Tutorial Sheet #04 (Computer Networks) TI: Define the following terms with proper example. i Transmission time ii. Propagation time iti, Round Trip Time iv. Back off time v. Vulnerable Time ‘T2: One hundred stations on a pure ALOHA network share a |-Mbps channel. If frames are 1000 bits long, find the throughput if each station is sending 10 frames per second. T3: A group of N stations shares a $6-kbps pure ALOHA channel. Each station outputs a 1000- bit frame on an average of once every 100 sec, even ifthe previous one has not yet been sent, What is the maximum value of N? T4: 1000 airline reservation stations are competing for the use of a single slotted ALOHA channel The average station makes 36 requests per hour. A slot is 100 usec, What is the approximate total channel load? TS: A pure ALOHA network transmits 200-bit frames using a shared channel with a 200 Kbps bandwidth. Find the throughput of the system, if the system (all stations put together) produces: i, 1000 frames per second ii. 500 frames per second iii, 250 frames per second ‘T6: Consider a network using the pure ALOHA medium access control protocol, where each frame is of length 1,000 bits. The channel transmission rate is | Mbps (=10* bits per second). The aggregate number of transmissions across all the nodes (including new frame transmissions and retransmitted frames due to collisions) is modelled as a Poisson process with a rate of 1,000 frames per second. What is the throughput of the network? ‘T7: A slotted ALOHA network transmits 200-bit frames using a shared channel with a 200 Kbps bandwidth. Find the throughput of the system, if the system (all stations put together) produces: i, 1000 frames per second ii, 500 frames per second iii, 250 frames per second T8: A group of N stations share 100 Kbps slotted ALOHA channel, Each station output, a $00 bits frame on an average of $000 ms; even if previous one has not been sent. What isthe required value of N? T9: Ina CSMA / CD network running at Gbps over 1 km cable with no repeaters, the signal speed in the cable is 200000 km/sec. What is minimum frame size? T10: Ina CDMA/CD network with a data rate of 10 Mbps, the minimum frame size is found to be 512 bits for the correct operation of the collision detection process. What should be the minimum frame size if we increase the data rate to 100 Mbps? wnTH: A network using CSMA/CD has a bandwidth of 10 Mbps. If the maximum propagation time (including the delays in the devices and ignoring the time needed to send a jamming signal is 25.6 Hts, what is the minimum size of the frame? TI2: A and B are the only two stations on Ethemet, Each has a steady queue of frames to send Both A B attempts to transmit a frame, collide and A wins first back off race. At the end of this successful transmission by A, both A and B attempt to transmit and collide. Find the probability that A wins the second back off race. TI3: Sixteen stations, numbered 1 through 16, are contending for the use of a shared channel by using the adaptive tree walk protocol. Ifall the stations whose addresses are odd numbers suddenly become ready at once, how many bit slots are needed to resolve the contention? T14: Sixteen stations, numbered 1 through 16, are contending for the use of a shared channel by using the adaptive tree walk protocol. If the stations (2, 3, 5, 9, 12, 14) suddenly become ready at once, how many bit slots are needed to resolve the contention? TIS: A network has a data transmission bandwidth of 20*10° bits per second. It uses CSMA/CD in the MAC layer. The maximum signal propagation time from one node to another node is 40 microseconds. What is the minimum size of a frame in the network in bytes. T16: Suppose nodes A and B are attached to opposite ends of the cable with propagation delay of 12.5 ms. Both nodes attempt to transmit at t=0. Frames collide and after first collision, A draws k=0 and B draws k=1 in the exponential back off protocol. Ignore the jam signal, At what time (in seconds), is A’s packet completely delivered at B if bandwidth of the link is 10 Mbps and packet size is 1000 bits. T17: The address 43:7B:6C:DE: 10:00 has been shown as the source address in an Ethernet frame. ‘The receiver has discarded the frame. Why? T18: An Ethernet MAC sub-layer receives 1510 bytes of data from the upper layer. Can the data be encapsulated in one frame? If not, how many frames need to be sent? What is the size of the data in each frame? 22