Computer Science 825 Quiz 1 Name _______________________ Terminology: the very highest layer is the APPLICATION LAYER the very lowest layer is the PHYSICAL LAYER 1. a. What is the lowest layer which is normally present in hosts but not in IMP's. b. At which layer is it most necessary that a common protocol be implemented within all nodes of a network. 2. Do protocols (as the term is normally used in networking, e.g in SDLC, TCP, or IP) define the rules under which a layer communicates a. With the layer above it b. With a peer layer in another node. c. With the layer below it. d. All of the above. 3. Two things that a protocol can do to earn the term "unreliable" are (1) deliver packets with bits that have been inverted and (2) lose packets. Identify two others: a. b. 4. For two separate implementations of a specific network architecture to interoperate correctly it is necessary that: a. Internal interlevel interfaces b. Intra level peer protocols be comptatible. be compatible c. Both a and b. d. Neither a. or b. 5. a. What is the minimum number of signalling states necessary to transmit 48,000 bits per second on a noise free channel that has a bandwidth of 4000hz. b. What would be the BAUD rate of a modem performing this function. 6. What bandwidth is required to support a bit rate of 100,000 BPS on a channel with a 40dB SNR? 7. 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. 8. Diagram an example of a 2 bit per baud phase shift modulation scheme which is self clocking and one which is not. a. Self clocking: b. Not self clocking: 9. 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. 10. 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. Computer Science 825 Quiz 2 Name _______________________ 1. 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 2. What bit rate is required to support a new "hi-fi" PCM phone that supports frequencies to 12Khz and quantizes the signal into 1024 discrete levels. 3. If packets are generated at random (exponentially distributed) by each station on a shared channel, then statically assigning 1/Nth of the bandwidth to each station (rather than having a single waiting queue) a. Will have no appreciable effect b. Will cause the delay to increase on the queueing delay. by a factor of N c. Will cause the delay to be reduced d. Will cause the delay to increase by a factor of N by N seconds. 4. 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 4000 bit packets are used. 5. 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 to send a complete packet is: a. 10000 / (P + H) b. 10000 / (P - H) c. 10000 * P d. P / 10000 6. 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) 7. Measurements of an infinite user pure aloha channel show that 40% of the slots are idle. What is the throughput, S. 8. As the load G on a pure aloha channel becomes VERY large the expected number of successful transmissions per packet time: a. Approaches zero. b. Increases linearly b. Approaches a fixed upper bound d. Increases exponentially asymptotically 9. 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. 1.5 Million 10. Multiplexing of voice and data channels is done in ISDN and ADSL as follows: a. FDM is used in both. b. TDM is used in both c. FDM is used in ISDN but d. TDM is used in ISDN but TDM is used in ADSL FDM is used in ADSL Computer Science 825 Quiz 3 Name _______________________ 1. Measurements of an infinite user slotted aloha channel show that 60% 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 1 starts transmitting that station 2 can hear the collision? d. What is the shortest possible amount of time after station 2 starts transmitting that station 2 can hear the collision. 3. The objective of the CS part of the CSMA-CD MAC protocol is to: a. Reduce the amount of time b. Reduce the number of caused by collisions that collisions that occur do occur c. Reduce the amount of idle d. All of the above. time in which all stations are silent 4. The objective of the CS part of the CSMA-CD MAC protocol is to: a. Reduce the amount of time b. Reduce the number of caused by collisions that collisions that occur do occur c. Reduce the amount of idle d. All of the above. time in which all stations are silent 5. 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. 6. 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_CARES 7. Suppose there are 20 stations on a token bus and that the THT = 10 msec and TRT4 = 150 msec. If all stations send priorty 6 traffic for 6 msec, how much time does each station have for class 4 traffic (Ignore token passing latencies). Computer Science 825 Quiz 4 Name _______________________ 1. 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) 2. What is the minimum Hamming distance of a code that is capable of doing double bit error CORRECTION. 3. In an 802.5 token ring system the responsibility for restoring the priority on a token to its original level lies initially with a. the station that made b. the last station to transmit the high priority reservation using the higher priority token c. the station that actually d. the monitor station issued the high priority token. 4. Both the "bitmap" and "binary countdown" MAC protocols are collision free. When a large number of stations exist on the network the size of a reservation frame is: a. the same for bitmap and b. larger for bitmap binary countdown c. larger for binary countdown 5. Show the sequence that would actually be transmitted AFTER the following message was subjected to BISYNCH style byte stuffing. Bisynch byte stuffing is used (Here the leading and trailing DLE STX and DLE ETX are the "real thing" indicating start and end of the message ------------------------------------------------------------------ | DLE | STX | 'A' | 'B' | DLE | 'C' | DLE | STX | DLE | DLE | ETX | ------------------------------------------------------------------ 6. Suppose a 7 bit codeword with ODD parity is being used in a single bit hamming ECC. Suppose the following codeword is received. 1 1 1 0 1 1 1 a1 a2 a3 a4 a5 a6 a7 a. Which bit if any is in error? 7. 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 8. Suppose a codeword consists of 2400 bits and a distance 3 Hamming Code is used to correct bursts of 60 bits or less. How many bits in the codeword must be used as ECC bits. (Schemes involving fractional bits are not likely to be warmly received.) 9. 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. 10. 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. 11. Suppose a codeword contains "n" total bits. It is broken down as "m" msg bits and "r" ECC bits. Which of the following correctly characterizes the relationship between n, m, and r for single bit error correction to be done: r m n m r a. 2 * 2 <= 2 b. (n + 1) * 2 < 2 m n c. (n + 1) * 2 < 2 d. None of the above. Computer Science 825 Quiz 5 Name _______________________ 1. Suppose a CRC generator polynomial is x^4 + x^2 + 1 a. Draw the pre-multiplying shift register implementation b. Does this polynomial contain (x + 1) as a factor? 2. Suppose A generator polynomial of x + 1 is used. Answer the following T or F ___ a. No double bit errors in which the 2 error bits are adjacent in the message will be 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. 3. Suppose a generator polynomial of G(x) = x^5 is used. G(x) can detect a. Some, but not all, of the errors b. All errors involving the involving the last 5 bits of the last 5 bits of the message message and some but not all of the but and some errors that do not errors that don't involve the last involve the last 5 bits. 5 bits. c. All errors involving any of d. All single bit errors but no more the last 5 bits of the message than that. but no errors not involving any of the last 5 bits. 4. For the premultiplying version of a 4 stage shift register to work correctly, the register must be initialized to a. 0 b. The first 4 bits of the message c. The last 4 bits of the d. Either a. or b. will work message 5. Consider the following shift register: a. What will be the contents of the shift register after the input digits 1 and 1 are processed. b. What generator polynomial is represented by this shift register. 6. 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. 7. 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 8. 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. 9. 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. nxtrecv may be < nxtack ____ d. nxtsend may be < nxtrcv Computer Science 825 Quiz 6 Name _______________________ 1. 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 negligible 2. Receiver buffering w/ out of propogation delay. order retransmission ___ c. High errors and very long propogation delay 3. 2. Suppose that a satellite link has an EARTH to SATELLITE propogation delay is 50 ms. Suppose bit transmission rate is 100,000 bits per second and packets are 1000 bits long. a. What will the efficiency of this channel be if stop and wait protocal 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. 3. 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 4. 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 5. Suppose there are N bits in the sequence number. The value of the counting semaphore numslots is related to wpcount as follows: a. numslots - wpcount = N b. numslots + wpcount = send - queue c. send - ack = numslots - wpcount d. numslots + wpcount = (2 ^ N) - 1 6. One flaw in the protocol as presented was susceptibility to deadlock. As written, the protocol presented in class becomes deadlocked when: a. any readlink process is blocked b. all readlink processes are in dequeue due to lack of free blocked in dequeue due to buffers. lack of free buffers c. the network layer input process d. Either (a.) or (c.) occurs blocks in dequeue because its input queue is empty 7. In order to solve the deadlock problem it is necessary to allocate dedicated input buffers and modify the dequeue routine in what way? 8. Aside from the deadlock problem, what were the other two "fatal flaws", in the sample router protocol? a - b - 9. A general sliding window protocol with receiver buffering and out of order retransmision uses a 3 bit sequence number and a sender window size of 6. What is the largest safe size for the receiver window? a. 1 b. 2 c. 6 d. 7 Computer Science 825 Quiz 7 Name _______________________ 1. 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. 2. 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. 3. Which of the following is NOT a use of supervisory frames in SDLC a. Sending a standalone ack b. Seeing if another station is back up after a crash. b. Polling d. Telling another station to temporarily stop sending. 4. 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 seq # to 7. b. XOR current seq # w/ 0xff c. Both a and b. d. Neither a nor b. 5. 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. 6. 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. Suppose two stations are connected by a path that is N hops long and the probability of a successful transmission over each hop is p. 7. 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. N / p b. p / N c. 1 / p d. 1 / Np 8. Identify the class of service provided to the transport layer by each of the following network layers. ___ a. IBM SNA 1. Unreliable connection oriented ___ b. IP 2. Reliable connection oriented ___ c. ATM 3. Unreliable connectionless 4. Reliable connectionless 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. The basic backward learning routing algorithm learns only for the better. A mechanism that can be used to discover changes for the worse in the topology is to: a. Use duplexed tables and b. Periodically use flooding. periodically initialize them to all dests unknown c. Add a time stamp to the d. All of the above. packets. Computer Science 825 Quiz 8 Name _______________________ 1. 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. The size of a routing info packet in Bellman-Ford is of order 1. M 2. N 3. N ^ 2 4. N * M c. The number of routing packets transmissions (for the entire network) at each Bellman-Ford exchange is proportional to: 1. M 2. N 3. N ^ 2 4. M ^ 2 5. N * M 2. Suppose the Bellman-Ford routing algorithm is being used and station B receives the following routing updates from neighbors A, C and E A C E Cost VIA A 0 6 1 | --------------------------------- B 6 11 2 | -------------------------------- C 3 0 4 | -------------------------------- D 8 5 2 | -------------------------------- E 2 9 0 | -------------------------------- F 11 2 7 | -------------------------------- Suppose BA delay = 8, BC delay = 2 and BE delay = 12 Complete the routing table for B. (Break ties alphabetically) 3. 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. Flooding ______ c. Spanning tree. 4. 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. 5. 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? 6. 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. 7. The problem of "Counting to infinity" when a link goes down is associated with which routing algorithm: a. SPF b. Backward learning c. Bellman - Ford d. Flooding 8. The method used to route the routing information exchange packets themselves in an OSPF network is: a. OSPF b. Backward learning c. Bellman - Ford d. Flooding 9. Which packet dropping scheme is more effective in targeting agressive connections a. Random drop b. Drop tail c. No difference 10. The type of network layer service to which BOTH preallocation of resources and packet discarding are readily used in congestion management is: a. unreliable connectionless b. reliable connectionless c. reliable connection oriented d. unreliable connection oriented Computer Science 825 Quiz 9 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 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. 4. 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. 5. 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". 6. 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 7. The Network Layer Protocol of SNA is: a. Connectionless and unreliable b. Connectionless and reliable c. Connection oriented and d. Connection oriented and reliable unreliable 8. Suppose the following is a diagram of an SNA network: B E / \ / \ A D G \ / \ / C F Answer the following T or F. ___ a. Nodes B and C can both have explicit routes with the identity (3, F). ___ b. For node A to have a functional explicit route with identity (3, G), node D must also have an explicit route with identity (3, G). ___ c. Nodes B and C cannot both have explicit routes to G with B's route passing through F and C's passing through E. 9. Creating an SNA session involves bindings of logical/physical entities at 5 layers. Order the entities from (1) to (5) where (1) is the lowest (physical) layer and (5) is the application layer. ___ a. Explicit route ___ b. Class of service ___ c. Link ___ d. Transmission group ___ e. Virtual route Computer Science 825 Quiz A Name _______________________ 1. When an SNA VR manager receives a pacing response before the pacing count reaches 0 and it doesn't contain CRWI or RWI it a. Sets the pacing count to b. Increments the current pacing the current pacing group group size by 1. size. c. Adds the current pacing d. Sets the pacing count to the group size to the pacing maximum pacing group size. count. 2. The VR pacing group size in a SNA network determines the number of outstanding packets a. on a single SNA connection b. between a pair of host systems c. on a SNA Virtual route d. in a SNA network 3. a. What is the maximum number of networks and hosts for each of the three classes of network used in the INTERNET Max Nets Max Hosts Class A Class B Class C b. Which class of net does a node whose address is 128.215.17.139 belong to. 4. Which of the following pairs of Classless IP address prefixes can be aggregated under a single new prefix a. 130.127.x.x/16 b. 130.126.x.x/16 130.128.x.x/16 130.127.x.x/16 c. Both d. Neither 5. 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. 6. 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 7. The type of service provided by IP and ATM is properly contrasted as follows: a. IP provides unreliable service b. IP provides connection but ATM is reliable. oriented service but ATM is connection less c. ATM provides unreliable service b. ATM provides connection but IP is reliable. oriented service but IP is connection less 8. The number of distinct ATM addresses (not connection id's) is: a. 1 b. 2^8 c. 2^20 d. 2^160 9. 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 10. In an ATM network routing decisions: a. Must be made by the sysadmin b. May be made dynamically before the network is activated. at connection setup time c. May be made dynamically on a per cell basis as in IP. Computer Science 825 Quiz B Name _______________________ 1. Which one of the ATM service classes employs explicit congestion feedback mechanisms: a. CBR b. VBR c. ABR d. UBR 2. We identified two characteristics of a class C network which make construction of a reliable transport far more difficult than constructing a reliable datalink protocol. What were they? a - b - 3. Suppose Tomlinson's clock proposal is used with a 20 bit sequence number and a clock that ticks 8192 times a second. Suppose maximum packet lifetime is 60 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 3/4 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). 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. 4. A delayed duplicate SYN2 received in the SYN-sent state is detected because: a. The SEQ number is wrong. b. The ACK number is wrong. c. Both SEQ and ACK are d. Undetected and causes the known to be wrong. recipient to enter the established state. 5. A delayed duplicate SYN2 received in the CLOSED / LISTEN state is detected because: a. The SEQ number is wrong. b. The ACK number is wrong. c. Undetected and causes the d. SYN2 is an unexpected packet recipient to enter the in the CLOSED/LISTEN State. established state. 6. A delayed duplicate SYN1 received in the CLOSED / LISTEN state is detected because: a. The SEQ number is wrong. b. The ACK number is wrong. c. Undetected and responded d. SYN1 is an unexpected packet to with SYN2. in the CLOSED/LISTEN State. 7. A delayed duplicate SYN1 received in the ESTABLISHED 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. 8. The delayed duplicate problem could also be solved by the use of unique TSAP addresses. What is the principle disadvantage of using this approach? 9. The TCP protocol contains TWO distinct flow control mechanisms what are two problems that they attempt to address: a - b - Computer Science 825 Quiz C Name _______________________ 1. Suppose a TCP connection has SND.UNA = 2200 and SND.NXT = 3450 and a packet arrives with ACK = 2800 and WINDOW = 4000. What size are the offered and usable windows now? offered - usable - 2. Suppose a TCP connection has SND.UNA = 2400 and SND.NXT = 3450 and a packet arrives with ACK = 3200 and WINDOW = 800. 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 6000 bytes of transmit buffer space. At what sequence number will the application be "put to sleep" if no additional acks are received. 3. Suppose an application has an allocation of 10,000 bytes of TCP receive buffer space. The last byte that the application has consumed is 3000 and the present offered window is 8000. What is RCV.NXT? 4. In Socket level TCP/IP programming the selection of the UDP or TCP transport protocol is made in which of the following function calls: a. socket() b. bind() c. accept() d. listen() 5. The call which causes the server application to block while waiting for a connection request is: a. socket() b. bind() c. accept() d. listen() 6. The relationship between SND.UNA and SND.NXT to RCV.NXT at the other end of a connection is: a. snd.una <= rcv.nxt <= snd.nxt c. snd.una <= snd.nxt <= rcv.nxt b. rcv.nxt <= snd.una <= snd.nxt d. none of the above 7. If a TCP receives a packet whose sequence number is less than its its current "ack" number it should: a. buffer the packet but not b. Buffer the packet and update change its current "ack" it ack number to 1 + last byte ack number. received in the packet. c. discard the packet and not d. Either b. or c. can be done. change its ack number. 8. If a TCP receives a packet whose sequence number is greater than its current "ack" number but still within the receiver window it should: a. buffer the packet but not b. Buffer the packet and update change its current "ack" it ack number to 1 + last byte ack number. received in the packet. c. discard the packet and not d. Either b. or c. can be done. change its ack number. 9. In an outgoing TCP packet the value of the ACK field in the header is set to the present value of: a. SND.NXT b. SND.UNA c. RCV.NXT d. RCV.UNA