Quiz 4 (SCSR 1213 – Network Communications) 1.What are some of the possible services that a link-layer protocol can offer to the network layer? Which of these link-layer services have corresponding services in IP? In TCP? 2. Suppose the information content of a packet is the bit pattern 1110 0110 1001 1101 and an even parity scheme is being used. What would the value of the field containing the parity bits be for the case of a two-dimensional parity scheme?. Your answer should be such that a minimum-length checksum field is used. Each row of 2-D parity scheme contains 4 bits from the data. 3. Show (give an example other than the one in Figure 5.5) that two-dimensional parity checks can correct and detect a single bit error. Show (give an example of) a double-bit error that can be detected but not corrected. 4. Consider the 7-bit generator, G=10011, and suppose that D has the value 1010101010. What is the value of R? 5. Consider the previous problem, but suppose that D has the value a. 1001010101. b. 0101101010. c. 1010100000. 6. Clearly explain how the following random access MAC protocols works: a. slotted ALOHA b. CSMA/CD 7. How big is the MAC address space? The IPv4 address space? The IPv6 address space? 8. Why is an ARP query sent within a broadcast frame? Why is an ARP response sent within a frame with a specific destination MAC address? 9. Suppose nodes A, B, and C each attach to the same broadcast LAN (through their adapters). If A sends thousands of IP datagrams to B with each encapsulating frame addressed to the MAC address of B, will C’s adapter process these frames? If so, will C’s adapter pass the IP datagrams in these frames to the network layer C? How would your answers change if A sends frames with the MAC broadcast address? ͳ Quiz as done for the single-router example in Section 5. Repeat (a).1. Will Host E ask router R1 to help forward the datagram? Why? In the Ethernet frame containing the IP datagram.xxx.3.33: Three subnets (1.33 (b).xxx. Consider Figure 5. interconnected by router (a). Enumerate (detail) all the steps involved.33 in Question 10.33 (a).168. Consider sending an IP datagram from Host E to Host F. Will E perform an ARP query to find B’s MAC address? Why? In the Ethernet frame (containing the IP datagram destined to ʹ . 11.168.xxx.2. Consider three LANs interconnected by two routers. for Subnet 2 uses addresses of the form 192. (a) (b) Figure 5.4. what are the source and destination IP and MAC addresses? b. IP addresses and MAC addresses assignment (b) a.10. and assume that E’s ARP cache does not contain B’s MAC address. and label the router between subnets 2 and 3 as R1. Consider sending an IP datagram from Host E to Host B. IP addresses and MAC addresses have been assigned to all of the adapters and interfaces as shown in Figure 5. path 2. Suppose E would like to send an IP datagram to B. now assuming that the ARP table in the sending host is empty (and the other tables are up to date). Suppose all of the ARP tables are up to date.168. b. Clearly indicates IP and MAC addresses for path 1. a. and for Subnet 3 use addresses of the form 192.1 (text book). as shown in Figure 5. and path 3. For Subnet 1 use addresses of the form 192. and 3). 2. Now we replace the router between subnets 1 and 2 with a switch S1. (iii) from the right router to F.B) that is delivered to router R1. such as routers and switches. C. B. Further suppose that the switch S1’s forwarding table contains entries for Host B and router R1 only. You are to fill in Table 1 below and indicate the source/destination MAC and IP addresses at different points during the transmission. Consider the previous problem (Question 11). Provide MAC addresses and IP addresses for the interfaces at Host A. Give the source and destination MAC addresses in the frame encapsulating this IP datagram as the frame is transmitted (i) from A to the switch. What actions will switch S1 perform once it receives the ARP request message? Will router R1 also receive this ARP request message? If so. 15. and Host F. what are the source and destination IP and MAC addresses? c. You will examine a situation where PC-A sends data to PC-B. Hosts A. will R1 forward the message to Subnet 3? Once Host B receives this ARP request message. Also give the source and destination IP addresses in the IP datagram encapsulated within the frame at each of these points in time 14. Give the source and destination MAC addresses in the frame encapsulating this IP datagram as the frame is transmitted (i) from A to the left router. Answer questions (a)–(c) in the previous problem in this new context. Some devices. But will it send an ARP query message to ask for A’s MAC address? Why? What will switch S1 do once it receives an ARP response message from Host B? 12. The matching names for the IP and MAC addresses of each device is given on the figure. ͵ . Figure below shows several networks connected to each other. both routers. therefore multiple addresses are assigned to them. (ii) from the left router to the right router. (ii) from the switch to the right router. Suppose Host A sends a datagram to Host F. and D and the right router are all star-connected into this switch. A will broadcast an ARP request message. Suppose Host A would like to send an IP datagram to Host B. it will send back to Host A an ARP response message. Also give the source and destination IP addresses in the IP datagram encapsulated within the frame at each of these points in time.33 is replaced by a switch. Suppose now that the leftmost router in Figure 5. 13. (iii) from the right router to F. and neither A’s ARP cache contains B’s MAC address nor does B’s ARP cache contain A’s MAC address. Thus. Consider Figure 5. have multiple interfaces. You do not need to use complete IP and MAC addresses.33 in Question 10. but suppose now that the router between subnets 2 and 3 is replaced by a switch. Explain in details. Initially. C. a. and maintained in switch table? This is considered as basic operation of a switch which is done automatically. A’. Ͷ . Six nodes (A. B’. switch table in router is empty. suppose node A (with MAC address A) want to send datagram to node A’ (with MAC address A’). c. and C’) are connected to a router using star topology as shown in the following figure. how self-learning process is done so that the final switch table is updated as shown below. B. As shown in the following figure. How are entries created. How does switch know A’ reachable via interface 4. B’ reachable via interface 5? b.16.