INTERNET AND ADHOC SERVICE DISCOVERY

BY: NEHA CHAUDHARY

• Mobile ad hoc networks are characterized by their highly

dynamic, multi-hop, and infrastructure-less nature.

• In this dynamic environment, different nodes offering

different services may enter and leave the network at

any time.

• Efficient and timely service discovery is a prerequisite for

good utilization of shared resources on the network.

• Service discovery allows devices to automatically locate

network services with their attributes and to advertise

their own capabilities to the rest of the network.

Challenges in service discovery in MANET

• The first challenge is enabling resource-

constrained, wireless devices to discover

services dynamically.

• The second one is enabling service discovery

in large mobile ad hoc networks.

SERVICE DISCOVERY ARCHITECTURE

CENTRALIZED DIRECTORY ARCHITECTURE

DIRECTORY-LESS ARCHITECTUREDIRECTORY-BASED ARCHITECTURE.

DISTRIBUTED DIRECTORY ARCHITECTURE.

INFRASTRUCTURE-LESS INFRASTRUCTURE-BASED

CENTRALIZED DIRECTORY ARCHITECTURE

1. SLP2. Jini3. Salutation

SERVICE LOCATION PROTOCOL(SLP)

• The Service Location Protocol (SLP) is a service

discovery Protocol that allows computers and other

devices to find services in a local area network without

prior configuration.

• Each service must have a URL that is used to locate the

service. Additionally it may have an unlimited number of

name/value pairs, called attributes.

SLP has two different modes of operation:(1) when a DA is present, it collects all service information

advertised by SAs, and UAs unicast their requests to the

DA.

(2) when there is not a DA, UAs repeatedly multicast the

request. SAs listen for these multicast requests and

unicast responses to the UA.

• SLP provides a flexible and scalable framework for

providing hosts with access to information about the

existence, location, and configuration of networked

services by scope mechanism.

• SLP uses service scope, which is a collection of services

within certain domain, to achieve scalability.

SLP ROLES

• SLP has three different roles for devices.

• User Agents (UA) are devices that search for

services.

• Service Agents (SA) are devices that announce

one or more services.

• Directory Agents (DA) are devices that cache

services.

Client

UA

Service

SA

DA

Service Request(multicast)

Service Reply

Service re

gister

Service ACK

Service reply

Service REQ

Ver Type Len Flags ExtOffset XID LangLen LangSLP Data

8 8 24 16 24 16 16 - -

The SLPv2 packet structure

Jini

•It provides a platform for clients to locate services.

•The purpose of a Jini system is to federate users, devices

and services into a distributed system.

•The notion of a service is the central concept of Jini.

•A service (represented as Java object) is a software entity

providing any kind of computation or controlling a hardware

device.

• Each Jini subsystem contains a set of lookup services

that maintains the dynamic information about services in

network.

• Clients can use Jini lookup services or download java

code to access the services.

SALUTATION

• Salutation is the major cooperation architecture to solve

the problems of service discovery and utilization among

the appliances/equipment in an environment of

widespread connectivity and mobility.

• The Salutation architecture defines an entity called the

Salutation Manager (SLM).

• Functions of SLM• Service registry• Service discovery• Service availability• Service session management

Service location architecture

• Service co-ordinator based architecture• Distributed query based architecture• Hybrid service location architecture

SERVICE CO-ORDINATOR BASED ARCHITECTURE

• In this architecture the node which is better equipped acts as

Service co-ordinator.

• It acts as service collection point

• SCs broadcast their presence in the n/w so that

servers in the neighborhood are aware of the SCs.

• Server register their services and access information with

the SCs

• If advertisement scope is too narrow this will result in

less service registered.(less burden on SC)

• If scope of advertisement is too wide it results in more

control traffic because more servers replying to SCs.

• Validity of the SCs over time and space is reflected by

frequency of advertisement send by SCs.

• Updation of the list of the services is reflected by

frequency of the registration by server

DISTRIBUTED QUERY BASED ARCHITECTURE

• No service coordinator

• Client broadcast the service query to the neighbours.

• Server that receive the query will send the directed reply

• The success of service search depend on the scope of

the broadcast and also the percentage and location

distribution of server in the network

Hybrid service location architecture

• It improves the service availability by using distributed

approach

• And improves the scalability by using SC based scheme.

• Service availability defines how many service query

request made by client can be fulfilled by SCs or server

in the network.