Section 11

Presentation Transcript

Part 11 Data Link Control and Protocols

11.1 Flow and Error Control Flow Control Error Control

Note : Flow control alludes to an arrangement of techniques used to confine the measure of information that the sender can send before sitting tight for affirmation.

Note : Error control in the information interface layer depends on programmed rehash ask for, which is the retransmission of information.

11.2 Stop-and-Wait ARQ Operation Bidirectional Transmission

11.1 Normal operation

11.2 Stop-and-Wait ARQ, lost edge

11.3 Stop-and-Wait ARQ, lost ACK outline

Note : In Stop-and-Wait ARQ, numbering outlines keeps the holding of copy edges.

11.4 Stop-and-Wait ARQ, deferred ACK

Note : Numbered affirmations are required if an affirmation is postponed and the following casing is lost.

11.5 Piggybacking

11.3 Go-Back-N ARQ Sequence Number Sender and Receiver Sliding Window Control Variables and Timers Acknowledgment Resending Frames Operation

11.6 Sender sliding window

11.7 Receiver sliding window

11.8 Control factors

11.9 Go-Back-N ARQ, typical operation

11.10 Go-Back-N ARQ, lost edge

11.11 Go-Back-N ARQ: sender window estimate

Note : In Go-Back-N ARQ, the extent of the sender window must be under 2m; the span of the recipient window is dependably 1.

11.4 Selective-Repeat ARQ Sender and Receiver Windows Operation Sender Window Size Bidirectional Transmission Pipelining

11.12 Selective Repeat ARQ, sender and recipient windows

11.13 Selective Repeat ARQ, lost edge

Note : In Selective Repeat ARQ, the extent of the sender and collector window must be at most one-portion of 2 m .

11.14 Selective Repeat ARQ, sender window measure

Example 1 In a Stop-and-Wait ARQ framework, the data transmission of the line is 1 Mbps, and 1 bit takes 20 ms to make a round trek. What is the data transmission postpone item? On the off chance that the framework information edges are 1000 bits long, what is the usage rate of the connection? Arrangement The transfer speed postpone item is 1  10 6  20  10 - 3 = 20,000 bits The framework can send 20,000 bits amid the time it takes for the information to go from the sender to the recipient and afterward back once more. Be that as it may, the framework sends just 1000 bits. We can state that the connection use is just 1000/20,000, or 5%. Hence, for a connection with high transfer speed or long postponement, utilization of Stop-and-Wait ARQ squanders the limit of the connection.

Example 2 What is the usage rate of the connection in Example 1 if the connection utilizes Go-Back-N ARQ with a 15-outline succession? Arrangement The transfer speed postpone item is still 20,000. The framework can send up to 15 outlines or 15,000 bits amid a round trek. This implies the usage is 15,000/20,000, or 75 percent. Obviously, if there are harmed outlines, the usage rate is considerably less on the grounds that edges must be loathe.

11.5 HDLC Configurations and Transfer Modes Frames Frame Format Examples Data Transparency

11.15 NRM

11.16 ABM

11.17 HDLC outline

11.18 HDLC outline sorts

11.19 I-outline

11.20 S-outline control field in HDLC

11.21 U-outline control field in HDLC

Table 11.1 U-outline control charge and reaction

Example 3 Figure 11.22 demonstrates a trade utilizing piggybacking where is no blunder. Station A starts the trading of data with an I-outline numbered 0 took after by another I-outline numbered 1. Station B piggybacks its affirmation of both casings onto an I-edge of its own. Station B's first I-edge is additionally numbered 0 [N(S) field] and contains a 2 in its N(R) field, recognizing the receipt of An's edges 1 and 0 and demonstrating that it anticipates that edge 2 will land next. Station B transmits its second and third I-outlines (numbered 1 and 2) preceding tolerating further casings from station A. Its N(R) data, in this way, has not changed: B outlines 1 and 2 demonstrate that station B is as yet anticipating that A casing 2 should touch base next.

11.22 Example 3

Example 4 In Example 3, assume outline 1 sent from station B to station A has a blunder. Station An illuminates station B to resend outlines 1 and 2 (the framework is utilizing the Go-Back-N component). Station A sends a reject supervisory edge to declare the mistake in casing 1. Figure 11.23 demonstrates the trade.

11.23 Example 4

Note : Bit stuffing is the way toward including one additional 0 at whatever point there are five back to back 1s in the information so that the collector does not mix up the information for a banner.

11.24 Bit stuffing and expulsion

11.25 Bit stuffing in HDLC