Suppose a router's drop policy is to drop the highest-cost packet whenever queues are full, where it defines the "cost" of a packet to be the product of its size by the time remaining that it will spend in the queue. (Note that in calculating cost it is equivalent to use the sum of the sizes of the earlier packets in lieu of remaining time.) (a) What advantages and disadvantages might such a policy offer, compared to tail drop? (b) Give an example of a sequence of queued packets for which dropping the highest-cost packet differs from dropping the largest packet. (c) Give an example where two packets exchange their relative cost ranks as time progresses.

Suppose a router's drop policy is to drop the highest-cost packet whenever queues are full, where it defines the "cost" of a packet to be the product of its size by the time remaining that it will spend in the queue. (Note that in calculating cost it is equivalent to use the sum of the sizes of the earlier packets in lieu of remaining time.) (a) What advantages and disadvantages might such a policy offer, compared to tail drop? (b) Give an example of a sequence of queued packets for which dropping the highest-cost packet differs from dropping the largest packet. (c) Give an example where two packets exchange their relative cost ranks as time progresses.

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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Deficit round-robin is a scheduling scheme that operates as follows. The scheduler visits the queues inround-robin fashion. A deficit counter is maintained for each queue. When the scheduler visits a queue,the scheduler adds a quantum of service to the deficit counter, and compares the resulting value to thelength of the packet at the head of the line. If the counter is larger, the packet is served and the counter isreduced by the packet length. If not, the deficit is saved for the next visit. Suppose that a system has fourqueues and that these contain packets of length 16, 10, 12 and 8 and that the quantum is 4 units. Show thedeficit counter at each queue as a function of time and indicate when the packets are transmitted.
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5.03-5. Dijkstra's Algorithm (3, part 5). Consider the network shown below, and Dijkstra's link-state algorithm. Suppose that Dijkstra's algorithm has been run to compute the least cost paths from node E to all other nodes. Now suppose that source node E has a packet to send to destination node A. What is the first router to which E will forward this packet on its path to A? OF (A) 3 2 4 B 8 D 10 4 E 4 2 F
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QUESTION 77 Consider the network topology shown below with routers labeled A through F, inclusive. Each link is labeled with its "cost" for routing purposes. The link state routing algorithm is used in this network. (a)Show how Djikstra's algorithm works to compute paths from Router E to all other routers (show your answer in a table format similar to the one used in the lectures). (b)Show the final forwarding table at Router E after completion of the algorithm.
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Suppose a routing algorithm identifies paths that are “best” in the sense that: (1) minimum number ofhops, (2) minimum delay, or (3) maximum available bandwidth. Identify conditions under which the pathsproduced by the different criteria are the same? are different?
The graph abstruction of a network with a set of routers {s, v, w, x, y, z} is given in figure 1. The link costs are given in the figure. Using Dijkstra's link state algorithm suppose you want to find the shortest path from router 's' to all the other routers. Write the order in which the shortest path is found from router 's' to all the other routers. [The shortest path found in the first iteration should come first in the order and the shortest path found in the last iteration should come last in the order]
The graph abstruction of a network with a set of routers {s, v, w, x, y, z} is given in figure 1. The link costs are given in the figure. Using Dijkstra's link state algorithm suppose you want to find the shortest path from router 's' to all the other routers. Write the order in which the shortest path is found from router 's' to all the other routers. [The shortest path found in the first iteration should come first in the order and the shortest path found in the last iteration should come last in the order] 3 V W 8 9. S 7 6 5.
If the WFQ mechanism is used in scheduling the following queues. When does each packet leave the system. ((i, h) means h-th packetof the i-th queue). The weight of the i-th queue is twice the weight of the queues k, j and it must be serviced twice. The size of each input packet is specified on it. Qk A 25 3 2 A A 1 0 WFQ 0- 1 unit/sec Arrival time
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Problem 2. Consider a packet of L bits that is sent over a path of Q links (i.e., a source and destination connected by a sequence of (Q-1) routers or switches). Each link transmits at R bps. This packet is the only traffic transmitted by the network (so there are no queuing delays) and the propagation delay and processing delay at routers are negligible. How long does it take to send this packet from source to destination if the network is: a) a packet-switched datagram network b) a circuit-switched network. Assume that bandwidth of R bps on each link is sliced into five individual circuits, so that cach circuit receives (R/5) bandwidth. Also assume that the circuit setup time is t,.. Give an expression for the number of links Q such that the packet delivery from the sender to the receiver will be faster over the packet-switched network, and the expression for the number of links Q such that the circuit-switched network will be faster.