Naming And Directory Services Geetika Sharma 09/22/200 8 CSC8320

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

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.

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

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

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

Resolution Process [1] Locating an object. Name Resolution o Maps names to addresses. o Fundamental function of DOS. o 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!)

Namespace [1] 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.

Naming Structures [1] Service/Object Attributes Name structuresAttribute partitioning Flat structure Hierarchical structure name-based resolution (white pages) Structure-free attribute-based resolution (yellow pages) Physical Organizational Functional

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

X.500 Cont..

Enhancement Caching Replication

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

CORBAName Service [5]

CORBA Cont.. Using the Naming Service [6] 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.

References 1. Randy Chow,Theodore Johnson, “Distributed Operating Systems & Algorithms”, ccess_Protocol ccess_Protocol 3. James E Kurose, Keith W.Ross, 2007,Computer Networking, 4 th Edition. 4. Macaire, A. and Carlier, D 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 , 1999) IDE&coll=GUIDE IDE&coll=GUIDE 5. CORBA ming.html

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