Web Protocols

CSC 342 - Web Technologies

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