Steven A. Ridder wrote: > > Just so I make sure I'm not lost, a bit-sync. protocol is one > that has > predefined fields that signify SOF/delimiters/protocol type > (like Ethernet) > and a bi-sync. protocol does not? It just sends characters, > and after a > predetermined number of bytes have been sent receives an ack of > some sort > (L2). Do bi-synch protocols have fields?
My personal opinion is that it is easier to contrast character-oriented protocols to bit-synchronous protocols rather than vice versa. Predefined characters in c-o protocols convey meaningful information (again the ACK is a good example that is intuitive for most people. Priscilla also provided a thorough list of others relative to PPP). They are historically half-duplex. One device sends a block of information and then specific, pre-defined characters are exchanged regarding the status of that block transfer. Just FYI: I think bi-synch was actually an IBM proprietary term/protocol that became synonomous with c-o. B-s protocol devices are "bit-aware" and require no character-level synchronization. They are first of all bit-synchronized amongst themselves and then secondly frame syncronized. This frame synchronization is achieved on bit boundaries. I used the DS-1 frame as an example earlier. That is a fixed length frame. I think it might be helpful to consider that there are variable lenght frame technologies out there as well. Bit patterns (embedded or in-band to the data flow) help devices keep track of where things start and where things end. Contrast this to some End of Text (EOT) or End of Frame (EOF) character being sent out of band from the data flow itself (start-stop if you will). Frankly, Priscilla opened my mind to the possibilty that I understand most of the fundamental concepts but that I had never given enough careful consideration to each individuals protocols status as b-s or c-o. So I'll leave it to her to address specific protocols. > > If a L2 protocols sends acks, does that make it a bi-synch > protocol? > > So, wouldn't PPP still be a bit-sync. protocol because of the > fields it does > have fields (address, control, etc,.)? Or am I confused. You have to read Priscilla's earlier post carefully to see the nuances that allow ppp to fall under the c-o category. Regards, Scott Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=34770&t=34629 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
