DCE is client/server architecture, defined by the Open Software Foundation (OSF) that provides Open System platform to address the challenges of distributed computing.

DCE is middleware software sandwiched between the application and the operating system layer.

Goals of DCE:

• It should run on different computers, operating systems and networks in a distributed system.
• It should provide a coherent seamless platform for distributed applications.
• It should provide a mechanism for clock synchronization on different machines.
• It should provide tools which make it easier to write distributed applications where multiple users at multiple locations can work together.
• Provide extensive tools for authentication authorization.

DCE architecture:

• DCE cell:

The DCE system is highly scalable.To accommodate such large systems DCE uses the concept of cells. A cell is the basic unit of operation in the DCE which breaks down a large system into smaller, manageable units.

• DCE Components: DCE uses various technologies that form the components such as:

1.Thread package

• It is a package that provides a programming model for building concurrent applications. It is a collection of user-level library procedures that supports the creation, management, and synchronization of multiple threads.
• It was designed to minimize the impact on the existing software that could convert single threaded into multithreaded one.
• Threads facility is not provided by many operating systems and DCE components require threads, hence threads package is included in DCE.

2.Remote procedure call

• A procedure call is a method of implementing the Client/Server Communication.
• The procedure call is translated into network communications by the underlying RPC mechanism.
• In DCE RPC, one or more DCE RPC interfaces are defined using the DCE interface definition language (IDL). Each interface comprises a set of associated RPC calls each with their input and output parameters.
• 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.

3.Name service

The Name service of DCE include

a. Cell Directory Service (CDS):The CDS manages a database of information about the resources in a group of machines called a DCE cell.

b. Global Directory Service (GDS):The Global Directory Service implements an international, standard directory service and provides a global namespace that connects the local DCE cells into one worldwide hierarchy.

c. Global Directory Agent (GDA): The GDA acts as a go-between for cell and global directory services.

4.Distributed file service

• Distributed File service is a worldwide distributed file system which allows users to access and share files stored on a file server anywhere on the network without knowing the physical location of the file.
• It provides characteristics such as high performance, high availability and location transparency and is able to perform tasks like replicating data; log file system data, quick recovery during crash etc.

5.Time service

• The DCE Time Service (DTS) provides synchronized time on the computers.
• It enables distributed applications on different computers to determine event sequencing, duration, and scheduling participating in a Distributed Computing Environment.
• DTS also provides services which return a time range to an application, which compare time ranges from different machines.

6.Scheduling and synchronization

• Scheduling determines how long a thread runs and which thread will run next.
• It uses three algorithms namely FIFO, Round Robin, or the Default algorithm.
• Synchronization prevents multiple threads from accessing the same resource at the same time.

7.Security service

• There are three aspects to DCE security which provide resource protection within a system against illegitimate access. They are:
• Authentication: This identifies that a DCE user or service is allowed to use a particular service.
• Secure communications: Communication over the network can be checked for tampering or encrypted for privacy.
• Authorization: The permission to access the service is given after authorization.
• These are services are provided using Registry Service, Privilege Service, Access Control List (ACL) Facility, and Login Facility etc.

Advantages of DCE

1. Supports portability and interoperability
2. Supports distributed file service