International Journal

on Marine Navigation

and Safety of Sea Transportation

Volume 1

Number1

March 2007

Internet Based Integration of Multi-Ship

Handling Simulators with IP Multicast

Jinbiao Chen, Songqing Shao, Qinyou Hu & Mingming Zhang

Merchant Marine College, Shanghai Maritime University, Shanghai, China

ABSTRACT: IP multicast is a cost-effective method to accelerate data transmission rate and reduce network

delay as well. This paper presents an improved IP multicast method to realize the interaction of internet based

multi-ship handling simulators. The result of the experiments shows that with the new method, the availability

of network resources and compatibility of the systems are tremendously enhanced.

1 GENERAL INSTRUCTIONS

Currently, ship handling simulators have been

widely used among maritime education, training and

related researches. Though the current systems of

ship handling simulators can train interactively on a

local area network, the students trained come from

the same university or company, which are

inconsistent with the actual navigation environment.

Navigation is an international activity. Several ships

from different countries may navigate in the same

water area. Interaction between them will occur in a

variety of acts. Therefore, the ship simulators all

over the world should be interactive so that the

students who come from different countries or

regions can manipulate their simulators in the same

virtual water through internet. However, with the

increase in the number of ship handling simulators,

network communication constantly rising, which

may result in network communication delay or

congestion. Based on the analysis of the data flow

system, this paper presents IP multicast method to

control the data redundancy and bandwidth

occupation. By using such method, the data

transmission rate of network system is tremendously

increased. Finally, its feasibility is verified by

experiments in the real system.

2 IP MULTICAST PRINCIPLE

2.1 IP Multicast meaning and communication

pattern

IP multicast is a bandwidth-conserving technology

that reduces traffic by simultaneously delivering a

single stream of information to potentially thousands

of corporate recipients. Multicast group members are

dynamic, that is, each member can join in or leave

the IP Multicast group at any time and each member

locates in various independently physical networks.

IP Multicast communication pattern: when a

source sends same data to multiple hosts using

traditional IP communication, it needs to send data

packet to every client. However, when using IP

multicast, such source only needs to send data packet

to a particular IP multicast group without burdening

the source or the receivers while using a minimum of

network, resulting in the most efficient delivery of

data to multiple receivers. (as shown in figure 1).

Currently, applications that take advantage of

multicast include video conferencing, corporate

communications, computer-supported cooperative

work C5CW, interactive Simulation and FTP, etc.

2.2 IP Multicast addresses

The Internet Assigned Numbers Authority (IANA)

controls the assignment of IP multicast addresses.

IANA has assigned the IPv4 Class D address space

to be used for IP multicast. Therefore, all IP

multicast group addresses fall in the range from

224.0.0.0 through 239.255.255.255.

Addresses in the range from 224.0.1.0 through

238.255.255.255 are called globally scoped addresses.

These addresses are used to multicast data between

organizations and across the Internet.

Addresses in the range from 239.0.0.0 to

239.255.255.255 are called limited scope addresses

or administratively scoped addresses. These addresses

are described in RFC 2365, Administratively Scoped

IP Multicast, to be constrained to a local group or

organization. Companies, universities, or other

organizations can use limited scope addresses to

have local multicast applications that will not be

forwarded outside their domain.

In multicast communication, two addresses are

needed: an IP address and a multicast Ethernet

addresses. IP Multicast addresses are representative

for a group of receivers. They accept the data, which

is sent to the entire group. Because IP packets should

be encapsulated in an Ethernet frames, Ethernet

multicast addresses are needed. For normal work of

Multicast, hosts should be able to receive unicast

and multicast data. Thus the hosts need to address a

number of IP and Ethernet and Ethernet and IP

addresses serve for unicast communications.

Ethernet and IP Multicast addresses are used for

multicast communication. If the host is not prepared

to receive multicast addresses, zero is set for

multicast addresses.

2.2 Multicast system structure

IP Multicast in communication needs to complete

two basic tasks; one is how to add a member to

multicast group, the other is how to sent multicast

information to each recipient. In order to solve those

problems, two basic protocols are introduced:

Protocol between the host and router, that is,

multicast members management protocol and

Protocol between the router and router, multicast

routing protocol. Internet Group Management

Protocol is IGMP. IGMP protocol, which is used to

connect hosts, works between the two routers. IGMP

is used to dynamically register individual hosts in a

multicast group on a particular LAN. Hosts identify

group memberships by sending IGMP messages to

their local multicast router. Under IGMP, routers

listen to IGMP messages and periodically send out

queries to discover which groups are active or

inactive on a particular subnet. IGMP works in the

layer. Router can control the multicast. The

second-layer equipment, IGMP Snooping can

restrain the distribution of data in 2ed layer of

network. Multicast routing protocols running on

multicast routers between trees and routing for

multicast packets transmitted building.

Fig. 1. Multicast group sketch map

2.3 IGMP protocol

Before the establishment of a multicast routers

connection and delivery of multicast group

members’ information, it must determine whether

one or more hosts exist on a local network.

Therefore, multicast routers and IP Multicast must

use IGMP for information communication between

group members. IGMP multicast routers can be used

to judge whether there are multicast group members,

if there exist members of multicast, multicast router

will be added to a specific multicast group and send

multicast data to the new adding host. Therefore,

IGMP is used to notify router connected directly,

adding it into a multicast group IGMP can make the

multicast network be dynamic and flexible.

2.4 IP Multicast routing protocol

IP Multicast routing protocol is a crucial factor for

transmission multicast information flow in routing

network. It overcomes bottleneck of single cast

communication model and reduces cost of sending

the same data to the several recipients. This is the

main reason why IP Multicast application developed

greatly. In multicast network, trees for data flow in

multicast network should be established according to

multicast route protocol data so that a single path

can be formed between transmission source and

multicast members, ensuring that each data packet

was transmitted to the purpose of IP addresses.

3 IP MULTICAST APPLICATION

IN INTERNET BASED INTERGRATION

OF SHIP HANDLING SIMULATOR

In fact, internet based integration of multi-ship

handling simulators is a distributed interactive

system composed of several simulators located in

different countries or regions through internet. All

the training simulator in a virtual sea need exchange

information constantly. To ensure the state

unification of the simulators in the same virtual

water, a high quality of real-time performance is

required. Meanwhile, a simulator can join in virtual

water and can withdraw at any time. This requires a

good scalability and reliability. Taking these

demands of the entire system into account, the

system must minimize network delay and avoid

congestion. UDP and IP Multicast technology can be

used to reduce the data packet transmission and

improve network data transmission rate.

3.1 Integration of Internet data flow analysis

Because the system is based on UDP and IP

Multicast, its structure is the tree structure, which

can ensure its expansion, flexibility and network

data transmission rates. System has a control centre

which is responsible for transmitting information,

task decomposition, matching and management.

Exchanging data between all the simulators and

control centre directly affects the reliability of the

system or even success. System information is as

follows: control centre data to various simulators:

1 Environmental Information: Virtual waters

including the code of the waters, the direction of

wind, the velocity of wind, the direction of flow,

the flow velocity, day / night, visibility and so on.

2 Simulator information: Mainly including country,

company name, type, and its compatibility.

3 Ship information: ship’s name, call sign, owner,

shape, length, breadth, draft, depth, course, speed,

longitude, latitude and rate of turn.

4 Control information: mainly including start and

exit of the control centre, start and exit of a

simulator, add or delete one model ship on the

system and so on.

3.1.1 The simulator data to the control centre

1 Simulator information: Mainly including:

country, company name, type, and compatibility.

2 Ships information controlled by simulator:

simulator’s name, ship’s name, call sign, owner,

shape, length, breadth, depth, course, speed,

longitude, latitude and rate of turn.

3 Join in or exit the simulator system information.

When a training simulator wants to join in virtual

waters, it will send “join in” information to the

control centre (including information simulator).

After the success of accession, the simulator

regularly sends all vessels and simulator information

to control centre. Control centre regularly send the

virtual water information to all the training

simulators in the same waters to ensure that all

simulators is in the same environment. When the

control centre received simulator information and

the ships which are controlled by this simulator,

control centre will send these messages to all the

training simulator in the same waters. When the

control centre received a simulator’s “leaving”

information, the control centre will send this

message to all other waters in the same virtual

training simulator. Other simulators will remove all

the ships controlled by this simulator.

3.2 Data packets and data exchange

1 Control Centre is the highest-level multicast

communications and is the general control centre

of the whole communications network, which

occupies a separate group multicast addresses.

Control Centre controls the transmission of

information and manages all the multicast

addresses.

2 The simulator is the second layer of multicast

communications. According to system

requirements, all the data exchange are only

constrained in the simulators as well as between

the control centre in the same waters. So all

simulators in the same virtual waters set up a

multicast group and shared a multicast address.

First of all, simulator data is sent to the control

centre (control centre monitor the state of all

simulators). Subsequently, the control centre

transmits these data to multicast group. Ship

Simulator Internet Integration Architecture is

shown in the figure 2.

3.3 Dynamic foundation of the multicast tree

The control centre adds to pre-defined multicast

addresses automatically in procedure initialization.

Simulators in the same virtual water are set up to a

multicast group.

After the control centre finish initialization,

simulators will be added to the waters. If the

simulator is the first one to join virtual water, IGMP

will assign a multicast group address, the other

training simulator can join in this multicast group

one by one. The multicast group is dynamic, that is,

one can always join in a multicast group and leave. If

a multicast group has no simulator, the IGMP will

cancel multicast group automatically.

1 When a simulator wants to join in a virtual area,

that is, want to join in a multicast group, This

simulator will send a notice to local IGMP

multicast routers on the verge of its wish to join

in the multicast group.

2 When the adjacent routers receive the message

that a simulator wants to join in a multicast

group, this router tracks on the multicast group

dynamically. After tracking the multicast group,

multicast routing protocol is used to connect the

simulator to multicast tree on the edge of the

original multicast routers.

3 When the source and the receiver establish

multicast routing, source along multicast routing

begin to send data to various recipients.

Fig. 2. Ship Simulator Internet Integration Architecture

3.1 Multicast Communication and the results based

on Winsock

The system apply with the communication and UDP,

the control centre relies on JADE3.3 platform,

JBuilder9.0 programming tools were used. Terminal

simulator uses Winsock based on the Windows

platform. VC++6.0 network programming to realize

network communication. Process control and

multicast data use different socket types. Multicast

data and control data are corresponding to two

sockets, the collection and sending of data use

different port addresses, which can increase the

success rate of receiving data. As the using of UDP

can not guarantee the quality of communications,

related work for handling data error during

collecting and sending are disposed in the program.

According to the actual operating situation, this

method is highly efficient and effectively solves the

network congestion. Table 1 contains the actual

system contrast results of single cast and multicast.

Table 1 Data contrast between single cast and multicast

Average

times of the

network

block

Average delay

time of the

network

The size of

system may

withstand the

biggest data cast

single cast 10/10h 1.5s 5KB

multicast 1/10h 0.5s 6KB

4 CONCLUSIONS

Results can be seen from the actual operating

system. The IP multicast method presented in this

paper can effectively decrease the network

congestion and highly improve the data transmission

rate. An internet based integration of multi-ship

simulator is achieved by dynamic allocation of

multicast group members. Any simulators can join in

or withdraw the virtual water at any time. In the

future, we will continue our work to improve error

control and transmission reliability.

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