Data Plane Assignment

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Florida International University *

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4513

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Electrical Engineering

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Apr 3, 2024

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Network Layer - Data Plane Assignment 1. Consider sending a packet from a source host to a destination host over a fixed route. List the delay components in the end-to-end delay. Which of these delays are constant and which are variable? The delay components are: a) Transmission delay b) Queuing delay c) Processing delay d) Propagation delay Of the all the delay components, the transmission, propagation, and processing delays are constant, and the queuing is considered variable. 2. Suppose end system A wants to send a large file to end system B. At a very high level, describe how end system A creates packets from the file. When one of these packets arrives to a packet switch, what information in the packet does the switch use to determine the link onto which the packet is forwarded? Why is packet switching in the Internet analogous to driving from one city to another and asking directions along the way? End system A breaks up or divides the files into chunks. For each of the chunks, a header is added thus creating a packet. Each of these packets contain the IP address of the destination, system B. When one of these packets arrives at a packet switch, the destination address in the header is used to determine which link the packet must be sent to. Each packet that is sent has the destination or address in the header. Asking which direction to take is analogous to a packet asking which outgoing link it should be forwarded to. 3. Consider a router buffer preceding an outbound link. In this problem, you will use Little’s formula, a famous formula from queuing theory. Let N denote the average number of packets in the buffer plus the packet being transmitted. Let a denote the rate of packets arriving at the link. Let d denote the average total delay (i.e., the queuing delay plus the transmission delay) experienced by a packet. Little’s formula is N = a · d. Suppose that on average, the buffer contains 10 packets, and the average packet queuing delay is 10 msec. The link’s transmission rate is 100 packets/sec. Using Little’s formula, what is the aver- age packet arrival rate, assuming there is no packet loss? Transmission delay = L/R L=1 packet R = 100 packets/sec Transmission delay = 1/100 sec = 0.010 sec

Queuing delay = 10 msec => .010sec Total delay = .010sec + .010sec = .020 sec Little formula N = a . d 10 = a x .020 sec A = 10/.020 sec Ans = 500 packets /sec Average packet arrival rate = 500 packets/sec 4. a. Generalize Equation 1.2 in Section 1.4.3 for heterogeneous processing rates, transmission rates, and propagation delays. Repeat(a), but now also suppose that there is an average queuing delay of d queue at each node. a) End to end delay = transmission delay + propagation delay b) end to end delay = transmission delay + propagation delay + queuing delay 5. In BitTorrent, suppose Alice provides chunks to Bob throughout a 30-second interval. Will Bob necessarily return the favor and provide chunks to Alice in this same interval? Why or why not? BitTorrent is a popular P2P protocol for the distribution of files. Bob will not necessarily provide chunks to Alice, she must be in the top four neighbors of Bob and send message to her, this might not occur even if Alice is providing chunks to Bob throughout a 30-second interval 6. Consider a new peer Alice that joins BitTorrent without possessing any chunks. Without any chunks, she cannot become a top-four uploader for any of the other peers since she has nothing to upload. How then will Alice get her first chunk? BitTorrent randomly picks a peer and optimistically unchokes the peer for a period of time. Using random neighbor selection, Alice will get her first chunk when she is selected as optimistically unchoked peer by one of the neigbors. 7. Consider a DHT with a mesh overlay topology (that is, every peer tracks all peers in the system). What are the advantages and disadvantages of such a design? What are the advantages and disadvantages of a circular DHT (with no shortcuts)? Advantages of DHT with a mesh overlay topology DHT means Distributed Hast Tables. One of the advantages is the fact that a single hop will be used to route a message to the peer. The other is that there are bi-directional links between

each peer other than the broadcasting peer which then creates multiple delivery paths from the source to other peers. Disadvantages of DHT with a mesh overlay topology The mesh overlay topology is a very complex design. The process of tracking of all peers by each peer is very consuming. Advantages of Circular DHT (with no shortcuts) Each of the peer only tracks two peers and as such is a less consuming process. Disadvantages of Circular DHT (with no shortcuts) There is a reduction in the number of messages sent per query. O(N) hopes are required to route message to a peer responsible for the key. 8. List at least four different applications that are naturally suitable for P2P architectures. (Hint: File distribution and instant messaging are two.) a) File Distribution b) Instant Messaging c) Video Streaming d) Distributed Computing 9. Read RFC 959 for FTP. List all of the client commands that are supported by the RFC. Access control commands: USER, PASS, ACT, CWD, CDUP, SMNT, REIN, QUIT. Service commands: RETR, STOR, STOU, APPE, ALLO, REST, RNFR, RNTO, ABOR, DELE, RMD, MRD, PWD, LIST, NLST, SITE, SYST, STAT, HELP, NOOP. Transfer parameter commands: PORT, PASV, TYPE STRU, MODE.

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