HOW TO CONFIGURE QoS MANAGEMENT BY PCRF ON GGSN

A case study involving Huawei UGW & NSN PCRF.

SOLUTION REQUIREMENT:

The requirement is to use QoS management by PCRF function for all subscribers of a specific APN. According to this requirement the PCRF must specify the Uplink/Downlink bitrate for subsribers by Gx interface and PCRF must change the bitrate at any time. After this is triggered,the UGW must use these bitrate values from PCRF and update PDP context to SGSN side (In turn SGSN must update RAB to RNC side). 

Threre is configuration on UGW:

CONFIGURE INTERWORKING PARAMETERS ((PCEF<>PCRF)):

1. Configure Gx intetrface (PCEF<>PCRF) (refer to product documentation for detailed explanation, depending on version of product you are working on):

-pcc-view

-pcrf sdp_pcrf_test host AAAA realm BBBB ip 10.2.X.X port 3870 vpn Gx-SDP

-gx-local-info group 1 instance 1 host YYYY realm ZZZZ product-name ugw9811

-pcrf-group sdp_group_test pcrf sdp_pcrf_test

-pcrf-group-binding pcrf-group sdp_group_test

DISABLE THE GLOBAL PCC SWITCH SO THAT WE DONT AFFECT ALL APN'S IN THE UGW:

2. Disable global PCC switch:

-pcc-view

-pcc-switch disable

ENABLE THE PCC-SWITCH ON THE DESIRED TEST APN, ENSURE TO BIND RELATED PCRF GROUP:

3. Enable PCC switch for necessary APN and bind PCRF-group from step 1 to this APN:

-apn testgx

-pcrf-group-binding pcrf-group sdp_group_test

-pcc-switch enable reporting-level-default rg metering-method-default volume

CREATE A FILTER/FILTER GROUP IN UGW TO HANDLE THE ANY TO ANY TRAFFIC FLOW:

4. Create filter (allow any to any), filter-group and bind the filter-group to a rule. No need to bind an action to this rule:

-service-view

-filter f_qos_test l34-protocol any

-filter-group fg_qos_test filter f_qos_test

-rule qos_test filter-group fg_qos_test

Note: The PCRF will return some static rule for subscribers and name of this rule must be configured in this step.

CONFIGURE A USER PROFILE AND USER PROFILE GROUP TO BE BOUND TO TEST APN:

5. Bind the rule to user profile and user-profile-group, and then bind it to APN:

-service-view

-user-profile up_qos_test

-rule-binding qos_test

-user-profile-group upg_qos_test

-user-profile-binding user-profile-group upg_qos_test user-profile up_qos_test

-apn testgx

-user-profile-group-binding upg_qos_test

UGW configuration is now completed. Now i need to give some insights related to the configuration in the PCRF.

For this test case you need guarantee that PCRF returns next mandatory AVPs in CCA-I message: charging-rule-install,charging-rule-name (as configured in step 4), bearer-id, qos-information (qci, max-req-bw-up, max-req-bw-down, gar-req-bw-up, gar-req-bw-down, bearer-id).

These AVPs are mandatory so that the UGW can effect QoS management.

Below, i present the signalling flow for QoS management by PCRF function and i will try to explain each message from 45 (Create PDP) to 52 (Update PDP Context Response):

As shown in Message Number 45, The Create PDP Context Request was sent with the normal MBR, This must be the HLR subscribed MBR configured under the APN the subscriber is using to access. i.e. 8Mbps (Uplink & Downlink)

As shown in Message Number 46,The GGSN sends CCR-I with the requested QoS from the Create PDP Message as shown below:

Next, In Message Number 47, the PCRF sends CCA-I to GGSN with Modified QoS as 128Kbps as shown below:

The GGSN then sends Create PDP Context response to SGSN with QoS information as Updated in CCA-I from PCRF as shown below:

Next the PCRF sends Re-Authorization-Request to the GGSN requesting QoS Modification to 64Kbps as shown below:

Note: The RAR message from PCRF may not include charging-rule-install AVP, only QoS-infromation is enough. For this requirement

The GGSN sends Re-Authorization-Response to the PCRF accepting the QoS Update from PCRF as shown below, we can see Diameter Result Code 2001, Meaning Success:

Next, we expect Update PDP Request from the GGSN towards the SGSN to Update the PDP Level QoS Information to that sent by the RAR message from PCRF, As we see below, Update PDP Request is sent with QoS information as MBR UL/DL = 64Kbps (Protocol between GGSN<>SGSN is GTP):

Finally, we expect Update PDP Response from SGSN towards GGSN to confirm that the QoS Information has been successfully updated into the SGSN as shown below, we see MBR UL/DL as 64Kbps:

NOTE:P.S. Qos management by PCRF Function must be supported by RNC as well.Usually we may need to enable "RAB modification" feature on the RNC,otherwise RNC will not update RAB and SGSN will reject PDP contect modification from GGSN.

Finally, Whenever you are testing any Feature in the Packet Core, It is important to go step by step as you do the analysis, Analyze traces using Wireshark, It saves time and helps in understanding the call Flows better and locating what the cause of failure is if it exists.

For now, it's a wrap, Until the Next Update, Stay Tuned!!

#PerfectionIsANorm