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Data Link Protocols Asynchronous Protocols Synchronous Protocols Character-Oriented Protocols Bit-Oriented Protocols

Data Link Protocols Asynchronous Protocols Synchronous Protocols –Character-Oriented Protocols –Bit-Oriented Protocols

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Page 1: Data Link Protocols Asynchronous Protocols Synchronous Protocols –Character-Oriented Protocols –Bit-Oriented Protocols

Data Link Protocols• Asynchronous Protocols

• Synchronous Protocols– Character-Oriented Protocols– Bit-Oriented Protocols

Page 2: Data Link Protocols Asynchronous Protocols Synchronous Protocols –Character-Oriented Protocols –Bit-Oriented Protocols

Data Link Protocol Categories

A protocol in data communications is the set of rules or specifications used to implement one or more layers of 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 protocol is a set of specifications used to implement the data link layerData link protocol is a set of specifications used to implement the data link layer

Page 3: Data Link Protocols Asynchronous Protocols Synchronous Protocols –Character-Oriented Protocols –Bit-Oriented Protocols

Asynchronous protocols- treat each character in a bit stream independently - use start and stop bits to frame the data units- inexpensive- used primarily in modems

Synchronous protocols- take the whole bit stream and chop it into characters

of equal size- faster than asynchronous transmission

Data Link Protocol Categories

Page 4: Data Link Protocols Asynchronous Protocols Synchronous Protocols –Character-Oriented Protocols –Bit-Oriented Protocols

Asynchronous Protocols

Page 5: Data Link Protocols Asynchronous Protocols Synchronous Protocols –Character-Oriented Protocols –Bit-Oriented Protocols

XMODEM Frame

- half-duplex stop-and-wait ARQ protocol- half-duplex stop-and-wait ARQ protocol

SOH –Start of Header (1 byte)CRC - Cyclic Redundancy CheckSOH –Start of Header (1 byte)CRC - Cyclic Redundancy Check

Signal from receiver side - ACK - NAK - CAN (cancel)

Signal from receiver side - ACK - NAK - CAN (cancel)

Page 6: Data Link Protocols Asynchronous Protocols Synchronous Protocols –Character-Oriented Protocols –Bit-Oriented Protocols

• YMODEM– similar to XMODEM– Major differences

• Data unit = 1024 bytes• CANs = 2• Multiple files can be sent simultaneously

• ZMODEM– Combining features of both XMODEM and YMODEM

• BLAST (Blocked asynchronous transmission)– More powerful than XMODEM.– Full-duplex

• KERMIT– Most widely used asynchronous protocol

Page 7: Data Link Protocols Asynchronous Protocols Synchronous Protocols –Character-Oriented Protocols –Bit-Oriented Protocols

Synchronous Protocols

Character-oriented protocols (or byte-oriented protocols)- the frame or packet is interpreted as a series of characters

Character-oriented protocols (or byte-oriented protocols)- the frame or packet is interpreted as a series of characters

Bit-oriented protocols- the frame or packet is interpreted as a series of bits

Bit-oriented protocols- the frame or packet is interpreted as a series of bits

Page 8: Data Link Protocols Asynchronous Protocols Synchronous Protocols –Character-Oriented Protocols –Bit-Oriented Protocols

Character-Oriented Protocols

Page 9: Data Link Protocols Asynchronous Protocols Synchronous Protocols –Character-Oriented Protocols –Bit-Oriented Protocols

Binary Synchronous Communication (BSC)

Supports half-duplex transmissionUses stop-and-wait ARQ flow control and error correction Supports half-duplex transmissionUses stop-and-wait ARQ flow control and error correction

- the best-known character-oriented protocol- the best-known character-oriented protocol

Page 10: Data Link Protocols Asynchronous Protocols Synchronous Protocols –Character-Oriented Protocols –Bit-Oriented Protocols

Data Frame

BSC Frame with Header

Multiblock Frame

Simple Data Frame

SYN – 0010110STX – 0000010ETX – 0000011

SOH – 0000001ITB – 0011111

Page 11: Data Link Protocols Asynchronous Protocols Synchronous Protocols –Character-Oriented Protocols –Bit-Oriented Protocols

Multiframe Transmission

ETB – 0010111ETB – 0010111

Page 12: Data Link Protocols Asynchronous Protocols Synchronous Protocols –Character-Oriented Protocols –Bit-Oriented Protocols

BSC Control Frames

Page 13: Data Link Protocols Asynchronous Protocols Synchronous Protocols –Character-Oriented Protocols –Bit-Oriented Protocols

BSC Control Frames cont…

Page 14: Data Link Protocols Asynchronous Protocols Synchronous Protocols –Character-Oriented Protocols –Bit-Oriented Protocols

SDLC – Synchronous Data Link ControlHDLC – High-Level Data Link ControlLAPs – Link Access ProtocolsLAN – Local Area Nelwork

IBM ISO ITU-T IEEE

Bit-Oriented Protocols

Page 15: Data Link Protocols Asynchronous Protocols Synchronous Protocols –Character-Oriented Protocols –Bit-Oriented Protocols

HDLC

Supports half/full duplex communications over point to point or multipoint links

Characterized by: station types, configuration, response modes

Station Types: Primary – issues commands Secondary – issues responses Combined – issues both command & response

Page 16: Data Link Protocols Asynchronous Protocols Synchronous Protocols –Character-Oriented Protocols –Bit-Oriented Protocols

HDLC Configuration

HDLC does not support balanced multipointHDLC does not support balanced multipoint

Page 17: Data Link Protocols Asynchronous Protocols Synchronous Protocols –Character-Oriented Protocols –Bit-Oriented Protocols

Figure 11-15

HDLC ModesWho controls the link

NRM – Normal Response Mode ( unbalanced configuration)ARM – Asynchronous Response ModeABM – Asynchronous Balanced Mode

* Mode for symmetrical & balanced can be set using U-frames

Page 18: Data Link Protocols Asynchronous Protocols Synchronous Protocols –Character-Oriented Protocols –Bit-Oriented Protocols

HDLC Frame Types

Unnumbered frameUnnumbered frame

Information frameInformation frame

Supervisory frameSupervisory frame

Page 19: Data Link Protocols Asynchronous Protocols Synchronous Protocols –Character-Oriented Protocols –Bit-Oriented Protocols

HDLC Flag F& FCS field

Page 20: Data Link Protocols Asynchronous Protocols Synchronous Protocols –Character-Oriented Protocols –Bit-Oriented Protocols

HDLC Address Field

Page 21: Data Link Protocols Asynchronous Protocols Synchronous Protocols –Character-Oriented Protocols –Bit-Oriented Protocols

HDLC Control Field

Code (S-frame) – carry coded flow and error control informationCode (U-frame) – identify the type of U-frame and its functionCode (S-frame) – carry coded flow and error control informationCode (U-frame) – identify the type of U-frame and its function

Page 22: Data Link Protocols Asynchronous Protocols Synchronous Protocols –Character-Oriented Protocols –Bit-Oriented Protocols
Page 23: Data Link Protocols Asynchronous Protocols Synchronous Protocols –Character-Oriented Protocols –Bit-Oriented Protocols

Use of P/F Field

Page 24: Data Link Protocols Asynchronous Protocols Synchronous Protocols –Character-Oriented Protocols –Bit-Oriented Protocols

U-Frame Control Field

Page 25: Data Link Protocols Asynchronous Protocols Synchronous Protocols –Character-Oriented Protocols –Bit-Oriented Protocols

U-Frame Control Field

Set NRMSet NRM (extended)Set ARMSet ARM (extended)

Set NRMSet NRM (extended)Set ARMSet ARM (extended)

Unnumbered infoDisconnectRequest disconnectSet initialization modeUnnumbered poll

Unnumbered infoDisconnectRequest disconnectSet initialization modeUnnumbered poll

Frame rejectExchange IDResetRequest information mode

Frame rejectExchange IDResetRequest information mode