# Recent questions tagged go-back-n

1
Visit the Go-Back-N Java applet at the companion Web site. Have the source send five packets, and then pause the animation before any of the five packets reach the destination. Then kill the first packet and resume the animation. Describe what happens ... packet reach the destination and kill the first acknowledgment. Describe again what happens. Finally, try sending six packets. What happens?
2
In go back n arq, the reciever window size is 1 and the sender window size is let's suppose 3.Now if the sender sends the frames with sequence numbers in order 0,1,2 and the reciever sends cumulative acknowledgement with number 3 and now expects a frame number ... order and sender must keep on time out and sending the frames again.plz explain how will this be resolved or am I missing something?
1 vote
3
A Go-Back-5 ARQ scheme is employed on a 200 meters cable between two nodes A and B to send frames of size 10,000 bits with bit rate 1 Mbps and bit error probability of 10$^{-5}$. Headers and acknowledgements are 20 bytes each. The Speed of propagation of ... parameter (except for the cable length), what is the maximum distance between the two nodes for which S&W will be as efficient as a GBN.
4
Consider two computers A and B are connected through a network of 30 Mbps. Assume the distance between them is 3000km and the signal propagation speed is same as the speed of light and the packet size is 12 KB. What is the minimum number of bits required for window to achieve 100% of utilization during GoBack-N and selective repeat protocol? A . 5 and 6 B. 6 and 7 C. 6 and 6 D. 7 and 8
1 vote
5
I was going through this question; The link A-R is instantaneous , but the R->B link transmits only 1 packet each second , one at a time . Assume A sends to B using sliding window protocol with window size =4 , For time t=2 , state what packets arrive ... zero is not yet acknowledged. Is this wrong? Or I am wrong and sliding window protocol means Selective Repeat and it sends ACK for each frame?
1 vote
6
I am unable to understand their explanation,can anyone explain it in a better way?
7
Consider two computers A and B are connected through a network of 30 Mbps.Assume the distance between them is 3000km and the signal propagation speed is same as the speed of light and the packet size is 12 KB. What is minimum number of bits required for window to achieve 100% utilization during GBN and SR protocol ?
8
Assume 2 computers are connected via a network. The network uses Go-Back 7 sliding window protocol for maintaining flow control. It is observed that every 5th packet that has been sent through the network is lost. What will be the number of extra packets that has to be resent for transmitting 10 such packet through the network? With explanation.
1 vote
9
Assume 2 computers are connected via a network. The network uses GB-7 sliding window protocol for flow control.It is observed that every 5th packet that has been sent is lost. The number of extra packets needs to resend Number of total packets transmitted by sender for sending 10 packets .
10
11
A colony is set up on moon. The 10 Mbps link from the earth to the lunar colony measures about 242,000 miles. Assume that the signal propagation speed is 186,000 miles per second. Calculate the minimum round trip time for the link. Using RTT as the ... sender and receiver ends. SRP with window size 8 and negligible processing delay. Go Back-n with window size 64 and negligible processing delay.
12
answer given is 11. I am Getting 3
1 vote
13
Sender Window Size is 7 and every 3rd packet is lost/corrupted. So, how to find channel utilization!?
1 vote
14
Consider the use of 10 K-bit size frames on a 10 Mbps satellite channel with 270 ms delay. What is the link utilization for stop-and-wait ARQ technique assuming P = 10-3? My doubt - In frame size 10 K-bit, what should you take value of K? i.e K as 1000 bits or K = 1024 bits? I'm more ... ) = (10 K-bit) / (10 Mbps) = 1 msec Hence, a = 270/1 = 270 Link utilization = 0.999/(1+2*270) ≈0.0018 =0.18%
15
Consider the GBN protocol with sender and receiver window size as 5.Suppose client sends data 0,1,2,3,4 and only data packet 2 is lost and all ACKs are lost. What will be the content of receiver and sender window. Before Senders timeout value expires ? A. Sender: 01234 , Receiver : 01234 B. Sender: 23456 , Receiver : 01234 C. Sender: 23456 , Receiver : 23456 D. Sender: 01234 , Receiver : 23456
1 vote
16
A 20 Kbps Satellite link has a propagation delay of 400 ms. The transmitter employs the "go back n ARQ" scheme with n set to 10. Assuming that each frame is 100 bytes long, what is the efficiency of channel? (with 2 decimal places)
17
Station A needs to send a message consisting of 10 packets to station B using a sliding window of size 4. All packets are ready and can be transferred immediately.Selective repeat and GBN are used at 2 different times and every 5th packet get lost for both protocols.( ... number of transmissions that A has to make in selective repeat and GBN respectively to ensure safe delivery to B. Then x+y= ?
18
A channel has bit rate of $1 \hspace{0.1cm} Mbps$ and propagation delay of $270 \hspace{0.1cm} msec$ .Frame size is of $125 \hspace{0.1cm} bytes$ . Acknowledgement is always piggibacked onto data frames .Four bit sequence no. Is used .ignore header size,then what is maximum achievable channel utilization for GO-BACK-N? $1.48\%$ $0.18\%$ $2.95\%$ $2.78\%$
1 vote
19
Consider GBN with sender's window size of n . Suppose that at time t , the next in order packet the receiver is expecting has a sequence number of 'k' . Assume that the medium does not reorder messages , then what are the possible sets of sequence numbers at time t . Assume the sender already received ACK for k-1 packets .
20
Consider a network connecting two systems, ‘A’ and ‘B’ located 6000 km apart. The propagation speed of media is 2 × 106 mps. It is needed to design a Go-Back-7 sliding window protocol for this network. The average packet size is 107 bits. If network used as its full capacity, then the bandwidth of network is__________ Mbps. Here full capacity means efficiency is 100%.
21
22
Consider a network connecting two systems, ‘A’ and ‘B’ located 6000 km apart. The propagation speed of media is 2 × 106 mps. It is needed to design a Go-Back-7 sliding window protocol for this network. The average packet size is 107 bits. If network used as its full capacity, then the bandwidth of network is__________ Mbps
1 vote
23
I'm getting 81, but the answer given is 80. Please verify and explain.
24
A link has a transmission speed of 500 × 106 bpsec. Assume acknowledgment has negligible transmission delay, and its one way propagation delay is 2 sec. Also assumes that the processing delays at nodes are also negligible. If data packet size is 107 bits, then the efficiency of Go-Back-7 protocol is _______ (in %)
25
Compute approx. optimal window size, when packet size is 53 B, RTT is 60 micro-sec and bottleneck bandwidth is 155Kbps.
26
Two stations A and B are connected via a point to point link. A sends frames to B using Go-Back-N protocol with a window size of 7 and sequence number is of 3 bits. A sends all the frames one by one but B's ACK-3 for frame 3 is not reached to A. But before the timer expires, B received frame 4 and sent ACK-4 but ... starts from 0) a) 0 1 2 3 4 6 b) 3 4 5 6 0 1 2 c) 5 6 7 0 1 2 3 d) 5 6 0 1 2 3 4
1 vote
27
Hi Guys, Do you know formula for efficiency of Stop-and-Wait, Selective Reject and Go-Back-N ARQ when error probability is p ? PS: Although i am mentioning the link for answer but if you want to add some additional info.(or some more elegant proof for the formula) then it will be really helpful for all readers. :)
The efficiency of a Go-Back-N protocol is $\eta = \frac{N}{1+ 2 *\frac{Propogation Delay}{Transmission Delay}}$ In this equation what is the exact value of N. Is it the one given in Go-Back-N or (2N-1).