May 2004
doc.: 802.21_wired_wireless_LAN_handover_r0
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
Samsung AIT
May 2004
doc.: 802.21_wired_wireless_LAN_handover_r0
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
Samsung AIT
May 2004
doc.: 802.21_wired_wireless_LAN_handover_r0
Background & Concepts (1)
Source: A. Alimian and B. Aboba, Doc.: IEEE 802.11-04/0377r1, slide 5
Layer
Item
L2
802.11 scan (passive)
L2
802.11 scan (active)
L2
IPv4 Best Case (ms)
IPv4 Worst Case (ms)
IPv6 Best Case (ms)
IPv6 Worst Case (ms)
0 (cached)
1 sec (wait for Beacon
)
0 (cached)
1 sec (wait for Beacon)
20
300
20
300
802.11 assoc/reassoc
(no IAPP)
4
20
4
20
L2
802.11 assoc/reassoc
(w/ IAPP)
20
80
20
80
L2
802.1X authentication
(full)
750
1200
750
1200
L2
802.1X Fast resume
150
300
150
300
L2
Fast handoff (4-way h
andshake only)
10
80
10
80
L3
DHCPv4 (6to4 scenari
o 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
Samsung AIT
May 2004
doc.: 802.21_wired_wireless_LAN_handover_r0
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.
Samsung AIT
May 2004
doc.: 802.21_wired_wireless_LAN_handover_r0
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.
Samsung AIT
May 2004
doc.: 802.21_wired_wireless_LAN_handover_r0
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
Samsung AIT
May 2004
doc.: 802.21_wired_wireless_LAN_handover_r0
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
Samsung AIT
May 2004
doc.: 802.21_wired_wireless_LAN_handover_r0
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
–-
Samsung AIT
May 2004
doc.: 802.21_wired_wireless_LAN_handover_r0
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
Samsung AIT
May 2004
doc.: 802.21_wired_wireless_LAN_handover_r0
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.
Samsung AIT
May 2004
doc.: 802.21_wired_wireless_LAN_handover_r0
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".
Samsung AIT
May 2004
doc.: 802.21_wired_wireless_LAN_handover_r0
Detailed Procedures (1)
Start
• Interface Initialization
Full Scan in Wireless
LAN Interface
– 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
Target AP?
YES
Authentication
Association
(Target AP->
Active AP)
Indication to
Upper Layers
IP Address
Configuration for
Wireless LAN Interface
Wired LAN
Interface
Initialization
IP Address
Configuration for Wired
LAN Interface
Samsung AIT
May 2004
doc.: 802.21_wired_wireless_LAN_handover_r0
Detailed Procedures (2)
• 802.3->802.11
Link_Down (802.3;
other parameters.)
Link_Switch
NO
(Local; 802.11; Nope,
etc.)
Active AP?
Scan for
Qualified AP
YES
Link_Switch
(Local; 802.11; BSSID of
Active AP, etc.)
Authentication
Association
Layer 3
Change?
YES
Binding Update
L4 Adjustment
IP Address
Configuration for
Wireless LAN Interface
– With active AP
available, the handoff
latency introduced by
Binding Update can
meet the
requirements of realtime services
– Without active AP
(not covered by
802.11 WLAN), the
handoff latency is
much longer
(If required)
Samsung AIT
May 2004
doc.: 802.21_wired_wireless_LAN_handover_r0
Detailed Procedures (3)
Wired LAN Interface
Initialization
Link_Up Trigger
(Type: 802.3, etc.)
IP Address
Configuration for
Wired LAN interface
• 802.11->802.3
– Establish new
session by wired
LAN interface
Link_Switch (802.11;
other parameters)
Layer 3
Change?
YES
NO
Binding Update
L4 Adjustment
(if required)
Samsung AIT
May 2004
doc.: 802.21_wired_wireless_LAN_handover_r0
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.
Samsung AIT
May 2004
doc.: 802.21_wired_wireless_LAN_handover_r0
Comments?
• Other mechanisms for optimization
• Other related standard work
•?
Samsung AIT