Categories of Data Link Protocols-Cont

ZMODEM •Newer Protocol •Combines features of -    XMODEM and -    YMODEM BLAST o    Blocked Asynchronous Transmission o    More powerful than XMODEM o    Full Duplex o    Sliding Window Flow Control o    Allows transfer of Data and Binary Files KERMIT o    Designed at Columbia University o    Most Widely used Asynchronous Protocol o    File Transfer protocol is similar in operation to XMODEM, with sender waiting for an NAK before it starts TX o    Kermit allows the transmission of control characters as Text Synchronous Protocols Speed of synchronous TX makes it a better choice over Asynchronous T for LAN, MAN and WAN technology Classes of Synchronous Protocols Synchronous Protocols can be divided into two main classes:    Character - Oriented Protocols    Bit - Oriented Protocols Character - Oriented Protocols o    Also called Byte- Oriented Protocol o    These protocols interpret a transmission frame or packet as a succession of characters, each usually composed of one byte o    All control information is in the form of an existing character encoding system Bit - Oriented Protocols These  protocols  interpret  a  transmission  frame  or  packet  as  a  succession  of individual bits, made meaningful by their placement in the frame Control  information  can  be  one  or  multiple  bits  depending  on  the  information embodied in the pattern o    Character -Oriented Protocols are not as efficient as bit - oriented protocols and are seldom used o    They are easy to comprehend and employ the same logic as bit-oriented protocols o    Their study will provide the basis for studying the other data link layer protocols o    In all data link protocols, control information is inserted in the data frame as separate control frames or as addition to existing data frames o    In  character  oriented  protocols,  this  info  is  in  the  form  of  code  words  taken  from existing character sets such as ASCII o    IBN's BSC is the best known character oriented protocol Binary Synchronous Communication (BSC) o    Developed by IBM in 1964 o    Usable in both point-to-point and multiple communications o    It supports half-duplex TX using stop-and-wait ARQ flow control o    Does not support full duplex TX or sliding window protocol