Tham khảo tài liệu 'kỹ thuật truyền dữ liệu 11', giáo dục - đào tạo, cao đẳng - đại học phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | APTER 11 Data Link Protocols In general the word protocol refers to a set of rules or conventions for executing a particular task. In data communications protocol is used in a narrower sense to mean the set of rules or specifications used to implement one or more layers of the OSI model. We have already encountered the EIA 232-D interface which is a protocol used at the physical layer in the OSI model. A protocol in data communications is the set of rules or specifications used to implement one or more layers of the OSI model. Data link protocols are sets of specifications used to implement the data link layer. To this end they contain rules for line discipline flow control and error handling among others. A data link protocol is a set of specifications used to-implement the data link layer. Data link protocols can be divided into two subgroups asynchronous protocols and synchronous protocols see Figure . Asynchronous protocols treat each character in a bit stream independently. Synchronous protocols take the whole bit stream and chop it into characters of equal size. Figure Data link protocol categories 329 330 CHAPTER 11 DATA LINK PROTOCOLS ASYNCHRONOUS PROTOCOLS A number of asynchronous data link protocols have been developed over the last several decades some of which are shown in Figure . Today these protocols are employed mainly in modems. Due to its inherent slowness stemming from the required additions of start and stop bits and extended spaces between frames asynchronous transmission at this level is being replaced by higher-speed synchronous mechanisms. Figure Asynchronous protocols Asynchronous protocols XMODEMI YMODEmỊ ZMODEMI BLAST I Kermit Others Asynchronous protocols are not complex and are inexpensive to implement. As discussed in Chapter 6 in asynchronous transmission a data unit is transmitted with no timing coordination between sender and receiver. A receiver does not need to know exactly when a data unit is sent it only
