notes Web Protocols

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Protocols

A communication Standard so that computers can transfer data and instructions accurately.

Network Layers

There are 4 (in this course) Network layers each have different protocols and are responsible for parts of data transmission.

Application Layer

Many protocols

HTTP Hypertext Transfer Protocol used for web communication
FTP File Transfer Protocol used for transferring files
POP/IMAP/SMTP Email protocols for transferring and storing email
DNS Domain name service for resolving domain names to IP addresses

HTTP

An Application Protocol for hypermedia information

standard response request

Development by Internet Engineering Task Force (IETF) and World Wide Web Consortium (W3C)

Transport Layer

Ensures Transmissions arrive in order an without error

Internet Layer

Establishes connection, routing and addressing

IPV4
IPV6 An IP address is needed by every computer on the internet

IPV4

Uses 4x8-bit numbers so 4,294,967,296 addresses they are now gone.

Reserved Addresses

127.0.0.1 - LocalHost (the computer itself)

192.168.*.* - Private Networks

10.0.*.* - Private Networks

There are other reserved addresses

NAT Network Address Translation

Used in part to overcome the shortage of IPV4 addresses

A device connects to a router
The router opens a port and
The router connects to the external resource
Data is passed through the router to the device

The port number is added to the end of an Ip address e.g 213.31.218.101:5001 is port 5001 at address 213.31.218.101

A single IP address is need for the router all of the internal computers use one of the reserved addresses for private networks

IPV6

Uses 8x16-bit numbers 340 undecillion numbers (a lot)

Link Layer

Responsible for transmission of raw bits *MAC

Domain Name

DNS Domain Name system acts an a contact list for servers

Translates Human readable Name to IP addresses

Hierarchical distributed naming system

The Domain Name is Linked to an IP address, e.g www.google.com would be given an ip address that can be used to communicate with the servers

can be broken down

Server1. - Fourth level
www. - Third-Level
FunCode. - Second Level
com - Top-Level Domain (TLD)

Server1.www.FunCode.com

A tree of domain Names are created.

Root Zone (TLD) is controlled by the Internet Assigned Numbers Authority (IANA)

Different registrars assign domain names beneath this

Registrars check with interNIC for the names

Domain names are case insensitive

Resolving A Domain Name

Default Base

When connecting to a network the computer is given a DNS server (root)

When Resolving a domain name

The computer asks the root server
The root server provides the top level domain
The top level domain which provides a sub domain server
Repeat until the address is found

Caching

The previous steps are extensive so DNS caching is used.

The computer points to a caching server
The caching server checks if it has the address in memory
- If it does return the memory
- If not perform the other steps
Any requests are saved to memory for next time.

DNS records have a TTL (time to live) which dictates how ling they are valid for

URL

http://www.FunCode.com/index.php?page=17#article

ftp://example.com/abc.txt -> sends an FTP request on port 21 http://example.com/abc.txt -> sends an HTTP request on port 80

No guarantee of a response

Path

A request requests a file the path specifies the file

/ is the root folder for the webserver

if a file is not specified one is usually selected usually index.html

path is case sensitive

Query String :

SEE GET

Fragment

Requests a portion of a page.

Browser will usually jump to the location in the page

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