The Selective IP Traffic Offload (SIPTO) feature defined in 3GPP Release10 specifications allows the operator to
streamline an established PDN connection by re-assigning a new PGW that is geographically closer to the current UE
location. However, as noted in TS 23.401, PGW relocation implies a change in IP address, which means that
performing SIPTO may disrupt any ongoing services.
With the introduction of SIPTO at the Local Network (SIPTO@LN) feature, the PGW (alias Local Gateway) is moved
even further towards the network edge and service disruptions due to SIPTO is likely to increase because of the much
smaller "coverage" of the Local Gateway.
One way to mitigate the effects of relocating the PGW is to prohibit SIPTO operation for UEs in Connected mode,
reference TS 23.401. While this is an improvement compared to blindly performed SIPTO, it still does not address
the issue of smooth PGW relocation for UEs with long-lived and real-time IP flows (e.g. long conference / video call,
large file transfers, etc.).
Service disruption due to IP address change does not have the same effect on short-lived and long-lived/real-time flows:
for short-lived flows (e.g. web browsing) the user may not notice anything, or in the worst-case may have to
briefly interact with the user interface (e.g. by clicking again on the web page link following a network
connection lost" error);
for long-lived and real time flows, the effect can be detrimental (e.g. the user would be disconnected from the
conference, and has to re-dial the bridge number, enter password, etc.; similar effect applies to VPN traffic).
The UE is in the best position to identify the presence of any long-lived and real-time flows and is therefore in the best
position to advise the network whether SIPTO can be performed without much disruption or any disruption at all.
Moreover, for supporting applications the UE may also be able to pro-actively move the long-lived and real-time flows
on a new IP address (i.e. on a new PDN connection) before the previous IP address (i.e. old PDN connection) is
removed. The MMTel set of applications shall be studied in this regard as well as the possibilities for other types of
applications. An example of such application is the IMS that allows the change of media transport addresses for an
ongoing session using the IMS Service Continuity mechanisms defined in TS 23.237.
The present document studies methods and procedures that could be used, based on end-user preferences and with
benefit from the UE's knowledge of established IP flow type, to provide information to the network so that it can
consider the end-user expectation regarding local PGW change in case of SIPTO use.
This TR considers use cases and identifies potential requirements for network consideration of the
following items regarding the change of local PGW in use for SIPTO:
end-user experience and preferences; and
UE's knowledge of ongoing IP flow types.