1. A Fast Handover Mechanism Using Cross-Layer Collaboration for Mobile Networks in High-Speed Trains
Tetsuya Arita and Fumio Teraoka
Graduate School of Science and Technology, Keio University, Japan

2. Introduction High-Speed Trains Passengers Business
Spend long hours on a train
Less transfer
Can’t use all applications because of narrowband
Business
Demands for monitoring the train using video streaming

3. The Goal of this Research
To provide the communication environment faster than 1 Gbps to High-speed train
There are three requirements for the goal
Communication Speed
The current wireless LAN technologies (WiFi and WiMAX) cannot satisfy this requirement
Session Continuity
Fast Handover Mechanism

4. Communication Speed over 1Gbps
Infrared Comm. Device (IR-CD)
has been developed by Prof. Shinichiro Haruyama* and Railway Technical Research Institute
* Graduate School of System Design and Management, Keio University
Front view
Rear view
Infrared laser
Serial Interface
Beacon
Ethernet Interface
SPEC
Speed : 1.25 Gbps
Range : 360m
Feature : Directional
Power cable
Power Switch
Receive Level

5. Session Continuity Network Mobility (NEMO) Basic Support [RFC3936]
The network mobility protocol in IPv6
Mobile Router (MR)
executes handovers and provides mobile node with mobility-transparent connectivity
Home Agent (HA)
manages the binding of Home Address (HoA) and Care-of Address (CoA)
Home network
(4) Communication
HoA
Correspondent Node MR HA
Mobile network
(3)
Foreign Network
CoA
(2)
Mobile network
(1)
Movement MR
(2) Register CoA and MNP with HA
(3) IPv6–in IPv6 tunnel

6. Fast Handover Mechanism
Conventional Handover Procedure
takes more than 1 sec
1. Waiting for receiving Router Advertisement (RA) message
2. The Duplicate Address Detection (DAD) procedure
new AR HA
(4) RA
(6)BU
(7)BA
(3) wait for RA
(5) DAD
Network Layer
Mobile Node
Total disruption time (more than 1 sec)
Link Layer
(1) comm. quality getting worse
(2) L2 handover
BU : Binding Update message
BA : Binding Acknowledgement message

7. L3-Driven Fast Handover
L3-Driven Fast Handover [RFC5184]
Developed in our laboratory
Using cross-layer collaboration
We defined link layer primitives
new AR HA
(8)BU
(9)BA
(4) pre-DAD
Network Layer
(2) L2-LinkStatus Changed
(3) L2-PoAList
(7) L2-LinkUp
(5) L2-Link Connect
Mobile Node
Total disruption time (10-15 ms)
Link Layer
(1) comm. quality getting worse
(6) L2 handover

8. Proposal: Fast Handover Mechanism For the IR-CD
Eliminating DAD processing Time
DAD process
In case of WiFi
It is possible to predict handovers by Receive Signal Strength Indicator
Execute DAD before handovers
In case of IR-CD
It is impossible to predict handovers
Cannot execute DAD before handover
Single administration organization
A Railway company
Assign each mobile router a unique interface identifier
Therefore, the proposed mechanism disables DAD processing
In case of WiFi, execute DAD before handover
It is possible to predict handover by RSSI
In case of IR-CD, it is impossible to execute DAD before handover

9. Proposal: Fast Handover Mechanism For the IR-CD
Eliminating Waiting Time to Detect Link Layer Handover
In case of IR-CD
MR and IR-CD are connected by Ethernet cable
Link state between MR and IR-CD is always LinkUp state
IR-CD is regarded as a repeater
Connect IR-CD to MR with Data cable and Control cable
Control cable can notify MR of the infrared link state (LinkUp/LinkDown)
L3-Deriven Fast Handover
Notification of L2-LinkUp
WiFi device can detect the link status
Infrared Comm. Device on the train
Infrared Comm. Device on the ground
Data cable(1 Gbps)
Infrared Laser
LinkUp/LinkDown
Control cable
Train

10. Proposal: Fast Handover Mechanism For the IR-CD
The Proposed Procedure
new AR HA
(5) RS
(6) RA
(7) BU
(8) BA
Network Layer
(2) L2-Linkdown
(4) L2-Linkup
Mobile Router
Total disruption time
Link Layer
(1) Linkdown frame
(3) Linkup frame
Infrared communication device

11. Implementation Environment OS : NetBSD 4.99 SHISA
An implementation of Mobile IPv6 and NEMO BS on NetBSD
fhod (fast handover daemon) on NetBSD
Daemon to achieve fast handover
fhod
mrd
nemonetd
Mobility Socket
Routing Socket
kernel
userland
Binding
Update
Database
Destination
Options header
module
Management
Neighbor
Discovery
Address
Routing table
Routing
table
Tunneling
Forwarding
Our implementation
Module diagram of our implementation
based on SHISA

12. Message Flow Message Flow in L3 Handover tunnel Train MR IR-CD fhod
mrd
nemonetd
Prev. AR
new AR HA
Link disconnected
(1)Linkdown
Link connected
(3)Linkup
(5) RS
(6) RA
(7) BU
(8) BA
Tunnel
estab.
tunnel

13. Evaluation – Handover Time -
Test network
Emulate the train environment
IR-CD MR AR HA
1.7 msec
0.3 msec
4.0 msec
train
ground
0.003msec
Linkup RS RA BU BA
Details of Handover Time
router HA CN
AR-1
AR-2
無線環境エミュレータにスクリプト読ませてる図
列車の走行をエミュレートしている
本研究室で開発したを明記
scenario
Wireless
Environment
Emulator MR
Data cable
Control cable
CN: Correspondent Node
LFN: Local Fixed Node
LFN

14. Evaluation – Packet Loss Ratio -
configuration
10 IR-CDs are connected to a single AR
a handover occurs per 5 seconds
A train runs at 300km/h and IR-CD is installed every 420m
a L3 Handover occurs in 10 handovers
packet loss never occurs on the infrared link
L2 handover time
10ms, 50ms, 100ms
RTT between MR and HA
0 – 30 ms
UDP packet were sent form CN to MR at 1 Mbps
ハンドオヴぁ時間の単位
仮に１００msでも
Even in the worst case,
The average packet loss ratio is about 2%.

15. Conclusion The goal of this research
To provide the mobile network in high-speed train with high-speed connectivity (more than 1 Gbps)
We proposed a fast handover mechanism
Using cross-layer collaboration for mobile network installed in High- speed train
Defined the Linkup control frame
MR can immediately start handover procedure
The measurements show that
handover time is approximately 6.0ms + L2 handover time
packet loss ratio is approximately 2 % in the worst case.

16. Thank you for your attention.