1. Jini Tutorial, Part 2
Jini Overview

2. Tutorial outline Part 1 Introduction Part 2 Overview of Jini Part 3
Distributed systems
Java basics
Remote Method Invocation (RMI)
Part 2 Overview of Jini
Goals
Architecture
Basic concepts, protocols
Part 3
Jini Programming
Part 4 Advanced topics
Mobile Jini access
Adaptive user interfaces
Security

3. Why Jini?
Distributed computing is more difficult than local computing because of:
Network latency,
Concurrency issues,
Memory management,
Partial failure.

4. Jini goals Jini™ Network Technology by Sun Microsystems “Plug-and-use”
A device should instantly usable when plugged into the network, just like a phone set – no installation, etc should be required
Reliable service-based architecture
Spontaneous networking based on discovery and mobile code
Self-healing
Erase the distinction between hardware and software (everything is a service)
Protocol-independence
To make writing distributed programs easier.

5. Properties Based on the Java programming language.
Homogeneous network
Architecture independence
Dynamic environment
Programming interfaces designed for robustness.
Services may come and go without administration.
Federation, not central control.
Jini can be used with both hardware as well as software services:
Everything is represented by Java Objects.
Everything is located and accessed through Java Interfaces.

6. Tutorial outline Part 1 Introduction Part 2 Overview of Jini Part 3
Distributed systems
Java basics
Remote Method Invocation (RMI)
Part 2 Overview of Jini
Goals
Architecture
Basic concepts, protocols
Part 3
Jini Programming
Part 4 Advanced topics
Mobile Jini access
Adaptive user interfaces
Security

7. Key participants Service Client Lookup Service
A service is an entity that another program, service or user can use. It can be a piece of computation, a hardware device or software.
Client
A Jini device or component that becomes the member of the federation in order to use a Jini service.
Lookup Service
The central element of a Jini federation. The lookup service (also known as the service locator or service registrar) keeps track of the services offered in the federation.
Repository of available services.
Stores each service as Java objects.
Clients download services on demand.

8. Basic terms Spontaneous networking Federation Discovery Leasing
Communication is established dynamically without installing drivers and carrying out manual configuration
Federation
A set of software components and devices creating a distributed system that are part of a Jini network at a given time.
Discovery
The mechanism used to locate lookup services in order to advertise a new service in the network or find a service for use.
Leasing
Jini services grant resource usage in a time-based manner. If the period of the grant (lease) is not renewed before its expiration, the grant will be withdrawn at the end of the period.
Distributed event
Components of a Jini system can notify each other when some change in their state occurs.
Transaction

9. Jini Technologies

10. Jini Architecture Jini Network services Applications JavaSpaces
Other services
Network
services
Lookup
Jini
Discovery/Join
RMI
Java
Java
Java
Solaris
Solaris
Solaris
Mac
Windows
SPARC
PowerPC
x86

11. Jini Extends the Java Platform

12. Jini Operation The fundamental behaviour is defined by three protocols
Discovery – how to locate the Lookup Service
Join – how to register with the LS and export services
Lookup – how to find suitable services
Main operation steps
Services export their services (in the form of Java objects)
Clients locate services and download objects or execution
Client-Service interaction (formation of a federation) is governed by need

13. Jini Operation (cont’d)
Lookup services are dynamically discovered by clients and services
Services register service proxies in JLUSs
Clients lookup and download service proxies from discovered JLUSs by interface and/ or attributes
Lookup Service A
Lookup Service B
Jini Service
backend
service proxy
ServiceItem
ServiceID serviceID
Object service
Entry[] attributeSets
Jini Client
template

14. The notion of groups Group Aut Group IRT Group KNT LUS 3: Aut
LUS 1: IRT
LUS 5: IRT, KNT
LUS 6: Aut, KNT
LUS 4: Aut
LUS 2: IRT

15. Tutorial outline Part 1 Introduction Part 2 Overview of Jini Part 3
Distributed systems
Java basics
Remote Method Invocation (RMI)
Part 2 Overview of Jini
Goals
Architecture
Basic concepts, protocols
Part 3
Jini Programming
Part 4 Advanced topics
Mobile Jini access
Adaptive user interfaces
Security

16. The discovery protocol
Two forms of discovery
Multicast, using UDP multicast
Finding services at unknown but multicast-reach locations using group names
Unicast, using TCP/IP
Finding services at known locations
URL: jini://hostname:port/
Forms
Client discovery
At startup; problem with latecomer services
Service announcement
At startup; problem with latecomer clients

17. Multicast discovery protocol

18. Multicast announcement protocol

19. Unicast discovery protocol

20. Join protocol (services)
Wait randomly at startup
Up to 15 sec
Perform unicast discovery with known LUSs
If groups ≠{} perform multicast for given groups
Register with discovered and/or announced LUSs
Perform periodic lease renewal
On connection failure
Re-register with persistent LUSs
Forget multicast discovered ones, wait for announcement
Making changes
Attribute change with all registered LUSs
Register/unregister with specific LUSs
Join/leave groups
If a service is asked to join a group, it adds the name of that group to the persistent set of groups to join and either starts or continues to perform multicast discovery using this augmented group.
If the service is requested to leave a group, the steps are a little more complex:
1. It removes that group from the persistent set of groups to join.
2. It removes all lookup services that match only that group in the set of groups it is interested in from the set it has discovered using multicast discovery, and unregisters from those lookup services.
3. It either continues to perform multicast discovery with the reduced set of groups or, if the set has been reduced to empty, ceases multicast discovery.

21. Lookup protocol Client creates template Sends template to LUS
Describes the type of service sought after
Sends template to LUS
LUS performs template matching
LUS returns result
1 or more ServiceItem objects

22. Matching Strict matching Match if Using marshalled objects
Comparing fields
Match if
A) identical serviceIDs (tmpl can be null) and
B) item service is instance of every tmpl service types and
C) item attributes contain at least one match for each attribute in tmpl
ServiceID
Set of service interfaces
Set of attribute objects
ServiceTemplate
ServiceID
Object implementing interfaces
Set of attribute objects
ServiceItem

23.       Examples 2 null Template 1 null Template 2 1 Printer
Location(VE,IRT) PrinterProp(15,colour)
Service
null
Fax
Template 3 
null
Printer
Template 4 
null
Printer
Location(VE,KNT)
Template 5 2
Printer
Location(VE,IRT) PrinterProp(null, colour)
Template 6  

24. Leasing Problem Traditional solution: system administration:
Partial failure in distributed systems can lead to unchecked resource consumption.
Traditional solution: system administration:
Error-prone,
Costly,
Only happens when it is too late.

25. What are Leases? Time-based grants of resources or services.
Provides a method of managing resources in an environment where network failures can, and do, occur
Loose contracts between grantor and holder.
Negotiated for a set period of time.
Can be shared or exclusive.

26. Distributed events in Jini
Enables Java event model to work in a distributed network.
Register interest, receive notification.
Allows for use of event managers.
Can use numerous distributed delivery models:
Push, pull, filter...
Uses leasing protocol.

27. Transaction model in Jini
Designed for distributed object coordination: light weight, object-oriented.
Supports:
Nested transactions;
Various levels of ACID properties (Atomicity, Consistency, Isolation, Durability).
Uses leasing protocol.
Implemented in Transaction Manager service – another Jini service (mahalo).

28. Nested Transactions

29. More Information The Jini Specification Home pages Online tutorials
Online tutorials
pandonia.canberra.edu.au/java/jini/tutorial/ Jini.xml
ch04.html
notes/index.html

30. Books (not all)