Web Protocols

The Internet Protocol Suite

The Internet protocol suite is conceptually divided into four layers:
- Link layer: physical connectivity
- Internet Layer: network-to-network
- Transport Layer: host-to-host
- Application Layer: process-to-process

Web Specific Protocols

Internet Layer:
- Internet Protocol (IP)
Transport Layer:
- Transmission Control Protocol (TCP)
Application Layer:
- Domain Name System (DNS)
- Hypertext Transfer Protocol (HTTP)
- Transport Layer Security (TLS)

Internet Protocol (IP)

The Internet Protocol (IP) performs two basic functions:
- Host addressing and identification
- Packet routing
IP packets may be lost, duplicated, or arrive out-of-order

Transmission Control Protocol (TCP)

The Transmissions Control Protocol (TCP) provides a reliable communication mechanism on top of IP
The main points of TCP data transfer:
- ordered data
- retransmission of lost packets
- error-free data transfer
- flow control
- congestion control

Domain Name System (DNS)

The Domain Name System (DNS) maps internet domain names to IP addresses
A domain name locates an entity on the internet using a human-readable name
The IP address of a domain name is retrieved by querying a DNS name server
- If the name is inside the server’s domain, then an authoritative response is returned
- If the name is outside the server’s domain, then the request is made to another DNS name server or a cached response is returned

Hypertext Transfer Protocol (HTTP)

HTTP is a request-response protocol in the client-server computing model
Form of a request:
- Request line: [request method] [resource] HTTP/1.1
- request header fields
- empty line
- optional message body
Form of a response:
- Response line: HTTP/1.1 [status code] [reason message]
- response header fields
- empty line
- optional message body

HTTP Example

Request:

GET /index.html HTTP/1.1
Host: www.example.com

Response:

HTTP/1.1 200 OK
Content-Type: text/html; charset=UTF-8
Content-Length: 79
<html>
<head><title>Title</title></head>
<body><h1>Example</h1></body>
</html

HTTP Request Methods

GET: requests a representation of the specified resource
HEAD: requests a representation of the specified resource without the message body
POST: requests that the server accept the data in the message body
PUT: requests that the server store the data in the message body under the specified URI
DELETE: requests that the server delete the resource
TRACE: echoes the received request
OPTIONS: returns the HTTP methods that the server supports for the specified URI
CONNECT: converts the request to a TCP/IP tunnel
PATCH: requests a partial modification to a resource

Uniform Resource Locator (URL)

scheme:[//user:password@]host[:port]][/]path[?query][#fragment]

scheme: e.g. http, ftp, mailto, file
authority:
- authentication: user name and password
- host: name or IP address
- port
path: contains data source
query: contains attribute-value pairs
fragment: contains fragment identifier providing direction to a secondary source