IP Flow Mobility and Seamless Offload(IFOM)

Unlike LIPA or SIPTO that are dependent on upstream network nodes to provide the optimization of routing different types of traffic, IFOM relies on the handset to achieve this functionality. It explicitly calls for the use of simultaneous connections to both macro network, e.g., LTE, UMTS and WiFi. Therefore, IFOM, unlike LIPA and SIPTO, is truly a release 10-onward only technology and it is not applicable for user terminals pre-Release 10. IFOM is being specified via 3GPP TS 23.261 [1]. Following diagram shows the interconnectivity model for IFOM capable UE.

IFOM uses an Internet Engineering Task Force (IETF) Request For Comments (RFC), Dual Stack Mobile IPv6 (DSMIPv6) (RFC-5555) [2].

Since IFOM is based on DSMIPv6, it is independent of the macro network flavor. It can be used for a green-field LTE deployment as well as a legacy GPRS packet core.

Earlier on we looked at the mobile network industry attempts of integration between packet core and WLAN networks. Common characteristic of those efforts was the limitation of the UE, its ability to use one radio interface at a time. Therefore, in earlier interworking scenarios UE was forced to use/select one radio network and make a selection to move to an alternative radio for all its traffic. Today many smartphones, data cards with connection managers already have this capability, i.e., when the UE detects the presence of an alternative access network such as a home WiFi AP, it terminates the radio bearers on the macro network and initiates a WiFi connection. Since WiFi access network and packet core integration is not commonly implemented, user typically loses her active data session and re-establishes another one.

Similarly access to some operator provided services may not be achieved over WiFi. Considering this limitation both iPhone IOS and Android enabled smartphones to have simultaneous radio access but limited this functionality to sending MMS over the macro network while being connected to WiFi only.

IFOM provides simultaneous attachment to two alternate access networks. This allows fine granularity of IP Flow mobility between access networks. Using IFOM, it will be possible to select particular flows per UE and bind them to one of two different tunnels between the UE and the DSMIPv6 Home Agent (HA) that can be implemented within a P-GW or GGSN. DSMIPv6 requires a dual-stack (IPv4 or IPv6) capable UE. It is independent of the access network that can be IPv4 or IPv6.

参考：3G and 4G wireless blog