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Considerations regarding L2&L3 Schemes in 802.3/802.11 Handover

Considerations regarding L2&L3 Schemes in 802.3/802.11 Handover. Xiaoyu Liu xiaoyu.liu@samsung.com Youn-Hee Han yh21.han@samsung.com 2004-05-06. Contents. Background and Concepts 802.3/802.11 Vertical H/O Analysis Proposed Procedures Initialization Handover from 802.3 to 802.11

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Considerations regarding L2&L3 Schemes in 802.3/802.11 Handover

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  1. Considerations regarding L2&L3 Schemes in 802.3/802.11 Handover Xiaoyu Liu xiaoyu.liu@samsung.com Youn-Hee Han yh21.han@samsung.com 2004-05-06

  2. Contents • Background and Concepts • 802.3/802.11 Vertical H/O Analysis • Proposed Procedures • Initialization • Handover from 802.3 to 802.11 • Handover from 802.11 to 802.3 • Impacts on Standard and Proposal • Other issues for discussion

  3. Background & Concepts (1) Source: A. Alimian and B. Aboba, Doc.: IEEE 802.11-04/0377r1, slide 5

  4. Background & Concepts (2) • Hard Handoff (Break-before-Make) • The Mobile Node (MN) maintains only one link to the network attachment; Removing the old link before establishing a new one. • Soft Handoff (Make-before-Break) • The MN maintains simultaneously at least two links to the network attachment • “Semi-Soft” Handoff • The Mobile Node (MN) maintains the current link to the network attachment while performs part of the procedures to set up a new link.

  5. Handoff Scenario Analysis (1) • 802.3 -> 802.11 Example Use Case • Both wired and wireless LAN interface are available. A costumer is watching a movie using the wired LAN interface (default setting). He wants to move to another room and plugs out the Ethernet connector. The system automatically switches the session to the wireless LAN interface, without any perceptible service interruption. • Key Points in the Handoff • Wireline-to-Wireless Switch • Interruption/link switch time is unpredictable for the system (user behavior) • Mobile Node does not move before the current session is interrupted. • Implications • Current communication broken abruptly • No coverage overlapping area typically in wireless systems • No transition time like wireless-to-wireless switch • The position of neighbor wireless APs are unlikely to change • Costumer should get certain indication whether or not the plug-out will interrupt the current session.

  6. Handoff Scenario Analysis (2) • 802.11 -> 802.3 Example use Case • A costumer is using wireless LAN interface to watch a movie, he plugs in the Ethernet connector. If the system successfully establishes a new session (two simultaneous data flows during this transition time), it switch the session from wireless LAN interface to wired LAN interface (only one data flow left). • Key Points in the Handoff • Wireless-to-Wireline Switch • Link switch is based on the user preference (wired LAN is cheaper and of higher quality) • Interruption time is predictable (controlled by system) • Implications • Current communication broken gradually • Redundant connection is possible • Transition time before the new link is setup

  7. Handoff Strategies Analysis (1) • 802.3 –> 802.11 • Hard Handoff • Long latency due to the slow start-up of wireless interface (refer to the typical latency in slide 3) • Soft Handoff • Have to maintain two active sessions permanently because the interruption time is unpredictable • Complexity and power consumption • “Semi-Soft” Handoff • Only part of the L2&L3 procedures to set up a new connection is executed (Scan/Authentication/Association/L3 Address Configuration) • Should meet the performance requirements • Best choice for wireline-to-wireless handoff

  8. Handoff Strategies Analysis (2) • 802.11 –> 802.3 • Hard Handoff • Latency (not necessary) • Soft Handoff • Seamless handoff • Maintain two active connections only during the transition time before the new connection is setup • Best choice for wireless-to-wireline handoff • “Semi-Soft” Handoff • -

  9. Handoff Decision • 802.3 -> 802.11 • Plug-out Ethernet connector • 802.11 -> 802.3 • When both 802.11 and 802.3 interfaces are connected (Ethernet connector plugged in), user preference can dictate which one is preferred • It is reasonable that the default preference should be set to wired LAN interface

  10. Proposed L2&L3 Procedures Summary (1) • L2 & L3 Initialization (Performed only once) • Wireless LAN interface • Scans and selects best AP (set as Active AP) • L2 link set up (association/authentication) • L3 IP address configuration (router discovery, DAD) • Wired LAN interface • L2 initialization • L3 configuration • Maintenance of Association in WLAN interface • Receives beacon from the Active AP periodically to keep the association • Note: Because the mobile node does not move when the costumer uses the Ethernet, the neighboring APs are unlikely to change. Thus, the STA just needs to keep its association with the Active AP. The full scanning is not necessary.

  11. Proposed L2&L3 Procedures Summary (2) • Procedures in 802.3 -> 802.11 handoff • L3: Binding Update (low latency) • L4: TCP adjustment (if required) • Procedures in 802.11 -> 802.3 handoff • There is a transition time after the user plugs in Ethernet connector and before the system drops 802.11 connection. So two connections can be maintained during this interval, i.e. "Soft-Handoff".

  12. Start IP Address Configuration for Wireless LAN Interface IP Address Configuration for Wired LAN Interface Target AP? Full Scan in Wireless LAN Interface Authentication Indication to Upper Layers Detailed Procedures (1) • Interface Initialization • L2 & L3 Address Configuration • Target AP is the best qualified AP which can be used as the network attachment at any time. • Target AP info is stored in MN and updated periodically to maintain its validity. • Wired LAN link is selected with higher priority than Wireless LAN link when both are available. NO YES Association(Target AP->Active AP) Wired LAN Interface Initialization

  13. Binding Update Link_Switch (Local; 802.11; BSSID of Active AP, etc.) Link_Switch (Local; 802.11; Nope, etc.) Active AP? Link_Down (802.3; other parameters.) Authentication Association Detailed Procedures (2) • 802.3->802.11 • With active AP available, the handoff latency introduced by Binding Update can meet the requirements of real-time services • Without active AP (not covered by 802.11 WLAN), the handoff latency is much longer NO Scan for Qualified AP YES Layer 3 Change? IP Address Configuration for Wireless LAN Interface YES L4 Adjustment (If required)

  14. Binding Update Wired LAN Interface Initialization Link_Switch (802.11; other parameters) Layer 3 Change? Link_Up Trigger (Type: 802.3, etc.) L4 Adjustment (if required) Detailed Procedures (3) • 802.11->802.3 • Establish new session by wired LAN interface IP Address Configuration for Wired LAN interface YES NO

  15. Impacts on Standard • Existing Primitive Types • L2 Triggers • Link_Up (Type: 802.3) • Link_Down (Type: 802.3) • L2 and Upper Layer Interaction • Link_Switch (announcement of MAC address change) • Other Messages • Messages for the hint of Active AP info to/from upper layers to indicate whether or not plugging out Ethernet connector will interrupt the session.

  16. Comments? • Other mechanisms for optimization • Other related standard work • ?

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