The document discusses the application layer of the OSI model and domain name system resolution process. It provides details on: 1) The application layer enables users to access network services like file transfer, email, and directory services. 2) Domain name resolution involves a multi-step process where the domain name is queried to root servers, TLD servers, and authoritative name servers to obtain the IP address. 3) HTTP is the protocol for transferring data like text, images, video between servers and clients on the web. It uses request-response messages and status codes to indicate success or errors.

1. Application Layer
Afsana Begum

2. Functions of this layer
 The application layer is responsible for
providing services to the user.
 It enables the user, whether human or
software, to access the network.
 Services Provided are:
 File transfer, access & management
 Mail services
 Directory services

3. Domain
Name
System
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4. IPAddress:
Domain Name Space
Domain Name
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173.194.203.106
https://www.google.com/

5. Domain name space (Hierarchical)
1st step: write www.abc.com, request will go to “resolver”
2nd step: request will go from resolver to root server (13 root
server available), root server reply to resolver
3rd step: request will go from resolver to Generic server/Country
server, (TLD-Top Level Domain) it will reply to resolver
4th step: request will go from resolver to Authoritative server
(crickinfo), Authoritative server will reply to resolver with specific
IP.
5th step: Resolver will go to the specific IP hosted server.
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6. February
2003
slideset 1 -6
Concept: Resolving process &
Cache
Resolver
Question: www.ripe.net
A
www.ripe.net A ?
Caching
forwarder
(recursive)
root-server
www.ripe.net A ?
Ask net server @ X.gtld-servers.net (+ glue)
gtld-server
www.ripe.net A ?
Ask ripe server @ ns.ripe.net (+ glue)
ripe-server
www.ripe.net A ?
192.168.5.10
192.168.5.10
Add to cache

7. HTTP
7
HTTP
O Protocol for transfer of various data
formats between server and client
O Plaintext
O Hypertext
O Images
O Video
O Sound
O Meta-information also transferred

8. HTTP
8
Uniform Resources
O URI
O Uniform Resource Identifier
O Collection of URL’s and URN’s

9. HTTP
Uniform Resources
O URL
O Uniform Resource Locator
O Refers to an existing protocol
O http:, wais:, ftp:, mailto:, gopher:, news:
O Points to a document on a specific server
O URN
O Uniform Resource Name
O Globally unique, persistent identifier
O Independent of location
(For more detail:
https://en.wikipedia.org/wiki/Uniform_Resource
_Name)

10. HTTP
10
URL and HTTP
O All parts of URL, except parameters, used
with http
O Port can be omitted so long as referenced
host is running on port listed in your
/etc/services file
O Usually port 80

11. HTTP
11
Communication
O Server tells client what type of information
is coming before information arrives
O File extensions
O .html .htm
O .txt
O .ps
O .au
O .gif .tiff .jpeg
O .mpeg
O .vrml .wrl
O .java

12. HTTP
12
HTTP 1.0
O Defines request-response conversation
O Server replies with response
O http specifies syntax
O Does not handle network connectivity or
how information is transmitted
O TCP/IP does this

13. HTTP
13
HTTP 1.0
O HTTP request
O Method
O URI
O Protocol version
O Optional other information
O Method [Request URI] HTTP/1.0 <CRLF>

14. HTTP
14
HTTP 1.0
O Method
O Get
O Returns object
O Head
O Returns information about object
O Post
O Sends information to be stored on server or
as input to script

15. HTTP
15
HTTP 1.0
O Method
O Put
O Sends new copy of existing object to server
O Usually not allowed
O Delete
O Deletes object
O Usually not allowed

16. HTTP
16
HTTP 1.0
O Other information
O Authorization
O User password
GET /X/Y/Z.HTML HTTP 1.0
User Agent: Prodigy-WB/1.3e
Accept: text/plain
Accept: text/html
Accept: application/postscript
Accept: image/gif
O Accept: */*

17. HTTP
17
HTTP 1.0
O HTTP response
O Status line
O HTTP-version Status-code Reason
O Status-codes 1xx - Informational
O Reserved for future use

18. HTTP
18
HTTP 1.0
O HTTP response
O Status line
O Status-codes 2xx - Success
O The action was successfully received,
understood, and accepted
O 200 OK
O 201 POST command successful
O 202 Request accepted
O 203 GET or HEAD request fulfilled
O 204 No content

19. HTTP
19
HTTP 1.0
O HTTP response
O Status line
O Status-codes 3xx - Redirection
O Further action must be taken in order to
complete request
O 300 Resource found at multiple
locations
O 301 Resource moved permanently
O 302 Resource moved temporarily
O 304 Resource has not modified (since date)

20. HTTP
20
HTTP 1.0
O HTTP response
O Status line
O Status-codes 4xx - Client error
O The request contains bad syntax or cannot be
fulfilled
O 400 Bad request from client
O 401 Unauthorized request
O 402 Payment required for request
O 403 Resource access forbidden
O 404 Resource not found
O 405 Method not allowed for resource
O 406 Resource type not acceptable