Glossary and Terminology

This section defines many of the references made throughout the manual. The definitions are simplistic and are meant mainly for those unfamiliar with the references. The Terminology section pertaining to "Parameter Formats" provides details on the formatting expectations of 4D Internet Commands common parameters.

NIC: "Network Information Center". For the most part, the Internet is an unregulated entity. There is no centralized authority or control over its use or growth. However, there are some basic administrative needs such as domain name and IP address assignments that could only be effectively carried out if controlled by a single agency. The NIC is the group responsible for such administrative tasks.

RFC: "Request for Comments." Most of the 4D Internet Commands are based upon standards defined to handle Internet communication. The standard methodologies, descriptions and protocols used throughout the Internet are defined within documents known as RFCs. Appendix D, Additional Information... contains references to some WWW sites with pointers to many of the RFC documents. The 4D Internet Commands package does its best to protect you from a need to reference these documents, though anyone programming their own communications via the low-level TCP routines should become familiar with them.

TCP/IP Addresses, Host Names and Domain Names: An IP address is a reference to a specific machine somewhere out in the world. The IP address is formatted as a string containing four numeric values separated by periods (i.e. "207.94.15.3"). Each numeric part of the address can contain a value between zero and 255. By applying some mathematical functions to an IP address, its value can be squeezed down into an equivalent Long Integer number, which this document will refer to as the ip_LongInt.

In order for a site (i.e. a Company, College, etc.) to put their computers on the Internet, some assurances must be taken that their IP addresses won't conflict with other machines on the network. Institutions (and often individuals) will register their site with the NIC in order to obtain a Domain Name. Domain Names provide a system of easy-to-remember Internet addresses, which can be translated by the Domain Name System (DNS) into the numeric addresses (Internet Protocol [IP] numbers) used by the network. This system allows a more readable format such as "www.4D.com" or "ftp.4D.com".

Domain Name = "4D.com"

The relationship between a Host name and its corresponding IP address is stored in a database known as a DNS (Domain Name System). These servers communicate with one another to exchange any new or changed data in the domain name lists throughout the world. The TCP/IP control panel provides a means to 'point' your computer to a DNS, which will then resolve all domain name references you use.

It is important to understand that all domain name servers have a corresponding IP address. However, not all IP addresses have a corresponding domain name server. Also, a "Mail Address" such as "jsmith@4D.com" does not reference that person's specific computer or IP address. The mail address would direct its delivery to the machine with the IP address represented by resolving the domain "4D.com". The mail would be delivered to the POP3 server running on that machine, which would then hold the mail for its user named "jsmith".

Domain Name: The Domain Name is an addressing construct used for identifying and locating computers on the Internet. Domain names provide a system of easy-to-remember Internet addresses, which can be translated by the Domain Name System (DNS) into the numeric addresses (Internet Protocol [IP] numbers) used by the network. A domain name is hierarchical and often conveys information about the type of entity using the domain name. A domain name is simply a label that represents a domain, which is a subset of the total domain name space. Domain names at the same level of the hierarchy must be unique, for example there can be only one com at the top level of the hierarchy, and only one 4D.com at the next level of the hierarchy. If your organization's name is "CompanyName" you could register the domain name "CompanyName.com" and your e-mail address could be "UserName@CompanyName.com". Your customers would also be able to access your organization's web site by visiting "www.companyName.com" with their Web browser.

Domain Name System (DNS): A distributed database of information that is used to translate domain names, which are easy for humans to remember and use, into Internet Protocol (IP) numbers, which are what computers need to find each other on the Internet. People working on computers around the globe maintain their specific portion of this database, and the data held in each portion of the database is made available to all computers and users on the Internet. The DNS comprises computers, data files, software, and people working together.

Encoding: Encoding converts a file from one format to another so that a file can be moved across different computer systems which may not all support the same character sets. The most common form of encoding is binary-hexadecimal (Binhex) encoding. Binhex encoding is the default encoding option for any attachments that you add to messages. While encoding creates a new file that is larger than the original, it converts the data fork, resource fork, and Finder information into a character file which can easily be sent as an attachment. 4D Internet Commands support the most common encoding methods, including Binhex, Base64, AppleSingle, AppleDouble, UUEncode and MacBinary.

Encryption: Encryption is used to intentionally scramble the contents of messages. Messages are encrypted using an external encryption program such as PGP, for the sole purpose of increasing the privacy of messages. The encrypted text must then be decrypted before it can be read. 4D Internet Commands do NOT provide any means for encrypting text.

Compression: Is used as a means of reducing the space taken up by a file. In order to compress a file, the file must be run through an application such as Stuffit Deluxe™ Compact Pro™ or WinZip™. These files must then be decompressed using the application in order to return the file to its original format. When files are compressed using compression applications, it is common for those applications to append a suffix to the original name of the file. Below are some common suffixes and their respective applications.

Filename.SIT - Stuffit application
Filename.CPT - Compact Pro application
Filename.DD - Disk Doubler application
Filename.ZIP - Winzip application
Filename.SEA - Self Extracting Archive. These files are Macintosh stand-alone applications and will decompress themselves when the user double-clicks on them because application code for decompression is included. Due to the addition of this code, self-extracting archives are generally larger than if the file was created as Filename.SIT or Filename.CPT. However since the user doesn't need to have the compression application, this option may be advantageous to the end user.

It is important to remember that once compressed, a file still needs to be encoded prior to transmission to ensure that the file is properly transferred from machine to machine on its way to its ultimate destination.