Considerations regarding L2&L3 Schemes in 802.3/802.11 Handover

May 2004 doc.: 802.21_wired_wireless_LAN_handover_r0

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Considerations regarding L2&L3 Schemes in 802.3/802.11 Handover

Xiaoyu [email protected]

Youn-Hee [email protected]

2004-05-06


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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


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Background & Concepts (1)

Layer Item IPv4 Best Case (ms) IPv4 Worst Case (ms) IPv6 Best Case (ms) IPv6 Worst Case (ms)

L2802.11 scan (passive) 0 (cached)

1 sec (wait for Beacon) 0 (cached) 1 sec (wait for Beacon)

L2 802.11 scan (active) 20 300 20 300

L2802.11 assoc/reassoc (no IAPP) 4 20 4 20

L2802.11 assoc/reassoc (w/ IAPP) 20 80 20 80

L2802.1X authentication (full) 750 1200 750 1200

L2 802.1X Fast resume 150 300 150 300

L2Fast handoff (4-way handshake only) 10 80 10 80

L3DHCPv4 (6to4 scenario only) 200 500 0 0

L3 IPv4 DAD 0 (DNA) 3000 0 0

L3 Initial RS/RA 0 0 5 10

L3 Wait for more RAs 0 0 0 1500

L3 IPv6 DAD 0 0 0 (Optimistic DAD) 1000

L3 MN-HA BU 0 200 0 200

L3 MN-CN BU 100 200 100 200

L4 TCP adjustment 0 Varies 0 Varies

Source: A. Alimian and B. Aboba, Doc.: IEEE 802.11-04/0377r1, slide 5


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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.


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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 i

nterrupt the current session.


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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 cheap

er 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


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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 i

nterruption 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


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Handoff Strategies Analysis (2)

• 802.11 –> 802.3– Hard Handoff– Latency (not necessary)

• Soft Handoff– Seamless handoff– Maintain two active connections only during the transit

ion time before the new connection is setup– Best choice for wireless-to-wireline handoff

• “Semi-Soft” Handoff– -


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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


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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 assoc

iation– Note: Because the mobile node does not move when the costume

r 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.


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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".


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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.

YES

NO

Start

Full Scan in Wireless LAN Interface

Target AP?

Authentication

Association(Target AP->Active AP)

IP Address Configuration for

Wireless LAN Interface

Wired LAN Interface

Initialization

IP Address Configuration for Wired

LAN Interface

Indication to Upper Layers


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• 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

YES

NO

Link_Down (802.3; other parameters.)

Active AP?

Binding Update

L4 Adjustment

(If required)

Scan for Qualified AP

Link_Switch

(Local; 802.11; BSSID of Active AP, etc.) Authentication

Association

IP Address Configuration for

Wireless LAN Interface

Link_Switch

(Local; 802.11; Nope, etc.)

Layer 3 Change?

YES


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• 802.11->802.3– Establish new

session by wired LAN interface

Binding Update

Wired LAN Interface Initialization

Link_Up Trigger (Type: 802.3, etc.)

Link_Switch (802.11; other parameters)

IP Address Configuration for Wired LAN

interface

Layer 3 Change?

L4 Adjustment

(if required)

NO

YES


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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 l

ayers to indicate whether or not plugging out Ethernet connector will interrupt the session.


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Comments?

• Other mechanisms for optimization• Other related standard work• ?

Considerations regarding L2&L3 Schemes in 802.3/802.11 Handover

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