Naming And Directory Services

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Naming And Directory Services

• Geetika Sharma

CSC8320
09/22/2008
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Outline

• Name Directory Services
• Resolution Process
• NameSpace
• Name Structures
• X.500
• Brief History
• Case Studies Latest Technologies

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Why do we need it?

• Making a request to a service or accessing an
  object by means of interprocess communication
  requires that one must first locate the service
  or object. 1
• Service? abstractions of objects.
• Object? users, computers, communication links
  or other resources such as files.

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Name Service or Directory Service

• A Name Service is a generic way of describing how
  a named object can be addressed and subsequently
  located by using its address.1
• E.g. X.500 by CCITT

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Purpose

• Enable user to reference network resources with
  short names instead of real addresses
• Locate object by attributes
• Provide a layer of abstraction so that the
  network resources can be managed independently
  without service interruption
• Added value, such as security, etc.

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Brief History 3

• 1970s a single file HOSTS.TXT stores the IP-name
  mapping of the entire Internet
• Problems?
• Name conflicts
• Server overload (updates, queries, etc.)
• Lots of human effort
• 
  
• Hence, Domain Name System was designed.
• It is a Hierarchical naming system for computers,
  services, or any
• resource participating in the Internet.
  
• ROOT
• com/edu
• 
  yahoo.com/gsu

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Resolution Process1

• Locating an object.
• Name Resolution
• Maps names to addresses.
• Fundamental function of DOS.
• Implemented by one or more name servers.
• Address Resolution Maps logical addresses
• to network routes that show how an object can
• be physically located. (Network Problem!)

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Namespace1

• Object Attributes - Files with a version number
  creation date /User by student id
• We are interested in 2 special attributes
  Name Address.
• A collection of names, recognized by a name
  service, with their corresponding attributes and
  addresses.

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Naming Structures1
Service/Object Attributes Name structures Attribute partitioning
ltarrtibutesgt ltname, attributes, addressgt ltname, type, attributes, addressgt Flat structure Hierarchical structure name-based resolution (white pages) Structure-free attribute-based resolution (yellow pages) Physical ltuser.host.networkgt Organizational ltuser.org.deptgt Functional ltprofessor.csgt
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X.500 A Storage Model

• DIB Directory information base.
• DIT Directory Information Tree.
• Naming domain a sub-name space for which there
  is a single administrative authority for name
  management.
• Naming Context basic units for distributing the
  info base to Directory Service Agents.
• DSA The server for the name service.
• DUA Directory User Agent

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X.500 Cont..
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X.500 Cont..
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Enhancement

• Caching
• Replication

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Case Studies Latest Technologies

• LDAP
• Lightweight Directory Access Protocol is a
• networking protocol for querying and modifying
• directory services running over TCP/IP.2
• PNDS- Personal Naming Directory Service for
  Mobile internet users. 4
• CORBA

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CORBA Name Service5
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CORBA Cont..

• Using the Naming Service6
• To use the Naming Service, you must first write
  the server and client code that finds and/or
  creates the namespace and the objects in the
  namespace. Before running the client and server,
  you must start the Naming Service and tell the
  client and server where to find it.
• STEPS
• The server invokes the bind method to associate a
  logical name with an object reference.
• The Naming Service adds this object
  reference/name binding to its namespace database.
  
• A client application invokes the resolve method
  to obtain an object reference with this name.
• The client uses an object reference to invoke
  methods on the target object.

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References

• Randy Chow,Theodore Johnson, Distributed
  Operating Systems Algorithms, 1998
• http//en.wikipedia.org/wiki/Lightweight_Directory
  _Access_Protocol
• James E Kurose, Keith W.Ross, 2007,Computer
  Networking, 4th Edition.
• Macaire, A. and Carlier, D. 1999. A personal
  naming and directory service for mobile internet
  users. In Proceedings of the USENIX Workshop on
  Smartcard Technology on USENIX Workshop on
  Smartcard Technology (Chicago, Illinois, May 10 -
  11, 1999) http//portal.acm.org/citation.cfm?id12
  67131dlGUIDEcollGUIDE
• CORBA - http//edocs.bea.com/wle/naming/over.htm,
  
• http//java.sun.com/j2se/1.4.2/docs/guide/idl/jidl
  Naming.html

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• THANK YOU

Any Questions?