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Name And Directory Services

Name And Directory Services . Harshal Jhaveri. Outline. Introduction Name services and Directory services Resolution Object attribute and Name structures Name space and Information base References. Introduction.

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Name And Directory Services

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  1. Name And Directory Services Harshal Jhaveri

  2. Outline • Introduction • Name services and Directory services • Resolution • Object attribute and Name structures • Name space and Information base • References

  3. Introduction • What is it? A Name Service is a generic way of describing how a named object can be addressed and subsequently located by using its address.[1] • Why needed? Making a request to a service or accessing an object by means of inter-process communication requires that one must first locate the service or object. • Service? Service are abstractions of objects. They are usually represented by processes with a service access point. • Objects? Object may be users, computers, communication links or other resources such as files. (Chow, Johnson, 1997)

  4. Name services and Directory services • Services and Objects are normally identified by textual names. Alternatively, if names are unknown, service or object entities can be described by using attributes associated with them. • Although services and objects have distinct meanings, their naming issues are similar • Name and Directory services, in a narrow sense are look-up operations. • The terms name service and directory service are often used interchangeably (Chow, Johnson, 1997)

  5. Resolution • Any object entity in a system must be named and located before it can be used. • The operation of locating an object is called a resolution process. • Each object entity has a logical address in the OS and physical location in the network. • Resolution process has two stages • Name resolution – Maps names to address • Address resolution – Maps addresses to routes that show how an object can be physically located. (Chow, Johnson, 1997)

  6. Object Attribute • Object entity is characterized by it attributes • Name resolution has two special object attributes. Name and Address • Name Space – The collection of names which are recognized by a name service, with their corresponding attributes and addresses. (Chow, Johnson, 1997)

  7. Name Structures

  8. Name Space and InformationBase • Using X.500 terminology, the conceptual data model for storing and representing object information is called the Directory Information Base (DIB). • The Directory Service (DS) of the CCITT X.500 standard provides structural and syntactic rules for specifying a DIB in a hierarchical Directory Information Tree (DIT). • A large name space and its corresponding DIT can be decomposed and distributed into naming domains and naming contexts. • Naming contexts are the basic units for distributing the information base to Directory Service Agents (DSAs), which are the servers for the name service. (Chow, Johnson, 1997)

  9. A name resolution process is initiated by a Directory User Agent (DUA), working on behalf of a user process. • The resolution request is sent from one DSA to another until the object is found in the DIT and returned to the DUA. • Whether the resolution scheme is structured and name-based or structure-free and attribute-based, the interaction among DSAs can be in one of the four modes shown in the following figure. (Chow, Johnson, 1997)

  10. References • Randy Chow,Theodore Johnson, “Distributed Operating Systems & Algorithms”, 1998 2. http://en.wikipedia.org/wiki/Flat_memory_model

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