As discussed in the OSI protocol stack, oneway a data link layer handles transmissionerrors is by requesting damaged frames tobe retransmitted (i.e. by sending a NACK,Not ACKnowledgment). If the frame arrivedsuccessfully, an ACK would be sent instead.Let probability of a frame being transmittedcorrectly be p.a) Find the probability, kq , of a framerequiring exactly k transmissionsb) If p=0.3, what is the mean number oftransmissions required to send a frame ifacknowledgements (ACKS and NACKS) arenever lost? Hint: If you don't already knowthis, the mean number would simply be: 1kk kq | = | Andc) What if some NACKS are lost, would thatincrease or decrease (or not change) themean number of transmissions to send aframe? Explain briefly.

OSI (Open Systems Interconnection) is a reference model for how applications communicate over a…

As discussed in the OSI protocol stack, one way a data link layer handles transmission errors is by requesting damaged frames to be retransmitted (i.e. by sending a NACK, Not ACKnowledgment). If the frame arrived successfully, an ACK would be sent instead. Let probability of a frame being transmitted

As discussed in the OSI protocol stack, one way a data link layer handles transmission errors is by requesting damaged frames to be retransmitted (i.e. by sending a NACK, Not ACKnowledgment). If the frame arrived successfully, an ACK would be sent instead. Let probability of a frame being transmitted

Database System Concepts

7th Edition

ISBN:9780078022159

Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Chapter1: Introduction

Section: Chapter Questions

Problem 1PE

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In the generic SR protocol, the sender transmits a message as soon as it is available (if it is in the window) without waiting for an acknowledgment. Suppose now that we want an SR protocol that sends messages two at a time. That is, the sender will send a pair of messages and will send the next pair of messages only when it knows that both messages in the first pair have been received correctly.Supposethat the channel may lose messages but will not corrupt or reorder messages. i) Outline an error-control protocol for the unidirectional rdt of messages. ii) Give an FSM description of the sender and receiver. iii) Describe the format of the packets sent between sender and receiver and vice versa. iv) If you use any procedure calls other than those in SR protocol (for example, udt_send(), start_timer(), rdt_rcv(), and so on),clearly state their actions. v) Give an example (a timeline trace of sender and receiver) showing how your protocol recovers from a lost packet
NAKs are handled in protocol 6's code for frame arrival.If the incoming frame is a NAK and another condition is satisfied, this section gets activated.Describe a situation in which this other condition is critical.
In a bit-oriented link-layer protocol, the start and end of a frame are each marked by a flag, which is a sequence of exactly 6 consecutive 1 bits. Bit stuffing is used during the rest of the frame: after sending 5 consecutive 1 bits, a 0 is added. The bits below contain an example frame, with the leftmost bit received first. The content of the frame is a sequence of bytes, sent most significant bit first. Put the values of the first four bytes of the frame content, in order, in the four answer boxes below. You may enter the values in either decimal (e.g. 76, 123) or hexadecimal (e.g. 2a, f7). 00101011111010001111110011100111110000111101111101010110100010010011111101101100100 57−240−123−229
Consider a simple protocol for transferring files over a link. After some initial negotiation, A sends data packets of size 1 KB to B; B then replies with an acknowledgment. A always waits for each ACK before sending the next data packet; this is known as stop-and-wait. Packets that are overdue are presumed lost and are retransmitted. (a) In the absence of any packet losses or duplications, explain why it is not necessary to include any "sequence number" data in the packet headers. (b) Suppose that the link can lose occasional packets, but that packets that do arrive always arrive in the order sent. Is a 2-bit sequence number (that is, N mod 4) enough for A and B to detect and resend any lost packets? Is a 1-bit sequence number enough? (c) Now suppose that the link can deliver out of order and that sometimes a packet can be delivered as much as 1 minute after subsequent packets. How does this change the sequence number requirements?
In protocol 6, the code for frame arrival has a section used for NAKs. This section is invoked if the incoming frame is a NAK and another condition is met. Give a scenario where the presence of this other condition is essential.
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In the discussion of ARQ protocol in Section 3.3.3, a scenario was outlined that resulted in the receiver accepting two copies of the same frame due to a loss of acknowledgement frame. Is it possible that a receiver may accept multiple copies of the same frame when none of the frames (message or acknowledgement) are lost?
A sender with window size (W=3) is connected to a go back N receiver by a link with bandwidth =106 bytes/second and propagation delay of 0.25 msec. The receiver sends Positive ACK for correctly received in order packets. For each packet sent, the sender sets a timer with time out value of 5 msec. On receiving an ack for that packet, the timer is cancelled. If the timer expires, that packet is retransmitted immediately. Assume that the sender sends packets 1, 2, and 3 (at t=0, packet size =1000 Bytes) and packet 2 is lost. NO other packet is lost. Under this scheme , at what time (in msec) would all the packets been received at the receiver.
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MCQ 1.Suppose 4 packets are received in a burst at a token bucket shaper, which has 1 token in the bucket at the time of arrival (t=0). Tokens are refilled at the rate of 1 token per 5 time units, with the first of the (new) tokens arriving at time t=2. Assume that the shaping buffer is very large. At what times are the packets eventually transmitted? Choose the most appropriate response. The choices list the scheduling times of the packets in order (packet 1, packet 2, packet 3, packet 4). A:2, 7, 12, 17 B:5, 10, 15, 20 C:0, 2, 7, 12 D: 0, 5, 10, 15
Consider sending a file of F bits over a path of Q links. Each link transmits at R bits per second (bps). The network is lightly loaded so that there are no queueing delays. When a form of packet switching is used, the F bits are broken up into packets, each packet with L bits, of which h bits of it are header. Propagation delay is negligible. Let F = 5x104, Q = 20, R = 1 Mbps, L = 1000, and h = 10. b) Suppose the network is a packet-switched datagram network and a connectionless service is used. How long does it take to send the file?