Transcript Wireless Optimization for Java RMI

Middleware for Nomadic
Computing
Stefano Campadello
Presentation Outline
• Nomadic Computing issues
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Communication Issues
Mobility Issues
Device Issues
Security Issues
• Middleware for Distributed Computing
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WAP
Java RMI
Corba
Presentation Outline
• Enhancing the Middleware
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Dolmen
Nomadic RMI
Wireless CORBA
• Conclusions
Nomadic Computing
What’s it?
Nomadic Computing
”The essence of a nomadic environment
is to automatically adjust all aspects of
user’s computing, communications,
and storage functionality in a
transparent and integrated fashion” – L.
Kleinrock, 1997
Anytime, Anywhere
• A user wants to:
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use her laptop during a flight and upload her work once
disembarked
follow financial information independently from the
location and time
instantiate a communication during a disaster recovery
mission
access the Internet or Intranet services while on the
move.
The Challenges in Mobile Computing
Communication Issues
• Low Bandwidth
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sending long files requires long time: the chance of
experiencing network failures is high
a graphical user interface can act in a bizarre way
• High bandwidth variability
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Bandwidth can increase/decrease four orders of magnitude
depending on local conditions (connected/wireless). Ex:
videoconference
• Disconnection
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File system can lock up for a remote server to allow access
After reconnections conflicts are possible
Mobility Issues
• Address Migration
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Physical location != network address
To communicate with a mobile computer is necessary to
know its most recent address
• Location-dependent information
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Some information depend on location, as local printers
or local currency.
In a mobile environment these information cannot be
stored statically and they must be found dynamically
Devices Issues
• Power limitation
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Energy supply is a bottleneck for mobile devices
Bigger batteries => more weight
The user wants long-lasting AND light devices
• User Interface and Display Issues
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Size constrains force to use small user interface
Small display size makes access to remote service difficult
Input devices must be redesign (keyboard -> pen-based
recognition)
Hand-writing and sound recognition
Security Issues
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Identification
Certification
Privacy
Insecure channels
Insecure devices (can be stolen)
...
Middleware for Distributed Computing
Middleware for Distributed Computing
• Remote Procedure Call (RPC)
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1976. Provides communication across a network between
programs written in a high-level language
Using procedure calls mechanism is easier than building a
communication paradigm
It presumes the existence of TCP/IP or UDP
Its use is in decline: not implemented in object oriented
programming languages
• Java RMI
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1998. Same concept implemented in Java.
More later...
Remote Procedure Call (RPC)
Client
program
Service
daemon
Machine B
RPC Call
Invoke
service
Call service
Machine A
Service
executes
RPC returns
requested
completed
return reply
Program
continues
Middleware for Distributed Computing
• Wireless Application Protocol
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Designed for Nomadic devices
It provides Internet access for phones and small PDAs
WAP - Architecture
WAP – Architecture
WAP – Architecture 2.0
Middleware for Distributed Computing
• OMG CORBA
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1989. Provides interoperability between objects in a
heterogeneous, distributed environment
Interfaces specified in OMG IDL
Not suited for wireless networks, since it requires reliable
communication
Not suited for mobile device, since the terminal cannot change
its point-of-presence
• Microsoft COM and DCOM
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COM allows binary interoperability between distributed
objetcs
NOT platform independent and proprietary protocols
OMG CORBA – Architecture
Interface
Repository
Client
IDL
Compiler
OBJ
Implementation
Repository
Object
(Servant)
in args
operation()
REF
out args +
return
IDL
SKEL
DII
ORB CORE
IDL
STUBS
DSI
ORB
INTERFACE
Object Adapter
GIOP/IIOP
Enhancing the Nomadic Layers
Nomadic Computing - Layered
APPLICATIONS
MIDDLEWARE
(IIOP/RMI/ACTIVE-X)
TRANSPORT LAYER
(TCP/IP)
RADIO LINK
Improving Long Thin Networks
• Slow Start and Congesting Avoidance
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the system assumes the network is congested while packets are
dropped for corruption
• Delayed ACKs
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the dimension of the sender’s window depends on the number
of ACKs it receives. Adaptation is slow
• Three-way Handshake
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data transfer is possible only after the handshake is completed.
Long latency makes short transactions unattractive
• Lenght of TCP/IP headers
Improving TCP over Wireless
• Solutions:
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modify or eliminate slow start
Use larger initial windows
Count the data acknowlegde not the number of ACK
Change the spacingbetween ACKs
Compress headers or compress IP payload
SNOOP (Berkeley)
• Split connection approach, but maintaining end-to-end
semantic
• retransmission of lost packets only locally
• suppression of duplicate ACKs from receiver to sender
Improving Client-Server Paradigm
• Satyanarayanan [1996]:
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Extremes of adaptation: laissez-fair and applicationtransparent Improving Client-Server Paradigm
Application-aware
(collaboration)
Laissez-faire
(no system support)
Application-transparent
(no changes to applications)
Enhancing the Communication Layer
• Example: Coda File System
Applications
Mobile
File Server
File
System
APIs
Mobile File System APIs
File System Proxy
Mobile Host
Fixed Network
Mowgli Project
Monads
• Adaptation agents for Nomadic Application.
• The key work is ”prediction” through learning
Addressing the Mobility Issues
• Mobile IP
Enhancing The Middleware Layer
Nomadic RMI
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
Java RMI - Layers
Logical Path
Server Program
Client Program
Skeleton (JDK 1.1)
Stub
Remote Reference Layer
Remote Reference Layer
Transport Layer
The Internet
Transport Layer
Java RMI - Protocol
Server Virtual Machine
Client Virtual Machine
Client
Client Object
Object
Registry
Registry
2
3
Server
Server
1
Remote
Remote Object
Object
6
8
Stub
Stub
5
4
7
Skeleton
Skeleton
Java RMI in a Nutshell
Client
Server
Lookup(): where is Hello?
Registry
Registry
Hello is here
Client
Client
Send the me stub
Stub-server
Server-stub
Here is the stub
DGC messages
invokeMethod()
Stub
“ReturnValue”
Server
Server
Java RMI in a Nutshell
Client
Server
Lookup(): where is Hello?
Registry
Registry
Hello is here
Client
Client
Send the me stub
Stub-server
Server-stub
Here is the stub
DGC messages
invokeMethod()
Stub
“ReturnValue”
Server
Server
“Hello World” Example
Client
TCP 2
Registry
TCP 1
Header
ProtocolAck, EPId
EPId, Lookup()
ServerRef
Header
ProtocolAck, EPId
EPId, dirty()
Lease
Ping
Ping Ack
Parallel
Parallel
DGCAck
Ping
Ping Ack
sayHello()
“Hello World”
...
clean()
clean result
Server
Data traffic analysis
55 (6%)
41 (4%)
831 (85%)
52 (5%)
Server and
Registry to
Client
(bytes)
276 (42%)
37 (6%)
305 (46%)
40 (6%)
331 (20%)
78 (5%)
1136 (69%)
92 (6%)
979 (100%)
658 (100%)
1637 (100%)
Client to Server and
Registry
(bytes)
Registry Lookup
Invocation Data
DGC Data
Protocol
Overhead
Total
Total
(bytes)
RMI Optimization
• Maintain compatibility with Java RMI
specifications
• Avoid redundancy in communication protocol
• Use compression and caching to minimize data
transmission
Java RMI Optimization
• Protocol
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Use of Mediators to minimize the exchange of data
through the wireless link.
• Data Communication
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Optimized Communication: Compress and Optimize data
communication
• Class Loading
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If possible, avoid to download stubs
Protocol Optimization
• The idea is to de-couple the connection between
the client and the server using mediators.
Mobile Node
Access Node
Naming
Client
RMIAgent
RMIProxy
Wireless Link
Optimized RMI
Mobile Node
FakeStub
FakeStubs
Access Node
Registry
Registry
Agent
Agent
Proxy
Proxy
Server
Server
Cache
Cache
Monads
Monads
Registry
Registry
Client
Client
Client
Client
Registry
Registry
Server
Server
Optimized RMI
Mobile Node
FakeStub
FakeStubs
Access Node
Registry
Registry
Agent
Agent
Proxy
Proxy
Server
Server
Cache
Cache
Monads
Monads
Registry
Registry
Client
Client
Client
Client
Registry
Registry
Server
Server
Optimized Remote Invocation
Client
Client
RMI
RMI Agent
Agent
Registry
Registry
RMI
RMI Proxy
Proxy
Header
Protocol
Ack
Lookup()
In cache?
lookup
Lookup()
ServerRef
InternalRef
AgentRef
Header
Protocol
Cache and mark
for sync
dirty()
First?
Lease
Ack
Header
dirty()
count[ref]++
Protocol
Ack
Lease
DGCAck
Header
Protocol
Ack
DGCAck
sayHello ()
sayHello()
sayHello ()
“Hello World”
“Hello World”
“Hello World”
...
clean()
Last?
clean()
clean result
clean result
clean()
clean result
Server
Server
Comparison between RMI and RMI
Java RMI
Optimized
RMI
Improvement
Registry
Invocation
7.1 sec
1.7 sec
Remote
Invocation
1.3 sec
0.6 sec
8.4 sec
2.3 sec
417%
216%
365%
Total
Test Arrangements
• Operating Systems
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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)
Test Arrangements
• Java Virtual Machine
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Sun JDK 1.2.2 (Linux and Windows)
• Wireless communication
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GSM HSCSD (5 configurations)
• Benchmark Suite
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KaRMI from University of Karlsruhe
Lookup Results (windows)
Lookup Differences
Invocation Results
Image Uplink (Linux)
Invocation Results
Two-way Text uplink
Nomadic RMI
• The previous solution does not support mobility
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If the connection between mobile host and RMI Agent is
interrupted the system is in an unstable state
• RMI (Nomadic RMI) Protocol addresses this
problem
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It allows Handover between different access points
Nomadic RMI
Enhancing The Middleware Layer
Wireless CORBA
Issues of CORBA in Nomadic
Environment
• IIOP servers are not expected to change their
transport connection endpoint
• IIOP and the transport connections are supposed
to be reliable
• It is not possible to change network interface
during an IIOP connection
• Connections are expected to enjoy high
bandwidth
Wireless CORBA – Architecture
Home domain
Home
Location
Agent
Terminal
Bridge
Terminal
Domain
Access
Bridge
Access
Bridge
GIOP
tunnel
Visited domain
Access
Bridge
Access
Bridge
wCORBA Framework
• Mobile IOR
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Identifies the terminal on which the target object resides
And its Access Bridge
• Home Location Agent
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Keeps track of the current location of the terminal
• Access Bridge
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End-point of the GIOP tunnel in the network side
• Terminal Bridge
• GIOP tunnel
wCORBA Framework
• Terminal Bridge
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End-point of the GIOP tunnel on the terminal side
• GIOP tunnel
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Is the means to transmit GIOP messages between the
Terminal Bridge and the Access Bridge
Wireless CORBA - GIOP Tunneling
Protocol
CORBA invocations
Object
Object
GIOP messages
GIOP
GTP
GIOP
GTP
msgs
GTP
GTP adaptation layer
GTP adaptation layer
transport
transport
Terminal ORB
Access Bridge ORB
IIOP
TCP
IIOP messages
IIOP
TCP
TCP byte stream
peer ORB
Wireless CORBA – Handoff
old AB
TB
new AB
HLA
start_handoff
HandoffTunnelRequest
transport_address_request
Establishment of transport connectivity
EstablishTunnelRequest
location_upadte
EstablishTunnelReply
ArrivingTerminalNotification
HandoffTunnelReply
handoff_completed
ReleaseTunnelRequest
ReleaseTunnelReply
HandoffNotification
notify other ABs
DepartingTerminalNotification
report_handoff_status