DISTRIBUTED SYSTEMS - NAMING

DISTRIBUTED SYSTEMS - NAMING

1. NAMES - IDENTIFIERS - ADDRESSES

   • A name in a distributed system is a string of bits or characters that is used to refer to an entity. An entity in a distributed system can be practically anything.
   • To operate on an entity, it is necessary to access it, for which we need an access point. An access point is yet another, but special, kind of entity in a distributed system. The name of an access point is called an address.
   • A true identifier is a name that has the following properties
     • An identifier refers to at most one entity.
     • Each entity is referred to by at most one identifier.
     • An identifier always refers to the same entity

2. FLAT NAMING

   • identifiers are simply random bit strings, which we conveniently refer to as unstructured, or flat names
     • SIMPLE SOLUTIONS
       • Broadcasting
         • Consider a distributed system built on a computer network that offers efficient broadcasting facilities
       • Forwarding pointers
         • Another popular approach to locating mobile entities is to make use of forwarding pointers
           • when an entity moves from A to B, it leaves behind in A a reference to its new location at B.
     • Home-based approaches
       • A popular approach to supporting mobile entities in large-scale networks is to introduce a home location, which keeps track of the current location of an entity.
         • The home-based approach is used as a fall-back mechanism for location services based on forwarding pointers. Another example where the homebased approach is followed is in Mobile IP

3. STRUCTURED NAMING

   • naming systems generally support structured names that are composed from simple, human-readable names.
     • NAME SPACES
       • Name spaces for structured names can be represented as a labeled, directed graph with two types of nodes.
     • NAME RESOLUTION
       • More generally, given a path name, it should be possible to look up any information stored in the node referred to by that name. The process of looking up a name is called name resolution
     • THE DNS NAME SPACE
       • The DNS name space is hierarchically organized as a rooted tree. A label is a case-insensitive string made up of alphanumeric characters. A label has a maximum length of 63 characters; the length of a complete path name is restricted to 255 characters

4. Attribute-based naming

   • There are many ways in which descriptions can be provided, but a popular one in distributed systems is to describe an entity in terms of (attribute, value) pairs, generally referred to as attribute-based naming.
     • DIRECTORY SERVICES
       • Attribute-based naming systems are also known as directory services, whereas systems that support structured naming are generally called naming systems.
     • Hierarchical implementations: LDAP
       • This approach has been widely adopted, for example, in Microsoft’s Active Directory service and other systems
       • Many of these systems use, or rely on the lightweight directory access protocol commonly referred simply as LDAP. The LDAP directory service has been derived from OSI’s X.500 directory service.

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