LIPA and SIPTO

I guess LIPA and SIPTO are hot topics nowadays. But what exactly are they referring to? How do these solutions provide value to customer/mobile operator?

LIPA is the abbrievation of "LOCAL IP ACCESS"

SIPTO is the abbrievation of "Selected IP Traffic Offload"

Both LIPA and SIPTO divert certain IP traffic (local residential/enterprise access for LIPA, some selected IP traffic for SIPTO) from operator's EPC P-GW. Control plane is not affected, MM, SM messages still terminates at EPC.

Solution 1)

To support LIPA/SIPTO, below network elements changes are required:

A new element called "Local PDN Gateway", i.e. L-GW is introduced. The L-GW is part of the access network, and it is responsible for:

- Filtering packets based on predefined policy

- UE IP address assignment;

- Direct tunnelling between L-GW and RAN in connected mode;

When a UE is camped on a cell, it can be signalled by NAS signalling or by AS SIBs that LIPA/SIPTO can be supported, or the UE could detect the cell belongs to a pre-defined list of cells. if LIPA/SIPTO is supported, the UE could potentially initiate another LIPA/SIPTO PDN connection.

The LIPA connection establishment is no much different with traditional connection establishment, apart from that a pre-defined APN is used (or received from NAS signalling), then at the PDP activation, S-GW will establish a tunnel with L-GW instead of P-GW.

Solution 2)

A OPM (Offload Processing Module) is collocated with eNB, which has NAT and routing functions. The UE establishes a LIPA enabled connection by using standard signalling procedures. The same PDN connection is used for both traffic to public network and traffic to local home/enterprise network. The OPM decides if an uplink traffic should be routed to S-GW or to the collcated NAT function. This is transparent to UE.

Because downlink packet is now addressing to OPM rather than directly addressing to UE. when the OPM (eNB) receives downlink packet, it needs to send MME a paging indication if the UE is in idle model, then the UE can be paged and downlink packet can be transferred after UE has established connection with network.

Solution 3)

There are many other candidate solutions, for details please refer to 3GPP TR 23.829.