DATA LINK CONTROL PROTOCOLS 2 Introduction  Data link control layer – often abbreviated simply to data link layer – is concerned with the transfer of data over a serial data link  The transmission mode may be either asynchronous or synchronous and based on either a character-oriented or a bit-oriented transmission control protocol  The data link layer is fundamental to the operation of all data communication applications 3 Introduction  Depending on the application, the user service provided by the data link layer may be either a simple best-try (connectionless) service or a reliable (connection-oriented) service 4 Introduction  The connectionless service  means that although error check bits are used to detect errors, any frames that are found to contain transmission errors are simply discarded by the link layer protocol entity.  It is also referred to as an unacknowledged service  Retransmission becomes a function of a higher layer protocol 5 Introduction  The connection-oriented service  Data link protocol employs error and flow control procedures to provide a reliable service  To achieve this, prior to sending any data (information frames), a logical connection between the two data link layer protocol entities is established (using L_Connect service)  All data is transfer using a suitable retransmission and flow control protocol  When all data has been exchanged, the logical connection is clear (using L_Disconnect service) 6 Introduction 7 Application Environments  In some instances the data link protocols are located in the two communicating DTEs, and the protocol is said to operate on an end-to- end basis  In others, data link protocols operates over the local link connecting, for example, the DTE to a network, the protocol is said to have only local significance 8 Application Environments  The data link topology may be  Point-to-point circuit  Direct physical connection  Operates on an end-to-end basis 9 Application Envirionments 10 Application Environments  The data link topology may be  Multipoint or multidrop topology  Single transmission line – known as a bus or data highway – is used to connect all the computer together.  Normally used in applications that involve a single master (supervisory) computer communicating with a distributed community of slave computers [...]... Character-oriented Protocols – Half-duplex Protocols  BSC 25 Character-oriented Protocols – Half-duplex Protocols  BSC 26 Character-oriented Protocols – Half-duplex Protocols  BSC 27 Character-oriented Protocols – Half-duplex Protocols  BSC  Protocol operation 28 Character-oriented Protocols – Half-duplex Protocols  BSC 29 Character-oriented Protocols – Half-duplex Protocols  BSC 30 Character-oriented... Point-to-point data link  Stop and Wait ARQ 16 Character-oriented Protocols – Simplex protocols 17 Character-oriented Protocols – Simplex protocols  Kermit:  Frame format 18 Character-oriented Protocols – Simplex protocols  Kermit:  Frame format 19 Character-oriented Protocols – Simplex protocols  Kermit  Protocol operation 20 Character-oriented Protocols – Half-duplex Protocols  Most character-oriented... Character-oriented Protocols – Half-duplex Protocols  BSC  Protocol performance 31 Character-oriented Protocols – Duplex Protocols  A few character-oriented protocols operate in fullduplex mode  Character-oriented, full duplex protocols  ARPANET 32 Character-oriented Protocols – Duplex Protocols  ARPANET 33 Bit-oriented Protocols  All new data link protocols are bit-oriented protocols  Such protocols. .. Character-oriented Protocols  Simplex protocols  Half-duplex protocols  Full-duplex protocols 14 Character-oriented Protocols – Simplex protocols  Simplest since it allows a simplex – one direction only – transfer of data from one DTE to another  Point-to-point data link topology  The most widely used protocols for this function is Kermit 15 Character-oriented Protocols – Simplex protocols  Kermit:  Synchronous... transmission control characters to signal the start and end of frame – known as frame delimiting 34 Bit-oriented Protocols – HDLC (High-level Data Link Control)  Network configuration  Point-to-point with single primary and secondary  Multipoint with single primary and multiple secondary  Point-to-point with two primaries and two secondaries 35 Bit-oriented Protocols – HDLC (High-level Data Link Control) ... character-oriented protocols operate in the halfduplex, stop and wait mode  The best known is BSC 21 Character-oriented Protocols – Half-duplex Protocols  BSC:  Synchronous transmission  Connection-oriented protocol  Multipoint network/ multidrop bus network 22 Character-oriented Protocols – Half-duplex Protocols  BSC 23 Character-oriented Protocols – Half-duplex Protocols  BSC:  Frame format  Data ... Character-oriented Protocols  Character-oriented protocols   are in use in both point-to-point and multipoint applications Are characterized by the selected transmission control characters used to perform the various transmission control function associated with link management, start of frame and end of frame – frame delimiting, error control and data transparency 13 Character-oriented Protocols . DATA LINK CONTROL PROTOCOLS 2 Introduction  Data link control layer – often abbreviated simply to data link layer – is concerned with the transfer of data over a serial data link  The. (normally)  Point-to-point data link  Stop and Wait ARQ 17 Character-oriented Protocols – Simplex protocols 18 Character-oriented Protocols – Simplex protocols  Kermit:  Frame format 19 Character-oriented. the data link protocols are located in the two communicating DTEs, and the protocol is said to operate on an end-to- end basis  In others, data link protocols operates over the local link