8/2/2019 DS Presentation Ravi Raj
1/15
TOPIC-Naming Entity
Presented byRavi Raj Gupta
09MUBCS034
PRESENTATION
SUBMITTED to-
Mr.Amit BhatiCSE Dept.
8/2/2019 DS Presentation Ravi Raj
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
8/2/2019 DS Presentation Ravi Raj
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
8/2/2019 DS Presentation Ravi Raj
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
8/2/2019 DS Presentation Ravi Raj
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
8/2/2019 DS Presentation Ravi Raj
6/15
General Naming Graph
8/2/2019 DS Presentation Ravi Raj
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
8/2/2019 DS Presentation Ravi Raj
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
8/2/2019 DS Presentation Ravi Raj
9/15
Mounted File System
8/2/2019 DS Presentation Ravi Raj
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
8/2/2019 DS Presentation Ravi Raj
11/15
Global Name Service (GNS)
8/2/2019 DS Presentation Ravi Raj
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
8/2/2019 DS Presentation Ravi Raj
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
8/2/2019 DS Presentation Ravi Raj
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
8/2/2019 DS Presentation Ravi Raj
15/15
Top Related