Problematic Reviews In Service Selection Computer Science Essay

Published Date: 02 Nov 2017

Mamta Rani Shruti Mishra

Gurgaon Institute of Technology & Management

Abstract: - Service Discovery and Service selection in Mobile Ad Hoc Network (MANET) is challenging because of the absence of any underlying infrastructure. The nodes in a MANET offer spontaneous and variable connectivity. Service discovery uses piggybacking service information in routing messages. The traditional solutions present for the service discovery and their selection in the network are not enough for the users to provide them the services when they are not in their network. So in this paper we will raise some problematic issues that are faced by the users when they are mobile and use the services present in the network. And also we are trying to find the solution of these problems.

Keywords: - MANET, RREQ, RREP, AODV

Introduction

MANET is the major research domains. It is a kind of the network that does not require any infrastructure. Ad hoc networks do not have any fixed topology. The nodes in the network self configure to communicate information beyond their individual transmission range by routing packets over intermediate nodes. Each node can work as a router, client and server which cache the service providers in vicinity. .

Much of the research has been done in static network for discovering a service. The emergence of wireless communications and mobile computing devices has created the need for developing service discovery protocols and architectures targeted to mobile environments. Most important the proliferation of Mobile Ad-Hoc Networks has introduced new requirements to service discovery due to the nature and inherent characteristics of these networks.

Fig. 1Mobile Ad-hoc network

MANET are the ultimate scenarios where the nodes sharing a common stack of lower layer technologies are able to form a temporary communication network in order to facilitate instant networking needs. MANET nodes may have very little or no knowledge at all about the identities and capabilities of each other [1]. In addition, MANETs are characterized by their highly dynamic, multi-hop, and infrastructure-less nature. The dynamic nature arises from the facts that

(i) nodes are free to move,

(ii) the adverse channel conditions of the wireless medium (e.g. multi-path fading, shadowing, interference, collisions, etc.) may be in effect,

(iii) node failures may occur because of the limited energy of the battery-charged devices, and

(iv) nodes may frequently join or leave the network at will.

Basic building block for service discovery protocols for MANETs, is broadcasting. Every node in the network has to broadcast the message about its service. Then the nodes will query about services provided by other entities. The nodes will select the appropriate matched services and then those services will be invoked. In the past all the work done have been presented in the context of node stability but in the case of MANET there are multiple problems that arise which we are going to discuss here.

Despite the existence of a number of survey papers regarding service discovery protocols ([2], [3]) we believe that a comprehensive overview of techniques and open issues for service discovery in MANETs would be useful. It is the purpose of this paper to provide a comprehensive review on the state of the art regarding service discovery approaches for MANETs. In the following we will try to make a categorization of service discovery approaches according to the mechanisms they utilize and their features.

The rest of the paper is organized as follows: Section II contains a brief introduction to AODV. Section III will contain the previous work. Section IV will contain the description of service discovery and service selection. In the last we will present the problems in the service discovery and the proposed solution.

2. AODV

In this section we will give overview how AODV helps to discover the service and how to select the best service among all those provided in the network. This is the protocol based on service location protocol. From the survey of Network Research Group it has been shown that AODV has been obtained from integration of the SLP with the reactive ad hoc routing protocol. After integration, the control overhead and latency required for discovering services has been improved [4]. Since QoS is essential in real-time high-quality applications, has been used QoS-aware service discovery protocol in AODV. All the routing protocols work best in the network layer as the support provided at this layer is the most appropriate service. In AODV, the process of discovering the route is a two step process:-

Route discovery (Fig. 2)

Route Maintenance process.

Following are the features/properties of AODV [7]:

Uses an expanding ring search technique by setting different TTL values each time a RREQ is sent to control flooding of control information in the network.

The usage of HELLO messages makes AODV self-reliant and hence there is no dependence on the link layer to manage connectivity issues.

Both unicasting and multicasting capability in built-in AODV in addition to broadcasting, no additional enhancements required. This makes the protocol attractive for a wide range of applications.

AODV uses symmetric links between neighboring nodes.

Provides loop free routes with the use of sequence numbers.

With some improvements as in [5] [6] AODV can maintain / detect multiple disjoint loop free paths between source and destination.

These two processes help to discover a node by broadcasting messages. Route discovery and route maintenance cycle is followed in the AODV protocol. The throughput of AODV protocol is better than that of other protocols.

Fig. 2 Route Discovery Process

In Fig. 2 suppose when node s wants to create a route to the destination D, Node s will broadcast the RREQ message. Whenever a node wants to transmit a packet to another node, it will broadcast a route request message (RREQ). The neighbor node receiving the message will forward this to the destination node or if this is the destination node then it will reply via a route reply message (RREP). The message will contain reverse path identification in the RREP message. If the link breaks while transferring of the messages then a route error (RERR) message will be sent to the source node. This process can be shown by flowchart (Fig. 3).

Fig. 3 Flowchart for route discovery

AODV is an on demand protocol that will generate the route whenever there is a need by the node to communicate with other nodes. Overhead is reduced by not maintaining the route table all the time. We can use AODV for service selection as AODV can perform better than other protocols in case of node mobility. We can show this by the simulation results in Fig 4.

Fig. 4 Node Mobility vs. throughput

3. Previous Work

Much of the researches have been done on service discovery in [10], [11], [12], [13]. According to this research services can be selected at network layer much faster than that of the services available at network layer. All the researchers are try to provide much faster service at lower bandwidth as MANET is bandwidth constraint. Service selection strategies also have been proposed. In this paper we have define all the problems still remaining in the service discovery and service selection and have proposed some of the solutions which we are trying to implement.

4. Service Discovery and Service selection

4.1 Service Discovery with AODV

We define service as a resource that helps other entities to fulfill their task. And an environment is created with the help of service that is loosely coupled and interoperable. Service discovery (or resource discovery) is an important area. Service discovery provides functionality to automatically discover capabilities and to advertise own capabilities to the network. Using service discovery, users can search for services by name, type or class and utilize those services without any further knowledge about the underlying network architecture.

Fig. 5 Service Discovery Architecture

Whenever a node requires a service, it performs a lookup in its services table, which contains information about services it provides as well as those provided by other nodes. The information about others services are acquired when the node participates in a service discovery process, while the information about the services it offers is set when the node is initialized (or when a new service is initialized within the node). Each row in this table contains the service identifier (a string that uniquely identifies the service), the service port, the protocol used, its IP address, a lifetime, a list of attributes that varies with the type of service, and a URL path. A lifetime is used to keep information up to date, which is mandatory in ad-hoc networks where there are frequent changes in topology Figure 5[8] shows the structure of the services table.

Fig. 5 Services table

AODV is one of the most prominent on-demand routing protocols for MANETs, and based on some ideas sketched by Koodli and Perkins in an Internet draft [9]. Whenever the discovery of services occurs in the network, we will find multiple services and there must be some criteria to select best service among present multiple services. There can be multiple service discovery modes:

Reactive Mode

Proactive Mode

Hybrid Mode

4.2 Service Selection Strategy

Whenever a node finds any of the service in the network, It will compare its service with the available services. If the available service is better than that of its service then it will invoke that service. This invoking can be of two types

User Automated

Automatic

In the former strategy, The user will be completely involved for invoking a service and user will itself decide whether to invoke that service or not. While in the later the selection of service will be automatic and fast too. The overhead will be low for the users. So, now a day’s automatic service invocation is preferred than that of the user automated.

To invoke the best service there must be some criteria. And the previous research has been done in [10] where two strategies have been used for selecting the optimized service. These two strategies are either to select from the number of hop counts or via the remaining energy.

Service selection strategies can be evaluated on the basis of:

Service provider lifetime(Fig. 6)

Number of discovered providers(Fig. 7)

Number of successful service invocation.(Fig. 8)

Fig. 6

Fig. 7

Fig. 8

4. Problems in service discovery and service selection

There are number of problems still remaining in the service discovery and service selection:

Whenever a node is providing a service, there are number of chances of misusing that service. That means if a user has invoked a service we can not stop that user from not using that service that may be a security issue. For example 26/11 can occur again.

Suppose a node S has the service for one user D but the node is mobile so it may happen that whenever S is broadcasting the service D is not present in the network and when node D is coming in the network it will not find those services. So there will be greater loss of the bandwidth.

5. Proposed Solution

There are some solutions of these problems

In the former problem we can provide the users for sending an acknowledgement including their intended use and only to provide those features of our services.

In the second problem we can invoke a random number generator that will broadcast its service randomly so that a node wants to invoke a service can find the service easily.

6. Future Work:

We are trying to implement these solution by using qualnet on AODV based MANET. These will enhance the performance of the network and also the number of invocation of services will be increased by it and the security issue can also be removed by these solutions.