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.