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
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.
1/29/2023
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
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
