Giving a Little Life To LIPA- Data Offload in the Home and Office


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Giving a Little Life To LIPA- Data Offload in the Home and Office

  1. 1. Giving a Little Life to LIPA - Data Offload in the Home and OfficePosted by kitkilgour on Apr 6, 2012 6:11:06 AMIn my last couple of posts, I looked at the different dimensions of ‘offload’, with possibilities of makingbest use of radio spectrum, either by using small cells or combining with WiFi. In this post I’ll look atgetting new services from cellular and offloading data from an operator’s core network as well.From a Service Provider’s perspective there is a desire to be able to offer comparable local services inthe home and the enterprise to those that a nomadic WiFi user with additional software can achieve inthe same place, but with the added advantage of doing it from a cellular handset and the ability to keepa connection whilst roaming. This means that services in the home, such as uploading photos from yourphone to your PC or media server, streaming music or movies from a home media system or printing outdocuments and pictures should be available (some early demonstrations of femtocell connected homeconcepts that we put together at ip.access can be seen here) In a business premises, access thecorporate intranet, printing, and short-code dialling the extension of a colleague are also handy. Someof the business services are already available from operators as a value added service, but at some costand complexity, as Figure 1 below helps show. It shows the traditional core network layout for a 3Gsystem that I have used earlier but with a home or enterprise network added near the local broadbandmodem. The traditional route for the data is shown with a thin red line, and the ideal Direct Route fromthe Broadband Modem to an enterprise or home router is a thicker line. The key point to note is thatdata has to traverse the operator’s network to the anchoring routers (GGSN) before it can be sent to anexternal network such as the home or an enterprise. If you are already attached to a cell in the home orenterprise where you want to access data or make a call, this is clearly highly inefficient. For servinglarge businesses, the price premium an operator can charge may justify this inefficiency and thebusiness service may be provided by a particular GGSN router which then securely tunnels the data backinto the enterprise, but the economics as they stand may not make sense for the normal home user orsmall business. Figure 1: Traditional tunnelled access to business premises, and optmized offload routeTo achieve this simplification, what we have done in 3GPP is to specify a new user service known as LIPA(Local IP Access). Normally, what happens when a mobile requests a data service is that the SGSN that
  2. 2. handles all the control decisions (shown towards the right of the figure) is asked to arrange for a router(GGSN) to provide the requested service and once the details are confirmed and addresses of the smallcell and GGSN exchanged as endpoints, user data can flow to and from external networks. So far whathas been specified is that a cut-down GGSN, called a Local Gateway, can be co-located with thefemtocell and when a mobile device asks for a connected service, the femtocell offers the SGSN theaddress of the Local Gateway to act as the GGSN. Depending on permissions and the nature of therequested service, the SGSN may accept and then allocate the Local Gateway for the service. The radiobearers that support the service are indicated to the femtocell so that it can directly send the user datato the Local Gateway without sending to the Core Network at all. We arrive at the diagram in Figure 2below, with the local user data taking the direct route and not going near the core network. Figure 2: Femtocell enhanced with Local Gateway to provide local offloadThis is clearly a benefit for both service provider and user as long as the user experience matches up tothe alternatives. In fact, to enable users to get the full connected home experience, the Local Gateway isboosted to make sure that it forwards all the necessary broadcast messages from the local network thatenable seamless service discovery of printers and other UPnP devices.What next in this area? There are still refinements being worked on, such as having the Local Gatewayseparate from the femtocell; this will give more flexibility and also enable continued service betweenmore than one femtocell as the user walks around the office or a large home. In a slightly differentdirection, there is the natural question that if a home or enterprise network also has external internetaccess, once youve got a Local Gateway can it be used to route all the internet traffic from the mobilerather than just local traffic? in 3GPP terms, this is known as SIPTO (Selective IP Traffic Offload) and isbeing discussed at the moment. Its feasible but needs a bit more work to handle making the choicesbetween when a core network GGSN is needed to provide or monitor the service, and when LocalGateway is possible. Perhaps more another time. For more discussion on Mobility, visit our Service Provider Mobility Community: