What is the use of Sy interface?

Question

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

Answer 1

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.

Source: www.lteandbeyond.com/2012/10/the-sy-interface-between-pcrf-and-ocs.html

Answer 2

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:

PCRF------SLR------>OCS
OCS------- SLA-----------PCRF

OCS---------SNR------------->PCRF
PCRF--------SNA-------------------OCS

PCRF----------STR--------------------OCS
OCS-------------STA--------------------PCRF

Hope it will provide the basics info of Sy interface.

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