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•DCE
distributed computing environment
It is defined by the open software
foundation(OSF).
It is an architecture, a set of standard service,
and application programs, built on top of the
existing operating system which hides the
differences among individual computers.
used to support the development and usage of
distributed applications in a single distributed
system. It use client/server model.
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1) can run on many different computers, operating
systems (Unix, Os/2, VMS,windows) and networks
in a distributed system, Provide a coherent
seamless platform for running distributed
applications.
2) Provide a mechanism for synchronizing clocks
on different machines.
3) Provide tools to make it easier to write
distributed applications in which multiple users at
multiple locations can work together.
4)Provide extensive tools for authentication and
access protection
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DCE cell: the basic unit of operation in the DCE.
A cell is a group of users, systems,and
resources that are typically centered around a
common purpose and that share a common
DCE services. It is an administrative domain
that allows users,machines, and resources to
be managed through functions distributed
within the network in which they are in.
Members working on the same project in an
organization are likely belong to the same cell.
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DCE threads
DCE remote procedure call
DCE directory service: cell directory service; global
directory service
DCE distributed time service
DCE security service
Distributed file service
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Thread services;
RPC;
time service;
directory services;
security service.
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DCE thread package: a collection of user-level
library procedures that allow processes to
create,delete, and manipulate threads. multiple
tasks could occur at the same time to complete a
process(work). It is designed to minimize the
impact on the existing software: a single threaded
program can be converted into multithreaded one
by setting parameter indicating that more threads
will be used. All threads in a process share the
same address space, file system, and other process
resources. Each thread has its own program
counter, stack,and registers.
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determines how long a thread may run and which thread
will run next.
Three algorithms:
FIFO: search and locate the priority queue with one or
more threads from highest to lowest, run the first
thread on this queue until finish by blocking or exiting.
Round robin:the scheduler locates the highest
populated queue and runs each thread for a fixed
quantum.
Default algorithm: it uses a time-sliced round-robin
algorithm to run the threads on all queues, the higher
the priority the larger the quantum a thread gets.
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Mutexes: prevent multiple threads from
accessing the same resource at the same time.
Condition variable: it is used with mutexes
to manage synchronization.e.g.: a thread
could use mutexes to gain exclusive access to
a resource, if this resource is not available, the
thread waits on a condition variable that
atomically suspends the threads and releases
the mutexes. Later, when another thread
signals the condition variable, the waiting
thread is restarted.
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DCE is based on the client/server model. RPC package
of DCE allows a client process to call a procedure on a
remote computer. It allows application programmer to
extend the local procedure call to a distributed
environment. The application programmer doesn’t
have to be concerned with the detail of the network
communications between client and server nodes.
RPC hides communication detail and removes system
and hardware dependencies. It can automatically
handle data type conversions between the client and
the server without considering whether they run on
the same or different architecture, or have same or
different byte ordering.
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Provide up-to-date addressing information by
keeping track of where all resources (user,
machine, file, server…) are located. So users
can identify these resources by names and
gain access to them without needing to know
where they are located
It’s distributed service--- the information that
forms database is stored in different places.
A replicated service: the information is
replicated and stored in more than one
location which make it more readily available
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It enables distributed applications on
different computers to determine event
sequencing, duration, and scheduling.
Keeps clocks on separate computers
participating in a distributed system
synchronization.
It uses universal coordinated time(UTC) to
synchronize DCE host’s time.
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Controls interactions between clients and servers.
It allows client and servers to authenticate each
other and perform authenticated RPC.
Offers integrity and privacy of communications
without having password appearing on the network
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Controls access to resources by authorization;
Principal: is a user or process that needs to
communicate securely. It could be a server,
computers, cells or users.
Authentication: is the process of verifying a
principal’s network identity.
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It’s a worldwide distributed file system;
Allows users to access and share files stored on a
file server anywhere on the network without
knowing the physical location of the file;
The physical file system (DCE local file system) is
able to do several tasks: Replicate data; log file
system data, enable quick recovering after a crash;
Simple administration by dividing the file system
into easily managed units; Associate access control
list with files and directory.
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1) The services provided by DCE is much
easier to use than the ones found in other
computer networking environments: i.e.:
the DCE remote procedure call provide a
much simpler way for communicating
between software modules running on
different system than using socket calls.
2) the DCE security service provides a
reliable way to determine if a user in a
distributed system should be allowed to
perform certain action.
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3)supports portability and interoperability
by hiding differences among the various
hardware,software,and networking
elements in a large network.
4) supports distributed file service which
means files present on workstation in a
network are available to this network.