2. Disclaimer:This presentation is prepared by trainees of
baabtra as a part of mentoring program. This is not official
document of baabtra –Mentoring Partner
Baabtra-Mentoring Partner is the mentoring division of baabte System Technologies Pvt .
Ltd
4. Introduction
• Operating System: provide common services to
applications: IO, communication, storage.
• With multiprogramming: include abstracting shared
resource.
• Local Area Network: birth of Network OS to provide
access to network resources.
• We need similar services for Wide Area Network
distributed applications.
4
5. Introduction (cont)
• World Wide Web is the most widely used
applications on the Internet.
• Web made geographically distributed read-only data
easy to use, but geographically distributed
computing resources are not.
• The result is that wide area applications that require
access to remote CPU cycles, memory, or disk must
be programmed in an ad hoc and application-specific
manner.
• =>Increase complexity!
5
6. Introduction (cont)
• WebOS: a framework for supporting applications that
are geographically distributed, highly
available, incrementally scalable, and dynamically
reconfiguring.
• WebOS includes:
– Resource discovery
– A global namespace
– Remote process execution
– Resource management
– Authentication and security
6
7. Resource Discovery
– To provide the best overall system
performance, client applications must be able to
dynamically locate the server able to deliver the
highest quality of service.
– Resource discovery includes mapping a service
name to multiple servers, an algorithm for
balancing load among available servers, and
maintaining enough state to perform fail-over if a
server becomes unavailable.
– These operations are performed through Smart
Clients.
7
8. Wide Area File System
– To support replication and wide-scale
sharing, WebOS provides a cache coherent wide
area file system.
– WebOS extends to wide area applications running
in a secure HTTP name space the same
interface, caching, and performance of existing
distributed file systems.
8
9. Security and Authentication
– To support applications operating across
organizational boundaries, WebOS defines a
model of trust providing both security guarantees
and an interface for authenticating the identity of
principals.
– A key enabling feature is fine-grained control of
capabilities provided to remote processes
executing on behalf of principals.
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10. • WebOS Security model Step 1: users transfer some
portion of their access rights
to webOS server when
attempting to access a
remote resource
Step 2: WebOS servers
communicate using SSL
Step 3: The remote server
checks if the proper
credentials are held in local
ACL’s
11. Process Control
– In WebOS, executing a process on a remote node
should be as simple as the corresponding local
operation.
– The underlying system is responsible for
authenticating the identity of the requester and
determining if the proper access rights are held.
11
12. Global Namespace
• Many applications share state and transfer
control using network communication
• Parallel applications use shared memory or
message passing
• Using frameworks: global cache coherent file
systems for communication and
synchronization
• Requirements: authentication, security and
fault tolerance
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13. Global Namespace
• provides a unified way of mapping multiple
NFS(Network File System is a file sharing protocol
used on Unix systems ) or CIFS(Common Internet File
System is a protocol developed by Microsoft)
presented resources under a single Hierarchical
logical data structure
• allows resources which are not physically located to
participate in this structure
• allow data to be replicated and moved around the
enterprise without compromising data access
13
14. WebOS Applications
• Internet Chat:
- The Internet Chat application is a simple
client and server application.
- The Chat Client stack contains the scripts
for the client, and would be distributed to
each person on the network.
- The Chat Server stack contains the scripts
for the chat server.
14
16. WebOS Applications(cont.)
• Internet Chat(cont.):
- The initial implementation:
+1200 lines of Java code in the client
+4200 lines of C++ code in the server.
- By using WebFS :
+ 850 lines in the client
+ The WebFS interface entirely replaced the
4200 lines of chat server code.
16
17. • Advantages
1 occupies little hard disk space
2 occupy small CPU resources
3 can be obtained at any OS with web browser
• Disadvantages that needs to be improved
1 easy to be hacked
2 can not be obtained offline
3 can not program on the local hardware so USB disk
and CDROM can not be used.
4 more bandwidth is needed for multiple programs to run
simultaneously
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