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Communication Protocol Definitions
 

Asynchronous Protocols

Asynchronous communications requires start and stop bits be present around every byte of data transmitted in order to maintain synchronization. Although this requires more overhead and is thus 'slower', it is inexpensive and easy to setup. Common async protocols supported Kermit, XMODEM, and ZMODEM.

Xmodem

Xmodem is one of the most widely available asynchronous file transfer protocols over serial lines (e.g. between modems). Although Xmodem is a relatively simple protocol, it is fairly effective at detecting errors by sending data in 128-byte blocks allowing the receiver to request retransmission of a corrupted packet.

Zmodem

Zmodem protocol is improvement to Xmodem that provides faster transfer rates and better error handling. Unlike Xmodem, Zmodem does not wait for positive acknowledgement after each block is sent, but rather sends blocks in rapid succession.

Kermit

Kermit is an accurate, flexible, and customizable asynchronous communication protocol developed by the Kermit Project at Columbia University for the purpose of transferring text and binary files without errors over telephone lines. It includes terminal emulation. Due to its limited packet size it is very inefficient by today's standards.

UUCP

Abbreviation for Unix-to-Unix Copy. It uses a group of commands, programs, and files, present on most UNIX systems (uucp, aux, uucico, uustat, and uuname) to exchange data with another system over a variety of methods like modems and TCP/IP networks.

Synchronous protocols

Synchronous communications uses a 'clock' to maintain synchronization, resulting in less overhead and greater throughput. However, this requires more sophisticated equipment, making it more costly to implement. Common synchronous protocols supported BISYNC and SDLC/SNA.

Bisync

Bit-Synchronous (or Bisync for short) protocol is a method of data transmission used on synchronous serial connections, usually modems. It is typically character oriented and half-duplex. A half-duplex channel is one that can carry information in both directions, but not at the same time. It operates with EBCDIC or ASCII character sets. It requires that every message be acknowledged (ACK) or negatively acknowledged (NACK).

SNA

SNA (Systems Network Architecture) it's a proprietary IBM communications protocol, connection-oriented, and virtual circuit network architecture for interchanging data in a sort-and-forward fashion.

Internet

AS1

AS1 (Applicability Statement 1) is a specification or standard for communications to securely exchange data and documents in any form over the Internet using email/SMTP (Simple Mail Transfer Protocol) and SMIME (Secure Multi-Purpose Internet Mail Extensions). Security, authentication, and integrity are assured by the use of encryption and digital signatures. Another important feature is non-repudiation, which makes it impossible for the recipient to deny having received it.

AS2

AS2 (Applicability Statement 2) is an extension of the earlier version AS1. It defines ways to securely exchange data and documents in any form over the Internet using HTTP (Hypertext Transfer Protocol) and SMIME (Secure Multi-Purpose Internet Mail Extensions). Security, authentication, and integrity are assured by the use of encryption and digital signatures. Another important feature is non-repudiation, which makes it impossible for the recipient to deny having received it.

FTP

FTP (File Transfer Protocol) is a specification or standard for sending files from one computer to another on TCP/IP networks such as the Internet. It uses two separate connections using two different TCP/IP ports. Control Connection act as a regular telnet session and is used to exchange commands and replies. Data Connection is a full duplex connection over which data is transferred.

Email

Email sort for electronic mail is a method of composing, sending and receiving messages across a network. It usually uses SMTP (Simple Mail Transfer Protocol) to relay messages from the original client to server and from server to server until it reaches the final SMTP server where it can be retrieved. The 2 most common protocols used to retrieve data from an email server are POP (Post Office Protocol) and IMAP (Internet Message Access Protocol).

MQSeries

MQSeries also known as WebSphere MQ is an IBM proprietary message queuing protocol and provides more facilities than a communications protocol, like queues, publish facilities, and guaranteed delivery.