Data link control protocol(1)
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The document outlines Data Link Control Protocol (DLCP), highlighting its role in managing orderly data exchange between OSI protocol layer 2 devices and describing two network types: primary/secondary and peer-to-peer. It details DLCP functions, including line discipline, flow control, and error control, along with methods of implementation such as enquiry/acknowledgement and poll/select for line discipline, and stop-and-wait and sliding window for flow control. Error control mechanisms are discussed, with an emphasis on Automatic Repeat reQuest (ARQ) methods for error detection and correction.
Data link control protocol(1)
- 1. Lecture 01 Data-Link Protocols Prepared by: Engr. Jeffrey Des B. Binwag Chapter 23 Electronic Communications Sytems , Fifth Editon By: Wayne Tomasi ECE @Saint Louis University, Baguio City 1
- 2. Data Link Control Protocol (DLCP) • A set of rules implementing and governing an orderly exchange of data between OSI Protocol Layer 2 devices. • Perform certain network functions that ensure a coordinated transfer of data. ECE @Saint Louis University, Baguio City 2
- 3. TYPES OF NETWORK • PRIMARY/SECONDARY (MASTER/SLAVE ) A centrally controlled network where a primary station (master) enacts procedures that determine which station is transmitting and which is receiving at any given instant. All the rest of the stations are secondary stations (slaves) whose data communication actions are controlled by the primary. • PEER-TO-PEER A type of network where all connected stations are equal (peers), and share equal access to the network. When a station wishes to transmit on this network, it has to contend with all the rest of the stations with an intent to transmit. ECE @Saint Louis University, Baguio City 3
- 4. FUNCTIONS OF DLCP • LINE DISCIPLINE • FLOW CONTROL • ERROR CONTROL ECE @Saint Louis University, Baguio City 4
- 5. LINE DISCIPLINE • The process of coordinating half-duplex transmission on a data communications network by: – Establishing logical continuity between source and destination stations before data transfer, and – Ensuring that the destination station is ready and capable of receiving data • Fundamental Methods of implementation – Enquiry/ Acknowledgement (ENQ/ACK) – Poll/ Selection (POLL/SELECT) ECE @Saint Louis University, Baguio City 5
- 6. ENQ/ACK • Best suited to simple network environments like two-point networks • ENQUIRY – A frame or packet of data which identifies the receiving station and solicits the receiving station to determine if it is ready to receive data • ACKNOWLEDGEMENT – ACK. Positive Acknowledgment (Ready to receive) – NAK. Negative Acknowledgement (Not ready to receive, Message received with error) ECE @Saint Louis University, Baguio City 6
- 7. ENQ/ACK ENQ STATION A ACK STATION B MESSAGE 1 ACK MESSAGE 2 NAK MESSAGE 2 ACK MESSAGE 3 (EOT) ACK Time ECE @Saint Louis University, Baguio City 7
- 8. POLL/SELECT • Best suited to centrally controlled data communications networks using multipoint topology • POLL – A solicitation sent from the primary to the secondary to determine if the secondary has data to transmit – Sent to one station at a time – Secondary responds with either a message or a negative acknowledgement (NAK) • SELECTION – How the primary designates a secondary as a destination, a query if the destination is ready to receive data – Can be broadcast to all secondary stations – Secondary stations respond with either a positive acknowledgement (ACK) or a negative acknowledgement (NAK) ECE @Saint Louis University, Baguio City 8
- 9. POLL/SELECT PRIMARY SECONDARY A SECONDARY B SECONDARY C Poll A NAK Poll B Message Selection B ACK Message Selection C NAK Time ECE @Saint Louis University, Baguio City 9
- 10. FLOW CONTROL • Defines a set of procedures that tells the transmitting station how much data it can send before it must stop transmitting and wait for an acknowledgement from the destination • Fundamental Methods of implementation – Stop-and-wait – Sliding Window ECE @Saint Louis University, Baguio City 10
- 11. STOP-AND-WAIT FLOW CONTROL • The transmitting station sends one message frame and then waits for an acknowledgment before sending the next frame • Advantage is simplicity • Disadvantage is its poor network utilization ECE @Saint Louis University, Baguio City 11
- 12. STOP-AND-WAIT FLOW CONTROL Message Frame 1 STATION A (Source) ACK STATION B (Destination) Message Frame 2 ACK Message Frame 3 NAK Message Frame 3 ACK Message Frame 4 (EOT) ACK Time ECE @Saint Louis University, Baguio City 12
- 13. SLIDING WINDOW FLOW CONTROL • The transmitting station sends several message frames in succession before receiving an acknowledgement • Advantage is faster speed of transmission (better network utilization) compared to Stopand-wait flow control • Disadvantage is the complexity of its design ECE @Saint Louis University, Baguio City 13
- 14. SLIDING WINDOW FLOW CONTROL Message Frame 0 0 STATION A (Source) STATION B (Destination) Message Frame 1 1 Message Frame 2 2 0 to (2n-1) receptacles ... ... ... 2n-1 Message Frame (n-1) (EOT) ACK Time ECE @Saint Louis University, Baguio City 14
- 15. ERROR CONTROL • A process encoding overhead codes into a message frame for the detection of errors when they occur and the provision for the correction of the said errors • Error detection may be achieved by various error codes like LRC, VRC, or CRC • Error correction in the OSI Layer 2 is implemented by Automatic Request for Retransmission (ARQ) • Errors that cannot be resolved by ARQ are referred for resolution to the higher OSI layers ECE @Saint Louis University, Baguio City 15
- 16. TYPES OF ARQ • Stop-and-Wait ARQ – A message frame is retransmitted if the source receives a negative acknowledgment from the destination • Sliding Window ARQ – Go-back-n-frames • The errored frame and all frames transmitted after it are retransmitted even if the subsequent frames have no error – Selective Reject (SREJ) • Only the errored frames are retransmitted ECE @Saint Louis University, Baguio City 16 (END)