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A Methodology for Mobile IP Evaluation at California Capital
Corridor Inter-City Rail
Kazuhiro Yamada1*, Harsh Verma2, Bensen Chiou1,
Jean-Luc Ygnace3, Hamed Benouar1
1 California Center for Innovative Transportation, UC Berkeley, USA
2105 Bancroft Way, Berkeley CA 94720
Tel: +1(510)642-5082, E-mail: [email protected]
http://www.calccit.org
2 GLOCOL Inc, USA
3 INRETS, France
ABSTRACT
This paper presents the methodology for Mobile IP Trial Evaluation at Californias Capital
Corridor Inter-City Rail project [1] [2]. The goal of the project is to pursue Pilot
Demonstrations to provide Wireless LAN, High speed Internet connectivity and Info-centric
Services on trains and this started with an initial co-operation in Californias Capitol
Corridors AMTRAK service subsidized by California Department of Transportation
(Caltrans) managed by the Capitol Corridor Joint Powers Authority with similar efforts at
SNCF in France and co-operation between French technology center of excellence INRETS,
GLOCOL USA and the University of California (Berkeley). The Trains Connected
Partnership Project Work Group was set up to focus on emerging standards, technologies andevaluations which have received interest from various Rail Authorities. The focus is to
understand the best ways to incorporate satellite communication, Wi-Fi, Wi-Max, Mobile IP
and various promising technologies into broader applications such as passenger service, train
operations, safety and security. This paper reports seamless roaming simulations over
different systems using Mobile IP.
INTRODUCTION
During the next five to ten years, most rail system riders in North America and Europe are
expected to have onboard wireless Internet access (Wi-Fi), according to some industryestimates. Currently, there are many applications in these regions, mostly in the pilot stages.
A few services are offered on a commercial basis in the U.K, - GNER (Great North East
Railway) [3], Virgin Trains from London to Birmingham, Manchester and Glasgow [4], and
Southerns Brighton Express [5], in Northern Europe countries and also between Paris and
Brussels on the Thalys high speed trains [6]. In India the service is also offered by Railtel on
Delhi-Amritsar and Delhi-Bhopal train routes [7]. Similar services are used by train riders in
Canada and in the U.S.
The most promising solution today is probably the satellite communication systems because
there is no need for specific infrastructure along the track to provide the service almost
everywhere even in remote areas. The main drawbacks to guarantee connectivity and QoS are
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due to the satellite visibility due to the occurrence of mask effects related to the specific
railways environments (tunnels, cutting, lattice mast supporting the catenaries, etc).
In order to overcome this deficiency, this paper focuses on the combination system of a
satellite access and discontinuous terrestrial networks which have to be divided into several
sub-networks. The largest difference from the system with only one satellite is the system hasmany different sub-networks along the track. Trains have to go across these networks as they
go. To change sub-networks on the way, they have to seamlessly roam from one sub-network
to another. This paper reports seamless roaming simulations for the mobile environment.
RELEVANCE OF THE PROJECT
The project is part of the CALFRANCE transportation research cooperation agreement
between France and California. It involves a public/private partnership to dramatically
increase the attractiveness of train passenger transportation in both areas and to speed up the
market deployment of passenger services by solving major technological barriers in the fieldof internet connectivity and telecommunication. The partnership is organized with global
industry players from both countries, major train operators, outstanding academic teams and
supported by DOTs who are really concerned by the economic viability of the train passenger
transportation sector.
Providing new services is essential to make railway transport more attractive. New services
making the distances seem shorter and the train journeys more pleasant and efficient is a
favorable way of attracting new travelers to trains which is one of the best transportation
systems for conservation of natural resources and protection of environment.
STATEMENT OF WORK
This task covers the technical side of the project. This task intends to conduct simulations and
demonstrations to provide WirelessLAN, Internet connectivity and Info-centric services on
Capitol Corridor in California using a terrestrial network system instead of a satellite
communication. In order to achieve the seamless handover Mobile IP was employed. It is a
world standard technology by IETF, Internet Engineering Task Force, and any devices which
support IP can support Mobile IP. To take Mobile IP into the Wi-Fi on trains system, Mobile
IP has to be optimized to roam seamlessly even faster. This paper introduces first how to
optimize Mobile IP to have it roam faster and then shows some trials and their results.
MOBILE IP FASTER ROAMING
Mobile IP allows entire networks and their subnets to be mobile and maintain all IP
connectivity, transparent to the IP hosts connecting through the network. In IP networks,
routing is based on stationary IP addresses. A device on a network is reachable through
normal IP routing by the IP address which is assigned on the network. A device sitting on a
network inside a moving medium such as an automobile, bus or train, as it roams away from
its home network, is no longer reachable by using normal IP routing. This results in the active
sessions of the device being terminated. Mobile IP enables users to keep the same IP addresswhile traveling to a different network, ensuring that a roaming individual can continue
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communication without sessions or connections being dropped.
Mobile IP, however, takes several seconds to complete a roaming. In order to apply Mobile
IP to transportation systems, the roaming time has to be reduced. In a roaming process, after
Mobile Router, or MR, moves to a new network, it has to wait for a periodical advertisement
from a Foreign Agent, or FA, to detect the movement. A Mobile Router does not start theregistration process until it detects the movement. In order to make a roaming faster this
waiting time has to be reduced.
SNMP version 3 linkup/linkdown traps can be used to reduce the waiting time. SNMPv3
linkup/linkdown traps can watch the interface condition on a Mobile Router. When the
wireless interface finds a new radio signal and comes up, the trap informs the Mobile Router
and then it solicits an advertisement to the Foreign Agent which is on the back of the wireless
connection. Figure 1 shows the roaming process time with and without SNMPv3 traps. In the
case without SNMPv3 traps, default case, the waiting time for the next advertisement is
3,460ms under the condition of every five seconds of the advertisement interval. In the case
with SNMPv3 traps the waiting time is just 20ms. At the same time when the wirelessinterface linkups the SNMPv3 trap tells the Mobile Router of the information and it solicits
an advertisement. The waiting time for 20ms starts with the solicitation leaving the Mobile
Router, or the wireless interface linkups, and ends with an advertisement from the Foreign
Agent arriving at the Mobile Router. The SNMPv3 trap dramatically reduced the mobile ip
roaming process time. This feature was used in the following Mobile Environment
Simulations.
Figure 1 Mobile IP Roaming Process with SNMPv3 trap
MOBILE ENVIRNMENT SIMULATIONS SYSTEM
The network topology which was set up for the simulations is shown in figure 2. Three
Foreign Agents are set up. One of them is wirelessly connected with the Home Agent. The
Mobile Router has a Mobile Network which includes PCs and an IP camera. In order to
access to the IP camera, a static private IP address is allocated to it and the address is
statically translated to a static global IP address at the Home Agent. IP addresses shown in
figure 1 are used for the simulation in a laboratory. They should be properly re-configured to
each network environment in each simulation.
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Figure 2 Network Topology for the Simulations
SIMULATION IN A LABORATORY
In this phase of the simulation mobile network was tested in the moving environment at
walking speed. Three Foreign Agents were installed far apart from each other, located at
three corners in CCIT, California Center for Innovative Transportation (See figure 3). The
Mobile Router was carried by foot within CCIT first and a video from the IP camera which is
attached to the Mobile Router was monitored from outside the mobile IP network through the
internet. Continuous pings from a PC outside mobile IP network to the IP camera were issued
and monitored.
Figure 3 Laboratory Test 1
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When the Mobile Router was in the close vicinity of one of the Foreign Agents, pings and the
video from the IP camera were stable. At the moment the Mobile Router moved from one
Foreign Agent to another, one or two pings were lost in many cases. No ping was lost in the
best case. Even in the best case, however, the video froze for about a second. The time delays
associated with the handover include two components first, the association time for Bridges
to associate and second, the Mobile IP process time. It was observed that the time delay ofthe interface linkdown/up was 500ms, while the Mobile IP process time was reduced by the
SNMPv3 traps to 48ms.The sum of both time delays add up to 548ms. Pings are the burst
data which are sent every one second. This interval sometimes enables pings to avoid their
loss by chance. On the other hand video is a streaming data which is sent continuously. Video
data can not avoid its loss while Mobile IP is processing. Video is also an application which
takes a little bit longer time to establish a connection than ping which is ICMP message. This
might have made the latency longer. Even though Mobile IP is employed, a short isolated
time is unavoidable. It is mandated to use middleware which controls delay and jitter to make
video or VoIP smooth.
For the second step the Mobile Router was taken outside CCIT. In this case two ForeignAgents, FA1 and FA2 in the figure 3, worked as an agent. FA1 and FA2 were set up just next
to windows and they made their coverage area outside CCIT (See figure 4). The results were
the same as an in-CCIT test.
Figure 4 Laboratory Test 2
SIMULATION IN A CAR ENVIRNMENT
In this phase of the test mobile network was tested in the moving environment at car speed.
The ground system such as FAs and BRs were set up on the Richmond campus for PATH
(California Partners for Advanced Transit and Highways) (See figure 5). The Mobile Router
was installed in a car which was moving on a street at 25mph. The PC in the building 180
issued continuous pings and monitored the video from the IP camera on a car. The car was
repeatedly traveling on the street back to forth. The ping turn around time was measured on
the way.
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Figure 5 Test system
Results
The result was the same as the one from the lab test. Mobile IP supported the seamless
roaming. Figure 6 shows the ping turn around time. The x-axis of the graph shows the
number of the pings and the numbers themselves do not link to anything such as the distance.
The x signs on the graph show No ping reply. There are two humps around ping number
is 50 and 110. They are roaming points. The Mobile router on the car which came from left in
the figure 5 roamed from Foreign Agent 3 to Foreign Agent 1 around ping number is 50 and
also roamed from Foreign Agent 1to Foreign Agent 2 around ping number is 110. Therefore
this result shows that the car speed does not affect mobile IP at all.
Figure 6 shows one more interesting result. The ping turn around time gradually goes up just
before the handover and suddenly comes down and stable in both cases. This is because of
Wi-Fi default specifications. Once Wi-Fi gets associated with one of the access points, it
persists in the connection until it loses the connection due to a reason such as going out of the
radio range even if it sees another better connection. In this trail as the Mobile Router on the
car goes right, the radio intension deteriorates. This caused the longer ping turn around time,
as it went right. It went far right, it eventually lost the connection to the Foreign Agent 3
because it went out of the range of the bridge attached to the Foreign Agent 3. Just after thisdisconnection the Mobile Router saw a strong radio from the bridge attached to Foreign
Agent 1, and then it connected to the agent. The strong wireless connection to Foreign Agent
1 provided the Mobile Router with the stable communication to the internet. This was why
the ping turn around time got short and stable just after the handover.
This result shows that the ping turn around time before the handover can be reduced (the
handover can be finished before the time gets longer) if wi-fi is optimized to choose the most
suitable bridge to be associated with. This must make the roaming performance even better.
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0
500
1000
1500
2000
Figure 6 Ping Turn around Time
CONCLUSION
SNMPv3 trap reduced Mobile IP handover process time (waiting time for the next
advertisement) from 3,460ms under the condition of every five seconds of advertisement
interval to 20ms and Mobile IP worked well.
The simulation environment provided an excellent test-bed to identify issues and concerns as
a phased testing, installation and deployment could be considered. The results in a car
environment simulation show Mobile IP itself can be applied to transportation systems. On
the other hand they also show the optimization of Mobile IP is not all needed. Mobile IP
works on the Layer-three which does not work without the Layer-two connection. In order to
make the performance in the figure 6 even better layer-two technology must be customized tochoose the most suitable bridge to be associated with. After the optimization of layer-two, the
layer-four connection will also have to be customized. The other Layer connections also must
be optimized at the next step.
REFERENCE
[1] Verma, H, Ygnace, J.L., Benouar, H, Trains Connected Project, ITS World Congress at
Nagoya Japan, October 2004.
[2] CalFrance consortium, Trains Connected; Internet on rails and beyond to improve thefuture of transportation. Proposal submitted to the California Dot and the French Dot,
November 2004.
[3] http://www.icomera.com/customers_case_studies_gner.asp
[4] http://www.wi-fiplanet.com/columns/article.php/3486706
[5] http://www.techworld.com/mobility/features/index.cfm?FeatureID=1351
[6] http://www.thalys.com/be/en/wi-fi/overview
[7] http://newswww.bbc.net.uk/1/hi/business/3835525.stm
xxx x
Ping turn around time (ms)
http://www.icomera.com/customers_case_studies_gner.asphttp://www.icomera.com/customers_case_studies_gner.asphttp://www.wi-fiplanet.com/columns/article.php/3486706http://www.techworld.com/mobility/features/index.cfm?FeatureID=1351http://www.thalys.com/be/en/wi-fi/overviewhttp://newswww.bbc.net.uk/1/hi/business/3835525.stmhttp://www.icomera.com/customers_case_studies_gner.asphttp://www.wi-fiplanet.com/columns/article.php/3486706http://www.techworld.com/mobility/features/index.cfm?FeatureID=1351http://www.thalys.com/be/en/wi-fi/overviewhttp://newswww.bbc.net.uk/1/hi/business/3835525.stm