Computer Science 825 Quiz 1 Name _______________________ 1. a. Which of the seven layers of the ISO model is the LOWEST layer having end to end responsibilites. b. Which of the seven layers of the ISO model would typically be responsible for code translation (e.g. EBCDIC <-> ASCII). c. Which of the seven layers of the ISO model is the HIGHEST layer that resides in the communcations subnet. d. Which of the seven layers of the ISO model is responsible for checkpointing and recovery from network failures. 2. PROTOCOLs define 3 aspects of messages passed in a network. One is the SYNTAX. What are the other two? a. b. 3. 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. b. With the layer below it. d. All of the above. 4. Match the service classes with the appropriate applications (No answer should be used more than once.) ___ a. File transfer 1. Unreliable Conn Less datagram ___ b. Digitized Voice 2. Reliable Conn Less Request/reply ___ c. E-Mail 3. Reliable Conn oriented byte stream ___ d. Remote login 4. Unreliable Conn oriented byte stream ___ e. Database queries 5. Reliable Conn Less datagram 6. Reliable Conn oriented message stream 7. Unreliable Conn oriented message stream 5. 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. --------------------- More on the back ---------------- 6. At each layer of the ISO model existing network architectures (ISO_OSI, SNA, ARPANET) define: a. Exactly one protocol b. Zero or more protocols. 7. 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. Computer Science 825 Quiz 2 Name _______________________ 1. What is the minimum number of distinct signalling states that can be used to transmit data at a rate of 24,000 bits per second on a channel with a bandwidth of 4000 hz (show work for partial credit). 2. What is the minimum SNR (in db) that will sustain a data rate of 24,000 bits per second on a 4000hz channel? 3. Write the expression for a general modulated sine wave carrier and identify the parameters that are varied in each of the standard modulation schemes: (the answers to b, c, and d should be variables in the expression you provide in a.) a. f(t) = b. Phase c. Amplitude d. Frequency 3. Give an example of a 1 bit per baud phase shift modulation scheme which is self clocking and one which is not. a. Self clocking: b. Not self clocking: 4. The relationship between the efficiency of asynchronous versus synchonous signalling is (efficiency = %bandwidth used to transmit data as opposed to being used for synchronization): a. Asynchronous is always b. Synchronous is always more more efficient. efficient. c. Asynchonous is more efficient d. Synchonous is more efficient for byte sized packets but for byte sized packets but synchronous is more efficient asynchronous is more efficient for large blocks for large blocks 5. In the model of synchonous transmission that we described in class a. the clock on the receiver b. the clock on the receiver modem was driven by the USART was driven by the receiving USART. receiver modem. c. independent clocks were used d. No clocking at all was in the modem and the USART. required. 6. In the models of synchronous and asynchonous transmission signalling between the U(S)ART and modem using the RS-232 interface is best described as: a. Base band and parallel b. Base band and serial c. Modulated carrier and parallel d. Modulated carrier and serial. 7. The suitability of using independent clocks in a UART and an asynchonous modem when compared to the use of independent clocks in a usart and a synchronous modem is: a. independent clocks are more b. independent clocks are suitable in asynch because more suitable in asynch resynchronization must occur because lower bit rates after each byte is transmitted. are used. c. independent clocks are more d. they are perfectly suitable suitable in synchronous because in both. there is less starting and stopping. e. they are totally unsuitable in both. Computer Science 825 Quiz 3 Name _______________________ 1. Suppose a new "improved" fidelity PCM telphone service has an bit rate of 288,000 bits per second and that the maximum frequency carried by the channel is 12 Khz. How many discrete signal levels are being captured by the PCM encoding?? 2. Suppose a network has links that carry data at a rate of 20,000 bits per second. Suppose Node A and Node B are connected by a path that requires 8 hops (retransmissions). a. What is the minimum time required to send a 400,000 bit message 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 10000 bit packets are used. 3. The rate at which data is transmitted on a PCM telephone channel is a. 4000 bits / second b. 8000 bits / second c. 64000 bits / second d. 64000 bytes / second 4. The main advantage of using a multiplexor to attach a remote cluster of ASCII terminals to a Unix machine is that it reduces the required number of a. Computer ports c. Ports and Phone lines. b. Phone lines. d. Ports, phone lines and terminals. 5. Provide the number (>=0) of each of the following components needed to attach a cluster of 4 remote IBM 3270 style terminals to an IBM communication controller. ____ Telephone lines ____ Modems ____ Multiplexors ____ Communication controller ports 6. The main reason digital channels have much lower error rates than analog when used over long distances is: a. Digital signalling is more c. Digital signals are amplified powerful than analog. rather than regenerated. b. Digital signals are regenerated d. Digital channels have much higher rather than amplified. SNR's than analog. 7. We described three categories of multiplexing (S)TDM, ATDM, and FDM. Indicate which classe(s) are appropriate for each of the following types of signalling: a. Analog b. Digital 8. Which type(s) of multiplexing was particularly desirable for very bursty loads? 9. The class of data service provided by ISDN is best categorized as a. Connection oriented reliable b. Connection less unreliable bit stream. data gram. c. Connection oriented unreliable d. Connection oriented unreliable message stream. bit stream. Computer Science 825 Quiz 4 Name _______________________ 1. Measurements of an infinite user slotted aloha channel show that 20% of the slots are idle. a. What is the total load (mean number of transmission attempts per packet time) = G. b. What is the throughput in packets / packet time. 2. The main reason slotted aloha has a higher sustainable throughput than pure aloha is: a. Slotted aloha uses fixed b. Forcing all transmissions to size packets but pure aloha start on a slot boundary uses variable size packets. reduces the window of collision vulnerability. c. Contention intervals in slotted d. Slotted aloha uses smaller aloha are packet times but packet sizes to reduce the contention intervals in pure are window of collision vulnerability. signal propogation times. 3. As the load G on a pure or slotted aloha channel increases, the expected number of attempts per successful transmission: a. Approaches zero. b. Increases linearly b. Approaches a fixed upper bound d. Increases exponentially asymptotically 4. 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 given slot is: a. p c. p * k * (1 - k) ^ (p - 1) b. (k ^ p) * (1 - p) ^ (k - 1) d. None of the above. 5. If the probability computed above is denoted A, then the probability that a contention interval will last exactly j slots is: a. A ^ j c. A / j b. ((1 - A) ^ (j - 1)) * A d. None of the above. 6. Answer the following T or F. ___ a. Increasing the pysical length of a CSMA CD LAN will increase the length of the contention interval and thus make the efficiency of the LAN higher. ___ b. Increasing the average packet size will tend to make the efficiency of a CSMA CD LAN higher. ___ c. Increasing the bit rate of a CSMA CD LAN will make its efficiency higher. 7. In the performance models we derived for slotted aloha and for CSMA-CD the maximum effective utilization = efficiency = throughput in packets per packet time was: a. Independent of packet size b. Independent of packet size in CSMA in both aloha and CSMA but dependent on packet size in aloha. c. Dependent on packet size b. Independent of packet size in aloha in both aloha and CSMA but dependent on packet size in CSMA. 8. The main reason(s) that higher efficiencies are possible in CSMA-CD LAN's than in aloha is/are: a. Higher bit rates are used b. CSMA's window of collision on LANS than in satellites. vulnerabilty is typically much smaller than a packet time. c. CSMA stations can detect d. Both b and c. collisions and stop transmitting. Computer Science 825 Quiz 5 Name _______________________ 1. Suppose a token bus system has 3 priority classes 3, 2, and 1. The token holding times for the classes are respectively 800us 400us and 200us. What percent of the bandwidth is dedicated to class 2 traffic? 2. a. Suppose a token ring transmits data at a rate of 10,000,000 bits per second. How many microseconds does it take to take to transmit 1 bit. b. Suppose signal propogation speed is 200,000,000 m/sec and the stations on a token ring are an average of 40 meters distant from each other. How many microseconds does it take the signal to propogate from one station to another. c. Suppose the ring has 100 stations and each station introduces a propogation delay of 1 bit time. What is the average delay (in usec) experienced by a station after it becomes ready but before it can begin transmitting on an IDLE RING. (Hint: Divide the maximum time by 2). 3. For the IEEE token bus match the control packet that will be generated as a result of each of the following conditions. Some answeres may be used 0 times or more that one time! ____ a. A station recognizes a WHO_FOLLOWS 1. SOLICIT_SUCCESSOR_2 packet naming its predececessor. 2. WHO_FOLLOWS ____ b. A station wishes to leave the net in an orderly way. 3. SET_SUCCESSOR ____ c. A collision occurs when two 4. RESOLVE_CONTENTION stations try to claim the token at the same time. 5. CLAIM_TOKEN ____ d. A station wishes to respond to a 6. SOLICIT_SUCCESSOR SOLICIT_SUCCESSOR frame. ____ e. A station times out twice after sending a WHO_FOLLOWS frame. 4. Two standard measures of network performance are sustainable throughput and mean packet delay. High sustainable throughput is good and low mean packet delay is good. For each of the following select the answer that bests compares CSMA/CD with token passing. Assume identical transmission speeds. a. Sustainable throughput at very high loads 1. CSMA/CD is better 2. Token passing is better 3. No measureable difference b. Packet delay at very high loads 1. CSMA/CD is better 2. Token passing is better 3. No measureable difference c. Packet delay at very low loads 1. CSMA/CD is better 2. Token passing is better 3. No measureable difference 5. The effect of packet size on sustainable throughtput in bytes per second (assume standard headers + user data are included in byte / second computations) is: a. More significant in token b. More significant in CSMA-CD passing than in CSMA-CD than in token ring c. Completely insignificant d. Very significant in both. in both. 6. In an 802.5 token ring system suppose the following events occur: Station A transmits to E using priority 3 token Station C makes a priority 5 reservation Station A generates a priority 5 token Station B transmits a priority 5 message to station C Station B transmits a priority 5 token Station C transmits a priority 5 message to station B Who is responsible for regenerating a priority 3 token? Computer Science 825 Quiz 6 Name _______________________ 1. Suppose the MLMA MAC protocol is being used and station addresses consist of 3 decimal numbers. If stations 500, 501, 503, 199, 198, and 197 all become ready at the same time. How many decades will be required to identify the ready stations. 2. The objective of the reservation based Aloha Schemes was to a. Act like TDM at both b. Act like Aloha at low loads high and low loads. and TDM at high. c. Act like TDM at high d. Act like Aloha at low loads loads and Aloha at lows. and Aloha at high. 3. Reservation aloha schemes collect consequtive packet slots into larger units called GROUPs. The size of a group: a. is unrestricted. b. must be no more than the two way propogation delay c. must be >= than the d. must be >= than the two way propogation delay one way propogation delay. 4. A disadvantage of the use of the reservation method that had permanently assigned slots (Binder's) was: a. It was not easy to add or b. One station could end up hogging delete stations while the the entire net's bandwidth for long network was active. periods of time. c. A station with much data d. Both a. and b. to send was not guaranteed access to its slot in all successive frames once it started transmitting. 5. Suppose a 15 bit codeword with ODD parity is being used in a single bit hamming ECC. Suppose the following codeword is received. 1 1 0 1 1 0 0 1 1 0 1 0 0 1 0 -------------------------------------------- 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 a. Which bit if any is in error? b. Suppose a multiple bit error occurs. Circle the correct description of the result. 1. The fact that there is a multibit error can be detected, but the error can't be corrected. 2. The multibit 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 multibit error will be undetected and the corrected value will be either the wrong codeword or it might be the correct codeword. 4. The multibit error will be undetected and the corrected value MAY be an illegal code word. c. How many error detection bits must be reserved to do single bit error DETECTION (NNOOTT CCOORREECCTTIIOONN!!) on an n-bit code word. 6. Suppose 800 bit code words are to be transmitted and it is desired to use a Hamming code to correct error bursts of up to 40 bits. How many of the 800 bits must be used for ECC. Computer Science 825 Quiz 7 Name _______________________ 1. Consider the following shift register: a. What will be the contents of the shift register after the digits 1 and 0 are processed? b. What generator polynomial is represented by this shift register. c. Does this shift register represent standard long division or is it the pre-multiplying version? (Yes in not the correct answer). 2. a. Suppose a CRC generator polonomial G(x) = x ^ 3. Precisely what errors can it detect? b. Compute the first 3 bits of the following quotient by using long division.. Show your work. ___________________________ 1 0 1 0 1 | 1 0 0 1 0 1 1 0 0 1 1 0 1 1 c. What characteristic of a generator polynomial will guarantee that all errors consisting of an odd number of bits will be detected. 3. The size of the largest error burst that a CRC can guarantee detection of is: a. The number of terms in the c. 16 generator b. The degree of the generator d. The degree of the generator + 1 4. Use of a CRC in data transmissions provides a. Good error detection and b. Good error detection and error correction capability. limited error correction. c. Good error detection and d. Limited error detection no error correction and good error correction. 5. In protocol 1 in the book, frames didn't carry sequence #'s and no ACKS or CRC's were used. Which of the following is NOT a disadvantage of the use of protocol 1. a. A fast sender could overrun b. Undetected duplications of a slow receiver packets could take place. c. Packets could be lost. d. Damaged packets could be accepted. 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 Computer Science 825 Quiz 8 Name _______________________ 1. Show how a sliding window protocol that uses a 2 bit sequence number, a sender window size of 3, and a receiver window size of 3 can fail. 2. A buffer in the protocol discussed in class cycled though a number of queues.. Associate each transition with the process that effected it. (Some answers may be used more than once or not at all). ____ 1. Read pending to network a. Writelink process input. ____ 2. Network input to link b. Readlink process station output c. Timeout process ____ 3. Link output to sender window. d. Network layer process ___ 4. Sender window to free e. Queuemsg process list 3. Suppose that a satellite channel is in use and the EARTH to SATELLITE propogation delay is 135 ms. Suppose packets are 1000 bits long and the transmission rate is 100,000 bits per second. a. What will be the efficiency of the channel if a stop and wait protocol is used. b. How many bits should the sequence number have in order to obtain 100% efficiency using a go back N protocol (assume channel is error free). c. How large (in packets) must the RWS be in order to use a Go Back N sliding window protocol. 4. Match the amount of channel time lost each time an isolated error occurs in each of the following environments: ____ a. Go Back N 1. The two way propogation delay ____ b. Selective repeat 2. One way propogation delay. ____ c. Selective reject 3. One packet time 4. The timeout interval 5. Two times the timeout interval 5. The queuemsg procedure in the protocol 5 implementation could be blocked two possible conditions. What were the conditions and what events would eventually lead to unblocking? Condition | Unblocked by.. when... 1. | | | --------------------------------------------------------- | 2. | | | 6. Identify one deficiency of the protocol 5 implementation that would HAVE TO BE corrected before it could be successfully used in a real network. Computer Science 825 Quiz 9 Name _______________________ 1. 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. 2. a. In SDLC, PRECISELY how can a receiver of a frame tell whether the frame is a supervisory, unnumbered, or information frame. b. In SDLC, PRECISELY how can a receiver of a supervisory frame tell whether the frame is Receiver Ready or Receiver Not Ready. 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 followin is NOT a use of supervisory frames in SDLC a. Sending a standalone ack b. Resetting sequence numbers after a crash. b. Polling d. Responding to a poll when a secondary has no data to send now. 6. 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. 7. Justify the answer you selected in 6. 8. In the IEEE 802.2 standard LLC protocol, three classes of service were defined.. One is acknowledged datagram. Name the other two. a. b. c. Which of the three service classes operates most similarly to the normal flow of information packets in SDLC. d. Which of the three general SDLC/HDLC frame types (INFO/SUP/UNNUM) was used to carry data in the acknowledged datagram service. Computer Science 825 Quiz A 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. BISDN c. Unreliable connectionless d. Reliable connectionless 2. Answer the following T or F: ___ a. Connection oriented service generally requires less addressing overhead in packet headers. ___ b. Node failures are less disruptive to connection oriented implementations than to datagram implementations. ___ c. Guaranteed service rates are easier to provied using connection oriented implementations than connection less implementations. ___ d. Avoiding congestion through preallocation of resources is generally easier in a connectionless implementation than a connection oriented. ___ e. Keeping loads balanced is generally easier in a connection less implementation than in a connection oriented. 3. Suppose a virtual circuit is created from the host at node C to host at node E and that is passes through D and F. Update the routing tables. 4. Identify the principal disadvantage(s) of each of the following routing algorithms: a. Static tables b. Flooding c. Hot potato d. Backward learning 5. 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 SPF within the entire network is proportional to: 1. M 2. N 3. N ^ 2 4. M ^ 2 5. N * M Computer Science 825 Quiz B Name _______________________ 1. Suppose the Bellman-Ford routing algorithm is being used and station B receives the following routing updates from neighbors A and E A E Cost VIA A 0 9 | | ------------------------------ B 5 2 | | ----------------------------- C 3 9 | | ----------------------------- D 8 2 | | ----------------------------- E 6 0 | | ----------------------------- F 11 7 | | -------------------------------- Suppose BA delay = 2 and BE delay = 4. Complete the routing table for B., 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 proportional to: 1. M 2. N 3. N ** 2 4. N * M b. Routing information exchanges in the Bellman-Ford ARPANET scheme took place at least as often as once a 1. Second 2. Minute 3. Hour 4. Day 3. In the internets use of Bellman-Ford and SPF routing delays were measured as: a. Average packet delay time b. Instantaneous queue length in B-F in both B-F and SPF. and average delay in SPF. c. Average delay in B-F and d. Instantaneous queue length in SPF instantaneous queue length and in BF. in SPF. 4. When flow control is used as a congestion control mechanism does it work better when implemented as: a. Host to Host b. Process to Process c. Process to Host. d. Works just the same in all environments. 5. Suppose network addresses are 9 descimal digits and all network addresses are in use. a. How many entries must a flat routing table have. (A flat routing table has an entry for each node in the network). b. Suppose a hierarchichal addressing/routing scheme is used in which the 10 digits bits are partitioned as a 2 digit region code followed by a 3 digit locality code followed by a 5 digit local address. How many routing table entries are now required? 6. Order the following broadcast algorithms according to the number of packet transmissions needed to complete a broadcast (1 = least transmissions; 4 = most). ______ a. Reverse Path Forwarding ______ b. Spanning tree. ______ c. Flooding ______ d. Multidestination 7. Identify all environments in which preallocation of buffers is a feasible way in which to do congestion control. a. Unreliable datagram b. Unreliable connection oriented. c. Reliable connection oriented. 8. Identify all environments in which packet discarding is a feasible way in which to do congestion control. a. Unreliable datagram b. Unreliable connection oriented. c. Reliable connection oriented. Computer Science 825 Quiz C Name _______________________ 1. The primary purpose of the use of the Spanning Tree in the transparent bridge is to: a. Control congestion. b. Ensure optimal routing c. Prevent packet looping. d. All of the above. 2. Which of the following routing techniques is periodically us both in transparent and source routing bridges. a. Flooding b. Backward learning. c. SPF d. Static tables. 3. If multiple Links exist between SNA nodes, it is possible to group them all into a single transmission group or to create as many transmission groups as there are links.. What is the advantage of each approach. a. Single TG b. As many TG's as Links 4. Suppose the following is a diagram of an SNA network: A D / \ / \ Z C F \ / \ / B E Answer the following T or F. ___ a. Nodes Z and B can't both have explicit routes with the identity (3, F). ___ b. For node A to have a functional explicit route with identity (3, F), node C must also have an explicit route with identity (3, F). ___ c. Nodes A and B can't both have explicit routes with the identity (3, F) where A's (3,F) passes through D and C's (3, F) passes through E. ___ d. Nodes A and B can both have explicit routes to F with A's called (3, F) and B's called (4, F) where A's (3,F) passes through D and B's (4, F) passes through E. Suppose nodes C, D, and F's static tables contain the following entries: Dest ER# Via/TG Dest ER# Via/TG Dest ER# Via/TG C: A 2 1 D: A 2 1 F: A 7 1 A 7 2 A 9 1 A 8 2 A 9 2 A 11 1 A 9 2 If A activates (F,3) what must the reverse ER be?? 5. A VR manager receiving a packet with the Change Window Reply Indicator must: a. Stop sending immediately b. Set the current pacing group size to the minimum pacing group size. c. Decrement the current d. Increment the current pacing group pacing group size. size. 6. A VR manager receiving a packet with the Reset Window Indicator must: a. Stop sending immediately b. Set the current pacing group size to the minimum pacing group size. c. Decrement the current d. Increment the current pacing group pacing group size. size. 7. 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 126.215.17.139 belong to. Computer Science 825 Quiz D Name _______________________ 1. Suppose Tomlinson's clock proposal is used with a 18 bit sequence number and a clock that ticks once a millisecond. Suppose maximum packet lifetime is 50 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 every 4 milliseconds. 2. Suppose a TCP connection has SND.UNA = 2000 and SND.NXT = 3250 and a packet arrives with ACK = 2200 and WINDOW = 3000. What size are the offered and usable windows now? offered - usable - 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. 3. A delayed duplicate SYN2 received 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. SYN2 is an unexpected packet known to be wrong. in the SYN sent state. 4. A delayed duplicate SYN1 received in the CLOSED / LISTEN state is a. detected because of wrong b. Detected because of wrong ACK SEQ number. number. c. Undetected and responded d. Responded to with a SYN 1. to with a SYN2. 5. 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. 6. Identify the ISO network class (A, B, or C) that each of the following ISO transport classes is designed to work above. _____ a. Multiplexing Class (2) _____ b. Error detection and recovery class(4) _____ c. Simple class(0). 7. a. Which of the above transport classes is the TCP in? b. What is the difference between network classes A and B. c. The ISO defined 4 transport service primitives: Three of them are T-CONNECT T-DISCONNECT and T-DATA... what was the forth one? Computer Science 825 Quiz E Name _______________________ 1. 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. connect() d. listen() 2. For each of the following functions indicate S if the function is used in constructing a TCP/IP server such as the one we studied, C if it is used in the client, and B if it is used in both the client and server. ____ a. accept() ____ b. connect() ____ c. bind() ____ d. socket() ____ e. listen() 3. In the client / server model that we studied, the accept() function call returns: a. The same handle passed to b. A handle to a different socket accept as a parameter. that is bound to the same port as the original handle. c. A handle to a different socket that is bound to a different port from the original handle. 4. A significant disadvantage to the flow control method proposed by Belsnes is: a. It leads to excessive waits b. Its use of unbounded window for pacing responses and sizes can exacerbate congestion causes low throughput. problems. c. It forces all connections to use the same window size regardless of the length of the connection. 5. When the senders and receivers have roughly equivalent power the transport window sizes should be: a. 1 packet b. Independent of the number of hops between specific senders and receivers. c. Larger for very distant d. Smaller for very distant senders and receivers than senders and receivers than for very close senders and for very close senders and receivers. receivers. 6. Suppose a receiver in a stop and wait file transfer protocol uses an ack then write policy and the sender uses a policy of always 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) 7. The ISO's counterpart to the SNA "bracket" is the a. dialog b. activity c. synchonization point. d. session level connect 6. Computer Science 825 Quiz F Name _______________________ 1. a. What is the minimum SNR (in db) that will sustain a data rate of 32,000 bits per second on a 8000hz channel? b. How many signalling states will be needed to achieve this bit rate. 2. Answer the following T or F. (Hint: distinguish between maximum throughput and efficiency before answering). ___ a. Increasing the pysical length of a CSMA CD LAN will increase the length of the contention interval and thus make the efficiency of the LAN higher. ___ b. Decreasing the average packet size will tend to make the efficiency of a CSMA CD LAN higher by producing shorter average contention intervals. ___ c. Decreasing the bit rate of a CSMA CD LAN will make its efficiency lower because more time will be spent transmitting a given packet. 3. a. Draw the long division (non premultiplying) shift register for division by the following genarator: x^5 + x^2 + 1 b. What is the longest error burst that the above generator is guaranteed to detect. 4. Show how a sliding window protocol that uses a 2 bit sequence number, a sender window size of 3, and a receiver window size of 2 can fail. 5. Match the amount of channel time lost each time an isolated error occurs in each of the following environments: ____ a. Go Back N 1. The two way propogation delay ____ b. Selective repeat 2. One way propogation delay. ____ c. Selective reject 3. One packet time 4. The timeout interval 5. Two times the timeout interval 6. Suppose the Bellman-Ford routing algorithm is being used and station B receives the following routing updates from neighbors A and E A E Cost VIA A 0 5 | | ------------------------------ B 3 3 | | ----------------------------- C 6 9 | | ----------------------------- D 5 4 | | ----------------------------- E 3 0 | | ----------------------------- Suppose BA delay = 4 and BE delay = 3. Complete the routing table for B., 7. Suppose Tomlinson's clock proposal is used with a 16 bit sequence number and a clock that ticks once a millisecond. Suppose maximum packet lifetime is 10 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 every 10 milliseconds. 8. Suppose a TCP connection has SND.UNA = 2000 and SND.NXT = 3250 and a packet arrives with ACK = 2010 and WINDOW = 1250. What size are the offered and usable windows now? offered - usable -