Wireless Java RMI

1
Wireless Java RMI

• Stefano Campadello
• Oskari Koskimies, Kimmo Raatikainen
• Dept. of Computer Science, University of Helsinki
• Heikki Helin
• Sonera Ltd.

2
Monads

• ww.cs.helsinki.fi/research/monads
• Investigating the use of Adaptive Agents for
  Nomadic Users
• Intelligent Mobile Agents
• Partners Nokia (M.P. and R.C.), Sonera and Tekes.

3
Wireless Environments

• Characteristics
• Low bandwidth
• Long and variable delays
• Sudden or unwanted disconnection
• High costs
• connection costs (/sec)
• transmission costs(/byte)

4
Remote Method Invocation

• RMI protocol interface lets Java objects on
  different hosts communicate with each other in a
  transparent way
• Clients can invoke methods of a remote object as
  if they were local methods
• Preserve the object oriented paradigm in
  distributed computing

5
Java RMI in a Nutshell
Client
Server
Registry
Registry
Client
Client
Stub-server
Server-stub
DGC
messages
Server
Server
6
Java RMI in a Nutshell
8.4 Sec!
Client
Server
Registry
Registry
Client
Client
Stub-server
Server-stub
DGC
messages
Server
Server
7
Hello World Example
8
Data traffic analysis
9
RMI Optimization

• Maintain compatibility with Java RMI
  specifications
• Avoid redundancy in communication protocol
• Use compression and caching to minimize data
  transmission

10
Java RMI Optimization

• Protocol
• Use of Mediators to minimize the exchange of data
  through the wireless link.
• Data Communication
• Optimized Communication Compress and Optimize
  data communication
• StubClass Loading
• If possible, avoid to download stubs

11
Protocol Optimization

• The idea is to de-couple the connection between
  the client and the server using mediators.

Wireless Link
12
Optimized RMI
Mobile Node
FakeStub
FakeStubs
Access Node
Registry
Registry
Agent
Agent
Proxy
Proxy
Server
Server
Monads Registry
Monads
Registry
Client
Client
Client
Client
Registry
Registry
Server
Server
13
Optimized RMI
Mobile Node
FakeStub
FakeStubs
Access Node
Registry
Registry
Agent
Agent
Proxy
Proxy
Server
Server
Monads Registry
Monads
Registry
Client
Client
Client
Client
Registry
Registry
Server
Server
14
Optimized Remote Invocation
RMI Agent
Registry
Server
Client
RMI Proxy
RMI Agent
Registry
Server
Client
RMI Proxy
Header
Protocol
Ack
Lookup()
In cache?
lookup
Lookup()
ServerRef
InternalRef
AgentRef
Cache and mark
dirty()
First?
for sync
Header
Lease
Protocol
Ack
Header
dirty()
Protocol
Ack
countref
Lease
DGCAck
Header
Protocol
Ack
DGCAck
sayHello
()
sayHello()
sayHello
()
Hello World
Hello World
Hello World
...
clean()
clean()
Last?
clean()
clean result
clean result
clean result
15
Comparison between Normal RMI and Optimized RMI
16
Test Arrangments

• Operating Systems
• Clients
• Windows98
• Linux (Red Hat 6.1, kernel 2.2.14)
• Server
• Windows NT (SP 6)
• Linux (Red Hat 6.1, kernel 2.2.14)

17
Test Arrangements

• Java Virtual Machine
• Sun JDK 1.2.2 (Linux and Windows)
• Wireless communication
• GSM HSCSD (5 configurations)
• Benchmark Suite
• KaRMI from University of Karlsruhe

18
Lookup Results (windows)
19
Lookup Differences
20
Invocation ResultsImage Uplink (Linux)
21
Invocation Results Two-way Text uplink
22
Conclusions

• Designers cannot just plug-in wireless
  communication to existing solutions
• Wireless issues extend their influence also to
  middleware component and eventually to
  applications
• Solutions are there, just mostly ignored