TSIN02 Internetworking
Transcription
TSIN02 Internetworking
TSIN02 Internetworking General networking Daniel Persson Exercise 1 Show the communication at the application layer for the following simple private internet: Exercise 2 Show the communication at the application layer for the following simple private internet: Exercise 3 Describe three possible reasons to why a sender does not receive an ACK for a transmitted packet! Exercise 4 Describe the hidden terminal problem! Exercise 5 Describe two different ways of performing channel partitioning! Exercise 6 You are to design a wireless system that reads railway sensor data over the Internet, and use GSM-Railway (GSM-R) – a GSM standard for railway applications. It is important that the system is robust. It is known that commercial GSM bands disturb GSM-R. Therefore, you choose to use a strong link layer repetition code: 0 1 0000 1111 a) Assume that the channel and digital modulation gives you an effective binary symmetric channel, with a transition probability less than 0.5 for a transition between 0 and 1, and assume further that there is equal probability for that the codeword 0000 and the codeword 1111 are used at the encoder. How do you maximum likelihood (ML)-decode 0001? b) How do you ML-decode 1101? c) How do you ML-decode 1100? d) Is decoding always giving the right answer? Exercise 7 Ethernet uses CSMA-CD. User 1 starts transmitting at time 0, and user 2 starts to transmit 1 microseconds later. The users are situated at a distance of 900 m from each other. Assume that the propagation speed of the signal is the speed of light. The jamming signal lasts one microsecond. a) When does user 2 detect user 1’s signal? b) When is the first time that user 1 can start retransmitting? Exercise 8 Why is CSMA-CD chosen for Ethernet, while CSMA-CA is chosen for WIFI? Exercise 9 What is the range of addresses in the following blocks: a) 123.56.77.32/29 b) 200.17.21.128/27 c) 17.34.16.0/23 d) 180.34.64.64/30 Exercise 10 An ISP is granted a block of addresses starting with 150.80.0.0/16. The ISP wants to distribute these blocks to customers as follows: a) The first group has 200 medium-size businesses, each needs 128 addresses. b) The second group has 400 small businesses, each needs 16 addresses. c) The third group has 2048 households, each needs 4 addresses. Design the subnets for the businesses and the households and give the slash (CIDR) notation for each subblock. Find out how many addresses are still available after these allocations. 1 General networking TSIN02 Internetworking Daniel Persson Exercise 11 A large number of consecutive IP addresses are available starting at 198.16.0.0. Suppose that four organisations A, B, C and D request 4000, 2000, 4000, 8000 addresses respectively, and in that order. For each of these, give the first IP address assigned, the last address assigned, and the subnetwork address in the CIDR notation. Exercise 12 A router has the following (CIDR) entries in its routing table: Address/mask Next hop 135.46.56.0/22 Interface 0 135.46.60.0/22 Interface 1 192.53.40.0/23 Router 1 default Router 2 For each of the following IP addresses, what does the router do if a packet with that destination address arrives? a) 135.46.63.10 b) 135.46.52.2 c) 135.46.57.14 d) 192.53.40.7 e) 192.53.56.7 Exercise 13 For a given IP address 201.14.78.65 and the subnet mask 255.255.255.224, what is the subnet address (in slash notation)? Exercise 14 Show the shortest form of the following IPv6 adresses: a) 2340:1ABC:119A:A000:0000:0000:0000:0000 b) 0000:00AA:0000:0000:0000:0000:119A:A231 c) 2340:0000:2222:0000:0000:119A:A001:0000 d) 0000:0000:0000:2340:0000:0000:0000:0000 Exercise 15 The network layer divides the datagrams into smaller datagrams if they are bigger than the MTU of a link layer over which they are to be sent. a) Write down an advantages of having a large MTU. b) Write down an advantage of having a small MTU. Exercise 16 Host A sends an ICMP query message to host B, but never receives an answer. Give three possible causes and the corresponding course of actions for host A. Exercise 17 In the figure below, a router is connected to some (sub)networks. The figure also shows the routing table for the router. A datagram arrives at one of the router interfaces. To which interface is the datagram forwarded when the destination address is a) 145.14.192.71? b) 135.11.80.21? 2 General networking TSIN02 Internetworking Daniel Persson Exercise 18 A datagram arrives to at router R1 in the figure below. The figure also shows the routing table for router R1. To which interface is the datagram forwarded when the destination address is a) 201.4.16.70? b) 202.70.20.30? 3 General networking TSIN02 Internetworking Daniel Persson Exercise 19 You will transport the final of Eurovision song contest via IP-TV to a majority of the European households from Copenhagen 2014. The problem is that the IP network in Copenhagen will be overloaded when unicasting such a massive flood of packets to all the households. Instead you plan to set up a network layer multicast service. To better understand the problem, you model the distribution network as a tree, where each node is connecting to 2 nodes at each level, and where there are 28 levels. The households are all on level 28, and all nodes on this level are households. a) For every datagram that has to be delivered to the households, how many unicast packets will need to be sent on the most charged link? b) Same question in the case of a perfect multicast, where each node receives one datagram, and retransmits two copies, one for each link? Exercise 20 How does each router table look in a network with three routers A, B, and C, where all routers connect to each other, but where the transport cost between router A and B; and A and C are 1; while the cost between routers B and C is 3? Exercise 21 A router has three interfaces, each of them connected to a subnet. a) What is the computational complexity for forwarding the packet on the right interface? What is the storage complexity associated with the sorting? b) What would the complexity be if the IP addresses were not organized in subnets? What is the storage complexity associated with the sorting? Exercise 22 a) Why is fragmentation performed at the network layer? b) Discuss why we need to reassembly at the final destination, not at each router. Exercise 23 A home user has installed a switch to link her ADSL modem M, her two laptop computers A and B, and her husband’s desktop H. M is on switch interface 1, A is on switch interface 2, B is on switch interface 3, and H is on switch interface 4. How are frames forwarded by the switch after that the following frames have been sent: A to H, B to M, M to B, M to A? The switch’s forwarding table is initially empty. Assume that the computers know their destination IP and MAC addresses. Exercise 24 In the same network, assume again that the switch’s forwarding table is empty. Assume now that the host A wants to send a message to host B, and that A knows B’s IP address, but not B’s MAC address. a) List the steps until the first packet is sent, if A would be using ARP. Also discuss the switch’s behaviour! b) List the steps if A would not be using ARP c) Which strategy of that in (a) and that in (b) is best, and why? Exercise 25 1/2 of the users served by an ISP tend to use real time speech communication over the Internet, and use 10 kbit/s each. 1/4 of the users tend to like to stream mp3 songs, and use 100 kbit/s each. ¼ of the users like video applications, and use 1Mbit/s. The ISP routers connecting to the backbone can only handle 1 Gb/s. The ISP considers two choices: 1) Continue business as usual with the TCP/IP stack 2) Take part in a worldwide initiative to implement IntServ to get QoS. The ISP would then have to guarantee video quality to all users. a) How many more users would the ISP be able to serve while continuing using TCP/IP alone, compared to when IntServ is used? b) What happens if 1/8 of the music-listeners started to prefer a new music video service if we use TCP/IP, and with IntServ, with the user allocation in (a)? c) What are the pros and cons of non-circuit-switched networks? 4 TSIN02 Internetworking General networking Daniel Persson d) To what extent does a connection-oriented service help a non-circuit-switched network? e) What is a virtual circuit? Exercise 26 Which parameters does a newly added host in a network need to know in order to communicate outside the local network? Exercise 27 A DHCP packet in encapsulated in a UDP packet, which is encapsulated in an IP packet, which is encapsulated in an Ethernet frame. Find the efficiency of a DHCP packet when no option is used. The efficiency in this case is measured in the number of bytes in the DHCP packet to the total number of bytes transmitted on the physical layer. Exercise 28 Why does a newly added host need to know a) the IP address of a router? b) the IP address of a name server? c) its subnet? Exercise 29 Which are the two address allocations provided by DHCP? Describe when they are used! Exercise 30 A user Ada connects a new computer to an Ethernet LAN, opens a browser, and types in google.com. Well at google, she types in the word “guitar”. She gets a list of sites and accesses guitar.com. What happens on the different TCP/IP stack layers? Exercise 31 a) A name space that maps each address to a unique name can be organized in two ways. Describe these two ways of organizing the name space! b) What is the difference between a root server, a primary server, and a secondary server? c) Which are the three sections of the domain name space (tree)? Describe them! d) What does “name-address resolution” mean? e) What is the difference between recursive resolution and iterative resolution? Exercise 32 Is registration required if the mobile host acts as a foreign agent? Explain your answer. Exercise 33 Redraw Figure 10.7 in the course book (also shown below) with the corresponding data transfer path if the mobile host acts as a foreign agent. 1 4 2 3 Exercise 34 We have the following IP addresses in a mobile IP scenario shown below: 5 TSIN02 Internetworking General networking Daniel Persson Mobile host home address: Mobile host care-of address: Remote host address: Home agent address: 130.45.6.7/16 14.56.8.9/8 200.4.7.14/24 130.45.10.20/16 Let us define a simplified IP datagram in the following way: HEADER | DATA = O.H.F. | S.IP | D.IP | DATA where O.H.F. = Other Header Fields (with details that we are not so interested in here), S.IP = Source IP address, and D.IP = Destination IP address. Show the contents of a simplified IP datagram sent from the remote host to the home agent. Exercise 35 Using the information in Exercise 11, show the contents of a simplified IP datagram sent by the home agent to/via the foreign agent. Use tunnelling. Exercise 36 Using the information in Exercise 11, show the contents of a simplified IP datagram sent by the foreign agent to the mobile host. Exercise 37 Using the information in Exercise 11, show the contents of a simplified IP datagram sent by the mobile host to the remote host. Exercise 38 What type of inefficiency do we have in Exercise 5? Explain your answer. 1 4 2 3 Exercise 39 Are both UDP and IP unreliable to the same degree? Why or why not? Exercise 40 A client uses UDP to send data to a server. The data length is 16 bytes. a) What is efficiency of this transmission at the transport layer, in terms of the ratio of data bytes to the total number of transmitted bytes? b) What is the corresponding efficiency at the network layer (assume no options for the IP datagram header)? Exercise 41 TCP is sending data at 1 megabyte per second (8Mbps). If the sequence number starts with 7000, how long does it take before the sequence number goes back to zero? 6 General networking TSIN02 Internetworking Daniel Persson Exercise 42 Compare the TCP segment header and the UDP datagram header. Make a table, like the one below, where you list all the fields in the TCP segment header and all the fields in the UDP datagram header. Explain shortly in the rightmost column the purpose of each field. Fields Source port numbers …. …. UDP TCP Purpose You should fill in this field… …. …. Exercise 43 UDP is a message-oriented protocol, TCP is a byte-oriented protocol. If an application needs to protect the boundaries of its messages, which protocol should be used, UDP or TCP? Exercise 44 In a TCP connection, the value of cwnd is 3000 and the value of rwnd is 5000. The host has sent 2.000 bytes, which has not yet been acknowledged. How many more bytes can be sent? Exercise 45 A TCP connection is using a window size of 10.000 bytes and the previous acknowledgement number was 22.001. It receives a segment with acknowledgement number 24.001 and a window size advertisement of 12.000. Draw a diagram to show the situation of the window before and after. 7