INTEREST BASED GROUP MANAGEMENT MECHANISMS

FOR E-LEARNING DESIGN USING THE PEER-TO-PEER

TECHNOLOGIES

Surya Bahadur Kathayat

Information and Communication Technology(ICT) Program, Asian Institute of Technology (AIT), Thailand

Nandana Rajatheva

Telecommunication(TC) Program, Asian Institute of Technology (AIT), Thailand

Keywords: Application Layer Multicasting, e-Learning, Group Management, Peer-to-Peer (P2P) Technologies.

Abstract: Traditional client-server based e-Learning architecture has many limitations. There is the overhead in a

single learning server and inefficient use of resources. There is a lack of real-time interactive ness among

learning group members therefore learning is not effective. There is also difficulty in the collaborative work

because learners may have different interest, may feel lonely and may leave the system as well.

Synchronous, any time and any where, and interactive e-Learning architecture where every learner in the

learning group can contribute their resources like in traditional class-room based system, is the requirement

of next generation e-Learning architecture. In this paper we purpose novel mechanisms for next generation

e-Learning architecture using alternative technologies, peer-to-peer technologies. The proposed framework

is based on P2P architecture for scalability, robustness, efficient sharing of resources and interactivity.

Purposed system also incorporate efficient and reliable interest based e-Learning grouping and management

mechanisms in the top of application layer. Such Interest based interactive P2P based group management

mechanisms for e-Learning will combine the tools that are already available, independent of the installed

infrastructure and offer a great deal of potential for workgroup collaboration, communities of practice, and

self-directed learning.

1 BACKGROUND

Various forms of e-Learning that have been

deployed so far are based on client-server

technology where learning management server plays

a key role providing contents, connectivity and

services to the members of the learning system, as

shown in figure 1. Though client-server system in

the e-Learning is easy to implement and cost

beneficial there is wastage of resources in the

system, less interactive and collaborative besides the

possibility of single point overhead and failure.

Peer-to-Peer (Nowell et al, 2002), though is not a

new technology, however only recently has been

exploited throughout the Music and entertainment

industry especially sharing content files (Lee et al.,

2002) containing audio, video, data or anything in

digital format, and real-time data. As the peers in the

Peer-to-Peer computer network relies on the

computing power and bandwidth of the participants

in the network rather than concentrating these in a

relatively few servers, P2P technology will also help

many of the limitations of the traditional e-learning

system.

Basic motive of this work is that P2P, in concept,

can also be a natural tool for educators allowing the

Figure 1: Traditional e-Learning Model.

339

Bahadur Kathayat S. and Rajatheva N. (2006).

INTEREST BASED GROUP MANAGEMENT MECHANISMS FOR E-LEARNING DESIGN USING THE PEER-TO-PEER TECHNOLOGIES.

In Proceedings of WEBIST 2006 - Second International Conference on Web Information Systems and Technologies - Society, e-Business and

e-Government / e-Learning, pages 339-346

DOI: 10.5220/0001241603390346

 SciTePress

group collaboration, management and sharing of

resources for a constructivist approach to the

learning. One scenario of such motive is briefly

explained as below. In the traditional e-Learning

system, single learning management server is

responsible for handling large number of users

which limits the problem of scalability, overhead,

and inefficient use of resources. Besides that the

interest of the different learner may be different and

so that it is very difficult to do a collaborative work.

If there is lack of collaboration then a user may feel

lonely and there is chance of leaving the system and

hence the effectiveness of the learning system will

be significantly reduced. These limitations are

inevitable even if it is assumed that if there is only a

single common interest group, like learners of a

single class room, in the client-server based e-

Learning system. Therefore it is interesting to group

the users of e-Learning system according to their

interest and apply decentralized P2P technology

within and among such groups. This approach will

result better resource utilization because every peer

can contribute their resources and more interactive

ness because each peer can communicate in two

ways either group mode via overlay multicasting or

peer mode with other peer.

There are many users in the realistic large

learning domain and we assume that these users

represent the node or peer in the overlay network

(Zhang and Hu, 2003). Different peers may have

different interest so peers having common interest

will be organized together to form a group. There

will be two possibilities; either the peer may join the

already existing group or peer may create its own

group and other peers may join it later. So there will

be two categories of the users in the group creators

or leaders and the normal users. For simplicity, if we

assume that learning will be done by chatting (not

limited to this) then interactive e-learning scenario in

such particular case will be as follows:

First the creator, say c1, will create a group

according to its interest, say computer network, and

seeking for the other interested peers. If other peer,

say p1, in the overlay network also have the same

interest in the computer network, it will first find out

the creator ‘c1’ and then pop-up chat window will

appear for the learning by chatting. Similarly if other

peers having same interest may find the group and

join the group learning process. As shown in the

Figure 2, there will be many possible cases. Most

likely case is that one peer may have more than one

interest and would like to participate in on the

multiple groups. For example peer ‘p1’ may have

common interest in the computer network and it is

already the member of the group ‘g1’, peer p1 may

also have interest in the database design so it may

wish to join the database group, say g2, (at the same

time) and get involved in the learning process.

Another likely case will be that there will be

more than one groups having nearly common

interest and either members or groups leaders may

wish to merge these groups. It is also interesting to

consider peer in a particular group may leave the

group and or may wish to create another group

having different interest than that of the current

group and advertise its group members.

Briefly, framework of P2P groups’ management

mechanisms (interest based group formation,

efficient group communication and groups

management) will be proposed (potential use in

collaborative learning) to incorporate interactive

ness among the members, allow the efficient use of

resources reducing the overhead in the server and

single point of failure, and add scalability,

decentralization and many more.

Rest of the paper is organized as below. Section

2 describes the statement of the problem and section

3 discusses about the objective and scope of this

work. Section 4 explains briefly about the related

literature on the P2P technology and grouping

mechanisms. Finally section 5 of this paper

discusses about the proposed system. Peer-to-Peer

interest based grouping mechanism, efficient data

delivery mechanism and management mechanisms,

and learning environment model are also included in

last section.

2 PROBLEM STATEMENT

Existing Client-Server (C/S) based e-Learning

systems are facing many problems like inefficient

use of resources, single point overhead and failure,

limited interaction among the members, scalability

etc. With these limitations, C/S based e-Learning

could not be significant alternative to the traditional

classroom-based learning. P2P technology, which is

a hot technology recently for the online music and

file sharing, has potential applications on the e-

Learning as well. However, to date, there is very

limited use of P2P in the e-Learning. From

instructors’ point of view, it is challenging and

interesting to create interest based group, sub-group

formation, and merging groups having similar

interest. From the students’ point of view, the

challenge is to join into the group having specific

interest and to get the multiple group membership.

Common challenge for both is to efficiently

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distribute messages to other members.

To the best knowledge there are no existing e-

Learning models for the collaborative learning using

the structured P2P network especially for interest

based group formation, for merging of two groups

having nearly similar common interests and also

group splitting or sub-grouping if the interest among

the members of the group are in conflict. Therefore

it is interesting to the design a semi-decentralized e-

Learning framework that will provide efficient and

more effective, collaborative and synchronous

learning environment.

3 OBJECTIVES AND SCOPE

The major objectives of this research is to purposing

a design of the group management mechanism for

structured P2P network which will incorporate

virtual ring interest based group formation, multi-

virtual ring based data delivery mechanism, and

group merging and group splitting.

This work focuses on more fundamental issues

like peer organization, group communication and

fundamental management issues for the

collaborative synchronous e-Learning. Peer

organization includes basically group formation

based on an efficient multicast group ring; joining

nodes, leaving nodes in the group are also handled

with ring repair mechanism. Data forwarding will be

based on the multi-virtual multicast-ring (multi-

unicast and unicast based) and group leader plays an

important role for the group communication. The

potential scope of proposed mechanisms or

algorithms is that these can be suitably applied for

the synchronous, effective, and collaborative e-

Learning system.

4 RELATED LITERATURES

4.1 P2p Technology

According to (Rowstronand and Druschel, 2001),

P2P is a network architecture in which nodes are

relatively equal, in the sense that each node is in

principle capable of performing each of the

functions necessary to support the network. In

(Pandurangan, 2001), P2P systems are defined as the

distributed systems without any centralized control

or hierarchical organization. The software running at

each node is equivalent in functionality.

There are three types of well-defined P2P

architectures namely pure, hybrid and hierarchical

architectures. In pure P2P architecture (Schollmeier,

2002), all functions and all relevant digital objects

are distributed across many nodes, such that no node

is critical to the network's operation and hence no

node can exercise control over the network.

Flooding and document routing algorithms are used

for peer search and resource discovery in this P2P

architecture. An example of pure P2P architecture is

original Gnutella. In hybrid architecture, index is

centralized like C/S system, therefore peers first

contact the central peer to locate other peers and

shared resources. Example of hybrid architecture is

Napster (Thilliez et al., 2003) where the index is

accessed in client-server mode, whereas the digital

objects are transferred directly among peers. In

hierarchical architecture, index is hierarchically

structured and accordingly hierarchy of normal peers

and super peers are maintained.

GRID computing architecture also seems like

P2P but there are some differences. Grid computing

is a means whereby available processing resources

can be located, used and coordinated; whereas P2P

encompasses both processing and data resources.

Grid computing also differs from P2P in that it is

largely pragmatic engineering effort, rather than

scientifically designed architecture (Zhuge, 2005).

4.2 Grouping Mechanisms in P2P

Distribute hash tables (Eastlake and Jones, 2001; Sit

and Morris, 2002) are the core for the routing in the

P2P networks. Major structured P2P protocols are

Pastry (Zhang and Hu, 2003), Tapestry (Zhao et al.,

2004), Chord (Stoica et al., 2001), CAN (Ratnasamy

et al., 2001) etc. All of them take, as input, a key

and, in response, route a message to the node

responsible for that key. The keys are strings of

digits of some length. Nodes have identifiers, taken

Group

Members

Group

Figure 2: P2P Group Formations.

INTEREST BASED GROUP MANAGEMENT MECHANISMS FOR E-LEARNING DESIGN USING THE

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from the same space as the keys (i.e. same number

of digits). Each node maintains a routing table

consisting of a small subset of nodes in the system.

When a node receives a query for a key for which it

is not responsible, the node routes the query to the

neighbor node that makes the most “progress”

towards resolving the query. The notion of progress

differs from algorithm to algorithm, but in general it

is defined in terms of some distance between the

identifier of the current node and the identifier of the

queried key. Some group multicasting algorithms are

pastry based SCRIBE (Castro and

Rowstron, 2002)

which is a reverse-path forwarding tree based

publish/subscribe System, Tapestry based Bayeux

(Zhao et al., 2001) which uses forward-path

forwarding tree, and Brog (Zhang and Hu, 2003)

which uses the same concept but the multicast is

formed by the hybrid approach i.e. reverse path and

forward path tree approach. Controlled and directed

flooding concepts are also used for the mini-CAN

and CHORD multicasting (Ratnasamy et al., 2001).

In distributed environment (Plaxton et al., 1997)

group multicasting can be done either by mesh or

multicast tree or ring. Mesh strategy provides more

than one path between the group members and in

tree case a single path is established between any

pair of nodes. It is also feasible to apply a mesh first

followed by tree construction algorithm to

implement overlay multicast. Mesh provides routing

stability and QoS but Tree approach have

advantages in terms of link stress, no routing loops

and simplicity. Traditional tree approaches use root

based approaches for forwarding the messages

which is well suited for the 1-to-m multicast. If the

sender desires to send the message to the multicast

group, it sends the message to the root which in turn

forwards the message along the tree to all receivers.

Network efficiency can be improved by using a

source based tree algorithms in which each source

builds an optimal tree from the source to all

receivers in the group. However this approach

introduces more overload as each node must run the

routing algorithm and must maintain large amount of

supporting information. So there are different

alternatives for the overlay multicast protocols and

existing initiatives tends to focus on the specific

optimization parameters for the targeted application

environment. Most Tree based approaches are

proposed and implemented in the structured P2P

overlay that has lower data delivery percentage with

no back up path to each member (as in ring

topology) but provide lower path stretch or link

stresses.

5 PROPOSED SYSTEM

5.1 Technological Infrastructure

Both instructors and students in the e-Learning, like

in the class room based learning, construct their own

domain and it is at least somewhat different from

others. These are self organizing and towards

decentralization. Recent technological developments

on the self-organizing and decentralized P2P

network substrate, like Pastry (Zhang and Hu, 2003),

Tapestry (

Zhao et al., 2004), CHORD (Stoica et al.,

2001), and CAN (Ratnasamy et al., 2001), point to a

new paradigm for research and for building

distributed applications. Each of these overlays

implements a scalable, fault-tolerant distributed hash

table for node ID, object ID representation and also

for limiting the number of routing hops to locate

them. So the new platform for e-Learning will be

designed on such substrates where each instructor

and/or learner node ID (based on IP address) and

their class or group IDs (Based on Group Name) is

uniquely obtained and uniformly distributed using

the SHA-1 (Sit and Morris, 2002) hash function.

Every node is identified by m-bits on the overlay

network. All the nodes that are the members of all

the particular groups will be the nodes in the

common domain. Interest based groups like classes

and common domain is like university where there

are many mini-domains.

5.2 Peer Organization in Group

Here, Ring Based Group formation over the overlay

network is proposed, such mechanisms to the best of

knowledge, in structured P2P network, are not

proposed and implemented yet. Main limitation of

the ring based multicast group is the routing delay,

but node degree is constant and they are suitable for

secure, reliable and ordered delivery of messages,

and effective against single node failure. If the

routing delay is reduced in the ring topology, then it

will be suitable for more cases, therefore a similar

group formation mechanism (virtually multi-ring

group multicast) is proposed here. Groups are

assumed to be a medium sized classes having 10 -

100 peers and the group ID will determine or

represent the group’s interest.

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5.2.1 Group Formation Mechanism

One node, having sufficient resources like

bandwidth (BW), CPU, memory etc and willing to

contribute more resources, can create a group

specifying its interest in the structured P2P substrate

and wait for other nodes. Other nodes will join

according to their own interest; the virtual ring

topology will be maintained in the overlay network.

If any node wants to join the pre-existing ring, it will

request a found first peer (bootstrap node) on the

ring and the peer on the ring replies to the requesting

node and forward the request towards the root i.e.

leader of the group. After getting an

acknowledgement from the leader, bootstrap node

will reply to the requesting node along with its

neighbor information (IP address, other existing

group information) so that requesting node can join

the ring. Then all these nodes (bootstrap node,

neighboring node and requesting node) will update

the neighbor list and the leader will update group

information. Group Leader will send periodic live

signal, root information, number of nodes in the

system. When the particular node leaves the group,

then neighbor nodes will know about it from the

regular neighbor update information and accordingly

maintain their new neighbor list and inform to the

group leader to maintain updated correct group

information.

5.2.2 Efficient Data Delivery Mechanism

Each learning peer will contain more than one (say

√N/2) successor and predecessor list, so virtually

there will be more than one ring (say √N/2 rings) for

multicasting the group message. Each peer will get

N (number of nodes in the group) from the group

information circulated by the instructor (root node).

Each node will also issue special request signal

(node address, SUB-COUNT) in each direction to

maintain neighbor list. The initial setting for SUB-

COUNT value is √N/2. When the ring node get that

special request signal, there will be two possibilities

at the node, (i) node will reply (node address) to the

requester if SUB-COUNT is greater than zero and

then forward that request signal by decrementing the

Figure 3: Group Ring and virtual multi-ring.

INTEREST BASED GROUP MANAGEMENT MECHANISMS FOR E-LEARNING DESIGN USING THE

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343

SUB-COUNT value by 1, (ii) node will discard and

terminate the special request signal if SUB-COUNT

is equal to or less than zero.

Root node can control and manage the token for

ordered data-delivery within the group. Each node

willing to send data has to send data to all of its

neighbors (say √N/2) using the multi-unicast

mechanism, other peers will forward the message to

the highest successor/predecessor (formation of

multiple virtual rings). Each node in the group can

forward message to the original ring and

corresponding virtual ring. This mechanism will also

reduce the overhead in the node and routing delay

(in terms of hops) at most will be improved by √N/2

times than normal ring which can be mathematically

expanded as

i. Source node can send data to

number of

nodes in once in both direction of ring.

ii. Since

nodes get message in one hop, 1

node will get message in average

hop

(unitary method) with reference to the original

ring.

iii.

nodes (half of the nodes in symmetrical

ring) will get message in

N Hops

iv. Without multiple-virtual mechanism,

nodes in the ring will get message in

hops.

v. Therefore routing delay improved will be

improved as

times

As an example shown in the Figure 3, there are

16 nodes in a ring i.e. in a group. According to the

proposed data delivery mechanism, there will be

√16/2 = 2 virtual-rings in the group ring. The routing

delay will be improved (optimum case) by 2 times.

Similarly if there are 100 nodes in the system, there

will be 5 virtual rings within the group ring and

routing delay will be reduced by 5 times. Besides

reducing the routing delay, concept of the virtual

ring will be useful as the backup link to the normal

ring in the case of the failure of the particular node

in the normal ring. Each node will keep the source

information and maximum sequence number of the

packet that it received from that source. Each node

will then forward the received packet if that packet

is not already received from the corresponding

source; otherwise it simply discards. Suppose at time

t, node ‘3’ get the packet ‘n’ from node ‘1’ in one

hop using virtual ring. At time t’ (t’ > t), if node ‘3’

get the same packet from node ‘2’, node ‘3’ will

simply ignore it which is shown by thick line in

Figure 3.

5.2.3 Group Merging and Splitting

As the interest of the peer or the learner may change

from time to time, it should be able to participate in

different groups having corresponding interests

accordingly, so group merging and splitting have

significant importance in the e-Learning.

For the sub-grouping, a peer having different

interest than the current group first create a new

group and deliver the message to the existing group

members so that interested peers join it later. This

sub-grouping is not be limited to the existing group

members; rather other group peers having same

interest may join the newly formed group. After

negotiation between the two group leaders, leader

for the newly formed common group is selected and

that manages the groups.

For the group merging, there are different

possible cases such as (i) one particular peer may be

the member of two groups and may know that two

groups are engaging in the similar activities, it will

then inform its leaders and two leaders can

communicate and exchange the information to

merge the group (ii) one leader may be the member

of the another group and these two can share the

information to merge the group.

5.3 Implementation Model

Learners are in application layers, internet based

overlay network. Each user run the standalone

application software (P2P software developed using

Jdk1.4.2) specifying its interests. Learners may have

different interests and there may be more than one

learner in the system having common interest. A

peer first tries to find out the existing groups with its

interest and if such groups are not found it creates a

new group (we assume that group creator have

sufficient resources) and wait for other peers to join

it. Once there are two or more members in the

group, they communicate with each other and

discussion goes on (currently only messaging). Also

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in different cases as mentioned in the earlier section,

two groups can merge together and be involved in

the collaborative learning.

6 PRELIMINARY RESULTS

Experiments are going on parallel in two different

scenarios. First is the deployment of these

algorithms in the Internet. Using the FreePastry-

1.4.2 structured peer-to-peer platform, algorithms

are implemented (some in implementing phase)

varying the control variable (SUBCOUNT) to

control the number virtual rings. The results shown

in Figure 4 are some results with data measured

using 10 nodes (physically in the same laboratory) in

the internet and running the developed software on

each. Software is written in Java Jdk-1.4.2 version.

These preliminary results clearly show that there is

significant reduction in the delay in MVRing case

compared to RING case i.e. amount of time to

multicast the message in the group. Now,

experiments are towards increasing the number of

nodes to 100s of numbers and physically from

different locations.

Besides that we are conducting research to

calculate the node stress on each nodes and link

stress between the nodes, fault tolerance of the

proposed data delivery mechanism to compare its

efficiency with that of existing tree based group

communication mechanisms.

Second scenario of the experiment we are

conducting is the modeling of the internet in transit-

stub topology using GT-ITM topology generator and

simulating the performance evaluation of the

proposed algorithms using Network Simulator (NS-

2). In this case the nodes in the group are chosen

randomly and hence it is obviously not necessary

that neighbor node is the nearest node in terms of

time. Results as shown in Figure 4 show the latency

profile for the scenarios first where P2P code is run

on 10 machines and RING and MVRING algorithms

are compared with exactly implemented SCRIBE.

Figure 5 shows the result of second scenario. The

average latency that each node experience from its

predecessor in the case of the multiple-virtual ring

cases is about 2000 ms, 1700ms and 1500ms for

number of nodes (n) 50, 150 and 500 respectively,

while these values are 2600ms, 2700ms and 2900ms

in case of pure ring based grouping and data delivery

mechanism.

From the results in Figure 4 and Figure 5, it is

shown that nodes clear that latency in case of the

MVRing is significantly improved than in the RING

case and quite better compared to SCRIBE as well.

Experiments are going on to measure node stress,

link stress, fault tolerance of systems and efficiency

of the data delivery mechanisms.

7 CONCLUSIONS

Decentralization addresses the overhead in a

particular machine and all members of the learning

group can share resources among each other.

Grouping of the learners according to their interest

in P2P technology increases interactive ness and

effective collaboration in the e-learning system. The

virtual multi-ring based data delivery mechanism for

the application layer group multicasting adds the

reliable communication among group members.

Finally, the instructors and learners having variable

interest with time can be handled by the interest

based group merging and group splitting.

500

1000

1500

2000

2500

3000

50 150 500

Nodes

Avg latency

Mvring

Ring

Average Latency Profile

100

120

140

160

180

s1 s2 s3 s4 s5 s6 s7 s8

Scribe

Ring

Mvring

Figure 4: Average Latency profile. Figure 5: Latency Profile for n=50,150,500.

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