1. Distributed computing environment
By:
Manish Bhardwaj

2. Distributed Computing Environment (DCE)
Introduction
Originally developed by Open Software Foundation (OSF), which is now called The Open Group (
Provides a set of tools and services which simplify and support the development and operation of distributed applications
an example of “middleware”
a layer of software that sits on top of the host operating system (e.g., UNIX) and networking services, and provides a single, transparent distributed computing environment
based on the Client/Server Model

3. Why Use DCE?
Harnesses available computing resources
Increases availability
Facilitates collaborative work and minimizes storage limitations
Tracks data and programs that move around
Accommodates heterogeneous data
Helps maintain distributed applications
Helps synchronize events
Protects distributed resources

5. DCE Services

6. DCE Supporting Models
Client/Server Model RPC Model Data Sharing Model Distributed Object Model

7. Application Of DCE
Microsoft DCOM ODBC

8. DCE Architecture Overview

9. Components of DCE Process and Thread
Provides Programming layout for concurrent applicati-ons.
Create and control multiple threads of execution in a single process.
Synchronization to access for global data within an a-pplication .

10. RPC
Provide tools to provide client –Server application.
Provides basis for all communication in DCE.
N/w and Protocol independent.
Secure communication b/n client and server.
Automatically convert data to appropriate format needed by client and servers.

11. DTS
Time Service is provided in synchronization.
Maps time sources from external source to other external destination.

12. Name Services
CDS( cell directory service), GDS( global directory service) and global directory agent (GDA) are there.
Naming is provided uniquely and location transparen--cy is achieved.

13. Security Service
Authentication and authorization to protect system resources against illegitimate access.

14. DFS
Ensures
Location Transparency
High Performance
High availability
Provides file services to clients of other file systems.

15. DCE RPC
the fundamental communications mechanism
allows direct calls to procedures on remote systems as if they were local procedure calls
simplifies the development of distributed applications by eliminating the need to explicitly program the network communications between the client and server
masks differences in data representations on different hardware platforms, allowing distributed programs to work transparently across heterogeneous systems

16. How DCE RPC works ?

17. Binding in RPC
Client must be able to find the server before
making an RPC call.
This can be done by asking the directory service
for the location of the server.
Server should first advertise itself in the directory
by adding its namespace, interfaces implemented, protocols used for communication and location

18. Example for RPC

19. Directory Services
DCE Cell Directory Service (CDS) is the mechanism for logically naming objects within a DCE cell (a group of client and server machines)
Applications identify resources by name, without needing to know where the resources are located
DCE cells can also participate in a worldwide directory service using the DCE Global Directory (GDS), which is based on the X.500 standard, or the Internet-system Domain Name Service (DNS)

20. Distributed Time Service
Problem with clocks in distributed environment DCE/DTS provides synchronized time for users in distributed computing environment Supports event sequencing, duration and scheduling Synchronized with UTC, an international time standard

21. Keeps machine’s local time synchronized by querying the time servers
Time Clerk
Keeps machine’s local time synchronized by querying the time servers
Time Server
Answers the time queries
Could query other time servers
Three different Types
Local Time Server
Global Time server
Courier Time Server

22. DCE/DTS Courier time server synchronizes with a global time server
DTS time format is UTC (an universal standard supported by NIST) – broadcast by a variety of sources

23. Security Service
DCE Security Service provides the mechanisms for writing applications that support secure communications between clients and servers
enables processes on different machines to be certain of one another’s identities (authentication)
allows a server to determine whether a given user is authorized to access a particular resource (authorization)
supports several protection levels for messages as they travel across the network

24. DCE Security Service
Provides trustworthy identification of users, clients,
servers and systems (principles)
Provides integrity and privacy of communications 2
way authentication scheme.
Ensures security by implementing a trusted third party approach based on Kerberos technology

25. Three Co-operative services Registry Service Authentication Service
Manages cell’s security database
Authentication Service
Provides trustworthy identification
Privilege Service
Provides authorization information
Additional Facilities
Access Control List
List of authorized users for a resource
Login Facility
Initializing the user’s security environment

26. Working of DCE/Security service

27. Distrusted File Service
DCE Distributed File Service (DFS) is a high-performance, scalable, secure method for sharing remote files
DFS appears to the user as a local file systems, providing access to files form anywhere in the network for any user, with the same filename used by all (uniform file access)
DFS includes many advanced features not found in traditional distributed file systems, including caching, security, and scalability over wide-area networks

28. DCE Distributed File System
It is a distributed client/server application built over underlying DCE components
Features of DCE/DFS
Uniform File Access
Intracell Location Transparency
Performance
Availability
Integration
Interoperation
Standards – POSIX

29. DFS data is organized at three levels
Files and Directories
FileSets
Aggregates

30. DCE/DFS Components Cache Manager File Exporter Token Manager
Client side of DFS and uses local cache for access
File Exporter
Server side of DFS
Runs on a DFS file server machine
Token Manager
Synchronize access to files by multiple clients by issuing token that carry access rights.
Types of tokens
Data Tokens
Status Tokens
Lock Tokens
Open Tokens

31. Additional File Servers
DCE Local File System
Physical file system provided within DCE for storage of files
More powerful than UNIX file system
Flexible Data Protection through ACL
Ability to replicate, backup and move transparently
Logging for fast recovery after a crash
Additional File Servers
FileSet Server
Basic Overseer Server
Replication Server
Update Server
Backup Server
Fileset Location Server

32. DCE/DFS

33. Distributed Time Service
Provides a way to synchronize the clocks on the different machines in a distributed system
Threads
DCE supports multi-threaded applications
i.e., programs that use “lightweight” processes to perform many actions concurrently
DCE Threads are based on the POSIX threading standard

34. The Domain of the Distributed Environment
DCE Cells
The Domain of the Distributed Environment
DCE can provide scalable computing environment
- Small environment
* two network hosts
* typically consists of a single group of users who
share common goals
- large environment
* a network (or internetworks) of thousands of hosts
* typically consists of a diverse groups of users,
each group having its own goals and pool of shared resources
a cell is the basic unit of operation and administration
a cell is a group of users, hosts, and resources that share common DCE services

35. Distributed Operation in a DCE Cell
Cell Configurations
at a minimum, a cell includes CDS, Security Service and Time Service
Distributed Operation in a DCE Cell

36. DCE Client and Server Software

37. A Simple DCE Cell

38. Cell with DFS and Multiple DCE Clients

39. Cells and Naming
The DCE Directory Service consists of two directory services: CDS & GDS
CDS manages names inside cells
GDS manages names outside cells and between cells
GDS is an implementation of a directory standard known as X.500 Directory Service (XDS)

40. Domain Name Service (DNS)
- another widely used existing global name service
- used primarily as a name service for Internet host names
although DNS is not a part of DCE, support for cells to address each other through DNS is provided
Global Directory Agent (GDA) makes inter-cell communication possible

42. - begins with the … prefix
DCE naming environment supports two kinds of names: Global and Local (cell-relative) names
Global Names
- begins with the … prefix
- can refer to an object within a cell or an object outside of a cell
Example 1 - uses X.500 name for global cell name
Example 2 - uses DNS name for global cell name

43. - do not include a global cell name - begins with the /.: prefix
Local Names
- do not include a global cell name
- begins with the /.: prefix
Example:
/…/C=US/O=XYZ/OU=Portland/subsys/PriceMax/price_server1
/.:/subsys/PriceMax/price_server 1
are equivalent when used within the cell named
/…/C=US/O=XYZ/OU=Portland

44. Junctions
some services connect into the cell by means of specialized CDS entries called “junctions”
contain binding information that enables a client to connect to a server outside the Directory Service (e.g., Security Service, DFS)
Example 1 - Security Service Junction(/.:/sec)
Example 2 - DFS Junction (/.:/fs)

45. DCE RPC
Enhanced version of the HP’s NCS (Network Computing System) RPC
DCE threads allow increased concurrency in servers and clients
supports TCP and UDP transport services
authenticated RPC supported
Interface Definition Language
the service interfaces are defined by DCE IDL
a universal unique identifier (UUID) in the interface distinguishes this interface form any other interface
UUIDs are generated by uuidgen

46. Distributed Application Development Tasks

47. DCE client (runtime library) finds a server using a two-step process
Binding
DCE client (runtime library) finds a server using a two-step process
The client gets the server’s host address from the CDS
The client finds the server process address by searching the host’s endpoint map (which is maintained by RPC daemon, rpcd)
Basic server initialization steps:
Register each interface with the server runtime library
Register protocol sequences that the server will use for RPCs
Advertise the server location to clients
Listen for remote procedure calls

48. Advertising Server Interface

49. Finding a Server

50. More on DCE
More information on DCE can be found from The Open Group (
Free DCE software can be downloaded from (