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Lesson 11 Uniform Resource Locator
ObjectiveDescribe the Functions, Components, and Types of URLs.

Uniform Resource Locator

A URL, or Uniform Resource Locator, specifies a unique address to a resource on the Internet. A resource can be a specific Web page, a document, or an image. URLs are occasionally called URIs, or Uniform Resource Identifiers.

Parts of a URL

Delimiters separate the parts of a URL address. The first part of a URL indicates which protocol to use; the second part specifies where the resource is located.

The Parts of a URL
you will learn about the definition of each part of the URL in the diagram below.

Difference between a URL and a Domain Name

This can be a confusing point, but it is an important one. In a nutshell, using the Internet address, the Domain Name is, everything to the right of the
The URL is everything including the You will be asked many times in your future for just the domain when registering or searching for domains. Other times, you will be asked for the full URL. It is important to understand the difference between these terms.

Internet Security

Components url Parts

Types of URLs

A URL describes the location of a specific file on a specific computer connected to the Internet. There are three types of URLs based on where the files are located relative to the document. The table below describes the types of URLs and their general syntax.

Type Description Syntax
  1. Address expressed relative to the originating document
  2. Easy to move set of documents if the positions of the document relate to each other remain constant
  3. Best used when files are related to one another and kept in proximity
Local absolute
  1. Start at a fixed point and specify a fixed path to the file from that point
  2. Best used for most links in which documents reside on the same server
Fully qualified absolute
  1. Defines the entire URL
  2. Easiest to move
  3. Best used when different servers are required
  4. Must be changed whenever the server name changes

Software Defined Networks
In addition to the functions of URLs discussed so far, there are other uses for URLs.

Port numbers

There are two kinds of ports on a computer, hardware and software ports. Hardware ports identify a particular device. Software ports identify the first instruction of a program used to handle common routines, such as a modem request. Ports are identified by a number (possibly hexidecimal, so they may also contain letters).
You may recall in our URL MouseOver above, that software port numbers identify the sending and receiving application. Over the years, a PC or Macintosh have software ports that are typically assigned values of 256 or less. Ports numbered from 256 to1024 are assigned to services developed as part of the UNIX operating system. The table below identifies the port numbers for common Internet services. Recalling the port number in our MouseOver as 80, what service does this designate?

Internet Services and their Port Numbers

Service Port Number
File Transfer Protocol 21
Telnet 23
(SMTP) Simple Mail Transfer Protocol 25
Gopher 70
Finger 79
HTTP: Hypertext Trasnfer Protocol 80
Network News Transfer Protocol 119
Secure Hypertext Transfer Protocol 443
MS SQL Server 1443

Internet Services Port Numbers

Click the link below to review what you have learned about port numbers related to common Internet services.
Internet Services Port Numbers

TCP/IP Guide