2.0 (2012-10

answer Oct 19, 2016 by Sanjeet Singh
Similar Questions
+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
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 !!!

+1 vote

Am trying to integrate between PCRF & OCS of different Vendors using an Sy interface. Policy configuration and integration is fine but for some of the cases am getting a 4001 (Diameter_Authetication_Rejected) in SLA.

As I understand, Authentication is not part of Sy interface. Can anyone let me know the possible scenarios where the 4001 RC can occur on an Sy interface.

+4 votes

For one subscriber with MSISDN 1234567:

Provisioning in PCRF SPR: Policy_A, Policy_B, Policy_C
OCS active Services: Service_A, Service_B, Service_C

Each PCRF Policy corresponds to OCS Service respectively.

When PCRF requests counters status from OCS in SLR(initial), it does not explicitly specify which counters it needs. PCRF sends MSISDN in [ Subscription-Id ] AVP in SLR(initial). OCS sends all available counters in SLA.

How PCRF will identify which counter(s) is for which policy? How this mapping will be done ?

+4 votes

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).

+1 vote

Is it possible to use Credit-Control-Failure-Handling AVP in Gx interface. If so, how?

My query is when PCEF sends a CCRequest to PCRF and PCRF does not reply anything, so in that case will that be possible to use Credit-Control-Failure-Handling(CCFH) avp.

Does this behavior allowed as per 3GPP Standards or its upto the customization of the product. Any reference are highly appreciable.

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