SIPTO (Selected IP Traffic Offload) Function

Before we jump in to SIPTO it would be suggested that you visit Traffic Break-Out in LTE for better understanding of concept, let see how service (i.e. Internet) is given in LTE. After subscriber authorization and authentication S-GW and P-GW (SE-GW) are used to provide service to subscriber. Now it is just common sense that it would be better for service, for resource (RAN) management point of view and less in cost as well if service is given by SE-GW that is nearest (Geo-graphically) to UE (subscriber). Now SIPTO is a way to route traffic from closest point to UE. Only specific traffic is routed/served from closest point that is why it called as SELECT IP Traffic Offload (SIPTO).

General architecture of SIPTO

  
Let’s take an example, there is a subscriber of an operator in India uses video.internet.com APN to view videos by using SE-GW of India, now this operator has roaming agreement with various countries. Subscriber travelled to Japan then to get internet access it should use SE-GW of Japan rather than India if it is allowed for SIPTO. In Lay man term, an e-node B (Tower) in Japan should access Service Providing Nodes in Japan once authentication and authorization is done otherwise it shall automatically increase round trip time if it uses Indian Serving nodes.  More Simpler it would be better to get electricity from nearest Poll or getting water from nearest water tank rather than own state poll or tank while you are on travel.

Formally, SIPTO function enable an operator to offload certain type of traffic to Service providing node that is closed to UE in ACCESS network.  In LTE, SIPTO over RAN is possible be selecting S-GW and P-GW that is geographically closest to UE.

Complete offload is generally done with the help of LIPA that we shall discuss later.

Permissions for SIPTO to an APN are stored in HSS. SIPTO can be applied in both Roaming and non-Roaming cases. If HSS indicates that VPLMN address allocation is not allowed then SIPTO is not provided.

As LTE  and technology is growing there for various concept are invented such as H-Enode B and L-GW that can be used for SIPTO.  As we Know there are two major entities in SIPTO (1) Gateways (2) E-NodeB, thus optimization can be done at two places either Gateways or E-NodeB so concept of L-GW comes because of optimization/Enhancements at Gateways and H-Enode B comes because of optimization/Enhancements at E-NodeB. 


SIPTO at the Local Network with L-GW function,Here traffic is offloaded with architecture-2  that is self explanatory from below Image. 

 

Your Comments /Suggestions and Questions are always welcome,  shall clarify with best of knowledge. So feel free to put Questions.