Last few blogs I have argued the needs for augmenting LTE with WiFi. In parallel I was trying to catch up with the progress in 3GPP with respect to traffic offloading. They have three proposals on the table:
- Local IP Access (LIPA)
- Selected IP Traffic Offload (SIPTO)
- IP Flow Mobility (IFOM)
LIPA addresses the need for access to local devices (file/media servers, printers) at home or office via user devices that are typically connected to the macro network. It achieves the local traffic (break-out) connectivity with the help of a femtocell supersized to include P-GW or GGSN functionality. Following figure is from 3GPP TS 23.829.
SIPTO addresses the need to break out traffic closer to RAN but (above it). It solves congestion in operator’s packet core by placing Internet connectivity closer to RNC. This is already offered by many vendors today (including Juniper, Tellabs, Cisco). I am not convinced that it has significant value since the real congestion is in the radio, that is limited by Shannon’s law. Any current issues with core networks are temporary and will be resolved by reliance on Moore’s law. Following figure from 3GPP TS 23.829 would give an idea about what SIPTO is about.
IFOM is based upon the Dual Stack Mobile IPv6 (DSMIPv6). Furthermore it assumes user equipment can use two radios (WiFi and a macro network radio link) simultaneously. It is defined in 3GPP TS 23.261. It is what I would describe as an end-to-end solution. It is dependent on user equipment and Home Agent (HA) (typically co-located with P-GW or GGSN) intelligence. It has no bearing on radio access network. It can be equally applicable for Wimax, EV-DO, etc. Following figure is my simplification to describe it.
I believe IFOM has the highest chance of success even though the recent history of mobile IP based solutions is full of disappointments. Unfortunately mobile IP has never made into the mainstream consumer grade technology, and stayed limited to the enterprise domain. However, the last three years have significantly shifted the mobile communications industry especially with the arrival of iPhone (IOS) and Android as well as the amazing computational power in these devices. Both iPhone and Android already provide limited dual radio capability, e.g., ability to send MMS over GPRS/3G while being connected to WiFi for local access. What is missing is to enhance this capability with DSMIPv6, implement HA in the packet core and come up with smart algorithms for IP flow mobility based on quality, cost, network status, user preference, etc. DSMIPv6 solves other problems such as the introduction of IPv6 for LTE devices while WiFi radio access networks continue to stay as IPv4.
I have been looking at companies who are coming up with IPR in this field. One interesting company is SNR Labs (www.snrlabs.com) based in Plano, TX. They have been working on this since 2007 and they seem to be partnering with Intel for long time.
Considering 802.21 turned out to be somewhat a disappointment, one needs to be cautious with respect to the future of this field. Probably fate of 802.21 was too closely tied to future of Wimax.
IP flow mobility using mobile IP looks more promising compared to previous attempts using mobile IP, 802.21 or LIPA, SIPTO that are dependent on femtocells. As soon as IOS and Android support for DSMIPv6 becomes available, future of traffic offload will be settled.