What are the asynchronous protocols in data link layer?

What are the asynchronous protocols in data link layer?

Asynchronous protocols of a layer of linkage of information treat every character in a bits flow independently. They have developed a variety of asynchronous protocols. Some of the most important are going to discuss:

XMODEM
YMODEM
ZMODEM
BLAST
KERMIT

XMODEM

It is a protocol of simple transference of files used to transfer files from a PC to another of asynchronous communication. It is a Protocol of modem developed in 1978, which transmits the information in blocks of 128 bytes of correction of errors.

There are two more versions of the Protocol of transference of files XMODEM. One, XMODEM 1 K transmits information in blocks of 1 kilobyte and uses one more crosscheck.

Another XMODEM-CRC incorporates a crosscheck of cyclical redundancy of 2 bytes to detect transmission errors.

YMODEM

YMODEM is a change of the Protocol of transference of files XMODEM. It divides the information in blocks, where every block consists of the character of a beginning of heading, a number of blocks, 1 kilobyte of information and a sum of crosscheck.

Also it incorporates the aptitude to send several files in the same meeting (session) and ring finger the operation of transference of files by means of the transmission of two can (Cancel) characters in a line.

ZMODEM

ZMODEM is a protocol error for correction modes. It is a more recent protocol and it combines the characteristics of XMODEM and YMODEM.

Modems that in accordance with the protocol ZMODEM send information in blocks of 512 bytes. If a block comes and an error is detected, he (she) returns himself a 'NAK' (negative recognition) and the block they suffer.

BLAST

Blast is a lack of asynchronous transmission protocol. It is more powerful than XMODEM. BLAST uses full-duplex operation with blue window flow control. It allows the transfer of information and binaries.

KERMIT

It is used to transfer files between PC and mainframes for line (figure) standard telephone. Detects transmission errors verify each block of information.

Kermit is a protocol of well-known (family) used in numerous packages of software designed for communications phone lines (figures).

The information is transmitted in units of variable length (packages), which are normally up to 96 bytes in length, and checks each packet transmission error.

Control characters are converted into printable characters in the standard ASCII (codes 32 to 126 decimal) and can therefore be transferred without the risk of misinterpretation at the receiving end.