multiple paths protocol for a cluster type network

*Correspondence to: Hiroshi Mineno, Graduate School of Science and Engineering, Shizuoka University, 3-5-1 Johoku,Hamamatsu 432-8011, Japan.

CCC 1074}5351/99/060391}13$17.50 Received 25 February 1999Copyright ( 1999 John Wiley & Sons, Ltd. Accepted 30 May 1999

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS

Int. J. Commun. Syst. 12, 391}403 (1999)

Multiple paths protocol for a cluster type network

Hiroshi Mineno1*, Susumu Ishihara2, Ken Ohta3, Masahiro Aono4,Tetsuo Ideguchi5 and Tadanori Mizuno2

1 NTT Corp., 3-9-11 Midori-cho, Musashino, Tokyo 180-8585, Japan2 Faculty of Information, Shizuoka University, 3-5-1 Johoku, Hamamatsu 432-8011, Japan

3 NTT Mobile Communications4 Graduate School of Science and Engineering, Shizuoka University, 3-5-1 Johoku, Hamamatsu 432-8011, Japan5 Faculty of Information Science and Technology, Aichi Prefectural University, Nagakute, Aichi 480-1198, Japan

SUMMARY

Nowadays we can access the Internet by carrying a portable computer and using wireless communication.The wireless network with personal handy phone system (PHS) and portable cellular telephone has onlyrates of tens of Kbps to a few Mbps. Compared with the cable network, the transfer rate cannot generallysatisfy a highly developed communication service such as large "le transfer and real-time communications.This paper proposes a protocol, SHAKE, for sharing multiple paths in a cluster type network that is a kindof LAN in which some mobile hosts temporarily connect mutually. SHAKE provides the functions forcomposing a cluster type network, and dispersing tra$c e$ciently by measuring transfer rate and round-triptime. As a mobile host has only a low transfer capacity for individuals to communicate with the outside, ifwhole capacities of other hosts which compose a cluster type network are shared, we can get larger transfercapacity and satisfy the required communication services. Copyright ( 1999 John Wiley & Sons, Ltd.

KEY WORDS: mobile computing; cluster type network; tra$c dispersion; sharing multiple paths

1. Introduction

With the rapid development of the network technology and the improvement of the computer'sperformance, we can access the Internet by carrying a portable computer and using wirelesscommunications. At present, the wireless networks with personal handy phone system (PHS),portable cellular telephone or in-house wireless LAN has only rates ranging from tens of Kbps toa few Mbps. Compared with wired networks, the transfer rate cannot generally satisfy a highlydeveloped communication services such as transfer of large "les or multimedia data, and real-timecommunication which should guarantee the delay time. This means that the demand for capacitymay sometimes exceed what is available, and packets may be lost.

In this paper, we propose a protocol SHAKE (SHAred multiple paths protocol for a cluster-type networK Environment), for sharing multiple paths in a cluster-type network. Cluster-typenetwork is a kind of LAN in which some mobile hosts are temporarily connected. In mobile unitssuch as trains, ship and aircraft where some persons gather, there are two ways to increase thetransmission capacity by composing the cluster type network. One is that, a host which has

Figure 1. An example of the system

a larger or more stable path is made to represent and communicate with the outside, and othermobile hosts which connect the cluster type network do not need to have their own outside path.The other is that, as a mobile host has only low transmission capacity for individuals tocommunicate with outside, if whole capacities of other hosts which compose cluster network areshared, we can get larger transfer capacity and spread burst tra$c equally.

We focus on the latter (Figure 1). We can select several kinds of paths to communicate withoutside. So the communication media such as PHS or portable cellular telephone can be freelyselected by each mobile host. When di!erent paths are used for communication, the quality ofeach path such as transfer rate, delay time, and the rate of packet loss are di!erent, and for thisreason, it is important to consider how to distribute the burst tra$c and how to reconstruct thepackets.

This paper is organized as follows. The next section describes the background of this researchwork and the related research works; Section 3 describes the shared multiple paths protocol,SHAKE and its functions; Section 4 deals with the implementation of the prototype and Sec-tion 5 concludes this paper.

2. Related works

2.1. Trazc dispersion

Generally, aggregating the resource can improve the performance and e$ciency in sharedsystems or communication networks.1 One of the resource aggregation methods is that the tra$cis transmitted in parallel through multiple paths.

Maxemchuk presented that for load balancing and fault handling in packet-switched networks,it is better in space rather than in time to disperse the tra$c.2}4 According to this method,a message from a source is distributed into several submessages, which are transmitted in parallelover di!erent paths in the network. And as a transmission error on one path is independent fromerrors on the other paths, forward error correcting codes can be successfully used. Furthermore,in an algorithm proposed by Lee and Liew,5 the tra$c from a source is partitioned intosubmessages, each consisting of K packets.

392 H. MINENO ET AL.

Copyright ( 1999 John Wiley & Sons, Ltd. Int. J. Commun. Syst. 12, 391}403 (1999)

This algorithm encodes the K packets into N'K packets, which are transmitted in parallelthrough N separate paths. When any K of the N packets are received correctly, the originalmessage can be reconstructed, and if the bit error detection is used for every packet, the algorithmis capable of correcting N}K packet errors in each submessage.

IETF standardizes multilink point-to-point protocol (MP) with the technique which consists ofa number of di!erent switched WAN services such as ISDN and ATM to form a virtual path.6,7 Itcan strengthen the functions of point-to-point protocol (PPP) data communications between twopoints, and a number of virtual connections can be set up between equipment by takingadvantage of the characteristics of switched WAN service. If necessary, the bandwidth whicha user requested can be divided, and a number of physical lines and virtual lines can be used asa single logical line.

The technology of aggregating multiple communication paths and dispersing tra$c into eachcommunication path are being developed to improve the performance and the e$ciency oftransmission. They are generally used to communicate with di!erent kinds of WAN lines that areaggregated among routers.

2.2. Mobile distributed co-operation system

In a mobile computing environment, a mobile host works as a terminal for personal operation.Furthermore it is also known to form a group wherein mobile hosts co-operate with one another.There are many mobile groupware that support co-operation among a number of mobile hosts.

In an area where a number of mobile hosts can communicate mutually, a number of mobilehosts can construct a temporary network to support co-operation for people gathered in the area.The network is called cluster-type network or ad hoc network, and research work has beenundertaken in this regard.8}10

In addition, it was also considered how to communicate with outside networks. One method isthat in some kinds of transportations such as train, ship or aircraft, if there is a communicationsystem with high communication capacity which works as a representative of all mobile hosts tocommunicate with outside networks, the transfer time and cost can be reduced. And the other isthat, as a mobile host has only low transfer rate for individuals to communicate with outsidenetworks, if whole transmission capacities of the hosts composing the cluster network are shared,we can get larger transmission capacity.

So the cluster has some advantages which a single mobile host does not have and thecommunication protocol in which other hosts' communication capacity can be shared is calledSHAKE, which we are developing. By using this protocol, the communication paths of mobilehosts composing the cluster are shared and they are considered logically one path.

3. Shared multiple paths

3.1. SHAKE

We think there are several advantages of the sharing multiple paths: the end-to-end transferrate of data can be increased and the delay time reduced. The burst tra$c is dispersed into severalpaths and network load is equalized. Transmission errors on each path are independent fromerrors on the other paths. To transfer excess packets, the characteristics of delay time and packetloss on di!erent paths should be reduced, and the transmission reliability should be improved.

MULTIPLE PATHS PROTOCOL FOR A CLUSTER TYPE NETWORK 393


Figure 2. SHAKE protocol stack

We can form a cluster in which each mobile host can gather anywhere. Any mobile hostin a cluster can freely select any kind of medium for communication between the clusterand the outside network, if one of the mobile hosts can transfer data by relaying the other'spath.

We are now developing the SHAKE protocol to realize the shared multiple paths. SHAKE isimplemented in all mobile hosts which form a cluster (cluster means cluster type network) and at"xed hosts which are connected to the Internet and communicate with one of mobile hosts ina cluster (Figure 2). And for easy to implement SHAKE, it is built between the transport layer andthe application layer. So for mobile hosts which are not implemented SHAKE cannot sharemultiple paths.

In the cluster, we call a mobile host that has a communication path with outside network (likeInternet) as a relay host. Each relay host in the cluster has two network interfaces: one is used tocommunicate with outside network, and the other is assigned the local private IP address beforeforming a cluster. Cluster is formed by using Ethernet, serial cable, wireless LAN, IrDA and so on,and the shape of the network can be considered as ring type network or star type network.A mobile host can freely select any communication path and any kind of medium to communicatewith the outside. For those hosts that have no link with the outside, the communication can bealso done through the relay hosts. The logical link which connects each mobile host to form thecluster is called the &cluster link'. A mobile host became a part of the cluster if it is connected bya cluster link.

3.2. Functions of SHAKE

As a protocol of transport layer, SHAKE uses TCP to transmit data. TCP connection isformed between mobile hosts in the cluster and "xed hosts in the Internet. There are three kinds



Figure 3. Illustration of SHAKE modules

of SHAKE packets which go through this connection, each identi"ed by special SHAKE header;the "rst is data packet that contains data from the application layer; the second is control packet toform a cluster, and the last is report packet which is used to report communication status. Theprotocol SHAKE is realized from the following four modules:

f Link monitoring module.f Path selecting module.f Data processing module.f SHAKE management module.

The relationship among these modules is shown in Figure 3. From these modules, we canrealize the SHAKE for sharing multiple paths in cluster type networks.

3.2.1. Link monitoring module. This module monitors the status of communication paths withoutside networks and estimates the sending rate. Here the status of communication paths meanthe theoretical bandwidth of the medium, throughput which changes actively, transit delay, cut ofcommunication paths, etc. And if a notable change of the status has occured, it changes thesending rate so that each path's bandwidth is e!ectively used.

Here we discuss the estimation of sending rate for transferring data. The method is to controlthe de"nite amount of data which pass the network. We consider the network as a large bu!er (wecall it a network bu!er) which has its own queue and sending rate. For using each path e!ectively,it is better to leave network bu!er in a constant value to avoid that the receiving bu!er in theobject is often empty. But a problem will occur if too much data is sent, which can cause thetransit delay largely; so it is important to control the amount of data in the network bu!er. As inFigure 3, it seems that each communication path has a bu!er and all bu!ers are managed by thelink monitoring module. The SHAKE evaluates how many packets have been sent to the objectand how many packets still overstock in each network bu!er. The SHAKE can estimate sendingrate to maintain the amount of data in all network bu!ers.



The remaining amount of data in network bu!ers can be evaluated as follows. In a sendinghost, each of the dispersed packets is added a sending time stamp ST

1in SHAKE header and sent

to the receiving host. On the other side, at regular intervals, the receiving host sends backa receiving report to the sending host, which contains the newest received packet's ST

1, RT

1which is the time it received, RT

2which is the time this report was sent, and R

3%#7which is the rate

of receiving. So when the sending host received the report at the time ST2, the sending host can

estimate the RTT by the following expression. And to avoid the wide #uctuations of RTT!7'

which means average of RTT, it is estimated as follows by using low-pass "lter: (0(a)1).

RTT"(ST2!ST

1)!(RT

2!RT

1) (1)

RTTavg"(1!a)RTTavg#aRTT (2)

And then Buf#63

which means current network bu!er is estimated as follows by using the R3#7

,RTT

!7', and RTT

.*/which is the minimum RTT value till the time:

Bufcur"Rrcv(RTTavg!RTTmin) (3)

Comparing the expected value Buf$%4

with current amount of data in network bu!er Buf#63

, thesending rate R

4/$is increased if the expected value is small, or reduced if the expected value is large.

And using the receiving rate R3#7

in the receiving report, we can calculate the accurate sending rate:

Rsnd"Rrcv#(Bufdes!Bufcur)

interval(4)

3.2.2. Path selecting module. A sending host obtains information about communication pathswith the outside from the link monitoring module, and then distributes the data packets whichcome from the application layer. If each communication path has the same length, type,throughput and transmission delay, the packets can be distributed equally to each of communica-tion paths in order. However, actually, in each path, characters of network are di!erent since eachpath can be selected freely by mobile hosts. So the distribution rate of each path must be changedaccording to the status of each communication path. This is done by analysing the informationabout the sending rate R

4/$, and disconnection report from link monitoring module.

The distribution procedure is to distribute packets according to the rate of each path's R4/$

,and adjust the amount of data in each network bu!er. If there are n paths in cluster and thesending rate is R

iin path i (i)n), the packet distribution rate P

iof path i can be calculated as

follows. And according to the packet distribution rate Pi, the packets can be distributed for each

communication path.

Pi"

Ri

+nk/1

Rk

(5)

3.2.3. Data processing module. The received data from the application layer are divided intoa number of packets. Each packet is transmitted to transport layer after the addition of a specialheader of SHAKE. This packet is a data packet, and the header includes: packet identi"er (data),link number, packet length, sequence number, ST

1, and data. Also there is a report packet which

includes packet identi"er (report), link number, packet length, ST1, RT

1, RT

2, and receiving rate

of the link. Figures 4 and 5 show the format of each SHAKE packet. Finally, there is a controlpacket which is only used to form a cluster and make a link table.



Figure 4. Data packet format

Figure 5. Report packet format

When each host receives a SHAKE packet, it identi"es whether it is a data packet or a reportpacket or a control packet by checking the identi"er in the header, and according to the linknumber in the header, it judges where to relay the packet. Each host has a table which relates hostto link number. So if the packet is destined towards the host itself, the packet is given to theapplication and the others are relayed to the next host.

Here we explain how to put in order the received data packets with irregular sequence sincethey were transmitted from multiple paths. Although the path selecting module selects paths fromwhich packets are received by destination in right sequence, it is actually di$cult to do thiscompletely because of di!erent characters like transit delay and length of each path. If a packetwith irregular sequence is received by SHAKE, it cannot be given to the application directly.SHAKE will store it in the bu!er temporarily, and then if any packet which can be given to theapplication is received, SHAKE will check the bu!er to "nd out if there is any packet with thefollowing sequence number. If there is, of course it will be given to the application, and SHAKEwill continue to search whether there is any packet else in the bu!er. If no one else, SHAKEreceives the next packet and repeats the above process.

3.2.4. SHAKE management module. The work of this module includes controlling the othermodules, forming the cluster, ensuring communication paths and so on. The application of the upperlayer need not consider how and on which paths are selected to the transmission data. It realizes theshared multilink procedure by using multimedia through multiple paths to form a logical path.

4. Implementation

In this section, we present the implementation environment and the evaluation of the prototypewhich we are developing now.



4.1. The implementation environment

The cluster network is formed by mobile hosts (Toshiba SatellitePro420, CPU: Pentium100 MHz, Memory: 16.0 MB, and Mitsubishi Amity SP, CPU: 486DX4-75 MHz, Memory:16.0 MB) which is installed Windows95 and with two PCMCIA card slots. For sending packetswithin the cluster, the network interface which is connected to the cluster is assigned the privateIP address like 192.168.X.X, and each host connected with about 1 ms 10Base-T and four-portHUB to form a cluster. The other network interface is assigned a normal IP address to connect tothe Internet, which may be assigned by DHCP or decided value.

For the implementation of the SHAKE prototype, we developed a simply special data transferapplication with Visual C##, and the SHAKE is used in the communication section of theapplication. It is implemented at all mobile hosts which form a cluster, and the host in the Internetwhich communicates with the one of the host in the cluster network. Then it can divide an applicationdata into a number of determined size SHAKE packets and distribute them to the destination. And inthe destination, the received packets is re-constructed and given to the application in order.

4.2. The status of prototype

The present link monitoring module forms a path information table of all end-to-end pathinformation when the cluster is formed, and the information is updated by receiving the reportpackets. When some new hosts are added to the cluster, new sections are added to this table afternew connections. It performs the role of a routing table indicated among link numbers and relayhosts and the destination host, and it contains a variety of information on theoretical bandwidth,round-trip delay, and receiving rate. These values are estimated by receiving report packets from thereceiving host at regular intervals, and each link's suitable sending rate is also estimated by this report.

The path selecting module searches whether the destination host is in the information tablewhen the application requests for sending data, and then it checks the path, and simply sends thedata through these paths in an order. That is to say, the function that can change the packetdistribution rate according to the each path's sending rate is being developed.

The data processing module is almost completely implemented. It divides application data intoa number of SHAKE packets, and adds a special SHAKE header to each packet.

When the packet is received, it is processed to determine if it is relayed or to be given to theapplication according to the information of header. If the packet is to be given to the application,it should be put back in order since it may be transmitted in di!erent paths and received in irregularsequence. In the present method, the sequence number in SHAKE header will be checked todetermine the action. If the packet cannot be given to the application, it is stored in bu!er and itssequence number will be used as a key for searching. When a new packet is received and given to theapplication, the SHAKE checks if the next packet is stored in bu!er. If it is, the packet will be takenout and given to the application, then the receiver repeats the above processing.

The tasks of SHAKE management module are checking among hosts and managing any othermodules. It communicates with the application directly, and opens an additional window ofSHAKE for requesting the formation of a cluster.

4.3. Experiments

In our experiments, we used two mobile hosts to form a cluster network, and used wirelessLAN links (2.4 GHz frequency hopping spread spectrum) for communication with outside



Figure 7. Experiment 2


networks. We did the following three kinds of experiments:

1. In experiment 1, we used one access point for wireless LAN, and the mobile host communi-cates with the "xed host which is connected to our laboratory's LAN by wireless LAN(Figure 6).

2. In experiment 2, we used one access point for wireless LAN, and two wireless LAN adaptersfor sharing the paths. The cluster is formed by two mobile hosts; only one of thesecommunicates with the "xed host which is connected to the laboratory's LAN (Figure 7).

3. In experiment 3, we used two access points. We set up two channels for them to share thecommunication paths under the situation where they do not a!ect each other. The cluster isformed by two mobile hosts, and the same experiment is repeated (Figure 8).

The used "le is about 4 Mbytes (4139 kbytes) AVI "le. It was sent from the client host in thecluster to the server host in a "xed network. Then in the server host, we investigated the amountof received data and the receiving time of data (which means the time between receiving the "rstdata packet and the last data packets), and the throughput is estimated at the server host. Therelationship is shown in the graphs (Figure 9).

Next we conducted above experiments with PHS terminals on PIAFS mode. PHS internetaccess forum standards (PIAFS) is the data transmission standards to operate a high-speed datacommunication service with 32 Kbps access via PHS. This environment is shown in Figure 10.

4.4. Results

There are six graphs in Figure 9. Graphs (1), (3) and (5) show the relationship between thereceived time and the amount of received data, and graph (2), (4) and (6) show the average of thethroughput which is calculated when "ve data packets are received. Graphs (1) and (2) are theresults of experiment 1, graphs (3) and (4) are for experiment 2, and graphs (5) and (6) are forexperiment 3.

The results show that to form a cluster network and share multiple paths can reduce thetransmission time and improve the throughput compared with using a single wireless LANadapter. When one wireless path is used, the average of throughput is about 410 Kbps, and when




Figure 9. Results of wireless LAN experiments

Figure 10. Experiment with PHS terminals

two wireless paths are used with the same access point, the average is about 491 Kbps. In spite ofsharing the same channel with two wireless LAN adapters, the average of throughput has shownlittle improvment (20%). If the using channels are di!er from, the throughput is better (65%).

The communication speed is changed according to di!erent conditions, but the average ofthroughput which is guaranteed by the manufacture company is about 400 Kbps. So boththe throughputs we calculated from graphs (2) and (4) of Figure 9 are the results we expected. Andwe know that by sharing the same channel, we can use the channel e!ectively and the aver-age throughput nearly approaches the limit value for using one channel.



Figure 11. Experiment with PHS terminals

From the results of experiment 3, graphs (5) and (6), we could get the 65% higher throughputthan using one wireless path. The value is not yet twofold, but if the prototype is developedfurther, we may improve the throughput better. And in graph (6), the average throughput isunstable. We think that this is due to the function of resequencing packets. Some functions, suchas the sending rate control and the distribution rate control, were not implemented in the presentprototype, so many packets that are received are out of order. After we implement the functions,the performance could be better.

Next, we will discuss the results of the experiments with PHS terminals on PIAFS mode.The results are shown in the graph (Figure 11). Graphs (1) and (2) are the results of experi-ment 1 via PIAFS access point in Nagoya, and the average throughput is about 19 Kbps,and graphs (3) and (4) are the results of experiment 1 via PIAFS access point in Hamamatsu,and the average throughput is about 26 Kbps. Nagoya is about 100 km away from Hama-matsu, so the di!erence in delay between them was about 80 ms (calculated from the measuredRTT). Graphs (5) and (6) are the results of using two PIAFS links. Compared with the caseof using one PIAFS link, the average throughput is 93% more than the sum of the former twocases.

5. Conclusions

We proposed a protocol, SHAKE, for sharing multiple paths in a cluster type network in whicha number of mobile hosts are temporarily connected. Each host in the cluster can share otherhosts' communication links. SHAKE consists of four parts: link monitoring module, pathselecting module, data processing module and SHAKE management module. Till date we haveimplemented the prototype of SHAKE and completed communication tests with wireless LANsystems and PHS terminals.



Henceforth, we plan to continue the implementation of the protocol, to simulate the a!ection ofa cluster's size, to evaluate the e$ciency of control of transmission rate and data transmissionwith distributed packets, and so on.

Acknowledgements

The authors gratefully acknowledge the help of Junshu Lu who assisted us with English, andNicholas F. Maxemchuk who supported several references.

References

1. E. Gustafsson and G. Karlsson, &A literature survey on tra$c dispersion', IEEE Network, 11(2), 28}36 (1997).2. N. F. Maxemchuk, &Dispersity routing', ICC'75, 41-10}41-12 (1975).3. N. F. Maxemchuk, &Dispersity routing in high-speed networks', Comput. Networks ISDN Systems, 25(6), 645}661

(1993).4. N. F. Maxemchuk, &Dispersity routing in ATM network', IEEE INFOCOM'93, 347}357 (1993).5. T. T. Lee and S. C. Liew, &Parallel communications for ATM network control and management', IEEE

G¸OBECOM193, 1, 442}446 (1993).6. K. Sklower, B. Lloyd, G. McGregor and D. Carr, &The PPP multilink protocol (MP)', RFC1717, November 1994.7. K. Sklower, B. Lloyd, G. McGregor, D. Carr and T. Coradetti, &The PPP multilink protocol (MP)', RFC1990, August

1996.8. P. Gupta and P. R. Kumar, &A system and tra$c dependent adaptive routing algorithm for ad hoc networks', in Proc.

IEEE 36th Conf. Decision Control, pp. 2375}2380, 1997.9. B. Das, R. Sivakumar and V. Bharghavan, &Routing in ad hoc networks using a spine', in Proc. 6th Int. Conf. Computer

Communications and Networks, September 1997.10. &Mobile Ad Hoc Networking (MANet)', http://tonnant.itd.nrl.navy.mil/manet/manet}home.html.

Authors: biographies:

Hiroshi Mineno received the BE, and the ME degrees from Shizuoka University, Japan in 1997and 1999. In 1999, he joined NTT Corp. His research interests include mobile computing,computer networks, and distributed systems. He is a member of Information ProcessingSociety of Japan.

Susumu Ishihara received his BSEE and PhD degrees in 1994 and 1999 from NagoyaUniversity, Japan. From 1998 to 1999, he was a Special Researcher of JSPS fellowship. Since1999, he is a research associate in the Department of Computer Science, Faculty of Informa-tion, Shizuoka University, Japan. His research interests are in the design and analysis of localarea networks, distributed computer systems and mobile computing. He is a member of theInformation Processing Society of Japan and of the Institute of Electronics, Information andCommunication Engineers.



Ken Ohta received the BE, ME, and DE degrees from Shizuoka University, Japan in 1994,1996, and 1998, respectively. In 1999, he joined Multimedia Laboratories, NTT MobileCommunications Network Inc. (NTT DoCoMo). His research interests include mobile com-puting, computer networks, and distributed systems. He is a member of the InformationProcessing Society of Japan and of the Institute of Electronics, Information and Communica-tion Engineers.

Masahiro Aono received the BS degree from the Nagoya Institute of Technology in 1969. In1969, he joined Mitsubishi Electric Corp. He has been engaged in development of air tra$ccontrol system and so on. He is a member of Information Processing Society of Japan and ofthe Institute of Electronics, Information and Communication Engineers.

Tetsuo Ideguchi graduated from the University of Electronic-Communication in 1972. Sincejoining Mitsubishi Electric Corporation in 1972, he had been engaged in R&D of networkarchitecture, communication processing methods and so on. He received the Dr Eng degreefrom Tohoku University in 1993. In 1998, he joined the Faculty of Information Science andTechnology, Aichi Prefectural University. His research interests include computer networks,network management, distributed systems and mobile computing. He is a member of theInformation Processing Society of Japan, and of the Institute of Electronics, Information andCommunication Engineers and IEEE.

Tadanori Mizuno received the BE degree in Industrial Engineering from the Nagoya Instituteof Technology in 1968 and received the PhD degree in computer science from KyushuUniversity, Japan, in 1987. In 1968, he joined Mitsubishi Electric Corp. Since 1993, he isa Professor of Faculty of Engineering, Shizuoka University, Japan. He moved to the Faculty ofInformation, Shizuoka University in 1995. His research interests include mobile computing,distributed computing, computer networks, and protocol engineering. He is a member of theInformation Processing Society of Japan, the Institute of Electronics, Information and Com-munication Engineers, the IEEE Computer Society and ACM.



multiple paths protocol for a cluster type network

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