Computer Science 825 Quiz 1 Name _______________________ Terminology: the very highest layer is the APPLICATION LAYER the very lowest layer is the PHYSICAL LAYER 1. Which of the following is not a disadvantage of incorporating network protocols directly into an application (as opposed to having a general networking subsystem in the OS). a. It makes it harder to migrate b. It makes the performance of to new hardware technologies the application worse. c. It takes longer to write d. The applications tend to the applications. be less reliable. 2. What is the highest layer that must be present in every Router/IMP in a store and forward network. 3. What is the lowest layer that is present in Host nodes but is not present in Router/IMP nodes. 4. Protocol headers used by a layer N are handled by layer K (K > N) as follows: a. The are removed before b. They are treated as user data. the packet arrives at Layer K c. They are deleted by layer K. 5. The maximum useful BAUD (or sampling) rate on a channel which passes harmonics between 15 KHz and 20 KHz and filters out all others is: a. 10,000 baud b. 20,000 baud c. 5,000 baud d. Unlimited 6. Suppose a channel has a bandwidth of 2 KHz what is the minimum useful baud/sample time "t". 7. What is the minimum number of distinct signalling states required to transmit 24,000 bits / second on a 4Khz bandwidth channel. 8. Two things that a protocol can do to earn the term "unreliable" are (1) deliver packets with bits that have been inverted and (2) drop or lose packets. Identify two others: a. b. 9. For each of the following layers identify the interoperability requirement that best characterizes it: ____ a. Datalink 1 - End point to end point ____ b. Network 2 - Adjacent node to adjacent node (hop to hop) ____ c. Transport 3 - global 10. From the perspective of building a correct implementation of a protocol, the easiest type of service to provide is: a. reliable connection oriented b. unreliable connection oriented c. reliable connection less d. unreliable connection less 11. Place the following protocols at the correct location in the boxes below: TCP, IP, ATM Connection Connection Oriented Less ___________________________________ | | | Reliable | | | | | | |_________________|_______________| | | | Unreliable| | | | | | |_________________|_______________| Computer Science 825 Quiz 2 Name _______________________ 1. What is the minimum SNR (in db) that will support a data rate of 100,000 bits per second on a 5000hz channel? 2. Recall the Bell 212A modem discussed in class. It signalled using 4 phase angles, 45, 135, 225, and 315 degrees. When a long burst of 00000000000000000000 is transmitted, a. The modem will emit a b. There will be a +45 degree pure sine wave of the form phase shift in the signal f(t) = sin(wt + 45deg) every bit time. for the duration of the burst c. There will be a +45 degree phase shift every other bit time. 3. What bit rate is required to support a new "hi-fi" PCM phone that supports frequencies to 12Khz and quantizes the signal into 4096 discrete levels. 4. Suppose a PCM scheme supports a bit rate of 120,000 bps and quantizes the signal into 64 distinct levels. What is the highest frequency that it can carry? 5. In the T-1 / DS-1 multiplexed telephone circuit a frame consists of a. 8 slots b. 24 slots c. 64,000 slots d. 1.544 M slots 6. The rate at which Frames are sent (frames/sec) a. Is faster in STS-1 than in b. Is slower in STS-1 than DS-1 DS-1 c. Is the same in STS-1 and DS-1 7. The number of voice telephone connections that can be simultaneously multiplexed onto a single OC-1/STS-1 circuit is closest to: a. 51 b. 775 c. 6,480 d. 1.544 Million 8. The use of very small slot sizes is a. Inefficient and shouldn't b. Generally shouldn't be used for be used in eiterh STDM or ATDM SDTM but is OK for ATDM c. Generally shouldn't be used d. Perfectly OK for both for ATDM but is OK for STDM 9. Suppose a network has links that carry data at a rate of 10,000 bits per second. Suppose Node A and Node B are connected by a path that requires 8 hops (transmissions). a. What is the minimum time required to send a 1,000,000 bit message from A to B if message switching is used. b. Suppose packet switching is used and no additional bits are required for headers. How long will it take to send the entire message if 2000 bit packets are used. 10. Suppose headers of length 200 bits are used in the packet switching scheme described above. Suppose packet size remains at 2000 bits which now includes header+data bits). Under this new scheme: a. How many packets must be sent? b. How long will it be before the LAST packet leaves the original sender Computer Science 851 Quiz 3 Name _______________________ 1. Measurements of an infinite user slotted aloha channel show that packet transmission attempts occur in 60% of the slots: a. What is the total load (mean number of transmission attempts per packet time) = G. b. What is the throughput (S). c. In what percentage of the slots do collisions occur? 2. For a slotted aloha system for each value of "S" (except the S corresponding to G = 1.0) there are two different values of G which will result in the throughput being "S". For a given "S" the average delay before a packet is successfully transmitted is: a. The same for both "G"s b. Larger for the small "G" than for the big "G". c. Larger for the big "G" d. Totally independent of than for the small "G". the "G" value. 3. If k stations share a CSMA-CD bus and the probability that any station will transmit on a given contention slot is "p", then the probability that a successful transmission will take place in a slot is: a. p c. k * p * (1 - k) ^ (p - 1) b. p * (1 - p) ^ (k - 1) d. None of the above. 4. In the analytical model of the CSMA-CD bus described in class, suppose each station tries to transmit with a probability of 1/2 on each slot. As k becomes large, the probability of one station successfully acquiring the channel during a given contention slot: a. approaches 1 b. approaches 0 c. converges to 1/2 d. converges to 1/e 5. The main function of the CD portion of a CSMA-CD protocol is to: a. Reduce the probability that b. Reduce amount of wasted time a collision will occur. when a collision occurs. c. Ensure that no collisions d. Both a and b. occur at all. 6. Suppose that the average length of a contention interval on a CSMA bus is C and that the average time to transmit a packet is P. The efficiency of the channel is: a. P / C b. (P + C) / P c. P / (P + C) d. None of the above 7. Answer the following T or F. (Assume only the parameter indicated is being varied and all of the others remain fixed in each case. This question refers to a "traditional" shared bus ethernet.) ___ a. Increasing the average packet size will tend to make the efficiency of a CSMA CD LAN higher. ___ b. Decreasing the bit transmission rate from 10 Mbps to 1 Mbps increase the efficiency of a CSMA LAN 8. Suppose the value "t" represents the ONE WAY signal propogation delay between two stations on an ethernet and that the two stations transmit and cause a collision. Suppose station 1 began transmitting first and station 2 began transmitting second. Hint: the correct answers can be drawn (w/ replacement} from the following "urn": {0 t/2 2t 8t} \ t/4 4t / \____t____/ a. What is the shortest possible amount of time after station 1 starts transmitting that station 1 can hear the collision? b. What is the shortest possible amount of time after station 2 starts transmitting that station 1 can hear the collision. 9. Each time an IEEE 802.3 Ethernet station suffers a collision (without having a successful transmission) the mean delay until its next attempt a. Increase by tau (the one b. Increases by 2 * tau way prop delay). c. Doubles d. Increases by a factor of 2 ^ n where n is the number of collisions 10. When compared to 1 persistent protocols, p persistence tends to have a. more time wasted on b. less loss of time when collisions but less idle time collisions do occur c. smaller number of collisions d. better performance at very but larger amounts of idle low loads but worse performance time. under high loads. Computer Science 825 Quiz 4 Name _______________________ 1. For the IEEE token bus match the control packets with the conditions underwhich they are used. (Some answers may or may not be used multiple times and some may or may not be used at all.) ____ a. A station recognizes a WHO_FOLLOWS 1. SOLICIT_SUCCESSOR_2 packet specifying its predecessors address. 2. SET_SUCCESSOR_2 ____ b. A station wishes to leave the net. 3. WHO_FOLLOWS ____ c. A station transmits the token twice 4. RESOLVE_CONTENTION without hearing its successor transmit a token or a packet. 5. CLAIM_TOKEN ____ d. A station wishes to invite a new 6. SOLICIT_SUCCESSOR station to enter the network. 7. SET_SUCCESSOR 8. WHO_KNOWS 2. Starvation of all priority classes other than class 6 on all hosts class 6 can occur on an IEEE 802.4 token bus: (N = # of stations). a. Never b. Any time all stations have a large backlog of class 6 traffic c. Only if THT >= TRT 4 d. Only if N * THT > TRT4 3. When a token ring interface is operating in receive mode bits flow: a. into one of the onboard b. through the store and forward receive buffers buffer and on to the next station c. into the "bit-bucket" d. Both a. and b. 4. In a token ring on which of the following should the "Monitor" bit NEVER be set. (Check all that apply) ___ a. A high priority data frame. ___ b. A high priority token ___ c. A 0 priority token. 5. In a token bus suppose that THT = 20 msec, there are 30 stations, and TRT4 = 750ms. Suppose ALL stations have an infinite backlog of class 6 traffic, ONE station also has an infinite backlog of class 4 traffic, and no stations have any other traffic. For how long can the station with class 4 traffic send each time it gets the token. 6. Identify all pairs of the following 4 chip sequences that are NOT mutually orthogonal a. (+1 +1 -1 -1) b. (+1 -1 +1 -1) c. (-1 +1 -1 +1) 7. Simultaneous transmissions of data can occur simultaneously and non-destructively on which of the following LANs (Check ALL that apply) a. An ethernet using "shared b. A switched ethernet. bus. c. A token bus d. A token ring e. An ATM LAN 8. Answer the following TB, TR, or B depending upon whether the maintenance function is required in the MAC layer protocol of the token bus, token ring or both. ____ a. recovery from a lost monitor station ____ b. recovery from a lost token ____ c. admitting a new station to the network ____ d. removal of "orphan" frames 9. The use of large (as opposed to small) maximum token holding times under heavy loads on a token ring will provide: a. increased efficiency b. decreased efficiency c. have no effect on efficiency 10. What is the bandwidth in Hz of the range of frequencies that corresponds to all wavelengths between 1.0 x 10^(-6) m and 1.4 x 10 ^ (-6) m. 11. For each bit transmitted in a CDMA system how does the receiver decide whether the the chip sequence received represents a 0 bit or a 1 bit. IGNORE THE ISSUE OF MULTIPLE SENDERS SENDING AT ONCE HERE!! Computer Science 825 Quiz 5 Name _______________________ 1. The bit rate on an 802.11b wireless lan is closest to: a. a 10 Mbps Ethernet b. a 100 Mbps Ethernet c. a 1 Gbps Ethernet d. a 10 Gbps Ethernet 2. Which of the following does 802.3 ethernet DO but 802.11 wireless does NOT DO. (Identify ALL that apply) a. sense the carrier before b. detect collisions transmitting c. Jam the medium after a collision is detected 3. The primary motivation for the use of fragmentation in 802.11 but not in 802.3 (ethernet) is: a. Ethernet has a higher b. 802.11 uses much larger bit rate packets c. 802.11 has a much higher bit error probability 4. Which best characterizes the physical layers of DSL and DOCSIS a. Both use shared medium b. Dedicated point to point physical channels channels are used in both c. DSL uses shared but d. DSL uses dedicate but DOCSIS uses dedicated DOCSIS uses shared 5. The actual bandwidth in Mhz available on the PHYSICAL channel a. is much greater in DOCSIS b. is much greater in DSL than with DSL than in DOCSIS c. is about the same in both 6. In an 802.11b network, stations must execute the backoff procedure (i.e. draw a random number of slots to delay) a. Every time a packet is sent b. Only if the channel is initially sensed busy c. Only after a collision occurs 7. In an 802.11b network suppose that while station A is waiting for its backoff slot counter to count down to zero station B begins transmission. Which best characterizes the behavior of station A during the transmission of station B. a. its backoff slot counter will b. the count down will be continue to count down and if suspended during station B's it reaches 0 station A will Tx Tx and will resume as soon as station B finishes as soon as station B finishes c. When station B finishes station d. When station B finishes, station A will reset the counter to its A will double the size of the CWin original starting value and draw a new random number and restart the countdown. restart the countdown. 8. In an 802.11 system which of the following can NOT be Tx'ed immediately following the SIFs but before the DIF's expires a. an ACK b. RTS c. CTS (Downstream means -> the end-user system ) (Upstream means -> the Cable modem ISP) 9. In DOCSIS the MAP a. is transmitted downstream and b. is transmitted upstream and describes how the downstream describes how the upstream channel is to be allocated channel is to be allocated a. is transmitted upstream and b. is transmitted downstream and describes how the downstream describes how the upstream channel is to be allocated channel is to be allocated 10. Suppose two cable modem customers are on the same cable segment and one wishes to send a file to another. Which of the following best describes the situation a. since they are on the same b. Since they are on the same cable segment the data can segment it is impossible for be sent directly from one CM them to exchange any IP to the other. packets at all. c. They can communicate but all packets must be sent upstream to the CMTS and then back downstream to the other CM Suppose that EXACTLY 2 stations, both with an infinite backlog of traffic are contending for access to a shared channel. Suppose station A always randomly sets its backoff counter to one of the values {0, 1} and station B always sets its counter to one of the values {0, 1, 2, 3} 11. In the long term in what fraction of the slots will station B be successful in starting a Tx a. 1/2 b. 1/4 c. 1/8 d. 1/16 12. In the long term in what fraction of the slots will there be collisions a. 1/2 b. 1/4 c. 1/8 d. 1/16 Hint: The easiest way to do this is just to enumerate all the possible combinations of backoff values and count 'em up. Computer Science 825 Quiz 6 Name _______________________ 1. Suppose a 7 bit codeword with ODD parity is being used in a single bit hamming ECC. Suppose the following codeword is received. 1 0 1 0 0 1 1 ------------------- 1 2 3 4 5 6 7 Which (if any) bit is in error? 2. In SDLC bit stuffing algorithm the loss of a start flag (framing character) can be detected by: a. The appearance of some 0's b. The appearance of some 1's where where there should only be 1's there should only be 0's. c. The appearance of all 1's d. The appearance of all 0's where where there should be a mix of there should be a mix of 1's 1's and 0's and 0's. 3. a. Suppose a single bit Hamming ECC is to be performed on a 2047 bit codeword. How many bits are in each of the parity checked groups (include the parity bit itself). b. How many bits does any pair of parity checked groups have in common with each other? c. How many distinct parity groups does bit 254 belong to. e. Suppose a two bit error occurs. Circle the correct description of the result. 1. The fact that there is a two error can be detected, but the error can't be corrected. 2. The two bit error will be undetected and the value that results from the correction process will be a legal code word but it will be the wrong one. 3. The two bit error will be undetected and the corrected value will be either the wrong codeword or it might be the correct codeword. 4. The two bit error will be undetected and the corrected value MAY be an illegal code word. 4. Suppose 4000 bit code words are to be transmitted and it is desired to use a Hamming code to correct error bursts of up to 50 bits. How many of the 4000 bits must be used for ECC. (Hint: Fractional bit based strategies are not likely to be rewarded!) 5. Consider the following shift register: a. What will be the contents of the shift register after the input digits 0 and 1 are processed. b. What generator polynomial is represented by this shift register. 6. Suppose A generator polynomial of x + 1 is used. Answer the following T or F ___ a. Some, but not all, double bit errors in which the 2 error bits are not adjacent in the message will be detected. ___ b. Some, but not all, double bit errors in which the 2 error bits are separated by exactly 1 correct bit will be detected. ___ c. All triple (not necessarily adjacent) bit errors can be caught. 7. In the error detection business it is in general easier to detect errors in which a. An even number of bits are b. An odd number of bits are inverted inverted c. It makes no difference 9. Suppose an 8 bit code word is used. How many code words are at a Hamming distance of exactly 2 from a given code word. a. 56 b. 64 c. 28 d. 16 10. Suppose a generator polynomial of G(x) = x^4 is used. G(x) can detect a. Some, but not all, of the errors b. All errors involving the involving the last 4 bits of the last 4 bits of the message message and some but not all of the but no errors that do not errors that don't involve the last involve the last 4 bits. 4 bits. c. All errors involving any of d. All single bit errors but no more the last 4 bits of the message than that. and some errors not involving any of the last 4 bits. Computer Science 851 Quiz 7 Name _______________________ 1. In protocol 2, ACK's were used but no sequence numbers were used on frames or ACK's. Which of the following problems could occur. a. Lost frames would go b. Lost ACK's would result in undetected. lost frames c. Lost acks would result in d. Lost frames would result in duplicate frames. duplicate frames. 2. In protocol 3, frames's had sequence numbers but ACKS did not. Protocol 3 could fail in the presence of: a. ACK's that were lost b. ACK's that were excessively delayed c. Frames that were lost. d. Either a or b 3. When protocol 3 failed, the failure resulted in: a. The loss of 2 frames b. The loss of 1 frame and the duplication of 1 frame. c. The duplication of 2 d. The loss of 1 frame frames. 4. One way to prevent the failure discussed in questions 2 and 3 is to NOT ACK duplicate frames that are received. However, this won't work either because it leads to: a. Deadlock on a lost ACK b. Deadlock on a lost frame c. Deadlock on either a lost frame or a lost ACK 5. Consider the following simplex connection.. Since the connection is simplex the sender side needs only nxtack and nxtsend state variables and the receiver side needs only nxtrecv. Assume that: the "ACK next frame expected" convention is used; the protocol uses sender and receiver window size = N; sequence numbers never wrap; and NO timeout and retransmits occur. nxtack --------------------> nxtrecv nxtsend Answer the following T or F. At any instant in time: ____ a. nxtack must always be < nxtrecv ____ b. nxtrecv may be > nxtack ____ c. nxtsend may be < nxtrcv 6. Suppose in a connection such as described in question 5 that after the connection has been idle for a while with nxtsend=nxtack=nxrecv=0 and the sender sends a burst of 5 packets. Which of the following values will reach "5" last a. nxtsend b. nxtrecv c. nxtack d. They will all reach 5 at the same instant 7. Suppose that a satellite link has a ROUND TRIP propagation delay of 500 ms. Suppose bit transmission rate is 100,000 bits per second and packets are 5000 bits long. a. What will the efficiency of this channel be if stop and wait protocol is used. b. How large (in packets) must the SWS be in order to obtain 100% efficiency if the channel is guaranteed error free. (i.e. give me the MINIMUM SWS I can use). c. What is the MINIMUM size of the seq/ack number in bits that is required to support receiver buffering with out of order retransmission. 8. Show how a sliding window protocol that uses a 2 bit sequence number, a sender window of 3 and a receiver window of 2 can fail. 9. For each of the following combinations of propogation delay and error rate identify the most suitable variation of sliding window protocol. (The most suitable choice is the SIMPLEST one that doesn't incur a big performance penalty.) ___ a. No errors but very long 1. Stop and Wait propogation delay ___ b. No errors and packet time 2. Go back N >> propogation delay. ___ c. High errors and very long 3. Selective reject propogation delay Computer Science 825 Quiz 8 Name _______________________ 1. A buffer in the protocol discussed in class cycled though a number of queues.. Associate each transition with the process that caused it. (Some answers may be used more than once or not at all). ____ 1. Read pending to network a. Network layer process input. ____ 2. Network input to link b. Queuemsg process station output c. Timeout process ____ 3. Link output to sender window. d. Writelink process ___ 4. Sender window to free e. Readlink process list 2. The sender window logic used three indexes: nxtsend; nxtqueue; and nxtack. We said these values always remained in a specific relative order. The order was a. send <= queue <= ack b. queue <= ack <= send c. ack <= queue <= send d. send <= ack <= queue e. None of the above 3. The value of the counting semaphore wpcount (that counted the number of packets waiting to be written is given by: (assume no sequence # wrap). a. queue - ack b. send - queue c. send - ack d. queue - send 4. Suppose the sequence number has 4 bits. Then the value of the semaphore numslots is: (assume modular arithmetic is properly handled) a. 16 - (queue - ack) b. 16 - (queue - send) c. 15 - (queue - send) d. 15 - (queue - ack) 5. When a process becomes blocked on a counting semaphore it necessarily depends upon some OTHER process to signal the semaphore and unblock it. For each of the following identify the process that is responsible for unblocking it AFTER IT BLOCKS ON A COUNTING SEMAPHORE. ___ a. network layer 1. queuemsg ___ b. readlink 2. readlink ___ c. writelink 3. writelink 4. network layer 6. Supervisory frames in SDLC carry a. Both sequence numbers and b. Sequence numbers but no ack ack numbers. numbers c. Ack numbers but no sequence d. No numbers at all. numbers. 7. Select the description which most accurately matches the use of the P/F bit in SDLC. a. 1 -> Poll and 0 -> Final b. The bit means poll or not poll when a secodary sends final or not final when a primary sends. c. The bit means poll or not d. The bit means poll or not poll poll to the sender final when the primary sends final or or not final to the receiver not final when a secondary sends. 8. Which of the following are NOT use(s) of supervisory frames in SDLC Circle ALL that are not. a. Sending a standalone ack b. Seeing if another station is back up after a crash. b. Responding negatively to d. Telling another station to a poll as in (I have nothing temporarily stop sending. to send right now). 9. Which of the following messages has suitable semantics for the unnumbered protocol. Hint: This question is NOT asking what specific frame types are in SDLC. It IS asking what limitations are on the semantics of messages in protocols in which frames and acks carry no numbers. a. Set current ack # to 0. b. XOR current seq # w/ 0xff c. Both a and b. d. Neither a nor b. 10. The "failure" that the unnumbered protocol is susceptible to is: a. Undetected loss b. Undetected duplication of of a frame. a frame. c. Reordering of frames d. Both a. and b. 11. In the SSCOP, when NO packets have been lost, a STAT packet will contain three fields. Identify what they are in a way the indicates you understand their usage (i.e. abstract notation such as N(X) doesn't get the job done). a - b - c - 12. In the SSCOP, when the last packet to have been received successfully and in order is 56 and the the packets that have been received since then include 58, 59, 60, 62, 63 The list part of the next "stat" packet should include: a. 58 60 62 b. 57 61 c. 57 58 61 d. 57 58 61 62 Computer Science 825 Quiz 9 Name _______________________ 1. Identify the class of service provided to the transport layer by each of the following network layers. ___ a. IBM SNA a. Unreliable connection oriented ___ b. Internet Protocol b. Reliable connection oriented ___ c. ATM c. Unreliable connectionless d. Reliable connectionless 2. The relationship between error rate and the desirability of using a reliable connection oriented network layer versus an unreliable datagram oriented network layer is that: a. Many hops with high error b. Many hops with high error rates favors datagram service rates favors reliable connection oriented service. c. The number of hops and the error rates have no particular effect. 3. In a network that uses SPF suppose rout station A constructs the following cost matrix To A B C D A 0 5 2 - F r B 3 0 4 3 o m C 3 2 0 9 D - 9 12 0 Draw the routing tree from node A to all destinations. Label the EDGEs of the graph in the order in which they are made permanent in the SPF algorithm. 4. The expected number of total transmissions to get a packet from one end to the other if a reliable network layer is used is: (The reliable network repeats transmissions at each hop until it succeeds). a. 1 / p b. 1 / Np c. N / p d. p / N 5. Each routing update packet propagates a. Across the entire net in SPF b. Only to adjacent neighbors in SPF and in Bellman-Ford and Bellman Ford c. Across entire net in SPF but d. Across entire net in B-F but only only to adjacent neighbors in B-F to adjacent neighbors is SPF 6. Let N = number of nodes in a network and M = the average number of links / node. a. The size of a routing info packet in Bellman-Ford is of order 1. M 2. N 3. N ^ 2 4. N ^ M b. The minimum number of routing packets transmissions at each complete exchange in Bellman Ford within the entire network is of order: 1. M 2. N 3. N ^ 2 4. M ^ 2 5. N * M c. The minimum number of routing packets transmissions at each complete exchange in SPF within the entire network is of order: 1. M 2. N 3. N ^ 2 4. M ^ 2 5. N * M 7. Suppose the Bellman-Ford routing algorithm is being used and station B receives the following routing updates from neighbors A, C and E Suppose BA delay = 1, BC delay = 5 and BE delay = 6 Complete the routing table for B., Total A C E Cost VIA A 0 2 6 | ------------ ---------- B 5 11 7 | ------------ ---------- C 2 0 6 | ------------ ---------- D 8 5 2 | ------------ ---------- E 6 8 0 | ------------ ---------- 8. In the network shown suppose all hosts know the optimal route to A (hop count metric) and A initiates a reverse path forwarding broadcast. How many unnecessary transmissions will occur? 9. The counting to infinity problem occurs in which of the following routing systems a. SPF b. Bellman-Ford c. Backward learning d. All of the above 10. Each routing update packet propagates a. Across the entire net in SPF b. Only to adjacent neighbors in SPF and in Bellman-Ford and Bellman Ford c. Across entire net in SPF but d. Across entire net in B-F but only only to adjacent neighbors in B-F to adjacent neighbors is SPF Computer Science 825 Quiz A Name _______________________ 1. Preallocation of resources is a practical mechanism for congestion avoidance a. Only for reliable connnection b. for either reliable or unreliable oriented network layers connection oriented networks c. Only for connection-less network d. Works fine for all of the above layers 2. Packet discarding is a practical mechanism for congestion avoidance a. Only for unreliable connnection b. for either reliable or unreliable less network layers connection less networks c. For unreliable connection d. Works fine for all of the above oriented and unreliable connection less network layers 3. Suppose that "leaky bucket" and "token bucket" admission control algorithms support identical maximal long-term sustained admission rates. Which of the following best characterizes their response to short high-rate arrival bursts: a. Leaky bucket allows short b. Token bucket allows short term admission rate to exceed term admission rate to exceed long term rates but token bucket long term rates but leaky bucket does not. does not. c. Both allow short term admission d. Neither allows short term rates rates to exceed long term rates. to exceed long term. 4. Suppose an ATM cell arrival process is found to have a mean arrival rate of 80 cells per second and the outgoing link can send at a rate of 100 cells per second. In the long term what percent of the time is the link busy? 5. Suppose that the arrival distribution is found to be approximately Gaussian (a.k.a. normal and bell-shaped-curve) with variance of about 36. Would you expect signficant queuing delays in such a system? Hint: For the Gaussian distribution P[observing a value more than three standard deviations from the mean] ~ 0.013.) a. Yes, huge queues b No, modest queues of around 5 cells most of the time. c. Almost no queuing 6. The likelihood of observing 200 arrivals in a given second is a. increases as the variance of b. decreases as the variance of the distribution increases increases c. is independent of the variance d. increases as either the variance and depends on the degree of or the self-similarity increases self-similarity. 7. Answer the following characterization of standard RED dropping algorithms T or F. ____ a. P[dropping] > 0 regardless of queue length ____ b. P[dropping] = 1 for all queue lengths > some N ____ c. P[dropping] always = 0 or 1 8. The primary objective of the spanning tree algorithm in a transparent bridge system is to: a. Reduce the number of b. Prevent indefinite packet looping. destination unknowns c. Ensure that the optimal d. All of the above. route is taken. 9. Which routing algorithm is used by the spanning tree bridge if the location of the destination node is UNKNOWN? a. Spanning tree. b. Flooding c. Backward learning. d. Shortest past first. 10. With respect to the objective of Shortest Path Routing, which of the two bridging techniques we studied is superior. a. Spanning tree b. Source routing c. Both provide optimal paths 11. Which routing algorithm does the spanning tree bridge employ in order to minimize the occurrences of destination unknowns. a. Spanning tree. b. Flooding c. Backward learning. d. Bellman-Ford. 12. Consider the bridged network shown. Circles are bridges and lines LANs. Mark each interface on each bridge "R", "D", or "N" depending up whether it is the "Root Port", "Designated bridge port for the LAN", on "NOT in the spanning tree". Computer Science 825 Quiz B Name _______________________ 1. In the old class based IP address assignment architecture, which class of net does a node whose address is 129.215.17.139 belong to. a. A b. B c. C d. D 2. IP datagrams can be up to 64K in size but the fragment offset field is only 13 bits. How is it possible to know where a fragment is supposed to be placed if a datagram is larger than 8KB? 3. In IPV4 fragmentation and reassembly are performed as follows: a. Both can occur anywhere b. Source host must fragment but reassembly is done just past the "bottleneck" router c. Fragmentation may occur d. Fragmentation always occurs at anywhere but reassembly occurs the source and reassembly at only at the destination. the destination. 4. Ten years ago it was predicted that the IP V4 address space would be exhausted by the year 2000. The widespread use of two new capabilities has greatly extended the life of the address space What are they called? Hint one has a 3 letter acronym and the other a 4 letter one. 1 - 2 - 5. Default routes are widely used for Internet scope routing by: a. Only host systems b. Host systems and routers in stub Autonomous systems c. All hosts and all routers in the internet 6. The full 20 byte ATM address is used in (circle all that require the full address). a. SVC setup b. Routing of individual cells of an established SVC c. PVC setup d. Routing of PVC cells 7. The number of address bytes that each ATM host "inherits" from the switch to which it is attached is: a. 6 b. 13 c. 14 d. 19 8. Provide the order in which the following components of an type 2 ATM address appear: __1__ a. The 0x47 that identifies this is a type 2 address _____ b. The 6 byte MAC address on a host systems ATM NIC ____ c. The international standards body that assigned the ATM network address (DIN, NIST, etc) ____ d. The selector (or ATM port) byte ____ e. The public ATM network identifier 9. The connection identifier (vpi, vci) for a new SVC is assigned by a. the switch to which the host b. the originating host O/S is connected c. the application program d. the destination host O/S 10. The connection identifier (vpi, vci) for a specific SVC a. never changes b. MUST change at each hop c. MAY change at each hop 11. Which of the following is an ATM network layer not permitted to do a. Discard cells b. Deliver cells with multiple bit errors c. Reorder cells d. All of the above 12. Suppose a host connected to router A wants to connect to router D through the path (A, B, E, D). Update the routing tables using the label switching algorithm described in class: (you will need to add one line to each of the 4 tables). Router A Router B Router E Router D From To From To From To From To H 0 B 0 A 0 E 0 G 0 D 0 E 0 H 0 H 1 B 1 A 1 E 1 B 0 F 0 K 0 F 0 B 0 C 0 E 0 A 0 B 1 F 1 K 1 F 1 H 2 C 1 G 0 E 2 B 2 G 0 H 0 E 0 D 0 B 0 Computer Science 825 Quiz C Name _______________________ Suppose a 3 way handshake is being used to establish a connection. Let SYN-1 represent a packet that carries SYN and no ack. Let SYN-2 represent a packet that carries both SYN and ACK that is sent in response to a SYN. 1. A delayed duplicate SYN1 received in the ESTABLISHED state is: a. Responded to with SYN2 b. Always causes TCP to crash. c. Responded to with RESET. d. Responded to with a data packet specifying current ACK and SEQ. 2. A delayed duplicate SYN2 received in the SYN-sent state is detected because: a. Both SEQ and ACK are b. Undetected and causes the known to be wrong. recipient to respond with a SYN-2 c. The SEQ number is wrong. d. The ACK number is wrong. 3. A delayed duplicate SYN1 received in the LISTEN state is: a. Responded to with RESET. b. Responded to with a data packet specifying current ACK and SEQ. c. Responded to with SYN2 d. Always causes TCP to crash. 4. Suppose Tomlinson's clock proposal is used with a 16 bit sequence number and a clock that ticks 1024 times a second. Suppose maximum packet lifetime is 20 seconds. a. What is the MINIMUM amount of time in seconds that can elapse before sequence number resynchronization must occur. b. How often will synchronization be needed if packets are generated at 15/16 the maximum allowed rate. c. If the initial sequence number is 0 what will be the sequence number at the time resequencing takes place. (in question b). 6. Suppose a TCP connection has SND.UNA = 4000 and SND.NXT = 8000 and a packet arrives with ACK = 6000 and WINDOW = 10000. a. How many more bytes may be transmitted before the sending TCP must stop sending because it runs out of usable space in the sender window. b. Suppose the sending application has an allocation of 16000 bytes of transmit buffer space. The application will be put to sleep when it tries to send a packet which contains what sequence number?? 7. Suppose receive buffer space is 20,000 bytes, rcv.buf = 2000 and rcv.nxt is 6000. a. What values will be sent in outgoing packets for WINDOW = ACK = b. What if a packet with SEQ = 7000 and length = 1000 is now received what will outgoing window and ack be now? WINDOW = ACK = c. What if a packet with SEQ = 6000 and length = 1000 is now received what will outgoing window and ack be now? WINDOW = ACK = d. Finally assume that the application reads 3000 bytes. what will outgoing window and ack be now? WINDOW = ACK = 8. Suppose a receiver in the stop and wait file transfer protocol uses an ack then write policy and the sender uses a policy of NEVER retransmitting after a crash. Identify whether each of the following sequence of events will result in correct behavior (OK) a lost packet (LOST) or a duplicate (DUP). AWC AC(W) C(AW)