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Sliding window protocol

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  • 1. 1 Sliding Window ProtocolA sliding window protocol is a feature of Packet based data transmissionprotocols. They are used where reliability in order to delivery of packetsis required, such as in data link layer as in the transmission control proto-col(TCP).1.1 FeaturesEach position of the transmission (Packets) is assigned a unique consecutivesequence number and the receiver uses the numbers to place received packetsin the correct order. i.e. • Discarding duplicate packets. • Identifying missing packets.1.2 ProblemThere is no limit of the size or sequence numbers that can be required inthis protocol.1.3 Approach to the ProblemThis problem can be chacked by placing a limit on the number of packetsthat can be transmitted or received at any given time.1.4 MeritsA sliding window protocol allows an unlimited numbers of packets to becommunicated using fixed sequence numbers.1.5 AlertnessFor highest possible throughput, it is important that the transmitter is notpermitted to stop sending by the sliding window protocol earlier than oneRound Trip Delay Time(RTT).RTT: It is the length of time it takes for a signal to be sent plus the lengthof time it takes for an acknowledge of that signal to be received.RTT = SendTime + AckTime2 Protocol based CommunicationIn communication based protocol , the receiver must acknowledge receivedpackets. If transmitter does not receive an acknowledgement within a rea-sonable time, it resends data. 1
  • 2. If a transmitter does not receive an acknowledgement it cannot know whetheractually receiver received the packet or not, or packet was damaged or itmay also happen that acknowledgement was sent but it was lost.3 Protocol OperationBasic terms used in it are - • Transmitter sequence number = n(t) • Receiver sequence number = n(r) • Transmitter window size = w(t) • Receiver window size = w(r)Window size must be greater than Zero. As we mentioned , n(t) is the nextpacket to be transmitted and the sequence number of this packet is not yetreceived and n(r) is the first packet not yet received. These both numbersare in increasing mode.3.1 Receiver Operationn(s) is one more than the sequence number of the highest sequence numberreceived. • Received a Packet • Updates its Variable • Transmit acknowledgement with the new n(r) • Transmitter keeps track of the highest acknowledgement it has received n(a)But it is uncertain about the packets n(a) and n(s).n(a)<= n(r)<= n(s)3.1.1 Some FactsThere are some facts that are listed below - • The highest acknowledgement received by the transmitter cannot be higher than the highest acknowledged by the receiver. n(a)<= n(r) 2
  • 3. • The span of fully received packets cannot extend beyond the end of the partially received packet. n(r)<=n(s). • The highest packet received cannot be higher than the highest packet send. n(s)<=n(t) • The highest packet sent is limited by the highest acknowledgement received and the transmit window size. n(t)<=n(a) +w(t)3.2 Transmitter OperationIf transmitter wants to send data, it may transmit upto w(t) packets aheadof the latest acknowledgement n(a). A transmitter can send packet numbern(t) if and only ifn(t) < n(a) +w(t)3.3 Benefit of Sliding Window ProtocolSome benefits of sliding window protocol - • Data Reliability • Data Integrity • Unlimited Sequence numbers are used 3.4 Drawback of Sliding Window Protocol • Ambiguity occurs • Maintaining a Sequence number is difficult 3
  • 4. Figure 1: Our proposed Architecture4 Connectionless Communication in Data Link LayerPacket switching network (connectionless network) is a data transmissionmethod in which each data packet carries some information. The connec-tionless communication mode has advantages over connection oriented com-munication. It allows multihop also in Data link layer.The data link layer supports reliable packet transmission between node tonode wireless connection. The sliding window protocol supports the reliabledata communication in data link layer. In our architecture all reliable datasare going to upper layer which ensures there is no missing of data.5 ConclusionIn our proposed architecture we mentioned how data can be sent with in-tegrity and reliablity as we want reliable communication in multihop routing.As data is very important and valuable, if we lose data then it has a greatimpact on a persons condition and also has some environmental influences. • So our proposed architecture refers Safety Critical Ad - Hoc routing Architecture. 4