DS Presentation Ravi Raj

8/2/2019 DS Presentation Ravi Raj

1/15

TOPIC-Naming Entity

Presented byRavi Raj Gupta

09MUBCS034

PRESENTATION

SUBMITTED to-

Mr.Amit BhatiCSE Dept.


2/15

Why naming is important?

Names are used to

Share resources

Uniquely identify entities

To refer locations, and so on

Name resolution allows a process toaccess the named entity


3/15

Naming Entities

Name string of characters used to referto an entity

Entity in DS can be anything, e.g., hosts,printers, disks, files, mailboxes, web pages,etc

Access Point To access an entity

Address name of access point

Access points of an entity may change


4/15

Identifier and True Identifiers

We need

single name of entity independent from the address ofthat entity location independent

Identifiers name that uniquely identifies anentity

True Identifier has three properties

Refers to at most one entity

Each entity is referred to by at most one identifier

Never reused

Differentiating point for Address and Identifier


5/15

Name Space

Names in DS are organized into Name Spaces Name Space represented as labeled, directed

graph Leaf node no outgoing edges Directory node number of labeled outgoing

edges Stores directory table containing entries for each

outgoing edge as a pair (edge label, node identifier)

Root Node only outgoing edges PathName sequence of labels

Absolute Path first node in path name is root Relative Path the opposite case


6/15

General Naming Graph


7/15

Name Resolution

The process of looking up a name Closure Mechanism Knowing how and where to start

name resolution

Mounting transparent way for name resolution with

different name spaces Mounted File System letting a directory node store

the identifier of a directory node from a different namespace (foreign name space)

Mount point directory node storing the node

identifier Mounting point directory node in the foreign name

space

Normally the mounting point is root


8/15

Mounted File System

During resolution, mounting point is looked up &resolution proceeds by accessing its directorytable

Mounting requires at least

Name of an access protocol (for communication) Name of the server (resolved to address) Name of mounting point in foreign name space

(resolved to node identifier in foreign NS)

Each of these names needs to be resolved Three names can be represented as URL

nfs://oslab.khu.ac.kr/home/faraz


9/15

Mounted File System


10/15

Global Name Service (GNS)

Another way to merge different name spaces

Mechanism add a new root node and makethe exiting root node its children

Problem Existing names need to be changed. E.g.,

home/faraz people/home/faraz

Expansion is generally hidden from user Has a significant performance overhead when

merging 100s or 1000s of name spaces


11/15

Global Name Service (GNS)


12/15

Implementation of Name Space

For large scale DS, name spaces areorganized hierarchically

Name Spaces are partitioned into three

logical layers Global Layer formed by highest-level

nodes

Administration Layer formed by directorynodes managed within a single organization

Managerial Layer formed by nodes thatmay typically change regularly


13/15

Implementation of Name Space

Item Global Administrational Managerial

Geographical scale of network Worldwide Organization Department

Total number of nodes Few Many Vast numbers

Responsiveness to lookups Seconds Milliseconds Immediate

Update propagation Lazy Immediate Immediate

Number of replicas Many None or few None

Is client-side caching applied? Yes Yes Sometimes


14/15

Implementation of NameResolution Assumptions

No replication of name servers

No client side caching

Each client has access to a local name server

Two possible implementations Iterative Name Resolution

Server will resolve the path name as far as it can, and returneach intermediate result to the client

Recursive Name Resolution A name server passes the result to the next name server

found by it


15/15

DS Presentation Ravi Raj

Documents

Transcript of DS Presentation Ravi Raj