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SOURCE: Alcatel-Lucent
CONTACT: Nancy Lee nylee@alcatel-lucent.comMudit Goel muditg@alcatel-lucent.com Satish K. satishk@alcatel-lucent.com
ABSTRACT: This contribution provides a discussion of the various considerations for Layer 2 and Layer 3 tunneling for Inter-Technology Handoff.
TITLE: Discussion of Layer 2 and Layer 3 Tunneling for Inter-Technology Handoff
3GPP2 TSG-A.4
RECOMMENDATION: For Discussion
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.
A40-20071105-xxx
2 | L2 and L3 Inter-Tech Handoff | November 2007 All Rights Reserved © Alcatel-Lucent 2007
Areas for Comparison of Layer 2 and Layer 3 Tunneling
• Security
• Source System Awareness
• Ability to Forward Stranded Data for Seamless/Lossless Handoff
• Resource Utilization
• Changes in UMB system for UMB to HRPD HO
• Changes in HRPD system for UMB to HRPD HO
• Changes in UMB system for HRPD to UMB HO
• Changes in HRPD system for HRPD to UMB HO
• Tunnel Anchoring in the UMB System During Mobility Events
3 | L2 and L3 Inter-Tech Handoff | November 2007 All Rights Reserved © Alcatel-Lucent 2007
Security
SourceRAN
SourceGateway
TargetRAN
AT
OperatorControlledIP Network Connecting
RAN Elements
UntrustedIP Network
L2 Tunneling is shown as the blue line. The communications between the source and target RAN remain under operator control.
L3 Tunneling is shown as the red line. The communications arrive at the target RAN from an untrusted network.
4 | L2 and L3 Inter-Tech Handoff | November 2007 All Rights Reserved © Alcatel-Lucent 2007
Security - Continued
In the Layer 2 Tunneling case, there is an assurance at the target RAN that the IP packets being forwarded are from the source RAN. A security association exists between the source and target RANs.
In the Layer 3 Tunneling case, the packets from the AT exit the top of the source sytem gateway (e.g., PDSN, AGW) into an untrusted network. The target RAN thus sees packets arriving from an unknown source. There is no guarantee that the packets are even from an AT attempting to handoff into the target RAN.
To solve the Layer 3 Tunneling case, additional firewall functions must be placed in the operator’s network to ensure that all packets arriving through this mechanism at the target RAN are truly from ATs on a source system.
5 | L2 and L3 Inter-Tech Handoff | November 2007 All Rights Reserved © Alcatel-Lucent 2007
Source System Awareness
Source system awareness means that the source system is aware of the fact that a handoff from itself to the target system is happening.
The source system can order the AT to initiate handoff earlier than the AT might decide on its own. This can make a large difference in handoff success rates when radio conditions deteriorate rapidly and unexpectedly in a given cell.
The source system can assist the AT both while idle and active by providing information on nearby cells of the target technology.
L2 tunneling includes source system awareness. This uses modifications to signaling on the source air interface.
L3 tunneling will require that the AT and source system signaling modifications on the source air interface as well to accomplish source system awareness. If source air interface modifications are made for L3, they might as well include the encapsulation needed for L2 tunneling.
6 | L2 and L3 Inter-Tech Handoff | November 2007 All Rights Reserved © Alcatel-Lucent 2007
Ability to Forward Stranded Data for Seamless/Lossless Handoff
When a mobile moves from one technology to another in a packet environment, it becomes very difficult to guarantee that all packets for the mobile are delivered. Packets can be delivered to the source RAN after the mobile has already departed for the target RAN. These are “stranded packets.”
To avoid loss of these packets, and the corresponding impact to the applications running on the mobile, a means for forwarding stranded data packets is needed.
A Layer 3 approach does not provide the opportunity to forward stranded packets, since the source system is unaware of the handoff activity. If the source system is made aware, the previous point applies that signaling encapsulation should then also be added to the air interface and L2 tunneling used.
Layer 2 tunneling involves the knowledge and cooperation of the source and target RAN elements. Data forwarding mechanisms have already been defined for this situation.
7 | L2 and L3 Inter-Tech Handoff | November 2007 All Rights Reserved © Alcatel-Lucent 2007
Resource Utilization
If an AT leaves a source system, and the source system cannot be notified of its successful arrival at the target system, the source system must keep its resources for that AT allocated for some additional period of time.
Layer 3 tunneling does not involve communication between the source and target RANs. Consequently, source system resources must be kept tied up longer than would be the case if the target RAN could notify the source RAN of the arrival of the AT on the target system (such as is done for A21).
Layer 2 tunneling includes the ability to communicate between source and target RANs, and consequently provides the capability for the target RAN to notify the source RAN of the presence of the AT on the target system. This allows the source RAN to recover its resources sooner.
8 | L2 and L3 Inter-Tech Handoff | November 2007 All Rights Reserved © Alcatel-Lucent 2007
Changes in UMB system for UMB to HRPD HO
Layer 2 Approach impacts
The UMB air interface must be able to tunnel HRPD signaling messages to the UMB RAN.
The UMB RAN must be able to tunnel HRPD signaling messages to the HRPD RAN.
The UMB RAN must make HRPD parameters available on the UMB air interface, including HRPD pilots and access parameters.
The UMB air interface must include extra messaging if the UMB system is to be aware of the handoff, and support the AT.
9 | L2 and L3 Inter-Tech Handoff | November 2007 All Rights Reserved © Alcatel-Lucent 2007
Changes in UMB system for UMB to HRPD HO - continued
Layer 3 Approach impacts
The UMB RAN must make HRPD parameters available on the UMB air interface, including HRPD pilots and access parameters.
The UMB air interface must include extra messaging if the UMB system is to be aware of the handoff, and support the AT.
The IP address of the correct HRPD RAN element must be provided to the AT.
If the AT is roaming and only supports 1 IP address, the IP packets containing signaling will be routed to the HA, which may be significantly distant. This adds latency to the AT-to-HRPD signaling path, and may cause timeouts.
10 | L2 and L3 Inter-Tech Handoff | November 2007 All Rights Reserved © Alcatel-Lucent 2007
Changes in HRPD system for UMB to HRPD HO
Both L2 and L3 approaches will require that an HRPD RAN entity receive and send the tunneled signaling. No difference for either approach.
11 | L2 and L3 Inter-Tech Handoff | November 2007 All Rights Reserved © Alcatel-Lucent 2007
Changes in UMB system for HRPD to UMB HO
Layer 2 Approach impacts
The HRPD air interface must be able to tunnel UMB signaling messages to the HRPD RAN.
The HRPD RAN must be able to tunnel UMB signaling messages to the UMB RAN.
The HRPD RAN must make UMB parameters available on the HRPD air interface, including UMB pilots and access parameters.
The HRPD air interface must include extra messaging if the HRPD system is to be aware of the handoff, and support the AT.
12 | L2 and L3 Inter-Tech Handoff | November 2007 All Rights Reserved © Alcatel-Lucent 2007
Changes in UMB system for HRPD to UMB HO - continued
Layer 3 Approach impacts
The HRPD RAN must make UMB parameters available on the HRPD air interface, including UMB pilots and access parameters.
The HRPD air interface must include extra messaging if the HRPD system is to be aware of the handoff, and support the AT.
The IP address of the correct UMB RAN element must be provided to the AT.
If the AT is roaming and only supports 1 IP address, the IP packets containing signaling will be routed to the HA, which may be significantly distant. This adds latency to the AT-to-UMB signaling path, and may cause timeouts.
13 | L2 and L3 Inter-Tech Handoff | November 2007 All Rights Reserved © Alcatel-Lucent 2007
Changes in UMB system for HRPD to UMB HO
Both L2 and L3 approaches will require that an UMB RAN entity receive and send the tunneled signaling. No difference for either approach.
14 | L2 and L3 Inter-Tech Handoff | November 2007 All Rights Reserved © Alcatel-Lucent 2007
Tunnel Anchoring in the UMB System During Mobility Events
The UMB RAN uses a distributed control approach. The various components, SRNC and eBS, can change and move very dynamically. The challenge becomes maintaining a tunneling connection to an endpoint in the UMB RAN.
If the handoff is to UMB, both L2 and L3 will terminate their tunnel at some UMB RAN element. If that element is allowed to move, the other end point will have difficulty in communicating.
If L2 tunneling is used, the communication is directly to the HRPD RAN, and notification is simpler.
If L3 tunneling is used, the communication is to the AT, and can be problematic when considering latency and creation of secure communications (e.g., IPSec).
If the handoff is from UMB, the L2 approach will need to handle this issue.
The common solution for both L2 and L3 is to lock the UMB RAN element during the pre-registration.
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