Friday, July 27, 2012

Few thoughts on Policy!

I have received many emails regarding dedicated bearers and mobile networks policy interface in past few months. This directly shows there is good amount of work being put in to make Gx interface work by both operators and telecom vendors. While Gx interface has been sitting for a while in UMTS networks, it dint have any interaction with mobile devices. What I mean is Gx was mainly used to enable statically configured rules, mainly DPI rules, on GGSN and was invisible to UE, except that operators had opportunity to do all sorts of weird stuff using user’s data.  Drop, police, charge differently.. Net Neutrality?
However with LTE, Gx seems to be playing significant role by establishing dedicated bearers. Policy Charging and Rule function is responsible for activating rules that lead to dedicated bearer creation, send rating group information that is used for charging, control qos etc.
Gy is cousin brother of Gx. Gy is charging interface towards OCS that is mainly (not necessarily) used for prepaid subscribers. Both Gx and Gy are Diameter based interfaces that run over TCP or SCTP. With 3GPP Release 8+ Gx was also given function of Gy, by enabling Usage Monitoring. This solution is already present in most pre release 8 gateways as proprietary solutions. So nice of 3GPP for making it a standard!
When subscriber attaches to a mobile network, GGSN sends a message (Diameter credit control request) to PCRF. This message carries quite a bit of information about UE. See 3GPP TS 29.212 for more details. Once this message is received, based on the subscription, PCRF may return new Qos, charging rules etc. Based on information, received from PCRF, PGW/GGSN may create a new dedicated bearer or modify qos etc.   Typically in UMTS networks, PCRF sends Bearer Identifies in charging rules, which tell GGSN to which bearer these rules should be applied.  In EPS PCRF just sends the rules and PGW decides to which bearer these rules need to be applied to. This means in UMTS PCRF was doing bearer binding and in LTE PGW is doing bearer binding.
We all have heard of Data plans where operators throttle user data after a certain limit. This can be nicely achieved by using the usage monitoring functionality over Gx. When a subscriber is created PCRF allocates some data volume with some qos. After that volume is reached PCRF may send new volume with downgraded qos.  This is very hard to achieve, not impossible though, using Gx and Gy interfaces as Gy doesn’t have any insight of user qos.
There are several advantages of Gx interface but that comes with additional TCP processing on the Gateways and additional cost for PCRF deployment.  Will post more!
Just when I was going to post this, I noticed an interested presentation in 3G4G blog by Zahid regarding PCC! Head on
PS - I am terribly busy with work. Couldn’t post anything for some time!  I also ignored few comments/emails. Apologies :-)

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