Computer Science 825 Quiz 1 Name _______________________ Terminology: the very highest layer is the APPLICATION LAYER = Layer N these questions refer to the ISO/OSI 7 layer model 1. a. Which of the seven layers of the ISO-OSI model is the LOWEST layer that is typically found in each host computer but not found in an router/switch/IMP b. Which layer is responsible for routing and congestion control. c. Which layer is traditionally responsible for making the physical layer to appear as an error free connection. 2. 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. 3. In the "apocalypse of the two elephants" what do the X and Y axes represent: X - Y - 4. For each of the following layers answer (E) if the layer has only endpoint-to-endpoint interoperability issues (P) if the layer has only point-to-point interoperability issues and (G) if the layer has global interoperability issues ___ a. Session ___ b. Data link ___ c. Network 5. 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 6. How many signalling states are needed to achieve a bit rate of 32000 bits / second while signalling at a rate of 4000 baud 7. Suppose a channel passes harmonics in the range 20Khz - 30Khz. In decribing bandwidth and bit rates "K" always represents 10^3 and not 2^10) a. What is the minimum useful duration (in seconds) for signalling states. b. How many distinct signaling states are needed to achieve a bit rate of 60,000 bps. 8. Enumerate four DISTINCT actions that a protocol might engage in to earn the title "unreliable: 1 - 2 - 3 - 4 - 9. 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 bandwidth is required to support a bit rate of 64,000 BPS on a channel with a 30dB SNR? 2. The main reason digital channels have much lower error rates than analog when used over long distances is: a. Digital signalling is baseband c. Digital signals are amplified instead of analog. rather than regenerated. b. Digital signals are regenerated d. Digital channels have much higher rather than amplified. SNR's than analog. 3. 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. 4. In addition to the phase angle, identify two other parameters of a sine wave signal that are commonly modulated. 1 - 2 - 5. The use of very small slot sizes in a TDM multiplexing scheme is: a. Inefficient and shouldn't b. Generally shouldn't be used for be used in either 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 6. 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 7. What bit rate is required to support a new "hi-fi" PCM phone that supports frequencies to 16Khz and quantizes the signal into 1024 discrete levels. 8. 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 200,000 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. 9. Suppose headers of length H bits are used in the packet switching scheme described above. Suppose packet size is P (where P now includes header+data bits). Under this new scheme the time required for a single transmission of a complete packet is: a. 10000 / (P + H) b. 10000 / (P - H) c. 10000 * P d. P / 10000 10. Under the new scheme the total number of packets that must now be transmitted is: a. 200,000 * P b. 200,000 / P c. 200,000 / (P + H) d. 200,000 / (P - H) 11. 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 Computer Science 825 Quiz 3 Name _______________________ 1. Measurements of an infinite user slotted aloha channel show that 40% of the slots are idle. a. What is the total load (mean number of transmission attempts per packet time) = G. b. What is the expected number of transmission attempts required for each successful transmission. c. Is the current load below or above the load required to obtain maximum throughput. 2. 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 longest possible amount of time after station 1 starts transmitting that station 1 can hear the collision? c. What is the longest possible amount of time after station 2 starts transmitting that station 2 can hear the collision? d. What is the shortest possible amount of time after station 1 starts transmitting that station 2 can hear the collision. 3. 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. 4. In a dual persistent protocol a station transmits with prob p when it initially sense a channel idle and with prob q when it has to wait for a busy channel to become idle. The proper relationship between p and q is: a. p < q b. p > q c. p = q d. q = 1 and p < q 5. If K stations share a CSMA 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 b. k * p * (1 - p) ^ (k - 1) c. p * (1 - p) * (k - 1) d. None of the above. 6. If the probability computed above is denoted A, then the probability that a contention interval will last exactly j slots is: a. A ^ j * (1 - A) ^ (j - 1) c. A / j b. (1 - A) ^ (j - 1) d. None of the above. 7. Parameters that effect the efficiency of a CSMA channel include the bit rate B, the packet size P, and the length of the wire L. For each parameter indicate whether increasing the value of the parameter will increase (I) or decrease (D) the efficiency of the channel (assuming the other characteristics don't change). ___ a. Bit rate ___ b. Packet size ___ c. Length of the wire 8. 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 9. Select the appropriate window of vulnerability for collision OCCURRENCE in each of the following MAC protocols: (n.b. the question says occurrence and not detection) ____ a. Pure aloha 1. One byte time 2. One packet time ____ b. Slotted aloha 3. Two packet times 4. The one way propogation delay ____ c. Ethernet style 5. The two way propogation delay CSMA-CD 6. Two times the bit rate Computer Science 825 Quiz 4 Name _______________________ 1. Multiple transmissions of data can occur simultaneously and non-destructively on which of the following LANs (Check ALL that apply) a. A shared bus CSMA CD ethernet b. A switched ethernet. c. A token bus d. A token ring e. An ATM LAN 2. 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 transmits WHO_FOLLOWS 1. SOLICIT_SUCCESSOR_2 and receives no response. 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 ____ e. A station recognizes a WHO_FOLLOWS packet specifying its predecessors 8. WHO_KNOWS address. 3. Starvation of all priority classes except 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 4. 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. 5. In a token ring, bits are drained into the "bit bucket" when the interface is operating in: a. recieve mode b. transmit mode c. store and forward mode d. all of the above 6. In a token bus suppose that THT = 10msec, there are 20 stations, and TRT4 = 300ms. 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. 7. 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. 8. The 802.5 token byte contains 4 fields: For each pair identify WHICH FIELD APPEARS BEFORE THE OTHER in the token. In each case identify the SPECIFIC PROBLEM that it would prevent the 802.5 from working as advertised if the order were inverted (assuming the use of a 1 bit store and forward buffer) a. P(riority) and R(eservation) b. M(onitor) and T(token) 9. In a token ring the monitor will drain a data frame a. the first time it sees b. the SECOND time it sees M=1 on the frame M=1 on the frame. c. the SECOND time is sees M=0 on the frame 10. 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 11. Are the following three 4 chip sequences mutually orthogonal? (+1 +1 -1 -1) (+1 -1 +1 -1) (-1 +1 -1 +1) Computer Science 825 Quiz 5 Name _______________________ 1. What difference(s) in the characteristics of the 802.11 wireless and 802.3 ethernets makes the RTS/CTS protocol useful in 802.11 but not useful in 802.3. 2. The RTS/CTS protocol is of primary benefit with: a. DCF b. PCF c. Equal benefit in both. 3. In what order do the following interframe slots appear in an 802.11 LAN. ___ a. DIFS ___ b. SIFS ___ c. PIFS 4. 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 5. Which of the following 802.11 variants uses the 5 GHz band: a. 802.11a b. 802.11b c. 802.11c d. 802.11g 6. In the standard bit stuffing the loss of an end 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. 7. Suppose a BISYNCH message consists of the following byte pattern while it is "on the wire". Write down the data part of the message AFTER the receiver removes the "stuffed" bytes. | this is the data part of the msg | ------------------------------------------------------------------ | DLE | STX | 'A' | DLE | DLE | 'B' | DLE | DLE | ETX | DLE | ETX | ------------------------------------------------------------------ 8. 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 9. 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 (Downstream means -> the end-user system ) (Upstream means -> the Cable modem ISP) 10. 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 11. The number of contention mini-slots per frame should a. increase as load increases b. decrease as load increases c. should be independent of load 12. 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 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. 0 1 1 0 0 1 1 -------------------- 1 2 3 4 5 6 7 Which (if any) bit is in error? 2. a. Suppose a single bit Hamming ECC is to be performed on a 127 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 33 belong to. d. 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. 3. Suppose 1000 bit code words are to be transmitted and it is desired to use a Hamming code to correct error bursts of up to 100 bits. How many of the 2000 bits must be used for ECC. (Hint: Fractional bit based strategies are not likely to be rewarded!) 4. Suppose a distance 3 Hamming code is being used. We all (hopefully) know that this code can correct single bit errors. We can also use such a code to do ERROR DETECTION ONLY. In such an application the best that the code can detect is: a. Single bit errors b. Double bit errors c. Triple bit errors d. No errors at all 5. Suppose A generator polynomial of x + 1 is used. Answer the following T or F ___ a. All double bit errors in which the 2 error bits are adjacent in the message will be UN-detected. ___ b. All double bit errors in which the 2 error bits are not adjacent in the message will be detected. ___ c. All triple (not necessarily adjacent) bit errors can be caught. 6. Suppose a generator polynomial of G(x) = x^3 is used. G(x) can detect a. Some, but not all, of the errors b. All errors involving the involving the last 3 bits of the last 3 bits of the message message and some but not all of the and some errors that do not errors that don't involve the last involve the last 3 bits. 3 bits. c. All errors involving any of d. All single bit errors but no more the last 3 bits of the message than that. but no errors not involving any of the last 3 bits. 7. 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. 8. 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 9. When protocol 3 failed, the failure resulted in: a. The loss of 1 frame b. The loss of 1 frame and the duplication of 1 frame. c. The duplication of 2 d. The loss of 2 frames frames. 10. The bisynch protocol introduced the use of the ENQ packet. An ENQ is used a. by the sender to request b. Used by the receiver to that the last ACK be request that the last retransmitted. packet be retransmitted c. Both of the above d. Neither of the above. Computer Science 825 Quiz 7 Name _______________________ 1. 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. 2. Suppose an ATM LAN has a ROUND TRIP propagation delay of 100 usec. Suppose bit transmission rate is 20 Mbps. What packet size in bits is required to obtain 90% efficiency using a Stop and Wait protocol. 3. Produce a packet exachange diagram similar to the one in the notes to 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. 4. 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 packet time 1. Stop and Wait << propagation delay ___ b. No errors but packet time 2. Receiver buffering w/ out of >> propagation delay. order retransmission ___ c. High errors and packet time << propagation delay 3. Receiver buffering w/ go back N sender 4. Go back N. 5. 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 6. 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 7. 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 8. 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) Computer Science 825 Quiz 8 Name _______________________ 1. Identify the two major capabilities that are required in a robust and reliable datalink protocol that were not implemented in the sample protocol. (Hint: possible susceptibility to deadlock under extreme loads is NOT one of them). a - b - 2. The address byte in an SDLC packet always carries the address of a. The sender b. The receiver c. The primary station. d. The secondary station. 3. 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. 4. 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. 5. Which of the following is NOT a use of supervisory frames in SDLC a. Sending a standalone ack b. Requesting initialization after power-on. b. Polling d. Telling another station to temporarily stop sending. 6. 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. Increment current seq # b. Set current seq to 0xff c. Both a and b. d. Neither a nor b. 7. Suppose unnumbered frames were given sequence numbers and ACK numbers just like data frames and that the receiver of an out of sequence unnumbered frame would discard it just as it would an out of sequence data frame. Would this make the functions performed with unnum frames work: a. Much better and more b. Work worse and less reliably. reliably. c. Make no appreciable difference. 8. 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. 9. Framing in ATM involves the use of a 40 bit shift register. 40 bits are used because: a. ATM cells are 40 bits long b. ATM cell headers are 40 bits long c. A degree 40 generator polynomial is used in the CRC. 10. 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 - 11. 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. The use of a RELIABLE network layer is more desirable a. with very unreliable links b. with very reliable links than with very reliable links than with very unreliable links c. has to relation to the reliability of the links. 2. 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 size of a routing info packet in Bellman-Ford is of order 1. M 2. N 3. N ^ 2 4. N * M 3. 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 = 2, BC delay = 4 and BE delay = 3. Complete the routing table for B., A C E Cost VIA A 0 9 6 | ------------ ---------- B 5 11 7 | ------------ ---------- C 2 0 3 | ------------ ---------- D 8 5 2 | ------------ ---------- E 6 8 0 | ------------ ---------- F 11 2 7 | ------------ ---------- 4. 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 5. The routing algorithm used to transmit routing updates in an SPF network is typically: a. Static tables built by b. Backward learning sysadmin c. Bellman-Ford d. Flooding 6. Routing loops can occur in SPF a. only when all nodes use the same b. only when some nodes use a cost matrix different matrix than others c. in both cases a. and b. d. Never, the SPF algorithm ALWAYS guarantees optimal routes 7. One of the problems with the original use of the Bellman-Ford algorithm in the ARPANet was unstable routing and loops. A contributing factor to the instability was that: a. Routing information was b. Old duplicate copies of often lost routing info was delivered c. Routing info exchanges d. Routing info exchanges were not frequent enough were too frequent. 8. Let N = number of nodes in a network and M = the average number of links / node. a. The size of each routing update packet transmitted in an SPF net is proportional to 1. M 2. N 3. N ^ 2 4. N * M b. In terms of computational complexity the SPF algorithm as performed by a single node 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 an SPF network within the entire network is of order: 1. M 2. N 3. N ^ 2 4. M ^ 2 5. N * M 9. In a network that uses SPF suppose station D constructs the following cost matrix To A B C D E A 0 2 - - 4 F B 5 0 6 - 9 r o C - 2 0 7 2 m D - - 12 0 4 E 1 9 2 5 0 What are the first two edges that will be constructed in building the optimal routing tree with node D as root. Note that the routing tree is a digraph and so edges should be identified as XY where X is the "source" node and Y the "dest" node. 10. The routed and gated routing daemons are primarily use for routing a. Within an AS b. between AS's c. Used for both purposes Computer Science 825 Quiz A Name _______________________ 1. a. Suppose network addresses are 20 decimal digits and flat routing tables are used. What is the maximum number of entries that may be required in a routing table. b. Suppose hierarchical routing is used and the addresses are partitioned as an 6 digit Area address; an 8 digit Network address and a 6 digit host addres. Now what is the maximum number of routing table entries. 2. Order the following broadcast algorithms according to the number of packet transmissions needed to complete a broadcast (1 = least transmissions; 3 = most). ______ a. Reverse Path Forwarding ______ b. Spanning tree. ______ c. Flooding 3. 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? 4. Suppose a wide-area multicast protocol is in effect and a router receives a message indicating that a host to which it was forwarding the multicast no longer wants to receive it. That request should be forwarded upstream toward the source of the m'cast if: a. there are no more hosts downstream b. there are additional hosts of the router who are receiving the downstream who continue mcast. to receive it. c. it must always be forwarded upstream d. it should never be forwarded upstream 5. 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 6. The main factor that determines whether or not packet-discarding can be used as a congestion control mechanism in a network layer is: a. Whether the network layer b. Whether the network layer is is connection oriented or reliable or unreliable connection less. c. Both are equally important. d. Neither is important at all. 7. 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. 8. Suppose three traffic arrival streams have the same mean arrival rate. Order the streams from 1 (smallest queue length) to 3 (largest queue length) according to the the following characteristics: ____ a. High variance ... no self-similarity ____ b. High variance ... high degree of self-similarity ____ c. Very low variance ... high degree of self-similarity. Suppose an ATM cell arrival process is found to have a mean arrival rate of 200 cells per second and the outgoing link can send at a rate of 250 cells per second. 9. In the long term what percent of the time is the link busy? 10. The observed queue length will increase a. only when more that 200 cells b. only when more than 250 arrive in a second cells arrive in a second c. only when more that 500 cells arrive in a second. 11. The likelihood of observing 400 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 and depends on the degree of self-similarity. Computer Science 825 Quiz B Name _______________________ 1. 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. 2. 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. 3. Which routing algorithm is used by the source routing bridge in routing "discovery" packets to the destination. a. Spanning tree. b. Flooding c. Backward learning. d. Shortest path first. 4. 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. 5. 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 6. 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". 7. If multiple Links exist between SNA nodes, it is possible to group them all into a single transmission group or to create several transmission groups having a smaller number of links.. What is the advantage of each approach. a. Single TG with all the links b. Multiple TGs with fewer links 8. Suppose nodes B, D, and F's static tables contain the following entries: Dest ER# Via/TG Dest ER# Via/TG Dest ER# Via/TG B: A 2 1 D: A 2 1 F: A 1 1 A 8 3 A 9 1 A 7 2 A 9 3 A 11 1 A 9 2 If A activates (7,F) through B then D what are the possible ER number(s) for the reverse ER. 9. The relationship between SNA session and Virtual Routes is that a. Many VR's may concurrently b. Many sessions may be assigned assigned to a single session to a single VR (application layer connection) c. There is a one to one mapping between sessions and VR's 10. The normal lower bound for Pacing Group Size in a SNA VR is: a. 1 packet b. the number of connections using the VR c. The number of hops on the VR d. the number of hops * the number of connections 11. When a SNA VR manager receives a Pacing Response before it completes sending a full pacing group, it should: a. reduce the current pacing b. increase the current pacing group size by 1 group size by 1 c. Don't change the pacing d. set the current pacing group group size size to the minimum size. Computer Science 825 Quiz C Name _______________________ 1. 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. 2. In the old class based IP address assignment architecture, which class of net does a node whose address is 120.215.17.139 belong to. a. A b. B c. C d. D 3. 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? 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. The number of distinct ATM addresses that can normally be associated with a particular end system is: a. 1 b. 2^8 c. 2^20 d. 2^160 7. The full end-system 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 8. 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 9. The number of address bytes that each ATM host "inherits" from the NIC hardware is: a. 6 b. 13 c. 7 d. 19 10. The connection identifier (vpi, vci) for an SVC is assigned by a. the edge switch b. the originating host O/S c. the application program 11. The connection identifier (vpi, vci) for a specific SVC a. never changes b. MUST change at each hop c. MAY change at each hop 12. Which of the following is NOT one of the factors used in defining the ORIGINAL ATM service categories a. reliable vs non reliable b. real time vs non real time service c. connection oriented vs d. constant vs variable bit connection less service rate 13. Which was of the following was NOT a design objective of IPV6. a. Enlarge the internet address b. Provide better support space. for mobile hosts. c. Provide additional fragmentation d. Reduce computing time and table facilities to make it more ATM size requirments in backbone compatible. routers Computer Science 825 Quiz D Name _______________________ 1. The principal factor that makes it more difficult to construct a reliable transport protocol over an unreliable network layer than to construct a reliable data link protocol over an unreliable wire is: a. An unreliable network layer b. An unreliable network layer may lose packets but wire can cause out of order delivery cannot. with big delays but a wire cannot. c. The unreliable network layer d. Both a. and b. apply equally. will never deliver damaged packets like the wire does. 2. An implementation of Tomlinson's strategy requires: a. A real time clock that ticks at b. A known upper bound on packet least as fast as packets can be lifetime. generated. c. A real time clock that ticks no d. Both a. and b. faster than packets can be generated. 3. Suppose Tomlinson's clock proposal is used with a 18 bit sequence number and a clock that ticks 4096 times a second. Suppose maximum packet lifetime is 9 seconds. a. What is the MINIMUM amount of time that can elapse before sequence number resynchronization must occur. b. How often will synchronization be needed if a packet is generated at 3/4 the maximum rate. 6. Suppose a TCP connection has SND.UNA = 2800 and SND.NXT = 3400 and a packet arrives with ACK = 3200 and WINDOW = 1000. 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 20000 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 an application has an allocation of 8,000 bytes of TCP receive buffer space. The last byte that the application has consumed is 4000 and the present offered window is 7000. What is RCV.NXT? 8. Now suppose the application consumes 500 additional bytes of data and the receiver sends a standalone ACK. This packet will carry ACK = and WINDOW = 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. 9. 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. 10. A delayed duplicate SYN1 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.