Protocols

Q-Link via Cougar Courier
 
There are many different types of file transfer protocols .  The two most popular used by Commodore systems are Punter and XModem .  So far , Punter file transfers are Commodore specific and only systems run on a Commodore computer can have it available .  XModem is pretty much universal and should be available on most BBS ' s no matter what type of computer it is run on . 

Other file tranfer protocols include XModem , CRC , YModem , Kermits , Rainbow , ASCII and a few others .  Even though they all have different names , they all accomplish the same thing .  They are designed to allow one computer to send a file to another computer . 

The main difference between all the various file transfer protocols is how the program checks for errors during the actual file transfer .  When a file is sent over the phone lines , it is sent in ' packets ' or ' blocks '.  Each packet or block contains a specific number of bytes .  As each block is sent one or more extra bytes are added to the block .  These extra bytes are put in to allow the receiving computer to verify the fact that it received a ' good ' block .  Things such as line noise , weak connections or improper timing can cause a bad ' block ' to be received . 

The receiving computer then tells the transmitting computer that it received a ' good ' block or ' bad ' block .  If the block is good , the transmitting computer sends the next block .  If it ' s ' bad ' it re - transmits the previous block . 

It ' s possible that the receiving computer could tell the transmitting computer that it received a ' good ' block when it actually got a ' bad ' block .  That would mean that the file may not work at all or that it may have serious bugs in it .  That ' s why there are so many different file transfer protocols available .  As time goes on , programmers add better error checking routines thereby making the protocol more reliable . 

At the present time , to the best of my knowledge , no protocol available to the Commodore world has an error checking routine better than Punter .  When calling long distance or under adverse phone line conditions , Punter is the best protocol to use .  Most BBS ' s and terminal programs also have the ability to shorten the number of bytes in a block when using Punter .  This is especially handy when trying to transfer files when conditions are not the best .  Shortening the size of the block means that error checking is done more frequently and makes the transfer more reliable .