1 | tunneling method – inter-tech. ho | august 2007 title: a tunneling method for inter-technology...

1 | Tunneling Method – Inter-tech. HO | August 2007

Title: A Tunneling Method for Inter-Technology Handoff Source:

Mike Dolan, Alcatel-Lucent, [email protected] Abstract: This contribution provides a discussion of a tunneling method for inter-technology handoff using a tunnel across the radio interface to the source RAN, and another tunnel between the source and target RANs.

Proposal: Review and approve as the architectural approach for inter-technology handoffs in 3GPP2.

3GPP2 A40-20070827-011

The contributors grant a free, irrevocable license to 3GPP2 and its Organizational Partners to incorporate text or other copyrightable material contained in the contribution and any modifications thereof in the creation of 3GPP2 publications; to copyright and sell in Organizational Partner's name any Organizational Partner's standards publication even though it may include all or portions of this contribution; and at the Organizational Partner's sole discretion to permit others to reproduce in whole or in part such contribution or the resulting Organizational Partner's standards publication. The contributors are also willing to grant licenses under such contributor copyrights to third parties on reasonable, non-discriminatory terms and conditions for purpose of practicing an Organizational Partner’s standard which incorporates this contribution.

This document has been prepared by the contributors to assist the development of specifications by 3GPP2. It is proposed to the Committee as a basis for discussion and is not to be construed as a binding proposal on the contributors. The contributors specifically reserves the right to amend or modify the material contained herein and to any intellectual property of the contributors other than provided in the copyright statement above.

mailto:[email protected]


Problem StatementSeamless handovers between different access technologies must be

possible.Seamless handovers must be supported when there are two radios and

when there is only a single radio.Each access technology must be able to evolve without impacting the

ability to perform seamless handover with other access technologies.A mechanism must be available for the RAN of one access technology to

communicate with the RAN of a different access technology. As we have found in the HRPD-1x handoff over A21, the ability of two RANs to exchange not only HO signaling, but also status information and radio parameters is a significant means of managing and optimizing inter-RAN handoffs.

Network control of handoffs is a major requirement for many operators.The source RAN and target RAN must both be involved in the control of

the handoff; the source RAN to command that it take place and to manage the handoff, the target RAN to establish resources.


Tunneling protocol across the radio interface

A tunneling protocol across the radio interface will allow the mobile and the currently accessed RAN to transfer messages/data for a different access network in a way that uses the awareness of the handoff preparation and execution to facilitate handoff success. For example, a mobile can transfer signaling for a RAN of type B via a RAN of type A.

Mobile

RAN1 Type=A RAN2 Type=B

An additional tunnel between the two RANs allows the relaying of signaling to/from the target RAN, along with exchange of status, parameters, and other information between the two RANs. This is the function performed by A21 for HRPD to 1xRTT handoffs.


Requirements of Mobile to RAN tunneling.

The mobile must be able to ask for the existence of RANs of other types, and their identities.

The mobile must be able to ask for the control information for another RAN type than the one it is currently using. (If this is not stored in the currently serving RAN, then an inter-RAN tunneling (inter-RaT) message will exist to ask the other RAN for that information.)

The mobile must be able to send signaling/data to a second RAN type using a mechanism over the current air interface. The message sent by the mobile provides the identity of the RAN to which the signaling/data is addressed. If only one target RAN is made available to the mobile by the serving RAN, the identity of the target RAN may be unnecessary.


Inter-RAN Tunneling (Inter-RaT)

Mobile


Source=Mob1Dest=RAN2

RAN2 Signaling

Source=Mob1Dest=RAN2

RAN2 Signaling

Proxy=RAN1


Inter-RAN Communication


Source=RAN2Type=Sys Info

RAN2 System

Information

Dest=RAN1


Possible Messages for Mobile to RAN tunneling

Mobile to RAN: Available RANs Request (requests a list of available RANs with a

RAN-ID and a RAN-Type for each) Control Info Request [RAN-ID] (requests a set of control information

for the indicated RAN in the format used by that RAN type) Send to RAN Request [RAN-ID, Mobile-ID, Seq-No, signaling/data]

(used to send signaling/data to a different RAN, returns an Ack/Nack)

Send to Mobile Ack [Ack/Nack, Seq-No] (used to Ack/Nack signaling/data sent from a different RAN to the mobile via the serving RAN)


Possible Messages for RAN to Mobile tunneling

RAN to Mobile: Available RANs Response (provides a list of available RANs with a

RAN-ID and a RAN-Type for each) Control Info Response [RAN-ID, Control Info] (provides a set of

control information for the RAN indicated in the format used by that RAN type)

Send to Mobile Request [RAN-ID, Mobile-ID, Seq-No, signaling/data] (used to send signaling/data received from a different RAN to the mobile, returns an Ack/Nack)

Send to RAN Ack [Ack/Nack, Seq-No] (used to Ack/Nack signaling/data sent from the mobile to a different RAN via the serving RAN)


Possible Messages for RAN to RAN tunneling – 1 of 2 RAN to RAN:

Control Info Request (requests a set of control information for the receiving RAN in the format used by that RAN type)

Control Info Response [RAN-ID, RAN-Type, RAN-Info] (provides a set of control information for the sending RAN in the format used by that RAN type, can be sent autonomously)

Send to Mobile Request [Mobile-ID, Seq-No, signaling/data] (used to send signaling/data to the mobile via a different RAN, returns an Ack/Nack)

Send to Mobile Response [Mobile-ID, SeqNo, Ack/Nack] (used to Ack/Nack a Send to Mobile Request message)

Send to RAN Request [Mobile-ID, Seq-No, signaling/data] (used to forward signaling/data to the targeted RAN from a mobile, returns an Ack/Nack)

Send to RAN Response [Mobile-ID, SeqNo, Ack/Nack] (used to Ack/Nack a Send to RAN Request message)


Possible Messages for RAN to RAN tunneling – 2 of 2 RAN to RAN:

IP Packet Forward [Mobile-ID, IP Packet, Seq-No] (forwards an IP packet from the source RAN to the target RAN for transmission to the mobile)

IP Packet Forward Ack [Mobile-ID, Seq-No] (acknowledges an IP packet that was forwarded to the target RAN)


Issues and Possible Solutions

Issue: How is the signaling carried across the tunnel specified? Possible Solution: Each air interface standard will need to decide the level

of PDU that will be tunneled across another air interface. That is, if RAN1 is forwarding signaling from the mobile to RAN2, then the signaling for RAN2 must specify the exact contents of the signaling/data that will be sent inter-RAN using tunneling.

Issue: Each technology cannot be expected to know how to provide power or other measurements for other technologies.

Possible Solution: The assumption is the serving RAN will make it possible for the mobile to tune some/all of its resources to the target technology to generate such measurements. Power measurements for the target technology are then included in the tunneled signaling, with the expectation being that the signaling message(s) for that technology that normally carry power measurements will be used and tunneled.


Issues and Possible Solutions (Cont.)

Issue: How can network control be exercised for handoffs? Possible Solution: The serving air interface will define signaling that

will command the mobile to prepare for and then execute the handoff.

Issue: What can be done to allow stranded packets on the source RAN to be forwarded to the target RAN for delivery to the mobile?

Possible Solution: Stranded packets can be sent back to gateways that can relay them to the target RAN. Any processing of those stranded packets must be reversed, so that plain IP packets are forwarded to the target gateway. E.g., Van Jacobson compression may need to be reversed before forwarding.

1 | tunneling method – inter-tech. ho | august 2007 title: a tunneling method for inter-technology...

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